JPS6253586B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method of softening annealing (hereinafter simply referred to as annealing) an Al alloy plate that serves as a substrate for a magnetic disk, and in particular, a method for softening and annealing Al alloy plates that are used as substrates for magnetic disks. The present invention relates to an annealing method that can reduce the amount of damage. [Conventional technology] Conventionally, Al-
Mg-based alloys, especially 5086 alloy, are known. However, in view of the current trend towards miniaturization and larger capacity of magnetic disk systems incorporated in electronic computers, there is a growing demand for the development of high-density magnetic disks, and magnetic disks with radial and circular Requirements for flatness (both microscopic and macroscopic) in the circumferential direction are becoming extremely strict. Therefore, the magnetic disk substrate itself, which is the material of the magnetic disk, must be supplied as a highly flat disk or donut plate, and precision cutting and polishing techniques for the surface of the magnetic disk substrate have made significant progress. . [Problems to be solved by the invention] Even if cutting and polishing can be performed with high precision, surface defects and distortions contained in the material itself can be removed or eliminated by precision cutting and polishing. It's not a thing. Therefore, various studies are being conducted on the material side, such as suppressing the crystallization of intermetallic compounds by improving the purity of the raw metal, or increasing the solidification rate to dissolve and disperse intermetallic compounds. Measures are being taken to increase the Although such improvements have led to significant improvements in micro pits after precision cutting and precision polishing, defects in micro waviness remain as an unresolved issue. The cause of this microwaviness remains unclear, and according to research conducted by the present inventors, it has nothing to do with intermetallic compounds and is influenced by the recrystallized grain size of the material. It became clear. Therefore, the present inventors set the problem of devising heat treatment conditions and how much the average crystal grain size could be reduced by such devising, and as a result of various studies, they completed the present invention. [Technical means for solving the problem] That is, the present invention provides a method for softening an Al alloy plate for magnetic disk substrates containing Mg: 3 to 6% by weight (hereinafter simply expressed as %) at 10°C/ Raise the temperature to 280 to 550℃ at a heating rate of 1 minute or more, and 1 minute within the same temperature range.
The main point is that an Al alloy plate for magnetic disk substrates with less minute waviness can be obtained by cooling after holding for ~60 minutes and suppressing the average crystal grain size (hereinafter simply referred to as crystal grain size) to 25 μm or less. It has the following. [Function] First, the material Al alloy will be explained. This Al alloy 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 must be contained in an amount of 3% or more. However, if it is too large, Al-Mg precipitates are likely to form at grain boundaries during annealing, and non-metallic inclusions of MgO are formed due to high-temperature oxidation during melting and casting, reducing surface precision. It should be kept below. That is, since Al-Mg precipitates and MgO are discontinuous with the Al matrix, and MgO is harder than the Al matrix, when the substrate is machined or polished, the surface remains as protrusions or falls off. Then a hole will appear. As a result, even if sufficient polishing is performed, good surface precision cannot be obtained. The alloy components other than Mg have no direct relation to the effects of the present invention, and any alloy components can be included as long as they do not have a negative effect on the general properties. However, the most common one is the aforementioned 5086 alloy, and it is desirable that the alloy components other than Mg be as small as possible. However, due to the actual situation in terms of manufacturing, the following is a supplementary description of the permissible elements and permissible content. That is, as already described in JP-A No. 57-47853, in order to suppress the coarsening of intermetallic compounds and make the material suitable for high recording density, Mn≦0.4%, Cr≦0.1%, Ti ≦0.01
%, Si≦0.1%, and Fe≦0.2%, and this idea is also applied to the present invention as far as the alloy composition is concerned. If you add more,
It is desirable to regulate Cu≦1.0% and Zn≦1.0%. In other words, Mn has the effect of increasing the corrosion resistance of the alloy plate, and Fe has the effect of increasing the strength and cutting/polishing properties of the alloy plate.
If the amount of both is too large, coarse Al-Fe-Mn crystallized substances are likely to be formed, so Mn should be 0.4% or less, respectively.
It is desirable that Fe content be 0.2% or less. Like Mn, Cr has the effect of increasing the corrosion resistance of the alloy plate, but if it exceeds 0.1%, it is not preferable because it coarsens the Al--Fe--Mn system crystallized substances and reduces surface precision. If Si is present in an amount exceeding 0.1%, Mg-Si type coarse compounds are likely to be formed, and it is desirable that Si be present in an amount of 0.1% or less. Ti and B are effective elements for refining the ingot structure and preventing micro-segregation, and in order to exhibit these effects significantly, Ti: 0.001% or more and B:
It is desirable to add 0.0005% or more alone or in combination. Cu and Zn are effective in improving the strength of this alloy, but if they are added in large quantities, Al-Mg-Cu, Mg-Zn, etc. will precipitate at the grain boundaries during cooling after annealing, which may cause problems such as precision polishing. It was easy for problems to occur. however,
If the cooling rate is within the range recommended by the present invention, Cu≦
