JPH0288741A - Stock for high recording density disk and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture the title stock in the use of a low purity Al metal by subjecting an ingot of an Al-Mg alloy having specific compsn. to soaking treatment under specific conditions and regulating the rolling-starting temp. CONSTITUTION:An ingot of an Al-Mg alloy contg., by weight, 3 to 5% Mg and 0.015 to 0.030% Si, is subjected to soaking treatment at 500 to 560 deg.C soaking temp. for >=1hr holding time. The ingot is then subjected to hot rolling at >=500 deg.C rolling-starting temp. into a stock for a magnetic disk. In this way, the stock for a high density disk contg. <=4mum Mg-Si crystallized material and sufficient for an application-type disk can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an aluminum alloy plate for high-density magnetic disks and a method for manufacturing the same.

(Prior Art) Aluminum alloy is used as a magnetic disk material because of its light weight, non-magnetic properties, and rigidity that can withstand high-speed rotation. The aluminum alloy plate (blank material) for magnetic disks is processed into a substrate for disks (substrate material) by precision surface finishing such as precision cutting or precision polishing.
After performing pretreatment such as degreasing, a magnetic film is formed.

As magnetic recording density has improved in recent years, the flying height of the magnetic head has become lower and lower, and the recording unit area has become smaller. For this reason, requirements for the flatness of the substrate l-material and requirements for the phenomenon of minute irregularities on the surface of the substrate material are becoming increasingly strict.

Furthermore, due to intensifying competition in the electronics industry, there has been a trend toward lower costs for magnetic disks. For this reason, low-cost, high-quality materials are also required for blank materials and substrate materials.

(Problems to be Solved by the Invention) Conventionally, it has been thought that the internal quality of a blank material requires that all intermetallic compounds be small. This is because intermetallic compounds have higher hardness than the aluminum alloy matrix, so during cutting or polishing, they remain as protrusions or fall off to form holes, resulting in local changes in the thickness of the magnetic film, which can easily cause recording errors. It's for a reason.

For this reason, in the past, ultra-high purity aluminum, that is, 99°99% pure aluminum, as disclosed in Japanese Patent Publication No. 62-32260
Proposals were made to make intermetallic compounds finer by using bare metals.

However, blank materials using ultra-high-purity Al ingots are very expensive, even if they are of high quality, and have not been mass-produced in the computer industry.

In addition, use for coated discs, where cost is particularly important, could not be considered.

However, recently, as shown in JP-A-63-96254, attempts have been made to use low-purity Al ingots, and in terms of finer intermetallic compounds, ultra-high-purity Al ingots have been used. It's not a satisfying comparison.

The present invention has been made in view of the above circumstances, and
Instead of using high-purity Al ingots to produce high-density blanks, which has been proposed as the main method in the past, we now use relatively low-purity AP ingots to support high-density recording at low cost. The purpose is to provide a material and a method by which it can be manufactured.

(Means for Solving the Problems) In order to achieve the above object, the high recording density disk material of the present invention contains Mg: 3 to 5% and Si: o.

The Al-Mg alloy containing 15% to 0.030% is characterized in that the size of Mg-Si crystallized substances is 4 μm or less.

Moreover, the manufacturing method includes Mg: 3 to 5% and Sj: 0.
The ingot of Al-Mg alloy containing 15% to 0.030% was heated at a soaking temperature of 500°C to 560°C and a holding time of 111 r.
It is characterized in that the above-described soaking treatment is performed, and then hot rolling is performed at a rolling amount starting temperature of 500° C. or higher.

The present invention will be explained in more detail below.

First, we will show some findings related to Al ingot purity, that is, some investigative points that made it possible to avoid the use of high-purity Al ingots.

As mentioned above, it has been thought that the main cause of recording errors on magnetic disks on the material side is protrusions and pits on the surface of the substrate material. For this reason, the presence of coarse intermetallic compounds was considered unacceptable.

However, after numerous studies and analyzes of recording errors on magnetic disks, it has been found that most recording errors are caused by pits on the material side, and that recording errors caused by protrusions are extremely rare. In other words, they discovered that in order to eliminate recording errors, it is sufficient to eliminate pits.

Next, regarding the cause of the formation of these pits, it was conventionally thought that they were formed by intermetallic compounds falling off during precision cutting. Regarding this point, a detailed f7R observation of the surface revealed that specific intermetallic compounds ( It was discovered that Mg-Si crystallized substances dissolve and form pits very frequently.

