JP6169950B2 - Aluminum alloy substrate for magnetic disk - Google Patents

Description

  The present invention relates to an aluminum alloy substrate for a magnetic disk that is excellent in heat resistance, smoothness and flatness and has sufficient strength even after high-temperature heating.

An aluminum alloy magnetic disk used for a storage device of a computer has JIS 5086 (Mg: 3.5 to 4.5 mass% (hereinafter simply referred to as%), which has excellent plating properties and excellent mechanical properties and workability. ), Fe ≦ 0.50%, Si ≦ 0.40%, Mn: 0.20 to 0.70%, Cr: 0.05 to 0.25%, Cu ≦ 0.10%, Ti ≦ 0. 15%, Zn ≦ 0.25%, balance Al and inevitable impurities) aluminum alloy substrate, aluminum alloy substrate with reduced intermetallic compounds in the matrix by limiting Fe, Si, etc., impurities in JIS5086, or Cu It is manufactured from an aluminum alloy substrate or the like in which plating properties are improved by intentionally adding Zn or Zn.
A general aluminum alloy magnetic disk is manufactured by first producing an annular aluminum alloy substrate and then attaching a magnetic material to the surface of the alloy substrate.
For example, an aluminum alloy magnetic disk made of the JIS 5086 alloy is manufactured by the following process. First, the ingot is hot-rolled, and then cold-rolled while annealing to produce a rolled material. Next, an annular aluminum alloy substrate is produced by a process of punching the rolled material into an annular shape, laminating aluminum alloy plates having an annular shape, and performing annealing (pressure annealing) by pressing from both sides and flattening. The
The annular aluminum alloy substrate thus manufactured is subjected to cutting, grinding, degreasing, etching, zincate treatment (Zn substitution treatment) as a pretreatment, and then Ni—P, which is a hard nonmagnetic metal, as a base treatment. After the electroless plating is performed and the plating surface is polished, a magnetic material is sputtered to produce an aluminum alloy magnetic disk.
Incidentally, in recent years, magnetic disks are required to have a large capacity and high density due to the need for multimedia and the like, and a heat-assisted magnetic recording system is expected as a recording system that achieves a surface recording density of 1 Tb / in ² or more. ing. The heat-assisted magnetic recording method is a method in which recording is performed by heating a magnetic material having a high coercive force with a laser beam to reduce the coercive force of the magnetic material.
At present, Fe—Pt system and the like are being studied as magnetic materials having high coercive force, but Fe—Pt system is sputtering at a higher temperature (about 600 ° C.) than conventional Co—Cr—Pt system magnetic materials. Is known to be necessary. When sputtering is performed at 600 ° C. using a JIS5086 aluminum alloy substrate that is currently widely used, the aluminum alloy substrate is strongly desired to have heat resistance at high temperatures.
In order to improve the recording density of the magnetic disk, it is necessary to make the flying height of the magnetic head with respect to the magnetic disk smaller and more stable. For this purpose, high smoothness and flatness are required for aluminum alloy substrates for magnetic disks.
Under such circumstances, in recent years, excellent heat resistance, smoothness and flatness are strongly desired for aluminum alloy substrates, and various studies have been made.

In Patent Document 1, Zr or the like is selectively added to JIS5086 in which impurities such as Fe and Si are limited, and the heating temperature of the pressure annealing is set to 350 ° C. or more and the temperature increase / decrease rate is 2 ° C./min or less. Thus, heat resistance, smoothness and flatness are improved.
JP2012-099179A

  However, the method disclosed in Patent Document 1 only assumes that sputtering of a magnetic material is performed at 500 ° C. (paragraphs 0009 to 0012 of Patent Document 1), and melting occurs when heated at 600 ° C. As a result, smoothness and flatness may be deteriorated, and sufficient heat resistance, smoothness and flatness have not been obtained.

  In order to improve heat resistance with a JIS5086 aluminum alloy substrate that is commonly used, a method of reducing the amount of Mg and increasing the solidus temperature (melting point) can be considered, but the strength decreases due to reduction of the amount of Mg and high temperature heating. There was a problem of doing.

Therefore, an object of the present invention is to provide an aluminum alloy substrate for a magnetic disk that is excellent in heat resistance, smoothness, and flatness and has sufficient strength even after high-temperature heating.

