JPS62263955A - Manufacture of aluminum alloy sheet for magnetic disk - Google Patents

Abstract

PURPOSE:To improve strength and surface accuracy, by subjecting a cast plate of Al alloy in which Mg and Be are specified and the amounts of Si, Fe, Mn, Cr, and Ti are limited to annealing under prescribed conditions prior to cold rolling. CONSTITUTION:The Al alloy containing, by weight, 3.5-5.5% Mg and 0.5-50ppm Be and also containing <=0.04% Si, <=0.64% Fe, <=0.2% Mn, 0.06% Cr, and <=0.006% Ti is cast to 4-10mm thickness. Then this cast plate is annealed at 380-480 deg.C for 1-24hr, followed by cold rolling.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application J] The present invention relates to a method for manufacturing an aluminum alloy plate for magnetic disks, and more particularly, to a method for manufacturing highly reliable aluminum alloy plates for high recording density magnetic disks. It is.

[Prior Art] Conventionally, aluminum alloys have been used for magnetic disk substrates due to their non-magnetic properties, strength, heat resistance, and the like.

However, as magnetic recording density improves, the distance between the magnetic disk substrate and the magnetic head becomes smaller and smaller, and the recording unit area also becomes smaller, so it is required that the roughness of the magnetic disk substrate surface be as small as possible. and furthermore,
It is required that defects on the substrate surface be as small and as few as possible.

As an improvement measure to meet these demands, the present inventors have developed the following improvements to the conventional 5086 alloy: (1) As explained in Japanese Patent Publication No. 60-140, the crystallized compound is made finer by increasing the solidification rate ( 3μm or less) and improved surface precision by stabilizing the macrostructure. (2) We discovered problems with the surface line pattern during continuous thin plate casting and improved them by further limiting the thickness of the cast plate and heat treatment. proposed the invention described in Japanese Patent Application Laid-Open No. 57-185961.

However, with further increases in magnetic disk recording densities and improvements in precision cutting technology, there are demands for further improvements in dimensional accuracy and further miniaturization of crystallized compounds for materials.

Further, as magnetic films become thinner, it is required that the surface precision of the substrate does not deteriorate even during the processing process of the magnetic medium.

That is, in order to obtain a highly reliable high-density magnetic recording medium, it has become necessary to further refine the crystallized compound and to ensure surface accuracy during the steps after substrate processing.

However, although the surface precision of the substrate obtained by the manufacturing method described in the previous section is good, recording errors may occur when used as a magnetic medium, resulting in a lack of reliability. was there.

[Problems to be Solved by the Invention] As explained above, the present invention has been developed by the inventors of the present invention, who has conducted extensive research and studies in view of the various problems of the conventional methods of manufacturing aluminum alloy plates for magnetic disks. As a result, due to the presence of "hard spots" of Al-10 to 20 wt% Mg that are formed and rolled up inside the cast plate due to disturbances in the solidification state during casting, gas concentration occurs in this area, and as a result, We discovered that minute blisters (about 2000A in height) occur and cause recording errors.Based on this knowledge, we made the crystallized compound finer and reduced the [hard spots] generated during casting. We have developed a method for manufacturing highly reliable aluminum alloy plates for magnetic disks with high recording density.

[Means for Solving the Problems] The method for manufacturing an aluminum alloy plate for a magnetic disk according to the present invention is characterized by: Mg 3.5 to 5.5 wt%, Be 0.5 to 50 ppm
Contains impurities such as Si≦0.04wt%, Fe50.04wt%, Mn≦
0, 2wt%, Cr≦0.06wt%, Ti 50.
006wt%, with the remainder being AI, is cast into a sheet with a thickness of 4 to 10 mm by continuous thin plate casting method, and annealed at a temperature of 380 to 480°C for 1 to 24 hours before cold rolling. It is in.

The method for manufacturing an aluminum alloy plate for magnetic disks according to the present invention will be described in detail below.

First, the components and content ratios of the aluminum alloy used in the method of manufacturing an aluminum alloy plate for a magnetic disk according to the present invention will be explained.

Mg is an essential element for imparting a certain strength to the disk substrate, and depending on the dimensions of the disk substrate, Mg may be 2wt%.
The above may be sufficient, but considering a 14-inch (368 mm) diameter disk, it is necessary to contain 3.5 wt% or more, and if it is contained in excess of 5.5 wt%, [hard spots] are likely to be formed. As the temperature increases, the frequency of generation of MgO nonmetallic inclusions increases. Therefore, the Mg content is set to 3.5 to 5.5 wt%.

