JPH11315338A - Aluminum alloy for magnetic disk, excellent in zincate treatment property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy for magnetic disk substrate, causing no unevenness of a zincate film, capable of giving even and homogeneous surface characteristic free from defects after plating and final polishing, and satisfactorily applicable as a high density substrate. SOLUTION: The aluminum alloy for magnetic disk, excellent in zincate treatment property has a composition which consists of, by weight, 0.031-<0.050% Cu, 2.5-5.5% Mg, >0.05-0.7% Zn, 0.007-<0.05% Fe, and the balance Al with impurities and in which the contents of Si, Ti, and B as impurities are limited to <=0.05%, <=0.01%, and <=0.005%, respectively. Further, one or more kinds among <=0.1% (not including 0%, the same applies to the following) Mn, <=0.1% Cr, and <=0.2% V are incorporated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy for a magnetic disk excellent in zincate processing, and more particularly to an aluminum alloy for a magnetic disk excellent in zincate processing before a magnetic disk substrate is subjected to Ni-P plating.

[0002]

2. Description of the Related Art A magnetic disk used for a hard disk or the like of a computer is manufactured by precisely polishing the surface of an aluminum alloy substrate, and then performing zincate treatment and Ni-P.
It is manufactured by applying a plating process such as plating, finishing the plated surface by ultra-precision polishing, and sputtering a magnetic body.

The characteristics required of such an aluminum alloy substrate for a magnetic disk are that the surface precision after precision polishing or cutting is very good, the workability in polishing or the like is good, and the flatness of the entire aluminum alloy substrate is high. Good, good plating processability and zincate processability, no defects and unevenness after plating, few and small protrusions and holes that cause defects of the magnetic body,
It is a lightweight, non-magnetic material that has the strength to withstand processing during substrate fabrication and high-speed rotation during use.

As an aluminum alloy for a magnetic disk which satisfies the above-mentioned characteristics, a conventional alloy containing about 4% of Mg is used.
ISA 5086 alloy, aluminum alloy with improved plating properties by adding Cu and Zn to 5086 alloy is used,
Has received considerable praise in practical use.

However, as the density of the magnetic disk increases, requirements for defects and flatness of the substrate become more severe, and it becomes increasingly difficult to satisfy the requirements with conventional aluminum alloys. Many attempts have been made to improve conventional alloys. For example, while adding Cu and Zn, Al-Fe
An aluminum alloy substrate has been proposed which regulates the size and amount of an intermetallic compound containing as a main component, or an intermetallic compound containing Mg-Si as a main component, and has few defects after plating and can obtain a smooth plated surface. ing. (JP-A-2-11183
No. 9)

[0006] The addition of a very small amount of Cu of 0.05% or less, the Zn content is regulated to 0.1 to 1.5%, and the coexistence of these elements ensures uniformity and defect-free plating surface. An aluminum alloy substrate has also been proposed (JP-A-2-153).
No. 094), for the purpose of improving plating adhesion and reducing nodules and micropits on the plating surface, aluminum alloys for disks in which Cu is positively added and the size of the intermetallic compound is limited to 5 μm or less are also available. Proposed. (JP-A-2-159340)

Further, in order to obtain excellent flatness and eliminate surface defects after plating, Al-
Mg: 0.10 to 0.30%, Cu: 0.
An aluminum alloy sheet for a magnetic disk substrate is manufactured by containing 0.05 to 0.20% and Fe: 0.01 to 0.10% as essential components, and applying rapid heating and rapid cooling to intermediate annealing during the manufacturing process. It has also been suggested. (JP-A-7-331397)

In the manufacture of a magnetic disk substrate, a zincate treatment is performed before the plating treatment in order to increase the adhesion between the aluminum substrate and the plating layer. If the zincate treatment is non-uniform, unevenness occurs in the subsequent plating layer, and it is extremely important to finish the zincate uniformly. In the above conventional aluminum alloy substrate,
Even the slight unevenness generated by the zincate treatment often leads to unevenness (non-uniformity) after plating polishing, which causes a reduction in product quality and yield.

[0009]

SUMMARY OF THE INVENTION The present invention is based on the above-mentioned conventional aluminum alloy for magnetic disk substrates. And the composition of the aluminum alloy substrate for magnetic disks was pursued through various experiments, and the purpose was not to cause unevenness in the zincate treatment, and to be very good after plating. An object of the present invention is to provide an aluminum alloy for a magnetic disk which is excellent in zincate treatment property and can obtain various surface properties.

[0010]

The aluminum alloy for a magnetic disk excellent in zincate treatment according to the present invention for solving the above-mentioned problems is obtained by adding a trace amount of C to an Al-Mg alloy.
u, and precisely controlling the amount of addition to a specific range,
Further, it is basically based on coexistence of specific amounts of Zn and Fe.

That is, in the aluminum alloy for a magnetic disk of the present invention, Cu: 0.031% or more and less than 0.050%, Mg: 2.5-5.5%, Zn: more than 0.05% and 0.7% or more. %, Fe: 0.007% or more and less than 0.05%, Si as an impurity is 0.05% or less, Ti
Is limited to 0.01% or less, B is limited to 0.005% or less, and the first feature is that the balance consists of Al and impurities.

Further, Mn: 0.1 is added to the above components.
% Or less, Cr: 0.1% or less, V: 0.2% or less, and Be: 1 to 100
ppm as the second and third features.
0.85% ≧ Zn (%) + 5
A fourth characteristic is that Cu (%) ≧ 0.27%.

A fifth feature of the present invention is an aluminum alloy having the above composition, wherein the particle diameter of the Si—O-based nonmetallic compound present in the matrix of the aluminum alloy is 5 μm or less.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The components of the aluminum alloy for a magnetic disk according to the present invention and the reasons for limiting the same are described below. Cu is a component that functions to improve the non-uniformity of a zincate film. , Zincate crystals are finely and uniformly formed. The preferred content is 0.031% or more and less than 0.050%, and 0.03% or less.
If it is less than 1%, the zincate film is difficult to be dense, and the improvement effect is small. When the content exceeds 0.050%, the etching rate of the material is increased, and zinc oxide is likely to occur. Also, the corrosion resistance of the material is reduced.

[0015] Mg is an element necessary for obtaining the strength of the substrate itself, and its preferable content is in the range of 2.5 to 5.5%. If it is less than 2.5%, the grindability deteriorates and the strength is insufficient during processing and use. If it exceeds 5.5%, hot workability is reduced, and an Mg—Si-based compound is generated, which tends to cause plating defects. From the viewpoint of strength, it is preferably 3.5% or more, and is preferably 5% or less from the viewpoint of suppressing the formation of Mg-Si-based compounds.

Zn acts to improve the unevenness of the zincate film by coexisting with Cu. The preferable range of Zn content is more than 0.05% and 0.70% or less.
If it exceeds 0%, the etching rate of the material increases, so that zinc oxide is likely to occur, and the corrosion resistance of the material itself deteriorates. The more preferable content of Zn is 0.1 to
The range is 0.5%.

In the present invention, the uniformity of the zincate film is improved by the coexistence of Zn and Cu. However, this effect is due to the fact that Cu has a greater effect and that Cu has a greater effect on the reduction of corrosion resistance. Considering the above, in order to further effectively improve the zincate treatment property without deteriorating the corrosion resistance and obtain a dense and homogeneous zincate film, the relationship between the Cu content and the Zn content must be 0.85% ≧ Zn (% ) + 5C
It is preferable that u (%) ≧ 0.27%.

By coexisting a specific amount of Fe, the grindability is improved and the homogeneity of the zincate treatment is improved. The preferred content is in the range of 0.007% or more and less than 0.05%, and if the content is less than 0.007%, the effect is not sufficient.
Al-Fe-Si-based compounds are generated, and plating defects are likely to occur. The more preferable content range of Fe is 0.0
1 to 0.5%.

Mn, Cr and V are made to have uniform and fine crystal grains by adding one or more of these elements.
Improve grindability. The preferred content is Mn: 0.1
% Or less, Cr: 0.1% or less, V: 0.2% or less, and if added in excess of the upper limit, coarse intermetallic compounds increase and plating defects are likely to occur.

Be serves to prevent oxidation of the molten metal and to strictly control the Mg content. The preferred content is 10
The content is 0 ppm or less, and even if the content exceeds 100 ppm, the effect is saturated and no further remarkable improvement effect can be obtained.

In the present invention, it is important to strictly limit impurities in the aluminum alloy, in particular, Si, Ti and B. If the Si content exceeds 0.05%, coarse Mg-
Since a Si-based compound is generated and plating defects are likely to occur, Si is 0.05% or less, more preferably 0.03% or less.
%.

Ti and B are elements usually added for refining the cast structure of an aluminum alloy, and may be mixed as impurities when scrap is used.
If the content of Ti exceeds 0.01% and the content of B exceeds 0.005%, coarse intermetallic compounds increase and plating defects easily occur, so that Ti is 0.01% or less and B is 0.005% or less. Restrict to In addition, as other impurities, Zr, Ni,
If Pb or the like is less than 0.02%, it does not affect the properties of the aluminum alloy of the present invention.

An Al—Mg alloy is melted according to a conventional method.
In the case of casting, Si-O-based nonmetallic compounds are easily contained in the material due to the mixing of the furnace wall material and the release material, and when applied as a magnetic disk substrate, surface defects such as pits and blisters after plating are applied. May cause. Si- in the material
Most preferably, no O-based nonmetallic compound is included,
When a Si-O-based nonmetallic compound is present in the material matrix, it is necessary that the particle size (average of the major axis and the minor axis) be 5 μm or less.

The control of the above-mentioned Si-O type nonmetallic compound is as follows.
The adjustment is performed by adjusting the components in the alloy, in particular, controlling the Mg content, limiting the amount of Si as an impurity, and adjusting the conditions for homogenizing the ingot. By applying an aluminum alloy having a specific composition range and performing a homogenization treatment of the ingot under an adjusted condition in an atmosphere having an oxygen concentration lower than that of air enriched with nitrogen gas or inert gas, Si- The O-based nonmetal compound is reduced and miniaturized.

[0025]

Hereinafter, examples of the present invention will be described in comparison with comparative examples. Example 1 An aluminum alloy having the composition shown in Table 1 was ingot-formed by DC casting, the surface of the casting surface was cut, and then an ingot homogenization treatment was performed at 520 ° C. for 6 hours. Then 450 ° C
Hot rolling was started at this temperature, hot-rolled to a thickness of 4 mm, and cold-rolled to obtain a sheet material having a thickness of 0.8 mm.

From this plate material, an outer diameter of 96 mm and an inner diameter of 24 m
punch out a donut-shaped magnetic disk material
After annealing at 50 ° C. for 1 hour, grinding was performed to finish the surface. These magnetic disk materials were degreased, etched, and desmutted with a commercially available solvent, Ni-P plated after two zincate treatments, and mirror-finished by finish polishing.

With respect to the magnetic disk substrate manufactured through the above steps, the grindability (easiness of grinding) was relatively evaluated.
The condition of the zincate film and the surface condition after plating and final polishing were visually observed, and these were relatively evaluated. Also,
The number of minute defects after the final polishing was measured. These results
Table 2 shows the hardness of the material.

As shown in Table 2, the test material No. In Nos. 1 to 5, unevenness does not occur after plating and final polishing, and defects after polishing are hardly observed.
(The number of defects at the pass level is 2 / surface).
For No. 3, slight unevenness occurred during the zincate treatment, but no unevenness occurred after the final polishing.

[0029]

[Table 1] << Table Note >> Be content is ppm

[0030]

[Table 2] << Table Note >> Grindability: ○ (good) Zincate film condition: ○ (no unevenness) △ (slight unevenness) Surface condition after final polishing: ○ (no unevenness)

COMPARATIVE EXAMPLE 1 An aluminum alloy having the composition shown in Table 3 was ingoted by DC casting, processed in the same steps as in Example 1, and had a thickness of 0.1 mm.
8 mm plate material, punched into a donut shape as in Example 1, degreasing, etching, desmutting,
Two zincate treatments and Ni-P plating were performed, and mirror polishing was performed by finish polishing. In Table 3, those outside the conditions of the present invention are underlined.

With respect to the magnetic disk substrate manufactured through the above steps, the grindability (easiness of grinding) was relatively evaluated in the same manner as in Example 1, and the condition of the zincate film was visually observed.
By observing the surface condition after plating and final polishing, these were relatively evaluated. Further, the number of minute defects after the final polishing was measured. Table 4 shows these results together with the hardness of the material.

[0033]

[Table 3]

[0034]

[Table 4] << Table Note >> Grindability: ○ (good) △ (slightly bad) × (poor) Zincate film condition: ○ (no unevenness) △ (slight unevenness) × (with unevenness) Surface condition after final polishing: ○ ( (No unevenness) △ (slight unevenness) x (unevenness)

Test material No. No. 8 has a large amount of Fe, and the test material N
o. 6, 11, 13, 16 and 17 each have a large content of impurities Si, Mn, Cr, Ti and B and V, so that many fine defects occur after plating due to the formation of coarse intermetallic compounds. There has occurred. Test material No. 7 is Fe
The content is low. Test materials Nos. 9 and 10 did not have an appropriate Cu content. In Nos. 14 and 15, since the Zn content was not appropriate, unevenness occurred in the zincate treatment, and the unevenness remained after the final polishing. Note that no defect inspection was performed on the sample having unevenness after the final polishing.

Test material No. Test material No. 7 had a problem in grindability due to low Fe content. No. 12 has insufficient strength and poor grindability because the amount of Mg is small.

Example 2, Comparative Example 2 Aluminum alloy having composition of 4
After ingot casting was performed and the surface of the ingot was cut, ingot homogenization treatment was performed at 520 ° C. for 6 hours according to a conventional method. Then, hot rolling was started at a temperature of 450 ° C.
m, hot-rolled to a thickness of 0.8m
m plate material. (Test material No. 18)

No. 1 in Table 1. An aluminum alloy having the composition of No. 4 was ingot-formed by DC casting, the surface of the ingot was cut, and then the ingot was homogenized at 520 ° C. for 8 hours in a nitrogen gas-rich atmosphere. Then, hot rolling was started at a temperature of 480 ° C., hot-rolled to a thickness of 4 mm, and cold-rolled to obtain a 0.8 mm-thick plate. (Test material No.
19)

From these plates, an outer diameter of 96 mm and an inner diameter of 2 mm
A 4 mm doughnut-shaped magnetic disk material was punched out, annealed at 350 ° C. for 1 hour, and then ground with a grindstone to finish the surface. These magnetic disk materials are degreased, etched, and desmutted with a commercially available solvent, and subjected to Ni-P plating after two zincate treatments.
Mirror finishing was performed by finish polishing.

With respect to the magnetic disk substrate manufactured through the above steps, the particle size (average of the major axis and the minor axis) of the Si—O-based nonmetal compound in the substrate matrix was measured, and the condition of the zincate film was visually observed. By observing the surface condition after plating and final polishing, these were relatively evaluated. Further, the number of minute defects after the final polishing was measured. Table 5 shows the results.

[0041]

[Table 5]

[0042]

As described above, according to the present invention, no unevenness occurs after zincate treatment, and after plating and final polishing, uniform surface properties can be obtained without unevenness, which is sufficient for high-density substrates. The present invention provides an aluminum alloy for a magnetic disk substrate which can be applied to a magnetic disk.

Claims (5)

[Claims] 1. Cu: 0.031% (% by weight, the same applies hereinafter) to less than 0.050%, Mg: 2.5 to 5.5%,
Zn: more than 0.05% and 0.7% or less, Fe: 0.00
Containing 7% or more and less than 0.05%, Si as an impurity
0.05% or less, Ti 0.01% or less, B 0.0%
An aluminum alloy for a magnetic disk excellent in zincate treatment, characterized in that the content is limited to not more than 05% and the balance is Al and impurities. 2. Must contain at least one of Mn: 0.1% or less (excluding 0%, the same applies hereinafter), Cr: 0.1% or less, and V: 0.2% or less. The aluminum alloy for a magnetic disk according to claim 1, which is excellent in plating property. 3. The aluminum alloy for a magnetic disk excellent in zincate treatment according to claim 1, further comprising 1-100 ppm of Be. 4. The Cu content and the Zn content are 0.85
The aluminum alloy for a magnetic disk excellent in zincate treatment according to any one of claims 1 to 3, wherein a relation of% ≧ Zn (%) + 5Cu (%) ≧ 0.27% is satisfied. 5. An aluminum alloy having the composition according to claim 1, wherein the matrix of the aluminum alloy contains no Si—O-based non-metallic compound or the aluminum alloy has a Si—O-based non-metallic compound present in the matrix. An aluminum alloy for a magnetic disk having excellent zincate treatment properties, wherein the metal compound has a particle diameter (average of a major axis and a minor axis, hereinafter the same) of 5 μm or less.