1.0%, Zn≦1.0%, grain boundary precipitation is small, and some addition is allowed. Next, the softening annealing conditions for the Al alloy plate (hereinafter also simply referred to as a disk) will be explained. When annealing a disc, laminated annealing, which has been conventionally performed, is advantageous in terms of efficiency, and the present invention can also follow the conventional technology in this respect. The number of laminated layers should be determined according to the furnace capacity. In addition, considering the removal of plate distortion caused by rolling, punching, and cutting performed prior to annealing, it is desirable to perform annealing while applying a load to the plate surface of the laminated disk. In this case, the initial load should be about 1 to 20 tons per surface. As a heating means for annealing, electromagnetic induction heating with good control performance is recommended from the viewpoint of controlling the temperature increase rate and holding temperature, which will be described later.However, the present invention does not specify the heating means itself. Any heating means can be used as long as it does not cause any inconvenience in terms of temperature control such as controlling the heating rate or maintaining a predetermined temperature. First, in order to understand the influence of the temperature increase rate, we tried to find the relationship between the grain size of the annealed disk and the surface accuracy of the surface-cut disk.
The results shown in FIG. 1 were obtained. The relationship shown in Figure 1 is annealing disks with the same laminated state under the same conditions (strictly speaking, the conditions for the temperature increase rate are changed, but the annealing holding temperature, time, cooling rate, disk pressing force, etc. are the same) Furthermore, the results are shown when cutting under the same conditions. Surface roughness (μ
mRa) is a concept that numerically expresses minute waviness in a magnetic disk, and according to the figure, there is an extremely good correlation with the crystal grain size shown on the horizontal axis. It can be seen that the stricter the target for suppressing microwaviness, the smaller the crystal grain size must be. Therefore, the present inventors set the immediate target for suppressing microwaviness as a surface roughness of 0.015 μmRa, and in order to achieve this goal, it is necessary to ensure a crystal grain size of 25 μm or less for safety reasons. I came to the conclusion that there is. Next, we investigated the conditions for reducing the crystal grain size to 25 μm or less, and found that the recrystallization temperature and recrystallization grain size change depending on the component composition and degree of processing of the disk. Although the lower limit of the heating rate changes, we have learned that under general conditions it is possible to suppress the crystal grain size to 25 μm or less as long as the heating rate is maintained at 10°C/min or higher. In other words, the slower the heating rate, the coarser the crystal grains become, and the more surface roughness tends to increase, so to avoid this, a temperature increase of 10°C/min or more is set. That's why I did it. On the other hand, there is no upper limit to the temperature increase rate from the perspective of refining recrystallized grains, but if the temperature increase is too rapid, temperature non-uniformity will occur in the laminated disks, impairing the uniformity of the product.
It is desirable to keep the temperature below 500℃/min. The ultimate annealing temperature should be determined according to the desired degree of softening, but from the basic point of ensuring fine recrystallized grains, it needs to be 280 to 550 °C, and the annealing time should be 1 to 550 °C. It should be 60 minutes.
This is because if the temperature is less than 280°C, recrystallization will not progress sufficiently, and if it exceeds 550°C, the above-mentioned burning phenomenon peculiar to Mg-containing Al alloys will occur. Again 1
If the heating time is less than 60 minutes, the heating will be completed before the temperature gradient that occurs when the laminated disk is heated is completely resolved, resulting in insufficient recrystallization. On the other hand, if it exceeds 60 minutes, the crystal grains will tend to become coarse. be. During the annealing period (1~
60 minutes), as long as the temperature is within the range of 280 to 550℃, temperature changes can be tolerated, but if the temperature difference at this time is too large, the annealing effect may be uneven, so it should be kept as constant as possible. It is desirable to hold it at temperature. Next, preferred conditions for cooling will be described. Cooling may be performed by blowing gas into the furnace, or by moving the laminated disks to another predetermined cooling furnace or device for cooling. Essentially, the disc is cooled to 150°C at a cooling rate of 0.5 to 10°C/min. If the cooling rate is less than 0.5℃/min,
In the case of soft annealing, recrystallized grains tend to become coarse, and solute elements tend to precipitate at grain boundaries in any purpose of annealing. Also, if it exceeds 10℃/min, the cooling rate is too fast,
Due to thermal stress, it is difficult for the plate to have sufficient flatness. The most desirable cooling rate range varies slightly depending on the number of laminated disks, plate thickness, outer diameter, inner diameter, applied load, annealing temperature, etc., but is generally 1 to 5° C./min. In addition, the effect of cooling rate on strain and precipitation is almost non-existent in the region below 150°C.
℃, cooling may be performed within the above cooling rate range, and thereafter, rapid cooling or slow cooling may be performed. Incidentally, in the manufacturing process of the disk, in practice, semi-hard annealing is often performed prior to softening annealing, as shown in the aforementioned prior invention (Japanese Patent Laid-Open No. 57-47853). However, the presence or absence of semi-hard annealing has no bearing on the implementation of the present invention, and in the following examples, satisfactory results can be obtained regardless of the presence or absence of semi-hard annealing. [Examples] Example 1 An ingot having the composition shown in Table 1 was obtained, and subjected to soaking treatment, hot rolling, and cold rolling to obtain a 2 mm ^t plate.