That is, conventionally, A Q -Fe, A Q -Mn
Fe, Al-Mn, Al-Cr, Mg-8i, Al-F
Efforts have been made to make high-purity ingots to reduce the size and number of all crystallized substances such as e-8i series, but based on the above findings, strict control of Mg-8i series crystallized substances is required. Therefore, it was found that there is no need to treat other types of crystallized substances as harshly as when using high-purity metals. In addition, if the size of the Mg-8i item is 4 μm or less,
We have found that it is possible to achieve a sufficiently high density for a coated disc.

Next, the relationship with the composition will be shown in connection with the refinement of Mg-8i crystallized substances.

First, since the Mg-3i product is formed of Mg and Si, naturally, the smaller the content of both elements, the less the formation of crystallized substances. However, Mg is an essential element in order to obtain sufficient strength as a material for magnetic disks, and therefore Mg must be added in an amount of 3% or more.

Further, Si is an element that is inevitably mixed in, no matter what purity of Al metal is used. When a high-purity aluminum base metal of 99.99% (eg, 99.992%) is used, a blank containing approximately 0.008% or less of Si is usually obtained. In this case, the Mg-8i crystallized product is 4
Although it is less than μl, it is very expensive. 99°90 is a cheaper metal compared to this very expensive bullion.
~99.97%/l 0.02~0 when using bullion
．． A blank material with a Si content of 0.3% is obtained, but when this amount of Si is contained, a large amount of Mg-8i products are formed, which often causes recording errors.

However, as explained below, in the present invention.

Using such a low-priced Al ingot, the Si content is 0.
Even if the content is 0.015 to 0.030%, it is possible to obtain a blank material that can be used as a high-density disk material.

First, the reason for limiting the chemical components in the present invention will be explained.

Si: 01015~0.030% As mentioned above, from the point of view of the ingot used, Si is 0.
．． 0.015% or more and 0.030% or less.

Setting the Si content to 0.015% or more is not economical, since if it is less than 0.015%, Mg-8i products have no choice but to use expensive high-purity ingots even if they are miniaturized. Because it will disappear. On the other hand, if it exceeds 0.030%, it becomes difficult to refine Mg-Si crystallized substances even in the process according to the present invention.

Mg: 3-5% Mg is an essential element for imparting strength, and it is necessary to add 3% or more. However, if it exceeds 5%, inclusions such as MgO are likely to be formed during casting, and Mg-8i
Since system crystallized substances also tend to become coarse, they need to be controlled to 5% or less.

Note that since Fe facilitates the formation of crystallized substances such as Al--Fe, it is desirable that the amount of Fe be small. When using ordinary low-purity Al ingot, Fe is 0.07 due to the Si content regulation mentioned above.
It becomes 0% or less. As described above, from the viewpoint of products, it is desirable to have a small amount of Fe, but in order to prevent hot cracking, which will be described later, it is desirable that Fe be added, and it is preferably contained in an amount of 0.025% or more.

Although Mn is not directly related to the distribution of Mg-Si crystallized substances,
In order to prevent coarsening of products such as AQ-Mn-Fe and AQ-Mn, it is desirable to keep the content to 0.3% or less.

Other elements do not affect the effects of the present invention as long as they are impurities.

Next, the reason for limiting the conditions for the manufacturing process in the present invention will be explained.

Various experiments were conducted to obtain a disc material with the above composition and surface properties.

Al-Mg alloy No. 1 with the chemical composition shown in Table 1
The influence of the homogenization heating temperature on the Mg-Si crystallized products was investigated for the ingots. The results are shown in FIG. In order to obtain the results shown in Figure 1, the ingots after each heat treatment were mirror-cut, and then 50 mm were cut using a scanning electron microscope.
Measure an area of 10 ml112 at 0x magnification, define crystallized matter of 1 μm or more and less than 2 μm as 2 μm, and measure 2 μm or more and 3 μm.
Crystallized substances with a diameter of less than 3 μm are expressed as 3 μm (the same applies hereinafter).

As is clear from Figure 1, it was conventionally common knowledge that the number and size of Mg-8L crystallized substances (in the form of Mg and Si) decrease monotonically as the temperature increases; Unlike, Mg-Si crystallized products have a soaking temperature of 400~
At 450°C, it grows from the as-cast state, and when raised to a higher temperature, it becomes smaller again.

From this result, it was found that the soaking temperature needed to be 500°C or higher.

