JP2012214846A - Aluminum alloy sheet for molding process and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Al-Mg-Si-based alloy sheet that has enough moldability and strength as an automotive panel etc. and does not cause defective appearance after molding and coating under severe molding conditions, and a method for producing the same.SOLUTION: The aluminum alloy sheet for molding process is produced by subjecting an aluminum alloy containing 0.4-1.5 mass% of Si, 0.4-1.0 mass% of Mg, 0.1-1.0 mass% of Fe, and 0.1-0.5 mass% of Mn, with the balance comprising Al and unavoidable impurities to casting; homogenizing heat treatment; hot rolling such that the initiation temperature is 350-450°C and the end temperature is (445-3r)°C or more relative to the rolling reduction r% in the final pass; cold rolling; solution treatment; and quenching treatment. Furthermore, in the central part in the sheet thickness direction of a cross-section surface including the rolling direction, an Al-Mn-Fe(-Si)-based intermetallic compound with an equivalent circle diameter of 2.0 μm or more has an area rate of 0.4% or more and a number density of 1,350 pieces/mmor more.

Description

  The present invention relates to an Al—Mg—Si alloy plate that is pressed and formed into an automotive panel or the like, and more particularly, to an aluminum alloy plate excellent in surface properties and a method for manufacturing the same.

  In recent years, in order to improve the fuel efficiency of automobiles, the application of aluminum materials, which are lightweight and excellent in formability and bake hardenability, is increasing in place of steel materials that have been used so far.

  Among automotive members, examples of the aluminum material applied to a panel structure such as an outer panel (outer plate) and an inner panel (inner plate) include high-strength JIS 5000,6000 series aluminum alloy materials. In particular, Al-Mg-Si alloy materials such as 6000 series have excellent age-hardening ability, so that the formability of the panel after molding is ensured while ensuring low formability during press working and bending. It has a bake hard property that the yield strength is improved by heating at the time of artificial aging (curing) treatment at a relatively low temperature such as paint baking treatment, and the required strength is obtained (see, for example, Patent Document 1).

  As a plate material for a panel structure, particularly an outer panel, in addition to formability and strength, the appearance of the surface after being manufactured into the panel structure is required, but the 6000 series aluminum alloy plate is formed by press working or the like. Later, rough skin is likely to occur, and the surface after coating tends to have a poor appearance such as a ridging mark. Therefore, an Al—Mg—Si alloy plate that can prevent appearance defects such as ridging marks has been developed.

  The ridging mark is a striped unevenness along the rolling direction that was formed on the surface of the plate by molding. As a result of detailed verification, the stacking of the total plastic deformation amount in the thickness direction is Has been found to form. That is, whether or not a ridging mark is generated is determined by the degree of distribution (bias) for each crystal orientation component in the direction perpendicular to the rolling (width) direction. Therefore, in addition to refinement of crystal grains to prevent rough skin, the crystal area ratio is specified for each orientation so that the orientation of the crystals is not aligned in a specific direction (patents) References 2 to 5), Al—Mg—Si based alloy plates that define the precipitation of intermetallic compounds that are the core of recrystallization have been developed (Patent Document 6). And in order to obtain such fine and randomly oriented crystals, a predetermined amount of Mn or the like for forming an intermetallic compound is added, or ingot homogenization treatment or solution treatment after cold rolling is conducted with a predetermined heat treatment. It is known to perform under conditions, or to control the processing rate and reduction ratio in hot rolling and cold rolling, and further the start temperature and end temperature in hot rolling.

JP 2008-303449 A Japanese Patent No. 4063388 JP 2009-263781 A Japanese Patent No. 4499369 Japanese Patent No. 4202894 Japanese Patent No. 4328242

  However, Patent Document 2 is difficult to produce stably because the end temperature of hot rolling is highly regulated, and Patent Document 5 is liable to cause scratches on the surface to suppress the speed of hot finish rolling. There is room for improvement in manufacturing conditions. Furthermore, when the press processing conditions become severe due to enlargement of the panel structure, complexity of the shape, or thinning, etc., appearance defects such as ridging marks are more likely to occur, and the Al—Mg—Si alloy in Patent Documents 2 to 6 A board is not enough.

  The present invention has been made in view of the above problems, and has sufficient formability and strength as an automotive panel or the like, and does not cause poor appearance after molding under thinning or severe processing conditions, and further after coating. An object of the present invention is to provide an Al—Mg—Si alloy plate having excellent surface properties and a method for producing the same.

  In order to solve the above-mentioned problems, the present inventors have a high density of intermetallic compounds that serve as nuclei in the recrystallization in addition to the rolling conditions for refining the recrystallized structure previously invented. In this case, it has been found that the recrystallized structure is further refined because each intermetallic compound becomes a nucleus, and the orientation of the recrystallized crystal tends to be random. In view of this, for the intermetallic compounds appearing in the cross section of the aluminum alloy plate, we have intensively studied the appropriate values of the size and distribution state and the conditions for crystallizing and precipitating the intermetallic compounds.

That is, the aluminum alloy plate for forming according to the present invention has Si: 0.4 to 1.5 mass%, Mg: 0.4 to 1.0 mass%, Fe: 0.1 to 1.0 mass%, Mn: 0.1 to 0.5% by mass, and the balance is formed of an aluminum alloy composed of Al and inevitable impurities. And this aluminum alloy sheet for forming processing has an area ratio of an Al—Mn—Fe (—Si) intermetallic compound having an equivalent circle diameter of 2.0 μm or more at the center in the thickness direction of the cross section including the rolling direction. : 0.4% or more, number density: 1350 / mm ² or more. The aluminum alloy for forming is further Cu: 0.05 to 1.0% by mass, Cr: 0.15% by mass or less, Zr: 0.15% by mass or less, Ti: 0.007 to 0.10% by mass. It is preferable to contain at least one kind of Zn, and Zn may be contained in an amount of 0.5% by mass or less.

  As described above, an Al—Mg—Si alloy containing a predetermined amount of Si and Mg has high formability and strength, and a sufficient amount of metal is added by adding a predetermined amount of Mn and Fe. By precipitating intermetallic compounds, a fine recrystallized structure is obtained with such intermetallic compounds as nuclei, and random crystal orientations are obtained. Appearance does not occur.

