EP2130931B2

EP2130931B2 - Method for producing aluminum alloy thick plate

Info

Publication number: EP2130931B2
Application number: EP08722912.6A
Authority: EP
Inventors: Kazunori Kobayashi; Kenji Tokuda; Tomoharu Kato; Takashi Inaba
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 2007-03-30
Filing date: 2008-03-27
Publication date: 2022-08-03
Anticipated expiration: 2028-03-27
Also published as: KR20110118186A; TW201245462A; EP2130931A4; TWI383053B; KR101151563B1; EP2130931B1; TWI468527B; KR101197952B1; EP2130931A1; WO2008123355A1; KR20090117951A; TW200900512A

Description

The present invention relates to methods for manufacturing aluminum alloy thick plates.

Background Art

Aluminum alloy materials such as aluminum alloy thick plates are generally used for various applications including semiconductor-related devices such as base substrates, transport devices, and vacuum chambers; electrical and electronic parts and their manufacturing devices; household articles; and mechanical parts.
Such aluminum alloy materials are generally manufactured by melting aluminum alloy ingots, and casting the molten material to give a slab, conducting a heat treatment for homogenization, if necessary, and then rolling the slab to a predetermined thickness (see, for example, Paragraphs 0037 to 0045 of Patent Document 1).
As mold materials used for press molds, steels and cast steel are typically used for mass production, while zinc alloy cast materials and aluminum alloy cast materials are used for prototype production. In recent years, there has been a trend of producing multiple varieties in small amounts, and therefore ductile materials such as rolled or forged aluminum alloys are widely spread for middle-to-small-scale production.
Patent Document 1: Japanese Unexamined Patent Application Publication ( JP-A) No. 2005-344173
EP-A-2 034 035 discloses a method for manufacturing an aluminum alloy thick plate, the method comprising: a melting step for melting an aluminum alloy; a hydrogen gas removal step for removing hydrogen gas from the aluminum alloy melted in the melting step; a filtration step for removing mediators from the aluminum alloy from which hydrogen gas is removed in the hydrogen gas removal step; a casting step for casting the aluminum alloy from which the mediator is removed in the filtration step to produce a slab; and a slicing step for slicing the slab into a predetermined thickness, which are carried out in the order stated (cf. claim 1).
However, the method for manufacturing aluminum alloy materials by rolling has the following problems:

(1) In the method in which rolling is carried out after casting, control of the surface condition and flatness (especially the flatness in the longitudinal direction) of the rolledplate is carried out only by pressure rolls, and a thick oxide film is generated on the surface of the rolled plate by hot rolling, and controlling the surface condition and flatness is difficult.
(2) Since it is difficult to control the thickness of the plate by pressure rolls, it is difficult to improve the accuracy of plate thickness; the size of intermetallic compounds increases at the center of the thickness direction of the plate, and thus when anodization is conducted, the surface and cross section in the thickness direction of the plate often suffer from unevenness. Additionally, when a slab is rolled, the number of operation steps increases with an increasing number of rolling procedures, whereby the cost is disadvantageously increased.

Under these circumstances, the present invention has been made and an object thereof is to provide a method for manufacturing an aluminum alloy thick plate, which method enables improved accuracy of plate thickness with high productivity and good controllability of surface condition and flatness. Generally, an aluminum alloy thick plate which is manufactured by the procedures of the manufacturing method excels in surface condition, flatness, and accuracy of plate thickness.
According to a first embodiment of the present invention, there is provided a method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Mg in a content of 1.5 percent by mass or more and 12.0 percent by mass or less, and further containing at least one member selected from the group consisting of Si in a content of 0.7 percent by mass or less, Fe in a content of 0.8 percent by mass or less, Cu in a content of 0.6 percent by mass or less, Mn in a content of 1.0 percent by mass or less, Cr in a content of 0.5 percent by mass or less, Zn in a content of 0.4 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.3 percent by mass or less, with the remainder being aluminum and inevitable impurities. The method includes in the following order: a melting step of melting the aluminum alloy; a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy; a filtration step of filtering the aluminum alloy, from which hydrogen gas has been removed, to remove inclusions from the aluminum alloy; a semi-continuous casting step of casting the aluminum alloy, from which inclusions have been removed, into a slab; a slicing step of slicing the slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness; and a heat treatment step of thermally treating the aluminum alloy thick plate having a predetermined thickness by holding the same at a temperature of 400°C or higher but lower than its melting point for one hour or longer.
According to a second embodiment of the present invention, there is provided a method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Mn in a content of 0.3 percent by mass or more and 1.6 percent by mass or less, and further containing at least one member selected from the group consisting of Si in a.content of 0.7 percent by mass or less, Fe in a content of 0.8 percent by mass or less, Cu in a content of 0.5 percent by mass or less, Mg in a content of 1.5 percent by mass or less, Cr in a content of 0.3 percent by mass or less, Zn in a content of 0.4 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.3 percent by mass or less, with the remainder being aluminum and inevitable impurities. The method includes in the following order: a melting step of melting the aluminum alloy; a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy; a filtration step of filtering the aluminum alloy, from which hydrogen gas has been removed, to remove inclusions from the aluminum alloy; a semi-continuous casting step of casting the aluminum alloy, from which inclusions have been removed, into a slab; a slicing step of slicing the slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness; and a heat treatment step of thermally treating the aluminum alloy thick plate having a predetermined thickness by holding the same at a temperature of 400°C or higher but lower than its melting point for one hour or longer.
According to a third embodiment of the present invention, there is provided a method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Si in a content of 0.2 percent by mass or more and 1.6 percent by mass or less and Mg in a content of 0.3 percent by mass or more and 1.5 percent by mass or less, and further containing at least one member selected from the group consisting of Fe in a content of 0.8 percent by mass or less, Cu in a content of 1.0 percent by mass or less, Mn in a content of 0.6 percent by mass or less, Cr in a content of 0.5 percent by mass or less, Zn in a content of 0.4 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.3 percent by mass or less, with the remainder being aluminum and inevitable impurities. The method includes in the following order: a melting step of melting the aluminum alloy; a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy; a filtration step of filtering the aluminum alloy, from which hydrogen gas has been removed, to remove inclusions from the aluminum alloy; a semi-continuous casting step of casting the aluminum alloy, from which inclusions have been removed, into a slab; a slicing step of slicing the slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness; and a heat treatment step of thermally treating the aluminum alloy thick plate having a predetermined thickness by holding the same at a temperature of 400°C or higher but lower than its melting point for one hour or longer.
According to a fourth embodiment of the present invention, there is provided a method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Mg in a content of 0.4 percent by mass or more and 4.0 percent by mass or less and Zn in a content of 3.0 percent by mass or more and 9.0 percent by mass or less, and further containing at least one member selected from the group consisting of Si in a content of 0.7 percent by mass or less, Fe in a content of 0.8 percent by mass or less, Cu in a content of 3.0 percent by mass or less, Mn in a content of 0.8 percent by mass or less, Cr in a content of 0.5 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.25 percent by mass or less, with the remainder being aluminum and inevitable impurities. The method includes in the following order: a melting step of melting the aluminum alloy; a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy; a filtration step of filtering the aluminum alloy, from which hydrogen gas has been removed, to remove inclusions from the aluminum alloy; a semi-continuous casting step of casting the aluminum alloy, from which inclusions have been removed, into a slab; a slicing step of slicing the slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness; and a heat treatment step of thermally treating the aluminum alloy thick plate having a predetermined thickness by holding the same at a temperature of 350°C or higher but lower than its melting point for one hour or longer.
In the first to fourth embodiments of the present invention, the following configurations are preferred:

(A) Subsequent to the heat treatment step, the surface of the aluminum alloy thick plate is subjected to a surface smoothing treatment, as a surface smoothing treatment step. In this configuration, the surface smoothing treatment is preferably carried out by at least one process selected from the group consisting of cutting, grinding, and polishing.
(B) In the slicing step, a central portion in a thickness direction is removed from the slab, in which the central portion has two substantially identical thicknesses in the thickness direction from the center of the thickness direction to the both surfaces of the central portion, respectively, and has a total thickness of from one-thirtieth to one-fifth the thickness T of the slab (T/30 to T/5).

According to a fifth embodiment of the present invention, there is provided a method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Mg in a content of 1.5 percent by mass or more and 12.0 percent by mass or less, and further containing at least one member selected from the group consisting of Si in a content of 0.7 percent by mass or less, Fe in a content of 0.8 percent by mass or less, Cu in a content of 0.6 percent by mass or less, Mn in a content of 1.0 percent by mass or less, Cr in a content of 0.5 percent by mass or less, Zn in a content of 0.4 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.3 percent by mass or less, with the remainder being aluminum and inevitable impurities. The method includes in the following order: a melting step of melting the aluminum alloy; a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy; a filtration step of filtering the aluminum alloy, from which hydrogen gas has been removed, to remove inclusions from the aluminum alloy; a semi-continuous casting step of casting the aluminium alloy, from which inclusions have been removed, into a slab; a heat treatment step of thermally treating the slab by holding the same at a temperature of 200°C to 350°C for one hour or longer; and a slicing step of slicing the thermally treated slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness, and wherein the slicing step comprises removing a central portion in a thickness direction from the slab, the central portion having two substantially identical thicknesses in the thickness direction from the center of the thickness direction to the both surfaces of the central portion, respectively, and having a total thickness of from one-thirtieth to one-fifth the thickness T of the slab (T/30 to T/5).
According to a sixth embodiment of the present invention, there is provided a method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Mn in a content of 0.3 percent by mass or more and 1.6 percent by mass or less, and further containing at least one member selected from the group consisting of Si in a content of 0.7 percent by mass or less, Fe in a content of 0.8 percent by mass or less, Cu in a content of 0.5 percent by mass or less, Mg in a content of 1.5 percent by mass or less, Cr in a content of 0.3 percent by mass or less, Zn in a content of 0.4 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.3 percent by mass or less, with the remainder being aluminum and inevitable impurities. The method includes in the following order: a melting step of melting the aluminum alloy; a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy; a filtration step of filtering the aluminum alloy, from which hydrogen gas has been removed, to remove inclusions from the aluminum alloy; a semi-continuous casting step of casting the aluminum alloy, from which inclusions have been removed, into a slab; a heat treatment step of thermally treating the slab by holding the same at a temperature of 200°C to 350°C for one hour or longer; and a slicing step of slicing the thermally treated slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness, and wherein the slicing step comprises removing a central portion in a thickness direction from the slab, the central portion having two substantially identical thicknesses in the thickness direction from the center of the thickness direction to the both surfaces of the central portion, respectively, and having a total thickness of from one-thirtieth to one-fifth the thickness T of the slab (T/30 to T/5).
According to a seventh embodiment of the present invention, there is provided a method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Si in a content of 0.2 percent by mass or more and 1.6 percent by mass or less and Mg in a content of 0.3 percent by mass or more and 1.5 percent by mass or less, and further containing at least one member selected from the group consisting of Fe in a content of 0.8 percent by mass or less, Cu in a content of 1.0 percent by mass or less, Mn in a content of 0.6 percent by mass or less, Cr in a content of 0.5 percent by mass or less, Zn in a content of 0.4 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.3 percent by mass or less, with the remainder being aluminum and inevitable impurities. The method includes in the following order: a melting step of melting the aluminum alloy; a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy; a filtration step of filtering the aluminum alloy, from which hydrogen gas has been removed, to remove inclusions from the aluminum alloy; a semi-continuous casting step of casting the aluminum alloy, from which inclusions have been removed, into a slab; a heat treatment step of thermally treating the slab by holding the same at a temperature of 200°C or higher but lower than 400°C for one hour or longer; and a slicing step of slicing the thermally treated slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness.
According to an eighth embodiment of the present invention, there is provided a method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Mg in a content of 0.4 percent by mass or more and 4.0 percent by mass or less and Zn in a content of 3.0 percent by mass or more and 9.0 percent by mass or less, and further containing at least one member selected from the group consisting of Si in a content of 0.7 percent by mass or less, Fe in a content of 0.8 percent by mass or less, Cu in a content of 3.0 percent by mass or less, Mn in a content of 0.8 percent by mass or less, Cr in a content of 0.5 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.25 percent by mass or less, with the remainder being aluminum and inevitable impurities. The method includes in the following order: a melting step of melting the aluminum alloy; a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy; a filtration step of filtering the aluminum alloy, from which hydrogen gas has been removed, to remove inclusions from the aluminum alloy; a semi-continuous casting step of casting the aluminum alloy, from which inclusions have been removed, into a slab; a heat treatment step of thermally treating the slab by holding the same at a temperature of 200°C or higher but lower than 350°C for one hour or longer; and a slicing step of slicing the thermally treated slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness.
In the fifth to eighth embodiments of the present invention, the following configuration is preferred:

(C) Subsequent to the slicing step, the surface of the aluminum alloy thick plate having a predetermined thickness is subjected to a surface smoothing treatment, as a surface smoothing treatment step. In this configuration, the surface smoothing treatment is preferably carried out by at least one process selected from the group consisting of cutting, grinding, and polishing. In the seventh and eighth embodiments of the present invention, the following configuration is preferred and in the fifth and sixth embodiments of the present invention it is mandatory:
(D) In the slicing step, a central portion in a thickness direction is removed from the slab, in which the central portion has two substantially identical thicknesses in the thickness direction from the center of the thickness direction to the both surfaces of the central portion, respectively, and has a total thickness of from one-thirtieth to one-fifth the thickness T of the slab (T/30 to T/5).

According to a ninth embodiment of the present invention, there is provided a method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Mg in a content of 1.5 percent by mass or more and 12.0 percent by mass or less, and further containing at least one member selected from the group consisting of Si in a content of 0.7 percent by mass or less, Fe in a content of 0.8 percent by mass or less, Cu in a content of 0.6 percent by mass or less, Mn in a content of 1.0 percent by mass or less, Cr in a content of 0.5 percent by mass or less, Zn in a content of 0.4 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.3 percent by mass or less, with the remainder being aluminum and inevitable impurities. The method includes in the following order: a melting step of melting the aluminum alloy; a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy; a filtration step of filtering the aluminum alloy, from which hydrogen gas has been removed, to remove inclusions from the aluminum alloy; a semi-continuous casting step of casting the aluminum alloy, from which inclusions have been removed, into a slab; a slicing step of slicing the slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness; and a heat treatment step of thermally treating the aluminum alloy thick plate having a predetermined thickness by holding the same at a temperature of 200°C or higher but lower than 400°C for one hour or longer.
According to a tenth embodiment of the present invention, there is provided a method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Mn in a content of 0.3 percent by mass or more and 1.6 percent by mass or less, and further containing at least one member selected from the group consisting of Si in a content of 0.7 percent by mass or less, Fe in a content of 0.8 percent by mass or less, Cu in a content of 0.5 percent by mass or less, Mg in a content of 1.5 percent by mass or less, Cr in a content of 0.3 percent by mass or less, Zn in a content of 0.4 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.3 percent by mass or less, with the remainder being aluminum and inevitable impurities. The method includes in the following order: a melting step of melting the aluminum alloy; a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy; a filtration step of filtering the aluminum alloy, from which hydrogen gas has been removed, to remove inclusions from the aluminum alloy; a semi-continuous casting step of casting the aluminum alloy, from which inclusions have been removed, into a slab; a slicing step of slicing the slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness; and a heat treatment step of thermally treating the aluminum alloy thick plate having a predetermined thickness by holding the same at a temperature of 200°C or higher but lower than 400°C for one hour or longer.
According to an eleventh embodiment of the present invention, there is provided a method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Si in a content of 0.2 percent by mass or more and 1.6 percent by mass or less and Mg in a content of 0.3 percent by mass or more and 1.5 percent by mass or less, and further containing at least one member selected from the group consisting of Fe in a content of 0.8 percent by mass or less, Cu in a content of 1.0 percent by mass or less, Mn in a content of 0.6 percent by mass or less, Cr in a content of 0.5 percent by mass or less, Zn in a content of 0.4 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.3 percent by mass or less, with the remainder being aluminum and inevitable impurities. The method includes in the following order: a melting step of melting the aluminum alloy; a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy; a filtration step of filtering the aluminum alloy, from which hydrogen gas has been removed, to remove inclusions from the aluminum alloy; a semi-continuous casting step of casting the aluminum alloy, from which inclusions have been removed, into a slab; a slicing step of slicing the slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness; and a heat treatment step of thermally treating the aluminum alloy thick plate having a predetermined thickness by holding the same at a temperature of 200°C or higher but lower than 400°C for one hour or longer.
According to a twelfth embodiment of the present invention, there is provided a method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Mg in a content of 0.4 percent by mass or more and 4.0 percent by mass or less and Zn in a content of 3.0 percent by mass or more and 9.0 percent by mass or less, and further containing at least one member selected from the group consisting of Si in a content of 0.7 percent by mass or less, Fe in a content of 0.8 percent by mass or less, Cu in a content of 3.0 percent by mass or less, Mn in a content of 0.8 percent by mass or less, Cr in a content of 0.5 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.25 percent by mass or less, with the remainder being aluminum and inevitable impurities. The method includes in the following order: a melting step of melting the aluminum alloy; a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy; a filtration step of filtering the aluminum alloy, from which hydrogen gas has been removed, to remove inclusions from the aluminum alloy; a semi-continuous casting step of casting the aluminum alloy, from which inclusions have been removed, into a slab; a slicing step of slicing the slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness; and a heat treatment step of thermally treating the aluminum alloy thick plate having a predetermined thickness by holding the same at a temperature of 200°C or higher but lower than 350°C for one hour or longer.
In the ninth to twelfth embodiments of the present invention, the following configurations are preferred:

(E) Subsequent to the heat treatment step, the surface of the aluminum alloy thick plate is subjected to a surface smoothing treatment, as a surface smoothing treatment step. In this configuration, the surface smoothing treatment is preferably carried out by at least one process selected from the group consisting of cutting, grinding, and polishing.
(F) In the slicing step, a central portion in a thickness direction is removed from the slab, in which the central portion has two substantially identical thicknesses in the thickness direction from the center of the thickness direction to the both surfaces of the central portion, respectively, and has a total thickness of from one-thirtieth to one-fifth the thickness T of the slab (T/30 to T/5).

Generally, there is provided an aluminum alloy thick plate which is manufactured by the method for manufacturing an aluminum alloy thick plate, according to any one of the first to twelfth embodiments of the present invention, and includes crystal grains having an average grain size of 400 µm or less.