The effect of the homogenization heating temperature on the distribution of Mg-3i crystallized substances was investigated for an ingot of Al-Mg alloy Nα2 having the chemical components shown in Table 1. The results are shown in FIG.

This result shows that the Mg-8i crystallized product decreases monotonically until the soaking temperature reaches 560°C.

However, since problems such as burning tend to occur when the temperature exceeds 560°C, it has been found that the temperature needs to be lower than 560°C.

The influence of the temperature increase rate, cooling rate, and holding time during homogenization heating on the distribution of Mg-Si crystallized substances was investigated for the ingot of Al-Mg alloy &3 having the chemical composition shown in Table 1. Ta.

The results are shown in FIGS. 3, 4, and 5, respectively.

From FIGS. 3 and 4, it can be seen that the temperature increase rate does not affect the distribution of Mg-Si crystallized substances, but the cooling rate has a large effect on the distribution, and the slower the cooling, the more Mg-Si It is observed that the number of crystallized substances increases (becomes larger). Furthermore, from Fig. 5, it can be seen that the longer the holding time is, the smaller the Mg-8L crystallized substances are, and the holding time is at least 1 h.
It turns out that more than r is required.

An ingot with the same composition as in Experimental Example 3 was subjected to homogenization heating under the conditions shown in Figure 6, and Mg-8 under the homogenization heating conditions was applied.
We investigated the effect on the i-item product distribution.

As shown in Figure 6, the results show that under heating conditions including slow cooling at 40°C, even if the composition is the same, Mg-Si
It is recognized that there are a large number of system crystallized substances.

Furthermore, a small ingot with a thickness of 15 mm was cut out from the ingot with the above composition, and after the above homogenization heat treatment, it was hot rolled to a thickness of 2 mm without air cooling, and the results of measuring Mg-Si crystallized substances were reported. It is shown in Figure 7. From this result, it can be seen that the distribution of Mg-Si crystallized substances in the ingot after homogenization heat treatment maintains its tendency even after hot rolling.

Major failure j - After cutting an ingot of Al-Mg alloy Nα4 having the chemical composition shown in Table 1, it was heated at 540℃ for 10 hours, hot rolling was started at 530, 500, and 470℃, and it was finished with a thickness of 6III11. did. After this, the Mg-S
The i-series crystallized product was evaluated. The results are shown in Table 2.

Note that the cold rolled plate in this example was evaluated at a magnification of 1000 times. Further, rolling order 1.2.3 in Table 2 is the order in which hot rolling was performed. Normally, when soaking in a batch furnace, a specific number of pieces are soaked all at once, and then they are taken out one by one and hot rolled.

At this time, when the ingot is removed from the furnace at the end, the temperature of the ingot naturally decreases, resulting in the same situation as if it had been slowly cooled. For this reason, the hot rolling temperature often decreases as shown in Table 2.

From the results in Table 2, the Mg-Si crystallized substances in cold-rolled sheets increase rapidly when the hot rolling start temperature is less than 500°C, so the hot rolling start temperature needs to be 500°C or higher. I understand that. The reason for this is as shown in Experimental Examples 1 and 3. Conventionally, it was common sense to set the hot rolling start temperature to about 470°C or less to prevent hot cracking, etc., but this did not allow Mg-S
Whereas the size of i-type crystallized substances was only reduced at most 5 μm or more, the effect of increasing the hot rolling start temperature is significant.

In addition, when the hot rolling start temperature is as high as 530°C, Mg-
Although Si-based crystallized substances are made finer, surface cracks are likely to occur in the initial stage of hot rolling. This is thought to be due to the formation of huge crystal grains on the surface of the rolled plate due to the introduction of rapid strain at high temperatures, and therefore, it is necessary to reduce the strain rate. In this regard, it has been separately confirmed that in order to prevent surface cracking, it is preferable to control the Fe content to 0.025% or more in order to suppress the formation of coarse crystal grains as much as possible.

Therefore, the hot rolling start temperature is set at 500°C or higher, and the Fe content is set at 0.025% or higher, preferably 0.04%.
In order to prevent hot cracking, F
In consideration of preventing an increase in AuFe-based products due to an increase in e content, the temperature is preferably 500 to 560°C, more preferably 510 to 530°C.

[Margin below 1 Based on the knowledge obtained from the above experiments, 1. The manufacturing process conditions according to the present invention are as follows: First, an ingot of Al-Mg alloy having the composition described above is heated at a soaking temperature of 500 to 560°C and a holding time. 1h
It is necessary to perform a soaking treatment of r or more. In the subsequent hot rolling, it is necessary to set the rolling start temperature to 500° C. or higher.

Note that other conditions in the soaking treatment are not particularly limited, but
The heating rate is preferably higher than 40°C/hr,
Cooling such as air cooling or water cooling is preferable. In addition, in hot rolling, the strain rate is preferably determined in relation to the amount of Fe, and 15 (
It is desirable that it be as low as 1/sec) or less.

Next, examples of the present invention will be shown. It goes without saying that the above-mentioned experimental examples can also be considered as examples of the present invention.

(Example) Casting of Ag-Mg alloy Nα1 having the chemical composition shown in Table 3 obtained by melting and casting low-purity Al ingot (99.92 to 99.94%) by a conventional method. 540℃X for the lump
After performing soaking treatment for 20 hours, hot rolling was performed under the conditions shown in Table 4, and cold rolling was performed to obtain a thickness of 2 mm. In addition,
The average strain rate is for a plate thickness of 15n+m or more, and the strain rate ε (1/sec) is where n: Roll rotation speed (
rpm) r: Machining rate = (Output side thickness) / (Inlet side thickness) Ho: Inlet side plate thickness (, m) Ro = Roll radius (IIIll) It was determined by the following formula.

In addition to examining the surface condition of the hot rough rolled sheets, the cold rolled sheets were evaluated for Mg-8i crystallized substances. The results are shown in Table 4. In addition, the crystallized material was measured with a scanning electron microscope at 1000
An area of 10 mm2 was measured at double magnification.

From Table 4, it can be seen that if the hot rolling conditions were appropriate, there would be no defects at all, and the properties as a high-density disk material would be satisfied. In addition, the strain rate 20 in Table 4
(1/sec) is the conventional rolling condition.

(Comparative example) Al-Mg alloy Nα2 (
After soaking the ingot with a high Si content at 550°C for 6 hours, hot rolling was started at 530°C to reduce the ingot thickness (360mm
) to the average strain rate of hot rough rolling with a thickness of 15 mm to 10
(1/sec), then hot rolled to a thickness of 4.5 mm, and further cold rolled to a thickness of 2 mm.

Thereafter, Mg-8i crystallized substances were evaluated on the mirror surface cut by 0.11IIl from the surface. As a result, it was found that in a composition with a large amount of Si and outside the range of the present invention, there were 8 Mg-8i crystallized substances/mm2 with a size of 5 μm or more, making it unsuitable as a material for a high-density disk.

[Blank below] (Effects of the Invention) As detailed above, according to the process of the present invention, even if relatively low-purity aluminum metal is used, a high-density disk material sufficient for coated disks can be produced. Obtainable. Therefore, the manufacturing cost is high purity metal9
Compared to the case of using 9.99% aluminum ingot, the amount is less than half, which is a very large effect in terms of manufacturing industrial products.

[Brief explanation of drawings]

Figures 1 and 2 are diagrams showing the influence of homogenization heating temperature on the distribution of Mg-8i crystallized substances, and Figures 3 to 5 respectively.
The figure is a diagram showing the influence of the temperature increase rate, cooling rate, and holding time of homogenization treatment on the distribution of Mg-Si crystallized substances,
Figure 3 shows the case of heating rate, Figure 4 shows the case of cooling rate, Figure 5 shows the case of holding time, and Figure 6 shows the case of MgSi-based products under various heat history homogenization treatment conditions. FIG. 7 is a diagram showing the results of evaluating the distribution of Mg--Si crystallized substances in a hot rolled sheet during homogenization treatment.

Claims (4)

[Claims] (1) In weight% (the same applies hereinafter), Mg: 3 to 5% and S
A material for a high recording density magnetic disk, characterized in that an Al-Mg alloy containing i:0.015 to 0.030% has a Mg-Si crystallized substance of 4 μm or less. (2) Mg: 3-5% and Si: 0.015-0.03
The ingot of Al-Mg alloy containing 0%
1. A method for producing a material for a high recording density disk, which comprises performing soaking treatment at 00 to 560°C for a holding time of 1 hr or more, and then hot rolling at a rolling start temperature of 500°C or more. (3) The strain rate of rough rolling in hot rolling is 15 (1/s
ec) The method according to claim 2. (4) The method according to claim 2, wherein a low-purity Al ingot is used.