  Further, the method for producing an aluminum alloy plate for forming according to the present invention comprises a casting step of casting the ingot by melting the aluminum alloy of the above components, and the ingot for 1 hour at a temperature in the range of 500 to 580 ° C. A homogenization heat treatment step for homogenization by the above heat treatment, a hot rolling step for producing a hot-rolled sheet by hot rolling the homogenized ingot at a temperature in the range of 350 to 450 ° C, and A cold rolling process in which a hot rolled sheet is cold rolled at a total rolling rate of 40% or more to produce a cold rolled sheet, and the cold rolled sheet is heated until reaching a temperature in the range of 500 to 560 ° C. And a solution treatment step of cooling to room temperature later. In the hot rolling step, at least one rolling pass with a reduction rate of 40% or more is performed when the plate thickness reaches 100 mm or less and 30 mm or more, and in the final rolling pass, the reduction rate (% ) Is expressed by r, rolling is performed such that the end temperature is (445-3r) ° C. or higher.

  In this way, in the hot rolling process, a coarse structure is eliminated by rolling a rolling pass in a predetermined thickness range with a sufficient reduction rate, and the end temperature is a predetermined value corresponding to the reduction rate of the final rolling pass. By doing so, recrystallization is promoted after completion. As a result, an aluminum alloy plate having a fine recrystallized structure made of crystals of random orientation can be obtained without intermediate annealing before cold rolling.

  According to the aluminum alloy sheet for forming according to the present invention, an automotive panel that has sufficient formability and strength and does not cause appearance defects such as ridging marks on the surface after painting even if it is molded under severe processing conditions. Etc. can be manufactured. And according to the manufacturing method of the aluminum alloy plate for shaping | molding which concerns on this invention, the aluminum alloy plate for shaping | molding processing which has the said effect can be manufactured with sufficient productivity.

It is sectional drawing explaining the method of a ball head overhang | projection formability test. It is a side view explaining the method of flat hem processing. It is a profile figure explaining the measuring method of surface roughness.

An aluminum alloy plate for forming according to the present invention (hereinafter referred to as an aluminum alloy plate) is formed into a desired shape by pressing or the like, and then painted and baked on the surface to produce an automotive panel structure or the like. It is a plate material to be made. The aluminum alloy plate according to the present invention does not particularly define a plate thickness, but is generally about 1.0 mm as a plate material formed on such a panel structure of an automobile.
Hereinafter, the form for implement | achieving the aluminum alloy plate which concerns on this invention is demonstrated.

The aluminum alloy plate according to the present invention has Si: 0.4 to 1.5 mass%, Mg: 0.4 to 1.0 mass%, Fe: 0.1 to 1.0 mass%, Mn: 0.1 It is formed of an aluminum alloy containing ~ 0.5% by mass, the balance being Al and inevitable impurities, and, like a general aluminum alloy plate, melting, casting, hot rolling, cold rolling (The details of the manufacturing method will be described later). Or the said aluminum alloy may contain Cu: 0.05-1.0 mass% further. The aluminum alloy plate according to the present invention has an area of an Al-Mn-Fe (-Si) intermetallic compound having a circle-equivalent diameter of 2.0 μm or more at the center in the thickness direction of the cross section including the rolling direction. Rate: 0.4% or more, number density: 1350 / mm ² or more. Hereinafter, each element which comprises the aluminum alloy plate which concerns on this invention is demonstrated.

[Components of aluminum alloy]
(Si: 0.4-1.5 mass%)
Si is mixed into the aluminum alloy as a metal base impurity, and has the effect of improving the strength by solid solution strengthening in the aluminum alloy. Further, when coexisting with Mg, it is artificial at low temperatures such as paint baking treatment. During the aging treatment, an Mg—Si based intermetallic compound (Mg ₂ Si) is generated and contributes to strength improvement. In order to obtain sufficient strength due to these effects, the Si content is 0.4% by mass or more, preferably 0.6% by mass or more. On the other hand, if the content of Si exceeds 1.5% by mass, the crystallized product is generated at the time of solidification in casting, and the precipitate is generated as a coarse product at the time of subsequent cooling, and remains in the subsequent steps. Formability is lowered, and further, intergranular cracking occurs, so that weldability is lowered. Therefore, the Si content is 1.5% by mass or less, and preferably 1.3% by mass or less.

(Mg: 0.4-1.0% by mass)
Mg has the effect of improving the strength by solid solution strengthening in an aluminum alloy, and when coexisting with Si, during artificial aging treatment at low temperature such as paint baking treatment, between Mg-Si based metals such as Mg ₂ Si A compound is produced and contributes to strength improvement. In order to obtain sufficient strength due to these effects, the Mg content is set to 0.4% by mass or more. On the other hand, if the Mg content exceeds 1.0% by mass, the intermetallic compound becomes coarse at the time of casting and crystallizes and precipitates, and remains after the subsequent process, so that the formability is lowered. To do. Therefore, the Mg content is 1.0% by mass or less, preferably 0.8% by mass or less.

(Fe: 0.1 to 1.0% by mass)
Fe is mixed in the aluminum alloy as a metal impurity, and in the aluminum alloy, Al—Mn—Fe intermetallic compound such as Al ₆ (Mn, Fe) together with Mn and Si, Al ₁₂ An Al—Mn—Fe—Si intermetallic compound such as (Mn, Fe) ₃ Si is produced. When these intermetallic compounds are crystallized at the time of casting, after hot rolling, recrystallization proceeds with the crystallized material as a nucleus, and a fine and random texture is formed. In order to obtain a fine recrystallized structure with an appropriate amount of crystallized material, the Fe content is 0.1% by mass or more, preferably 0.15% by mass or more, more preferably 0.2% by mass or more. is there. In addition, by allowing a certain amount of Fe, a large amount of scrap material or the like can be mixed with the raw material of the aluminum alloy, thereby improving recyclability. However, if the Fe content exceeds 1.0% by mass, the intermetallic compound is coarsely produced, and the strength and formability deteriorate. Therefore, the Fe content is 1.0% by mass or less.

(Mn: 0.1 to 0.5% by mass)
Mn is an Al—Mn—Fe-based intermetallic compound such as Al ₆ (Mn, Fe) and Al—Mn—Fe— such as Al ₁₂ (Mn, Fe) ₃ Si together with Fe and Si. Si-based intermetallic compound is generated. When these intermetallic compounds are crystallized at the time of casting, after hot rolling, recrystallization proceeds with the crystallized material as a nucleus, and a fine and random texture is formed. In order to obtain a fine recrystallized structure with an appropriate amount of crystallized matter, the Mn content is set to 0.1% by mass or more. On the other hand, when the content of Mn exceeds 0.5% by mass, the intermetallic compound is coarsely produced, and the strength and formability are lowered. Therefore, the Mn content is 0.5 mass% or less.