Effects of the Invention

According to the first to fourth embodiments of the present invention, the resulting aluminum alloy thick plate includes finer intermetallic compounds and has improved strength, because the material aluminum alloy has contents of predetermined elements controlled within predetermined ranges. The hydrogen gas removal step removes hydrogen to thereby control the concentration of hydrogen in the slab. Therefore, even if crystal grains in the slab become coarse, hydrogen is not accumulated or enriched at the grain boundary near the surface of the slab. This suppresses blistering of the slab and peeling of the aluminum alloy thick plate resulting from the blistering, and also suppresses potential defects on the surface of the thick plates which appear as surface defects of the thick plate. The aluminum alloy thick plate has improved strength. The filtration step removes inclusions such as oxides and non-metals from the aluminum alloy. Slicing the slab in the slicing step reduces the thickness of the oxide film; improves the surface condition, flatness and accuracy of the plate thickness of the aluminum alloy thick plate; and also improves its productivity. In addition, the heat treatment step thermally treats the aluminum alloy thick plate to thereby remove the internal stress of the aluminum alloy and uniformize its inner structure.
According to the first to fourth embodiments of the present invention, therefore, the aluminum alloy thick plate can have improved strength. The aluminum alloy thick plate is manufactured by slicing a slab, and this eliminates necessity to reduce its thickness by hot rolling unlike in known aluminum alloy thick plates. This simplifies operation steps and thereby improves the productivity. This also eliminates unevenness (uneven color) of the surface and cross section of the thick plate; and improves the flatness, surface condition after anodization, and accuracy of plate thickness. By thermally treating the sliced aluminum alloy thick plate having a predetermined thickness at a temperature of 400°C (or 350°C) or higher but lower than its melting point, the internal stress of the aluminum alloy thick plate can be removed and its inner structure can be uniformized. Thus, the aluminum alloy thick plate can have good flatness and satisfactory accuracy of plate thickness and can maintain its satisfactory strength.
The configuration (A) helps to further improve the surface condition and flatness of the aluminum alloy thick plate and eliminates the gas accumulation of the surface of the thick plate, because the surface is further smoothened. The resulting aluminum alloy thick plate, if used as a vacuum chamber, can provide an improved degree of vacuum.
The configuration (B) helps to provide an aluminum alloy thick plate excellent in appearance quality even after anodization, because the central portion of the slab is removed, which central portion will often cause unevenness in the surface and cross section of the aluminum alloy thick plate after anodization. This configuration also helps to reduce the within-lot variation.
According to the fifth to eighth embodiments of the present invention, the aluminum alloy thick plate can include finer intermetallic compounds and have higher strength, because the material aluminum alloy has contents of predetermined elements controlled within predetermined ranges. The hydrogen gas removal step removes hydrogen gas to thereby control the concentration of hydrogen in the slab. Therefore, even if crystal grains in the slab become coarse, hydrogen is not accumulated or enriched at the grain boundary near the surface of the slab. This suppresses blistering of the slab and peeling of the aluminum alloy thick plate resulting from the blistering; suppresses potential defects on the surface of the thick plates which appear as surface defects of the thick plate; and improves the strength of the aluminum alloy thick plate. The filtration step removes inclusions such as oxides and non-metals from the aluminum alloy. The heat treatment step thermally treats the slab to eliminate the internal stress and to uniformize the inner structure thereof. The slicing step slices the slab so as to reduce the thickness of the oxide film and to improve the surface condition, flatness and accuracy of the plate thickness of the aluminum alloy thick plate, as well as its productivity.
According to the fifth to eighth embodiments of the present invention, therefore, the aluminum alloy thick plate can have improved balance among its flatness, strength, and cutting property. Specifically, the heat treatment at a temperature of 200°C to 350°C (fifth and sixth embodiment), 200°C or higher but lower than 400°C (seventh embodiment) (or 350°C (eighth embodiment)) applied to the slab suppresses the increase in ductility. This helps to remove the internal stress and to uniformize the inner structure of the thick plate without adversely affecting the cutting property (chip breakability) . The resulting aluminum alloy thick plate can thereby have good flatness and satisfactory accuracy of plate thickness and can maintain its satisfactory strength. The aluminum alloy thick plate is manufactured by slicing a slab. This eliminates necessity to reduce its thickness by hot rolling unlike in known aluminum alloy thick plates; simplifies operation steps and improves the productivity; and also eliminates surface unevenness (uneven color) of the cross section of the thick plate and improves the flatness, quality of appearance after anodization, and accuracy of plate thickness.
The configuration (C) helps to further improve the surface condition and flatness of the aluminum alloy thick plate and eliminates the gas accumulation of the surface of the thick plate, because the surface is further smoothened. The resulting aluminum alloy thick plate, if used as a vacuum chamber, can provide an improved degree of vacuum.
The configuration (D) helps to provide an aluminum alloy thick plate excellent in appearance quality even after anodization, because the central portion of the slab is removed, which central portion will often cause unevenness in the surface and cross section of the aluminum alloy thick plate after anodization. This configuration also helps to reduce the within-lot variation.
According to the ninth to twelfth embodiments of the present invention, the aluminum alloy thick plate includes finer intermetallic compounds and has improved strength, because the material aluminum alloy has contents of predetermined elements controlled within predetermined ranges. The hydrogen gas removal step removes hydrogen to thereby control the concentration of hydrogen in the slab. Therefore, even if crystal grains in the slab become coarse, hydrogen is not accumulated or enriched at the grain boundary near the surface of the slab. This suppresses blistering of the slab and peeling of the aluminum alloy thick plate resulting from the blistering; suppresses potential defects on the surface of the thick plates which appear as surface defects of the thick plate; and improves the strength of the aluminum alloy thick plate. The filtering step removes inclusions such as oxides and non-metals from the aluminum alloy. Slicing the slab in the slicing step reduces the thickness of the oxide film; improves the surface condition, flatness and accuracy of the plate thickness of the aluminum alloy thick plate; and improves the productivity of the aluminum alloy thick plate. In addition, the heat treatment step thermally treats the aluminum alloy thick plate to thereby remove the internal stress of the aluminum alloy and uniformize its inner structure.
According to the ninth to twelfth embodiments of the present invention, therefore, the aluminum alloy thick plate can have improved strength. The aluminum alloy thick plate is manufactured by slicing a slab, and this eliminates necessity to reduce its thickness by hot rolling unlike in known aluminum alloy thick plates. This simplifies operation steps; improves the productivity; eliminates unevenness (uneven color) of the surface and cross section of the thick plate; and improves the flatness, quality of appearance after anodization, and accuracy of plate thickness . Further, this also improves the balance among the flatness, strength, and cutting property of the aluminum alloy thick plate. The heat treatment at a temperature of 200°C or higher but lower than 400°C (or 350°C) applied to the sliced aluminum alloy thick plate having a predetermined thickness suppresses the increase in ductility, whereby helps to remove the internal stress and uniformize the inner structure of the aluminum alloy thick plate without adversely affecting the cutting property (chip breakability). The resulting aluminum alloy thick plate can thereby have good flatness and satisfactory accuracy of plate thickness and maintain its satisfactory strength.
The configuration (E) helps to further improve the surface condition and flatness of the aluminum alloy thick plate and eliminates the gas accumulation of the surface of the thick plate, because the surface is further smoothened. The resulting aluminum alloy thick plate, if used as a vacuum chamber, can provide an improved degree of vacuum.
The configuration (F) helps to provide an aluminum alloy thick plate excellent in appearance quality even after anodization, because the central portion of the slab is removed, which central portion will often cause unevenness in the surface and cross section of the aluminum alloy thick plate after anodization. This configuration also helps to reduce the within-lot variation.
The aluminum alloy thick plates obtained by the methods of the present invention excel in surface condition, flatness, and accuracy of plate thickness. They also have high quality, because their surface is smoothened and thereby is free from gas accumulation. They can be used in a wide variety of applications and can be recycled and used for other applications, because the surface appearance of them after anodization is substantially free from unevenness.

Brief Description of the Drawings

Fig. 1 is a flow chart of methods for manufacturing an aluminum alloy thick plate, according to the first to fourth embodiments and the ninth to twelfth embodiments of the present invention.
Fig. 2 is a schematic view showing a central portion in a thickness direction of the slab to be removed in the slicing step.
Fig. 3 is a flow chart of methods for manufacturing an aluminum alloy thick plate, according to the fifth to eighth embodiments of the present invention.

Reference Numerals

S1: melting step
S2: hydrogen gas removal step
S3: filtration step
S4: casting step
S5: slicing step or heat treatment step
S6: heat treatment step or slicing step
S7: surface smoothing treatment step
A: center of thickness direction
B: central portion in thickness direction
T: thickness
1: slab

Best Modes for Carrying Out the Invention

Methods, according to the present invention, for manufacturing aluminum alloy thick plates and resulting aluminum alloy thick plates will be illustrated in detail with reference to the attached drawings. The present invention will be illustrated below while being categorized as (A) the first to fourth embodiments of the present invention, (B) the fifth to eighth embodiments of the present invention, and (C) the ninth to twelfth embodiments of the present invention.

(A) Methods for Manufacturing Aluminum Alloy Thick Plates According to First to Fourth Embodiments of the Present Invention

(1) Outline of Manufacturing Methods

With reference to Fig. 1, With reference to Fig. 1, the methods for manufacturing an aluminum alloy thick plate (hereinafter also referred to as "thick plate" for the sake of convenience), according to the first to fourth embodiments of the present invention, each include a melting step (S1), a hydrogen gas removal step (S2), a filtration step (S3), a casting step (S4), a slicing step (S5), and a heat treatment step (S6) in this order. The methods may further include, where necessary, a surface smoothing treatment step (S7) subsequent to the heat treatment step (S6).
In these manufacturing methods, initially, aluminum alloy ingots are melted in the melting step (S1). Next, hydrogen gas is removed from the molten aluminum alloy in the hydrogen gas removal step (S2), and inclusions such as oxides and non-metals are removed therefrom in the filtration step (S3). Next, the resulting aluminum alloy is cast by a semi-continuous casting process into a slab in the casting step (S4). The slab is then sliced in the cast direction into an aluminum alloy thick plate having a predetermined thickness in the slicing step (S5). The aluminum alloy thick plate having a predetermined thickness is then subjected to a heat treatment in the heat treatment step (S6) and, where necessary, subjected to a surface smoothing treatment in the surface smoothing treatment step (S7).

(2) Aluminum Alloys

The manufacturing methods according to the first, second, third, and fourth embodiments of the present invention use a 5000 series Al-Mg alloy, a 3000 series Al-Mn alloy, a 6000 series Al-Mg-Si alloy, and a 7000 series Al-Zn-Mg alloy, respectively, as a raw material aluminum alloy. The details of them are as follows.

(2-1) First Embodiment of the Present Invention

According to the first embodiment of the present invention, a 5000 series Al-Mg alloy is used. The aluminum alloy contains Mg in a content of 1.5 percent by mass or more and 12.0 percent by mass or less, and further contains at least one member selected from the group consisting of Si in a content of 0.7 percent by mass or less, Fe in a content of 0.8 percent by mass or less, Cu in a content of 0.6 percent by mass or less, Mn in a content of 1.0 percent by mass or less, Cr in a content of 0.5 percent by mass or less, Zn in a content of 0.4 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.3 percent by mass or less, with the remainder being aluminum and inevitable impurities.
The reasons why the contents of the respective components are specified will be described below.

[Mg: 1.5 percent by mass or more and 12.0 percent by mass or less]

Magnesium (Mg) serves to improve the strength of the aluminum alloy. Mg, if its content is less than 1.5 percent by mass, may not exhibit the activity sufficiently. In contrast, Mg, if its content is more than 12.0 percent by mass, may significantly adversely affect the casting ability, and this may impede the manufacture of the product. Accordingly, the Mg content should be 1.5 percent by mass or more and 12.0 percent by mass or less.

[Si: 0.7 percent by mass or less]

Silicon (Si) serves to improve the strength of the aluminum alloy. Si is generally contained in the aluminum alloy as an impurity in the ingot and forms an Al- (Fe) - (Mn) -Si intermetallic compound together with Mn and Fe in the slab typically in the casting step (S4). Si, if its content is more than 0.7 percent by mass, may cause a coarse intermetallic compound in the slab to thereby often cause unevenness in the surface appearance after anodization. Accordingly, the Si content should be 0.7 percent by mass or less.

[Fe: 0.8 percent by mass or less]

Iron (Fe) allows crystal grains of the aluminum alloy to be finer and more stabilized and allows the aluminum alloy to have improved strength. Fe is generally contained in the aluminum alloy as an impurity in the ingot and forms an Al-Fe- (Mn) - (Si) intermetallic compound together with Mn and/or Si in the slab typically in the casting step (S4). Fe, if its content is more than 0.8 percent by mass, may cause a coarse intermetallic compound in the slab to thereby often cause unevenness in the surface appearance after anodization . Accordingly, the Fe content should be 0.8 percent by mass or less.

[Cu: 0.6 percent by mass or less]

Copper (Cu) serves to improve the strength of the aluminum alloy. However, a Cu content of 0.6 percent by mass is enough to ensure a sufficient strength to be used endurably as a thick plate. Accordingly, the Cu content should be 0.6 percent by mass or less.

[Mn: 1.0 percent by mass or less]

Manganese (Mn) is solidly dissolved in the aluminum alloy and thereby serves to improve the strength of the aluminum alloy. Mn, if its content is more than 1.0 percent by mass, may cause a coarse intermetallic compound to thereby often cause unevenness in the surface appearance after anodization. Accordingly, the Mn content should be 1.0 percent by mass or less.

[Cr: 0.5 percent by mass or less]

Chromium (Cr) serves to suppress the grain growth by depositing as a fine compound in the casting step (S4) and heat treatment step (S6). Cr, if its content is more than 0.5 percent by mass, may cause a coarse Al-Cr intermetallic compound as a primary crystal to thereby often cause unevenness in the surface appearance after anodization. Accordingly, the Cr content should be 0.5 percent by mass or less.

[Zn: 0.4 percent by mass or less]

Zinc (Zn) serves to improve the strength of the aluminum alloy. However, a Zn content of 0.4 percent by mass is enough to ensure a sufficient strength to be used endurably as a thick plate. Accordingly, the Zn content should be 0.4 percent by mass or less.

[Ti: 0.1 percent by mass or less]

Titanium (Ti) allows the slab to contain finer crystal grains. If the Ti content is more than 0.1 percent by mass, the activity may be saturated. Accordingly, the Ti content should be 0.1 percent by mass or less.

[Zr: 0.3 percent by mass or less]

Zirconium (Zr) allows the slab to contain finer crystal grains. If the Zr content is more than 0.3 percent by mass, the activity may be saturated. Accordingly, the Zr content should be 0.3 percent by mass or less.

[Al and inevitable impurities: the remainder]

The aluminum alloy contains the above-mentioned components, with the remainder being aluminum and inevitable impurities. Exemplary inevitable impurities include V and B. Each of such impurities, if its content is 0.01 percent by mass or less, will not affect the characteristic properties of the aluminum alloy thick plates according to the present invention.

(2-2) Second Embodiment of the Present Invention

According to the second embodiment of the present invention, a 3000 series Al-Mn alloy is used. The aluminum alloy contains Mn in a content of 0.3 percent by mass or more and 1.6 percent by mass or less, and further contains at least one member selected from the group consisting of Si in a content of 0.7 percent by mass or less, Fe in a content of 0.8 percent by mass or less, Cu in a content of 0.5 percent by mass or less, Mg in a content of 1.5 percent by mass or less, Cr in a content of 0.3 percent by mass or less, Zn in a content of 0.4 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.3 percent by mass or less, with the remainder being aluminum and inevitable impurities.
The reasons why the contents of the respective components are specified will be described below.
The reasons why the Si, Fe, Cu, Cr, Zn, Ti, and Zr contents are specified and the description on inevitable impurities are as with the Al-Mg alloy, and the description thereof is herein omitted.

[Mn: 0.3 percent by mass or more and 1.6 percent by mass or less]

Manganese (Mn) is solidly dissolved in the aluminum alloy and thereby serves to improve the strength of the aluminum alloy. Mn, if its content is less than 0.3 percent by mass, may not exhibit the activity sufficiently. In contrast, Mn, if its content is more than 1.6 percent by mass, may cause a coarse intermetallic compound, to thereby often cause unevenness in the surface appearance after anodization . Accordingly, the Mn content should be 0.3 percent by mass or more and 1.6 percent by mass or less.

[Mg: 1.5 percent by mass or less]

Magnesium (Mg) serves to improve the strength of the aluminum alloy. However, a Mg content of 1.5 percent by mass is enough to ensure a sufficient strength to be used endurably as a thick plate. Accordingly, the Mg content should be 1.5 percent by mass or less.

(2-3) Third Embodiment of the Present Invention

According to the third embodiment of the present invention, a 6000 series Al-Mg-Si alloy is used. The aluminum alloy contains Si in a content of 0.2 percent by mass or more and 1.6 percent by mass or less and Mg in a content of 0.3 percent by mass or more and 1.5 percent by mass or less, and further contains at least one member selected from the group consisting of Fe in a content of 0.8 percent by mass or less, Cu in a content of 1.0 percent by mass or less, Mn in a content of 0.6 percent by mass or less, Cr in a content of 0.5 percent by mass or less, Zn in a content of 0.4 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.3 percent by mass or less, with the remainder being aluminum and inevitable impurities.
The reasons why the contents of the respective components are specified will be described below.
The reasons why the Fe, Mn, Cr, Ti, and Zr contents are specified and the description on the inevitable impurities are as with the Al-Mg alloy, and the description thereof is herein omitted.

[Si: 0.2 percent by mass or more and 1.6 percent by mass or less]

Silicon (Si) serves to improve the strength of the aluminum alloy. Si is generally contained in the aluminum alloy as an impurity in the ingot and forms an Al-(Fe)-Si intermetallic compound and a Si intermetallic compound in the slab typically in the casting step (S4) . Si, if its content is less than 0.2 percent by mass, may not exhibit the activity sufficiently. In contrast, Si, if its content is more than 1.6 percent by mass, may cause a coarse Si intermetallic compound in the slab, to thereby often cause unevenness in the surface appearance after anodization. Accordingly, the Si content should be 0.2 percent by mass or more and 1.6 percent by mass or less.

[Mg: 0.3 percent by mass or more and 1.5 percent by mass or less]

Magnesium (Mg) forms Mg₂Si in the coexistence with Si to thereby serve to improve the strength of the aluminum alloy. Mg, if its content is less than 0.3 percent by mass, may not exhibit the activity sufficiently. In contrast, if the Mg content is more than 1.5 percent by mass, the activity may be saturated. Accordingly, the Mg content should be 0.3 percent by mass or more and 1.5 percent by mass or less.

[Cu: 1.0 percent by mass or less]

Copper (Cu) serves to improve the strength of the aluminum alloy. Cu, if its content is more than 1.0 percent by mass, may impair the corrosion resistance. Accordingly, the Cu content should be 1.0 percent by mass or less.

[Zn: 0.4 percent by mass or less]

Zn serves to improve-the strength of the aluminum alloy. Zn, if its content is more than 0.4 percent by mass, may impair the corrosion resistance. Accordingly, the Zn content should be 0.4 percent by mass or less.

(2-4) Fourth Embodiment of the Present Invention

According to the fourth embodiment of the present invention, a 7000 series Al-Zn-Mg alloy is used. The aluminum alloy contains Mg in a content of 0.4 percent by mass or more and 4.0 percent by mass or less and Zn in a content of 3.0 percent by mass or more and 9.0 percent by mass or less, and further contains at least one member selected from the group consisting of Si in a content of 0.7 percent by mass or less, Fe in a content of 0.8 percent by mass or less, Cu in a content of 3.0 percent by mass or less, Mn in a content of 0.8 percent by mass or less, Cr in a content of 0.5 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.25 percent by mass or less, with the remainder being aluminum and inevitable impurities.
The reasons why the contents of the respective components are specified will be described below.
The reasons why the Cr, Ti, and Zr contents are specified and the description of the inevitable impurities are as with the Al-Mg alloy, whereby the descriptions thereof are herein omitted.

[Mg: 0.4 percent by mass or more and 4.0 percent by mass or less]

Magnesium (Mg) serves to improve the strength of the aluminum alloy. Mg, if its content is less than 0.4 percent by mass, may not exhibit the activity sufficiently. In contrast, Mg, if its content is more than 4.0 percent by mass, may often cause unevenness in the surface appearance after anodization. Accordingly, the Mg content should be 0.4 percent by mass or more and 4.0 percent by mass or less.

[Zn: 3.0 percent by mass or more and 9.0 percent by mass or less]

Zinc (Zn) serves to improve the strength of the aluminum alloy. Zn, if its content is less than 3.0 percent by mass, may not exhibit the activity sufficiently. In contrast, Zn, if its content is more than 9.0 percent by mass, may often cause unevenness in the surface appearance after anodization. Accordingly, the Zn content should be 3.0 percent by mass or more and 9.0 percent by mass or less.

[Si: 0.7 percent by mass or less]

Silicon (Si) is generally contained in the aluminum alloy as an impurity in the ingot and forms an Al-(Fe)-Si intermetallic compound in the slab typically in the casting step (S4). Si, if its content is more than 0.7 percent by mass, may cause a coarse Al-(Fe)-Si intermetallic compound in the slab, to thereby often cause unevenness in the surface appearance after anodization. Accordingly, the Si content should be 0.7 percent by mass or less.

[Fe: 0.8 percent by mass or less]

Iron (Fe) is generally contained in the aluminum alloy as an impurity in the ingot and forms an Al-Fe intermetallic compound in the slab typically in the casting step (S4). Fe, if its content is more than 0.8 percent by mass, may cause a coarse Al-Fe intermetallic compound in the slab, to thereby often cause unevenness in the surface appearance after anodization. Accordingly, the Fe content should be 0.8 percent by mass or less.

[Cu: 3.0 percent by mass or less]

Copper (Cu) serves to improve the strength of the aluminum alloy. Cu, if its content is more than 3.0 percent by mass, may impair the corrosion resistance. Accordingly, the Cu content should be 3.0 percent by mass or less.

[Mn: 0.8 percent by mass or less]

Manganese (Mn) allows the crystal structure to be finer. Mn, if its content is more than 0.8 percent by mass, may cause a coarse intermetallic compound, to thereby often cause unevenness in the surface appearance after anodization. Accordingly, the Mn content should be 0.8 percent by mass or less.

(3) Details of Manufacturing Methods

Next, the respective steps in the manufacturing methods according to the first to fourth embodiments of the present invention will be described.

(3-1) Melting Step

The melting step (S1) is a step of melting the raw material aluminum alloy.

(3-2) Hydrogen Gas Removal Step

The hydrogen gas removal step (S2) is a step of removing hydrogen gas from the aluminum alloy which has been melted in the melting step (S1).
Hydrogen gas is generated typically from hydrogen in a fuel and from water and organic substances attached typically to the ingot. Hydrogen gas, if contained in a large content, will cause the following disadvantages.

[a] Pin holes are generated.
[b] The product has insufficient strength.
[c] Hydrogen is accumulated and enriched at the grain boundary in the vicinity of the surface of the slab. This causes blistering of the slab and peeling of the aluminum alloy thick plate resulting from the blistering; and also causes potential defects on the surface of the thick plate which appear as surface defects of the thick plate.

Accordingly, the amount of hydrogen gas is preferably 0.2 ml or less and more preferably 0.1 ml or less per 100 g of the aluminum alloy. Removal of hydrogen gas can be suitably carried out by subjecting a molten metal typically to a fluxing process, chlorine refining, or in-line refining, and it can be more suitably carried out by using a SNIF (spinning nozzle inert flotation) system and a porous plug (see JP-ANo. 2002-146447 ) in a hydrogen gas removing apparatus.
The concentration of hydrogen gas in a slab can be determined typically in the following manner. Specifically, a sample is cut out from the slab after the casting step; then subjected to ultrasonic cleaning with alcohol and acetone; and thereafter analyzed typically according to the inert gas fusion thermal conductivity method (LIS A06-1993).
The concentration of hydrogen gas in an aluminum alloy thick plate can be determined typically in the following manner. Specifically, a sample is cut out from the aluminum alloy thick plate. Next, the sample is immersed in an aqueous NaOH solution; then treated with nitric acid to remove an oxide film on the surface of the sample; and the treated sample is subjected to ultrasonic cleaning with alcohol and acetone and then analyzed according typically to the vacuum heat extraction capacitance method (LIS A06-1993).

(3-3) Filtration Step

The filtration step (S3) is a step of removing mainly oxide and non-metal inclusions from the aluminum alloy with a filtrating device. The filtrating device is provided typically with a ceramic tube with alumina particles of about 1 mm. The inclusions are removed by allowing a molten metal to pass through the ceramic tube.
The hydrogen gas removal step and the filtration step ensure high quality of the aluminum alloy, and the resulting aluminum alloy is made into a high-quality slab in the subsequent casting step (S4). These steps can suppress the generation of deposits of oxides (dross), and this reduces the effort and time for removing the dross.