Be is included to suppress the oxidation of Mg on the surface of the molten metal during continuous casting until it contacts cooling bodies such as water-cooled rolls and water-cooled belts. A thick oxide film is formed on the surface of the molten metal between the bodies, and this oxide film is periodically rolled into the casting material and disturbs the uniformity of the flow of the molten metal, which disturbs the solidification state of the cast plate and, as a result, increases the Mg concentration. 10~2h
t% of [hard spots] are formed, and in order to reduce this phenomenon, Be is added to form an extremely thin oxide film on the surface of the molten metal. It is necessary to contain 0.5 ppm or more, and if it is contained in excess of 50 ppm, the effect will be saturated, and it is wasteful and expensive to contain more than that. Therefore, the Be content is o, g~5
Set to 0 ppm.

Since St and Fe tend to form crystallized compounds such as AI-FeSMgpSi, the Si content was 50.04 wt% and Fe
The content is regulated to 50.04wt%.

Since Mn tends to form Al-Fe-Mn-based crystallized compounds, the Mn content is set to 60.2 wt%.

Cr is contained in the aluminum alloy used in the method for producing an aluminum plate alloy for magnetic disks according to the present invention because it has few impurities, so it is added to prevent the formation of coarse crystal grains when used as a disk substrate to make it a completely soft material. If the content exceeds 0.06 wt%, the Al-Fe crystallized compound tends to become coarser.

Therefore, the Cr content is regulated to 50.06 wt%.

Ti is extremely effective in refining ingot crystal grains, but Al
- It is necessary to use a small amount to form a Ti-based intermetallic compound, but if it is a small amount, no effect on fine grains can be expected.
Furthermore, due to the high purity, the compounds formed are small and few, so no structure adjustment is required. Therefore, the Ti content is set to 60.006 wt%.

As a component other than the above, Cu is allowed to be contained at an impurity level, but it is necessary to reduce the difference in directionality between crystal grains in the tendency of coarse recrystallized grains when used as a disk base and made into a completely soft material. It is effective in increasing machinability and grindability due to the combination of the effect and its own strength-improving effect, and for this reason, the content is allowed up to 0.3 wt%, but if it exceeds 0.3 wt%. If C is contained, Al-Mg-Cu precipitated compounds will be formed at the recrystallized grain boundaries, which will actually reduce the surface accuracy during precision cutting.
The u content is less than o3wt%.

Next, casting and heat treatment of the method for manufacturing an aluminum alloy plate for a magnetic disk according to the present invention will be explained.

When manufacturing a thin plate from the above-described aluminum alloy by continuous casting, when the molten aluminum alloy is supplied by the molten metal supply nozzle, N6. Ar,
The formation of an oxide film on the surface of the molten metal is prevented by supplying an inert gas such as N. The shielding by this inert gas, combined with the effect of containing Be, is effective in preventing oxidation of the surface of the molten metal, and as a result, it prevents solidification. It can suppress turbulence and has the effect of reducing "hard spots."Also, if the gas shield is a sealed method, there is almost no need for a flow rate, but if it is difficult to seal the casting machine due to the structure of the casting machine, a constant gas flow is required. One-sided type is preferable; in this case, the width (one side) is 5cc/cm per 1cm of cast plate.
It is preferable that the shielding gas supply amount be 500 cc/min or more. If the flow rate is too large, the flow of hot water between the nozzle and the roll tends to become uneven, so the shielding gas supply amount is preferably 500 cc/min or less. Under such circumstances, 4
Cast to a thickness of ~10 mm.

Next, before cold rolling this cast plate, it is annealed at a temperature of 380 to 480°C for 1 to 24 hours. Although this annealing is slight, the Mg content formed in the cast plate is 1
This is to diffuse 0 to 20 wt% of hard spots into a solid solution and render them harmless. At temperatures below 380°C, this effect is small, and at temperatures above 480°C, a burning phenomenon tends to occur in the hard spots. Therefore, the annealing temperature is 3
The temperature is 80 to 480°C.

Further, if the holding time is less than 1 hour, the effect of uniformly diffusing hard spots will be small, and if it exceeds 24 hours, the effect will be saturated and it will be useless. Therefore, the annealing time is 1 to 2
It will be 4 hours. In order to further perfect this diffusion effect, it is desirable to perform the second annealing at a temperature of 480 to 580°C for 1 to 24 hours.

Furthermore, if hard spot segregation is relatively small,
It is also possible to perform the first annealing at 480°C or higher.

