JP2005133134A - Aluminum alloy sheet for magnetic disk, and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum alloy sheet for a magnetic disk in which the production cost is reduced and the occurrence of the defect in the surface of an Ni-P plating film can be suppressed while maintaining its grindability at the time of producing a substrate for a magnetic disk, and to provide its production method. <P>SOLUTION: The aluminum alloy sheet is composed of an aluminum alloy containing, by mass, 0.005 to 0.05% Si, 0.005 to 0.05% Fe, 0.05 to 0.3% Cr, and 3.0 to 5.0% Mg, further comprising at least one or more kinds of metals selected from ≤0.1% Cu and ≤0.5% Zn, and also satisfying ≥0.1% (Zn+3×Cu), and the balance Al with inevitable impurities. The relation between the maximum size (μm) of an Mg-Si based intermetallic compound in the aluminum alloy sheet and the Si content (mass%) satisfies [the maximum size of the Mg-Si based intermetallic compound ≤the Si content×100]. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an aluminum alloy plate for a magnetic disk, and more particularly, to an aluminum alloy plate for a magnetic disk using a metal containing a large amount of impurities (a low purity metal) as a raw material, and a method for manufacturing the same.

  Generally, a magnetic disk device (Hard Disk Drive) which is one of external recording devices includes a magnetic disk for recording (storing) information and a magnetic head for writing or reproducing information on the magnetic disk. I have.

Recently, the performance of such magnetic disks and magnetic heads has been greatly improved, and in the near future, a surface recording density of 200 Gb / in ² is about to be achieved.

  In order to increase the recording density of the magnetic disk, it is necessary to stably float the magnetic head with a low flying height. For this purpose, high smoothness of the magnetic disk substrate is required. Conventionally, as a magnetic disk substrate, an aluminum alloy plate that is lightweight and non-magnetic and excellent in workability has been used, but it is difficult to obtain high smoothness of a magnetic disk substrate by itself. There is.

  Therefore, generally, a NiP plating film formed on the surface of an aluminum alloy plate with a thickness of about 10 μm is used as a magnetic disk substrate. Such a magnetic disk substrate is manufactured as follows.

  First, an aluminum alloy plate adjusted to a desired alloy type, tempering and plate thickness by melting, casting and rolling is punched into a predetermined annular substrate by a punching press. Next, in order to remove the processing residual stress in the annular substrate and improve the flatness, a plurality of punched annular substrates are stacked between spacers having high flatness, and the whole is annealed while being pressed ( Pressure annealing). Generally, this annealed product is called a blank. Thereafter, predetermined end face processing is performed on the inner peripheral edge and the outer peripheral edge of the blank.

  Thereafter, the blank subjected to the end face processing is set in a pocket of a carrier set in advance in a double-side grinding machine, and is ground by a grindstone until a target plate thickness is reached. However, even in this state, the required specification (high smoothness) as a magnetic disk substrate cannot be satisfied. After that, a NiP plating film is further formed on the ground surface of the blank and the surface is polished. Thus, a magnetic disk substrate is obtained.

  In a general magnetic disk, a base film for enhancing magnetic properties, a magnetic film made of a Co-based alloy, and a magnetic film are protected on a NiP plating film formed by electroless plating of the magnetic disk substrate. A protective film made of C is formed by sputtering.

  Thus, the aluminum alloy plate for magnetic disks is required to maintain the smoothness of the NiP plating film surface formed on the surface of the aluminum alloy plate as well as the grindability.

  In the grinding process of an aluminum alloy plate, it is known that an aluminum alloy having a lower Si content, which is an inevitable impurity, and a higher Fe content, is easier to grind. Therefore, conventionally, in order to improve the grindability of the aluminum alloy plate, an expensive high-purity aluminum ingot with a low Si content has been used as a raw material for the aluminum alloy plate.

In addition, it is known that Mg-Si intermetallic compound (Mg ₂ Si) formed in an aluminum alloy is related as one of the causes of pits and blisters that hinder the smoothness of the NiP plating film surface. It has been. Therefore, in order to maintain the smoothness of the NiP plating film surface, it is necessary to reduce such Mg ₂ Si, and for this purpose, high-purity aluminum bullion is used (see, for example, Patent Document 1). .