(3-4) Casting Step

The casting step (S4) is a step of producing a slab by forming a molten metal of the aluminum alloy typically with a casting apparatus into a predetermined shape such as a rectangular parallelepiped and solidifying the metal. Typically, a casting apparatus equipped with a water-cooled mold is used. A semi-continuous casting process is employed as the casting process. In the semi-continuous casting process, a molten metal of the aluminum alloy is injected from above into a water-cooled metallic mold having an open bottom, and the solidified aluminum alloy is successively withdrawn from the bottom of the water-cooled mold to give slabs having predetermined thickness. The semi-continuous casting process may be carried out vertically or horizontally.
The slicing step (S5) is a step of producing an aluminum alloy thick plate having a predetermined thickness by slicing the slab in the cast direction produced in the casting step (S4). The slab slicing process may be employed as a slicing process. The slab slicing process is a process for cutting out the slab in the cast direction by slicing the slab produced by the semi-continuous casting process typically with a band saw cutting apparatus, to give an aluminum alloy thick plate having a predetermined thickness. The thickness of the aluminum alloy thick plate is preferably 15 to 200 mm, but it is not particularly limited, and can be varied suitably depending on the intended use of the aluminum alloy thick plate .
A band saw is preferably used in the slicing process, but it is not particularly limited, and cutting may be also performed typically with a circular saw cutting apparatus, or by laser or water pressure.
Slicing the slab gives an aluminum alloy thick plate superior typically in surface condition, flatness, and accuracy of the plate thickness to a rolled product. For example, there can be obtained a thick plate having a flatness (amount of warpage) per 1 m in the casting direction of 0.4 mm or less per 1 m length in the evaluation of flatness, and the accuracy of the plate thickness of ±100 µm or less.
With reference to Fig. 2, a central portion B shaded with slanted lines is preferably removed in the first to fourth and seventh to twelfth embodiments and is mandatorily removed in the fifth and sixth embodiments in the slicing step (S5). The central portion B has two substantially identical thicknesses in a thickness direction from the center of the thickness direction A to the both surfaces of the central portion, respectively, and has a total thickness of from one-thirtieth to one-fifth the thickness T of the slab 1 (T/30 to T/5) . The central portion B in Fig. 2 is illustrated to have a thickness about one-fifth the thickness T. The thicknesses b1 and b2 of the upper and lower portions of the central portion B of the slab 1 are preferably equal to each other, but a difference between them of about 30% is acceptable. As used herein "the center of the thickness direction A" refers to a location which is the center of the slab 1 in the thickness direction and is located about a half the thickness T of the slab 1, i.e., a location of the slab 1 about T/2 deep.
The central portion B of the slab 1 is susceptive to unevenness in the surface and cross section of the thick plate after anodization. However, when the central portion B is removed by the slicing step (S5), and a thick plate excellent in quality of appearance after anodization with less within-lot variation can be obtained. Removal of a central portion having a thickness of less than T/30 (one-thirtieth the thickness T) may often cause a thick plate suffering from unevenness in the surface appearance after anodization and often cause a large within-lot variation. In contrast, if a central portion having a thickness of more than T/5 (one-fifth the thickness T) is removed, an excessively large amount of the portion is to be removed, and this may impair the productivity. Accordingly, the central portion B of the slab 1 is preferably removed in such an amount that the central portion has two substantially identical thicknesses in the thickness direction from the center of the thickness direction A to the both surfaces of the central portion, respectively, and has a total thickness of from one-thirtieth to one-fifth the thickness T of the slab 1 (T/30 to T/5).
After slicing the slab in the slicing step (S5), the subsequent heat treatment step (S6) is performed in which a heat treatment is conducted in order to remove the internal stress and to uniformize the inner structure. The heat treatment improves the flatness, accuracy of plate thickness, and quality of appearance after anodization.

(3-6) Heat Treatment Step

The heat treatment step (S6) is a step of carrying out a heat treatment (heat treatment for homogenization) on the aluminum alloy thick plate having a predetermined thickness produced in the slicing step (S5). The heat treatment may be carried out according to a common procedure. Specifically, when the aluminum alloy is a 5000 series Al-Mg alloy (the first embodiment of the present invention), a 3000 series Al-Mn alloy (the second embodiment of the present invention), and a 6000 series Al-Mg-Si alloy (the third embodiment of the present invention), the heat treatment is performed by holding the aluminum alloy thick plate at a temperature of 400°C or higher but lower than its melting point for one hour or longer. When the aluminum alloy is a 7000 series Al-Zn-Mg alloy (the fourth embodiment of the present invention), the heat treatment is performed by holding the aluminum alloy thick plate at a temperature of 350°C or higher but lower than its melting point for one hour or longer.
The slicing process of the slab obtained in the casting step (S4) allows the internal residual stress to be released, and this often causes warpage. According to the present invention, however, the sliced aluminum alloy thick plate having a predetermined thickness and subj ected to a heat treatment while being placed typically on a surface plate, and the resulting aluminum alloy thick plate thereby has improved flatness.
In the first to third embodiments of the present invention, a heat treatment, if conducted at a temperature of lower than 400°C, may not sufficiently help to remove the inner stress and to uniformize a solute element, which is segregated during casting, and the heat treatment may therefore not exhibit sufficient advantages. Accordingly, the treatment temperature herein should be 400°C or higher. If a heat treatment is conducted at a temperature equal to or higher than the melting point, part of the surface of the slab is melted, to cause an internal defect and to impair the strength/ductility. Accordingly, the treatment temperature should be lower than the melting point.
In the fourth embodiment of the present invention, a heat treatment, if conducted at a temperature of lower than 350°C, may not sufficiently help to remove the inner stress and to uniformize a solute element, which is segregated during casting, and therefore may exhibit less advantages. Accordingly, the treatment temperature herein should be 350°C or higher. If a heat treatment is conducted at a temperature equal to or higher than the melting point, part of the surface of the slab ismelted, to cause an internal defect and to impair the strength/ductility. Accordingly, the treatment temperature should be lower than the melting point.
A heat treatment, if conducted for a time shorter than one hour, may not sufficiently help intermetallic compounds to be solidly dissolved, and this may often cause the intermetallic compounds to be deposited. Accordingly, the treatment time should be one hour or longer. In contrast, a heat treatment, if conducted for a time of longer than about 8 hours, may be saturated in its effect, and this may cause energy loss. Accordingly, the treatment time is preferably controlled to be 8 hours or shorter.
The aluminum alloy thick plate after the heat treatment in the heat treatment step (S6) may be subjected to a surface smoothing treatment according to necessity in order to remove crystallized substances and oxides generated on the surface of the thick plate or to eliminate gas accumulation in the surface of the thick plate.

(3-7) Surface Smoothing Treatment Step

The surface smoothing treatment step (S7) is a step of subjecting the surface of the aluminum alloy thick plate produced in the heat treatment step (S6) to a surface smoothing treatment. Exemplary surface smoothing treatments include, but are not limited to, cutting such as end mill cutting and diamond bite cutting; grinding which faces the surface typically with a grindstone; and polishing such as buff polishing.
When the aluminum alloy thick plate is used for a vacuum chamber (chamber for a vacuum apparatus), it is especially effective to carry out a surface smoothing treatment. The reason therefor is as follows. Specifically, a vacuum chamber suffers from a decrease in the degree of vacuum therein caused by, when the chamber is decompressed to attain high vacuum, releasing of adsorbed gas from the inner surface of the chamber and releasing of gas atoms which are solidly dissolved in the thick plate onto the surface. This elongates the time which takes to reach a target degree of vacuum and thereby lowers production efficiency. Accordingly, the following conditions are required for the aluminum alloy thick plate used for a chamber: the amount of gas which adsorbs onto the surface of the thick plate positioned in an inner portion of the chamber is low; and the gas atoms which are solidly dissolved in the thick plate are not released even in high vacuum. The surface smoothing treatment herein satisfies these conditions.

(B) Methods for Manufacturing Aluminum Alloy Thick Plates According to Fifth to Eighth Embodiments of the Present Invention

(1) Outline of Manufacturing Methods

With reference to Fig. 3, the methods for manufacturing an aluminum alloy thick plate, according to the fifth to eighth embodiments of the present invention, each include a melting step (S1), a hydrogen gas removal step (S2), a filtration step (S3), a casting step (S4), a heat treatment step (S5), and a slicing step (S6) in this order. The methods may further include, where necessary, a surface smoothing treatment step (S7) subsequent to the slicing step (S6).
In these manufacturing methods, initially, a raw material aluminum alloy is melted in the melting step (S1). Next, hydrogen gas is removed from the molten aluminum alloy in the hydrogen gas removal step (S2), and inclusions such as oxides and non-metals are removed therefrom in the filtration step (S3). Next, the resulting aluminum alloy is cast by a semi-continuous casting process into a slab in the casting step (S4). The slab is subjected to a heat treatment in the heat treatment step (S5) and is then sliced in the cast direction into an aluminum alloy thick plate having a predetermined thickness in the slicing step (S6). Where necessary, the aluminum alloy thick plate having a predetermined thickness is further subjected to a surface smoothing treatment in the surface smoothing treatment step (S7).

(2) Aluminum Alloys

The manufacturing methods according to the fifth, sixth, seventh, and eighth embodiments of the present invention use, as a raw material aluminum alloy, a 5000 series Al-Mg alloy, a 3000 series Al-Mn alloy, a 6000 series Al-Mg-Si alloy, and a 7000 series Al-Zn-Mg alloy, respectively. The details of them are as follows.

(2-1) Fifth Embodiment of the Present Invention

A 5000 series Al-Mg alloy as in the first embodiment of the present invention is used in this embodiment. The composition and contents of components of the aluminum alloy, and the reasons why the contents are specified are as in the first embodiment of the present invention.

(2-2) Sixth Embodiment of the Present Invention

A 3000 series Al-Mn alloy as in the second embodiment of the present invention is used in this embodiment. The composition and contents of components of the aluminum alloy, and the reasons why the contents are specified are as in the second embodiment of the present invention.

(2-3) Seventh Embodiment of the Present Invention

A 6000 series Al-Mg-Si alloy as in the third embodiment of the present invention is used in this embodiment. The composition and contents of components of the aluminum alloy, and the reasons why the contents are specified are as in the third embodiment of the present invention.

(2-4) Eighth Embodiment of the Present Invention

A 7000 series Al-Zn-Mg alloy as in the fourth embodiment of the present invention is used in this embodiment. The composition and contents of components of the aluminum alloy, and the reasons why the contents are specified are as in the fourth embodiment of the present invention.

(3) Details of Manufacturing Methods

Next, the respective steps in the manufacturing methods according to the fifth to eighth embodiments of the present invention will be described.

(3-1) Melting Step

This step is the same as with the melting step (S1) in the first to fourth embodiments of the present invention.

(3-2) Hydrogen Gas Removal Step

This step is the same as with the hydrogen gas removal step (S2) in the first to fourth embodiments of the present invention.

(3-3) Filtration Step

This step is the same as with the filtration step (S3) in the first to fourth embodiments of the present invention.

(3-4) Casting Step

This step is the same as with the casting step (S4) in the first to fourth embodiments of the present invention.
Before slicing the slab produced in the casting step (S4), a heat treatment is carried out in the subsequent heat treatment step (S5), for the purpose of removing internal stress and uniformizing the inner structure. The heat treatment of the slab helps to improve the flatness, accuracy of plate thickness, and quality of appearance after anodization.

(3-5) Heat Treatment Step

The heat treatment step (S5) is a step of subjecting the slab produced in the casting step (S4) to a heat treatment (heat treatment for homogenization) . The heat treatment is carried out according to a common procedure. Specifically, when the aluminum alloy is a 5000 series Al-Mg alloy (the fifth embodiment of the present invention), a 3000 series Al-Mn alloy (the sixth embodiment of the present invention), and a 6000 series Al-Mg-Si alloy (the seventh embodiment of the present invention), the heat treatment is performed by holding the slab at a temperature of 200°C to 350°C (fifth and sixth embodiments) or 200°C or higher but lower than 400°C (seventh embodiment), both for one hour or longer. When the aluminum alloy is a 7000 series Al-Zn-Mg alloy (the eighth embodiment of the present invention), the heat treatment is performed by holding the slab at a temperature of 200°C or higher but lower than 350°C for one hour or longer.
In the fifth to seventh embodiments of the present invention, a heat treatment, if conducted at a temperature of lower than 200°C, may not sufficiently help to remove the inner stress and therefore may not exhibit satisfactory advantages. Accordingly, the treatment temperature should be 200°C or higher. In contrast, a heat treatment, if conducted at a temperature of more than 350°C (fith and sixth embodiments), or 400°C or higher (seventh embodiment), may excessively increase the ductility and lower the strength and cutting property. As used herein the term "cutting property" refers to chip breakability. Chips (scraps) are preferably formed as small or short pieces. This is because long chips become entangled with a working tool (blade) and are rotated therewith, and this damages the surface of the thick plate and breaks the tool. Accordingly, the treatment temperature should be at most 350°C (fifth and sixth embodiment), or lower than 400°C (seventh embodiment). A heat treatment performed under above-specified temperature conditions helps to improve the flatness and accuracy of plate thickness without adversely affecting the strength and cutting property.
In the eighth embodiment of the present invention, a heat treatment, if performed at a temperature of lower than 200°C, may not sufficiently help to remove the inner stress and therefore may not exhibit satisfactory advantages. Accordingly, the treatment temperature should be 200°C or higher. In contrast, a heat treatment, if conducted at a temperature of 350°C or higher, may excessively increase the ductility and lower the strength and cutting property. As used herein the term "cutting property" refers to chip breakability. Chips (scraps) are preferably formed as small or short pieces. This is because long chips become entangled with a working tool (blade) and are rotated therewith, and this damages the surface of the thick plate and breaks the tool. Accordingly, the treatment temperature should be lower than 350°C. A heat treatment performed under above-specified temperature conditions helps to improve the flatness and accuracy of plate thickness without adversely affecting the strength and cutting property.
A heat treatment, if conducted for a time shorter than one hour, may not sufficiently help intermetallic compounds to be solidly dissolved, and this may often cause the intermetallic compounds to be deposited. Accordingly, the treatment time should be one hour or longer. In contrast, a heat treatment, if conducted for a time of longer than about 8 hours, may be saturated in its effect, and this may cause energy loss. Accordingly, the treatment time is preferably controlled to be 8 hours or shorter.

(3-6) Slicing Step

The slicing step (S6) is a step of slicing the slab obtained in the heat treatment step (S5) into an aluminum alloy thick plate having a predetermined thickness. The details of this step are as with the slicing step (S5) in the first to fourth embodiments of the present invention, except that in the fifth and sixth embodiments the slicing step comprises removing a central portion in a thickness direction from the slab, the central portion having two substantially identical thicknesses in the thickness direction from the center of the thickness direction to the both surfaces of the central portion respectively, and having a total thickness of from one-thirtieth to one-fifth the thickness T of the slab (T/30 to T/5).
The aluminum alloy thick plate produced in the slicing step (S6) may be subjected to a surface smoothing treatment according to necessity in order to remove crystallized substances and oxides formed on the surface of the thick plate or to eliminate gas accumulation in the surface of the thick plate.

(3-7) Surface Smoothing Treatment Step

The surface smoothing treatment step (S7) is a step of subjecting the surface of the aluminum alloy thick plate produced in the slicing step (S6) to a surface smoothing treatment. The details of this step are as with the surface smoothing treatment step (S7) in the first to fourth embodiments of the present invention.

(C) Methods for Manufacturing Aluminum Alloy Thick Plates According to Ninth to Twelfth Embodiments of the Present Invention

(1) Outline of Manufacturing Methods

With reference to Fig. 1, the methods for manufacturing an aluminum alloy thick plate, according to the ninth to twelfth embodiments of the present invention, each include a melting step (S1), a hydrogen gas removal step (S2), a filtration step (S3), a casting step (S4), a slicing step (S5), and a heat treatment step (S6) in this order. The methods may further include, where necessary, a surface smoothing treatment step (S7) subsequent to the heat treatment step (S6).
In these manufacturing methods, initially, a raw material aluminum alloy is melted in the melting step (S1). Next, hydrogen gas is removed from the molten aluminum alloy in the hydrogen gas removal step (S2), and inclusions such as oxides and non-metals are removed therefrom in the filtration step (S3). Next, the resulting aluminum alloy is cast by a semi-continuous casting process into a slab in the casting step (S4). The slab is then sliced in the cast direction into an aluminum alloy thick plate having a predetermined thickness in the slicing step (S5). The aluminum alloy thick plate having a predetermined thickness is then subjected to a heat treatment in the heat treatment step (S6) and, where necessary, further subjected to a surface smoothing treatment in the surface smoothing treatment step (S7).

(2) Aluminum Alloys

The manufacturing methods according to the ninth, tenth, eleventh, and twelfth embodiments of the present invention use a 5000 series Al-Mg alloy, a 3000 series Al-Mn alloy, a 6000 series Al-Mg-Si alloy, and a 7000 series Al-Zn-Mg alloy, respectively, as a raw material aluminum alloy. The details of them are as follows.

(2-1) Ninth Embodiment of the Present Invention

(2-2) Tenth Embodiment of the Present Invention

(2-3) Eleventh Embodiment of the Present Invention

(2-4) Twelfth Embodiment of the Present Invention

(3) Details of Manufacturing Methods

Next, the respective steps in the manufacturing methods according to the ninth to twelfth embodiments of the present invention will be described below.

(3-1) Melting Step

(3-2) Hydrogen Gas Removal Step

(3-3) Filtration Step

(3-4) Casting Step

This step is the same as with the casting step (S4) in the first to fourth embodiments of the present invention.

(3-5) Slicing Step

This step is the same as with the slicing step (S5) in the first to fourth embodiments of the present invention.

(3-6) Heat Treatment Step

The heat treatment step (S6) is a step of carrying out a heat treatment (heat treatment for homogenization) on the aluminum alloy thick plate having a predetermined thickness produced in the slicing step (S5). The heat treatment may be carried out according to a common procedure. Specifically, when the aluminum alloy is a 5000 series Al-Mg alloy (the ninth embodiment of the present invention), a 3000 series Al-Mn alloy (the tenth embodiment of the present invention), and a 6000 series Al-Mg-Si alloy (the eleventh embodiment of the present invention), the heat treatment is performed by holding the aluminum alloy thick plate at a temperature of 200°C or higher but lower than 400°C for one hour or longer. When the aluminum alloy is a 7000 series Al-Zn-Mg alloy (the twelfth embodiment of the present invention), the heat treatment is performed by holding the aluminum alloy thick plate at a temperature of 200°C or higher but lower than 350°C for one hour or longer. The details of the other conditions and procedures are as with the heat treatment step (S6) in the first to fourth embodiments of the present invention.
In the ninth to eleventh embodiments of the present invention, a heat treatment, if conducted at a temperature of lower than 200°C may not sufficiently help to remove the inner stress and therefore may not exhibit satisfactory advantages. Accordingly, the treatment temperature should be 200°C or higher. In contrast, a heat treatment, if conducted at a temperature of 400°C or higher, may excessively increase the ductility and lower the strength and cutting property. As used herein the term "cutting property" refers to chip breakability. Chips (scraps) are preferably formed as small or short pieces. This is because long chips become entangled with a working tool (blade) and are rotated therewith, and this damages the surface of the thick plate and breaks the tool. Accordingly, the treatment temperature should be lower than 400°C. A heat treatment performed under above-specified temperature conditions helps to improve the flatness and accuracy of plate thickness without adversely affecting the strength and cutting property.
In the twelfth embodiment of the present invention, a heat treatment, if conducted at a temperature of lower than 200°C, may not sufficiently help to remove the inner stress and therefore may not exhibit satisfactory advantages. Accordingly, the treatment temperature should be 200°C or higher. In contrast, a heat treatment, if conducted at a temperature of 350°C or higher, may excessively increase the ductility and lower the strength and cutting property. As used herein the term "cutting property" refers to chip breakability. Chips (scraps) are preferably formed as small or short pieces. This is because long chips become entangled with a working tool (blade) and are rotated therewith, and this damages the surface of the thick plate and breaks the tool. Accordingly, the treatment temperature should be lower than 350°C. A heat treatment performed under above-specified temperature conditions helps to improve the flatness and accuracy of plate thickness without adversely affecting the strength and cutting property.
A heat treatment, if conducted for a time shorter than one hour, may not sufficiently help intermetallic compounds to be solidly dissolved, and this may often cause the intermetallic compounds to be deposited. Accordingly, the treatment time should be one hour or longer. In contrast, a heat treatment, if conducted for a time of longer than about 8 hours, may be saturated in its effect, and this may cause energy loss. Accordingly, the treatment time is preferably controlled to be 8 hours or shorter.

(3-7) Surface Smoothing Treatment Step

This step is the same as with the surface smoothing treatment step (S7) in the first to fourth embodiments of the present invention.
Next, aluminum alloy thick plates obtained by the method according to the present invention will be described below.
These aluminum alloy thick plates are manufactured by the procedures of the manufacturing method according to any one of the first to twelfth embodiments of the present invention and have an average crystal grain size of 400 µm or less.
The aluminum alloy thick plates obtained by the method according to the present invention have an average crystal grain size of 400 µm or less whereby can have improved quality of appearance after anodization and show a smaller within-lot variation.
A thick plate, if containing intermetallic compounds having large sizes, suffers from unevenness (uneven color) of the cross section and surface of the thick plate upon anodization. The aluminum alloy thick plates obtained by the method according to the present invention, however, contain intermetallic compounds with small sizes and are thereby resistant to such unevenness.
The measurement of the crystal grain size may be carried out, for example, in the following manner. Specifically, measurements are conducted in cross sections at four points, i.e., at thicknesses of T/5, 2T/5, 3T/5, and 4T/5 ranging from one surface of the slab to the other, wherein T represents the thickness of the slab, and the four measured data are averaged. These measured data are determined typically according to a cutting method. In the cutting method, cross sections of the aluminum alloy thick plate are etched according to a Barker method and are observed with an optical microscope.
The control of the average crystal grain size to 400 µm or less may be carried out typically in the following manner. Specifically, a cooling rate (average cooling rate from the liquidus temperature to the solidus temperature) during casting is set to be 0.2°C/second or more. Additionally, the aluminum alloy contains 0.1 percent by mass or less of Ti or 0.3 percent by mass or less of Zr and thereby the crystal grain size can be more finer (smaller) in the manufacturing methods according to the first to third embodiments, the fifth to seventh embodiments, and the ninth to eleventh embodiments of the present invention. The aluminum alloy contains 0.1 percent by mass or less of Ti or 0.25 percent by mass or less of Zr and thereby the crystal grain size can be more finer (smaller) in the manufacturing methods according to the fourth, eighth, and twelfth embodiments of the present invention.
The resulting aluminum alloy thick plates manufactured by the procedures of the manufacturing methods according to the first to twelfth embodiments of the present invention are satisfactory in the surface condition, flatness, and accuracy of plate thickness as described above and can be used for various applications including semiconductor-related devices such as base substrates, transport devices, and vacuum chambers; electrical and electronic parts and their manufacturing devices; household articles; and mechanical parts. Additionally, they can be recycled and used for other applications.
There is not need of considering about the corrosion resistance of the aluminum alloy thick plates. This is because thick plates for base substrates and for transport devices are used in clean rooms, they are thereby not required to have generic corrosion resistance. Even when the thick plates are used for vacuum chambers, high corrosion resistance is unnecessary since the environment hardly causes the thick plate to be exposed to a corrosive gas.
Preferred embodiments have been illustrated above, but the present invention is not limited to these embodiments.

