JP5836352B2 - Aluminum alloy substrate for magnetic disk and manufacturing method thereof - Google Patents

Description

  The present invention relates to an aluminum alloy substrate for a magnetic disk having high strength and excellent smoothness and a method for producing the same.

  JIS5086 (Mg: 3.5 to 4.5 mass%, Fe: 0.50 mass%), which has excellent plating properties and excellent mechanical properties and workability, is used for computer storage devices. Hereinafter, Si: 0.40 mass% or less, Mn: 0.20 to 0.70 mass%, Cr: 0.05 to 0.25 mass%, Cu: 0.10 mass% or less, Ti: 0.15 mass% or less, Zn: An aluminum alloy substrate containing 0.25 mass% or less (consisting of the balance Al and inevitable impurities), Fe, Si, etc., which are impurities in JIS5086, are limited to reduce intermetallic compounds in the matrix (matrix). Aluminum alloy substrate, or aluminum alloy substrate with improved plating by intentionally adding Cu or Zn It is manufactured from.

  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 annular aluminum alloy plates, and performing annealing (pressure annealing) by pressing from both sides and flattening. .

  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. Is electrolessly plated, and the plated surface is polished, and then 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 a high density because of the need for multimedia and the like. In order to increase the capacity, the number of magnetic disks mounted on a storage device is increasing, and accordingly, the thickness of the magnetic disk is required to be reduced. However, when the aluminum alloy substrate for a magnetic disk is thinned, the strength is lowered. Therefore, it is required to increase the strength of the aluminum alloy substrate.

  In order to increase 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 is required for an aluminum alloy substrate for a magnetic disk.

  From these circumstances, in recent years, high strength and high smoothness of aluminum alloy substrates are strongly desired, and various studies have been made.

  In Patent Document 1, 0.05 to 1 mass% of Mn is added to an Al—Mg-based alloy, and the recrystallization temperature of the aluminum alloy substrate is increased by setting the final cold rolling processing rate to 10 to 50%. A method for producing an Al substrate for a high-strength magnetic disk that has an unrecrystallized structure and a high strength is described.

  Patent Document 2 discloses an aluminum-based alloy plate for a magnetic disk in which smoothness is improved by cladding an Al-Mg alloy skin material containing as little impurities as possible and a core material having a composition similar to that of the skin material. And its manufacturing method is described.

  In Patent Document 3, a core material obtained by adding Zr having an effect of increasing the recrystallization temperature to an Al—Mg alloy is clad with a skin material made of an Al—Mg alloy that contains as little impurities as possible. An aluminum-based alloy plate for a magnetic disk and a method of manufacturing the same are described which have increased strength and improved smoothness with a recrystallized skin and a non-recrystallized core material during pressure annealing.

JP-A-63-223150 JP-A-10-310836 JP 61-012845 A

  However, in the method disclosed in Patent Document 1, since the amount of Mn added is large, a large number of coarse Al—Fe—Mn intermetallic compounds are present on the surface of the aluminum alloy substrate and fall off during the pretreatment for plating. There was a problem that large pits (dents) were generated and the smoothness of the plating surface was lowered.

  By using a clad material as disclosed in Patent Documents 2 and 3, the smoothness of the plating surface is improved, but the strength may be insufficient. Therefore, there remains a problem that high strength is required and the smoothness is not sufficient.

  The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to provide an aluminum alloy substrate for a magnetic disk that has high strength, excellent smoothness, does not impair plating properties, and has excellent mechanical properties. And

  The inventors of the present invention conducted intensive research and research on the relationship between the clad material and the core material, the distribution of Al-Mn intermetallic compounds in the core material, and the strength and smoothness. As a result, the distribution of the Al-Mn intermetallic compound of the core material is controlled by using the Al-Mg alloy with the impurity element content suppressed as much as possible as the skin material and using the Al-Mg-Mn alloy as the core material. It was found that high strength and smoothness can be obtained.

The present invention is the aluminum alloy substrate for a magnetic disk according to claim 1, wherein the core material is clad with a skin material on both sides, and the skin material is Mg: 3.0 to 6.0 mass%, Cu: 0.005 to 0.00. 150 mass%, Zn: 0.05-0.60 mass%, Cr: 0.010-0.300 mass%, Si: 0.001-0.030 mass%, Fe: 0.001-0.030 mass%, The balance material is composed of Al and inevitable impurities, and the core material contains Mg: 3.0 to 6.0 mass%, Mn: 1.0 to 2.0 mass%, the balance material is composed of Al and inevitable impurities, and the metal structure of the core material. and the aluminum alloy substrate for a magnetic disk Al-Mn intermetallic compound of a circle equivalent diameter 0.05~1.00μm is characterized in that it dispersed 30/100 [mu] m ³ or more in It was.