Japanese Patent Laid-Open No. 11-140577 (Claims 3, 4 and paragraph number [0014])

  However, the use of high-purity aluminum bullion has the advantage of improving grindability and suppressing defects such as pits and blisters on the surface of the NiP plating film when manufacturing a magnetic disk substrate, but at the same time increases the manufacturing cost. There is a problem. For this reason, even if it is a case where a low-cost low purity aluminum ingot is used, the technique which improves grindability and the technique which can suppress the defect of the NiP plating film surface are desired.

  The present invention has been made in view of such problems, and the manufacturing cost is low, and it is possible to suppress the occurrence of defects on the surface of the NiP plating film while maintaining grindability during the production of a magnetic disk substrate. An object of the present invention is to provide an aluminum alloy plate for a magnetic disk and a method for producing the same.

  In order to solve the above-mentioned problems, the invention described in claim 1 includes Si: 0.005 to 0.05 mass%, Fe: 0.005 to 0.05 mass%, and Cr: 0.05 to 0.3. And containing at least one of Cu: 0.1% by mass or less, Zn: 0.5% by mass or less, and (Zn-containing) (Amount + 3 × Cu content) is 0.1 mass% or more, and an aluminum alloy plate made of an aluminum alloy with the balance being Al and inevitable impurities, the Mg-Si intermetallic compound of the aluminum alloy plate The maximum size (μm) is configured as an aluminum alloy plate for a magnetic disk having a relationship of [maximum size of Mg-Si intermetallic compound ≦ Si content × 100] with respect to the Si content (mass%). It is.

  According to the above configuration, the composition of Si, Fe, Cr, Mg, Cu, and Zn is limited to a predetermined range, and the maximum size of the Mg-Si intermetallic compound is limited to a range corresponding to the Si content. The aluminum ingot used has low purity. In addition, the size and number of intermetallic compounds precipitated in the aluminum alloy become appropriate, and in particular, an Al—Fe intermetallic compound that improves the grindability of an aluminum alloy plate, and an Mg—Si system that reduces grindability. The size and number of intermetallic compounds are appropriate. In addition, in the pretreatment process of the electroless NiP plating process, the deposited intermetallic compounds (Al—Fe, Mg—Si, Al—Cr, etc.) are less dropped or dissolved, and are also dropped or dissolved. However, the size of the trace is extremely small and the number is small. Further, the size of the Mg—Si intermetallic compound existing in the NiP plating film is small and the number thereof is also reduced.

  The invention according to claim 2 is a first step of melting and casting the aluminum alloy according to claim 1 to produce an ingot, a second step of homogenizing heat treatment of the ingot, and the homogeneous An aluminum alloy plate comprising: a third step of hot rolling the heat-treated ingot to produce a rolled plate; and a fourth step of cold rolling the rolled plate at least once to produce an aluminum alloy plate In the manufacturing method, the fourth step was heated at an ultimate temperature of 500 ° C. or higher between the hot rolling and the final cold rolling of the cold rolling, and the ultimate temperature reached 500 ° C. or higher. This is a method for manufacturing an aluminum alloy plate for a magnetic disk, which includes a heat treatment step that is later cooled to 400 ° C. or less at a cooling rate of 10 ° C./min or more.

  According to the said structure, by heat-processing at the temperature of 500 degreeC or more, the Mg-Si type | system | group intermetallic compound which precipitated and grew by hot rolling is dissolved in an aluminum alloy. Moreover, by cooling at a cooling rate of 10 ° C./min or more, the time for the rolled plate to pass through the temperature range (over 400 ° C. and below 500 ° C.) at which the Mg—Si-based intermetallic compound is precipitated is shortened. Precipitation of Si-based intermetallic compounds is suppressed, the size is reduced, and the number is also reduced.

  According to such an aluminum alloy plate for a magnetic disk and a method for producing the same, the production cost can be reduced by using a low-purity aluminum ingot. In addition, by optimizing the size and number of intermetallic compounds, the aluminum alloy is maintained while maintaining the grindability of the aluminum alloy plate even when using a low-purity aluminum ingot. It is possible to suppress the occurrence of defects such as pits and blisters on the surface of the NiP plating film formed on the surface of the plate.

Hereinafter, the present invention will be described in detail.
The inventors of the present invention have made extensive studies on the relationship between the aluminum alloy composition and its intermetallic compound, the grindability of the aluminum alloy plate, and the defects generated on the surface of the NiP plating film formed on the surface of the aluminum alloy plate. As a result, the size and number of precipitated Mg-Si intermetallic compounds are affected, and if the Mg-Si intermetallic compound is dissolved in the aluminum alloy even if the amount of Si contained is increased, the grindability is improved. It has been found that defects such as pits and blisters generated on the surface of the NiP plating film are suppressed without inhibiting the above.

Further, the Mg—Si intermetallic compound is precipitated mainly at the time of casting, and then is solid-dissolved in the aluminum alloy by performing a homogenization heat treatment at 500 ° C. or higher. However, it precipitates and grows again by passing through a temperature range exceeding 400 ° C. and less than 500 ° C. in the hot rolling process.
The present inventors paid attention to this point, and examined the influence of heat treatment performed between the hot rolling process and the final cold rolling process on the Mg—Si intermetallic compound. As a result, it was found that the Mg—Si-based intermetallic compound was dissolved again and the size and number of the Mg—Si-based intermetallic compound were reduced by setting the temperature and the cooling rate of the heat treatment within a predetermined range.

The aluminum alloy plate for a magnetic disk of the present invention is obtained by limiting the composition of Si, Fe, Cr, Mg, Cu, Zn and the maximum size of the Mg—Si intermetallic compound to a predetermined range. The reason for limitation will be described below.
(1) Si: 0.005 to 0.05 mass%
Si is an impurity contained in the aluminum ingot and generates an Mg—Si intermetallic compound described later in a casting process or the like. In order to make Si less than 0.005% by mass, a high-purity aluminum ingot is required, which increases the manufacturing cost. On the other hand, when Si exceeds 0.05 mass%, the size of the Mg—Si intermetallic compound described later cannot be reduced and the number cannot be reduced, and the grindability of the aluminum alloy plate is lowered. It also leads to the generation of pits and blisters on the surface of the NiP plating film formed on the surface of the aluminum alloy plate.

(2) Fe: 0.005 to 0.05 mass%
Fe is also an impurity contained in the aluminum ingot, and produces an Al—Fe intermetallic compound in a casting process or the like. This Al—Fe-based intermetallic compound has the effect of improving the grindability of the aluminum alloy plate. In order to make Fe less than 0.005% by mass, a high-purity aluminum ingot is required, resulting in high manufacturing costs. It also leads to a decrease in grindability. On the other hand, when Fe exceeds 0.05% by mass, the size of the Al—Fe-based intermetallic compound increases and the number also increases. In the pretreatment step of the aluminum alloy plate grinding step and the electroless NiP plating treatment, Al The Fe-based intermetallic compound falls off or dissolves, and defects such as pits are easily generated on the NiP plating film surface.

(3) Cr: 0.05 to 0.3% by mass
Cr is an element that contributes to the refinement of crystal grains. When Cr is less than 0.05% by mass, coarse crystal grains having a maximum length exceeding 100 μm are easily generated. Such a non-uniform crystal grain structure results in non-uniform precipitation of Zn in a zincate process (zinc replacement process; for example, see Japanese Patent Laid-Open No. 6-131659) generally performed when forming a NiP plating film. easy. As a result, defects (deteriorating the roughness and waviness of the plating film surface) are likely to occur on the NiP plating film surface.

Further, when Cr exceeds 0.3% by mass, a coarse Al—Cr intermetallic compound, for example, CrAl ₇ is easily generated, and in the pretreatment step of the grinding process of the aluminum alloy plate and the electroless NiP plating treatment, Al—Cr-based intermetallic compounds fall off or dissolve, and defects such as pits are easily generated on the surface of the NiP plating film.

(4) Mg: 3.0 to 5.0 mass%
Mg is an element effective in improving the strength. If Mg is less than 3.0% by mass, the strength of the aluminum alloy plate is insufficient for a magnetic disk, and if Mg exceeds 5.0% by mass, it is hot. Rollability is poor and productivity is reduced.

(5) Cu: 0.1 mass% or less, Zn: containing at least one of 0.5 mass% or less, and (Zn content + 3 × Cu content) is 0.1 mass% or more Cu and Zn has the effect of depositing a zincate film uniformly in the pretreatment step (zincate treatment) of the electroless NiP plating treatment. At this time, Cu and Zn can be effective singly or in combination.

  When containing at least one of Cu exceeding 0.1% by mass and Zn exceeding 0.5% by mass, the size of the Al—Cu-based and Al—Zn-based intermetallic compounds formed by each of them In the grinding process of the aluminum alloy plate and the pretreatment process of the electroless NiP plating process, the intermetallic compound is dropped and dissolved, and defects such as pits are easily generated on the NiP plating film surface. Moreover, when (Zn content + 3 × Cu content) is less than 0.1 mass%, the effect of depositing the zincate film uniformly is small. As a result, defects (deteriorating the roughness and waviness of the plating film surface) are likely to occur on the NiP plating film surface.