  The inventors of the present invention conducted intensive research and research on the above-mentioned problems, in particular, the relationship between the components of the aluminum alloy substrate, the distribution state of the Al—Cu-based precipitates, heat resistance, smoothness, flatness after high-temperature heating, and strength. As a result, it has been found that by using a heat-treatable Al—Cu—Mg alloy as an aluminum alloy substrate for a magnetic disk, excellent heat resistance, smoothness, flatness, and sufficient strength can be obtained even after high-temperature heating. Specifically, by using a heat-treatable Al—Cu—Mg-based alloy having a solidus temperature exceeding 600 ° C. as an aluminum alloy substrate, melting is suppressed even when sputtering is performed at 600 ° C., and Cu is further suppressed during sputtering. It has been found that sufficient strength can be obtained even after high-temperature heating by solid solution and precipitation of the compound by subsequent aging at room temperature, and the present invention has been made.

The aluminum alloy substrate for a magnetic disk according to claim 1 of the present invention contains Cu: 0.5% or more and less than 2.0%, Mg: 0.1% or more and less than 1.0%, and the balance Al and inevitable impurities. The density of Al—Cu based precipitates having an equivalent circle diameter of 0.5 μm or more is 1.0 × 10 ⁵ pieces / mm ² or less.

Moreover, the aluminum alloy substrate for magnetic disks according to claim 2 of the present invention is the same as the alloy according to claim 1, further Zn: 0.05 to 1.0%, Cr: 0.03 to 0.3%, Zr: The density of Al—Cu-based precipitates containing one or more of 0.03 to 0.3% and having an equivalent circle diameter of 0.5 μm or more is 1.0 × 10 ⁵ pieces / mm ² or less. And

The method for producing an aluminum alloy plate for an aluminum alloy substrate for a magnetic disk according to the present invention is the method for producing an aluminum alloy substrate for a magnetic disk as described above, wherein the aluminum alloy ingot is subjected to a homogenization treatment and heated. In performing the cold rolling and the cold rolling, the homogenization treatment is performed at 450 ° C. or higher, and the time during which the temperature of the aluminum alloy is 380 ° C. to 430 ° C. from the end of the homogenization treatment to before the cold rolling is 15 minutes. By defining the following, an aluminum alloy plate substrate for a magnetic disk substrate having a density of Al-Cu based precipitates having an equivalent circle diameter of 0.5 μm or more of 1.0 × 10 ⁵ pieces / mm ² or less is manufactured. It is characterized by that.

  Since the aluminum alloy substrate for magnetic disks of the present invention is excellent in heat resistance, smoothness, flatness and strength, it is possible to provide an aluminum alloy substrate for magnetic disks which can be increased in capacity and density.

It is a figure which shows the flow of the process from the manufacturing process of an aluminum alloy substrate to manufacture of a magnetic disc.

Hereinafter, the present invention will be described in detail.
First, the manufacturing process of the magnetic disk from the manufacturing process of the aluminum alloy substrate will be described with reference to the flow shown in FIG.
Step 1: Blend into aluminum alloy composition as needed. For example, it mix | blends with the aluminum alloy of the component composition shown in Table 1 mentioned later.
Step 2: Cast the blended aluminum alloy.
Step 3: The ingot is chamfered and homogenized.
Step 4: Hot rolled to obtain a plate material.
Step 5: Cold-roll the hot-rolled plate to obtain an aluminum alloy rolled plate. Intermediate annealing during or before cold rolling (not required).
Step 6: A rolled aluminum alloy sheet is punched into an annular shape to form a disk blank.
Step 7: The disk blank is flattened by pressure annealing to produce an aluminum alloy substrate.
Step 8: The aluminum alloy substrate is cut and ground.
Step 9: Apply a ground treatment to the surface of the aluminum alloy substrate for magnetic disk.
Step 10: A magnetic material is attached to the surface of the ground surface by sputtering to obtain a magnetic disk.

  The composition of each composition of the aluminum alloy in Step 1 will be described in detail. The reasons for limiting the component composition of the aluminum alloy are as follows.

Cu: 0.5% or more and less than 2.0% Cu significantly improves the strength of the material by aging precipitation of Mg and Al ₂ CuMg after sputtering. If the Cu content is less than 0.5%, this effect cannot be sufficiently obtained. On the other hand, when the Cu content is 2.0% or more, a coarse compound is formed, and this compound is dropped during grinding, and large pits that cause a decrease in smoothness are generated. Therefore, the Cu content is 0.5% or more and less than 2.0%. In addition, the more preferable range of content of Cu is 1.0 to 1.5%.