(Cu: 0.05 to 1.0% by mass)
Cu dissolves in the aluminum alloy to increase work hardenability and improve the formability during press working. Further, Cu has an effect of promoting the formation of aging precipitates by an artificial aging treatment at a low temperature such as a paint baking treatment. In order to make these effects sufficient, the Cu content is preferably 0.05% by mass or more. On the other hand, if the Cu content exceeds 1.0% by mass, the work hardening becomes excessive and the formability is lowered, and the stress corrosion cracking resistance and the yarn rust resistance are remarkably deteriorated. Therefore, the Cu content is 1.0% by mass or less.

(Cr: 0.15 mass% or less, Zr: 0.15 mass% or less, Ti: 0.007 to 0.10 mass%, Zn: 0.5 mass% or less)
The aluminum alloy plate according to the present invention may contain, for example, Cr, Zn, Ti, Zr, and B as unavoidable impurities in addition to the above-described components. .15% by mass or less, Zn: 0.5% by mass or less, and Ti: 0.10% by mass or less are acceptable without impairing the effects of the present invention. Moreover, the effect | action which refines | miniaturizes the ingot structure | tissue of an aluminum alloy is acquired by adding Ti and B. In order to obtain such an effect, the ingot refining agent (TiB) having a composition in which Ti is 5 times the mass ratio of B is usually used as a molten metal (melting furnace, inclusion filter) in the form of a waffle or a rod. , Added to either the degassing device or the molten metal flow rate control device, before the slab solidification. In this case, by adding Ti (TiB) in such an amount that the Ti content in the aluminum alloy plate is 0.007% by mass or more, the crystal grains of the ingot are refined, and the formability of the aluminum alloy plate is improved. That is, in order to obtain the above effect, the Ti content is preferably set to 0.007% by mass or more, and in this case, B corresponding to the above composition is inevitably added. On the other hand, when the Ti content in the aluminum alloy plate exceeds 0.10% by mass, a coarse crystallized product is formed, and the formability of the aluminum alloy plate is lowered. Therefore, the Ti content is 0.10% by mass or less, and the B content is allowed according to the above composition.

  When each content of Cr and Zr exceeds 0.15% by mass, a coarse intermetallic compound is generated, the formability of the aluminum alloy plate is lowered, and the corrosion resistance is lowered. Similarly, when the Zn content exceeds 0.5% by mass, a coarse intermetallic compound is generated, the formability of the aluminum alloy plate is lowered, and the corrosion resistance is remarkably lowered. On the other hand, Cr and Zr have the effect of producing dispersed particles (dispersed phase) during the homogenization heat treatment and making the crystal grains finer when an aluminum alloy plate is produced. . Further, since Zn is added in a large amount to a clad material such as an aluminum alloy brazing sheet for a heat exchanger, it is contained in a large amount in a scrap material generated in the manufacturing process. Therefore, in the aluminum alloy plate according to the present invention, by allowing a certain amount of Zn, a large amount of the scrap material can be mixed with the raw material of the aluminum alloy, and the recyclability is improved.

[Intermetallic compound of aluminum alloy sheet]
(Area ratio of Al-Mn-Fe (-Si) intermetallic compound having an equivalent circle diameter of 2.0 μm or more at the center in the thickness direction of the cross section including the rolling direction: 0.4% or more, number density: 1350 / Mm ² or more)
The intermetallic compounds present in the aluminum alloy plate according to the present invention are mainly Al-Mn-Fe series such as Al ₆ (Mn, Fe), Al ₁₂ (Mn, Fe) ₃ Si, Al-Mn-Fe-Si. These are intermetallic compounds (hereinafter collectively referred to as “Al—Mn—Fe (—Si) intermetallic compounds”) and Mg—Si intermetallic compounds such as Mg ₂ Si. In the aluminum alloy sheet, among these intermetallic compounds, those having a certain size or more become the core of recrystallization after hot rolling. Here, since the aluminum alloy plate according to the present invention is subjected to a solution treatment after cold rolling, a part of Si and Mg is dissolved. Therefore, in an aluminum alloy sheet, it is difficult to specify the Mg—Si-based intermetallic compound that has become the nucleus of recrystallization after hot rolling, that is, before cold rolling, so Al—Mn—Fe (—Si ) Based on intermetallic compounds. That is, an Al—Mn—Fe (—Si) intermetallic compound having an equivalent circle diameter of 2.0 μm or more at the center in the thickness direction of the cross section (L-ST plane) including the rolling direction of the aluminum alloy plate is hot-rolled. It is presumed that it is an intermetallic compound that later became the nucleus of recrystallization.

An intermetallic compound having an equivalent circle diameter of 2.0 μm or more means that the area (cross-sectional area) of the intermetallic compound in the cross section of the aluminum alloy plate is not less than the area of a circle having a diameter of 2.0 μm. It corresponds to about 3 to 6 μm. And such an Al-Mn-Fe (-Si) type intermetallic compound has an area ratio of 0.4% or more and 1350 pieces / mm ² or more in the central part in the plate thickness direction of the cross section including the rolling direction of the aluminum alloy plate. If present, at the surface of the hot-rolled sheet, at least on the surface, intermetallic compounds (including Mg-Si intermetallic compounds) having a size that can be recrystallization nuclei are sufficiently distributed, fine and It can be determined that a recrystallized structure having a random orientation was formed. The distribution of such intermetallic compounds is controlled by the contents of the Mg, Si, Fe, and Mn and the production conditions described later.

  In the rolled plate, the intermetallic compound closer to the rolling surface, ie, the ingot surface, is more easily crushed and refined during rolling, so the size that is the core of recrystallization near the surface of the hot rolled plate is somewhat Many of the above intermetallic compounds tend to be crushed by subsequent cold rolling. Therefore, the aluminum alloy plate according to the present invention regulates the distribution of the intermetallic compound in the central portion in the plate thickness direction in which many relatively large intermetallic compounds are likely to exist (residual). The central portion in the plate thickness direction of the cross section specifically refers to a range corresponding to 55 to 70% of the plate thickness centering on a portion in the plate thickness direction 1/2. In the aluminum alloy sheet according to the present invention, the intermetallic compound in the cross section including the rolling direction is observed, and the distribution restriction target is selected based on the equivalent circle diameter.

  Application of a scanning electron microscope (SEM) is an example of the intermetallic compound detection means. Al-Mn-Fe (-Si) -based intermetallic compounds can be identified by contrast with the parent phase in the SEM composition (COMPO) image. Al-Mn-Fe-based intermetallic compounds and Al-Mn-Fe-Si-based metals The intermetallic compound appears whiter than the Al matrix, and the Mg—Si intermetallic compound appears blacker than the Al matrix. The intermetallic compound in the cross section of the aluminum alloy plate is cut out of the aluminum alloy plate, and the cut surface (L-ST surface) including the rolling direction and the plate thickness direction is mirror-finished by mechanical polishing to obtain an observation surface. A range corresponding to 55 to 70% of the plate thickness centering on a portion in the plate thickness direction 1/2 is observed. Preferably, a plurality of fields of view are observed and photographed at a magnification of about 100 times from an area within this range, and an Al-Mn-Fe (-Si) intermetallic compound having an equivalent circle diameter of 2.0 μm or more using an image processing apparatus or the like. The area ratio and number density can be measured.