(5) Maximum size of Mg-Si intermetallic compound:
The size and number of Mg—Si intermetallic compounds increase in proportion to the Si content, but also change depending on the homogenization heat treatment conditions and hot rolling. Usually, the Mg—Si intermetallic compound is dissolved in the aluminum alloy by the homogenization heat treatment. When hot rolling is performed after the homogenization heat treatment, the Mg—Si intermetallic compound is precipitated again in the aluminum alloy plate and grows.

  When the size and number of the Mg—Si based intermetallic compounds are increased, the grindability is excluded in the grinding process of the aluminum alloy sheet. Further, in the grinding process of the aluminum alloy plate and the pretreatment process of the electroless NiP plating process, the intermetallic compound is dropped or dissolved, and defects such as pits are easily generated on the NiP plating film surface. Further, when a large Mg—Si intermetallic compound exists in the NiP plating film, the NiP plating film does not grow from the surface of the Mg—Si intermetallic compound, and Mg— The Si-based intermetallic compound is covered. For this reason, voids in which the plating solution remains at the interface between the NiP plating film and the aluminum alloy plate are formed, and the surface of the NiP plating film is inflated by heating during sputtering of the magnetic film performed after the electroless NiP plating process. Such defects are likely to occur.

  Therefore, it is necessary to limit the maximum size of the Mg—Si based intermetallic compound to a range corresponding to the Si content. That is, it is necessary to satisfy [maximum size of Mg—Si intermetallic compound (μm) ≦ Si content (%) × 100]. As a result, the maximum size of the Mg—Si intermetallic compound is small regardless of the content of Si within the predetermined range (0.005 to 0.05 mass%). As a result, the aluminum alloy The distribution of the Mg—Si intermetallic compound formed in the plate shifts in the direction of decreasing size and decreasing number. FIG. 1 is a graph showing the distribution of Mg—Si based intermetallic compounds in an aluminum alloy plate, showing the aluminum alloy plate of the present invention and the conventional aluminum alloy plate having the same Si content. As shown in FIG. 1, when the maximum size of the Mg—Si-based intermetallic compound is set to [Si content (%) × 100] μm or less, the aluminum alloy plate of the present invention has an Mg—Si-based metal compared to the conventional one. It can be seen that the size of the intermetallic compound is small and the number is also small.

(6) Inevitable impurities Inevitable impurities include, for example, Zr, Ti, Mn, etc., and these cause generation of pits or nodules during the formation of the NiP plating film. It is preferable that the content is 0.02% by mass or less.

  Next, the method for producing an aluminum alloy plate for a magnetic disk according to the present invention includes a first step of melting and casting an aluminum alloy to produce an ingot, a second step of homogenizing heat treatment of the ingot, and the homogeneous A third step of hot-rolling the ingot that has been heat-treated to produce a rolled plate, and cold-rolling the rolled plate at least once or more, and performing a heat treatment from hot rolling to final cold rolling. And a fourth step of producing an aluminum alloy plate. Hereinafter, each step will be described.

(A) 1st process Melting | dissolving and casting are performed in accordance with a conventional method. In addition, various elements are added to the aluminum metal at the time of melting to obtain an aluminum alloy having a desired composition for a magnetic disk.

(B) 2nd process Homogenization heat processing is performed according to a conventional method, and it is preferable to carry out at 500 degreeC or more. By heating the ingot at 500 ° C. or higher, the Mg—Si intermetallic compound precipitated during casting is dissolved in the aluminum alloy. As a result, the size and number of Mg—Si intermetallic compounds precipitated in the ingot are reduced.

(C) 3rd process Hot rolling is performed in accordance with a conventional method. The Mg—Si intermetallic compound is precipitated and grows again by hot rolling.

(D) 4th process Cold rolling is performed at least once according to a conventional method. The heat treatment is performed by heating at an ultimate temperature of 500 ° C. or more and cooling to 400 ° C. or less at a cooling rate of 10 ° C./min or more. The heat treatment is performed from hot rolling to final cold rolling, that is, immediately after hot rolling or in the middle of a plurality of cold rollings. The cold rolling rate before and after the heat treatment is preferably 25% or more in order to prevent the crystal grains of the aluminum alloy plate from becoming coarse. Furthermore, you may anneal about 350 degreeC in which the Mg-Si type | system | group intermetallic compound does not precipitate in the middle of multiple times of cold rolling. By this annealing, characteristics such as the uniformity of the structure of the aluminum alloy plate are improved.
The reason for limiting the heat treatment conditions will be described below.