EXAMPLES

Some Examples (Experimental Examples) of the present invention will be illustrated below.

(1) First Experimental Example

This experimental example relates to the first embodiment of the present invention. The experimental example used 5000 series Al-Mg alloys as the aluminum alloys.

With reference to Table 1, Alloys 1A to 12A were used as example alloys; while Alloys 13A to 22A were used as comparative example alloys .

[Table 1]

Category	Number	Element (percent by mass)									Alloy type	Remarks
Category	Number	Mg	Si	Fe	Cu	Mn	Cr	Zn	Ti	Zr	Alloy type	Remarks
Example Alloy	Alloy 1A	2.4	0.1	0.3	-	-	-	-	0.01	-	5000 series
	Alloy 2A	2.4	0.1	0.3	-	0.3	-	-	0.01	-	5000 series
	Alloy 3A	5.0	0.1	0.3	-	-	-	-	0.01	-	5000 series
	Alloy 4A	8.0	0.1	0.3	-	-	-	-	0.01	0.1	5000 series
	Alloy 5A	11.0	0.1	0.3	-	-	-	-	0.01	-	5000 series
	Alloy 6A	5.0	0.3	0.5	0.3	-	-	-	0.01	-	5000 series
	Alloy 7A	5.0	0.1	0.3	-	0.05	-	-	0.01	-	5000 series
	Alloy 8A	5.0	0.1	0.3	-	-	0.05	-	0.01	-	5000 series
	Alloy 9A	5.0	0.1	0.3	-	0.7	0.3	-	0.01	0.1	5000 series
	Alloy 10A	5.0	0.1	0.3	-	0.05	-	0.3	0.01	-	5000 series
	Alloy 11A	2.5	0.1	0.3	-	-	0.15	-	0.01	-	5000 series	JIS 5052 alloy
	Alloy 12A	4.6	0.1	0.2	-	0.6	-	-	0.01	-	5000 series	JIS 5083 alloy
Comparative Example Alloy	Alloy 13A	1.2	0.1	0.3	-	-	-	-	0.01	-	5000 series	Mg content less than lower limit
	Alloy 14A	14.0	0.1	0.3	-	-	-	-	0.01	-	5000 series	Mg content more than upper limit
	Alloy 15A	5.0	0.8	0.3	-	-	-	-	0.01	-	5000 series	Si content more than upper limit
	Alloy 16A	5.0	0.1	1.0	-	-	-	-	0.01	-	5000 series	Fe content more than upper limit
	Alloy 17A	5.0	0.1	0.3	0.7	-	-	-	0.01	-	5000 series	Cu content more than upper limit
	Alloy 18A	5.0	0.1	0.3	-	1.2	-	-	0.01	-	5000 series	Mn content more than upper limit
	Alloy 19A	5.0	0.1	0.3	-	-	0.6	-	0.01	-	5000 series	Cr content more than upper limit
	Alloy 20A	5.0	0.1	0.3	-	-	-	0.5	0.01	-	5000 series	Zn content more than upper limit
	Alloy 21A	5.0	0.1	0.3	-	-	-	-	0.15	-	5000 series	Ti content more than upper limit
	Alloy 22A	5.0	0.1	0.3	-	-	-	-	0.01	0.4	5000 series	Zr content more than upper limit

(Treatments)

Initially, a series of slabs having a plate thickness of 500 mm was prepared by subjecting Alloys 1A to 22A to a melting step, a hydrogen gas removal step, a filtration step, and a casting step sequentially in this order.
Next, sliced samples and hot-rolled samples were prepared from the slabs. The sliced samples were prepared by subjecting the slabs to a slicing step, while the hot-rolled samples were prepared by subjecting the slabs to a heat treatment and subsequently to hot rolling. The sliced samples and hot-rolled samples are aluminum alloy thick plates each 20 mm thick, 1000 mm wide, and 2000 mm long.
Next, the sliced samples were further subjected to a heat treatment step in which they were held at a temperature of 500°C for 4 hours.
Accordingly, the resulting sliced samples are aluminum alloy thick plates manufactured by the procedures of the manufacturing method according to the first embodiment of the present invention, but the resulting hot-rolled samples are not. Among them, only the sliced samples using Alloys 1A to 22A correspond to examples according to the first embodiment of the present invention.
Next, the sliced samples and hot-rolled samples after the treatments. were tested for their properties as below.

In the flatness evaluation, the sliced samples were tested to determine their amounts of warpage (flatness) per 1 m in the casting direction, while the hot-rolled samples were tested to determine their amounts of warpage (flatness) per 1 m in the rolling direction. Samples having an amount of warpage of 0.4 mm or less per 1 m length were evaluated as having accepted flatness (Accepted), while those having an amount of warpage of more than 0.4 mm per 1 m length were evaluated as having unaccepted flatness (Failed).

In the evaluation of accuracy of plate thickness, thicknesses at six positions of each sample were measured with a micrometer. The six positions are the four corners of the sample thick plate, and two positions each located at a half the length of the long sides and 20 mm inside in the width direction of the thick plate. Samples having thicknesses of 19.94 mm or more and 20.06 mm or less at all the six positions were evaluated as having excellent accuracy of plate thickness (Excellent) ; and those having thicknesses of 19.90 mm or more and 20.10 mm or less at all the six positions were evaluated as having accepted accuracy of plate thickness (Accepted).

The strength test was conducted in the following manner. Specifically, JIS No. 5 test pieces were prepared from the aluminum alloy thick plates to perform tensile test thereon, and their tensile strength and 0.2%-proof stress were measured. Samples having a tensile strength of 180 N/mm² or more were evaluated as having accepted strength (Accepted) ; while those having a tensile strength of less than 180 N/mm² were evaluated as having unaccepted strength (Failed).

The anodizability evaluation was carried out in the following manner. Anodized aluminum films having a thickness of 10 µm were formed on surfaces and cross sections of the aluminum alloy thick plates by sulfuric acid anodization under conditions of 15% sulfuric acid, 20°C, and a current density of 2 A/dm². The appearances of surfaces and cross sections of the thick plates were observed. Samples showing no unevenness (uneven color) in their appearances were evaluated as having accepted anodizability (Accepted); while those showing unevenness in their appearances were evaluated as having unaccepted anodizability (Failed) .
Since the anodizability is affected by the crystal grain sizes of the thick plates, the average crystal grain sizes of the thick plates were determined. The measurements of the average crystal grain sizes were carried out in the following manner. Specifically, measurements were conducted in cross sections at four points, i.e., at thicknesses of T/5, 2T/5, 3T/5, and 4T/5 ranging from one surface of the slab to the other, wherein T represents the thickness of the slab, and the four measured data were averaged. These measured data were determined according to the cutting method. In the cutting method, cross sections of the aluminum alloy thick plate were etched according to the Barker method and were observed with an optical microscope.

The test results are shown in Tables 2 and 3.

[Table 2]

	Category	Number	Flatness		Accuracy of plate thickness	Strength			Appearance after anodization		Cross section structure
	Category	Number	(mm/m)	Evaluation	Evaluation	Tensile strength (N/mm²)	Proof stress (N/mm²)	Evaluation	Surface appearance	Cross section appearance	Average crystal grain size (µm)
Sliced Sample	Example	Alloy 1A	0.16	Accepted	Excellent	196	91	Accepted	Accepted	Accepted	180
		Alloy 2A	0.16	Accepted	Excellent	205	100	Accepted	Accepted	Accepted	180
		Alloy 3A	0.19	Accepted	Excellent	290	137	Accepted	Accepted	Accepted	170
		Alloy 4A	0.20	Accepted	Excellent	316	161	Accepted	Accepted	Accepted	160
		Alloy 5A	0.22	Accepted	Excellent	368	175	Accepted	Accepted	Accepted	140
		Alloy 6A	0.20	Accepted	Excellent	290	141	Accepted	Accepted	Accepted	170
		Alloy 7A	0.18	Accepted	Excellent	287	137	Accepted	Accepted	Accepted	160
		Alloy 8A	0.19	Accepted	Excellent	287	139	Accepted	Accepted	Accepted	160
		Alloy 9A	0.20	Accepted	Excellent	301	146	Accepted	Accepted	Accepted	150
		Alloy 10A	0.21	Accepted	Excellent	285	135	Accepted	Accepted	Accepted	170
		Alloy 11A	0.17	Accepted	Excellent	205	102	Accepted	Accepted	Accepted	170
		Alloy 12A	0.19	Accepted	Excellent	288	136	Accepted	Accepted	Accepted	160
	Comparative Example	Alloy 13A	0.15	Accepted	Excellent	155	62	Failed	Accepted	Accepted	220
		Alloy 14A	unproducible due to the generation of casting cracks
		Alloy 15A	0.20	Accepted	Excellent	292	' 143	Accepted	Failed	Accepted	160
		Alloy 16A	0.20	Accepted	Excellent	290	142	Accepted	Failed	Accepted	150
		Alloy 17A	0.21	Accepted	Excellent	305	156	Accepted	Accepted	Accepted	160
		Alloy 18A	0.21	Accepted	Excellent	308	155	Accepted	Failed	Accepted	140
		Alloy 19A	0.20	Accepted	Excellent	305	152	Accepted	Failed	Accepted	140
		Alloy 20A	0.19	Accepted	Excellent	287	138	Accepted	Accepted	Accepted	170
		Alloy 21A	0.19	Accepted	Excellent	292	142	Accepted	Accepted	Accepted	140
		Alloy 22A	0.19	Accepted	Excellent	294	148	Accepted	Accepted	Accepted	170

[Table 3]

	Category	Number	Flatness		Accuracy of plate thickness	Strength			Appearance after anodization		Cross section structure
	Category	Number	(mm/m)	Evaluation	Evaluation	Tensile strength (N/mm²)	Proof stress (N/mm²)	Evaluation	Surface appearance	Cross section appearance	Average crystal grain size (µm)
Hot-rolled Sample	Comparative Example	Alloy 1A	0.41	Failed	Excellent	212	105	Accepted	Accepted	Failed	170
		Alloy 2A	0.42	Failed	Excellent	221	110	Accepted	Accepted	Failed	150
		Alloy 3A	0.50	Failed	Accepted	303	144	Accepted	Accepted	Failed	160
		Alloy 4A	0.61	Failed	Accepted	321	168	Accepted	Accepted	Failed	140
		Alloy 5A	0.73	Failed	Accepted	388	202	Accepted	Accepted	Failed	130
		Alloy 6A	0.50	Failed	Accepted	312	158	Accepted	Accepted	Failed	160
		Alloy 7A	0.50	Failed	Accepted	304	155	Accepted	Accepted	Failed	150
		Alloy 8A	0.50	Failed	Accepted	309	156	Accepted	Accepted	Failed	150
		Alloy 9A	0.52	Failed	Accepted	321	162	Accepted	Accepted	Failed	140
		Alloy 10A	0.50	Failed	Accepted	310	150	Accepted	Accepted	Failed	160
		Alloy 11A	0.43	Failed	Excellent	232	133	Accepted	Accepted	Failed	160
		Alloy 12A	0.47	Failed	Accepted	312	165	Accepted	Accepted	Failed	140
		Alloy 13A	0.41	Failed	Excellent	178	92	Failed	Accepted	Failed	200
		Alloy 14A	unproducible due to the generation of casting cracks
		Alloy 15A	0.51	Failed	Accepted	305	145	Accepted	Failed	Failed	170
		Alloy 16A	0.52	Failed	Accepted	303	144	Accepted	Failed	Failed	160
		Alloy 17A	0.51	Failed	Accepted	314	158	Accepted	Accepted	Failed	150
		Alloy 18A	0.52	Failed	Accepted	320	157	Accepted	Failed	Failed	120
		Alloy 19A	0.52	Failed	Accepted	316	155	Accepted	Failed	Failed	120
		Alloy 20A	0.51	Failed	Accepted	300	143	Accepted	Accepted	Failed	150
		Alloy 21A	0.52	Failed	Accepted	306	147	Accepted	Accepted	Failed	160
		Alloy 22A	0.51	Failed	Accepted	310	154	Accepted	Accepted	Failed	130

Table 2 shows the test results of the sliced samples, in which Alloys 1A to 12A correspond to Examples, and Alloys 13A to 22A correspond to comparative examples. Table 3 shows the test results of the hot-rolled samples, in which all Alloys 1A to 22A correspond to comparative examples .

(Re: Sliced Samples)

With reference to Table 2, the samples using Alloys 1A to 13A and 15A to 22A had small processing strain and showed little warpage, i.e., they had satisfactory flatness . Additionally, they excelled in accuracy of plate thickness.
The sample using Alloy 14A contained Mg in a content of more than its upper limit in the material aluminum alloy, thereby suffered from casting cracks, and was unproducible. The sample using Alloy 13A contained Mg in a content of less than its lower limit in the material aluminum alloy and thereby had insufficient strength.
The samples using Alloys 1A to 13A, 17A, and 20A to 22A did not suffer from unevenness in their appearances of surfaces after anodization. The samples using Alloys 15A, 16A, 18A, and 19A contained Si, Fe, Mn, and Cr, respectively, in a content of more than the upper limit in the material aluminum alloy, thereby caused a coarse intermetallic compound, and suffered from unevenness in their appearances of surfaces after anodization. The samples using Alloys 1A to 13A and 15A to 22A did not suffer from unevenness in their appearances of cross sections after anodization.
The samples using Alloys 17A, 20A, 21A, and 22A contained Cu, Zn, Ti, and Zr, respectively, in a content of more than the upper limit in the material aluminum alloy, and advantages obtained therefrom were thereby saturated, resulting in inferior economical efficiency.

(Re: Hot-rolled Samples)

As is demonstrated in Table 3, the samples using Alloys 1A to 13A and 15A to 22A had accumulated processing strain and showed large warpage in the rolling direction. Specifically, they showed inferior flatness. Many of them showed somewhat inferior accuracy of plate thickness to the sliced samples.
The sample using Alloy 14A contained Mg in a content of more than the upper limit in the material aluminum alloy, suffered from casting cracks, and was unproducible. The sample using Alloy 13A contained Mg in a content of less than the lower limit in the material aluminum alloy and showed insufficient strength.
The samples using Alloys 15A, 16A, 18A, and 19A contained Si, Fe, Mn, and Cr, respectively, in a content of more than the upper limit in the material aluminum alloy, caused coarse intermetallic compounds, and suffered from unevenness in their appearances of surfaces after anodization. The samples using Alloys 1A to 13A and 15A to 22A suffered from unevenness in their appearances of cross sections after anodization.

(2) Second Experimental Example

This experimental example relates to the first embodiment of the present invention. The experimental example used Alloy 3A in Table 1.

(Treatments)

Initially, a series of slabs having a plate thickness of 500 mm was prepared by subjecting Alloy 3A to a melting step, a hydrogen gas removal step, a filtration step, and a casting step sequentially in this order.
Next, the slabs were further subjected to a slicing step to give sliced samples . The sliced samples are aluminum alloy thick plates each 20 mm thick, 1000 mm wide, and 2000 mm long.

The sliced samples were then subjected to a heat treatment step. Specifically, the sliced samples were further subjected to a heat treatment under conditions given in Table 4.

[Table 4]

	Category		Number	Heat treatment for uniformization	Flatness		Accuracy of plate thickness
	Category		Number	Heat treatment for uniformization	(mm/m)	Evaluation	Evaluation
Sliced Sample	Example	A1	Alloy 3A	420°C for2 hr	0.21	Excellent	Excellent
	Example	A2	Alloy 3A	500°C for 4 hr	0.19	Excellent	Excellent
	Comparative Example	A3	Alloy 3A	none	0.30	Accepted	Accepted
		A4	Alloy 3A	380°C for 4 hr	0.26	Accepted	Excellent
		A5	Alloy 3A	530°C for 2 hr	unproducible due to the generation of burning

Samples A1 and A2, whose heat treatment conditions satisfy the conditions according to the first embodiment of the present invention, correspond to examples according to the first embodiment of the present invention; whereas Samples A3 to A5, whose heat treatment conditions do not satisfy the conditions according to the first embodiment of the present invention, correspond to comparative examples.
Next, the sliced samples after the treatments were subjected to a flatness evaluation test and an evaluation test for accuracy of plate thickness.

In the flatness evaluation, the samples were tested to determine their amounts of warpage (flatness) per 1 m in the casting direction. Samples having an amount of warpage of 0.4 mm or less per 1 m length were evaluated as having accepted flatness (Accepted), and those having an amount of warpage of 0.25 mm or less per 1 m length were evaluated as having excellent flatness (Excellent).

The evaluation test for accuracy of plate thickness is as in First Experimental Example.
The test results are shown in Table 4.
As is demonstrated in Table 4, Examples A1 and A2, whose heat treatment conditions satisfy the conditions specified in the first embodiment of the present invention, excelled in flatness and accuracy of plate thickness. Comparative Example A3 did not undergo a heat treatment and was thereby somewhat inferior in flatness and accuracy of plate thickness to Examples A1 and A2. Comparative Example A4 underwent a heat treatment at a temperature lower than the temperature range specified in the first embodiment of the present invention (lower than 400°C) and was thereby somewhat inferior in flatness to Examples A1 and A2. Comparative Example A5 underwent a heat treatment at a temperature higher than the temperature range specified in the first embodiment of the present invention (higher than the melting point), whereby suffered from internal partial melting and resulting internal defects, and was unproducible.

(3) Third Experimental Example

This experimental example relates to the second embodiment of the present invention. The experimental example used 3000 series Al-Mn alloys as the aluminum alloys.

With reference to Table 5, Alloys 23A and 24A were used as example alloys; while Alloys 25A and 26A were used as comparative example alloys .

[Table 5]

Category	Number	Element (percent by mass)									Alloy type	Remarks
Category	Number	Mg	Si	Fe	Cu	Mn	Cr	Zn	Ti	Zr	Alloy type	Remarks
Example Alloy	Alloy 23A	-	0.1	0.3	-	0.5	-	-	0.01	-	3000 series
Example Alloy	Alloy 24A	-	0.1	0.4	-	0.9	-	-	0.01	-	3000 series
Comparative Example Alloy	Alloy 25A	-	0.1	0.4	-	0.2	-	-	0.01	-	3000 series	Mn content less than lower limit
Comparative Example Alloy	Alloy 26A	-	0.1	0.3	-	1.7	-	-	0.01	-	3000 series	Mn content more than upper limit

(Treatments)

Initially, a series of slabs having a plate thickness of 500 mm was prepared by subjecting Alloys 23A to 26A to a melting step, a hydrogen gas removal step, a filtration step, and a casting step sequentially in this order.
Next, sliced samples and hot-rolled samples were prepared from the slabs. The sliced samples were prepared by subjecting the slabs to a slicing step, while the hot-rolled samples were prepared by subjecting the slabs to a heat treatment and subsequently to hot rolling. The sliced samples and hot-rolled samples are aluminum alloy thick plates each 20 mm thick, 1000 mm wide, and 2000 mm long.
Next, the sliced samples were further subjected to a heat treatment step in which they were held at a temperature of 500°C for 4 hours.
Accordingly, the sliced samples after the treatments are aluminum alloy thick plates manufactured by the procedures of the manufacturing method according to the second embodiment of the present invention, whereas the hot-rolled samples after the treatments are not. Among them, only the sliced samples using Alloys 23A and 24A correspond to examples according to the second embodiment of the present invention.
Next, the prepared sliced samples and hot-rolled samples were further subjected to a flatness evaluation test, an evaluation test for accuracy of plate thickness, a strength test, and an anodizability evaluation test.
The procedures and criteria of the respective tests are as in First Experimental Example.
However, the properties of thick plates vary depending on the type of alloy used, and the criteria for the strength were modified as follows . Specifically, samples having a tensile strength of 90 N/mm² or more were evaluated as having accepted strength (Accepted), whereas those having a tensile strength of less than 90 N/mm² were evaluated as having unaccepted strength (Failed).

The test results are shown in Table 6.

[Table 6]

	Category	Number	Flatness		Accuracy of plate thickness	Strength			Appearance after anodization
	Category	Number	(mm/m)	Evaluation	Evaluation	Tensile strength (N/mm²)	Proof stress (N/mm²)	Evaluation	Surface appearance	Cross section appearance
Sliced Sample	Example	Alloy 23A	0.19	Accepted	Excellent	92	36	Accepted	Accepted	Accepted
	Example	Alloy 24A	0.21	Accepted	Excellent	99	37	Accepted	Accepted	Accepted
	Comparative Example	Alloy 25A	0.19	Accepted	Excellent	82	36	Failed	Accepted	Accepted
	Comparative Example	Alloy 26A	0.24	Accepted	Excellent	114	52	Accepted	Failed	Accepted
Hot-rolled Sample	Comparative Example	Alloy 23A	0.41	Failed	Excellent	112	54	Accepted	Accepted	Failed
		Alloy 24A	0.42	Failed	Accepted	116	57	Accepted	Accepted	Failed
		Alloy 25A	0.41	Failed	Excellent	98	50	Accepted	Accepted	Failed
		Alloy 26A	0.45	Failed	Accepted	138	70	Accepted	Failed	Failed

(Re: Sliced Samples)

As is demonstrated in Table 6, the samples using Alloys 23A to 26A had small processing strain and showed little warpage, i.e., they had satisfactory flatness. Additionally, they excelled in accuracy of plate thickness.
The sample using Alloy 25A contained Mn in a content less than the lower limit in the material aluminum alloy and thereby had insufficient strength. The sample using Alloy 26A contained Mn in a content of more than the upper limit in the material aluminum alloy, thereby caused coarse intermetallic compounds, and suffered from unevenness in its appearance of surface after anodization. The samples using Alloys 23A to 26A did not suffer from unevenness in their appearances of cross sections after anodization.