Mg: 0.1% or more and less than 1.0% Mg significantly improves the strength of the material by aging precipitation of Cu and Al ₂ CuMg after sputtering. If the Mg content is less than 0.1%, this effect cannot be sufficiently obtained. On the other hand, when the Mg content is 1.0% or more, the solidus temperature of the aluminum alloy substrate decreases. Therefore, the Mg content is 0.1% or more and less than 1.0%. In addition, the more preferable range of content of Mg is 0.3 to 0.8%.

In order to further improve the strength, the following elements may be added alone or in combination.
Mn: 0.5 to 1.6%
Mn forms an Al—Mn compound and contributes to dispersion strengthening. If the Mn content is less than 0.5%, the above effect cannot be obtained sufficiently. On the other hand, if it exceeds 1.6%, a coarse crystallized product is formed, and this crystallized product falls off during grinding. As a result, large pits that cause a decrease in smoothness are generated. Therefore, the Mn content is set to 0.5 to 1.6%. In addition, the more preferable range of content of Mn is 0.5 to 1.1%.
Zn: 0.05-1.0%
Zn precipitates as a compound after sputtering and contributes to strength improvement. If the added amount of Zn is less than 0.05%, the above effect cannot be obtained sufficiently, while if it exceeds 1.0%, the solidus temperature of the aluminum alloy substrate decreases. Therefore, the Zn content is 0.05 to 1.0%. A more preferable range of the Zn content is 0.1 to 0.8%.
Cr: 0.03-0.3%
Cr produces a fine intermetallic compound in the aluminum alloy and improves its strength. If the content is less than 0.03%, sufficient effects cannot be obtained. On the other hand, if it exceeds 0.3%, a coarse compound is formed, and this compound falls off during grinding and causes a decrease in smoothness. A pit is generated. Therefore, the Cr content is 0.03 to 0.3%. In addition, the more preferable range of Cr content is 0.05 to 0.2%.
Zr: 0.03-0.3%
Zr, like Cr, produces a fine intermetallic compound in an aluminum alloy and improves its strength. Further, the Al—Zr-based compound has an effect of suppressing coarsening of crystal grains during sputtering and suppressing deterioration of flatness. If the content is less than 0.03%, sufficient effects cannot be obtained. On the other hand, if it exceeds 0.3%, a coarse compound is formed, and this compound falls off during grinding and causes a decrease in smoothness. A pit is generated. Therefore, the Zr content is 0.03 to 0.3%. A more preferable range of the Zr content is 0.05 to 0.2%.

Impurity element
Si: 0.001% or more and less than 0.1% Si is usually mixed in the aluminum alloy as an unavoidable impurity, and improves its strength by solid solution and precipitation strengthening in the aluminum alloy. However, when a large amount of Cu coexists, it precipitates as a simple Si or Al-Cu-Si compound, and when Si becomes 0.1% or more, these precipitates become coarse, and these precipitates appear during grinding. There is a risk of generating large pits that fall off and cause a reduction in smoothness. On the other hand, removing Si from the aluminum ingot to less than 0.001% is not preferable because the aluminum ingot is refined with high purity, resulting in an increase in cost. Therefore, Si is preferably 0.001 or more and less than 0.1%. Note that a more preferable range of the Si content is 0.001% or more and 0.05% or less.
Fe: 0.001% or more and less than 0.1% Fe is usually mixed in an aluminum alloy as an unavoidable impurity, hardly dissolves in aluminum, and crystallizes as an Al—Mn—Fe compound. Precipitates and contributes to dispersion strengthening. However, if the content is 0.1% or more, a coarse Al—Mn—Fe-based compound is generated, and this compound may drop off during grinding, which may generate large pits that cause a decrease in smoothness. . On the other hand, removing Fe to less than 0.001% is not preferable because it refining aluminum ingots with high purity, resulting in high costs. The Fe content is preferably suppressed to less than 0.025%. Therefore, Fe is preferably 0.001 or more and less than 0.1%. A more preferable range of the Fe content is 0.001% or more and 0.05% or less.
Other impurities (for example, Ti, V, Ga, B, etc.) have characteristics as an aluminum alloy substrate obtained by the present invention as long as each is less than 0.03% and not more than 0.15% in total. There is no loss.

  Next, the metal structure before sputtering of the aluminum alloy substrate for magnetic disks of the present invention will be described.