Further, the present invention is the aluminum alloy substrate for a magnetic disk according to claim 2, in which a skin material is clad on both surfaces of a core material, and the skin material is Mg: 3.0 to 6.0 mass%, Cu: 0.005 to Contains 0.150 mass%, Zn: 0.05-0.60 mass%, Cr: 0.010-0.300 mass%, Si: 0.001-0.030 mass%, Fe: 0.001-0.030 mass% And the balance material is composed of Mg: 3.0 to 6.0 mass%, Mn: 1.0 to 2.0 mass%, Cr: 0.05 to 0.30 mass%, Zr: 0. 0.05 to 0.30 mass%, consisting of the balance Al and unavoidable impurities, and 30 Al / 1-Mn intermetallic compounds having an equivalent circle diameter of 0.05 to 1.00 μm in the metal structure of the core material / 1 It was an aluminum alloy substrate for a magnetic disk, characterized in that 0 .mu.m ³ or dispersion.

  Furthermore, the present invention provides the method for producing an aluminum alloy substrate for a magnetic disk according to claim 1 or 2 according to claim 3, wherein the homogenizing process is performed to homogenize the core material and the skin material. Including a hot rolling step for hot rolling the heat treatment material and a cold rolling step for cold rolling the hot rolled material. In the homogenization treatment step, the temperature of the combined material is more than 500 ° C and not more than 560 ° C. 1 to 20 hours, and in the hot rolling step, the rolling start temperature is less than 500 ° C.

  Since the aluminum alloy substrate for magnetic disks of the present invention has high strength and excellent smoothness, it can provide an aluminum alloy substrate for magnetic disks that can be increased in capacity, density, and thickness.

It is a flowchart of the process from the manufacturing process of the aluminum alloy substrate which concerns on this invention to manufacture of a magnetic disc.

Hereinafter, the present invention will be described in detail.
First, the manufacturing process from the manufacturing process of the aluminum alloy substrate to the manufacturing process of the magnetic disk will be described according to the flow shown in FIG.

1. Manufacturing Process (1) First, in the adjustment of the aluminum alloy in Step 1, it is blended into an aluminum alloy as required. For example, it mix | blends with the aluminum alloy of the component composition shown in Table 1 mentioned later.
(2) Next, in the production of the core material in step 2, the aluminum alloy blended in step 1 is cast, and the ingot is chamfered to obtain a core material.
(3) Next, in the preparation of the skin material in step 3, the blended aluminum alloy is cast, the ingot is chamfered, and further homogenized. Here, the homogenization process is not essential. After the homogenization treatment, it is hot-rolled to obtain a skin material.
(4) Next, in the homogenization processing of the laminated material in step 4, the core material and the skin material are combined to form a combined material, and the combined material is further homogenized.
(5) Next, in the hot rolling of step 5, the homogenized laminated material is hot rolled to obtain a plate material.
(6) Next, in the cold rolling in step 6, the hot-rolled plate material is cold-rolled to obtain an aluminum alloy rolled plate. Note that intermediate annealing may be performed during or before cold rolling.
(7) Next, in the production of the disc blank in step 7, the aluminum alloy rolled plate is punched into an annular shape to produce a disc blank.
(8) Next, in the pressure flattening process in step 8, the disk blank is flattened by pressure annealing to produce an aluminum alloy substrate.
(9) Next, in the grinding process in step 9, the aluminum alloy substrate is subjected to cutting and grinding, and further subjected to degreasing and etching.
(10) Next, in the zincate process of step 10, a zincate process (Zn substitution process) is performed on the surface of the aluminum alloy substrate for magnetic disks.
(11) Next, in the base plating process in step 11, a base process (Ni-P plating) is performed on the surface of the zincated substrate.
(12) Next, in the magnetic material attaching step of step 12, the magnetic material is attached to the surface of the substrate plated by sputtering by sputtering to obtain a magnetic disk.

2. Core Material Next, the core material of the aluminum alloy plate for magnetic disk according to the present invention will be described.
The aluminum alloy constituting the core material contains Mg: 3.0 to 6.0 mass% (also referred to as mass%, hereinafter simply referred to as “%”), Mn: 1.0 to 2.0%, and the balance Al. And inevitable impurities.

Mg: 3.0-6.0%
Mg is an element mainly having an effect of improving the strength of the aluminum alloy substrate.
If the Mg content is less than 3.0%, the effect cannot be sufficiently obtained. If the Mg content exceeds 6.0%, the deformation resistance during hot rolling increases, the rolling load increases, and the rolling load is the capacity of the rolling mill. If it exceeds, rolling is impossible. Therefore, the content of Mg is set to 3.0 to 6.0%. The content of Mg is preferably 3.5 to 5.5% in view of strength and ease of manufacture.