(Re: Hot-rolled Samples)

As is demonstrated in Table 6, the samples using Alloy 23A to 26A suffered from accumulated processing strain and showed large warpage in the rolling direction. Specifically, they showed inferior flatness. Many of them were somewhat inferior in accuracy of plate thickness to the corresponding sliced samples.
The sample using Alloy 25A contained Mn in a content of less than the lower limit in the material aluminum alloy and was thereby somewhat inferior in strength to the other hot-rolled samples. The sample using Alloy 26A contained Mn in a content of more than the upper limit in the material aluminum alloy, thereby caused coarse intermetallic compounds, and suffered from unevenness in its appearance of surface after anodization. The samples using Alloy 23A to 26A suffered from unevenness in their appearances of cross sections after anodization.

(4) Fourth Experimental Example

This experimental example relates to the third embodiment of the present invention. The experimental example used 6000 series Al-Mg-Si alloys as the aluminum alloys.

With reference to Table 7, Alloys 27A and 28A were used as example alloys; while Alloys 29A to 32A were used as comparative example alloys.

[Table 7]

Category	Num ber	Element (percent by mass)									Alloy type	Remarks
Category	Num ber	Mg	Si	Fe	Cu	Mn	Cr	Zn	Ti	Zr	Alloy type	Remarks
Example Alloy	Alloy 27A	1.0	0.5	0.5	0.3	0.1	0.2	0.2	0.02	-	6000 series
Example Alloy	Alloy 28A	0.5	1.0	0.2	-	0.1	-	-	0.02	-	6000 series
Comparative Example Alloy	Alloy 29A	0.9	0.1	0.5	-	0.1	-	-	0.02	-	6000 series	Si content less than lower limit
	Alloy 30A	0.9	1.8	0.4	-	0.1	-	-	0.02	-	6000 series	Si content more than upper limit
	Alloy 31A	0.2	0.5	0.5	-	0.1	-	-	0.02	-	6000 series	Mg content less than lower limit
	Alloy 32A	1.7	0.5	0.4	-	0.1	-	-	0.02	-	6000 series	Mg content more than upper limit

(Treatments)

Initially, a series of slabs having a plate thickness of 500 mm was prepared by subjecting Alloy 27A to 32A to a melting step, a hydrogen gas removal step, a filtration step, and a casting step sequentially in this order.
Next, sliced samples and hot-rolled samples were prepared from the slabs. The sliced samples were prepared by subjecting the slabs to a slicing step, while the hot-rolled samples were prepared by subjecting the slabs to a heat treatment and subsequently to hot rolling. The sliced samples and hot-rolled samples are aluminum alloy thick plates each 20 mm thick, 1000 mm wide, and 2000 mm long.
Next, the sliced samples were further subjected to a heat treatment step in which they were held at a temperature of 500°C for 4 hours.
The resulting sliced samples and hot-rolled samples were further subjected to a solution treatment at 520°C and subsequently to an aging treatment at 175°C for 8 hours.
Accordingly, the sliced samples after these treatments are aluminum alloy thick plates manufactured by the procedures of the manufacturing method according to the third embodiment of the present invention, whereas the hot-rolled samples after the treatments are not. Among them, only the sliced samples using Alloys 27A and 28A correspond to examples according to the third embodiment of the present invention.
Next, the sliced samples and hot-rolled samples after the treatments were subjected to a strength test and an anodizability evaluation test.
The procedures and criteria of the respective tests are as in First Experimental Example.
However, the properties of thick plates vary depending on the type of alloy used, and the criteria for the strength were modified as follows . Specifically, samples having a tensile strength of 200 N/mm² or more were evaluated as having accepted strength (Accepted), whereas those having a tensile strength of less than 200 N/mm² were evaluated as having unaccepted strength (Failed).

The test results are shown in Table 8.

[Table 8]

	Category	Number	Strength			Appearance after anodization
	Category	Number	Tensile strength (N/mm²)	Proof stress (N/mm²)	Evaluation	Surface appearance	Cross section appearance
Sliced Sample	Example	Alloy 27A	322	272	Accepted	Accepted	Accepted
	Example	Alloy 28A	296	250	Accepted	Accepted	Accepted
	Comparative Example	Alloy 29A	114	67	Failed	Accepted	Accepted
		Alloy 30A	342	302	Accepted	Failed	Accepted
		Alloy 31A	178	125	Failed	Accepted	Accepted
		Alloy 32A	210	124	Accepted	Accepted	Accepted
Hot-rolled Sample	Comparative Example	Alloy 27A	346	276	Accepted	Accepted	Failed
		Alloy 28A	318	276	Accepted	Accepted	Failed
		Alloy 29A	138	88	Failed	Accepted	Failed
		Alloy 30A	365	323	Accepted	Failed	Failed
		Alloy 31A	197	143	Failed	Accepted	Failed
		Alloy 32A	235	146	Accepted	Accepted	Failed

(Re: Sliced Samples)

As is demonstrated in Table 8, the samples using Alloys 29A and 31A contained Si and Mg, respectively, in a content of less than the lower limit in the material aluminum alloy and showed insufficient strength. The sample using Alloy 30A contained Si in a content of more than the upper limit in the material aluminum alloy, caused coarse intermetallic compounds, and suffered from unevenness in its appearance of surface after anodization. The sample using Alloy 32A contained Mg in a content of more than the upper limit in the material aluminum alloy, and advantages obtained therefrom were saturated, resulting in inferior economical efficiency. The samples using Alloys 27A to 32A did not suffer from unevenness in their appearances of cross sections after anodization.

(Re: Hot-rolled Samples)

As is demonstrated in Table 8, the samples using Alloys 29A and 31A contained Si and Mg, respectively, in a content of less than the lower limit in the material aluminum alloy and showed insufficient strength. The sample using Alloy 30A contained Si in a content of more than the upper limit in the material aluminum alloy, caused coarse intermetallic compounds, and suffered from unevenness in its appearance of surface after anodization. The sample using Alloy 32A contained Mg in a content of more than the upper limit in the material aluminum alloy, and advantages obtained therefrom were saturated, resulting in inferior economical efficiency. The samples using Alloy 27A to 32A suffered from unevenness in their appearances of cross sections after anodization.

(5) Fifth Experimental Example

This experimental example relates to the fourth embodiment of the present invention. The experimental example used 7000 series Al-Zn-Mg alloys as the aluminum alloys.

With reference to Table 9, Alloys 33A and 34A were used as example alloys, while Alloys 35A to 38A were used as comparative example alloys.

[Table 9]

Category	Number	Element (percent by mass)									Alloy type	Remarks
Category	Number	Mg	Si	Fe	Cu	Mn	Cr	Zn	Ti	Zr	Alloy type	Remarks
Example Alloy	Alloy 33A	2.5	0.1	0.2	1.8	-	0.2	5.5	0.02	-	7000 series
Example Alloy	Alloy 34A	3.5	0.2	0.2	2.0	-	-	8.5	0.02	0.2	7000 series
Comparative Example Alloy	Alloy 35A	0.3	0.1	0.2	2.2	-	0.1	4.0	0.02	-	7000 series	Mg content less than lower limit
	Alloy 36A	5.0	0.2	0.2	2.0	-	0.1	5.0	0.02	-	7000 series	Mg content more than upper limit
	Alloy 37A	2.5	0.1	0.2	2.2	-	0.1	2.4	0.02	-	7000 series	Zn content less than lower limit
	Alloy 38A	3.0	0.2	0.2	2.0	-	0.1	9.5	0.02	-	7000 series	Zn content more than upper limit

(Treatments)

Initially, a series of slabs having a plate thickness of 500 mm was prepared by subjecting Alloys 33A to 38A to a melting step, a hydrogen gas removal step, a filtration step, and a casting step sequentially in this order.
Next, sliced samples and hot-rolled samples were prepared from the slabs. The sliced samples were prepared by subjecting the slabs to a slicing step, while the hot-rolled samples were prepared by subjecting the slabs to a heat treatment and subsequently to hot rolling. The sliced samples and hot-rolled samples are aluminum alloy thick plates each 20 mm thick, 1000 mm wide, and 2000 mm long.
Next, the sliced samples were further subjected to a heat treatment step in which they were held at a temperature of 500°C for 4 hours.
The resulting sliced samples and hot-rolled samples were further subjected to a solution treatment at 470°C and subsequently to an aging treatment at 120°C for 48 hours.
Accordingly, the sliced samples after these treatments are aluminum alloy thick plates manufactured by the procedures of the manufacturing method according to the fourth embodiment of the present invention, whereas the hot-rolled samples after the treatments are not. Among them, only the sliced samples using Alloys 33A and 34A correspond to examples according to the fourth embodiment of the present invention.
Next, the sliced samples and hot-rolled samples after the treatments were subjected to a strength test and an anodizability evaluation test.
The procedures and criteria of the respective tests are as in First Experimental Example.
However, the properties of thick plates vary depending on the type of alloy used, and the criteria for the strength were modified as follows . Specifically, samples having a tensile strength of 250 N/mm² or more were evaluated as having accepted strength (Accepted), whereas those having a tensile strength of less than 250 N/mm² were evaluated as having unaccepted strength (Failed).

The test results are shown in Table 10.

[Table 10]

	Category	Number	Strength			Appearance after anodization
	Category	Number	Tensile strength (N/mm²)	Proof stress (N/mm²)	Evaluation	Surface appearance	Cross section appearance
Sliced Sample	Example	Alloy 33A	425	364	Accepted	Accepted	Accepted
	Example	Alloy 34A	513	450	Accepted	Accepted	Accepted
	Comparative Example	Alloy 35A	198	167	Failed	Accepted	Accepted
		Alloy 36A	289	189	Accepted	Failed	Accepted
		Alloy 37A	210	132	Failed	Accepted	Accepted
		Alloy 38A	605	526	Accepted	Failed	Accepted
Hot-rolled Sample	Comparative Example	Alloy 33A	442	380	Accepted	Accepted	Failed
		Alloy 34A	535	474	Accepted	Accepted	Failed
		Alloy 35A	212	174	Failed	Accepted	Failed
		Alloy 36A	305	203	Accepted	Failed	Failed
		Alloy 37A	227	148	Failed	Accepted	Failed
		Alloy 38A	616	536	Accepted	Failed	Failed

(Re: Sliced Samples)

As is demonstrated in Table 10, the samples using Alloys 35A and 37A contained Mg and Zn, respectively, in a content of less than the lower limit in the material aluminum alloy and showed insufficient strength. The samples using Alloys 36A and 38A contained Mg and Zn, respectively, in a content of more than the upper limit in the material aluminum alloy and suffered from unevenness in their appearances of surfaces after anodization. The samples using Alloys 33A to 38A did not suffer from unevenness in their appearances of cross sections after anodization.

(Re: Hot-rolled Samples)

As is demonstrated in Table 10, the samples using Alloys 35A and 37A contained Mg and Zn, respectively, in a content of less than the lower limit in the material aluminum alloy and showed insufficient strength. The samples using Alloys 36A and 38A contained Mg and Zn, respectively, in a content of more than the upper limit in the material aluminum alloy and suffered from unevenness in their appearances of surfaces after anodization. The samples using Alloys 33A to 38A suffered from unevenness in their appearances of cross sections after anodization .

(6) Sixth Experimental Example

This experimental example relates to the fifth embodiment of the present invention. The experimental example used 5000 series Al-Mg alloys as the aluminum alloys.

With reference to Table 11, Alloys 1B to 12B were used as example alloys; while Alloys 13B to 22B were used as comparative example alloys .

[Table 11]

Category	Number	Element (percent by mass)									Alloy type	Remarks
Category	Number	Mg	Si	Fe	Cu	Mn	Cr	Zn	Ti	Zr	Alloy type	Remarks
Example Alloy	Alloy 1B	2.6	0.1	0.3	-	-	-	-	0.01	-	5000 series
	Alloy 2B	2.6	0.1	0.3	-	0.3	-	-	0.01	-	5000 series
	Alloy 3B	4.5	0.1	0.3	-	-	-	-	0.01	-	5000 series
	Alloy 4B	7.5	0.1	0.3	-	-	-	-	0.01	0.1	5000 series
	Alloy 5B	10.5	0.1	0.3	-	-	-	-	0.01	-	5000 series
	Alloy 6B	4.5	0.3	0.5	0.3	-	-	-	0.01	-	5000 series
	Alloy 7B	4.5	0.1	0.3	-	0.05	-	-	0.01	-	5000 series
	Alloy 8B	4.5	0.1	0.3	-	-	0.05	-	0.01	-	5000 series
	Alloy 9B	4.5	0.1	0.3	-	0.7	0.3	-	0.01	0.1	5000 series
	Alloy 10B	4.5	0.1	0.3	-	0.05	-	0.3	0.01	-	5000 series
	Alloy 11B	2.5	0.1	0.3	-	-	0.15	-	0.01	-	5000 series	JIS 5052 alloy
	Alloy 12B	4.6	0.1	0.2	-	0.6	-	-	0.01	-	5000 series	JIS 5083 alloy
Comparative Example Alloy	Alloy 13B	1.3	0.1	0.3	-	-	-	-	0.01	-	5000 series	Mg content less than lower limit
	Alloy 14B	13.5	0.1	0.3	-	-	-	-	0.01	-	5000 series	Mg content more than upper limit
	Alloy 15B	4.5	0.8	0.3	-	-	-	-	0.01	-	5000 series	Si content more than upper limit
	Alloy 16B	4.5	0.1	1.0	-	-	-	-	0.01	-	5000 series	Fe content more than upper limit
	Alloy 17B	4.5	0.1	0.3	0.7	-	-	-	0.01	-	5000 series	Cu content more than upper limit
	Alloy 18B	4.5	0.1	0.3	-	1.2	-	-	0.01	-	5000 series	Mn content more than upper limit
	Alloy 19B	4.5	0.1	0.3	-	-	0.6	-	0.01	-	5000 series	Cr content more than upper limit
	Alloy 20B	4.5	0.1	0.3	-	-	-	0.5	0.01	-	5000 series	Zn content more than upper limit
	Alloy 21B	4.5	0.1	0.3	-	-	-	-	0.15	-	5000 series	Ti content more than upper limit
	Alloy 22B	4.5	0.1	0.3	-	-	-	-	0.01	0.4	5000 series	Zr content more than upper limit

(Treatments)

Initially, a series of slabs having a plate thickness of 500 mm was prepared by subjecting Alloys 1B to 22B to a melting step, a hydrogen gas removal step, a filtration step, and a casting step sequentially in this order.
Next, the slabs were further subjected to a treatment in a heat treatment step, in which they were held at a temperature of 350°C for 4 hours.
Next, sliced samples and hot-rolled samples were prepared from the thermally treated slabs. The sliced samples were prepared by slicing the slabs in a slicing step, while the hot-rolled samples were prepared by subjecting the slabs to hot rolling. The sliced samples andhot-rolled samples are aluminum alloy thick plates each 20 mm thick, 1000 mm wide, and 2000 mm long.
Accordingly, the sliced samples after these treatments are aluminum alloy thick plates manufactured by the procedures of the manufacturing method according to the fifth embodiment of the present invention, whereas the hot-rolled samples after the treatments are not. Among them, only the sliced samples using Alloys 1B to 22B correspond to examples according to the fifth embodiment of the present invention.
Next, the sliced samples and hot-rolled samples after the treatments were subjected to a flatness evaluation test, an evaluation test for accuracy of plate thickness, a strength test, and an anodizability evaluation test. The procedures and criteria of the respective tests are as in First Experimental Example.

The test results are shown in Tables 12 and 13.

[Table 12]

	Category	Number	Flatness		Accuracy of plate thickness	Strength			Appearance after anodization		Cross section structure
	Category	Number	(mm/m)	Evaluation	Evaluation	Tensile strength (N/mm²)	Proof stress (N/mm²)	Evaluation	Surface appearance	Cross section appearance	Average crystal grain size (µm)
Sliced Sample	Example	Alloy 1B	0.25	Accepted	Excellent	214	100	Accepted	Accepted	Accepted	170
		Alloy 2B	0.25	Accepted	Excellent	225	108	Accepted	Accepted	Accepted	170
		Alloy 3B	0.28	Accepted	Excellent	308	146	Accepted	Accepted	Accepted	170
		Alloy 4B	0.28	Accepted	Excellent	335	172	Accepted	Accepted	Accepted	150
		Alloy 5B	0.31	Accepted	Excellent	387	187	Accepted	Accepted	Accepted	140
		Alloy 6B	0.29	Accepted	Excellent	311	140	Accepted	Accepted	Accepted	160
		Alloy 7B	0.26	Accepted	Excellent	307	147	Accepted	Accepted	Accepted	150
		Alloy 8B	0.27	Accepted	Excellent	316	147	Accepted	Accepted	Accepted	150
		Alloy 9B	0.28	Accepted	Excellent	320	156	Accepted	Accepted	Accepted	150
		Alloy 10B	0.29	Accepted	Excellent	305	146	Accepted	Accepted	Accepted	160
		Alloy 11B	0.26	Accepted	Excellent	226	110	Accepted	Accepted	Accepted	160
		Alloy 12B	0.28	Accepted	Excellent	309	146	Accepted	Accepted	Accepted	150
	Comparative Example	Alloy 13B	0.25	Accepted	Excellent	175	72	Failed	Accepted	Accepted	210
		Alloy 14B	unproducible due to the generation of casting cracks
		Alloy 15B	0.29	Accepted	Excellent	310	152	Accepted	Failed	Accepted	160
		Alloy 16B	0.30	Accepted	Excellent	309	152	Accepted	Failed	Accepted	150
		Alloy 17B	0.29	Accepted	Excellent	324	167	Accepted	Accepted	Accepted	150
		Alloy 18B	0.30	Accepted	Excellent	328	165	Accepted	Failed	Accepted	130
		Alloy 19B	0.29	Accepted	Excellent	327	161	Accepted	Failed	Accepted	140
		Alloy 20B	0.28	Accepted	Excellent	308	149	Accepted	Accepted	Accepted	160
		Alloy 21B	0.29	Accepted	Excellent	315	150	Accepted	Accepted	Accepted	130
		Alloy 22B	0.28	Accepted	Excellent	316	157	Accepted	Accepted	Accepted	160

[Table 13]

	Category	Number	Flatness		Accuracy of plate thickness	Strength			Appearance after anodization		Cross section structure
	Category	Number	(mm/m)	Evaluation	Evaluation	Tensile strength (N/mm²)	Proof stress (N/mm²)	Evaluation	Surface appearance	Cross section appearance	Average crystal grain size (µm)
Hot-rolled Sample	Comparative Example	Alloy 1B	0.42	Failed	Excellent	215	103	Accepted	Accepted	Failed	160
		Alloy 2B	0.43	Failed	Excellent	224	108	Accepted	Accepted	Failed	150
		Alloy 3B	0.48	Failed	Accepted	293	139	Accepted	Accepted	Failed	170
		Alloy 4B	0.60	Failed	Accepted	312	162	Accepted	Accepted	Failed	140
		Alloy 5B	0.71	Failed	Accepted	379	197	Accepted	Accepted	Failed	140
		Alloy 6B	0.48	Failed	Excellent	302	154	Accepted	Accepted	Failed	160
		Alloy 7B	0.49	Failed	Accepted	295	150	Accepted	Accepted	Failed	160
		Alloy 8B	0.48	Failed	Accepted	298	151	Accepted	Accepted	Failed	150
		Alloy 9B	0.51	Failed	Accepted	310	157	Accepted	Accepted	Failed	150
		Alloy 10B	0.49	Failed	Accepted	299	145	Accepted	Accepted	Failed	160
		Alloy 11B	0.42	Failed	Excellent	222	126	Accepted	Accepted	Failed	170
		Alloy 12B	0.49	Failed	Accepted	303	160	Accepted	Accepted	Failed	150
		Alloy 13B	0.41	Failed	Excellent	179	95	Failed	Accepted	Failed	210
		Alloy 14B	unproducible due to the Generation of casting cracks
		Alloy 15B	0.49	Failed	Excellent	295	139	Accepted	Failed	Failed	170
		Alloy 16B	0.50	Failed	Accepted	294	139	Accepted	Failed	Failed	170
		Alloy 17B	0.49	Failed	Accepted	302	154	Accepted	Accepted	Failed	160
		Alloy 18B	0.49	Failed	Excellent	309	153	Accepted	Failed	Failed	130
		Alloy 19B	0.48	Failed	Accepted	306	150	Accepted	Failed	Failed	120
		Alloy 20B	0.49	Failed	Accepted	290	139	Accepted	Accepted	Failed	160
		Alloy 21B	0.50	Failed	Accepted	296	142	Accepted	Accepted	Failed	160
		Alloy 22B	0.49	Failed	Accepted	299	150	Accepted	Accepted	Failed	140

Table 12 shows the test results of the sliced samples. In Table 12, the samples using Alloys 1B to 12B correspond to examples according to the fifth embodiment of the present invention, whereas the samples using Alloys 13B to 22B correspond to comparative examples. Table 13 shows the test results of the hot-rolled samples. In Table 13, all the samples using Alloys 1B to 22B correspond to comparative examples.

(Re: Sliced Samples)

As is demonstrated in Table 12, the samples using Alloys 1B to 13B and 15B to 22B had small processing strain and showed little warpage, i.e., they had satisfactory flatness. Additionally, they excelled in accuracy of plate thickness.
The sample using Alloy 14B contained Mg in a content of more than the upper limit in the material aluminum alloy, thereby suffered from casting cracks, and was unproducible. The sample using Alloy 13B contained Mg in a content of less than the lower limit in the material aluminum alloy and showed insufficient strength.
The samples using Alloys 1B to 13B, 17B, and 20B to 22B did not suffer from unevenness in their appearances of surfaces after anodization . The samples using Alloys 15B, 16B, 18B, and 19B contained Si, Fe, Mn, and. Cr, respectively, in a content of more than the upper limit in the material aluminum alloy, caused coarse intermetallic compounds, and suffered from unevenness in their appearances of surfaces after anodization. The samples using Alloys 1B to 13B and 15B to 22B did not suffer from unevenness in their appearances of cross sections after anodization.
The samples using Alloys 17B, 20B, 21B, and 22B contained Cu, Zn, Ti, and Zr, respectively, in a content of more than the upper limit in the material aluminum alloy, and advantages obtained therefrom were saturated, resulting in inferior economical efficiency.

