JPH02179924A - Production of aluminum alloy plate for magnetic disk substrate - Google Patents

Abstract

PURPOSE:To improve polishing property of an Al-Mg aluminum alloy plate after annealed by wrapping and sealing the plate with an aluminum foil of >=99.0wt% purity and then annealing it. CONSTITUTION:On annealing the Al-Mg aluminum alloy plate, the plate is wrapped and sealed with an aluminum foil of >=99.0wt% purity and then annealed. For example, an aluminum alloy plate after deposited is sealed with aluminum foil of >=99.0wt% purity wrapping around the side, front and back surfaces thereof. This aluminum foil prevents oxygen fro entering onto the surface of the aluminum alloy plate during annealing. It also preferentially oxidizes during annealing to absorb oxygen existing in the inside of the package and to inhibit formation of a hard MgO layer caused by high temp. oxidation of the surface of the aluminum alloy plate. Thereby, polishing property of the plate after annealed is improved.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method for manufacturing an aluminum alloy plate to serve as a substrate for a magnetic disk, and in particular to an aluminum alloy plate for a magnetic disk substrate with improved processing and polishing properties after annealing. The present invention relates to a manufacturing method.

(Prior Art) A magnetic disk generally has a structure in which the surface of a substrate made of an aluminum alloy is coated with a magnetic material, and signals are recorded by magnetizing the magnetic coating. Good surface precision (small roughness, waviness, etc.) is required to ensure stable flying of the magnetic head and stability of recording characteristics.

Conventionally, there are 50 materials for such magnetic disk substrates.
An Al-Mg alloy such as 86 alloy is used, and after the so-called laminated annealing, in which substrates are punched out into circular shapes from this material are laminated and annealed, they are polished with a grindstone to achieve the required surface precision. .

(Problems to be Solved by the Invention) In the above-mentioned prior art, the At-Mg alloy has poor polishability (such as polishing residue and damage to the grinding wheel;
Clogging is likely to occur (it is extremely difficult to achieve a specified surface precision with one polishing. Therefore, in general,
Pre-polishing using a coarse-grained grindstone removes the hard surface layer and prepares the surface, followed by final precision polishing, but this has the disadvantage of lowering productivity and increasing manufacturing costs.

Therefore, as an annealing method to prevent high-temperature oxidation, a vacuum furnace or an inert atmosphere furnace can be used, but the equipment cost is high and it is not practical.

(Means for Solving the Problem) As a result of extensive research in view of the above-mentioned problems, the present inventors found that packaging with aluminum foil suppresses the formation of a hard surface layer during annealing of an Al-Mg alloy plate. According to this, the polishability after annealing is improved, it is possible to finish the surface to a specified level of precision with one polishing, and it is possible to manufacture aluminum alloy plates for magnetic disk substrates at low cost. Based on this knowledge, we have completed the present invention.

That is, the invention provides an aluminum alloy plate for a magnetic disk substrate, characterized in that when an Al-Mg-based aluminum alloy plate is annealed, the alloy plate is tightly wrapped with aluminum foil having a purity of 99.0 wt% or more. A manufacturing method is provided.

First, the aluminum alloy plate used in the present invention will be described. The aluminum alloy plate may be one containing substantially only Mg as an alloy component.

Mg is an essential element for imparting mechanical strength sufficient to withstand machining, polishing, etc. during substrate production, and its content is preferably 3 to 6 wt%. If the Mg content is too low, sufficient strength cannot be obtained, and if it is too high, Al
-Mg intermetallic compounds are produced, and MgO is significantly produced due to high-temperature oxidation during melting and casting, resulting in poor polishability.

Alloy components other than Mg have no direct relationship to the effects of the present invention, and any alloy components may be included as long as they do not have an adverse effect on general properties. A preferred alloy used in the present invention is 5086 alloy, and it is desirable that the alloy components other than Mg be as small as possible.

In the present invention, an alloy having the above composition is cast by a conventional method,
After soaking, hot rolling, and cold rolling, the aluminum alloy plate is punched into an annular shape to produce an aluminum alloy plate.

Next, the aluminum alloy plate is annealed, and the annealing method will be explained.

When annealing aluminum alloy plates, lamination annealing, which has been conventionally performed, is most advantageous in terms of efficiency, and the present invention can also use conventional techniques in this respect. After these aluminum alloy plates are laminated, their side surfaces, upper and lower surfaces are tightly wrapped with aluminum foil having a purity of 99.0 wt% or more. This aluminum foil.

As a result of the inventors' studies, the supply of enzymes to the surface of the aluminum alloy plate during annealing is cut off, and the oxygen present inside the packaging is absorbed through preferential oxidation during annealing, and the MgO It has the effect of suppressing the formation of a hard layer.

Improves polishability after annealing. The number of stacked aluminum alloy plates may be determined as appropriate depending on the volume of the furnace, and the annealing temperature is preferably 200 to 450°C and the annealing time is preferably 0.5 to 6 hours. It is better to perform annealing while applying a load to the plate surface of the laminated aluminum alloy plate for the purpose of removing plate distortion caused by cutting and machining. In this case, the initial load is about 1 to 20 tons per surface. is preferred. Note that the aluminum foil preferably has a thickness of about 10 μm.

As the heating means for annealing, any heating means can be employed as long as there are no disadvantages in terms of temperature control.

After the above-mentioned annealing, the surface of the aluminum alloy plate is smoothed, and this can be done by precision polishing using a fine-grained grindstone, precision cutting using a natural diamond cutting tool, or coining process described in JP-A-62-158532. Examples include, but are not limited to, any method that can smooth the surface of the aluminum alloy plate.

In the present invention, for example, preliminary polishing using a coarse grindstone is not required before precision polishing.

(Example) The present invention will be explained in more detail below based on examples.

Aluminum alloy with the composition shown in Table 1 (J I 5A5
086 alloy) was cast, face-side, soaked, hot-rolled, and cold-rolled according to a conventional method to obtain a plate having a thickness of 2 m111. From this cold-rolled plate with a thickness of 2 mm, the outer diameter is 10 mm and the inner diameter is 25 mm.
A donut-shaped disk was punched out. Seventy of these donut-shaped disks were stacked one on top of the other to correct rolling strain, and after being tightened with a load of 8 tons on a surface plate, one remained as it was (
(conventional method), and the other was tightly packed with pure aluminum foil (method of the present invention), and heated to 360°C in a conventional batch air oven.
It was annealed for 2 hours. Regarding these treated materials, the oxygen content and micro Vickers hardness of the plate surface were measured.

Furthermore, the polishability (finished state) was evaluated when final polishing was performed using a fine-grained whetstone without preliminary polishing.

These results are shown in Table 2.

From Table 2, it is clear that in the present invention, high-temperature oxidation of the plate surface during annealing is suppressed, the surface hardness is low (and the polishability during polishing is thicker), and the present invention is improved compared to the conventional method. be.

(Effects of the Invention) According to the present invention, an aluminum alloy plate for magnetic disk substrates can be obtained which has significantly superior polishability during polishing after annealing compared to conventional methods, and productivity can be increased by omitting the preliminary polishing step. This has excellent effects in that it is possible to improve performance and reduce manufacturing costs.

Patent applicant: Furukawa Aluminum Industry Co., Ltd. Kawa Thii Steel Co., Ltd. Table 1 Table 2

Claims (1)

[Claims] A method for producing an aluminum alloy plate for a magnetic disk substrate, which comprises: annealing an Al-Mg-based aluminum alloy plate by tightly packaging the alloy plate with aluminum foil having a purity of 99.0 wt% or more;