Mn: 1.0-2.0%
Mn is produced as a fine Al-Mn intermetallic compound, or partially dissolved in the matrix and exhibits the effect of suppressing the coarsening of recrystallized grains during pressure annealing, and mechanical strength such as strength It is an element that improves the characteristics. If the Mn content is less than 1.0%, the above effect cannot be obtained sufficiently. On the other hand, even if the Mn content exceeds 2.0%, the above effect is saturated, and no further remarkable improvement effect can be obtained. A preferable Mn content is 1.4 to 1.8%.

In order to further improve the strength of the core material, both or one of Cr and Zr may be added.
Cr: 0.05-0.30%
Cr is an element that is produced as a fine intermetallic compound, or is partly dissolved in the matrix, exerts the effect of suppressing the coarsening of recrystallized grains during pressure annealing, and improves mechanical properties such as strength. is there. If the Cr content is less than 0.05%, the above effects cannot be obtained sufficiently. On the other hand, even if the Cr content exceeds 0.3%, the above effect is saturated, and no further significant improvement effect can be obtained. Note that the above effect is further enhanced by the coexistence of Zr with Cr.

Zr: 0.05-0.30%
Zr is an element that is produced as a fine intermetallic compound or is partly dissolved in the matrix and exhibits the effect of suppressing the coarsening of recrystallized grains during pressure annealing, and improves mechanical properties such as strength. is there. If the Zr content is less than 0.05%, the above effect cannot be obtained sufficiently. On the other hand, even if the Zr content exceeds 0.3%, the above effect is saturated, and no further remarkable improvement effect can be obtained. As described above, when Zr and Cr coexist, the above effect is further increased.

Inevitable impurities In addition to the above elements, there are Al and inevitable impurities. Examples of inevitable impurities include Si, Fe, Ti, V, Ga, and B. Here, if both Si and Fe are 0.3% or less and the other elements are each 0.05% or less, the characteristics of the aluminum alloy substrate obtained in the present invention are not impaired.

3. Skin Material Next, the skin material of the aluminum alloy plate for magnetic disks according to the present invention will be described.
The aluminum alloy constituting the skin material is Mg: 3.0-6.0%, Cu: 0.005-0.150%, Zn: 0.05-0.60%, Cr: 0.01-0. It contains 30%, Si: 0.001 to 0.030%, Fe: 0.001 to 0.030%, and consists of the balance Al and inevitable impurities.

Mg: 3.0-6.0%
Mg is an element mainly having an effect of improving the strength of the aluminum alloy substrate. The reason why the Mg content is specified to be 3.0 to 6.0% is that the strength is insufficient if it is less than 3.0%, and if it exceeds 6.0%, the deformation resistance during hot rolling increases and rolling If the load increases and the rolling load exceeds the capacity of the rolling mill, rolling cannot be performed. The content of Mg is preferably 3.5 to 5.5% in view of strength and ease of manufacture.

Cu: 0.005-0.150%
Cu is an element that has the effect of reducing the amount of dissolved Al during the zincate treatment, and depositing the zincate film uniformly, thinly and densely. By such an effect, the smoothness of the plating surface made of Ni-P in the next step can be improved.

  The reason why the Cu content is specified to be 0.005 to 0.150% is as follows. If it is less than 0.005%, the above effect cannot be obtained sufficiently. On the other hand, if it exceeds 0.150%, a coarse Al—Cu—Mg—Zn-based intermetallic compound is generated, pits are generated after the plating treatment, and smoothness is lowered. Further, if it exceeds 0.150%, the corrosion resistance of the material itself is lowered, so that the zincate film produced by the zincate treatment becomes non-uniform, and the adhesion and smoothness of the plating are lowered. A preferable Cu content is 0.005 to 0.100%.

Zn: 0.05-0.60%
Zn, like Cu, is an element that has the effect of reducing the amount of Al dissolution at the time of zincate treatment, attaching a zincate film uniformly, thinly and densely, and improving the smoothness of the plating surface in the next step.

  The reason why the Zn content is specified to be 0.05 to 0.6% is as follows. If it is less than 0.05%, the above effect cannot be obtained sufficiently. On the other hand, if it exceeds 0.60%, a coarse Al—Cu—Mg—Zn-based intermetallic compound is generated, pits are generated after the plating treatment, and smoothness is lowered. Furthermore, if it exceeds 0.60%, the workability and corrosion resistance of the material itself are lowered. A preferable Zn content is 0.05 to 0.50%.

Cr: 0.010-0.300%
Cr produces fine intermetallic compounds at the time of casting, but a part thereof is dissolved in the matrix and contributes to strength improvement. In addition, it improves the machinability and grindability, and further refines the recrystallized structure to improve the adhesion of the plating layer.