  Next, the manufacturing method of the aluminum alloy plate for shaping | molding which concerns on this invention is demonstrated. The aluminum alloy plate according to the present invention includes a casting process for melting an aluminum alloy having the above components to cast an ingot, a soaking process for homogenizing the ingot by heat treatment, and hot rolling the ingot to heat it. A hot rolling process for forming a cold rolled sheet, a cold rolling process for cold rolling the hot rolled sheet to form a cold rolled sheet, and a solution for subjecting the cold rolled sheet to solution and quenching by heating and cooling Manufacturing process. Below, the conditions of each process are demonstrated.

[Casting process]
First, an aluminum alloy is melted, cast by a known semi-continuous casting method such as a DC casting method, and cooled to below the solidus temperature of the aluminum alloy to obtain an ingot.

[Soaking process]
Before rolling the ingot, it is necessary to perform a homogenization heat treatment (soaking) at a predetermined temperature. By applying heat treatment to the ingot, internal stress is removed, β-Mg ₂ Si segregated during casting and the structure are homogenized, and intermetallic compounds that crystallize during casting cooling and precipitate after that grow. Thus, it becomes an appropriate size that can become a nucleus of recrystallization after hot rolling.

(Heat treatment temperature: 500-580 ° C., heat treatment time: 1 hour or more)
In the soaking process, if the heat treatment temperature (ingot temperature) is less than 500 ° C., it takes time to homogenize the structure of the ingot, so that the productivity is lowered, and when the temperature is further lowered, the aluminum alloy plate according to the present invention It becomes difficult to homogenize the ingots of the components. On the other hand, when the heat treatment temperature exceeds 580 ° C., the ingot is locally remelted (burned) to deteriorate the surface properties of the plate, and further hot rolling becomes impossible. Therefore, in the soaking process, the heat treatment temperature is set to 500 ° C. or more and 580 ° C. or less. In addition, if the heat treatment time is less than 1 hour, homogenization of the ingot may not be completed. Therefore, the heat treatment time is set to 1 hour or more. On the other hand, the upper limit is not particularly limited. Therefore, 10 hours or less is preferable.

  Before rolling the ingot, it is necessary to perform chamfering by cutting and removing the surface layer of the ingot. Chamfering can be performed either before or after soaking. When chamfering is performed before soaking, it is preferable to start hot rolling immediately after the soaking so that the temperature drop of the ingot reaches a predetermined start temperature of hot rolling. . On the other hand, when chamfering is performed after soaking, the ingot is heated to the predetermined start temperature (preliminary heating) and then hot rolled.

[Hot rolling process]
The homogenized ingot is hot-rolled. First, rough rolling is performed on the ingot having a start temperature within a predetermined temperature range, and further, a desired sheet thickness is obtained by finish rolling, and a hot rolled sheet is obtained by winding at an end temperature equal to or higher than a predetermined temperature. The thickness of the hot-rolled sheet is the thickness of the aluminum alloy sheet, that is, the thickness of the cold-rolled sheet after the subsequent cold-rolling process, and the total rolling rate (cold working rate) in the cold-rolling process. Is set by reverse calculation, and specifically, a range of about 1.7 to 10 mm is preferable.

(Starting temperature: 350-450 ° C)
When rolling an ingot or the like having a temperature exceeding 450 ° C., the end temperature of hot rolling may become too high, and the structure is coarsened by subsequent recrystallization and finally produced into an aluminum alloy sheet. Since problems such as rough skin occur, the hot rolling start temperature is set to 450 ° C. or lower. On the other hand, if the temperature is low, it is difficult to increase the rolling reduction of one pass because the deformation resistance is large, the number of passes until the desired plate thickness is increased, the productivity is lowered, and the number of passes is increased. Repeatedly lowers the temperature further. If the temperature of the ingot is less than 350 ° C. at the start of hot rolling, the end temperature becomes too low to satisfy the predetermined temperature described later, so the hot rolling start temperature is set to 350 ° C. or higher. Such a start temperature is controlled by cooling the ingot to the start temperature after the preceding soaking or by preheating the ingot cooled after the soaking.

(Rolling pass of 40% or more rolling reduction at plate thickness of 100 to 30 mm: 1 pass or more)
Hot rolling can be performed in the range of about 30 to 50% reduction in one pass as in the case of general hot rolling of aluminum materials. In the present invention, the number of passes is reduced to increase productivity. In order to improve the temperature, and to suppress the temperature drop and recrystallize the end temperature to a predetermined value or higher as described later, it is preferable that the rolling reduction rate of each pass is high to some extent. In particular, it is necessary to carry out at least one rolling pass with a rolling reduction of 40% or more before the plate thickness becomes 100 mm or less and before it becomes thinner than 30 mm. When rolling is not performed at a high rolling reduction of 40% or more in the initial to middle stages of hot rolling (rough rolling), the crystal grains become coarse, and such a coarse structure is until the end of hot rolling (finish rolling). Remains. As a result, in subsequent recrystallization, even if the intermetallic compound is sufficiently distributed, it is difficult to obtain a fine crystal structure. Even if this rolling pass with a rolling reduction of 40% or more is performed on a rolled plate having a thickness of more than 100 mm, the deep rolling structure of the rolled plate tends to remain, whereas it is performed on a rolled plate having a thickness of less than 30 mm. However, since the absolute value of the amount of change in sheet thickness due to the rolling pass is small, the effect cannot be sufficiently obtained. In addition, the plate | board thickness limited to 100-30 mm points out the plate | board thickness just before rolling by a pass with a rolling reduction of 40% or more.