(Re: Hot-rolled Samples)

As is demonstrated in Table 13, the samples using Alloys 1B to 13B and 15B to 22B suffered from accumulated processing strain and showed large warpage in the rolling direction. Specifically, they showed inferior flatness. Many of them were somewhat inferior in accuracy of plate thickness to the corresponding sliced samples.
The sample using Alloy 14B contained Mg in a content of more than the upper limit in the material aluminum alloy, suffered from casting cracks, and was unproducible. The sample using Alloy 13B contained Mg in a content of less than the lower limit in the material aluminum alloy and showed insufficient strength.
The samples using Alloys 15B, 16B, 18B, and 19B contained Si, Fe, Mn, and Cr, respectively, in a content of more than the upper limit in the material aluminum alloy, caused coarse intermetallic compounds, and suffered from unevenness in their appearances of surfaces after anodization. The samples using Alloys 1B to 13B and 15B to 22B suffered from unevenness in their appearances of cross sections after anodization.

(7) Seventh Experimental Example

This experimental example relates to the fifth embodiment of the present invention. The experimental example used Alloy 3B in Table 11.

(Treatments)

Initially, a series of slabs having a plate thickness of 500 mm was prepared by subjecting Alloy 3B to a melting step, a hydrogen gas removal step, a filtration step, and a casting step sequentially in this order.
Next, the slabs were further subjected to a treatment in a heat treatment step, in which they were further subjected to a heat treatment under conditions given in Table 14.

The thermally treated slabs were sliced in a slicing step to give sliced samples. The sliced samples are aluminum alloy thick plates each 20 mm thick, 1000 mm wide, and 2000 mm long.

[Table 14]

	Category		Number	Heat treatment for uniformization	Flatness		Accuracy of plate hickness	Cutting property
	Category		Number	Heat treatment for uniformization	(mm/m)	Evaluation	Evaluation	(number of chips/ 10g)	Evaluation
Sliced Sample	Example	B1	Alloy 3B	350°C for 2 hr	0.28	Accepted	Excellent	1030	Accepted
	Example	B2	Alloy 3B	250°C for 4 hr	0.36	Accepted	Excellent	1140	Accepted
	Comparative Example	B3	Alloy 3B	none	0.44	Failed	Accepted	1290	Accepted
		B4	Alloy 3B	420°C for 4 hr	0.26	Accepted	Excellent	920	Failed
		B5	Alloy 3B	150°C for 2 hr	0.42	Failed	Accepted	1230	Accepted

Accordingly, Samples B1 and B2, whose heat treatment conditions satisfy the conditions specified in the fifth embodiment of the present invention, correspond to examples according to the fifth embodiment of the present invention; whereas Samples B3 to B5, whose heat treatment conditions do not satisfy the conditions specified in the fifth embodiment of the present invention, correspond to comparative examples.
The sliced samples after the treatments were subjected to a flatness evaluation test, an evaluation test for accuracy of plate thickness, and a cutting property evaluation test.

In the flatness evaluation, the samples were tested to determine their amounts of warpage (flatness) per 1 m in the casting direction. Samples having an amount of warpage of 0.4 mm or less per 1 m length were evaluated as having accepted flatness (Accepted), while those having an amount of warpage of more than 0.4 mm per 1 m length were evaluated as having unaccepted flatness (Failed).

The evaluation test for accuracy of plate thickness is as in First Experimental Example.

The evaluation of cutting property, i.e., chip breakability was performed by drilling a sample and measuring the number of chips per unit mass. Specifically, the sample was drilled with a drill having a diameter of 5 mm at a number of revolutions of 7000 rpm and a feed rate of 300 mm/minute, and the number of generated chips per 10 g was measured. Samples having a number of chips of 1000 or more per 10 g were evaluated as having accepted cutting property (Accepted) ; whereas those having a number of chips of less than 1000 per 10 g were evaluated as having unaccepted cutting property (Failed).
The test results are shown in Table 14.
As is demonstrated in Table 14, Examples B1 and B2, whose heat treatment conditions satisfy the conditions specified in the fifth embodiment of the present invention, excelled in flatness, accuracy of plate thickness, and cutting property. Comparative Example B3 did not undergo a heat treatment, thereby show poor flatness, and was somewhat inferior in accuracy of plate thickness to Examples B1 and B2. Comparative Example B4, whose heat treatment had been performed at a temperature higher than the range specified in the fifth embodiment of the present invention, was thereby inferior in cutting property. Comparative Example B5, whose heat treatment had been performed at a temperature lower than the range specified in the fifth embodiment of the present invention, thereby showed poor flatness, and was somewhat inferior in accuracy of plate thickness to Examples B1 and B2.

(8) Eighth Experimental Example

This experimental example relates to the sixth embodiment of the present invention. The experimental example used 3000 series Al-Mn alloys as the aluminum alloys.

With reference to Table 15, Alloys 23B and 24B were used as example alloys; while Alloys 25B and 26B were used as comparative example alloys .

[Table 15]

Category	Number	Element (percent by mass)									Alloy type	Remarks
Category	Number	Mg	Si	Fe	Cu	Mn	Cr	Zn	Ti	Zr	Alloy type	Remarks
Example Alloy	Alloy 23B	-	0.1	0.3	-	0.5	-	-	0.01	-	3000 series
Example Alloy	Alloy 24B	-	0.1	0.4	-	0.9	-	-	0.01	-	3000 series
Comparative Example Alloy	Alloy 25B	-	0.1	0.4	-	0.2	-	-	0.01	-	3000 series	Mn content less than lower limit
Comparative Example Alloy	Alloy 26B	-	0.1	0.3	-	1.7	-	-	0.01	-	3000 series	Mn content more than upper limit

(Treatments)

Initially, a series of slabs having a plate thickness of 500 mm was prepared by subj ecting Alloys 23B to 26B to a melting step, a hydrogen gas removal step, a filtration step, and a casting step sequentially in this order.
Next, the slabs were further subjected to a treatment in a heat treatment step, in which they were held at a temperature of 350°C for 4 hours.
Next, sliced samples and hot-rolled samples were prepared from the thermally treated slabs. The sliced samples were prepared by slicing the slabs in a slicing step, while the hot-rolled samples were prepared by subj ecting the slabs to hot rolling. The sliced samples and hot-rolled samples are aluminum alloy thick plates each 20 mm thick, 1000 mm wide, and 2000 mm long.
Accordingly, the sliced samples after these treatments are aluminum alloy thick plates manufactured by the procedures of the manufacturing method according to the sixth embodiment of the present invention, whereas the hot-rolled samples after the treatments are not. Among them, only the sliced samples using Alloys 23B and 24B correspond to examples according to the sixth embodiment of the present invention.
Next, the sliced samples and hot-rolled samples after the treatments were subjected to a flatness evaluation test, an evaluation test for accuracy of plate thickness, a strength test, and an anodizability evaluation test.
The procedures and criteria of the respective tests are as in First Experimental Example.
However, the properties of thick plates vary depending on the type of alloy used, and the criteria for the strength were modified as follows . Specifically, samples having a tensile strength of 90 N/mm² or more were evaluated as having accepted strength (Accepted); whereas those having a tensile strength of less than 90 N/mm² were evaluated as having unaccepted strength (Failed).

The test results are shown in Table 16.

[Table 16]

	Category	Number	Flatness		Accuracy of plate thickness	Strength			Appearance after anodization
	Category	Number	(mm/m)	Evaluation	Evaluation	Tensile strength (N/mm²)	Proof stress (N/mm²)	Evaluation	Surface appearance	Cross section appearance
Sliced Sample	Example	Alloy 23B	0.23	Accepted	Excellent	95	38	Accepted	Accepted	Accepted
	Example	Alloy 24B	0.23	Accepted	Excellent	101	39	Accepted	Accepted	Accepted
	Comparative Example	Alloy 25B	0.22	Accepted	Excellent	85	38	Failed	Accepted	Accepted
	Comparative Example	Alloy 26B	0.24	Accepted	Excellent	118	50	Accepted	Failed	Accepted
Hot-rolled Sample	Comparative Example	Alloy 23B	0.41	Failed	Excellent	113	54	Accepted	Accepted	Failed
		Alloy 24B	0.41	Failed	Accepted	116	56	Accepted	Accepted	Failed
		Alloy 25B	0.41	Failed	Excellent	97	49	Accepted	Accepted	Failed
		Alloy 26B	0.44	Failed	Accepted	140	71	Accepted	Failed	Failed

(Re: Sliced Samples)

As is demonstrated in Table 16, the samples using Alloys 23B to 26B had small processing strain and showed little warpage, i.e., they had satisfactory flatness. Additionally, they excelled in accuracy of plate thickness.
The sample using Alloy 25B contained Mn in a content less than the lower limit in the material aluminum alloy and thereby had insufficient strength. The sample using Alloy 26B contained Mn in a content of more than the upper limit in the material aluminum alloy, thereby caused coarse intermetallic compounds, and suffered from unevenness in its appearance of surface after anodization. The samples using Alloys 23B to 26B did not suffer from unevenness in their appearances of cross sections after anodization.

(Re: Hot-rolled Samples)

With reference to Table 16, the samples using Alloys 23B to 26B suffered from accumulated processing strain and showed large warpage in the rolling direction. Specifically, they showed inferior flatness. Many of them were somewhat inferior in accuracy of plate thickness to the corresponding sliced samples.
The sample using Alloy 25B contained Mn in a content of less than the lower limit in the material aluminum alloy and was thereby somewhat inferior in strength to the other hot-rolled samples. The sample using Alloy 26B contained Mn in a content of more than the upper limit in the material aluminum alloy, thereby caused coarse intermetallic compounds, and suffered from unevenness in its appearance of surface after anodization. The samples using Alloys 23B to 26B suffered from unevenness in their appearances of cross sections after anodization.

(9) Ninth Experimental Example

This experimental example relates to the seventh embodiment of the present invention. The experimental example used 6000 series Al-Mg-Si alloys as the aluminum alloys.

With reference to Table 17, Alloys 27B and 28B were used as example alloys; while Alloys 29B to 32B were used as comparative example alloys .

Table 17

Category	Number	Element (percent by mass)									Alloy type	Remarks
Category	Number	Mg	Si	Fe	Cu	Mn	Cr	Zn	Ti	Zr	Alloy type	Remarks
Example Alloy	Alloy 27B	0.9	0.5	0.5	0.3	0.1	0.2	0.2	0.02	-	6000 series
Example Alloy	Alloy 28B	0.5	0.9	0.2	-	0.1	-	-	0.02	-	6000 series
Comparative Example Alloy	Alloy 29B	0.9	0.1	0.5	-	0.1	-	-	0.02	-	6000 series	Si content less than lower limit
	Alloy 30B	0.9	1.8	0.4	-	0.1	-	-	0.02	-	6000 series	Si content more than upper limit
	Alloy 31B	0.2	0.5	0.5	-	0.1	-	-	0.02	-	6000 series	Mg content less than lower limit
	Alloy 32B	1.7	0.5	0.4	-	0.1	-	-	0.02	-	6000 series	Mg content more than upper limit

(Treatments)

Initially, a series of slabs having a plate thickness of 500 mm was prepared by subj ecting Alloys 27B to 32B to a melting step, a hydrogen gas removal step, a filtration step, and a casting step sequentially in this order.
Next, the slabs were further subjected to a treatment in a heat treatment step, in which they were held at a temperature of 350°C for 4 hours.
Next, sliced samples and hot-rolled samples were prepared from the thermally treated slabs. The sliced samples were prepared by slicing the slabs in a slicing step, while the hot-rolled samples were prepared by subj ecting the slabs to hot rolling. The sliced samples and hot-rolled samples are aluminum alloy thick plates each 20 mm thick, 1000 mm wide, and 2000 mm long.
The resulting sliced samples and hot-rolled samples were further subjected to a solution treatment at 520°C and subsequently to an aging treatment at 175°C for 8 hours.
Accordingly, the sliced samples after these treatments are aluminum alloy thick plates manufactured by the procedures of the manufacturing method according to the seventh embodiment of the present invention, whereas the hot-rolled samples after the treatments are not. Among them, only the sliced samples using Alloys 27B and 28B correspond to examples according to the seventh embodiment of the present invention.
Next, the sliced samples and hot-rolled samples after the treatments were subjected to a strength test and an anodizability evaluation test.
The procedures and criteria of the respective tests are as in First Experimental Example.
However, the properties of thick plates vary depending on the type of alloy used, and the criteria for the strength were modified as follows . Specifically, samples having a tensile strength of 200 N/mm² or more were evaluated as having accepted strength (Accepted) ; while those having a tensile strength of less.than 200 N/mm² were evaluated as having unaccepted strength (Failed).

The test results are shown in Table 18.

[Table 18]

	Category	Number	Strength			Appearance after anodization
	Category	Number	Tensile strength (N/mm²)	Proof stress (N/mm²)	Evaluation	Surface appearance	Cross section appearance
Sliced Sample	Example	Alloy 27B	320	272	Accepted	Accepted	Accepted
	Example	Alloy 28B	295	251	Accepted	Accepted	Accepted
	Comparative Example	Alloy 29B	112	65	Failed	Accepted	Accepted
		Alloy 30B	339	300	Accepted	Failed	Accepted
		Alloy 31B	175	122	Failed	Accepted	Accepted
		Alloy 32B	212	126	Accepted	Accepted	Accepted
Hot-rolled Sample	Comparative Example	Alloy 27B	346	273	Accepted	Accepted	Failed
		Alloy 28B	319	274	Accepted	Accepted	Failed
		Alloy 29B	135	86	Failed	Accepted	Failed
		Alloy 30B	362	322	Accepted	Failed	Failed
		Alloy 31B	198	143	Failed	Accepted	Failed
		Alloy 32B	233	145	Accepted	Accepted	Failed

(Re: Sliced Samples)

As is demonstrated in Table 18, the samples using Alloys 29B and 31B contained Si and Mg, respectively, in a content of less than the lower limit in the material aluminum alloy and showed insufficient strength. The sample using Alloy 30B contained Si in a content of more than the upper limit in the material aluminum alloy, thereby caused coarse intermetallic compounds, and suffered from unevenness in its appearance of surface after anodization. The sample using Alloy 32B contained Mg in a content of more than the upper limit in the material aluminum alloy, and advantages obtained therefrom were saturated, resulting in inferior economical efficiency. The samples using Alloys 27B to 32B did not suffer from unevenness in their appearances of cross sections after anodization.

(Re: Hot-rolled Samples)

As is demonstrated in Table 18, the samples using Alloys 29B and 31B contained Si and Mg, respectively, in a content of less than the lower limit in the material aluminum alloy and showed insufficient strength. The sample using Alloy 30B contained Si in a content of more than the upper limit in the material aluminum alloy, caused coarse intermetallic compounds, and suffered from unevenness in its appearance of surfaces after anodization. The sample using Alloy 32B contained Mg in a content of more than the upper limit in the material aluminum alloy, and advantages obtained therefrom were saturated, resulting in inferior economical efficiency. The samples using Alloys 27B to 32B suffered from unevenness in their appearances of cross sections after anodization.

(10) Tenth Experimental Example

This experimental example relates to the eighth embodiment of the present invention. The experimental example used 7000 series Al-Zn-Mg alloys as the aluminum alloys.

With reference to Table 19, Alloys 33B and 34B were used as example alloys; while Alloys 35B to 38B were used as comparative example alloys .

[Table 19]

Category	Number	Element (percent by mass)									Alloy type	Remarks
Category	Number	Mg	Si	Fe	Cu	Mn	Cr	Zn	Ti	Zr	Alloy type	Remarks
Example Alloy	Alloy 33B	2.5	0.1	0.2	1.8	-	0.2	4.0	0.02	-	7000 series
Example Alloy	Alloy 34B	3.5	0.2	0.2	2.0	-	-	8.0	0.02	0.2	7000 series
Comparative Example Alloy	Alloy 35B	0.3	0.1	0.2	2.2	-	0.1	4.0	0.02	-	7000 series	Mg content less than lower limit
	Alloy 36B	5.0	0.2	0.2	2.0	-	0.1	5.0	0.02	-	7000 series	Mg content more than upper limit
	Alloy 37B	2.5	0.1	0.2	2.2	-	0.1	2.4	0.02	-	7000 series	Zn content less than lower limit
	Alloy 38B	3.0	0.2	0.2	2.0	-	0.1	9.5	0.02	-	7000 series	Zn content more than upper limit

(Treatments)

Initially, a series of slabs having a plate thickness of 500 mm was prepared by subj ecting Alloys 33B to 38B to a melting step, a hydrogen gas removal step, a filtration step, and a casting step sequentially in this order.
Next, the slabs were further subjected to a treatment in a heat treatment step, in which they were held at a temperature of 300°C for 4 hours.
Next, sliced samples and hot-rolled samples were prepared from the thermally treated slabs. The sliced samples were prepared by slicing the slabs in a slicing step, while the hot-rolled samples were prepared by subj ecting the slabs to hot rolling. The sliced samples and hot-rolled samples are aluminum alloy thick plates each 20 mm thick, 1000 mm wide, and 2000 mm long.
The resulting sliced samples and hot-rolled samples were further subjected to a solution treatment at 470°C and subsequently to an aging treatment at 120°C for 48 hours.
Accordingly, the sliced samples after these treatments are aluminum alloy thick plates manufactured by the procedures of the manufacturing method according to the eighth embodiment of the present invention, whereas the hot-rolled samples after the treatments are not. Among them, only the sliced samples using Alloys 33B and 34B correspond to examples according to the eighth embodiment of the present invention.
Next, the sliced samples and hot-rolled samples after the treatments were subjected to a strength test and an anodizability evaluation test.
The procedures and criteria of the respective tests are as in First Experimental Example.
However, the properties of thick plates vary depending on the type of alloy used, and the criteria for the strength were modified as follows . Specifically, samples having a tensile strength of 250 N/mm² or more were evaluated as having accepted strength (Accepted) ; while those having a tensile strength of less than 250 N/mm² were evaluated as having unaccepted strength (Failed).

The test results are shown in Table 20.

[Table 20]

	Category	Number	Strength			Appearance after anodization
	Category	Number	Tensile strength (N/mm²)	Proof stress (N/mm²)	Evaluation	Surface appearance	Cross section appearance
Sliced Sample	Example	Alloy 33B	422	363	Accepted	Accepted	Accepted
	Example	Alloy 34B	510	449	Accepted	Accepted	Accepted
	Comparative Example	Alloy 35B	193	165	Failed	Accepted	Accepted
		Alloy 36B	287	188	Accepted	Failed	Accepted
		Alloy 37B	209	130	Failed	Accepted	Accepted
		Alloy 38B	602	525	Accepted	Failed	Accepted
Hot-rolled Sample	Comparative Example	Alloy 33B	441	380	Accepted	Accepted	Failed
		Alloy 34B	533	472	Accepted	Accepted	Failed
		Alloy 35B	210	172	Failed	Accepted	Failed
		Alloy 36B	303	202	Accepted	Failed	Failed
		Alloy 37B	224	146	Failed	Accepted	Failed
		Alloy 38B	614	535	Accepted	Failed	Failed

(Re: Sliced Samples)

As is demonstrated in Table 20, the samples using Alloy 35B and 37B contained Mg and Zn, respectively, in a content of less than the lower limit .in the material aluminum alloy and showed insufficient strength. The samples using Alloys 36B and 38B contained Mg and Zn, respectively, in a content of more than the upper limit in the material aluminum alloy and suffered from unevenness in their appearances of surfaces after anodization. The samples using Alloys 33B to 38B did not suffer from unevenness in their appearances of cross sections after anodization.

(Re: Hot-rolled Samples)

As is demonstrated in Table 20, the samples using Alloys 35B and 37B contained Mg and Zn, respectively, in a content of less than the lower limit in the material aluminum alloy and showed insufficient strength. The samples using Alloys 36B and 38B contained Mg and Zn, respectively, in a content of more than the upper limit in the material aluminum alloy and thereby suffered from unevenness in their appearances of surfaces after anodization. The samples using Alloys 33B to 38B suffered from unevenness in their appearances of cross sections after anodization.

(11) Eleventh Experimental Example

This experimental example relates to the ninth embodiment of the present invention. The experimental example used 5000 series Al-Mg alloys as the aluminum alloys.

With reference to Table 21, Alloys 1C to 12C were used as example alloys; while Alloys 13C to 22C were used as comparative example alloys .