Density of Al-Cu-based precipitates with an equivalent circle diameter of 0.5 μm or more is 1.0 × 10 ⁵ pieces / mm ² or less Al—Cu-based precipitates with an equivalent circle diameter of 0.5 μm or more (for example, Al—Cu or Al -Cu-Fe or Al-Cu-Mn, etc.) is relatively large in size, so it does not dissolve at the time of sputtering and hardly disappears. For this reason, Al—Cu-based precipitates remain even after sputtering, thereby reducing the amount of Cu solid solution after sputtering. If the solid solution amount of Cu after sputtering is low, the effect of increasing the strength due to aging precipitation of Al ₂ CuMg cannot be obtained sufficiently. Therefore, the density of Al—Cu-based precipitates having an equivalent circle diameter of 0.5 μm or more in the present invention is 1.0 × 10 ⁵ pieces / mm ² or less. Note that the preferable density of the Al—Cu-based precipitates having an equivalent circle diameter of 0.5 μm or more is 1 × 10 ⁴ pieces / mm ² or less. The lower limit of the dispersion density of the Al—Cu-based precipitates having an equivalent circle diameter of 0.5 μm or more is not particularly defined, but this lower limit is naturally determined by the composition of the aluminum alloy and the manufacturing process, and is adopted in the present invention. According to the alloy composition and the manufacturing process, about 1.0 × 10 ³ pieces / μm ³ is the lower limit of the dispersion density.
The density of Al—Cu-based precipitates having a circle-equivalent diameter of 0.5 μm or more was determined by observing the cross section of the aluminum alloy substrate with an SEM and analyzing the SEM image.

Next, a method for manufacturing an aluminum alloy substrate for a magnetic disk will be described.
The aluminum alloy ingot adjusted to the alloy composition range of the present invention in Step 1 is cast according to a conventional method such as a semi-continuous casting (DC casting) method (Step 2), and the resulting ingot is homogenized ( Step 3), hot rolling (step 4), and cold rolling (step 5) are performed to produce a rolled aluminum alloy sheet. All the processes are related to the distribution state of the Al—Cu-based precipitates, but the present inventors particularly maintain the temperature within a specific range immediately before Step 3 to Step 5, that is, from the end of the homogenization treatment to before cold rolling. (Residence) It was discovered that time greatly affects the present invention.

Homogenization retention temperature 450 ° C or higher If the homogenization retention temperature is 450 ° C or higher, Al-Cu-based precipitates with an equivalent circle diameter of 0.5 µm or more are dissolved in the matrix, and the density of the precipitates is Decrease. On the other hand, when holding at a temperature of less than 450 ° C., the density of Al—Cu-based precipitates having an equivalent circle diameter of 0.5 μm or more increases, and accordingly, the solid solution amount of Cu after sputtering decreases, and Al ₂ CuMg. The effect of increasing the strength due to aging precipitation is not sufficiently obtained. For this reason, the homogenization process is performed at a temperature of 450 ° C. or higher. The upper limit of the homogenization treatment temperature is not particularly set, but is preferably 560 ° C or lower. Also, in order to ensure the solid solution of the Al—Cu-based precipitates, the homogenization treatment time is 0.5 hours or more. Preferably it is 3 hours or more.

The time during which the temperature of the aluminum alloy is 380 ° C. to 430 ° C. is 15 minutes or less from the end of the homogenization treatment to before cold rolling In the temperature range of 380 ° C. to 430 ° C. from the end of the homogenization treatment to before cold rolling , Cu dissolved in the material is precipitated as a coarse Al-Cu compound. Therefore, if the temperature is maintained for more than 15 minutes, the density of Al—Cu based precipitates having an equivalent circle diameter of 0.5 μm or more exceeds 1.0 × 10 ⁵ pieces / mm ² . For this reason, the holding time in the temperature range of 380 ° C. to 430 ° C. from the end of the homogenization treatment to before cold rolling is 15 minutes or less. In addition, although a coarse Al-Cu type compound precipitates also in the temperature range over 430 degreeC and less than 450 degreeC, since there are few production | generation numbers of a precipitate, the influence can be disregarded.

  After the hot rolling is finished, the product is finished to the required product thickness by cold rolling (step 5). The conditions for cold rolling are not particularly limited, and may be determined according to the required product sheet strength and sheet thickness, and the rolling rate is 20 to 80%.

When annealing is performed during cold rolling or before and after cold rolling, a coarse Al—Cu compound precipitates when heated at 380 ° C. or higher, and is performed at a temperature lower than 380 ° C. It is more preferable to carry out at a temperature of 250 to 330 ° C. In addition, although it heats at less than 380 degreeC, an Al-Cu type compound will precipitate, but since it is a fine compound with an equivalent circle diameter of less than 0.5 micrometer, the influence can be disregarded.