(End temperature: (445- (final pass reduction ratio) × 3) ° C. or higher)
If the hot rolling sheet winding temperature (end temperature) is low at the end of the hot rolling process (at the end of hot finish rolling), the progress of recrystallization is insufficient after the final pass of hot finish rolling. The rolled structure remains on the hot rolled sheet. As described above, in the aluminum alloy plate according to the present invention, a fine recrystallized structure is formed with appropriately distributed intermetallic compounds as nuclei after hot rolling. Therefore, since it is necessary to be completely recrystallized before cold rolling, the hot rolled sheet in which the rolled structure remains needs a step of performing annealing (intermediate annealing) before cold rolling, Productivity decreases. On the other hand, the higher the rolling reduction in the final pass, the more likely the subsequent recrystallization proceeds. When the rolling reduction (%) of this final pass is represented by r, if the end temperature is (445-3r) ° C. or higher, the recrystallization is sufficiently advanced and completed at the time of winding the hot rolled sheet ( No rolling structure remains). That is, in the final pass of hot rolling, the end temperature may be lowered as the rolling reduction is higher. However, as described above, when the temperature of the rolled plate is lowered, the rolling resistance is increased due to the large deformation resistance. Becomes difficult. Therefore, the end temperature in the hot rolling process is set to be equal to or higher than the temperature according to the rolling reduction of the final pass. When the end temperature exceeds 400 ° C., the structure becomes coarse by recrystallization as described above, but it is difficult for the end temperature to exceed 400 ° C. due to the upper limit of the start temperature. Is not specified.

(Observation method of recrystallized structure of hot rolled sheet)
Here, a method for observing the progress of recrystallization of the hot-rolled sheet will be described. When the recrystallization is completed, equiaxed recrystallized grains, specifically, as shown in Japanese Patent No. 3491819, a plane parallel to the rolling surface (surface) of the hot rolled plate and a cross section including the rolling direction Recrystallized grains having an average aspect ratio in the range of 1 to 3 on each face are obtained. Specifically, the grain size d _{L in} the rolling direction, the grain size d _{LT in} the direction perpendicular to the rolling (width) direction, and the grain size d _ST in the sheet thickness direction of the hot rolled sheet structure are 1 ≦ d _L / d _LT ≦ 3, Those _satisfying 1 ≦ d _L / d _ST ≦ 3 are equiaxed recrystallized grains. On the other hand, when the average of the aspect ratios d _L / d _LT and d _L / d _ST exceeds 3, it indicates that the fiber structure of the rolled structure remains. Note that less than 1, for d _L by rolling d _LT, made it is not shorter than d _ST, not specified. d _L / d _LT is the surface of the hot-rolled plate, d _L / d _ST is the cross-section including the rolling direction of the hot-rolled plate, mechanically polished, and then electroetched to obtain an optical microscope (using a polarizing plate) It can measure by observing using.

[Cold rolling process]
(Total rolling ratio: 40% or more)
The hot-rolled sheet is cold-rolled to obtain a cold-rolled sheet having a predetermined aluminum alloy sheet thickness. In cold rolling, the higher the total rolling rate (cold working rate), the more distortion is accumulated, and the crystal grains of the recrystallized structure by the subsequent solution treatment become finer, and the surface properties are improved. If the total rolling rate is less than 40%, the recrystallized grains are coarsened by the solution treatment, and good surface properties after forming cannot be obtained. Therefore, cold rolling is performed at a total rolling rate of 40% or more. When the total rolling rate increases, the number of cold rolling passes increases and the productivity decreases, so 90% or less is preferable.

  According to the method for producing an aluminum alloy sheet according to the present invention, the recrystallization of the hot-rolled sheet is completed by setting the end temperature equal to or higher than the predetermined value in the hot-rolling process. There is no need to perform recrystallization by annealing (intermediate annealing) in the middle. In other words, when the specified hot rolling finish temperature is not reached, an aluminum alloy plate can be manufactured by performing recrystallization by performing intermediate annealing in the middle of hot rolling plate or cold rolling. . If the annealing temperature (temperature of the hot-rolled sheet) is insufficient, recrystallization does not proceed. On the other hand, if it is too high, the crystal grains become coarse and the crystal grains in the aluminum alloy sheet become coarse. Properties deteriorate. When applying a continuous annealing furnace in which the temperature rising rate of the hot-rolled sheet is fast, the annealing temperature is set to a range of 400 to 550 ° C., and the annealing time (passing time) is set to 30 seconds or less. On the other hand, when applying a batch type furnace, since the rate of temperature rise is slow, it is performed in the range of 300 to 450 ° C. for 1 to 10 hours. By performing such intermediate annealing, not only recrystallization of the hot-rolled plate, but also the crystal grains become finer, so that the surface properties of the aluminum alloy plate are further improved. Therefore, intermediate annealing may be further performed on the hot-rolled sheet that has been recrystallized at the end of hot rolling.

[Solution treatment process]
(Heating temperature: 500-560 ° C)
The cold-rolled sheet is heated to form a solution, and then cooled to room temperature (50 ° C. or lower) to be quenched to obtain the aluminum alloy sheet according to the present invention. By performing such treatment, as much of Mg and Si that existed as an intermetallic compound in the cold-rolled sheet can be dissolved as much as possible, and baking hardness by painting and baking after molding can be secured. . The solution treatment and quenching treatment can be performed in the same manner as a known Al—Mg—Si alloy material such as 6000 series. When the temperature of the cold-rolled sheet is less than 500 ° C., Mg and Si are not sufficiently dissolved, and the amount of solid solution is insufficient, so that the bake hardness cannot be obtained. On the other hand, when the cold-rolled plate exceeds 560 ° C., the elongation is remarkably reduced by eutectic melting, the crystal grains are coarsened and the plate surface is roughened, and the surface properties after coating are deteriorated. Therefore, the heating temperature of the cold rolled sheet is set to 500 to 560 ° C. Since the effect can be obtained if the cold-rolled sheet reaches a temperature in this range, it is not necessary to maintain this temperature, and even if the holding time is increased, the effect is not improved and the productivity is lowered. For 30 seconds or less. And, in cooling after reaching the heating temperature, if the cooling rate is slow, coarse Mg ₂ Si, Si, etc. are likely to precipitate at the grain boundary, and the formability is lowered, so it is rapidly cooled by water cooling (water quenching) or the like. Is preferred.

[Preliminary aging treatment process]
When the Al—Mg—Si alloy material that has been subjected to solution treatment and quenching treatment is left at room temperature, the strength (proof strength) gradually increases due to natural aging (room temperature aging), and the formability decreases accordingly. Therefore, in order to sufficiently improve the strength in advance and suppress subsequent changes with time, the aluminum alloy plate is further preliminarily aged in the same manner as a known Al-Mg-Si alloy material such as 6000 series. It is preferable to carry out the treatment. Specifically, after being kept at a temperature of 70 to 120 ° C. for 3 hours or more, it is allowed to cool to room temperature. If the treatment temperature is less than 70 ° C., sufficient strength after painting and baking cannot be obtained. On the other hand, if the temperature exceeds 120 ° C., the yield strength is excessive and the deformation resistance is large, so that the moldability is lowered.