[Table 21]

Category	Number	Element (percent by mass)									Alloy type	Remarks
Category	Number	Mg	Si	Fe	Cu	Mn	Cr	Zn	Ti	Zr	Alloy type	Remarks
Example Alloy	Alloy 1C	2.5	0.1	0.3	-	-	-	-	0.01	-	5000 series
	Alloy 2C	2.5	0.1	0.3	-	0.3	-	-	0.01	-	5000 series
	Alloy 3C	4.7	0.1	0.3	-	-	-	-	0.01	-	5000 series
	Alloy 4C	7.5	0.1	0.3	-	-	-	-	0.01	0.1	5000 series
	Alloy 5C	10.4	0.1	0.3	-	-	-	-	0.01	-	5000 series
	Alloy 6C	4.7	0.3	0.5	0.3	-	-	-	0.01	-	5000 series
	Alloy 7C	4.7	0.1	0.3	-	0.05	-	-	0.01	-	5000 series
	Alloy 8C	4.7	0.1	0.3	-	-	0.05	-	0.01	-	5000 series
	Alloy 9C	4.7	0.1	0.3	-	0.7	0.3	-	0.01	0.1	5000 series
	Alloy 10C	4.7	0.1	0.3	-	0.05	-	0.3	0.01	-	5000 series
	Alloy 11C	2.5	0.1	0.3	-	-	0.15	-	0.01	-	5000 series	JIS 5052 alloy
	Alloy 12C	4.7	0.1	0.2	-	0.6	-	-	0.01	-	5000 series	JIS 5083 alloy
Comparative Example Alloy	Alloy 13C	1.4	0.1	0.3	-	-	-	-	0.01	-	5000 series	Mg content less than lower limit
	Alloy 14C	13.0	0.1	0.3	-	-	-	-	0.01	-	5000 series	Mg content more than upper limit
	Alloy 15C	4.7	0.8	0.3	-	-	-	-	0.01	-	5000 series	Si content more than upper limit
	Alloy 16C	4.7	0.1	1.0	-	-	-	-	0.01	-	5000 series	Fe content more than upper limit
	Alloy 17C	4.7	0.1	0.3	0.7	-	-	-	0.01	-	5000 series	Cu content more than upper limit
	Alloy 18C	4.7	0.1	0.3	-	1.2	-	-	0.01	-	5000 series	Mn content more than upper limit
	Alloy 19C	4.7	0.1	0.3	-	-	0.6	-	0.01	-	5000 series	Cr content more than upper limit
	Alloy 20C	4.7	0.1	0.3	-	-	-	0.5	0.01	-	5000 series	Zn content more than upper limit
	Alloy 21C	4.7	0.1	0.3	-	-	-	-	0.15	-	5000 series	Ti content more than upper limit
	Alloy 22C	4.7	0.1	0.3	-	-	-	-	0.01	0.4	5000 series	Zr content more than upper limit

(Treatments)

Initially, a series of slabs having a plate thickness of 500 mm was prepared by subjecting Alloys 1C to 22C to a melting step, a hydrogen gas removal step, a filtration step, and a casting step sequentially in this order.
Next, sliced samples and hot-rolled samples were prepared from the slabs. The sliced samples were prepared by subjecting the slabs to a slicing step, while the hot-rolled samples were prepared by subjecting the slabs to a heat treatment and subsequently to hot rolling. The sliced samples and hot-rolled samples are aluminum alloy thick plates each 20 mm thick, 1000 mm wide, and 2000 mm long.
Next, the sliced samples were further subjected to a heat treatment step in which they were held at a temperature of 350°C for 4 hours.
Accordingly, the sliced samples after these treatments are aluminum alloy thick plates manufactured by the procedures of the manufacturing method according to the ninth embodiment of the present invention, whereas the hot-rolled samples after the treatments are not. Among them, only the sliced samples using Alloys 1C to 22C correspond to examples according to the ninth embodiment of the present invention.
Next, the sliced samples and hot-rolled samples after the treatments were subjected to a flatness evaluation test, an evaluation test for accuracy of plate thickness, a strength test, and an anodizability evaluation test. The procedures and criteria of the respective tests are as in First Experimental Example.
The average crystal grain sizes of the thick plates were determined in the same manner as in First Experimental Example, because the crystal grain size of a thick plate affects the anodizability thereof.

The test results are shown in Tables 22 and 23.

[Table 22]

	Category	Number	Flatness		Accuracy of plate hickness	Strength			Appearance after anodization		Cross section structure
	Category	Number	(mm/m)	Evaluation	Evaluation	Tensile strength (N/mm²)	Proof stress (N/mm²)	Evaluation	Surface appearance	Cross section appearance	Average crystal grain size (µm)
Sliced Sample	Example	Alloy 1C	0.24	Accepted	Excellent	218	103	Accepted	Accepted	Accepted	170
		Alloy 2C	0.24	Accepted	Excellent	229	112	Accepted	Accepted	Accepted	170
		Alloy 3C	0.27	Accepted	Excellent	309	147	Accepted	Accepted	Accepted	160
		Alloy 4C	0.27	Accepted	Excellent	336	173	Accepted	Accepted	Accepted	140
		Alloy 5C	0.29	Accepted	Excellent	384	185	Accepted	Accepted	Accepted	140
		Alloy 6C	0.27	Accepted	Excellent	315	142	Accepted	Accepted	Accepted	160
		Alloy 7C	0.25	Accepted	Excellent	310	148	Accepted	Accepted	Accepted	160
		Alloy 8C	0.26	Accepted	Excellent	320	149	Accepted	Accepted	Accepted	160
		Alloy 9C	0.27	Accepted	Excellent	323	158	Accepted	Accepted	Accepted	160
		Alloy 10C	0.28	Accepted	Excellent	308	149	Accepted	Accepted	Accepted	160
		Alloy 11C	0.25	Accepted	Excellent	228	113	Accepted	Accepted	Accepted	150
		Alloy 12C	0.27	Accepted	Excellent	310	147	Accepted	Accepted	Accepted	160
	Comparative Example	Alloy 13C	0.24	Accepted	Excellent	176	72	Failed	Accepted	Accepted	220
		Alloy 14C	unproducible due to the generation of casting cracks
		Alloy 15C	0.28	Accepted	Excellent	315	153	Accepted	Failed	Accepted	160
		Alloy 16C	0.30	Accepted	Excellent	314	154	Accepted	Failed	Accepted	160
		Alloy 17C	0.28	Accepted	Excellent	327	169	Accepted	Accepted	Accepted	160
		Alloy 18C	0.28	Accepted	Excellent	330	167	Accepted	Failed	Accepted	130
		Alloy 19C	0.27	Accepted	Excellent	330	163	Accepted	Failed	Accepted	130
		Alloy 20C	0.27	Accepted	Excellent	310	151	Accepted	Accepted	Accepted	150
		Alloy 21C	0.28	Accepted	Excellent	320	156	Accepted	Accepted	Accepted	130
		Alloy 22C	0.27	Accepted	Excellent	320	158	Accepted	Accepted	Accepted	160

[Table 23]

	Category	Number	Flatness		Accuracy of plate thickness	Strength			Appearance after anodization		Cross section structure
	Category	Number	(mm/m)	Evaluation	Evaluation	Tensile strength (N/mm²)	Proof stress (N/mm²)	Evaluation	Surface appearance	Cross section appearance	Average crystal grain size (µm)
Hot-rolled Sample	Comparative Example	Alloy 1C	0.43	Failed	Excellent	218	105	Accepted	Accepted	Failed	160
		Alloy 2C	0.44	Failed	Excellent	227	110	Accepted	Accepted	Failed	150
		Alloy 3C	0.48	Failed	Accepted	297	141	Accepted	Accepted	Failed	140
		Alloy 4C	0.61	Failed	Accepted	314	163	Accepted	Accepted	Failed	120
		Alloy 5C	0.70	Failed	Accepted	383	200	Accepted	Accepted	Failed	140
		Alloy 6C	0.48	Failed	Excellent	304	157	Accepted	Accepted	Failed	150
		Alloy 7C	0.48	Failed	Accepted	298	151	Accepted	Accepted	Failed	150
		Alloy 8C	0.48	Failed	Accepted	297	150	Accepted	Accepted	Failed	140
		Alloy 9C	0.52	Failed	Accepted	313	159	Accepted	Accepted	Failed	140
		Alloy 10C	0.50	Failed	Accepted	303	146	Accepted	Accepted	Failed	150
		Alloy 11C	0.43	Failed	Excellent	225	129	Accepted	Accepted	Failed	160
		Alloy 12C	0.49	Failed	Accepted	306	161	Accepted	Accepted	Failed	140
		Alloy 13C	0.42	Failed	Excellent	181	97	Accepted	Accepted	Failed	200
		Alloy 14C	unproducible due to the generation of casting cracks
		Alloy 15C	0.50	Failed	Excellent	299	142	Accepted	Failed	Failed	160
		Alloy 16C	0.49	Failed	Accepted	298	143	Accepted	Failed	Failed	160
		Alloy 17C	0.49	Failed	Accepted	307	156	Accepted	Accepted	Failed	150
		Alloy 18C	0.49	Failed	Excellent	312	156	Accepted	Failed	Failed	140
		Alloy 19C	0.49	Failed	Accepted	310	152	Accepted	Failed	Failed	130
		Alloy 20C	0.49	Failed	Accepted	295	142	Accepted	Accepted	Failed	150
		Alloy 21C	0.50	Failed	Accepted	299	144	Accepted	Accepted	Failed	150
		Alloy 22C	0.50	Failed	Accepted	303	152	Accepted	Accepted	Failed	150

Table 22 shows the test results of the sliced samples, in which the samples using Alloys 1C to 12C correspond to examples according to the ninth embodiment of the present invention; while the samples using Alloys 13C to 22C correspond to comparative examples. Table 23 shows the test results of the hot-rolled samples, in which all the samples using Alloys 1C to 22C correspond to comparative examples.

(Re: Sliced Samples)

As is demonstrated in Table 22, the samples using Alloys 1C to 13C and 15C to 22C had small processing strain and showed little warpage, i.e., they had satisfactory flatness. Additionally, they excelled in accuracy of plate thickness.
The sample using Alloy 14C contained Mg in a content of more than the upper limit in the material aluminum alloy, suffered from casting cracks, and was unproducible. The sample using Alloy 13C contained Mg in a content of less than the lower limit in the material aluminum alloy and showed insufficient strength.
The samples using Alloys 1C to 13C, 17C, and 20C to 22C did not suffer from unevenness in their appearances of surfaces after anodization. The samples using Alloys 15C, 16C, 18C, and 19C contained Si, Fe, Mn, and Cr, respectively, in a content of more than the upper limit in the material aluminum alloy, caused coarse intermetallic compounds, and suffered from unevenness in their appearances of surfaces after anodization. The samples using Alloys 1C to 13C and 15C to 22C did not suffer from unevenness in their appearances of cross sections after anodization.
The samples using Alloys 17C, 20C, 21C, and 22C contained Cu, Zn, Ti, and Zr, respectively, in a content of more than the upper limit in the material aluminum alloy, and advantages obtained therefrom were saturated, resulting in inferior economical efficiency.

(Re: Hot-rolled Samples)

As is demonstrated in Table 23, the samples using Alloys 1C to 13C and 15C to 22C suffered from accumulated processing strain and showed large warpage in the rolling direction. Specifically, they showed inferior flatness. Many of them were somewhat inferior in accuracy of plate thickness to the corresponding sliced samples.
The sample using Alloy 14C contained Mg in a content of more than the upper limit in the material aluminum alloy, suffered from casting cracks, and was unproducible. The sample using Alloy 13C contained Mg in a content of less than the lower limit in the material aluminum alloy and showed insufficient strength.
The samples using Alloy 15C, 16C, 18C, and 19C contain Si, Fe, Mn, and Cr, respectively, in a content of more than the upper limit, caused coarse intermetallic compounds, and suffered from unevenness in their appearances of surfaces after anodization. The samples using Alloys 1C to 13C and 15C to 22C suffered from unevenness in their appearances of cross sections after anodization.

(12) Twelfth Experimental Example

This experimental example relates to the ninth embodiment of the present invention. The experimental example used Alloy 3C in Table 21.

(Treatments)

Initially, a series of slabs having a plate thickness of 500 mm was prepared by subjecting Alloy 3C to a melting step, a hydrogen gas removal step, a filtration step, and a casting step sequentially in this order.
Next, the slabs were subjected to a slicing step to give sliced samples. The sliced samples are aluminum alloy thick plates each 20 mm thick, 1000 mm wide, and 2000 mm long.

Next, the sliced samples were further subjected to a heat treatment step, in which they were subjected to a heat treatment under conditions given in Table 24.

[Table 24]

	Category		Number	Heat treatment	Flatness		Accuracy of plate thickness	Chip breakability upon cutting
	Category		Number	Heat treatment	(mm/m)	Evaluation	Evaluation	(number/10 g)	Evaluation
Sliced Sample	Example	C1	Alloy 3C	350°C for 2 hr	0.26	Accepted	Excellent	1040	Accepted
	Example	C2	Alloy 3C	250°C for 4 hr	0.34	Accepted	Excellent	1170	Accepted
	Comparative Example	C3	Alloy 3C	none	0.45	Failed	Accepted	1340	Accepted
		C4	Alloy 3C	420°C for 4 hr	0.23	Accepted	Excellent	950	Failed
		C5	Alloy 3C	150°C for 2 hr	0.42	Failed	Accepted	1280	Accepted

Accordingly, Samples C1 and C2, whose heat treatment conditions satisfy the conditions specified in the ninth embodiment of the present invention, correspond to examples according to the ninth embodiment of the present invention; while Samples C3 to C5, whose heat treatment conditions do not satisfy the conditions specified in the ninth embodiment of the present invention, correspond to comparative examples.
The sliced samples after the treatments were subjected to a flatness evaluation test and an evaluation test for accuracy of plate thickness.

The cutting property evaluation test is as in Seventh Experimental Example.
The test results are shown in Table 24.
As is demonstrated in Table 24, Examples C1 and C2, whose heat treatment conditions satisfy the conditions specified in the ninth embodiment of the present invention, excelled in flatness, accuracy of plate thickness, and cutting property. Comparative Example C3, which did not undergo a heat treatment, showed poor flatness, and had somewhat inferior accuracy of plate thickness to Examples C1 and C2. Comparative Example C4 had been thermally treated at a temperature higher than the range specified in the ninth embodiment of the present invention and thereby showed poor cutting property. Comparative Example C5 had been thermally treated at a temperature lower than the range specified in the ninth embodiment of the present invention, thereby showed poor flatness, and was somewhat inferior in accuracy of plate thickness to Examples C1 and C2.

(13) Thirteenth Experimental Example

This experimental example relates to the tenth embodiment of the present invention. The experimental example used 3000 series Al-Mn alloys as the aluminum alloys.

With reference to Table 25, Alloys 23C and 24C were used as example alloys; while Alloys 25C and 26C were used as comparative example alloys .

[Table 25]

Category	Number	Element (percent by mass)									Alloy type	Remarks
Category	Number	Mg	Si	Fe	Cu	Mn	Cr	Zn	Ti	Zr	Alloy type	Remarks
Example Alloy	Alloy 23C	-	0.1	0.3	-	0.5	-	-	0.01	-	3000 series
Example Alloy	Alloy 24C	-	0.1	0.4	-	0.9	-	-	0.01	-	3000 series
Comparative Example Alloy	Alloy 25C	-	0.1	0.4	-	0.2	-	-	0.01	-	3000 series	Mn content less than lower limit
Comparative Example Alloy	Alloy 26C	-	0.1	0.3	-	1.7	-	-	0.01	-	3000 series	Mn content more than upper limit

(Treatments)

Initially, a series of slabs having a plate thickness of 500 mm was prepared by subj ecting Alloys 23C to 26C to a melting step, a hydrogen gas removal step, a filtration step, and a casting step sequentially in this order.
Next, sliced samples and hot-rolled samples were prepared from the slabs. The sliced samples were prepared by subjecting the slabs to a slicing step, while the hot-rolled samples were prepared by subjecting the slabs to a heat treatment and subsequently to hot rolling. The sliced samples and hot-rolled samples are aluminum alloy thick plates each 20 mm thick, 1000 mm wide, and 2000 mm long.
Next, the sliced samples were further subjected to a heat treatment step in which they were held at a temperature of 350°C for 4 hours.
Accordingly, the sliced samples after these treatments are aluminum alloy thick plates manufactured by the procedures of the manufacturing method according to the tenth embodiment of the present invention, whereas the hot-rolled samples after the treatments are not. Among them, only the sliced samples using Alloys 23C and 24C correspond to examples according to the tenth embodiment of the present invention.
Next, the sliced samples and hot-rolled samples after the treatments were subjected to a flatness evaluation test, an evaluation test for accuracy of plate thickness, a strength test, and an anodizability evaluation test.
The procedures and criteria of the respective tests are as in First Experimental Example.
However, the properties of thick plates vary depending on the type of alloy used, and the criteria for the strength were modified as follows . Specifically, samples having a tensile strength of 90 N/mm² or more were evaluated as having accepted strength (Accepted), whereas those having a tensile strength of less than 90 N/mm² were evaluated as having unaccepted strength (Failed).

The test results are shown in Table 26.

[Table 26]

	Category	Number	Flatness		Accuracy of plate thickness	Strength			Appearance after anodization
	Category	Number	(mm/m)	Evaluation	Evaluation	Tensile strength (N/mm²)	Proof stress (N/mm²)	Evaluation	Surface appearance	Cross section appearance
Sliced Sample	Example	Alloy 23C	0.22	Accepted	Excellent	98	40	Accepted	Accepted	Accepted
	Example	Alloy 24C	0.22	Accepted	Excellent	102	39	Accepted	Accepted	Accepted
	Comparative Example	Alloy 25C	0.22	Accepted	Excellent	86	38	Failed	Accepted	Accepted
	Comparative Example	Alloy 26C	0.23	Accepted	Excellent	121	51	Accepted	Failed	Accepted
Hot-rolled Sample	Comparative Example	Alloy 23C	0.41	Failed	Excellent	115	55	Accepted	Accepted	Failed
		Alloy 24C	0.42	Failed	Accepted	118	57	Accepted	Accepted	Failed
		Alloy 25C	0.41	Failed	Excellent	95	46	Accepted	Accepted	Failed
		Alloy 26C	0.44	Failed	Accepted	142	72	Accepted	Failed	Failed

(Re: Sliced Samples)

As is demonstrated in Table 26, the samples using Alloys 23C to 26C had small processing strain and showed little warpage, i.e., they had satisfactory flatness. Additionally, they excelled in accuracy of plate thickness.
The sample using Alloy 25C contained Mn in a content less than the lower limit in the material aluminum alloy and thereby had insufficient strength. The sample using Alloy 26C contained Mn in a content of more than the upper limit in the material aluminum alloy, thereby caused coarse intermetallic compounds, and suffered from unevenness in its appearance of surface after anodization. The samples using Alloys 23C to 26C didnot suffer from unevenness in their appearances of cross sections after anodization.

(Re: Hot-rolled Samples)

As is demonstrated in Table 26, the samples using Alloys 23C to 26C suffered from accumulated processing strain and showed large warpage in the rolling direction. Specifically, they showed inferior flatness. Many of them were somewhat inferior in accuracy of plate thickness to the corresponding sliced samples.
The sample using Alloy 25C contained Mn in a content of less than the lower limit in the material aluminum alloy and was thereby somewhat inferior in strength to the other hot-rolled samples. The sample using Alloy 26C contained Mn in a content of more than the upper limit in the material aluminum alloy, thereby caused coarse intermetallic compounds, and suffered from unevenness in its appearance of surface after anodization. The samples using Alloys 23C to 26C suffered from unevenness in their appearances of cross sections after anodization.

(14) Fourteenth Experimental Example

This experimental example relates to the eleventh embodiment of the present invention. The experimental example used 6000 series Al-Mg-Si alloys as the aluminum alloys.

With reference to Table 27, Alloys 27C and 28C were used as example alloys; while Alloys 29C to 32C were used as comparative example alloys .

[Table 27]

Category	Number	Element (percent by mass)									Alloy type	Remarks
Category	Number	Mg	Si	Fe	Cu	Mn	Cr	Zn	Ti	Zr	Alloy type	Remarks
Example Alloy	Alloy 27C	0.9	0.5	0.5	0.3	0.1	0.2	0.2	0.02	-	6000 series
Example Alloy	Alloy 28C	0.5	0.9	0.2	-	0.1	-	-	0.02	-	6000 series
Comparative Example Alloy	Alloy 29C	0.9	0.1	0.5	-	0.1	-	-	0.02	-	6000 series	Si content less than lower limit
	Alloy 30C	0.9	1.8	0.4	-	0.1	-	-	0.02	-	6000 series	Si content more than upper limit
	Alloy 31C	0.2	0.5	0.5	-	0.1	-	-	0.02	-	6000 series	Mg content less than lower limit
	Alloy 32C	1.7	0.5	0.4	-	0.1	-	-	0.02	-	6000 series	Mg content more than upper limit

(Treatments)

Initially, a series of slabs having a plate thickness of 500 mm was prepared by subj ecting Alloys 27C to 32C to a melting step, a hydrogen gas removal step, a filtration step, and a casting step sequentially in this order.
Next, sliced samples and hot-rolled samples were prepared from the slabs. The sliced samples were prepared by subjecting the slabs to a slicing step, while the hot-rolled samples were prepared by subj ecting the slabs to a heat treatment and subsequently to hot rolling. The sliced samples and hot-rolled samples are aluminum alloy thick plates each 20 mm thick, 1000 mm wide, and 2000 mm long.
Next, the sliced samples were further subjected to a heat treatment step in which they were held at a temperature of 350°C for 4 hours.
The resulting sliced samples and hot-rolled samples were further subjected to a solution treatment at 520°C and subsequently to an aging treatment at 175°C for 8 hours.
Accordingly, the sliced samples after these treatments are aluminum alloy thick plates manufactured by the procedures of the manufacturing method according to the eleventh embodiment of the present invention, whereas the hot-rolled samples after the treatments are not. Among them, only the sliced samples using Alloys 27C and 28C correspond to examples according to the eleventh embodiment of the present invention.
Next, the sliced samples and hot-rolled samples after the treatments were subjected to a strength test and an anodizability evaluation test.
The procedures and criteria of the respective tests are as in First Experimental Example.
However, the properties of thick plates vary depending on the type of alloy used, and the criteria for the strength were modified as follows . Specifically, samples having a tensile strength of 200 N/mm² or more were evaluated as having accepted strength (Accepted) ; while those having a tensile strength of less than 200 N/mm² were evaluated as having unaccepted strength (Failed).

The test results are shown in Table 28.

[Table 28]

	Category	Number	Strength			Appearance after anodization
	Category	Number	Tensile strength (N/mm²)	Proof stress (N/mm²)	Evaluation	Surface appearance	Cross section appearance
Sliced Sample	Example	Alloy 27C	317	269	Accepted	Accepted	Accepted
	Example	Alloy 28C	290	247	Accepted	Accepted	Accepted
	Comparative Example	Alloy 29C	110	64	Failed	Accepted	Accepted
		Alloy 30C	335	298	Accepted	Failed	Accepted
		Alloy 31C	172	120	Failed	Accepted	Accepted
		Alloy 32C	209	123	Accepted	Accepted	Accepted
Hot-rolled Sample	Comparative Example	Alloy 27C	343	272	Accepted	Accepted	Failed
		Alloy 28C	316	272	Accepted	Accepted	Failed
		Alloy 29C	132	84	Failed	Accepted	Failed
		Alloy 30C	359	319	Accepted	Failed	Failed
		Alloy 31C	197	142	Failed	Accepted	Failed
		Alloy 32C	228	141	Accepted	Accepted	Failed

(Re: Sliced Samples)

As is demonstrated in Table 28, the samples using Alloys 29C and 31C contained Si and Mg, respectively, in a content of less than its lower limit in the material aluminum alloy and showed insufficient strength. The sample using Alloy 30C contained Si in a content of more than the upper limit in the material aluminum alloy, caused coarse intermetallic compounds, and suffered from unevenness in their appearances of surfaces after anodization. The sample using Alloy 32C contained Mg in a content of more than the upper limit in the material aluminum alloy, and advantages obtained therefrom were saturated, resulting in inferior economical efficiency. The samples using Alloys 27C to 32C did not suffer from unevenness in their appearances of cross sections after anodization.