[Table] Materials and alloy plates with an outer diameter of 357mmφ and an inner diameter of 167mm.
It was made into a donut-shaped punched material (disk) for a board. For the purpose of correcting rolling strain, 87 sheets of the above materials were laminated and tightened using a surface plate with a load of 6 tons. This was placed in an induction heating furnace, and about 60KW of power was applied, and it took 11 minutes to reach 240℃ (heating rate: 19
℃/min) and held at the same temperature for 20 minutes, then taken out of the furnace to cool and semi-hard annealed. For comparison, semi-hard annealing was performed using an atmospheric annealing furnace (heating rate: 0.5°C/min, 240°C
x 2 hours). Even though the materials were the same, differences as shown in Table 2 were observed due to differences in annealing conditions.

[Table] In the examples using induction heating, the properties after annealing were not inferior at all even if the furnace time was significantly reduced.
It is clear that the effect of shortening the annealing time is achieved. Next, after semi-hard annealing the material and material as in the above example, both sides were cut by 0.1 mm on each side, 64 sheets were stacked with spacers, and then tightened with a load of 6 tons using a surface plate. Ta. This was placed in an induction heating furnace, heated at a rate of 18°C/min to 360°C, and held for 10 minutes for softening annealing. The input power was approximately 60KW. For comparison, both materials were subjected to softening annealing at 360°C for 2 hours while applying the same load and increasing the temperature at a rate of 0.67°C/min (40°C/hour). The properties after annealing were as shown in Table 3.

[Table] As shown in Table 3, all of the examples in which the technology of the present invention was applied to softening annealing had small grain sizes after annealing, and the micro waviness was also significantly smaller. ing. That is, it is clear that excellent microwaviness can be obtained in the present invention regardless of semi-hard annealing. Example 2

[Table] Aluminum alloys having the compositions shown in Table 4 were cast, faced, soaked, and cold-rolled to a thickness of 2 mm according to conventional methods. This 2mm thick plate has an outer diameter of about 357mmφ and an inner diameter of about 167mm.
It was made into a punched disk with a diameter of mmφ. In order to roll and straighten the discs, 87 of the discs were stacked, clamped on a surface plate with a load of 8 tons, and charged into an induction heating furnace with a power of approximately 60KW.
power was applied to reach the temperature of 255°C at a heating rate of 19°C/min, and after holding at 255°C for 10 minutes, the A alloy disc was heated to 150°C at a rate of 1°C/min, and the B alloy disc The C alloy was cooled to 150°C at a rate of 3°C/min, and the C alloy was cooled to 150°C at a rate of 4°C/min. In both cases, natural cooling was performed at 100°C or less.
For comparison, Alloy A was annealed at 240°C for 2 hours at a heating rate of approximately 40°C/hour under the same lamination pressure as above, and then was furnace cooled to 150°C at a cooling rate of 0.2°C/minute. and semi-hard annealed. Table 5 shows the results of measuring the flatness of these treated materials.

[Table] From Table 5, it is clear that when the annealing method according to the example is adopted, the circumferential waviness of the same Al alloy disc is improved. Example 3 Next, after semi-hard annealing, the same disks as in the above example were laminated with 70 disks with rough cutting of approximately 0.1 mm on each side and heated to 360℃ at a heating rate of 18℃/min.
After softening annealing by holding for 10 minutes at ℃, alloy A was heated to 2℃/
150 min, B alloy at 3°C/min, C alloy at 5°C/min.
It was cooled to ℃ and softened and annealed. The initial load is 6
tons/surface. For comparison, the A and C alloys were laminated and pressed at approximately 40°C/hour at 360°C.
℃, and annealed at 360℃ for 2 hours, and then cooled to 150℃ at a cooling rate of 0.2℃/min for softening annealing. Table 6 shows the flatness of each disk after the above annealing. Furthermore, Table 7 shows the characteristics of each disc when precision polished and finished.

【table】

[Table] As shown in Table 7, in Comparative Examples A and C in which the softening annealing conditions did not satisfy the present invention, there were defects mainly in the grain boundaries, and good flatness could not be obtained. Example 4 A 4 mm thick Al alloy thick plate was obtained by casting, facing, soaking, hot rolling, and cold rolling according to conventional methods. This thick plate was punched into a disk with an outer diameter of approximately 360 mmφ and an inner diameter of approximately 167 mmφ. The Al alloy composition is shown in Table 8 (not shown).

[Table] This disc was subjected to softening annealing as described below. In order to correct rolling strain, 46 of the above discs were stacked, clamped under a load of 1 ton, and charged into an induction heating furnace. 18
After heating to 360℃ at ℃/min and holding for 20 minutes,
Cooled to 150°C at a rate of °C/min. For comparison, the same laminated disks as above were heated to 369°C at a rate of approximately 40°C/Hr in an induction heating furnace, held at the same temperature for 2 hours, and then cooled to 150°C at a rate of 0.2°C/min. The crystal grain size and flatness of the obtained disks were as shown in Table 9.

〔Effect of the invention〕

Since the present invention is constructed as described above, it has excellent precision machinability, reduces minute waviness in the Al alloy plate, and is able to sufficiently respond to higher recording densities of magnetic disks.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between surface roughness and average grain size, and FIGS. 2 and 3 are explanatory diagrams showing the waviness evaluation test method.

Claims (1)

[Claims] 1. When softening and annealing an Al alloy plate for a magnetic disk substrate containing 3 to 6% by weight of Mg,
The generation of micro-waviness is characterized by raising the temperature to 280-550℃ at a heating rate of 1 minute or more, holding it within the same temperature range for 1-60 minutes, and then cooling it to suppress the average grain size to 25 μm or less. For small magnetic disk substrates
Softening annealing method for Al alloy plate. 2. The softening annealing method according to claim 1, wherein cooling to a temperature of 150°C is performed at a cooling rate of 0.5 to 10°C/min. 3 Impurities in the Al alloy: Si: 0.1% or less (weight%, same below) Fe: 0.2% or less Cu: 1.0% or less Mn: 0.4% or less Cr: 0.1% or less Zn: 1.0% or less Ti: 0.01% or less A softening annealing method according to claim 1 or 2, which is regulated by: