JPH07197170A - Aluminum alloy sheet for thin disk and its production - Google Patents

Abstract

PURPOSE:To obtain an Al alloy sheet for thin disk having excellent strength, plating adhesion and handleability by subjecting the alloy to hot-rolling in the specific condition or direct cold-rolling, after continuously casting the specific composition of Al-Mg series alloy into a thin sheet state by DC casting method. CONSTITUTION:Molten Al-Mg series alloy having composition consisting of, by weight, 5.5-7.5% Mg, and further containing 0.03-0.3% Cu, 0.1-0.5% Mn, or further containing <0.3% Zn, <=0.1% Fe and <=0.1% Si as inevitable impurities and satisfying >=3 Mn/Fe ratio, is cast by the DC casting method. After executing the soaking treatment to a cast ingot at >=510 deg.C, only the surface of the cast ingot is cooled with water, etc., containing oil, etc., and the hot- rolling is executed to the resulted ingot at <=5% draft until the surface temp. lowers to 450 deg.C, or the hot-rolling is executed to it after lowering the surface temp. to <=450 deg.C. On the other hand, as for Al alloy having 5.5-8.0% Mg and <0.5% Zn, after directly casting the molten Al alloy into the thin sheet having <=8mm thickness, only cold-rolling is applied without executing the hot-rolling to obtain the objective sheet material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy for thin-walled discs, and more particularly, to an aluminum alloy plate for thin-walled discs suitable for a hard disk substrate mounted on a small computer such as a notebook or palmtop, and a method for producing the same. Regarding

[0002]

2. Description of the Related Art Generally, a base material such as a magnetic disk used as a recording medium for a computer or the like is lightweight, non-magnetic, and
Aluminum alloys have been used for the reasons that they have rigidity, and that good surface accuracy can be easily obtained by precision processing and polishing. In particular, a 5000 series aluminum alloy such as 5086 has been used as a disk material through a coating type medium / thin film medium because of its excellent properties described above. In recent years, high density has been essential, and therefore thin film media are widely used. Further, at present, reduction of area / pits is aimed at for high density.

At present, with respect to the Al base, there is a strong demand for cost reduction as the price of hard disks decreases. In the conventional material, crystallized substances and the like on the surface of the aluminum alloy plate fall off during polishing, or crystallized substances are dissolved by the pretreatment of plating, which causes a plating defect or a very rough plated surface. there were.
Therefore, it becomes essential to perform relatively thick plating, and then polish a large amount to remove these plating defects, although the cost increases.

Therefore, in order to reduce the plating film thickness and the plating film polishing allowance, and to enable cost reduction, for example, using a metal with a purity of 99.9 to 99.99%, Fe · Si
Have been done. That is, 50
The crystallized substances produced in the 86 alloy include Mg-Si system and Al-Fe.
The system is known, and if the amount of Fe · Si decreases, these crystallized substances decrease, so that plating defects are less likely to occur.
Further, it was previously proposed that the number of plating defects can be reduced by adding Cu and Zn (Japanese Patent Publication No. 62-20).
No. 18).

On the other hand, in recent years, the Al substrate is required to have high strength. This is because, in recent years, small computers such as notebooks and palmtops are forming a large market, and in order to support these computers, hard disks in recent years are also strongly required to be thin and have a small diameter. For example, with regard to smaller diameters, small-diameter discs such as 2.5-inch discs are forming a large market.
Al substrate, which is called 30% thinner than conventional material, is now widely used.

[0006] Although the reduction in wall thickness is being further advanced at present, it has been found from the results of studies by the present inventors that the conventional Al alloy cannot cope with the reduction in wall thickness in the future. This is because the current disc material requires Ni-P plating on the Al substrate to harden the surface, but the plating film formed in this plating process has tension, and that tension is the surface. This is because the disk is deformed when the substrate is thinned because the back surface and the back surface are different. Also, the Al substrate is rapidly heated when sputtering the medium, but at this time the disc may be deformed due to the difference in tension between the front and back of the plating film, and further thinning causes the strength to drop sharply. , It turned out that it is easily deformed by handling.

Therefore, hard disk manufacturers
We are studying new substrates such as glass and carbon as the substrates for future thinning. Since these substrates have high hardness and strength, deformation is unlikely to occur and thinning is possible. However, these bases have the problems of higher cost and lower productivity than the conventional Al base. In addition, when a new base is used, the coefficient of thermal expansion and elastic coefficient are different from those of the conventional base, so that the design of the hard disk must be changed.

Therefore, it is the most excellent solution at present to improve the strength of Al alloy. For this purpose, the present inventors previously proposed a method for producing an aluminum alloy plate for a very small diameter thin disk in Japanese Patent Application No. 2-16354, but there is a problem that the hardness during handling is insufficient. On the other hand, magnetic disks are required to be further reduced in cost. Therefore, it is important to further reduce the thickness of the undercoat and to reduce the polishing allowance.
Therefore, it is necessary to reduce the number of plating defects and the defect size. In view of this point, it has been attempted to further increase the purity of the metal ingot, but it is known that this increase in purity lowers the strength of the Al base, and the same material is used for thinning that is considered to progress in the future. Cannot handle.

The present invention solves the above-mentioned drawbacks of the prior art,
It is an object of the present invention to provide an aluminum alloy plate for thin-walled discs, which has high strength and is excellent in plating property and handling resistance, corresponding to the reduction in thickness, and also to provide a manufacturing method thereof.

[0010]

The inventors of the present invention have conducted various studies in view of such circumstances, and as a result, in order to improve the plating property, high purification (that is, regulation of the amount of Fe / Si) is performed. )
It is unavoidable that the strengthening of the Al alloy must be solved by another factor while accepting this purifying.

Therefore, as a result of diligent examination of the composition and manufacturing process, the addition of Mg is most effective for increasing the strength of the Al alloy.
We have determined that the size does not deteriorate.

However, conventionally, the DC casting method has been applied to
When manufacturing an Al alloy plate with a g amount exceeding 5.0%,
It could not be used as a disc material because surface cracks and the like occurred in the hot rolling process. Therefore, as a result of investigating the cause of this crack, the present inventors found that when an Al alloy having a high Mg content was hot-rolled, a huge crystal grain was formed on the surface of the rolled plate due to the introduction of a rapid strain at high temperature. Since it was formed, it was determined that cracking occurred. Therefore, conventionally, hot rolling was performed at a low temperature of 450 ° C. with a composition having such a high Mg content.

On the other hand, it is indispensable that the size of the crystallized substance is small in the disk application. This is because if the crystallized product becomes coarse, the crystallized product will fall off during the grinding or plating process, causing plating defects. Here, hot rolling at a high temperature (500 ° C. or higher) is indispensable for refining crystallized substances. This is because the crystallized material becomes coarse when hot rolling is performed at a temperature of 500 ° C. or less.

As described above, in the case of an Al alloy for use as a disk, hot rolling at a low temperature is indispensable from the viewpoint of crack prevention, and high temperature soaking / hot rolling is indispensable because of problems in the subsequent steps. Due to this contradiction, up to now, Al alloys with a Mg content of 5.0% or more, which are likely to cause hot rolling cracking, have been conducted only at a research level without problems such as yield, productivity and cost. , Could not be applied to actual production.

Therefore, as a result of further research conducted by the present inventors to apply an Al alloy having a high Mg content to a disk material, Al
It was determined that hot rolling cracks do not occur if only the surface of the alloy ingot or plate has a low temperature. That is, if only the extreme surface layer of the plate has a low temperature, coarsening of crystal grains does not occur, so hot rolling cracks can be prevented, and since the inside of the ingot has a high temperature, crystallized substances may not coarsen. found. Further, although crystallized substances are coarsened on the surface of the plate, this portion is removed by grinding or the like, so that it practically does not serve as a disk. At that time, it is desirable to lower the temperature of only the outermost surface layer of the ingot or plate, and it is necessary to cool only the surface by cooling the surface with oil-containing water, etc., and to keep the temperature inside the ingot high. Is. Further, when the processing rate is low and the amount of strain introduced is small, coarsening of crystal grains does not occur, and thus cracks do not occur. Therefore, the same effect can be obtained by rolling so that the processing rate is low until the temperature of only the surface of the plate decreases.

Further, it has been clarified that the addition of Mn reduces the size of plating defects and is effective for further increasing the hardness. However, if too much Mn is added, the crystallized material will become coarse and cause plating pits, so it is necessary to control the content to 0.5% or less.

Based on the above findings, the manufacturing technique of the aluminum alloy plate for thin-walled discs to which the DC casting method was applied was completed.

On the other hand, as a result of subsequent research, in the case of this manufacturing technique, temperature control during hot rolling becomes very strict during mass production, and in terms of quality, it is very difficult to eliminate plating defects with the same material. However, it is difficult to say that it will be possible to fully cope with future high density.

That is, in thin film media, Ni-P plating is usually applied to the Al alloy substrate for surface hardening. However, when this plating treatment is performed, protrusions or dents on the plated surface, so-called nodule (plated surface Plating defects called protrusions) and pits (dents on the plated surface) occur. This plating defect is removed by polishing the plated film in a later step.
However, it has been found that extremely fine plating pits are likely to occur at the sites where such defects occur. Such pits have not been a cause of data errors in the past, but with the recent increase in density, such fine pits are becoming a cause of data errors. Therefore, in recent years, elimination of all plating defects has been studied.

As a result of diligent studies by the present inventors in this regard, they found that there is a correlation between the number and size of the plating defects and the number of Al-based crystallized substances and crystallized substance size. Further, the present inventors pursued the reason why the crystallized substance causes the plating defect, and as a result, the crystallized substance having a diameter of 6 μm or more is the first crystallized substance causing the plating defect. Investigated. Further, it has been found that such coarse crystallized substances cause plating defects due to the following reasons.

That is, in the case of a crystallized substance having a small size of 6 μm or less, it dissolves and falls off during the pretreatment of the plating, and the Ni-P after it is removed
Since it is leveled in the plating process, it does not cause plating defects. However, when the crystallized substance is as large as 6 μm or more, the crystallized substance is not completely dissolved during the pretreatment of the plating, and the crystallized substance remains in the Ni-P plating step. It was clarified that it does not precipitate but becomes a defect.

This crystallized substance is known to exist as Mg-Si system / Al-Fe system in the 5086 system.
When the amount is small, these crystallized substances are naturally small and it is possible to reduce plating defects. For example, the purity is 99.9.
Although it has been aimed to reduce the size of crystallized substances by using high purity metal such as 9%, it is impossible to eliminate coarse crystallized substances in spite of such high purification.

Therefore, the present inventors first examined the casting conditions, and found that the thinner the ingot, the faster the cooling rate, and the crystallized substances could be made finer. Also,
It was clarified that the crystallized substances generated at this time could not be easily reduced in the subsequent steps such as hot rolling and cold rolling. Therefore, it is essential to make the casting thickness as thin as possible.
It has been found that it is sufficient to cast to a size of mm or less.

Next, as a result of studying hot rolling,
It was clarified that no matter how high the temperature was during hot rolling, the number of crystallized substances increased. This is because the solid solution Si.Fe precipitates due to the strain generated during hot rolling. However, the higher the hot rolling temperature is, the more the precipitation amount of crystallized substances can be reduced. However, it was found that the most desirable thing is not to perform hot rolling. This hot rolling step is usually performed to make a square ingot into a plate shape, but it is not always necessary if the ingot thickness at the time of casting is thin as described above. On the other hand, the cold rolling step is an essential step for reducing the crystal grain size of the alloy and maintaining the strength, but since the cold rolling temperature is as low as 200 ° C. or less, solute precipitation does not occur,
It was found that the crystallized material did not coarsen in this step.

As described above, if the hot rolling step is omitted by the thin casting method for refining the crystallized substance during casting, the crystallized substance coarsening in the subsequent step can be eliminated, It was found that even with high Mg materials, stable quality and elimination of plating defects are possible. According to this thin casting method, M
It was also found that the solidification was completed even in the central part of the ingot before g was volatilized, and it was possible to cope with a higher Mg content.

Based on the above findings, the manufacturing technique of the aluminum alloy plate for thin-walled discs to which the thin plate continuous casting method is applied has been completed.

That is, in the present invention, as an essential element, M
g: 5.5-7.5%, Cu: 0.03-0.3
%, Mn: 0.1-0.5%, and if necessary, further Z
n: 0.3% or less, the balance consisting of Al and impurities, of which Fe and Si are Fe ≦ 0.1%,
It is regulated to Si ≦ 0.1% and the ratio of Mn amount and Fe amount (Mn / F
The gist is an aluminum alloy plate for a thin disk to which a DC casting method is applied, characterized in that e) is 3 or more.

The manufacturing method of the aluminum alloy having the above chemical composition is as follows: the ingot by DC casting is soaked at a high temperature of 510 ° C. or higher, then only the surface is cooled and rolled until the surface temperature reaches 450 ° C. It is characterized in that the hot rolling is performed at a rate of 5% or less, or the hot rolling is performed after the surface temperature becomes 450 ° C. or less.

Furthermore, in another aspect of the present invention, as an essential element, M
g: 5.5-8.0%, Cu: 0.03-0.3
%, Mn: 0.1-0.5%, and if necessary, further Z
n: 0.5% or less, the balance consisting of Al and impurities, of which Fe and Si are Fe ≦ 0.1%,
The gist is an aluminum alloy plate for thin-walled discs to which a thin plate continuous casting method is applied, which is characterized by being regulated to Si ≦ 0.1%.

Further, the manufacturing method is characterized in that an aluminum alloy having the above chemical composition is cast by a thin plate continuous casting method to a thickness of 8 mm or less, and then the hot rolling step is omitted and cold rolling is performed. There is.

[0031]

The present invention will be described in more detail below. First, the reasons for limiting the chemical composition of the Al alloy in the present invention will be explained.

Mg: Mg is the most effective element for improving the strength of the Al alloy base, and is usually added in an amount of about 4% as a disc material. However, with this addition amount, sufficient strength cannot be obtained when the metal purity is highly purified, so 5.5% or more is required to reduce the thickness with a highly pure material. But DC
In the case of the casting method, if the Mg content exceeds 7.5%, problems such as segregation become so great that it becomes very difficult to industrially use it. On the other hand, even if the thin plate continuous casting method is applied, the Mg content is large. If it exceeds 8.0%, problems such as segregation occur and it cannot be used industrially. Therefore, the content of Mg is 5.5 to 7.5%, preferably 6.2 to 7.5% in the DC casting method, and 5.5 to 8.0 in the thin plate continuous casting method. %.

Mn: Mn is an element necessary for promoting work hardness and raising the annealing recrystallization temperature. It also has the effect of reducing the size of plating defects. This is because a part of the coarse Al-Fe-based crystallized substance is replaced to form Al <Mn.Fe>, and as a result, the coarse Al-Fe-based crystallized substance is reduced. However, if the amount of Mn is less than 0.1%, this effect cannot be expected sufficiently, and if it exceeds 0.5%, pits (holes formed in plating) rapidly increase, which is not preferable. Therefore, the amount of Mn added is 0.1 to 0.1.
5%.

Addition of Mn / Fe: Mn has the above effect. However, in the case of the DC casting method, Mn with respect to the Fe amount
When the amount ratio (Mn / Fe) is Mn / Fe <3, very many pits are formed even within the above composition range. This is Mn /
When Fe <3, Mn is not too small compared to the Fe amount,
This is because coarse Al-Fe-based crystallized substances are produced together with the Al <Fe.Mn> -based crystallized substances. Here, the Al-Fe system crystallized substance causes the pits because the potential difference between the Al base and the Al-Fe system crystallized substance is large. Al <Fe ・ Mn
In the case of the> crystallized substance, a pit is unlikely to occur because the potential difference from the Al base is small. Therefore, in the case of the DC casting method, it is necessary to satisfy the relationship of Mn / Fe ≧ 3. It should be noted that Mn / Fe ≧ 5 is desirable, because it depends on the balance with the plating conditions whether or not a pit occurs.

Cu: Cu uniformly dissolves in the Al alloy, and has the effect of making the precipitation of Zn on the substrate surface during the zincate treatment uniform and fine. This can suppress the generation of nodules on the plated surface. However, if the Cu content is less than 0.03%, the above effects cannot be obtained, and the Cu content is 0.3%.
If it is added in excess, the amount of nodules is increased and the etching property of the crystal grain boundaries becomes excessive, and the smoothness of the plated surface is impaired. Therefore, the amount of Cu is set to 0.03 to 0.3%.

Zn: Zn also dissolves uniformly in the Al alloy to make the precipitation of Zn on the substrate surface during zincate uniform and fine, and has the effect of suppressing the generation of nodules. However, Z
It was found that the proper amount of n added greatly depends on the plating conditions. That is, when Zn is not added, nodules can be reduced when plating is performed under conditions where plating pits are unlikely to occur, but conversely, when plating is performed under conditions where plating pits are likely to occur, a large number of platings are performed. A pit will occur. On the other hand, if the addition amount is too large, the etching property of the crystal grain boundaries becomes excessive and causes plating defects. Therefore, the addition amount of Zn is preferably not added, and when it is added, it is 0.3% or less, preferably 0.08% or less in the case of DC casting, while it is 0% in the case of thin plate continuous casting. It should be less than 0.5%.

Fe: Fe mixes in as a metal impurity and easily forms an Al--Fe intermetallic compound in a casting process or the like. This intermetallic compound falls off during processing as a disk substrate, such as cutting, polishing and grinding during so-called substrate processing, and becomes a dent, and it also falls off during the plating pretreatment process, causing pits on the plated surface. Becomes Therefore, the Fe amount is 0.1% or less. The lower limit of the amount of Fe is not specified, but if it is 0.005% or less, extremely expensive metal such as 99.99% of purity is required, which is not only economically wasteful but also plating. However, since the effect of refining crystallized substances is saturated and a problem arises in the adhesion of plating, 0.005% or more is preferable.

Si: Si is also mixed in as a metal impurity and produces Mg-Si type crystallized substances in the casting process and the like. Since this Mg-Si system crystallized substance falls off in the plating pretreatment step and causes a plating pit, the amount of Si is 0.1.
% Or less. More preferably, it is 0.06% or less.
The lower limit of the Si amount is not specified, but
If it is less than 005%, an extremely expensive metal such as a purity of 99.99% is required, which is not only economically wasteful but also the effect of refining crystallized substances is saturated when plating is applied. , There is also a problem with the plating adhesion, so 0.0
05% or more is preferable.

In the aluminum alloy for disks according to the present invention, Cr, Ti, B other than these impurities are used.
Etc. may be included in the range permitted by the JIS5086 alloy.

Next, the manufacturing process of the present invention will be described.

First, an aluminum alloy having an appropriate metal purity is melted at a temperature equal to or higher than the melting point, and Mg, Mn, Cu, etc. are added so as to have an appropriate concentration. Then, casting is performed thereafter. There are DC casting method and thin plate continuous casting method as casting methods.
In the present invention, for the following reason, hot rolling is performed under specific conditions in the case of the DC casting method, and hot rolling is omitted in the case of the thin plate continuous casting method.

DC casting: 51 ingots obtained by DC casting
Soak at a temperature of 0 ° C or higher. Such high temperature soaking is necessary for refining crystallized substances. The crystallized substance is a general term for intermetallic compounds generated during casting, but when the crystallized substance becomes coarse, it is known that the crystallized substance falls off in the grinding or plating process, which causes plating defects. There is. Therefore, it is necessary to miniaturize the crystallized substances to prevent plating defects. In order to refine the crystallized substances, it is necessary to increase the cooling rate during casting to prevent coarse crystallized substances from forming and to form a solid solution of the crystallized substances generated during casting by soaking. Becomes Therefore, as a result of investigating the solid solution condition of the crystallized product by soaking, the present inventors have found that the crystallized product is rather coarsened by soaking below 510 ° C. This is because the crystallized substances do not form a solid solution in the Al base metal at a temperature lower than 510 ° C., and rather the intermetallic compounds gather around the crystallized substances. Note that 51
If the temperature is 0 ° C or higher, the crystallized substance becomes finer, but it is preferably 530 ° C or higher in order to complete soaking within a time period in consideration of productivity.

Continuous thin plate casting: On the other hand, in the case of continuous thin plate casting, the thickness of the ingot is preferably 8 mm or less. This is to increase the cooling rate during casting and refine the crystallized substances. If the thickness of the ingot exceeds 8 mm, not only the cooling rate becomes slow, but also the solute is concentrated in the central portion, which makes the portion extremely brittle, which is not preferable. The cooling rate becomes faster as the cast plate thickness becomes thinner, but the thickness of the Al alloy substrate for HDD is about 1.5 mm.
Since 0% or more is desirable, a thickness of 3 mm or less is not desirable. It is desirable that the ingot be soaked. This heat treatment is carried out in order to remove the casting strain and make rolling possible and to make the casting structure uniform. If the heat treatment temperature is 300 ° C. or lower, the homogenizing effect is not sufficient, and if it is 550 ° C. or higher, the Al alloy is melted.

Hot rolling: Only when DC casting is performed, hot rolling is performed thereafter. Conventionally, an Al-4.0% Mg alloy has been mainly used as an Al alloy for a disk, but with such an Al alloy, it has been necessary to perform hot rolling at 500 ° C. or higher. This is because, as described in the section of the soaking temperature, the crystallized substance becomes extremely coarse when the hot rolling start temperature becomes 500 ° C. or lower.

On the other hand, with an Al alloy containing 5.8% or more of Mg, when hot rolling is carried out at a high temperature of 500 ° C. or more, surface cracking occurs. Therefore, in order to prevent this cracking, it is necessary to reduce the amount of strain introduced until the temperature of the ingot or the hot-rolled sheet becomes 450 ° C. or less so that huge crystal grains do not occur. However, if the ingot or the whole rolled plate is kept at 450 ° C. or lower, as was conventionally done with Al alloys with a high Mg content,
As described above, the crystallized product becomes coarse. Therefore, when such a high-Mg alloy is applied to a disc, the inside of the ingot or hot-rolled sheet used as the disc is practically 5
It is necessary to keep the temperature above 00 ° C.

Therefore, as a result of repeated studies on the countermeasures, the present inventors reduced the temperature of only the surface of the ingot or the plate with water containing oil and the like, and kept the temperature at 500 at the center of the ingot.
It has been found that by keeping the temperature at or above 0 ° C., cracking on the surface can be prevented and the crystallized substance at the practically problematic portion can be made fine. Further, at that time, by introducing a rolling reduction of 5% or less until the temperature on the plate surface reaches 450 ° C., the amount of strain introduced at high temperature can be reduced, and cracking due to hot rolling can be prevented. I found that I can.

That is, the Al alloy ingot (or the thin plate continuous cast coil) is subjected to soaking and rolling. At this time, the soaking is carried out at a temperature of 510 ° C. or higher, preferably within 48 hours, and then, In the hot rolling, as described above, hot rolling is performed while suppressing the hot working rate to 5% or less until only the surface is lowered to 450 ° C. so that the plate does not crack.
Alternatively, it is necessary to reduce the temperature to 450 ° C. or lower before performing hot rolling without rolling until the surface temperature reaches 450 ° C. An appropriate refrigerant can be used for cooling the surface, but water containing oil or the like is preferable.

