JPH0347655A - Manufacture of aluminum alloy for magnetic disk base - Google Patents

Abstract

PURPOSE:To realize large capacity and high speed of a magnetic disk by casting an alloy of the specific plate thickness containing the specific concn. ranges of Mg and Zn, limited to the specific concn. or lower of Si and Fe in impurities and consisting of the balance Al with inevitable impurities. CONSTITUTION:The alloy containing 2 - 7wt.% Mg and 0.05 - 1.5% Zn and limited to <=0.15% Si and <=0.15% Fe in the impurities and consisting of the balance Al with inevitable impurities, is cast to 2 - 13mm plate thickness. After working the base to the prescribed thickness, specular finishing is executed to the surface and after that, non-electrolytic plating of non-magnetic hard metal, e.g. Ni-P is executed as the surface treatment for magnetic body coating. As improvement of plating, addition of a little quantity of Zn is effective. After that, this is made to the magnetic disk coated with the magnetic body, e.g. Co-Ni-P alloy by spattering or plating. By this method, the plating surface of the obtd. magnetic disk base has excellent flatness and uniformity, and the large capacity and high density of the magnetic disk can be obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing an aluminum alloy for magnetic disk substrates. 1. In particular, it improves the adhesion of electroless plating in base treatment plating and smoothes the surface after plating. , to eliminate defects.

[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 capacity and higher density, and the magnetic area per pit on a magnetic disk 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 abrasion resistance. For this reason, after processing the substrate to a predetermined thickness, the surface is mirror-finished, and then a hard non-magnetic metal is used as a base treatment for magnetic coating.
For example, a magnetic disk is used which is electrolessly plated with N1-P and then coated with a magnetic material, such as a Co-N1-P alloy, by 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 polishing, and surface defects such as pits do not appear.

(3) The adhesion and surface smoothness of electroless plating, which is the base treatment, are excellent, and defects such as pits do not appear even after plating.

As a magnetic disk substrate that satisfies these characteristics, J
IS 5086 alloy (Mg3.5-4.5w1%.

Fe≦0.50wt%, Si≦0.4Gvt%, Mn
0.20-0.7wt%, Cr 0.05-0.2
5w+%, Cu≦0.10wt%, T i <0.
15w1%, Zn≦tt, 25wt%, Ad balance) (hereinafter wt% is abbreviated as %) or J I S A 5
Used are alloys in which impurities such as Fe and 81 in the 086 alloy are regulated to reduce the amount of metal compounds formed in the matrix, and alloys in which Cu and Zn are added to the 5A5086 alloy to improve plating properties.

[Problem to be solved by the invention]

However, the substrate made of the above-mentioned IiS 5086 alloy has a problem that the electroless plating coating, which is a base treatment for the magnetic material coating, has poor adhesion, so the electroless plating coating may peel off during the magnetic material coating process or during use. was there. Furthermore, the surface smoothness of electroless plating was not sufficient. Furthermore, intermetallic compounds fall off during zincate treatment, which is a pretreatment step before knocking, and generate pits. If the electroless plating thickness is about 20 μm, these pits will often disappear by subsequent polishing, but
Recently, there has been a trend toward thinner plating, and there have been cases where pits remain even after boxing polishing after plating.

Furthermore, an aluminum alloy plate is punched to a predetermined size and then subjected to cutting or grinding, but intermetallic compounds may fall off during this process, resulting in pit defects. In order to improve the plating properties of magnetic disks, there is a strong desire to reduce the number and size of intermetallic compounds in the aluminum alloy used for the substrate, and various measures have been taken, but the results have not always been satisfactory. was not obtained.

In addition, with respect to conventional plating alloys, the reactivity during the plating pretreatment process was unstable, and local dissolution reactions occurred during the treatment, often resulting in uneven unevenness even after plating. In severe cases, smoothness was impaired over the entire surface.

Such unevenness on the plating surface gives a cloudy appearance to the plating surface and is called a Claraday (cloud-like) defect. This defect has a thick plating film,
It was possible to remove the defects when the amount of polishing was large, but in recent years, as the plating thickness has become thinner and the amount of polishing has been reduced, the persistence of these defects after polishing has become a major problem.

[Means to solve the problem]

In view of this, the present invention has been developed based on a detailed study of the behavior of various elements in the alloy and their reactivity during plating treatment.
In order to improve the adhesion of 1-P alloy plating and the smoothness of the plating surface, the dissolution reaction occurs uniformly in the pretreatment, the zincate film is thin and densely adhered, and the crystal grains are fine in structure, and the metal It was found that it is necessary that the growth of interstitial compounds be suppressed. Conventionally, Z is used to improve plating performance.
Adding a small amount of r+ is said to be effective, but by adding a small amount of Zn and cooling at a relatively high rate during casting, the adhesion of the plating film and the surface of the plating, which were insufficient with conventional casting methods, can be improved. It was confirmed that smoothness and defect-free properties were improved, and as a result of further studies, a method for manufacturing an aluminum alloy for magnetic disk substrates was developed.

That is, one of the manufacturing methods of the present invention is Mg 2 to 7%.

Contains Z n 0.05-1, 5%, and Si0.
Regulated to 15% or less, FeG, 1596 or less, remaining AA
This method is characterized by casting an alloy consisting of the above and unavoidable impurities to a thickness of 2 to 13 mm.

Another method of the present invention is Mg2 to 7%,
Contains Z n 0.05 to 1.5%, and further contains M n 0.
6% or less, Cr0.3% or less, Zr0.3% or lessT +
0.296 or less, Si is regulated to 0.15% or less, Feθ is 15% or less, and the balance is Al and unavoidable impurities. It is characterized by being cast to 13 mm.

[Effect]

The reason why the alloy composition is limited as described above in the present invention is as follows.

Mg is mainly used to obtain strength, and the reason why we limited its content to 2 to 7% is because if it is less than 2%, sufficient strength cannot be obtained, and if it exceeds 7%, Al-Mg intermetallic compounds are formed. At the same time, the formation of non-metallic inclusions such as MgO becomes significant due to high-temperature oxidation during melting and casting, which causes pit defects, and the preferable range is 3 to 6%.

When Zn is dissolved in a material, it makes the reactivity of the alloy uniform in acid and alkaline solutions, and also allows a thin, uniform and dense zincate film to be deposited on the subsequent electroless N1-P.
It works to improve the adhesion and surface smoothness of the alloy plating film. However, the Zn content was limited to 0.05 to 1.5% because these effects are insufficient if it is less than 0.05%, and if it exceeds 1.5%, rolling workability and corrosion resistance are reduced. This is because, especially in the plating process, the corrosion resistance of the material is poor, making the zincate treatment non-uniform and reducing the adhesion of the plating and the smoothness of the surface.

One or more of Mn, Cr, Zr, and Ti precipitate as fine compounds during homogenization treatment and/or during hot rolling and annealing, refine the re-solidification grade, and some of them Solid solution in the matrix and improves its strength. These effects improve the cutting and polishing properties of the substrate, and the grain refinement and solid solution of these elements in the matrix also improve the adhesion of the electroless N1-P alloy plating film. However, M n 0.6% or less Cr 0.3% or less,
The reason why Zr is limited to 13% or less and Ti is limited to 0.2% or less is that if the upper limit is exceeded, not only will excess elements be removed and wasted during the molten metal treatment using a filter during casting, but also coarse intermetallic compounds will be generated. This is because the particles fall off and form pit defects not only during alkali etching and zincate treatment, but also during cutting and polishing.

The impurities were limited to 0.15% or less of Fe and 0.15% or less of Si because Fe and Si hardly dissolve in solid solution in aluminum, but precipitate as intermetallic compounds, and if their amounts are large, Al-Fe system This is because they exist in large numbers as coarse intermetallic compounds such as Al-Fe-8i, and easily fall off during cutting, polishing, and zincate treatment of the substrate, resulting in pit defects. If each of the impurity elements is 0.1% or less, it will not affect the characteristics of the magnetic disk substrate.

Next, in the present invention, the casting method was specified by increasing the amount of solid solution of Zn, making the reactivity by acid and alkali uniform in the plating pre-treatment, and depositing a thin (dense) zincate film, which resulted in the plating. This is to improve the adhesion of the film and the smoothness of the plating surface, and to suppress the growth of AA-Zn-Mg-based 2Mg-Zn-based compounds and prevent pits caused by their falling off.

However, the thickness of the cast plate was specified as 2 to 13 mm.
This is because if it is less than 13 mm, the solidification state becomes unstable during casting and defects such as cracks and pinholes are likely to occur, and if it exceeds 13 mm, the cooling rate in the casting process will be low and the above-mentioned effect will not be achieved.

In the present invention, there are various methods for casting the plate to a thickness of 2 to 13 mm, such as the water-cooled roll method and the caster method, but whichever method is adopted, the characteristics of the magnetic disk substrate of the present invention will not be impaired. do not have. Further, heat treatment and processing after casting are carried out by conventional methods.

The magnetic disk substrate according to the present invention can be used not only as a magnetic disk substrate coated with a magnetic material but also as a coated type magnetic disk substrate.

〔Example〕

The present invention will be described below with reference to Examples.

Example 1 An A5 ingot with a purity of 99.9% or higher was melted, and alloying elements were added thereto to produce the composition shown in Table 1. After degassing this, it was filtered and cast into a plate material with a thickness of 6 mm and a width of 1100 mm using a water-cooled roll. This is 4
After homogenizing at 50°C for 8 hours, it was rolled to a thickness of 1.
It was made into a 5 mm plate material.

A disk with a diameter of 95 mm was punched out from this plate material and heated at 350°C.
After annealing for 2 hours, rough polishing and final polishing were performed to give a mirror finish. Degrease these with a commercially available solvent,
Etching was performed for 30 seconds with a 5% H2So4 aqueous solution at 70°C, and smut was removed for 30 seconds with a 30% HNO3 aqueous solution at room temperature. Subsequently, zincate treatment was performed, electroless N1-P alloy plating was performed, and the smoothness of the surface was examined.Furthermore, after finishing polishing, the appearance defects and adhesion of the plating film were examined. These results can be compared to the conventional monthly S
^5086 alloy (Mg4%, Mn0.5%, Cr0.2
%, Fe0.2%, Si0.07%.

A comparison with 0.01% Ti, 0.0196 Zn, and 0.0196% Al (I residual) is also listed in Table 1.

In addition, for zincate treatment, Arp 302ZN (product name)
Electroless N
1-P alloy plating was carried out using Knife Lad 719 (trade name: Okuno Pharmaceutical Co., Ltd.). The electroless N1-P alloy plating had a thickness of 15 μm, and after that, a polishing allowance of 2 μm was removed by final polishing (side cloth polishing), and the thickness was finished to 13 μm.

Regarding the surface smoothness, the center line roughness Ra specified by N5BO6fil was expressed as the average value of four points. The degree of surface defects can be determined by observing the surface using an optical microscope.
Items with concave or convex local unevenness (pits, etc.) or aggregates thereof with a maximum length exceeding 3 μm are recognized as X.
If there is no unevenness, or if there is unevenness, the size is 3 μm or less, it is indicated by a circle. For adhesion, after final polishing, cut out a 50mm square sample and use 400mm square samples.
Heat for 30 minutes at a temperature of °C and immediately cool with water to room temperature.
Peeling and blistering of the plating caused by the difference in thermal expansion between the 4 alloy and the N1-P alloy were investigated, and those with no peeling or blistering were marked with ◎, those with slight peeling and blistering were marked with ○, and those with a large amount of peeling and blistering were marked with X (◎ ○ marks pass, x marks fail).

As is clear from Table 1, the method according to the present invention:
It can be seen that the plating surface has excellent smoothness, no defects, and adhesion of the plating compared to the conventional method. On the other hand, it can be seen that those obtained by a comparative method outside the scope of the present invention are inferior in one or more of surface roughness, surface defects, and adhesion.

Example 2 Cast plates having the thicknesses shown in Table 2 were produced in the same manner as in Example 1 using the alloys shown in Table 2. This was processed in the same manner as in Example 1 to a thickness of 1.5 mm.

After making a disk with a diameter of 9.5 mm, it was annealed and finished to a mirror finish.

Plating treatment was performed, and the surface roughness after plating, appearance defects after final polishing, and adhesion were evaluated. The results are also listed in Table 2.

As is clear from Table 2, the samples produced by the method of the present invention are superior in surface roughness, surface defects, and adhesion than those produced by the comparative method, which is outside the scope of the present invention.

〔Effect of the invention〕

As described above, according to the present invention, the plating surface of the obtained magnetic disk substrate has excellent smoothness and uniformity, making it possible to increase the capacity and density of magnetic disks, and achieve remarkable industrial effects. It is something.

Claims (2)

[Claims] (1) Mg2-7wt%, Zn0.05-1.5wt%
Contains Si0.15wt% or less, Fe0.1 in impurities
A method for manufacturing an aluminum alloy for a magnetic disk substrate, characterized by casting an alloy with a thickness of 2 to 13 mm, with the balance being regulated to 5 wt% or less and consisting of Al and unavoidable impurities. (2) Mg2-7wt%, Zn0.05-1.5wt%
Contains Mn0.6wt% or less, Cr0.3wt%
The following contains one or more of Zr 0.3wt% or less and Ti 0.2wt% or less, and Si in the impurity.
The alloy is regulated to 0.15 wt% or less, Fe 0.15 wt% or less, and the balance is Al and unavoidable impurities.
A method for manufacturing an aluminum alloy for magnetic disk substrates, which comprises casting to a thickness of 13 mm.