[Mechanical properties of aluminum alloy sheet]
The aluminum alloy plate according to the present invention has a formability capable of press working and hem working to be formed into an automotive panel structure or the like, and has sufficient strength after forming, painting and baking. Specifically, for the aluminum alloy plate having a plate thickness of 1.0 mm that has been subjected to the pre-aging treatment, tensile strength: 200 MPa or more, 0.2% proof stress: 100 MPa to 150 MPa, elongation: 20% or more Become.

  As mentioned above, although the form for implementing this invention has been described, the Example which confirmed the effect of this invention is demonstrated concretely compared with the comparative example which does not satisfy | fill the requirements of this invention below. In addition, this invention is not limited to this Example.

[Sample preparation]
(Casting-Homogenization heat treatment)
An aluminum alloy having the composition shown in Table 1 was melted, and an ingot having a thickness of 600 mm was produced using a semi-continuous casting method. The ingot was homogenized by holding it at a heat treatment temperature of 550 ° C. for 5 hours, and then cooled to room temperature and subjected to a face grinding treatment.

(Hot rolling to cold rolling)
Next, the ingot was preheated and hot rolled (coarse rolling, finish rolling) at a start temperature of 400 ° C. to obtain a hot rolled plate having a plate thickness of 4.0 mm. In rough rolling, the plate thickness was set to 80 mm and the plate thickness was set to 40 mm in the next pass (the reduction ratio was 50%). Furthermore, the thickness of the plate immediately before the final pass of hot rolling (finish rolling) was set to 8 mm to obtain a hot rolled plate having a reduction ratio of 50% and a thickness of 4.0 mm, and wound at an end temperature of 320 ° C. The hot-rolled sheet was cold-rolled without annealing to produce a cold-rolled sheet having a sheet thickness of 1.0 mm (total rolling rate of 75%).

(Solution, quenching, preliminary aging, room temperature aging)
The cold-rolled sheet was heated in a continuous heat treatment furnace and held at an ultimate temperature of 550 ° C. for 10 seconds (solution treatment) and water-cooled (water quenching). Further, after being kept at 70 ° C. for 5 hours, it was allowed to cool to room temperature (preliminary aging treatment) and left at room temperature for 3 months (room temperature aging) to obtain an aluminum alloy sheet specimen.

(Measurement of Al-Mn-Fe (-Si) intermetallic compound distribution)
An aluminum alloy plate was cut out and filled with resin, and the surface including the rolling direction and the plate thickness direction was polished to be an observation surface to obtain a mirror surface. A scanning electron microscope (SEM) is used within a range of ± 0.25 mm (50% of the plate thickness) in the plate thickness direction centered on a half of the plate thickness direction of the mirror-finished surface. Then, 20 fields of view (total 5 mm ² ) were observed with a composition (COMPO) image at an acceleration voltage of 20 kV and a magnification of 100 times. The portion appearing whiter than the parent phase is regarded as an Al-Mn-Fe intermetallic compound and an Al-Mn-Fe-Si intermetallic compound (Al-Mn-Fe (-Si) intermetallic compound), and the equivalent circle diameter The total area and number of intermetallic compounds having a diameter of 2.0 μm or more were determined, and the area ratio and number density were calculated. Table 1 shows the area ratio and number density of Al—Mn—Fe (—Si) intermetallic compounds having an equivalent circle diameter of 2.0 μm or more at the center of the thickness of the cross section of the aluminum alloy plate.

[Evaluation]
About the test material of an aluminum alloy plate, ridging mark property, mechanical characteristics, formability, and bendability were evaluated by the following methods, and the results are shown in Table 1.

(Ridging mark properties)
As an index of ridging mark property, the unevenness difference on the surface of the aluminum alloy plate after press working was evaluated in the same manner as in Patent Document 6. Two types of test pieces were cut out from the aluminum alloy plate: a test piece having a length in the rolling direction of 40 mm × a length in the direction perpendicular to the roll of 200 mm and a test piece having a length in the rolling direction of 100 mm × a length in the direction of the perpendicular to the roll of 300 mm. By simulating press work on these test pieces and applying a stretch (tensile deformation) in the longitudinal direction (perpendicular to the rolling direction), a test piece having a rolling direction length of 40 mm has a plastic strain of 15% and a length in the rolling direction. A 100% test piece was given 10% plastic strain, respectively.

About each test piece, the profile of the unevenness | corrugation of the plate surface of the range of length 20mm was measured along the rolling right angle direction with the roughness meter. The profile to be measured (cross-sectional curve) is a curve obtained by combining a short-period roughness curve and a long-period waviness curve as shown by a broken line in FIG. A profile (waviness curve) averaged at the surface position is calculated, and the difference (unevenness difference, h in the figure) between the highest position P1 and the lowest position P2 obtained by the profile at a length of 20 mm (L in the figure) is calculated. did. When the unevenness difference is 12 μm or more, a ridging mark is further generated on the coated surface, and when the unevenness difference is 10 μm or more, a mild ridging mark is generated. Table 1 shows the average value of the unevenness difference (test piece with a rolling direction length of 40 mm: h ₄₀ , test piece with a rolling direction length of 100 mm: h ₁₀₀ ) measured in three places for each test piece. The average value h ₄₀ , h _{100 was used to} determine that no ridging marks were generated (h ₄₀ <10 μm) for a specimen having a length of 40 mm in the rolling direction (plastic strain 15%) and a specimen having a length of 100 mm in the rolling direction (plastic strain 10). %) That is mild or does not generate ridging marks (h ₁₀₀ <12 μm) is acceptable, and any test piece that does not generate ridging marks (h ₄₀ <10 μm, h ₁₀₀ <10 μm) is particularly excellent. Is indicated by “、”, and others (h ₄₀ <10 μm, 10 μm ≦ h ₁₀₀ <12 μm) are indicated by “◯”. A failure (at least one of h ₄₀ ≧ 10 μm and h ₁₀₀ ≧ 12 μm) is indicated by “x”.

(Mechanical properties: tensile strength, 0.2% proof stress, elongation)
An aluminum alloy plate was cut out to prepare a JIS No. 5 tensile test piece of 50 mm × 25 mm with the rolling direction as the longitudinal direction. The test piece was subjected to a tensile test at room temperature according to JISZ2241, and the tensile strength, 0.2% yield strength (As yield strength), and elongation were measured. In addition, an aluminum alloy plate was cut out in the same manner as described above to produce a JIS No. 5 tensile test piece, impressed with press working, painting, and baking treatment, 2% pre-strain was applied, and heat treatment was performed at 170 ° C. for 20 minutes. The heat treatment was performed. About this test piece, the tensile test was done and 0.2% yield strength (AB yield strength) was measured. Acceptance criteria were as follows: tensile strength: 200 MPa or more, As yield strength: 100 MPa to 150 MPa or less, elongation: 20% or more, AB yield strength: 170 MPa or more.

(Formability: Overhang formability)
Instead of evaluating the presence or absence of cracks in press working of an aluminum alloy plate, the limit overhang height by ball head overhang forming was evaluated. As a test piece, an aluminum alloy plate was cut into a length of 110 mm in the rolling direction and a length of 200 mm in the direction perpendicular to the rolling direction. As shown in FIG. 1, the test piece is fixed to a die having an inner diameter (hole diameter) of 102.8 mm, a shoulder radius Rd: 5.0 mm, and an outer diameter of 220 mm with a constant wrinkle holding force using a jig (blank holder). Fixed. Then, while keeping the gap between the die and the jig constant by sandwiching a shim (not shown) having the same thickness as that of the test piece, a ball head punch having a diameter of 100 mm (radius Rp: 50 mm) is placed on the surface of the test piece. The overhanging process was carried out by pushing in the vertical direction, and the limit value of the overhang height until cracking or constriction was observed was obtained. Those with a limit overhang of 30 mm or more are considered acceptable.

(Formability: Bendability)
As an evaluation of bendability, a bending process test simulating flat hem processing after being press-molded on an outer panel of an automobile was performed and evaluated. An aluminum alloy sheet is cut into a length of 180 mm in the rolling direction and a length of 30 mm in the direction perpendicular to the rolling, and a pre-strain of 10% is applied to simulate the press-formed state, and a bending test piece is produced. Then, the following bending process simulating the flat hem process shown in FIG.

  As shown in FIG. 2 (a), the shoulder radius R protrudes from the end in the longitudinal direction as a processing allowance (distance from the end portion bent to the inner side of the test piece after flat hem processing to the bent portion). : A die of 0.8 mm (0.8 times the plate thickness of the test piece) was pressed with a jig, and the machining allowance was bent to 90 ° by a punch (down flange process). Next, as shown in FIG. 2B, the machining allowance was further bent inward by about 45 ° (cumulative total of about 135 °) (pre-hem step). Finally, an aluminum alloy plate (inner panel material, see FIG. 2 (b)) having a thickness of 1.0 mm simulating an inner panel is inserted while the test piece is bent, as shown in FIG. 2 (c). In addition, the machining allowance was bent inward at approximately 180 ° so that the test pieces were in close contact with both surfaces of the inner panel material (flat hem process).

  The outer surface of the bent portion was visually observed over the entire width of the test piece (outer panel), and those that were not cracked, including minute ones, were regarded as passing the bendability. Further, Table 1 shows that “」 ”indicates that the surface is not rough, and“ ◯ ”indicates that the surface is rough. As for the defects, Table 1 shows “×” when micro cracks occurred and “XX” where large cracks occurred.

  As shown in Table 1, the test material No. Nos. 1 to 15 are examples in which the contents of the components of the aluminum alloy are within the scope of the present invention, and the conditions in the production method are within the scope of the present invention. The intermetallic compound crystallizes and precipitates in a sufficiently large size to form a texture of fine and randomly oriented crystals.In particular, the higher the number density of intermetallic compounds, the better the surface properties that do not generate ridging marks. In addition, mechanical properties such as proof stress and formability were also good as an aluminum alloy sheet for forming.

(Evaluation by components of aluminum alloy)
On the other hand, the test material No. 16 to 27 are comparative examples in which the components of the aluminum alloy do not satisfy the requirements of the present invention. Specimen No. Since 16, 20 and 22 were deficient in Si, Fe and Mn, respectively, the intermetallic compound was not sufficiently crystallized and precipitated, and as a result, ridging marks were generated on the surface after coating. In addition, specimen No. Nos. 16 and 18 lacked Si and Mg, respectively, so that strength such as proof stress was insufficient. The test material No. 28, each of the components satisfies the requirements of the present invention, Fe is the lower limit of the scope of the present invention, Mn is the test material No. Since there was not much to the vicinity of the upper limit as in 4, the intermetallic compound was not sufficiently crystallized and precipitated, and as a result, ridging marks were generated on the surface after coating.

  On the other hand, the test material No. Since 17, 19 and 24 were excessive in Si, Mg and Cu, respectively, the strength was excessive and the moldability was lowered. Furthermore, the test material No. 1 containing excessive Cu was used. No. 24 produced thread rust. Specimen No. 19, 21, 23, 25 to 27 have excessive amounts of Mg, Fe, Mn, Cr, Zn, and Ti, so that crystallized substances and precipitates become coarse and more frequently occur. The bendability decreased as a starting point of cracking.

  Sample No. of Example 1 above. Sample materials having the same aluminum alloy components as 1, 5, 7, and 14 and having different conditions in the final hot rolling pass were produced and evaluated in the same manner as in Example 1.

[Sample preparation]
(Casting-Homogenization heat treatment)
For an aluminum alloy having the composition shown in Table 2 (showing the test material No. of Example 1 as an alloy No.), an ingot having a thickness of 600 mm was prepared in the same manner as in Example 1, and 550 ° C x 5 hours Homogenizing heat treatment was performed to perform face grinding. However, the test material No. For No. 33, 480 ° C. × 9 hours, sample No. No. 34 was subjected to a homogenization heat treatment at 600 ° C. for 2 hours.

(Hot rolling)
Next, the ingot was subjected to hot rolling (coarse rolling, finish rolling) at a start temperature of 400 ° C. by preheating to obtain a hot rolled plate having a plate thickness of 4.0 mm. In the same manner as in Example 1, in rough rolling, the plate thickness was set to 80 mm, and the plate thickness was set to 40 mm in the next one pass (the reduction rate was 50%). In the final pass of hot rolling (finish rolling), the immediately preceding plate thickness is adjusted to obtain a hot rolled plate having a plate thickness of 4.0 mm at the rolling reduction shown in Table 2, and further wound at the end temperature shown in Table 2. I took it.

(Observation of hot rolled sheet structure of hot rolled sheet)
After hot rolling, the hot rolled sheet was cut out and the hot rolled sheet structure was observed to determine the progress of recrystallization. The surface of the hot-rolled plate was mechanically polished, and a surface parallel to the rolled surface at a portion of ¼ of the plate thickness from the surface was used as an observation surface. Further, the cross section including the rolling direction of the hot rolled plate was similarly mechanically polished to obtain an observation surface, and a half of the thickness of the cross section was taken as the observation region. Each observation surface was further subjected to electrolytic etching for 60 to 90 seconds at a voltage of 30 V using a 5% aqueous hydrofluoric acid solution (solution temperature: 20 to 30 ° C.), and then magnification using an optical microscope (using a polarizing plate). The hot rolled sheet structure was observed at 100 times. From the microscopic image, the particle diameters d _L , d _LT , and d _ST in the rolling direction, the direction perpendicular to the rolling direction, and the sheet thickness direction were measured by the line intercept method. The measurement line length of one measurement was 200 μm, and a total of 5 fields were observed with 5 lines per field for each direction, and the average value of each particle size was calculated. From the average value of each grain size, the aspect ratio d _L / d _LT in the plane parallel to the surface of the hot-rolled sheet and the aspect ratio d _L / d _ST in the cross section including the rolling direction are obtained, and 1 ≦ d _L / d _LT For hot-rolled sheets _satisfying ≦ 3 and 1 ≦ d _L / d _ST ≦ 3, equiaxed recrystallized grains are obtained, and it is determined that the recrystallization has been completed, and subsequent annealing is not performed. Was cold rolled. On the other hand, a hot-rolled sheet in which at least one of the aspect ratios d _L / d _LT and d _L / d _ST exceeds 3 is determined that recrystallization has not been completed, and the following intermediate annealing is performed. Then, cold rolling was performed.

(Intermediate annealing)
A hot-rolled sheet that has been determined that recrystallization has not been completed by observation of the hot-rolled sheet structure is 500 ° C. × 10 seconds in a continuous annealing furnace, or 350 ° C. × 5 hours in a batch-type furnace. Intermediate annealing was performed. Specifically, in a continuous annealing furnace, a hot-rolled sheet is heated to 500 ° C. at a heating rate of 20 ° C./second, and after 10 seconds of annealing time (passing time), to a room temperature at a cooling rate of 100 ° C./second. Cooled down. In the batch type furnace, the hot-rolled sheet was heated to 350 ° C. at a temperature rising rate of 20 ° C./hour, maintained for an annealing time of 5 hours, and then cooled to room temperature at a temperature decreasing rate of 20 ° C./hour. The specimens that were subjected to intermediate annealing in a continuous annealing furnace were “continuous”, and the specimens that were conducted in a batch-type furnace were “batch” in the specification column for intermediate annealing in Table 2, respectively. The specimens not performed are indicated by “−”.

(Cold rolling, solution treatment, quenching treatment, preliminary aging treatment)
The hot-rolled plate was cold-rolled in the same manner as in Example 1 to produce a cold-rolled plate having a plate thickness of 1.0 mm (total rolling rate of 75%). Further, in the same manner as in Example 1, the cold-rolled plate was subjected to a solution treatment at an ultimate temperature of 550 ° C., water-cooled (water quenching), preliminarily aged at 70 ° C. for 5 hours, and aged at room temperature for 3 months. Then, it was set as the test material of an aluminum alloy plate. In addition, in preparation of a test material, the test material which was not able to be measured and evaluated after the middle is indicated by “-” in each column of Table 2.

[Evaluation]
Similarly to Example 1, the Al-Mn-Fe (-Si) intermetallic compound distribution (area ratio and number density) was measured for the specimen of the aluminum alloy plate, and ridging mark properties, mechanical properties, and The moldability was evaluated and the results are shown in Table 2. In addition, the test material No. 1 of Example 1 was used. 1, 2, 7, and 14 are also shown in Table 2.

  As shown in Table 2, the test material No. 29, 30, 32, 36, 37, 40, and 41, the conditions of the final pass of the hot rolling are within the scope of the present invention in the same manner as in Example 1. Therefore, recrystallization occurs after winding on the hot rolled plate. Even after completion and cold rolling without intermediate annealing, the specimen No. Similar to 1, 5, 7, and 14, good surface properties without ridging marks were exhibited, and good results were obtained as the aluminum alloy plate for forming processing in terms of mechanical properties and formability.

  On the other hand, the test material No. In 31, 35, 38, and 39, the end temperature was too low with respect to the rolling reduction of the final pass, and recrystallization did not proceed sufficiently after the end of hot rolling, so intermediate annealing was performed before cold rolling. It was necessary to complete the recrystallization. Therefore, an aluminum alloy sheet for forming and showing good surface properties free from ridging marks as in the previous example was obtained, but the productivity was lowered.

  Specimen No. 33, the temperature of the homogenization heat treatment is low, the progress of the homogenization of the ingot structure is slow, the intermetallic compound is coarsened and the number density is insufficient, and the recrystallized structure does not become fine after the hot rolling is completed, A ridging mark occurred. Specimen No. In No. 34, the temperature of the homogenizing heat treatment was high, burning occurred in the ingot, and subsequent hot rolling became impossible.

Claims (4)

Si: 0.4 to 1.5 mass%, Mg: 0.4 to 1.0 mass%, Fe: 0.1 to 1.0 mass%, Mn: 0.1 to 0.5 mass% The balance is formed of an aluminum alloy consisting of Al and inevitable impurities,
In the central part in the plate thickness direction of the cross section including the rolling direction, the Al—Mn—Fe (—Si) -based intermetallic compound having an equivalent circle diameter of 2.0 μm or more has an area ratio of 0.4% or more and a number density of 1350. An aluminum alloy plate for forming, characterized by being at least pieces / mm ² .   The aluminum alloy sheet for forming according to claim 1, wherein the aluminum alloy further contains Cu: 0.05 to 1.0 mass%.   The aluminum alloy further contains at least one of Cr: 0.15 mass% or less, Zr: 0.15 mass% or less, Ti: 0.007 to 0.10 mass%, Zn: 0.5 mass% or less. The aluminum alloy sheet for forming according to claim 1 or 2. A casting process in which the aluminum alloy according to any one of claims 1 to 3 is melted to cast an ingot, and the ingot is subjected to a heat treatment at a temperature in the range of 500 to 580 ° C for 1 hour or more. A homogenizing heat treatment step for homogenizing, a hot rolling step for producing a hot rolled plate by hot rolling the homogenized ingot at a temperature in the range of 350 to 450 ° C., and the hot rolled plate A cold rolling step in which a cold rolled sheet is produced by cold rolling at a total rolling rate of 40% or more, and the cold rolled sheet is heated to a temperature in the range of 500 to 560 ° C. and then cooled to room temperature. A solution treatment step, and a method for producing a forming aluminum alloy plate,
In the hot rolling step, when a plate thickness of 100 mm or less and 30 mm or more is reached, at least one rolling pass with a reduction rate of 40% or more is performed, and the reduction rate (%) in the final rolling pass is represented by r. The method for producing an aluminum alloy sheet for forming, characterized by rolling so that the end temperature is (445-3r) ° C. or higher.

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