JPH10121178A - Aluminum alloy clad plate for high-capacity magnetic disk substrate excellent in zincate treatment and undercoat treatment and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive aluminum alloy clad plate for a high-capacity magnetic disk substrate in which zincate treatment and undercoating are performed well and a magnetic material is plated smoothly. SOLUTION: Mg 2.0 to 6.0 wt%, Cu 0.01 to 0.05 wt%, Zn
0.05 to 2.0 wt%, Mn less than 0.05 wt%, Cr at least one containing less than 0.05 wt%, Si and Fe as impurities respectively
0.05 wt% or less, and each other unavoidable impurity element
The skin material containing not more than 02 wt% and the balance of Al is at least Z
Aluminum alloy clad plate for high-capacity magnetic disk substrates excellent in zincate treatment and undercoating, containing less than 3.0 wt% of n and the remainder being clad on one or both sides of a core material composed of Al and unavoidable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inexpensive and high capacity aluminum alloy clad plate for a magnetic disk substrate, which has a good zincate treatment and a good undercoating, and a smooth plating of a magnetic material. About the method.

[0002]

2. Description of the Related Art In recent years, a magnetic disk has been required to have a large capacity and a high density due to needs of multimedia and the like, and a magnetic area per bit of the magnetic disk has been further miniaturized. The distance from the magnetic disk also tends to decrease. Under such circumstances, the formation of a smooth magnetic film on the magnetic disk is required. The substrate used for such a magnetic disk is required to have the following characteristics. Non heat treatment type (non precipitation hardening type)
It has sufficient strength to withstand high-speed rotation during various processing and use, obtains a good mirror surface without micro pits by polishing, and has a smooth surface after under plating and No defects occur and the adhesion of the underlying plating layer is good.

Conventionally, a magnetic disk substrate is provided with impurity elements such as Fe and Si which cause micropits or the like.
JIS-A-5086 alloy is used. And this substrate is hot rolled ingot (slab) obtained by semi-continuous casting method,
Next, cold rolling is performed while annealing is performed, and the rolled material is punched into a disc shape. This disc shape is subjected to cutting, grinding, polishing, degreasing, etching, zincate treatment as a pretreatment, and then Ni- as a base treatment. It is manufactured by subjecting a hard non-magnetic metal such as P to electroless plating and polishing, and then sputtering a magnetic material such as a Co-Ni-P alloy.

However, the JIS-A-5086 alloy substrate has insufficient surface smoothness after electroless plating. That is, cutting,
During pretreatment such as grinding, polishing, and zincate treatment, the intermetallic compound protrudes and remains or the intermetallic compound falls off, causing nodules (hemispherical protrusions) or Micro pits occur. The nodules collide with the magnetic head and cause a head crash, and the micro pits cause an electrical error. Therefore, to improve the surface quality of the magnetic disk, measures have been taken to reduce the number and size of the intermetallic compounds in the aluminum alloy substrate, but a sufficient effect has not always been obtained. Various other measures have been taken, but all have complicated processing steps and high manufacturing costs. The nodules may be caused by an Al-Fe intermetallic compound or the like protruding into the surface layer and this protruding portion being plated to form a nodule, or zincate growing preferentially in a small concave portion in a convex shape. May be plated to form nodules.

[0005] From the above, the present inventors have proposed a method for controlling a type of alloy element and the amount of addition thereof to obtain a base plating layer (electroless Ni-P alloy plating layer) with few defects to obtain a magnetic disk substrate. Proposed aluminum alloy plate (Japanese Unexamined Patent Publication No. 2-97
No. 639). This aluminum alloy plate for a magnetic disk substrate has already been put to practical use and has been highly evaluated. But,
This material is expensive due to the use of high purity bullion,
Also, the strength is not enough.

Recently, for the purpose of increasing the strength, an Al-Mg-Zn alloy (7000) of an age hardening type aluminum alloy has been used as a core material.
Al-Mg with good plating properties
An alloy clad with a base alloy (5000 series alloy) has been developed (JP-A-5-9633 and JP-A-5-43970). However, since this clad plate uses a 7000 series alloy containing a large amount of Zn (normally 4 wt% or more) as the core material, the potential difference between the core material and the skin material is large, and the core material is used in the etching process before zincate treatment. May be preferentially dissolved and a step may occur with the skin material. When the step is large, the step may be caught when the magnetic disk is loaded on the shaft, and the skin material may peel off. Further, if the compositions of the core material and the skin material are not properly combined, sufficient bonding strength may not be obtained by rolling welding.

[0007]

DISCLOSURE OF THE INVENTION The present inventors have reduced the natural potential difference between a matrix and an intermetallic compound (Al-Fe intermetallic compound or Mg ₂ Si intermetallic compound) to reduce micropits and nodules. A patent application was previously filed for a high-capacity aluminum alloy for a high-capacity magnetic disk substrate in which the occurrence of cracks was suppressed (Japanese Patent Application No. 8-258607). On the other hand, in the present invention, zincate treatment and base plating are performed favorably,
It is an object of the present invention to provide an inexpensive aluminum alloy clad plate for a high-capacity magnetic disk substrate on which a magnetic material is plated smoothly and a method for manufacturing the same.

As described above, the capacity of magnetic disks has been increasing year by year, and the density has been increasing. In recent years, a storage capacity of 2 GB / sheet or more has been required. This high capacity method includes:
It has been considered to reduce the flying height (glide height) of the magnetic head. However, as described above, nodules and micro pits may be formed on the front and back surfaces of the working substrate as described above. The effect of the nodules and micro pits increases as the glide height decreases. Further, in the polishing step after the base plating, the amount of polishing tends to be reduced from the viewpoint of preventing sagging of the end portion and economy. As a result, a situation in which nodules and micropits remain even after polishing has started to occur.
For this reason, reduction of nodules and micropits is one of the important issues to be solved for increasing the capacity of a magnetic disk.

In order to reduce nodules and micro pits,
A method using a high-purity metal with few impurity elements such as Si and Fe can be considered. For example, a method of using 99.99 wt% pure aluminum in place of 99.9 wt% pure aluminum, but 99.99 wt% pure aluminum
There is a problem that it is much more expensive than that of 9.9 wt% purity, and its amount is limited.

The present inventors have conducted various studies on the above-mentioned problems, and found that the zincate coating of the pretreatment is thin, uniform, and densely formed, and the underlying plating is formed thereon in order for the magnetic material to be plated smoothly. It was confirmed that it was necessary to provide a material that had no nodules or micropits and had fine crystal grains. It has been found that such a material excellent in zincate treatment and undercoat treatment can be produced by using a high-purity ingot and selecting the type and amount of the additive element. Also, by using a clad plate as the material and using high-purity metal only for the skin material forming the magnetic material, it was decided to avoid a significant increase in cost.

[0011]

According to the first aspect of the present invention,
Mg 2.0-6.0 wt%, Cu0.01-0.05wt%, Zn0.05-2.0wt%, at least one of Mn less than 0.05wt%, Cr less than 0.05wt%
Seeds, each containing 0.05 wt% or less of Si and Fe as impurities, each containing 0.02 wt% or less of other unavoidable impurity elements, and a skin material made up of Al with a balance of less than 3.0 wt% Zn and a balance of An aluminum alloy clad plate for a high-capacity magnetic disk substrate excellent in zincate treatment and undercoating, characterized in that it is clad on one or both sides of a core material composed of Al and unavoidable impurities.

According to a second aspect of the present invention, the composition of the core material and the skin material according to the first aspect is represented by the formula F = Si + Fe + 2Cu + 2Mn + 3Mg
+ 0.5Zn (where Si, Fe, Cu, Mn, Mg, and Zn are each wt%) and the F value (Fb) of the core material and the F value (F
An aluminum alloy clad plate for a high-capacity magnetic disk substrate, which is excellent in zincate processability and underlayer processability, wherein the ratio [Fb / Fs] to s) is 0.6 or more.

According to a third aspect of the present invention, there is provided an aluminum alloy clad for a high-capacity magnetic disk substrate, comprising subjecting a composite material obtained by cladding a skin material on one or both surfaces of an aluminum alloy core material to hot rolling, cold rolling and final annealing. In the sheet manufacturing method, cooling after hot rolling, cooling after intermediate annealing during cold rolling, and cooling after final annealing are each 240 to 15 times.
0 ° C at a rate of 30-600 ° C / hr.
4. The method for producing an aluminum alloy clad plate for a high-capacity magnetic disk substrate according to claim 3, wherein the rolling is performed three times or more at a rolling rate of 0% or more and at a total rolling rate of 60% or more.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The skin material used in the present invention is Mg, C
An aluminum alloy material containing u and Zn, and further containing one or two of Mn and Cr, and having an unavoidable impurity element regulated to a predetermined value or less. Among the alloying elements, Mg mainly improves the machinability and grindability to improve the surface quality of the skin material. The reason for defining the content to be 2.0 to 6.0 wt% is that if the content is less than 2.0 wt%, the effect cannot be sufficiently obtained, and
If it exceeds, an Al-Mg based intermetallic compound is generated,
Non-metallic inclusions such as MgO are generated in large quantities by high-temperature oxidation during melting and casting, which may cause micro-pits and the like. The content of Mg is particularly preferably 2.0 to 5.0% by weight in view of the balance between machinability and grindability and ease of production.

Cu and Zn reduce the amount of Al dissolved during the zincate treatment, and make the zincate film adhere uniformly, thinly and densely. As a result, the adhesion of the electroless plating (base plating) layer is improved. The reason why the content of Cu is specified to be 0.01 to 0.05 wt% is that if the content is less than 0.01 wt%, the effect is not sufficiently obtained, and if the content exceeds 0.05 wt%, the corrosion resistance of the material itself is reduced. When the corrosion resistance decreases, the zincate film becomes non-uniform, and the adhesion of the undercoat layer and the smoothness of the undercoat layer surface decrease. The reason for limiting the Zn content to 0.05 to 2.0 wt% is that if the content is less than 0.05 wt%, the effect cannot be sufficiently obtained.
If the content exceeds 2.0% by weight, workability and corrosion resistance are reduced.

Mn or Cr forms a fine intermetallic compound at the time of casting, but partly forms a solid solution in a matrix and contributes to improvement in strength. In addition, it enhances the machinability and grindability, further refines the recrystallized structure, and improves the adhesion of the base plating layer. The reason that the content of each of Mn and Cr is specified to be less than 0.05 wt% is that if it exceeds 0.05 wt%, an excessive amount is crystallized at the time of casting, and at the same time a coarse intermetallic compound is generated.
This is because the intermetallic compounds fall off during zincate treatment, cutting or grinding, and cause micropits and the like. Although Mn or Cr is effective even when used alone, its effect is further enhanced when coexisting. Since Mn combines with an Al-Fe compound to form an Al-Fe-Mn compound, the upper limit of Mn is preferably set to 0.03 wt%. Although not as much as Mn, the same tendency is observed for Cr, so the upper limit is preferably set to 0.04 wt%.

Of the unavoidable impurity elements, Si, Fe, and Ti hardly form a solid solution in aluminum, but exist as intermetallic compounds. The reason for specifying the upper limit of Si, Fe, Ti, etc. is that if these amounts are large, a large number of coarse intermetallic compounds such as Al-Fe system and Mg ₂ Si are generated, which may cause micro-pits and the like. It is. Also, other unavoidable impurity elements (for example, Ni,
B etc.) do not impair the properties of the alloy sheet obtained by the present invention if each is 0.02 wt% or less.

In the present invention, Zn in the core material makes the potential of the core material low. If the content of Zn is too large, the core material is preferentially dissolved in the etching step, causing a step at the boundary with the skin material, or in extreme cases, the skin material peels off. Therefore, its content is specified to be less than 3.0 wt%.

In the present invention, various methods can be applied to clad the skin material and the core material. In particular, the rolling pressure welding method used for the production of the brazing sheet has high productivity and is suitable. This rolling pressure welding method is performed by subjecting a combined material of a core material and a skin material to hot rolling, cold rolling, and final annealing. In the clad plate of the present invention, the Zn content of the core material is less than 3.0 wt%, and the formula: F = Si + Fe + 2Cu + 2Mn + 3Mg + 0.
Ratio of F value (Fb) of core material and F value (Fs) of skin material expressed as 5Zn (where Si, Fe, Cu, Mn, Mg, and Zn are each wt%) [Fb / Fs] But
When it is set to 0.6 or more, the joining by the rolling pressure welding method or the like is more preferably performed. When the ratio [Fb / Fs] is less than 0.6, that is, when the alloy concentration of the skin material increases and a difference occurs in the deformation resistance between the core material and the core material, the core material is preferentially rolled during hot rolling and the skin material is rolled. Is not sufficiently rolled, and the bonding strength is reduced. The relationship between Fb and Fs based on the above equation has been clarified through many experiments.

Since the aluminum alloy plate of the present invention is obtained by cladding a core material with a skin material, when increasing the purity of the metal to reduce defects such as micropits and nodules, high purity metal has a problem of surface defects. The core material may be an inexpensive low-purity metal as long as the above composition is satisfied. Therefore, the cost increase due to the use of the high-purity metal can be suppressed low.

Clad ratio per side of skin material in the above-mentioned rolling pressure welding method ｛[Thickness of skin material / (thickness of core material + thickness of skin material)] ×
100%｝ is preferably 30% or less. Cladding rate
If it exceeds 30%, the shearing force generated at the interface between the core material and the skin material at the time of pressure welding is weakened, and sufficient bonding strength cannot be obtained.

In the present invention, the intermetallic compound contained in the skin material falls off during alkali etching or zincate treatment, or during cutting and grinding of an aluminum alloy substrate, causing surface defects such as micropits. This flaw,
Reduced by grinding or electroless plating. But 10μm
The intermetallic compound exceeding the amount often ultimately remains as a harmful defect. Therefore, it is desirable that the diameter be 10 μm or less.

In the present invention, after the hot rolling, the intermediate annealing performed during the cold working, and the cooling process after the final annealing, 240 to
Cooling in the temperature range up to 150 ° C is performed at a cooling rate of 30-60
Perform at 0 ° C / hr. The temperature range is defined based on the reason that Mg ₂ Si does not precipitate at a temperature exceeding 240 ° C. and the deposition rate is slow at a temperature lower than 150 ° C. When the cooling rate is lower than 30 ° C / hr, the amount of Mg ₂ Si
If the temperature exceeds ℃ / hr, thermal strain occurs and the flatness of the raw material is reduced, so it is specified. In the cooling step, any cooling method can be applied, in particular, forced air cooling, mist quench injection,
A method such as passing through a water tank is simple and desirable. Here, the hot rolling of the combined material of the core material and the skin material may be performed by heating to a temperature at which rolling is possible. However, the hot rolling temperature is preferably in the range of 350 to 550 ° C. in consideration of the possibility of hot rolling and the problems of coarsening and melting of crystal grains of the rolled material.

In the present invention, the rolling reduction in one cold rolling is
20% or more, this cold rolling is performed 3 times or more, and the total rolling reduction is 60% or more, the Al-Fe intermetallic compound is sufficiently pulverized, and the micro pits and nodules after the base plating treatment Can be suppressed.

By satisfying the above cooling conditions and cold rolling conditions, the production of Mg ₂ Si and Al—Fe intermetallic compounds can be greatly reduced.

In producing the aluminum alloy sheet of the present invention by the rolling pressure welding method, the skin material is obtained by homogenizing an ingot obtained by a semi-continuous casting method and then hot rolling to a sheet material having a predetermined size. The temperature conditions for the homogenization and hot rolling at this time are optimally selected according to the composition of the skin material. However, if the temperature is too high, the crystal grains of the ingot become coarse, and in extreme cases, they melt. On the other hand, if the temperature is too low, the deformation resistance at the time of hot rolling increases, and if the temperature exceeds the capacity of the rolling mill, rolling cannot be performed. Taking these factors into consideration, the homogenization treatment temperature or the hot rolling start temperature is desirably 350 to 550 ° C. Further, when the raw sheet after hot rolling is washed with nitric acid, caustic soda, or the like, an oxide layer generated by hot working is removed, and the pressure contact with the core material afterwards is performed well.

On the other hand, as the core material, for example, a material obtained by homogenizing an ingot obtained by a semi-continuous casting method and having a uniform structure is used. If the oxide film is removed by grinding after homogenization,
Good pressure contact with the skin material. The temperature range of the homogenization treatment is desirably 350 to 550 ° C. as in the case of the skin material.

[0028]

The present invention will be described below in detail with reference to examples. (Example 1) A single-sided mating material prepared using a skin material and a core material having the compositions shown in Tables 1, 2 and 3 was reheated to 500 ° C, and the thickness was 2.
It was hot rolled to 30 mm and then cold rolled to 0.82 mm. Next, the cold-rolled material was cut into a predetermined size, and washed to prepare a clad plate having a clad ratio of about 10%.

The details of the method for producing the skin material and the core material, and the conditions for hot rolling, cold rolling and unwashing of the combined material are shown below. Production method of leather material: A 30mm thick ingot cast by the usual method is cut into 5mm on both sides to make 20mm thick and homogenized.
(450 ° C x 2hr + 520 ° C x 2hr), then hot-rolled to a 5mm thick sheet (rolling start temperature 470 ° C, end temperature 230 ° C, cooling rate 50 ° C / hr) Cut and unwash (wash with hot water → 3% nitric acid desmut (1 minute) → 5% caustic soda (5 minutes)
→ 3% nitric acid desmut (1 minute) → hot water washing. Manufacturing method of core material: A 60 mm thick ingot cast by a conventional method is homogenized (450 ° C. × 2 hours + 520 ° C. × 2 hours) and then cut into 10 mm on both sides to a thickness of 40 mm. Hot rolling of laminated material: Rolling start temperature 470 ° C, coil winding temperature 260 ° C, cooling rate 50 ° C / hr, sheet thickness 2.30mm. Cold rolling of laminated material: 1.60 mm in the first pass (30% reduction),
1.12mm at second pass (30% rolling reduction), 0.82mm at third pass (rolling reduction)
27%), total reduction 64%. Unwashing of laminated material: Same as unwashing of skin material.

A donut plate having an outer diameter of 96 mm and an inner diameter of 24 mm was punched from the clad plate, annealed at 340 ° C. for 4 hours, cooled at a cooling rate of 50 ° C./hr, and further subjected to grinding. Thereafter, surface treatment and electroless plating were performed according to the following procedure. That is, degreasing with acetone → immersing in a 5% NaOH aqueous solution (40 ° C) for 30 seconds and etching → desmutting with a 30% HNO ₃ aqueous solution (room temperature) for 30 seconds → double zincate treatment using ARB 302ZN (trade name, Okuno Pharmaceutical) → Electroless plating of Ni-P to a thickness of 17μm using Niclad 719 (trade name, Okuno Pharmaceutical Co., Ltd.)
m).

[0031] The presence or absence of a step at the end of the donut plate after etching, the adhesion of the electroless plating film, the surface roughness after polishing of the film, the surface quality of the film, and the corrosion resistance of the film were examined. The results are shown in Tables 3 and 4. Tables 3 and 4 also show the possibility of cladding. With regard to, those having no step were evaluated by visually observing the end portions. For, a sample of 50 mm ² was cut out from the electroless plated material, heated at 400 ° C. for 30 minutes, immediately cooled with water, and examined for peeling or blistering of the plating film. Is measured by a universal surface roughness meter SE-3H (manufactured by Kosaka Laboratories) using a center line roughness Ra (μ) specified in JIS-B-0601.
m) was measured at four points, and the average value was displayed. The surface roughness was determined to be acceptable when the average value of Ra was 0.5 μm or less, and was rejected when the average value exceeded 0.5 μm. Regarding, the surface was observed with a microscope, and those having no pits or nodules having a depth exceeding 3 μm were indicated by ○, and those having certain pits or nodules were indicated by ×. About electroless plating material in 1N hydrochloric acid solution (room temperature)
This was performed by observing the properties of the plating film after immersion for 24 hours. The film without peeling or swelling was indicated by ○, the one with a small number was indicated by △, and the one with a large number was indicated by ×.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

[Table 3]

As is clear from Tables 1 to 3, the products of the present invention
(Nos. 1 to 14) all showed good characteristics. In contrast, No. 15 of the comparative example product did not contain Cu in the skin material, and No. 16 had low adhesion of the base (electroless) plating layer in both cases because the Zn content of the skin material was small. . No.17
Due to the large amount of Zn, the adhesion of the underlying plating layer is significantly reduced,
In addition, the surface roughness and corrosion resistance decreased. No.18 is Mn in the skin material
Since no Cr was contained, the adhesion of the underlying plating layer was reduced. In Nos. 19 and 20, defects were generated on the surface of the base plating layer due to the large amount of impurity element Si or Fe in the skin material. In No. 21, since the skin material contained less Mg, a step was formed at the end of the donut plate, and the surface roughness of the base plating layer was reduced. No.22 is Mg of leather material
No. 23 had a large amount of Ti in the skin material, and both had defects on the underlying plating layer surface. No.24 and 28 are ratios [Fb / Fs]
Was less than 0.6, the core material and the skin material were not sufficiently bonded. Nos. 25, 26, 27 and 29 all had a large amount of Zn in the core material, so that a step occurred at the end of the donut plate. And No. 25 is Cu of leather material
No.26 has a large amount of Cu in the skin material, No.27 has a large amount of Cu in the skin material, and the skin material does not contain Mn and Cr. The properties were significantly reduced, and the surface roughness was also reduced. In No. 29, the adhesion was reduced due to the large amount of Cu in the skin material, and the surface roughness was also slightly reduced.

Example 2 Alloys of the alloys of the present invention shown in Table 1
A laminated material was prepared using the skin material and core material of No. 1 and the alloy No. 15 of the comparative material, and after reheating this laminated material to 500 ° C, hot rolling was started at 470 ° C to various thicknesses. Rolling, then 0.82mm
Was cold rolled. Next, the cold-rolled material was cut into a predetermined size and washed with a light to produce a clad plate. The coil winding temperature, cooling rate, plate thickness, cold rolling reduction ratio, and intermediate annealing conditions in hot rolling were variously changed. The unwashing was performed in the same manner as in Example 1. The production of the core material and the skin material was performed in the same manner as in Example 1. Next, a donut plate having an outer diameter of 96 mm and an inner diameter of 24 mm was punched from the clad plate, annealed at 340 ° C for 4 hours, cooled at a cooling rate of 20 ° C / hr, and further subjected to grinding. After that, the following quality evaluation was performed on those subjected to surface treatment and electroless plating according to the same procedure as in Example 1. Evaluation of the donut plate after the grinding process Mg ₂ Si: The number in a field of view of 3 mm ² was measured with a scanning electron microscope (SEM). Those exceeding 5 μm are 20 / mm ² or less as acceptable levels. Al-Fe-based intermetallic compound: The number in a visual field of 3 mm ² was measured by SEM. Those exceeding 5 μm are 10 / mm ² or less as acceptable levels.

Evaluation of donut plate after base plating Micro pits: The number in a visual field of 3 mm ² was measured with an optical microscope. When the number is less than 5, A is indicated, when 5 or more is less than 15, B is indicated, when 15 or more is less than 25, C is indicated, and when 25 or more is indicated, D. Nodule: The number in a visual field of 3 mm ² was counted with an optical microscope. The case where the number exceeding 10 μm is less than 5 is indicated as A, the case where the number is 5 or more and less than 15 is B, the case where the number is 15 or more and less than 25, and the case where the number is 25 or more.

Evaluation of Donut Plate After Etching The presence or absence of a step at the end face was examined. In the case of a healthy end face without a step, it was indicated by ○, and in the case of a step, × was indicated. Finally, the micro pits, nodules, and the properties of the end face are comprehensively evaluated.
To E were evaluated in five steps. A, B, C are acceptable levels,
X indicates rejection, and production failure indicates ━. The results are shown in Table 4 together with the production conditions.

[0039]

[Table 4]

As is clear from Table 4, all of the products of the present invention (samples Nos. 30 to 34) had few micropits and nodules, and had good end face properties. Was. In sample No. 34, the cooling rates after hot rolling and after final annealing were slow and the total rolling ratio was low, so that micropits and nodules having a larger size than the others increased. On the other hand, in Samples Nos. 35 to 38, since the alloy composition is out of the range of the present invention, Mg ₂ Si or A
Some of the compounds, such as l-Fe-based compounds, had a small content of 5 μm or more, but all of them generated many large-sized micropits or nodules, and all were rejected as a whole.

[0041]

As described above, the clad plate of the present invention has no step on the end face after etching, and is excellent in the adhesion of the base plating layer to the skin material, surface smoothness, corrosion resistance, and surface quality. Therefore, it is possible to increase the capacity and density of the magnetic disk. In addition, since a low-purity metal can be used as the core material, it is inexpensive and has a remarkable industrial effect.

Continuation of the front page (51) Int.Cl. ⁶ identification code FI G11B 5/84 G11B 5/84 Z // C22F 1/00 627 C22F 1/00 627 661 661D 685 685Z 686 686A 692 692A 694 694A G11B 5/62 G11B 5/62

Claims (3)

[Claims] 1. Mg 2.0-6.0 wt%, Cu 0.01-0.05 wt%, Zn
0.05 to 2.0 wt%, Mn less than 0.05 wt%, Cr at least one containing less than 0.05 wt%, each of Si and Fe as impurities
0.05 wt% or less, and each other unavoidable impurity element
The skin material containing not more than 02 wt% and the balance of Al is at least Z
Aluminum alloy for high-capacity magnetic disk substrates with excellent zincate and undercoating properties, characterized in that n is less than 3.0 wt% and the remainder is clad on one or both sides of a core material consisting of Al and unavoidable impurities Clad plate. 2. The composition of the core material and the skin material according to claim 1 is represented by the formula F = Si + Fe + 2Cu + 2Mn + 3Mg + 0.5Zn (where Si, Fe, Cu,
Mn, Mg, and Zn are each substituted by wt%). The ratio [Fb / Fs] of the F value (Fb) of the core material and the F value (Fs) of the skin material obtained by substituting into each wt% is
An aluminum alloy clad plate for high-capacity magnetic disk substrates that is excellent in zincate treatment and undercoat treatment, characterized by being 0.6 or more. 3. A method for producing an aluminum alloy clad plate for a high-capacity magnetic disk substrate, comprising subjecting a composite material in which a cladding material is clad on one or both sides of an aluminum alloy core material to hot rolling, cold rolling and final annealing. Cooling after hot rolling, cooling after intermediate annealing during cold rolling, and cooling after final annealing are performed at 240 to 150 ° C and 30 to 600 ° C / h, respectively.
4. The aluminum alloy for a high-capacity magnetic disk substrate according to claim 3, wherein the cold rolling is performed at a rolling rate of 20% or more at least three times, and the total rolling rate is 60% or more. Manufacturing method of clad plate.