Then, the aluminum alloy rolled plate manufactured in this way is processed according to a use.
In order to process the aluminum alloy rolled plate for a magnetic disk, the substrate is punched into an annular shape (step 6) and subjected to pressure annealing (step 7). The pressure annealing is performed at a temperature lower than 380 ° C. because a coarse Al—Cu compound precipitates when heated at 380 ° C. or higher. It is more preferable to carry out at a temperature of 250 to 330 ° C.
The flattened disk blank is cut and ground (step 8), and subjected to ground processing (step 9) and sputtering (step 10) to obtain a magnetic disk.

In the following, the present invention will be described in detail with reference to an embodiment using a magnetic disk substrate.
Step 1: A molten aluminum alloy having the composition shown in Table 1 was melted. In the alloy composition shown in Table 1, “-” indicates no addition.

Step 2: The aluminum alloy melt was made into an ingot having a thickness of 500 mm by a DC casting method.
Step 3: A homogenization treatment was performed under the conditions shown in Table 2.

Step 4: Hot rolling was performed to obtain a hot rolled sheet having a thickness of 3.0 mm.
Step 5: Example No. Hot rolled sheets other than the alloy No. 3 were rolled to a final sheet thickness of 1.0 mm by cold rolling (rolling ratio: 66.7%) without performing intermediate annealing to obtain rolled sheets.
Example No. In No. 3, first cold rolling (rolling rate: 33.3%) was performed, and then intermediate annealing was performed at 320 ° C. for 2 hours using a batch annealing furnace. Subsequently, it rolled to 1.0 mm of the final board thickness by the 2nd cold rolling (rolling rate 50.0%), and was set as the rolled sheet.

Step 6: A blank disc was produced by punching the rolled plate into an annular shape having an outer diameter of 96 mm and an inner diameter of 24 mm.
Step 7: The disc blank was subjected to pressure annealing at 325 ° C. for 4 hours.
Step 8: Grinding was performed after the end face processing.

  The following evaluation was performed on the aluminum alloy substrate for a magnetic disk after the cold rolling (step 5), after pressure annealing (step 7), and after grinding (step 8). Table 2 shows the time during which the aluminum alloy substrate was 380 ° C. to 430 ° C. from the end of the homogenization treatment to before cold rolling. Comparative Example No. Since 19, 20, 22, and 25 melt | dissolved when heated at 600 degreeC, the proof stress was not evaluated.

〔Heat-resistant〕
The heat resistance was evaluated by determining the solidus temperature of the aluminum alloy substrate after pressure annealing by thermal analysis. A case where the solidus temperature exceeded 600 ° C. was judged as excellent (◎), and a case where the solidus temperature was 600 ° C. or lower was judged as defective (×).

[Strength]
The aluminum alloy sheet after cold rolling was heated at 325 ° C. for 4 hours, then heated at 600 ° C./min using an infrared heating device, heated at 600 ° C. for 10 seconds, and kept at room temperature for 1 week. Then, the proof stress of the JIS5 test piece cut out in the rolling direction was measured. The measurement conditions were a gauge distance of 50 mm and a crosshead speed of 10 mm / min. A material having a yield strength of 100 MPa or more was regarded as excellent (◎), and a material having a yield strength of less than 100 MPa was regarded as defective (x).

[Density of Al-Cu-based precipitates having an equivalent circle diameter of 0.5 μm or more (pieces / mm ² )]
A composition (COMP) image of the cross section of the aluminum alloy substrate after pressure annealing was taken by SEM at a magnification of 1000 times (field of view: 0.2 mm ² ), and an Al—Cu based precipitate having an equivalent circle diameter of 0.5 μm or more. The density of was determined. Since the Al—Cu-based precipitate appears whiter than the matrix in the COMP image, the particles that appear white are counted as Al—Cu-based precipitates.

[Flatness]
The blank after pressure annealing is heated at 600 ° C./min with an infrared heating device, heated at 600 ° C. for 10 seconds, and the flatness of 30 sheets is measured with a flatness measuring instrument to evaluate the flatness. It was. A sample having a maximum flatness value of less than 5 μm was evaluated as excellent (◎), and a sample having a maximum flatness value of 5 μm or more was evaluated as defective (×). The flatness is a value measured with a ZyGO non-contact flatness measuring machine.

