JPH0347656A - 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 Cu, 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 0.001 - 1% Cu 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 Cu 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, and in particular improves the adhesion of electroless plating in base treatment plating, smoothes the plating surface, This makes it defect-free.

[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, polishing the surface, applying a mixture of magnetic powder and resin powder, and then heating it to form a magnetic film. It was getting worse.

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, N1-P alloy is electrolessly plated and then sputtered or plated to produce a magnetic material such as Co-N1.
-Magnetic disks coated with P alloy have come into use.

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 bi-sotho 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, I
Is 5086 alloy (Mg 3.5-4.5 wt%.

Fe≦0.5Qwt%, Si≦θ, 4[1wt%, M
n0.20~0.7wt%, CrIt, 05~
f1.25vt%, Cu≦0.10wt% Ti≦0.
l5wt%, Zn≦0.25wt%, Al balance) (
(Hereinafter, W1% is abbreviated as 96) or It^5086 alloy that controls impurities such as Fe and Si to reduce intermetallic compounds formed in the matrix, or It^5086 alloy that improves plating properties such as Cu and Zn. Alloys added to alloys are used.

[Problem to be solved by the invention J However, the substrate made of the moon 5A5086 alloy described above,
Since the adhesion of electroless plating, which is a base treatment for magnetic coating, is poor, there is a problem in that the electroless plating wave layer may peel off during the magnetic coating process or during use. Furthermore, the surface smoothness of electroless plating was not sufficient. Furthermore, intermetallic compounds fall off during zincate treatment, which is a pretreatment step for plating, and generate pits. If the electroless plating is about 20 μm thick, these pits will often disappear by subsequent broaching, but recently there has been a trend toward thinner plating, and even after plating and borsing, There have been cases where pits remain. Furthermore, although an aluminum alloy plate is punched to a predetermined size and then subjected to cutting or grinding, 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.

Furthermore, in conventional aluminum alloys for substrates, the reactivity during the pre-plating process is unstable, and local dissolution reactions occur during the process, often resulting in uneven unevenness even after plating. Ta. Such unevenness on the plating surface gives a cloudy appearance to the plating surface and is called a Claraday (cloud-like) defect.

These defects could be removed if the plating film was thick and the amount of polishing was large, but in recent years these defects have remained after polishing as the plating thickness has become thinner and the amount of polishing has decreased. has become a big problem.

[Means to solve the problem]

In view of the above, the present invention has been developed as a result of detailed studies on the behavior of various elements in aluminum alloys for substrates and their reactivity during plating processing. The dissolution reaction occurs uniformly in the pretreatment, and a thin and dense zincate film is formed.
We also found that it is necessary for the crystal grains to be structurally dense and for the growth of intermetallic compounds to be suppressed.Currently, adding a small amount of Cu has been considered effective for improving plating properties, but Cu It was discovered that by adding a small amount of and cooling at a relatively high rate during casting, the adhesion of the plating film, the smoothness of the plating surface, and the absence of defects, which were insufficient with conventional casting methods, were improved. However, as a result of further study, a method for manufacturing aluminum alloy for magnetic disk substrates was developed.

That is, one of the manufacturing methods of the present invention is that Mg2 to 7%, CuO1
It is characterized by casting an alloy with a plate thickness of 2 to 13 mm, containing 0.001 to 1.0%, and limiting the impurities to 0.15% or less of Si, 15% or less of Fe, and the remainder consisting of AI and unavoidable impurities. .

Another method of the present invention is that Mg2-7%, Cu0
．． 001 to 1%, and further M n 0.6% or less,
Contains one or more of the following: Cr013% or less, Zr0.3% or less, Ti0.2% or less, and S in the impurity.
iθ is limited to 15% or less, FeO2 is limited to 15% or less, and the alloy consisting of the remainder Al and unavoidable impurities is made into a plate with a thickness of 2 to 13 m.
It is characterized by being cast to m.

[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 for limiting its content to 2-7% is that if it is less than 2%, sufficient strength cannot be obtained, and if it exceeds 7%, IM-Mg intermetallic compounds are formed. At the same time, high-temperature oxidation during melting and casting increases the formation of non-metallic inclusions such as MgO, which causes pit defects, and the preferable range is 3 to 6%.

When Cu is dissolved in the material, it makes the reactivity of the alloy uniform in acid and alkaline solutions, makes the zincate film thin, uniform and dense, and then improves the adhesion of the electroless N1-P alloy plating film. and works to improve surface smoothness. Therefore, the Cu content was reduced to 0. The reason for limiting H to 1% is that below 0.0O1%, these effects are insufficient.
If it exceeds 1%, the reactivity in acid increases and the reactivity in alkaline solution is suppressed, which impairs the smoothness of the plating surface.The preferable range is 0.00.
It is 4 to 0.7%.

Mn, Cr, Zr, and Ti precipitate as fine compounds during homogenization treatment and/or during hot rolling and annealing, making the recrystallized grains finer, and the negative part dissolves in the matrix and increases its strength. Improve. 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, these contents should be reduced to Mn 0.6% or less, Cr 0.3% or less, and Zr 0.3%.
Below, we have limited Ti to one or more elements within the range of 0.2% or less, because if each upper limit is exceeded, excess elements will be removed during the molten metal treatment using a filter during casting and will be wasted. , coarse intermetallic compounds are generated, as well as alkali etching and zincate treatment.
It also falls off during cutting and polishing, resulting in pit defects.

Also, in the impurities Fe 0.15% or less, Si 0.15%
The following restrictions were made because Fe and Si hardly dissolve in solid solution in aluminum and precipitate as intermetallic compounds. This is because intermetallic compounds are present and easily fall off during cutting, polishing, and zincate treatment of the substrate, resulting in pit defects.

As for the internal impurity elements, if each is 0.1% or less, the properties of the aluminum alloy for magnetic disk substrates of the present invention are not affected.

Next, in the present invention, an alloy having the above composition is used with a plate thickness of 2 to 1 3
The purpose of casting in mm is to increase the solid solution amount of Cu, make the reactivity with acid and alkali uniform in the plating pre-treatment, adhere the zincate film thinly and densely, and improve the adhesion of the plating film and the smoothness of the plating surface. Improving sex, and even A
This is to suppress the growth of l-Cu-Mg-based and Al-Cu-Fe-based compounds and to prevent pits caused by their falling off. However, the reason why we limited the thickness of the cast plate to 2 to 13 mm is because if it is less than 2 mm, the solidification state will be unstable during casting.
This is because defects such as cracks and pinholes are likely to occur, and if the thickness exceeds 13 mm, the cooling rate in the casting process will be small (the above-mentioned effect will not be achieved).

Various casting methods such as a water-cooled roll method and a caster method are used for casting in the present invention, and regardless of which casting method is employed, the characteristics of the magnetic disk substrate will not be impaired. Further, heat treatment and processing after casting may be carried out by conventional methods.

Incidentally, the magnetic disk substrate manufactured by the manufacturing method of the present invention can also be used in a coated type.

〔Example〕

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

Example 1 Al ingots with a purity of 99.9% or higher were melted, and alloying elements were added thereto to produce the compositions shown in Table 1. This was degassed and filtered, and then cast using a water-cooled roll to a thickness of 5 mm and a width of 1100 mm. This cast plate was homogenized at 450° C. for 8 hours and then rolled into a plate having a thickness of 1.5 mm.

A disk with a diameter of 95 mm was punched out from this plate, annealed at 350°C for 2 hours, and then rough polished and finished polished to a mirror finish. These were degreased with a commercially available solvent, and
Etching was performed for 30 seconds with a 5% H2SO4 aqueous solution at °C, and smut removal was performed for 30 seconds with a 30% HNO3 aqueous solution at room temperature. Subsequently, zincate treatment is performed, and electroless N
After performing 1-P alloy plating, the surface smoothness was examined, and after final polishing, the appearance defects and adhesion of the plating film were examined, and these results were compared to the conventional 11SA508.
6 alloy (Mg4%, Mn0.5%, Cr0.2%, Fe
0.2%, Si 0.07%, Ti 0.01%.

A comparison with Zn0.01%, residual AI) 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 was then polished to a thickness of 2 μm by final polishing (side cloth polishing), resulting in a thickness of 13 μm.

Regarding surface smoothness, center line roughness Ra specified in IIS B 0601 was expressed as an average value of four points.

To determine the degree of surface defects, observe the surface using an optical microscope, and if local irregularities (pits, etc.) with a maximum length of more than 3 μm or aggregates thereof are observed, mark them with an X mark, or as unevenness. is not present, or even if it is present, it is 3μm
The following items are marked with a circle.

For adhesion, after final polishing, a 50 mm square sample was cut out and heated at 400°C for 30 minutes.
Immediately cool it with water to room temperature and check for peeling and blistering of the plating due to the difference in thermal expansion between the aluminum alloy and N1-P alloy. Those with no peeling or blistering are marked with ◎, those with slight peeling and blistering are marked with ○, and those with a large number of peelings and blisters are marked. Represented by an X. Note that ◎ and ○ marks pass, and X marks fail.

As is clear from Table 1, the plating surfaces obtained by the method of the present invention were smooth and defect-free.

It can be seen that the adhesion of the plating is excellent. On the other hand, it can be seen that those obtained by the comparative method outside the scope of the present invention are inferior in any one or more of the smoothness of the plating surface, the defect-free property, and the adhesion of the plating.

Example 2 A cast plate having the thickness shown in Table 2 was produced in the same manner as in Example 1, and processed in the same manner as in Actual Example 1 to a thickness of 1.5n+.
m, after forming a disk with a diameter of 95 mm, annealing, mirror finishing,
Plating treatment was performed, and the surface roughness after plating, surface defects after final polishing, and adhesion were evaluated in the same manner as in Example 1.

As is clear from Table 2, the products produced by the method of the present invention are excellent in surface roughness, surface defects, and adhesion. On the other hand, it can be seen that the comparative method in which the casting thickness is thicker is inferior in any one or more of surface roughness, surface defects, and adhesion.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to obtain a magnetic disk substrate with excellent plating surface smoothness and uniformity, and it is possible to achieve industrially remarkable results such as making it possible to increase the capacity and density of magnetic disks. It is effective.

Procedural support device (spontaneous) April 12, 1990 1゜Display of case 1999 Patent Application No. 178287 2゜Name of invention Method for manufacturing aluminum alloy for magnetic disk substrate 3, person making amendment Relationship with case Patent applicant address: 2-6-1 Marunouchi, Chiyoda-ku, Tokyo
Name: Furukawa Aluminum Industry Co., Ltd. 4, Agent address: 16 Kanda Kita Jorimono-cho, Chiyoda-ku, Tokyo 101 Ei Building 3rd floor (1) The word "f pit" is replaced with "1" in the fourth line from the bottom of page 2 of the statement. Correct with bit.

339-

Claims (2)

[Claims] (1) Contains Mg2-7wt%, Cu0.001-1wt%, Si0.15wt% or less, Fe0.15 among 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 limited to less than wt % and consisting of Al and unavoidable impurities. (2) Contains Mg 2 to 7 wt%, Cu 0.001 to 1 wt%, and further contains any one of Mn 0.6 wt% or less, Cr 0.3 wt% or less, Zr 0.3 wt% or less, Ti 0.2 wt% or less, or Contains two or more types, Si0 in impurities
．． Limited to 15 wt% or less, Fe 0.15 wt% or less,
An alloy consisting of the balance Al and unavoidable impurities is made into a plate with a thickness of 2 to 1
A method for manufacturing an aluminum alloy for magnetic disk substrates, which comprises casting to a thickness of 3 mm.