(Re: Hot-rolled Samples)

As is demonstrated in Table 28, the samples using Alloys 29C and 31C contain Si and Mg, respectively, in a content of less than the lower limit in the material aluminum alloy, and showed insufficient strength. The sample using Alloy 30C contained Si in a content of more than the upper limit in the material aluminum alloy, caused coarse intermetallic compounds, and suffered from unevenness in their appearances of surfaces after anodization. The sample using Alloy 32C contained Mg in a content of more than the upper limit in the material aluminum alloy, and advantages obtained therefrom were .saturated, resulting in inferior economical efficiency. The samples using Alloy 27C to 32C suffered from unevenness in their appearances of cross sections after anodization.

(15) Fifteenth Experimental Example

This experimental example relates to the twelfth embodiment of the present invention. The experimental example used 7000 series Al-Zn-Mg alloys as the aluminum alloys.

With reference to Table 29, Alloys 33C and 34C were used as example alloys; while Alloys 35C to 38C were used as comparative example alloys.

[Table 29]

Category	Number	Element (percent by mass)									Alloy type	Remarks
Category	Number	Mg	Si	Fe	Cu	Mn	Cr	Zn	Ti	Zr	Alloy type	Remarks
Example Alloy	Alloy 33C	2.4	0.1	0.2	1.8	-	0.2	4.0	0.02	-	7000 series
Example Alloy	Alloy 34C	3.6	0.2	0.2	2.0	-	-	8.0	0.02	0.2	7000 series
Comparative Example Alloy	Alloy 35C	0.3	0.1	0.2	2.2	-	0.1	4.0	0.02	-	7000 series	Mg content less than lower limit
	Alloy 36C	5.2	0.2	0.2	2.0	-	0.1	5.0	0.02	-	7000 series	Mg content more than upper limit
	Alloy 37C	2.4	0.1	0.2	2.2	-	0.1	2.4	0.02	-	7000 series	Zn content less than lower limit
	Alloy 38C	3.0	0.2	0.2	2.0	-	0.1	9.3	0.02	-	7000 series	Zn content more than upper limit

(Treatments)

Initially, a series of slabs having a plate thickness of 500 mm was prepared by subj ecting Alloys 33C to 38C to a melting step, a hydrogen gas removal step, a filtration step, and a casting step sequentially in this order.
Next, sliced samples and hot-rolled samples were prepared from the slabs. The sliced samples were prepared by subjecting the slabs to a slicing step, while the hot-rolled samples were prepared by subjecting the slabs to a heat treatment and subsequently to hot rolling. The sliced samples and hot-rolled samples are aluminum alloy thick plates each 20 mm thick, 1000 mm wide, and 2000 mm long.
Next, the sliced samples were further subjected to a heat treatment step in which they were held at a temperature of 300°C for 4 hours.
The resulting sliced samples and hot-rolled samples were further subjected to a solution treatment at 470°C and subsequently to an aging treatment at 120°C for 48 hours.
Accordingly, the sliced samples after these treatments are aluminum alloy thick plates manufactured by the procedures of the manufacturing method according to the twelfth embodiment of the present invention, whereas the hot-rolled samples after the treatments are not. Among them, only the sliced samples using Alloys 33C and 34C correspond to examples according to the twelfth embodiment of the present invention.
Next, the sliced samples and hot-rolled samples after the treatments were subjected to a strength test and an anodizability evaluation test.
The procedures and criteria of the respective tests are as in First Experimental Example.
However, the properties of thick plates vary depending on the type of alloy used, and the criteria for the strength were modified as follows . Specifically, samples having a tensile strength of 250 N/mm² or more were evaluated as having accepted strength (Accepted) ; while those having a tensile strength of less than 250 N/mm² were evaluated as having unaccepted strength (Failed).

The test results are shown in Table 30.

[Table 30]

	Category	Number	Strength			Appearance after anodization
	Category	Number	Tensile strength (N/mm²)	Proof stress (N/mm²)	Evaluation	Surface appearance	Cross section appearance
Sliced Sample	Example	Alloy 33C	418	360	Accepted	Accepted	Accepted
	Example	Alloy 34C	520	453	Accepted	Accepted	Accepted
	Comparative Example	Alloy 35C	189	162	Failed	Accepted	Accepted
		Alloy 36C	290	190	Accepted	Failed	Accepted
		Alloy 37C	208	131	Failed	Accepted	Accepted
		Alloy 38C	614	530	Accepted	Failed	Accepted
Hot-rolled Sample	Comparative Example	Alloy 33C	437	378	Accepted	Accepted	Failed
		Alloy 34C	549	478	Accepted	Accepted	Failed
		Alloy 35C	204	169	Failed	Accepted	Failed
		Alloy 36C	305	204	Accepted	Failed	Failed
		Alloy 37C	230	150	Failed	Accepted	Failed
		Alloy 38C	628	542	Accepted	Failed	Failed

(Re: Sliced Samples)

As is demonstrated in Table 30, the samples using Alloys 35C and 37C contained Mg and Zn, respectively, in a content of less than the lower limit in the material aluminum alloy, and showed insufficient strength. The samples using Alloys 36C and 38C contained Mg and Zn, respectively, in a content of more than the upper limit in the material aluminum alloy, and thereby suffered from unevenness in their appearances of surfaces after anodization. The samples using Alloys 33C to 38C did not suffer from unevenness in their appearances of cross sections after anodization.

(Re: Hot-rolled Samples)

As is demonstrated in Table 30, the samples using Alloys 35C and 37C contained Mg and Zn, respectively, in a content of less than the lower limit in the material aluminum alloy, and thereby showed insufficient strength. The samples using Alloys 36C and 38C contained Mg and Zn, respectively, in a content of more than the upper limit in the material aluminum alloy and thereby suffered from unevenness in their appearances of surfaces after anodization. The samples using Alloys 33C to 38C suffered from unevenness in their appearances of cross sections after anodization.

Industrial Applicability

Methods for manufacturing aluminum alloy thick plates, according to the present invention, show superior productivity, can easily control the surface condition and flatness to improve the accuracy of plate thickness, and are thereby industrially very useful.

Claims

A method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Mg in a content of 1.5 percent by mass or more and 12.0 percent by mass or less, and further containing at least one member selected from the group consisting of Si in a content of 0.7 percent by mass or less, Fe in a content of 0.8 percent by mass or less, Cu in a content of 0.6 percent by mass or less, Mn in a content of 1.0 percent by mass or less, Cr in a content of 0.5 percent by mass or less, Zn in a content of 0.4 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.3 percent by mass or less, with the remainder being aluminum and inevitable impurities,
the method comprising in the following order:
a melting step of melting the aluminum alloy;

a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy;

a filtration step of filtering the aluminum alloy, from which hydrogen gas have been removed, to remove inclusions from the aluminum alloy;

a casting step which is a semi-continuous casting process of casting the aluminum alloy, from which inclusions have been removed, into a slab;

a slicing step of slicing the slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness; and

a heat treatment step of thermally treating the aluminum alloy thick plate having a predetermined thickness by holding the same at a temperature of 400°C or higher but lower than its melting point for one hour or longer.
A method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Mn in a content of 0.3 percent by mass or more and 1.6 percent by mass or less, and further containing at least one member selected from the group consisting of Si in a content of 0.7 percent by mass or less, Fe in a content of 0.8 percent by mass or less, Cu in a content of 0.5 percent by mass or less, Mg in a content of 1.5 percent by mass or less, Cr in a content of 0.3 percent by mass or less, Zn in a content of 0.4 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.3 percent by mass or less, with the remainder being aluminum and inevitable impurities,
the method comprising in the following order:
a melting step of melting the aluminum alloy;

a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy;

a filtration step of filtering the aluminum alloy, from which hydrogen gas have been removed, to remove inclusions from the aluminum alloy;

a casting step which is a semi-continuous casting process of casting the aluminum alloy, from which inclusions have been removed, into a slab;

a slicing step of slicing the slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness; and

a heat treatment step of thermally treating the aluminum alloy thick plate having a predetermined thickness by holding the same at a temperature of 400°C or higher but lower than its melting point for one hour or longer.
A method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Si in a content of 0.2 percent by mass or more and 1.6 percent by mass or less and Mg in a content of 0.3 percent by mass or more and 1.5 percent by mass or less, and further containing at least one member selected from the group consisting of Fe in a content of 0.8 percent by mass or less, Cu in a content of 1.0 percent by mass or less, Mn in a content of 0.6 percent by mass or less, Cr in a content of 0.5 percent by mass or less, Zn in a content of 0.4 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.3 percent by mass or less, with the remainder being aluminum and inevitable impurities,
the method comprising in the following order:
a melting step of melting the aluminum alloy;

a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy;

a filtration step of filtering the aluminum alloy, from which hydrogen gas have been removed, to remove inclusions from the aluminum alloy;

a casting step which is a semi-continuous casting process of casting the aluminum alloy, from which inclusions have been removed, into a slab;

a slicing step of slicing the slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness; and

a heat treatment step of thermally treating the aluminum alloy thick plate having a predetermined thickness by holding the same at a temperature of 400°C or higher but lower than its melting point for one hour or longer.
A method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Mg in a content of 0.4 percent by mass or more and 4.0 percent by mass or less and Zn in a content of 3.0 percent by mass or more and 9.0 percent by mass or less, and further containing at least one member selected from the group consisting of Si in a content of 0.7 percent by mass or less, Fe in a content of 0.8 percent by mass or less, Cu in a content of 3.0 percent by mass or less, Mn in a content of 0.8 percent by mass or less, Cr in a content of 0.5 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.25 percent by mass or less, with the remainder being aluminum and inevitable impurities,
the method comprising in the following order:
a melting step of melting the aluminum alloy;

a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy;

a filtration step of filtering the aluminum alloy, from which hydrogen gas have been removed, to remove inclusions from the aluminum alloy;

a casting step which is a semi-continuous casting process of casting the aluminum alloy, from which inclusions have been removed, into a slab;

a slicing step of slicing the slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness; and

a heat treatment step of thermally treating the aluminum alloy thick plate having a predetermined thickness by holding the same at a temperature of 350°C or higher but lower than its melting point for one hour or longer.
The method for manufacturing an aluminum alloy thick plate, according to any one of claims 1 to 4, further comprising, subsequent to the heat treatment step, a surface smoothing treatment step of subjecting the surface of the aluminum alloy thick plate to a surface smoothing treatment.
The method for manufacturing an aluminum alloy thick plate, according to claim 5, wherein the surface smoothing treatment is carried out by at least one process selected from the group consisting of cutting, grinding, and polishing.
The method for manufacturing an aluminum alloy thick plate, according to any one of claims 1 to 4, wherein the slicing step comprises removing a central portion in a thickness direction from the slab, the central portion having two substantially identical thicknesses in the thickness direction from the center of the thickness direction to the both surfaces of the central portion, respectively, and having a total thickness of from one-thirtieth to one-fifth the thickness T of the slab (T/30 to T/5).
A method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Mg in a content of 1.5 percent by mass or more and 12.0 percent by mass or less, and further containing at least one member selected from the group consisting of Si in a content of 0.7 percent by mass or less, Fe in a content of 0.8 percent by mass or less, Cu in a content of 0.6 percent by mass or less, Mn in a content of 1.0 percent by mass or less, Cr in a content of 0.5 percent by mass or less, Zn in a content of 0.4 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.3 percent by mass or less, with the remainder being aluminum and inevitable impurities,
the method comprising in the following order:
a melting step of melting the aluminum alloy;

a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy;

a filtration step of filtering the aluminum alloy, from which hydrogen gas have been removed, to remove inclusions from the aluminum alloy;

a casting step which is a semi-continuous casting process of casting the aluminum alloy, from which inclusions have been removed, into a slab;

a heat treatment step of thermally treating the slab by holding the same at a temperature of 200°C to 350°C for one hour or longer; and

a slicing step of slicing the thermally treated slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness,

wherein the slicing step comprises removing a central portion in a thickness direction from the slab, the central portion having two substantially identical thicknesses in the thickness direction from the center of the thickness direction to the both surfaces of the central portion, respectively, and having a total thickness of from one-thirtieth to one-fifth the thickness T of the slab (T/30 to T/5).
A method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Mn in a content of 0.3 percent by mass or more and 1.6 percent by mass or less, and further containing at least one member selected from the group consisting of Si in a content of 0.7 percent by mass or less, Fe in a content of 0.8 percent by mass or less, Cu in a content of 0.5 percent by mass or less, Mg in a content of 1.5 percent by mass or less, Cr in a content of 0.3 percent by mass or less, Zn in a content of 0.4 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.3 percent by mass or less, with the remainder being aluminum and inevitable impurities,
the method comprising in the following order:
a melting step of melting the aluminum alloy;

a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy;

a filtration step of filtering the aluminum alloy, from which hydrogen gas have been removed, to remove inclusions from the aluminum alloy;

a casting step which is a semi-continuous casting process of casting the aluminum alloy, from which inclusions have been removed, into a slab;

a heat treatment step of thermally treating the slab by holding the same at a temperature of 200°C to 350°C for one hour or longer; and

a slicing step of slicing the thermally treated slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness,

wherein the slicing step comprises removing a central portion in a thickness direction from the slab, the central portion having two substantially identical thicknesses in the thickness direction from the center of the thickness direction to the both surfaces of the central portion, respectively, and having a total thickness of from one-thirtieth to one-fifth the thickness T of the slab (T/30 to T/5).
A method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Si in a content of 0.2 percent by mass or more and 1.6 percent by mass or less and Mg in a content of 0.3 percent by mass or more and 1.5 percent by mass or less, and further containing at least one member selected from the group consisting of Fe in a content of 0.8 percent by mass or less, Cu in a content of 1.0 percent by mass or less, Mn in a content of 0.6 percent by mass or less, Cr in a content of 0.5 percent by mass or less, Zn in a content of 0.4 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.3 percent by mass or less, with the remainder being aluminum and inevitable impurities,
the method comprising in the following order:
a melting step of melting the aluminum alloy;

a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy;

a filtration step of filtering the aluminum alloy, from which hydrogen gas have been removed, to remove inclusions from the aluminum alloy;

a casting step which is a semi-continuous casting process of casting the aluminum alloy, from which inclusions have been removed, into a slab;

a heat treatment step of thermally treating the slab by holding the same at a temperature of 200°C or higher but lower than 400°C for one hour or longer; and

a slicing step of slicing the thermally treated slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness.
A method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Mg in a content of 0.4 percent by mass or more and 4.0 percent by mass or less and Zn in a content of 3.0 percent by mass or more and 9.0 percent by mass or less, and further containing at least one member selected from the group consisting of Si in a content of 0.7 percent by mass or less, Fe in a content of 0.8 percent by mass or less, Cu in a content of 3.0 percent by mass or less, Mn in a content of 0.8 percent by mass or less, Cr in a content of 0.5 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.25 percent by mass or less, with the remainder being aluminum and inevitable impurities,
the method comprising in the following order:
a melting step of melting the aluminum alloy;

a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy;

a filtration step of filtering the aluminum alloy, from which hydrogen gas have been removed, to remove inclusions from the aluminum alloy;

a casting step which is a semi-continuous casting process of casting the aluminum alloy, from which inclusions have been removed, into a slab;

a heat treatment step of thermally treating the slab by holding the same at a temperature of 200°C or higher but lower than 350°C for one hour or longer; and

a slicing step of slicing the thermally treated slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness.
The method for manufacturing an aluminum alloy thick plate, according to any one of claims 8 to 11, further comprising, subsequent to the slicing step, a surface smoothing treatment step of subjecting the surface of the aluminum alloy thick plate having a predetermined thickness to a surface smoothing treatment.
The method for manufacturing an aluminum alloy thick plate, according to claim 12, wherein the surface smoothing treatment is carried out by at least one process selected from the group consisting of cutting, grinding, and polishing.
The method for manufacturing an aluminum alloy thick plate, according to claim 10 or 11, wherein the slicing step comprises removing a central portion in a thickness direction from the slab, the central portion having two substantially identical thicknesses in the thickness direction from the center of the thickness direction to the both surfaces of the central portion, respectively, and having a total thickness of from one-thirtieth to one-fifth the thickness T of the slab (T/30 to T/5).
A method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Mg in a content of 1.5 percent by mass or more and 12.0 percent by mass or less, and further containing at least one member selected from the group consisting of Si in a content of 0.7 percent by mass or less, Fe in a content of 0.8 percent by mass or less, Cu in a content of 0.6 percent by mass or less, Mn in a content of 1.0 percent by mass or less, Cr in a content of 0.5 percent by mass or less, Zn in a content of 0.4 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.3 percent by mass or less, with the remainder being aluminum and inevitable impurities,
the method comprising in the following order:
a melting step of melting the aluminum alloy;

a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy;

a filtration step of filtering the aluminum alloy, from which hydrogen gas have been removed, to remove inclusions from the aluminum alloy;

a casting step which is a semi-continuous casting process of casting the aluminum alloy, from which inclusions have been removed, into a slab;

a slicing step of slicing the slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness; and

a heat treatment step of thermally treating the aluminum alloy thick plate having a predetermined thickness by holding the same at a temperature of 200°C or higher but lower than 400°C for one hour or longer.
A method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Mn in a content of 0.3 percent by mass or more and 1.6 percent by mass or less, and further containing at least one member selected from the group consisting of Si in a content of 0.7 percent by mass or less, Fe in a content of 0.8 percent by mass or less, Cu in a content of 0.5 percent by mass or less, Mg in a content of 1.5 percent by mass or less, Cr in a content of 0.3 percent by mass or less, Zn in a content of 0.4 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.3 percent by mass or less, with the remainder being aluminum and inevitable impurities, the method comprising in the following order:
a melting step of melting the aluminum alloy;

a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy;

a filtration step of filtering the aluminum alloy, from which hydrogen gas have been removed, to remove inclusions from the aluminum alloy;

a casting step which is a semi-continuous casting process of casting the aluminum alloy, from which inclusions have been removed, into a slab;

a slicing step of slicing the slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness; and

a heat treatment step of thermally treating the aluminum alloy thick plate having a predetermined thickness by holding the same at a temperature of 200°C or higher but lower than 400°C for one hour or longer.
A method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Si in a content of 0.2 percent by mass or more and 1.6 percent by mass or less and Mg in a content of 0.3 percent by mass or more and 1.5 percent by mass or less, and further containing at least one member selected from the group consisting of Fe in a content of 0.8 percent by mass or less, Cu in a content of 1.0 percent by mass or less, Mn in a content of 0.6 percent by mass or less, Cr in a content of 0.5 percent by mass or less, Zn in a content of 0.4 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.3 percent by mass or less, with the remainder being aluminum and inevitable impurities,
the method comprising in the following order:
a melting step of melting the aluminum alloy;

a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy;

a filtration step of filtering the aluminum alloy, from which hydrogen gas have been removed, to remove inclusions from the aluminum alloy;

a casting step which is a semi-continuous casting process of casting the aluminum alloy, from which inclusions have been removed, into a slab;

a slicing step of slicing the slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness; and

a heat treatment step of thermally treating the aluminum alloy thick plate having a predetermined thickness by holding the same at a temperature of 200°C or higher but lower than 400°C for one hour or longer.
A method for manufacturing an aluminum alloy thick plate from an aluminum alloy, the aluminum alloy containing Mg in a content of 0.4 percent by mass or more and 4.0 percent by mass or less and Zn in a content of 3.0 percent by mass or more and 9.0 percent by mass or less, and further containing at least one member selected from the group consisting of Si in a content of 0.7 percent by mass or less, Fe in a content of 0.8 percent by mass or less, Cu in a content of 3.0 percent by mass or less, Mn in a content of 0.8 percent by mass or less, Cr in a content of 0.5 percent by mass or less, Ti in a content of 0.1 percent by mass or less, and Zr in a content of 0.25 percent by mass or less, with the remainder being aluminum and inevitable impurities,
the method comprising in the following order:
a melting step of melting the aluminum alloy;

a hydrogen gas removal step of removing hydrogen gas from the molten aluminum alloy;

a filtration step of filtering the aluminum alloy, from which hydrogen gas have been removed, to remove inclusions from the aluminum alloy;

a casting step which is a semi-continuous casting process of casting the aluminum alloy, from which inclusions have been removed, into a slab;

a slicing step of slicing the slab in the cast direction into an aluminum alloy thick plate having a predetermined thickness; and

a heat treatment step of thermally treating the aluminum alloy thick plate having a predetermined thickness by holding the same at a temperature of 200°C or higher but lower than 350°C for one hour or longer.
The method for manufacturing an aluminum alloy thick plate, according to any one of claims 15 to 18, further comprising, subsequent to the heat treatment step, a surface smoothing treatment step of subjecting the surface of the aluminum alloy thick plate to a surface smoothing treatment.
The method for manufacturing an aluminum alloy thick plate, according to claim 19, wherein the surface smoothing treatment is carried out by at least one process selected from the group consisting of cutting, grinding, and polishing.
The method for manufacturing an aluminum alloy thick plate, according to any one of claims 15 to 18, the slicing step comprises removing a central portion in a thickness direction from the slab, the central portion having two substantially identical thicknesses in the thickness direction from the center of the thickness direction to the both surfaces of the central portion, respectively, and having a total thickness of from one-thirtieth to one-fifth the thickness T of the slab (T/30 to T/5).