[Smoothness]
The blank after pressure annealing was heated at 600 ° C./min with an infrared heating device, heated at 600 ° C. for 10 sec, and ground, and then the roughness of the aluminum alloy substrate surface (arithmetic average roughness, Ten Ra) were measured, and the smoothness was evaluated by the average value. The measurement was performed by setting the measurement length to 8.00 mm and scanning in the direction perpendicular to the rolling. The case where the surface roughness Ra is less than 0.020 μm is determined to be excellent (◎), the case where Ra is 0.020 μm or more and less than 0.025 μm is determined to be good (◯ mark), and the case where Ra is 0.025 μm or more is defective ( X). The above evaluation results are shown in Table 3.

  As shown in Table 3, the example No. 1-No. In No. 15, an aluminum alloy substrate for a magnetic disk having excellent heat resistance, smoothness and flatness and sufficient strength even after high-temperature heating was obtained.

  On the other hand, Comparative Example No. Since 16 to 25 all contained elements that were not within the scope of the present invention, they were inferior in any of heat resistance, smoothness, flatness, and strength.

That is, Comparative Example No. No. 16 had a low yield strength due to a low Cu content.
Comparative Example No. Since No. 17 had a large Cu content, a coarse compound was formed, and this compound dropped off during grinding, resulting in a decrease in smoothness.
Comparative Example No. No. 18 had a low yield strength due to a low Mg content.
Comparative Example No. 19 and 20 had a high Mg content, so the solidus temperature decreased and the heat resistance deteriorated. Moreover, smoothness and flatness fell because heat resistance was bad.
Comparative Example No. Since No. 21 had a large Mn content, a coarse crystallized product was formed, and this crystallized product dropped off during the grinding process, resulting in a decrease in smoothness. Comparative Example No. No. 22 had a high Zn content, so the solidus temperature decreased and the heat resistance deteriorated. Moreover, smoothness and flatness fell because heat resistance was bad.
Comparative Example No. Since No. 23 had a large Cr content, a coarse compound was formed, and this compound dropped off during grinding, resulting in a decrease in smoothness.
Comparative Example No. Since No. 24 had a large Zr content, a coarse compound was formed, and this compound dropped out during the grinding process, resulting in a decrease in smoothness.
Comparative Example No. Since No. 25 had a high Mg content, the solidus temperature decreased and the heat resistance deteriorated. Moreover, smoothness and flatness fell because heat resistance was bad.
Comparative Example No. In No. 26, since the holding temperature for homogenization was low, many Al—Cu-based precipitates having an equivalent circle diameter of 0.5 μm or more were formed, and the yield strength was low.
Comparative Example No. In No. 27, the time from 380 ° C. to 430 ° C. from the end of the homogenization treatment to before cold rolling was too long, so a lot of Al—Cu-based precipitates with an equivalent circle diameter of 0.5 μm or more were formed, and the proof stress was low. It was.
As described above, when the aluminum alloy substrate of the present invention is heated at a high temperature, since the components are controlled, melting is suppressed, and excellent heat resistance, smoothness, and flatness are obtained. Moreover, it has the outstanding effect that the intensity | strength required as an aluminum alloy substrate for magnetic discs can be obtained by room temperature aging after high temperature heating.

Claims (3)

Cu: 0.5 mass% or more and less than 2.0 mass% (hereinafter simply referred to as “%”), Mg: 0.1% or more and less than 1.0%, consisting of the balance Al and unavoidable impurities, equivalent circle diameter An aluminum alloy substrate for a magnetic disk, wherein the density of Al-Cu precipitates of 0.5 µm or more is 1.0 x 10 ⁵ pieces / mm ² or less. Cu: 0.5% or more and less than 2.0%, Mg: 0.1% or more and less than 1.0%, Mn: 0.5 to 1.6%, Zn: 0.05 to 1.0 %, Cr: 0.03 to 0.3%, Zr: 0.03 to 0.3%, one or more of them, the balance being Al and inevitable impurities, Al having an equivalent circle diameter of 0.5 μm or more An aluminum alloy substrate for a magnetic disk, wherein the density of Cu-based precipitates is 1.0 × 10 ⁵ pieces / mm ² or less. The method for producing an aluminum alloy substrate for a magnetic disk according to claim 1 or 2, wherein the homogenization treatment is performed at 450 ° C or higher when the ingot is subjected to homogenization treatment and hot rolling or cold rolling is performed. A method for producing an aluminum alloy substrate for a magnetic disk, characterized in that the time during which the temperature of the aluminum alloy is 380 ° C. to 430 ° C. is defined as 15 minutes or less from the end of homogenization treatment to before cold rolling.

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