This annealed cast plate is cold rolled at a rolling rate of 20% or more, but if this rolling rate is less than 20%, recrystallized grains may become coarse during the complete softening process during processing as a base for a disk. However, during finishing cutting and grinding, steps due to coarse grains tend to occur, making it impossible to obtain sufficient surface precision.

Cold rolling is also necessary from the viewpoint of improving distortion removal and improving plate thickness accuracy. For this reason, it is preferable that the rolling reduction in cold rolling is 20% or more.

In addition, annealing to make a soft material is 320 in the badge method.
It is preferable to carry out the reaction at a temperature of -450°C for 1 - 10 hours, and particularly preferably at a temperature of 350 - 400°C. Also,
With the rapid heating method, even higher temperatures are possible.

[Example] An example of the method for manufacturing an aluminum alloy plate for a magnetic disk according to the present invention will be described.

Example 1 After melting and refining an aluminum alloy having the components and proportions shown in Table 1, the aluminum alloy was cast to the thickness shown in Table 1. In this case, Ar gas was supplied between the molten metal supply nozzle and the cooling body at a flow rate of 38 cc/min per Icm of one side of the cast plate to shield the molten metal surface. Further, the hydrogen gas content of the cast plate at this time was 0.23 cc/], OOg.

After annealing the cast plate at a temperature of 450°C for 4 hours, 2mm
Cold rolling was performed until the thickness was reached. Furthermore, the material was punched and strain-relieved annealed at a temperature of 350° C. for 4 hours to obtain a completely soft material, and then precision cut to obtain a disk base.

The distribution of crystallized compounds on this disk substrate was measured, and the results of the measurement of the maximum crystallized compound size are shown in Table 2. As is clear from Table 2, in the aluminum alloy used in the method for manufacturing an aluminum alloy plate for magnetic disks according to the present invention, the size of the crystallized compound is 2.0 μm or less. In addition, the surface accuracy of this work is 0.00 in both cases.
6 to 0007 μmRa, and no difference was observed in the measured values.

Furthermore, after forming a 12 μm anodic oxide film on these disk substrates at a current density of 3 A/dm2 in an oxalic acid aqueous solution at 30° C., a 15% 1-1. It was immersed in an SO4 aqueous solution for 15 minutes, and then polished using a polishing cloth and an abrasive.

The surface roughness after this polishing was 0 μmRmax.

That is, according to the method for manufacturing an aluminum alloy plate for a magnetic disk according to the present invention, it is easy to manufacture a base for a magnetic disk that can achieve high recording density.

As shown in Table 3, Cu content is effective for improving strength, but in N018, Al-Mg-
Since Cu-based grain boundary precipitates were preferentially dissolved and grooves were formed, it was unsuitable as a disk substrate.

Table 3 Example 2 An aluminum alloy having the components and proportions shown in Table 4 was melted and cast to a thickness of 7 mm. During casting, Ar gas was supplied in the amount shown in Table 4 into the gap between the molten metal supply nozzle and the cooling roll.

After annealing the cast plate under the annealing conditions shown in Table 5,
Cold rolling was performed to a thickness of m. Thereafter, further punching, strain relief annealing (at a temperature of 350° C. for 2 hours), and precision cutting were performed to obtain a disk base.

In addition, we also perform degreasing, surface treatment, magnetic coating, coating baking and drying (
Polishing was performed at a temperature of 250° C. for 1 hour) to obtain a magnetic disk.

Abnormalities (blisters) in these magnetic disks were determined and the results are shown in Table 5.

From this Table 5, it is clear that any method other than the manufacturing method of the aluminum alloy plate for magnetic disks according to the present invention lacks reliability in terms of the blistering rate and is unsuitable as a disk substrate. Burning occurred after 2 hours of annealing at a temperature of C, and the base was determined to be inappropriate at the time of precision cutting.

[Effects of the Invention] As explained above, since the method for manufacturing an aluminum alloy plate for a magnetic disk according to the present invention has the above configuration, it has good strength and surface precision. It has the advantage of being able to produce a highly reliable magnetic disk substrate with few recording errors and high recording density.

Claims (1)

[Claims] Contains 3.5 to 5.5 wt% Mg and 0.5 to 50 ppm Be, and as impurities, Si≦0.04 wt%, Fe≦0.04 wt%, Mn≦
0.2wt%, Cr≦0.06wt%, Ti≦0.00
6 wt%, and the balance is Al, cast into a plate with a thickness of 4 to 10 mm by continuous thin plate casting method, and annealed at a temperature of 380 to 480°C for 1 to 24 hours before cold rolling. A method for manufacturing an aluminum alloy plate for magnetic disks, characterized by: