JPH02205651A - Aluminum alloy for magnetic disk base - Google Patents

Abstract

PURPOSE:To obtain the aluminum alloy free from surface flaws at the time of executing substrate treatment of finishing the surface into the specular one and after the coating of magnetic material by particularly regulating the content Ga of or the like as impurity elements in an Mg-contg. Al alloy. CONSTITUTION:An alloy contg. as the element to be added, by weight, 1 to 8% Mg, regulative contg. as inevitable impurities <=0.1% Si, <=0.1% Fe and <=150ppm Ga and the balance Al with other inevitable impurities is prepd. If required, one or both of <=1.0% Cu and <=2% Zn and one or more kinds among <=1.0% Mn, <=0.4% Cr, <=0.2% Zr and <=0.2% Ti are furthermore selectively added to the above compsn.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an aluminum alloy for magnetic disk substrates,
In particular, surface defects are less likely to occur after surface treatment and magnetic material coating.

[Conventional technology]

Magnetic disks used in computer storage devices include
Generally, a substrate made of an aluminum alloy whose surface is coated with a magnetic material is used.

Such magnetic disks are manufactured by processing a substrate to a predetermined thickness, mirror-polishing the surface, applying a mixture of magnetic powder and resin powder, and then heating it to form a magnetic film. It is made.

In recent years, magnetic disks have been required to have larger capacities and higher densities, and the magnetic area per bit on magnetic disks has become smaller and smaller, and it is also necessary to reduce the gap between the magnetic head and the magnetic disk. As a result, it has become desirable for magnetic films to be thinner and have improved wear resistance. For this reason, after processing the substrate to a predetermined thickness, the surface is mirror-finished, and then chromate treatment is applied as a base treatment for magnetic coating.
A magnetic disk has been proposed which is coated with a magnetic material, such as a Co-N1-P alloy, by zincate treatment, electroless plating, alumite treatment, etc., polishing, and then sputtering or plating.

The substrate of such a magnetic disk is required to have the following characteristics.

(1) It is non-heat treated and has sufficient strength to withstand various processing and high speed rotation during use.

(2) It is lightweight, a good mirror surface can be obtained by cutting and polishing, and surface defects such as pits do not appear.

(3) The surface should have excellent smoothness even after surface treatment, etc., and defects such as pits should not appear.

As a magnetic disk substrate that satisfies these characteristics, J
ISA5086 alloy (Mg3.5-4.5wt%, F
e50.50wt%, SiS2.40wt%, Mn0.
20-0.7wt%, Cr 0.05-0.25wt%
, Cu≦0.10wt%, TiS2.15wt%, Zn
≦0, 25wt%, AP balance) or JISA508
Conventional alloys such as 5086 are alloys in which impurities such as Fe and Sl in 6 alloys are regulated to reduce the amount of metal compounds formed in the matrix, or An-Mg-based alloys in which additive elements Mn and Cr are regulated to a low level. In alloys and various developed alloys, impurities in the alloy, especially elements that tend to form relatively coarse intermetallic compounds such as Fe and Sl, are controlled to a low level in order to eliminate micro defects on the surface such as pits. . However, although micro defects such as surface pits are reduced in substrates made of these alloys, they are not necessarily at a satisfactory level. The reason for this is that even the highest purity AI2 metal of industrial purity is 99.99wt%.
Since the general metal used in alloys for magnetic disks is 99.9% to 99.99wt%, even at such purity, intermetallic compounds such as Fe etc. Therefore, although the occurrence of microscopic surface defects due to the shedding of such intermetallic compounds can be reduced by regulating impurities, it cannot be completely eliminated. As a result of detailed observation and examination of the relationship between the metal structure and the metal structure, the following findings were obtained. In other words, ■ All of the intermetallic compounds present in the material do not become surface defects such as pits, but compounds that become defects due to falling off, etc., remain without falling off even after processes such as cutting, and do not become defects. There are compounds.

■Furthermore, the ratio of compounds that cause defects to compounds that do not cause defects varies depending on the material (manufacturing loft).

■Regarding the size of compounds, those with a size of 15 μm or more are likely to cause surface defects regardless of the material, but it is difficult to see a correlation between whether compounds with a size smaller than that cause defects or not.

■ Even in the matrix, where the presence of intermetallic compounds was not confirmed, some materials were found to have extremely small defects after various processing. However, since such defects were extremely small, they did not pose a problem in the product.

In view of these facts, we became convinced that other factors were acting on the compounds that caused surface defects, making them more likely to fall off. Therefore, these intermetallic compounds were investigated in more detail, and the differences in composition and manufacturing conditions between materials that are prone to defects (manufacturing lofts) and materials that are less likely to cause defects were investigated.

As a result, a trace amount of Ga, which is normally included as an impurity in the material,
It has been found that when the intermetallic compound exists at the interface between the intermetallic compound and the matrix, the intermetallic compound is very likely to fall off, causing surface defects. Further, when the Ga content is high, minute bits may be formed even in the matrix.

The present invention has been made based on these findings.

That is, the first alloy of the present invention contains Mg1 to 8w as an additive element.
t%, and contains Sin as an impurity element.

1wt% or less, F e 0.1wt% or less, Ga 1
It is an aluminum alloy for magnetic disk substrates, which is regulated to 50pp- or less, and the remainder consists of other unavoidable impurities and Al.The second is Mg as an additive element.
1 to 8 wt%, and as an impurity element, Si0.1
wt% or less, Fe 0.1wt% or less, Ga 15
The aluminum alloy for magnetic disk substrates is regulated to 0 ppm or less and further contains one or two of Cu 1.0 wt% or Zn 2 wt% or less, and the balance is other unavoidable impurities and Al. , contains 1 to 8 wt% Mg as an additive element, and S as an impurity element.
i 0.1wt% or less, Fe 0.1wt% or less, G
a Regulated to 150pp- or less, and furthermore Mn1, OwL
% or less, Cr0.4wt% or less, Zr0.2wt% or less, Ti0.2i1t% or less, and the remainder is other unavoidable impurities and A.
The fourth is an aluminum alloy for magnetic disk substrates characterized by consisting of Mg1 to Mg1 as additive elements.
8 wt%, and as an impurity element, S i 0.
1wt% or less, F e 0.1wt% or less, Ga 1
50pp- or less, and any one or two of Cu1.0wt% or less, Zn2wL% or less, and M
n 10wt% or less, Cr 0.4wt% or less, Z r
An aluminum alloy for substrates of magnetic disks, which selectively contains one or more of 0.2wt% or less and 0.2iit% or less of TI, with the remainder consisting of other unavoidable impurities and Al. be.

[For production]

The reason why the alloy composition of the present invention alloy is limited to the above range is as follows (hereinafter -1% is simply abbreviated as %).

Mg is mainly used to obtain strength, and the reason why we limited its content to 1 to 8% is because if it is less than 1%, sufficient strength cannot be obtained, and as a result, Mg is (The straightness and acceleration characteristics of the magnetic head during rotation deteriorate.) If it exceeds 8%, Al-Mg intermetallic compounds are formed and non-metallic particles such as MgO are formed due to high temperature oxidation during melting and casting. This is because the formation of particles becomes significant and causes pit defects.

Regardless of the amount, Ga is unavoidably contained as an impurity in aluminum base metals and master alloys.According to research by the inventors, it is several hundred ppm in ordinary aluminum alloys, and in conventional memory disks. Even high-purity alloys used for the like generally contain about 100 to 300 pp- or more.

Until now, there had been no particular problem with aluminum alloys for magnetic disk substrates, so no regulations had been established regarding the Ga content. However, as mentioned above, research by the inventors has revealed that the Ga content causes surface defects. This is because Ga preferentially exists at the interface between the matrix and the intermetallic compound or at the grain boundaries, making the core brittle. Further, when the Ga content is large, Ga may cause microscopic aggregation within crystal grains. If a part weakened by Ga exists on or near the surface,
This portion is prone to surface defects.

When Ga exceeds 150ppρ■, such surface defects increase, so Ga is preferably 150pp- or less.
It is desirable to keep it below ppm.

Pretreatment such as zincate treatment and N1
- When performing electroless plating of hard non-magnetic metals such as P, it is necessary to add Zn and/or Cu.

Zn is a necessary element when performing zincate treatment as a base treatment for the magnetic disk base according to the present invention, and the reason why its content is limited to 2% or less is because if it exceeds 2%, rolling workability and corrosion resistance will decrease. This is because, especially in the plating process, the corrosion resistance of the material is poor, resulting in non-uniform zincate treatment, which reduces the adhesion of plating and the smoothness of the surface. By setting the Zn content within the above range, the amount of Al dissolved during the zincate treatment can be reduced and the smoothness during subsequent electroless plating can be improved.

Addition of Cu reduces the amount of Al dissolved during zincate treatment,
Furthermore, in order to adhere the zincate film thinly, uniformly and densely to improve the surface smoothness of the subsequent electroless plating, C
The reason why the u content is limited to 1.0% or less is that if the u content exceeds 1.0%, the rolling workability and corrosion resistance will be reduced, and the corrosion resistance of the material will be poor especially in the plating process, resulting in uneven zincate treatment. This is because the adhesion of the plating and the smoothness of the surface become poor.

Mn, Cr, Zr, and TI precipitate as fine compounds during homogenization treatment, hot rolling, and annealing, and refine the recrystallized grains, and some of them dissolve in the matrix to improve its strength. At the same time, it has the effect of improving the adhesion of electroless plating, and their interaction contributes to improving the cutting and polishing properties of the substrate and the adhesion of the N1-P plating film. If the above upper limit is exceeded, not only will excess elements be removed during the molten metal treatment using a filter during casting, resulting in waste, but also coarse intermetallic compounds will be generated, which will require not only alkali etching and zincate treatment, but also cutting and polishing. It also falls off during application, resulting in pit defects.

These Mn, Cr, Zr, and Ti may be added alone or in combination depending on the purpose.

Fe and Si, which are impurity elements each limited to 0.1% or less, are hardly dissolved in aluminum and precipitate as intermetallic compounds, but if their amounts are large, Al1-Fe system, This is because a large number of coarse intermetallic compounds such as Alfi-Fe-31 systems are present and easily fall off during cutting, polishing, zincate treatment, etc. of the substrate, resulting in pit defects.

Furthermore, if the other impurity elements are each 0.1% or less, they do not affect the properties of the alloy of the present invention.

It is desirable that the maximum diameter of the intermetallic compounds contained within 1 m of the alloy of the present invention be 15 μm or less.As mentioned above, the intermetallic compounds tend to fall off during cutting and cause pit defects. This is because the risk increases if the maximum diameter exceeds 15 μm. It is preferably 10 μm or less.

〔Example〕

Commercially available A1 metal with a purity of 99.5% or more is melted, alloying elements are added to it to prepare a molten alloy having the composition shown in Table 1, degassing and settling are performed, and then filtered. Then, the ingot was water-cooled and cast to obtain an ingot with a thickness of 350 mm, a medium size of 1000 mm, and a length of 2000 mm.

After facing both sides of this ingot, IOW on each side,
After soaking at a temperature of 80±30° C. for about 6 hours, the material was hot-rolled and then cold-rolled according to a conventional method to obtain a plate having a thickness of 1.5 cm.

A disk with a diameter of 95 cm was punched out from this plate material and heated at 350℃ for 2 hours.
After time annealing, rough polishing and final polishing were performed to create a mirror finish. The surfaces of these test materials were observed using an optical microscope, and the maximum diameter of intermetallic compounds was measured and the presence or absence of surface defects such as bits and scratches was investigated. The results are shown in Table 2.

As is clear from the above results, the alloy material of the present invention has virtually no defects such as pits, and the comparative material, which is outside the scope of the present invention,
It was also confirmed that the material had superior properties compared to the conventional JIS A3086 alloy material.

Inventive alloy! ! No. 12, Na3 (added with Zn and Cu) was subjected to zincate treatment and electroless NiP plating treatment, and as a result, the plating properties were good.

Table [Effects of the Invention] As stated above, when the alloy of the present invention is used as a magnetic disk substrate, even if the surface is polished to a mirror finish, surface defects such as bits do not occur, and the subsequent surface treatment It also has excellent effects such as not causing defects in other applications.

Claims (4)

[Claims] (1) Contains 1 to 8 wt% of Mg as an additive element, and 0.1 wt% or less of Si and 0.1 w of Fe as impurity elements.
An aluminum alloy for magnetic disk substrates, characterized in that the content of Ga is limited to 150 ppm or less, and the remainder consists of other unavoidable impurities and Al. (2) Contains 1 to 8 wt% of Mg as an additive element, and 0.1 wt% or less of Si and 0.1 wt% of Fe as impurity elements.
% or less, Ga150ppm or less, and Cu1
．． Any one or two of 0wt% or less Zn2wt% or less
An aluminum alloy for magnetic disk substrates, characterized in that it contains seeds, and the remainder consists of other inevitable impurities and Al. (3) Contains 1 to 8 wt% of Mg as an additive element, and 0.1 wt% or less of Si and 0.1 wt% of Fe as impurity elements.
% or less, Ga150ppm or less, and Mn1
．． 0wt% or less, Cr0.4wt% or less, Zr0.2w
An aluminum alloy for magnetic disk substrates, characterized in that it selectively contains one or more elements of 0.2wt% or less of Ti and 0.2wt% or less of Ti, with the remainder consisting of other unavoidable impurities and Al. (4) Contains 1 to 8 wt% of Mg as an additive element, and 0.1 wt% or less of Si, 0.1 wt% of Fe as an impurity element.
% or less, Ca150ppm or less, and Cu1
．． 0wt% or less, any one or two of Zn2wt% or less, Mn1.0wt or less, Cr0.4wt% or less,
An aluminum alloy for a substrate of a magnetic disk, which selectively contains one or more of Zr 0.2 wt% or less and Ti 0.2 wt% or less, with the remainder consisting of other inevitable impurities and Al.