  The reason why the Cr content is specified to be 0.010 to 0.300% is as follows. If it is less than 0.010%, the above effect cannot be obtained sufficiently. On the other hand, if it exceeds 0.300%, excess Al is crystallized during casting, and at the same time, a coarse Al-Cr intermetallic compound is generated, and the intermetallic compound is dropped during etching, zincate treatment, cutting and grinding. As a result, large pits are generated and the smoothness of the plated surface is lowered. A preferable Cr content is 0.010 to 0.200%.

Si: 0.001 to 0.030%
Since Si combines with Mg, which is an essential element of the present invention, to generate an intermetallic compound that becomes a defect in the plating layer, it is not preferable that Si be contained in the aluminum alloy. However, Si is an element that exists as an inevitable impurity in the aluminum ingot. For adjusting the composition of the aluminum alloy, an aluminum ingot having a high purity, for example, a purity of 99.9% or more is adopted, but Si is inevitably contained in such an ingot. Removing Si from the aluminum ingot to less than 0.001% results in refining the aluminum ingot with high purity, resulting in high cost. On the other hand, if the Si content exceeds 0.030%, a coarse Mg-Si intermetallic compound is generated, which causes generation of pits and the like. Therefore, the Si content is adjusted to 0.03% or less. A preferable Si content is 0.001% or more and less than 0.025%.

Fe: 0.001 to 0.030%
Fe hardly dissolves in aluminum and exists in an aluminum metal as an Al—Fe intermetallic compound. Fe present in the aluminum ingot binds to Al, which is an essential element of the present invention, and generates an intermetallic compound that becomes a defect in the plating layer. Therefore, it is not preferable that Fe be contained in the aluminum alloy. . However, removing Fe to less than 0.001% results in refining aluminum ingots with high purity, resulting in high costs. On the other hand, when the Fe content exceeds 0.03%, a coarse Al—Fe intermetallic compound is generated, which causes generation of pits and the like. A preferable Fe content is 0.001 to 0.025%.

Be: 0.0001 to 0.0050%
An aluminum alloy containing Mg is generally added with a small amount of Be in order to suppress molten metal oxidation of Mg during casting. Therefore, it is permissible to add a small amount of Be also in the aluminum alloy of the present invention. However, if the amount of Be added is less than 0.0001%, the above effect cannot be obtained. On the other hand, even if the amount of Be added exceeds 0.0050%, the above effect is saturated, and no further remarkable improvement effect can be obtained. Accordingly, the amount of Be added when Be is added is preferably 0.0001 to 0.0050%, and more preferably 0.0001 to 0.0025%.

Inevitable impurities In addition to the above elements, there are Al and inevitable impurities. Inevitable impurities include, for example, Ti, V, Ga, B, etc. excluding the Si and Fe. Here, if these elements are each 0.05% or less, the characteristics of the aluminum alloy substrate obtained in the present invention will not be impaired.

4). Next, the distribution state of the Al-Mn intermetallic compound in the core material of the aluminum alloy plate for a magnetic disk according to the present invention will be described.
As described above, in the metal structure of the core material, the volume of the Al—Mn intermetallic compound having a circle-equivalent diameter of 0.05 to 1.00 μm is 30/100 μm ³ or more, preferably 100/100 μm ³ or more. Disperse with density. Thereby, the coarsening of recrystallized grains is suppressed during pressure annealing, and mechanical properties such as strength can be improved. The dispersion density of Al—Mn intermetallic compounds having an equivalent circle diameter of 0.05 to 1.00 μm is less than 30/100 μm ³ , and the equivalent circle diameters of other Al—Mn based intermetallic compounds to be dispersed are 0.00. When the thickness is less than 05 μm, the recrystallized grains become coarse during pressure annealing, and the strength decreases. On the other hand, the dispersion density of the Al—Mn intermetallic compound having an equivalent circle diameter of 0.05 to 1.00 μm is less than 30/100 μm ³ , and the equivalent circle diameter of another Al—Mn based intermetallic compound to be dispersed is In the case of exceeding 1.00 μm, the recrystallized grains become coarse at the time of pressure annealing, and the strength decreases. The upper limit of the dispersion density of the Al—Mn intermetallic compound having an equivalent circle diameter of 0.05 to 1.00 μm is not particularly defined, but the upper limit is determined by the composition of the aluminum alloy and the manufacturing process. According to the alloy composition and manufacturing process employed in the invention, 2000 pieces / 100 μm ³ is the upper limit of the dispersion density.

  Among the Al-Mn intermetallic compounds dispersed in the metal structure of the core material, the recrystallized grains are coarsened during the pressure annealing for those having an equivalent circle diameter of less than 0.05 μm and more than 1.00 μm. Was not sufficiently suppressed, and thus was excluded from the object of dispersion density.

5. Crystal structure and strength and flatness of the core material Most of the strength of the clad material is carried by the core material. Since the strength of the core material increases as the crystal grain size becomes smaller, the crystal grain size of the core material is preferably 40 μm or less, and more preferably 30 μm or less. When the crystal grain size of the core material exceeds 40 μm, sufficient strength cannot be obtained. In addition, the structure of the core material and the skin material of the aluminum alloy plate for a magnetic disk according to the present invention is preferably a recrystallized structure with less distortion from the viewpoint of flatness.

6). Method for Producing Aluminum Alloy Substrate for Magnetic Disk Next, a method for producing an aluminum alloy substrate for magnetic disk according to the present invention will be described in detail. Each step in this manufacturing method is as shown in FIG. 1, and each step is related to the distribution state of the Al—Mn intermetallic compound of the core material. The present inventors paid particular attention to the holding temperature and holding time during the homogenization treatment of the core material and the skin material in Step 4 and the hot rolling start temperature in Step 5.

Step 1
The aluminum alloy for the core material and the skin material is prepared by putting an aluminum ingot or the like in a melting furnace and heating and melting as in the conventional case.

Step 2
When the aluminum alloy substrate for a magnetic disk according to the present invention is manufactured by the rolling pressure welding method, the core material of Step 2 shown in FIG. 1 is obtained by, for example, chamfering an ingot prepared by a semi-continuous casting (DC casting) method. Is used. After the casting, if the oxide film such as MgO is removed by performing mechanical removal such as chamfering or cutting, or chemical removal such as alkali cleaning, the pressure contact with the subsequent skin material is improved.

Step 3
The skin material of Step 3 is a face material of a predetermined dimension by chamfering and homogenizing the ingot obtained by the DC casting method and then hot rolling. The homogenization treatment may not be performed, but when it is performed, it is preferably performed at 350 to 550 ° C. for 1 hour or more. In performing hot rolling, the conditions are not particularly limited, and it is preferable that the hot rolling start temperature is 350 to 500 ° C. and the hot rolling end temperature is 260 to 380 ° C. Moreover, when the base plate after hot rolling is washed with nitric acid, caustic soda, or the like, an oxide film such as MgO generated by hot working is removed, and the pressure contact with the core material is made good.

Step 4
In the present invention, various methods can be applied to clad the core material and the skin material. For example, the rolling press-contact method normally used for manufacture of a brazing sheet etc. is mentioned. In this rolling press-contact method, homogenization treatment, hot rolling, and cold rolling are performed in this order on the combined material of the core material and the skin material.

  In the present invention, when cladding the core material and the skin material, the cladding ratio of the skin material (ratio of the skin material thickness to the total thickness of the clad material) is not particularly limited, but required product plate strength and flatness Depending on the amount of grinding, it is appropriately determined, preferably 3 to 30%, more preferably 5 to 20%.

  In step 4, a homogenization treatment is performed by holding the combined material of the core material and the skin material at a temperature exceeding 500 ° C. and not exceeding 560 ° C. for 1 to 20 hours. When the homogenization treatment temperature is 500 ° C. or less, the amount of Al—Mn intermetallic compound produced decreases, and the recrystallized grains become coarse during pressure annealing, resulting in a decrease in strength. On the other hand, when the homogenization treatment temperature exceeds 560 ° C., dissolution may occur in the laminated material. The homogenization treatment temperature is preferably 510 to 550 ° C. Further, when the homogenization treatment time is less than 1 hour, the generation of Al—Mn intermetallic compounds is reduced, and the recrystallized grains are coarsened during the pressure annealing, thereby reducing the strength. On the other hand, when the homogenization treatment time exceeds 20 hours, a large amount of coarse Al—Mn intermetallic compound is generated, and the effect of suppressing the coarsening of recrystallized grains during pressure annealing is reduced. Decreases. The homogenization time is preferably 3 to 10 hours.

  When homogenizing the core material and the skin material, it is necessary to suppress the generation of MgO at the interface between the core material and the skin as much as possible. For this purpose, when homogenizing an aluminum alloy having a composition that easily produces MgO, an inert gas such as nitrogen gas or argon gas; a reducing gas such as carbon monoxide; a decompressed gas such as vacuum; It is preferable to carry out in a non-oxidizing atmosphere.

Step 5
In the hot rolling of the laminated material in step 5, the hot rolling start temperature is set to less than 500 ° C. When the hot rolling start temperature is 500 ° C. or higher, a large amount of coarse Al—Mn intermetallic compound is produced during hot rolling, and the effect of suppressing the coarsening of recrystallized grains during pressure annealing is achieved. Since it decreases, the strength decreases. Note that the lower limit of the hot rolling start temperature depends on the composition of the aluminum alloy and the like, but is preferably 370 ° C, more preferably 400 ° C. Moreover, the hot rolling end temperature is not particularly limited, and is preferably 260 to 380 ° C.

Step 6
In Step 6, the hot-rolled laminated material is cold-rolled. Finish to the required product thickness by cold rolling. The conditions for cold rolling are not particularly limited, and may be determined as appropriate according to the required product plate strength and plate thickness. Usually, the rolling rate is 20 to 90%. Further, intermediate annealing may be performed during cold rolling or before cold rolling. The conditions for the intermediate annealing are not limited, and either continuous annealing using a continuous furnace or batch annealing using a batch furnace may be used. As annealing conditions, it is preferable to perform annealing treatment at a temperature of 280 to 450 ° C. for 0 to 10 hours. The annealing time of 0 hour means that the annealing is finished immediately after reaching a predetermined annealing time.

  The above is the method for manufacturing an aluminum alloy substrate for a magnetic disk according to the present invention. The magnetic disk is manufactured by the following steps 7 to 12 following these steps.

Steps 7-12
In step 7, the aluminum alloy rolled sheet after cold rolling or annealing is punched into an annular shape to produce a disk blank. Next, in step 8, the disk blank is subjected to a pressure flattening process by performing pressure annealing for 30 minutes or more in an atmosphere of 280 to 450 ° C., for example.

  Further, in step 9, the flattened disc blank is subjected to grinding and grinding. Thereafter, degreasing and etching may be performed as necessary. Next, a zincate process is performed in Step 10, a base plating process is performed in Step 11, and a magnetic material attaching process by sputtering is performed in Step 12, thereby producing a magnetic disk.

  Hereinafter, the present invention will be described in detail by way of examples of the present invention and comparative examples. First, each step of FIG. 1 will be described below.

(1) Step 1: A molten aluminum alloy (750 ° C.) having the composition shown in Table 1 was melted.
(2) Step 2: The molten aluminum alloy was made into an ingot having a thickness of 220 mm by the DC casting method, and the core material was made by chamfering both sides of 10 mm.
(3) Step 3: Alloy No. Aluminum alloy melts other than 29 were made into ingots with a thickness of 220 mm by the DC casting method. Next, both sides of the ingot were chamfered by 10 mm, homogenized at 550 ° C. for 6 hours in the air, and hot-rolled to obtain hot-rolled plates having the thicknesses shown in Table 2. Thereafter, the hot-rolled sheet was washed with caustic soda to prepare a skin material.
(4) Step 4: In Comparative Example 29, an aluminum alloy substrate sample having only a core material was used without using a skin material. Except for Comparative Example 29, the skin material was combined on both sides of the core material to make a combined material, and homogenization treatment was performed under the conditions shown in Table 2. Table 2 shows the clad rate and homogenization conditions. In order to control MgO, homogenization was performed in an inert gas (argon, nitrogen), a reducing gas (carbon monoxide), and a vacuum non-oxidizing atmosphere in addition to the air atmosphere.
(5) Step 5: Hot rolling was performed at the starting temperature under the conditions shown in Table 2 to obtain a hot rolled sheet having a thickness of 3.0 mm.
(6) Step 6: Rolled to a final plate thickness of 1.0 mm by cold rolling to obtain a rolled plate.
(7) Step 7: A disc blank was prepared by punching the rolled plate into an annular shape having an outer diameter of 96 mm and an inner diameter of 24 mm.
(8) Step 8: The disc blank was subjected to pressure annealing at 380 ° C. for 3 hours.
(9) Step 9: End face processing and grinding processing (surface 20 μm grinding) were performed. Then, after degreasing for 5 minutes at 60 ° C. with AD-68F (manufactured by Uemura Kogyo), etching is performed for 1 minute at 65 ° C. with AD-107F (manufactured by Uemura Kogyo), and 30% HNO ₃ aqueous solution (room temperature ) For 20 seconds.
(10) Step 10: Double zincate treatment was performed on the disk blank surface using AD-301F-3X (manufactured by Uemura Kogyo).
(11) Step 11: The electroless Ni-P plating solution (Nimden HDX (manufactured by Uemura Kogyo)) is electrolessly plated to a thickness of 17 μm on the zincate-treated surface, and then finished with a blanket. Polishing (polishing amount 4 μm) was performed.

  The following evaluation was performed on the aluminum alloy substrate for a magnetic disk after the cold rolling (step 6), after the pressure annealing (step 8), and after the plating treatment (step 11). In Comparative Example 25, dissolution of the aluminum alloy substrate sample occurred during the homogenization treatment, and the aluminum alloy substrate could not be produced. Further, in Comparative Examples 12 and 15, since the Mg content exceeded 6.0%, the deformation resistance at the time of hot rolling was increased, so that hot rolling could not be performed, and an aluminum alloy substrate sample could not be produced. Therefore, Comparative Examples 12, 15 and 25 are not evaluated as follows.

〔Strength〕
After the cold-rolled plate was heated at 380 ° C. for 3 hours, the proof strength (in the direction along the rolling direction) of the JIS No. 5 test piece cut out along the rolling direction was measured using an Instron type tensile tester manufactured by Shimadzu Corporation. Measured using AG-50kNG. The measurement conditions were a gauge distance of 50 mm and a crosshead speed of 10 mm / min. Those having a proof stress of 130 MPa or more were evaluated as excellent (◎), those with a proof strength of 120 MPa or more and less than 130 MPa were evaluated as good (◯), and those with a proof strength of less than 120 MPa were evaluated as poor (×).

[Distribution of Al-Mn intermetallic compound having a circle equivalent diameter of 0.05 to 1.00 μm of core material]
The distribution of Al—Mn intermetallic compounds having an equivalent circle diameter of 0.05 to 1.00 μm was measured as a volume density (pieces / 100 μm ³ ). The volume density was obtained from scanning transmission electron microscope (STEM) observation of a thickness section along the rolling direction using a blank core material after pressure annealing. The Al—Mn intermetallic compound was identified by STEM-EDS analysis. Observation is performed by taking STEM photographs at a plurality of locations so that a total field of view of 100 μm ³ is obtained, counting the number of Al-Mn intermetallic compounds having an equivalent circle diameter of 0.05 to 1.00 μm, and totaling 100 μm ^{3 as a} whole. The volume density (pieces / 100 μm ³ ) was determined from the number. In addition, such a measurement was performed 3 times and the arithmetic mean value was used as the volume density of the sample (pieces / 100 μm ³ ).

[Distribution of Al-Mn intermetallic compound with a core equivalent circle diameter exceeding 1.00 μm]
The distribution of Al—Mn intermetallic compounds having an equivalent circle diameter exceeding 1.00 μm was measured as a volume density (pieces / 100 μm ³ ). The volume density was measured by the same method as described above. For the distribution of Al—Mn-based intermetallic compounds having an equivalent circle diameter of less than 0.05 μm, it was difficult to measure the equivalent circle diameter and the number of existence by the above measurement method.

[Ni-P plating surface smoothness]
The surface of the aluminum alloy substrate after the Ni—P plating treatment was observed with an optical microscope (field of view: 1 mm ² ), the number of pits was counted, and the number per unit area (pieces / mm ² ) was obtained. In addition, such a measurement was performed 3 times and the arithmetic average value was made into the number per unit area (piece / m < ² >) of a sample. A case where the number of pits was less than 5 / mm ² was judged as excellent (（), and a case where the number of pits was 5 / mm ² or more was judged as defective (×).

〔Comprehensive evaluation〕
When the above evaluations were all composed of ◎, the overall evaluation was ◎ (passed). When the evaluation is composed of “で” and “○”, the overall evaluation is “good” (pass). When the evaluation includes x, the overall evaluation is x (failed). The above evaluation results are shown in Table 3.

  As shown in Table 3, in Examples 1 to 10 of the present invention, aluminum alloy substrates for magnetic disks having high strength and excellent smoothness were obtained.

  On the other hand, since all of the comparative examples included elements that deviated from the limiting conditions of the present invention, at least one of strength and smoothness was inferior, and the capacity, density, and thickness of the magnetic disk could be increased. An aluminum alloy substrate for a magnetic disk could not be obtained.

  That is, in Comparative Example 11, the yield strength was low because the Mg content in the core material was small.

  In Comparative Example 13, the proof stress was low because the Mn content of the core material was small and the Al—Mn intermetallic compound having an equivalent circle diameter of 0.05 to 1 μm was small.

  In Comparative Example 14, the yield strength was low because the content of Mg in the skin material was small.

  In Comparative Example 16, since the content of Cu in the skin material was small, the zincate film became non-uniform, and the smoothness of the plating surface was inferior.

  In Comparative Example 17, a coarse Al—Cu—Mg—Zn-based intermetallic compound was generated because the content of Cu in the skin material was large. As a result, this intermetallic compound dropped off during the plating pretreatment, and the smoothness of the plating surface was poor.

  In Comparative Example 18, since the zinc content of the skin material was small, the zincate film became non-uniform, and the smoothness of the plating surface was inferior.

  In Comparative Example 19, a coarse Al—Cu—Mg—Zn-based intermetallic compound was generated because the content of Zn in the skin material was large. As a result, this intermetallic compound dropped off during the plating pretreatment, and the smoothness of the plating surface was poor.

  In Comparative Example 20, since the content of Cr in the skin material was small, the crystal grains became coarse and the plating surface was inferior in smoothness.

  In Comparative Example 21, since the content of Cr in the skin material was large, a coarse Al—Cr intermetallic compound was generated. As a result, this intermetallic compound dropped off during the plating pretreatment, and the smoothness of the plating surface was poor.

  In Comparative Example 22, since the Fe content was large, a coarse Al—Fe intermetallic compound was generated. As a result, this intermetallic compound dropped off during the plating pretreatment, and the smoothness of the plating surface was poor.

  In Comparative Example 23, since the Si content was large, a coarse Mg-Si intermetallic compound was generated. As a result, this intermetallic compound dropped off during the plating pretreatment, and the smoothness of the plating surface was poor.

  In Comparative Example 24, since the holding temperature during the homogenization treatment was too low, the production of Al—Mn intermetallic compounds having an equivalent circle diameter of 0.05 to 1.00 μm was small, and the proof stress was low.

  In Comparative Example 26, since the holding time at the time of the homogenization treatment was too short, the generation of Al—Mn intermetallic compounds having an equivalent circle diameter of 0.05 to 1.00 μm was small, and the proof stress was low.

  In Comparative Example 27, since the holding time during the homogenization treatment was too long, the production of Al—Mn intermetallic compounds having an equivalent circle diameter of 0.05 to 1.00 μm was small and the proof stress was low.

  In Comparative Example 28, since the hot rolling start temperature was too high, the production of Al—Mn intermetallic compounds having an equivalent circle diameter of 0.05 to 1.00 μm was small, and the proof stress was low.

  In Comparative Example 29, no skin material was used, and since the holding temperature during the homogenization treatment was too low, the production of Al-Mn intermetallic compounds having an equivalent circle diameter of 0.05 to 1.00 μm was small and the yield strength was low. . In addition, a large number of coarse Al—Fe—Mn intermetallic compounds existed on the surface of the aluminum alloy substrate. As a result, this intermetallic compound dropped off during the plating pretreatment, and the smoothness of the plating surface was poor.

  As described above, in each of the comparative examples, either strength or smoothness was inferior, so that an aluminum alloy substrate for a magnetic disk capable of increasing the capacity, increasing the density, and reducing the thickness of the magnetic disk could not be obtained.

  According to the present invention, it is possible to provide an aluminum alloy substrate for a magnetic disk that can be increased in capacity, density, and thickness.

Claims (3)

An aluminum alloy substrate for a magnetic disk in which a skin material is clad on both sides of a core material, and the skin material is Mg: 3.0 to 6.0 mass%, Cu: 0.005 to 0.150 mass%, Zn: 0.05 -0.60 mass%, Cr: 0.010-0.300 mass%, Si: 0.001-0.030 mass%, Fe: 0.001-0.030 mass%, the balance consisting of Al and inevitable impurities The core material contains Mg: 3.0 to 6.0 mass%, Mn: 1.0 to 2.0 mass%, and is composed of the balance Al and unavoidable impurities, and has an equivalent circle diameter of 0.05 in the metal structure of the core material. An aluminum alloy substrate for a magnetic disk, wherein ˜1.00 μm Al—Mn intermetallic compound is dispersed at 30 pieces / 100 μm ³ or more. An aluminum alloy substrate for a magnetic disk in which a skin material is clad on both sides of a core material, and the skin material is Mg: 3.0 to 6.0 mass%, Cu: 0.005 to 0.150 mass%, Zn: 0.05 -0.60 mass%, Cr: 0.010-0.300 mass%, Si: 0.001-0.030 mass%, Fe: 0.001-0.030 mass%, the balance consisting of Al and inevitable impurities The core material contains Mg: 3.0 to 6.0 mass%, Mn: 1.0 to 2.0 mass%, Cr: 0.05 to 0.30 mass%, Zr: 0.05 to 0.30 mass%. , the balance Al and unavoidable impurities, that Al-Mn intermetallic compound of a circle equivalent diameter 0.05~1.00μm are dispersed 30/100 [mu] m ³ or more in the metal structure in heartwood Aluminum alloy substrate for a magnetic disk according to symptoms.   The method for producing an aluminum alloy substrate for a magnetic disk according to claim 1 or 2, wherein a homogenization treatment step for homogenizing the laminated material of the core material and the skin material, and heat for hot rolling the homogenization treatment material. A cold rolling step of cold rolling a hot rolled material and a hot rolled material, and in the homogenization treatment step, the laminated material is held at a temperature of more than 500 ° C and not more than 560 ° C for 1 to 20 hours, A method for producing an aluminum alloy substrate for a magnetic disk, wherein the rolling start temperature is less than 500 ° C. in the hot rolling step.

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