(Achieved temperature: 500 ° C or higher)
(C) When the rolled sheet hot-rolled in the third step or the rolled sheet obtained by cold-rolling the rolled sheet is heated at less than 500 ° C., the Mg—Si-based metal that is precipitated and grown again in the hot rolling The compound does not dissolve in the aluminum alloy, and a large Mg—Si-based intermetallic compound is deposited on the surface of the aluminum alloy plate. As a result, when the magnetic disk substrate is manufactured, the grindability of the aluminum alloy plate is lowered, and pits and blisters are easily generated on the surface of the NiP plating film formed on the surface of the aluminum alloy plate.

(Cooling rate: 10 ° C / min or more)
When the rolled sheet is cooled at a cooling rate of less than 10 ° C./min, the time for the rolled sheet to pass through the temperature range (exceeding 400 ° C. and less than 500 ° C.) where precipitation of the Mg—Si intermetallic compound occurs becomes long, and the aluminum alloy The Mg—Si intermetallic compound is precipitated and grows again on the plate surface.

Hereinafter, the effect of the Example which satisfy | fills the claim of this invention is demonstrated compared with the comparative example which remove | deviates from a claim.
An aluminum alloy having the composition shown in Table 1 was melted, an ingot having a thickness of 50 mm was produced by casting, the ingot was chamfered, and then heated at 540 ° C. for 8 hours for homogenization heat treatment. Thereafter, hot rolling and cold rolling were performed by the manufacturing process shown in Table 2 to produce an aluminum alloy plate having a thickness of 1.27 mm.
Further, the aluminum alloy plate was punched into an annular shape having an outer diameter of 95 mm and an inner diameter of 25 mm, a predetermined number of sheets were stacked, and after pressure annealing at 340 ° C., end face processing was performed to produce a 3.5-inch blank.

  The obtained aluminum alloy plate and blank were evaluated as follows, and the results are shown in Tables 3 and 4.

(1) Tensile strength After the cold-rolled aluminum alloy sheet was O-treated at 340 ° C, tensile test pieces according to JIS No. 5 were prepared so that the tensile direction was parallel to the rolling direction.
Then, the tensile test was implemented by JISZ2241 and the tensile strength was calculated | required.
The higher the tensile strength, the better. However, if it is 200 N / mm ² or more, it can be used as a magnetic disk substrate without any problem.

(2) Grinding speed About each blank punched to 3.5 inch size, it was ground after dressing using a double-sided grinding machine (-18B made by Speed Fam Co., Ltd.). The grinding speed was determined as the grinding amount per minute by measuring the grinding time at the secondary pressure.

(3) Maximum size of Mg-Si intermetallic compound The surface of the blank after grinding in (2) above was observed with a scanning electron microscope (SEM), and the maximum size of the Mg-Si intermetallic compound. The size was determined. The observation was performed by observing 20 field images of the composition image at a magnification of 1000 times, and measuring the maximum size of black particles (lighter elements than aluminum, most of which were Mg-Si intermetallic compounds). The measurement accuracy was 1 μm.

(4) State of zincate surface After the blanks after grinding were subjected to the treatment steps shown in the following (a) to (k), the Zn precipitation state and the pit generation state on the blank surface after treatment were observed by SEM. did. At that time, the Zn precipitation state was the same as the Zn precipitation state for each crystal grain. As for the occurrence of pits, ◯ indicates that the number is small and small, and x indicates that the number is large and large.

(Processing process)
(A) Alkali degreasing step: 60 ° C. × 2 minutes (b) Water washing step (c) Acid etching: 65 ° C. × 2 minutes (d) Water washing step (e) Nitric acid desmutting step: Room temperature × 1 minute (f) Water washing step ( g) Primary zincate process (h) Water washing process (i) Secondary zincate process (j) Water washing process (k) Drying process

  From the results in Tables 3 and 4, all of Examples 1 to 5 were good in any of tensile strength, grinding speed, and state of the zincate surface.

In Comparative Example 1, since Si exceeds the upper limit in the composition and the maximum size of the intermetallic compound Mg ₂ Si exceeds the upper limit, the grinding speed is slower than those in Examples 1 to 5, and the grindability is inferior. It was. Also, pits were generated on the zincate surface, leading to pits on the NiP plating film surface.

  Comparative Example 2 was good in all of the tensile strength, grinding speed, and zincate surface state, but the production cost is high because Si is less than the lower limit in the composition and a high-purity aluminum ingot is required. there were.

  In Comparative Example 3, since Fe exceeded the upper limit in the composition, pits were generated on the surface of the zincate, leading to pits on the surface of the NiP plating film. In Comparative Example 4, since Fe is less than the lower limit in the composition, the grinding speed is slower than those in Examples 1 to 5, the grindability is inferior, and a high-purity aluminum ingot is necessary, so that the manufacturing cost is low. Was expensive.

  In Comparative Example 5, since Mg was less than the lower limit in the composition, the tensile strength was low and the magnetic disk substrate was insufficient in strength and could not be used. Comparative Example 6 was good in all of the tensile strength, grinding speed, and zincate surface state, but because Mg exceeded the upper limit in the composition, the hot rolling property was poor and the productivity was inferior.

  In Comparative Example 7, since Cr was less than the lower limit in the composition, the crystal grains became coarse, and the Zn precipitation state on the surface of the zincate was not uniform. As a result, it resulted in defects on the NiP plating film surface.

  In Comparative Example 8, Cr exceeds the upper limit value in the composition, in Comparative Example 9, Cu exceeds the upper limit value in the composition, and in Comparative Example 10, since Zn exceeds the upper limit value in the composition, both generate pits on the surface of the zincate. This led to pits on the surface of the NiP plating film.

  Comparative Example 11 contains Cu and Zn in the composition, Comparative Example 12 contains only Cu in the composition, and Comparative Example 13 contains only Zn in the composition, both of which (Zn + 3 × Cu) are less than the lower limit value. The Zn deposition state on the zincate surface was uneven, leading to defects on the NiP plating film surface.

In Comparative Example 14 and Comparative Example 15, the cooling rate and the heat treatment attainment temperature are less than the lower limit values, respectively, and since Comparative Example 16 is not subjected to heat treatment from hot rolling to final cold rolling, In any case, the maximum size of Mg ₂ Si was large, the grinding speed was slower than in Examples 1 to 5, and pits were generated on the surface of the zincate. As a result, the grindability was inferior, leading to pits on the NiP plating film surface.

It is a graph which shows distribution of the Mg-Si type | system | group intermetallic compound in an aluminum alloy plate.

Claims (2)

Si: 0.005 to 0.05 mass%, Fe: 0.005 to 0.05 mass%, Cr: 0.05 to 0.3 mass%, Mg: 3.0 to 5.0 mass% With
Cu: 0.1 mass% or less, Zn: containing at least one of 0.5 mass% or less, and (Zn content + 3 × Cu content) is 0.1 mass% or more, and the balance An aluminum alloy plate made of aluminum and an aluminum alloy as an inevitable impurity,
The maximum size (μm) of the Mg—Si intermetallic compound of the aluminum alloy plate is relative to the Si content (% by mass).
[Maximum size of Mg—Si intermetallic compound ≦ Si content × 100]
An aluminum alloy plate for a magnetic disk, characterized in that: Si: 0.005 to 0.05 mass%, Fe: 0.005 to 0.05 mass%, Cr: 0.05 to 0.3 mass%, Mg: 3.0 to 5.0 mass% With
Cu: 0.1 mass% or less, Zn: containing at least one of 0.5 mass% or less, and (Zn content + 3 × Cu content) is 0.1 mass% or more, and the balance A first step of melting and casting Al and an inevitable impurity aluminum alloy to produce an ingot;
A second step of homogenizing heat treatment of the ingot;
A third step of hot rolling the homogenized heat-treated ingot to produce a rolled plate;
A method for producing an aluminum alloy plate, comprising: a fourth step of cold rolling the rolled plate at least once and producing an aluminum alloy plate,
The fourth step is heated at an ultimate temperature of 500 ° C. or higher between the hot rolling and the final cold rolling of the cold rolling, and after reaching the ultimate temperature of 500 ° C. or higher, the cooling rate is 10 ° C./min or higher. The manufacturing method of the aluminum alloy plate for magnetic discs characterized by including the heat processing process cooled to 400 degrees C or less by this.

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