On the other hand, in the case of thin plate continuous casting, hot rolling is omitted. The reason is as follows.

That is, hot rolling is an essential step in the normally used direct casting method, and is a step of forming an ingot having a thickness of 200 mm or more into a plate of 20 mm or less. As a result of diligent studies conducted by the present inventors on the same step, it was found that no matter how hot the hot rolling was performed, the crystallized material was coarsened in the other step. As a result of studying the cause of this, when rolling is performed at a high temperature of 300 ° C. or higher as in the same process, Si / Fe, etc. which are solid-solved in Al due to strain stress are Al-Fe / Mg-Si based intermetallic compounds. As a result, it was determined that the crystallized product was coarsened as a result. The crystallized product refers to, for example, an Al-Fe-based or Mg-Si-based intermetallic compound that is usually generated during casting, and the precipitate refers to a fine intermetallic compound that is generated by hot rolling or the like. It was clarified that coarsening of crystallized substances during hot rolling occurs because precipitation of the intermetallic compound occurs on the crystallized substances. Therefore, like the alloy of the present invention, in order to completely eliminate plating defects, it is necessary to omit hot rolling in an alloy in which coarse crystallized substances tend to be eliminated but compositionally crystallized substances are likely to occur. Becomes

Whether hot rolling is performed or omitted, cold rolling is then performed. In the cold rolling process, the plate thickness is reduced to a thickness that can be used as a disc. Since this step is performed at a low temperature of 200 ° C. or lower, it was found that the crystallized product was not coarsened. Further, since the crystal grain size is reduced by this step, it is an indispensable step when strength is intended as in the present invention.

The steps and conditions after the cold rolling step are not particularly limited. The rolled plate is punched, cut into a disk shape, and annealed as necessary to remove distortion. The above process is a so-called disc blank manufacturing process.

Roughness of an ordinary rolled plate is, for example, Ra = 0.1 to
Since it is as large as 0.5 μm as a disk substrate and it is necessary to further reduce the strain, the disk surface is removed by cutting or polishing, but in this case, removing the surface of less than 5 μm is not enough to remove the strain, and If it exceeds 50 μm, there is a problem in productivity and cost. Therefore, a grinding amount of 5 to 50 μm is suitable for a disc base of an aluminum alloy plate. After that, annealing is performed as necessary to remove the processing strain. The above process is what is called Al substrate processing.

Substrate is plated on this substrate.
The plating process usually includes a pretreatment process such as degreasing, etching, and Zn substitution, and an actual plating film forming process. A nonmagnetic material such as Ni-P is usually used for the plating film, but there is also a method of performing the same strike plating before the plating of Ni-P or the like. Since the plating process is performed for the purpose of imparting hardness to the surface, it is desirable to use a plating film with a thickness of at least 5 μm or more. If it is too thick, a large amount of plating solution is required, which is economically disadvantageous. Because there is 20
It is not preferable to set it to more than μm. By this plating process, a so-called base plating substrate can be manufactured.

Next, this base plating substrate is subjected to a polishing step to remove plating defects and obtain surface smoothness.
Further, so-called texture processing is performed as necessary, and a magnetic film is formed by sputtering or the like, and then used as a magnetic disk.

Next, examples of the present invention will be described.

[0056]

[Example 1]

The aluminum alloy having the chemical composition shown in Table 1 was ingot-cast and then face-cut into a 50 mm × 220 mm × 250 mm ingot. Then, soaking was performed at 520 ° C., and then hot rolling was performed under the conditions (hot rolling start temperature, working rate) shown in the table. At that time, water containing oil was used for cooling the plate surface. In this hot rolling, the plate surface temperature was measured and the presence or absence of cracks was investigated. The results are also shown in Table 1. The finished plate thickness in hot rolling was set to 6 mm, and then cold rolling was performed to 0.9 mm.

Next, this plate material is punched into a hollow disk having an outer diameter of 130 mm and an inner diameter of 40 mm, and the hollow disk is heated at 340 ° C. for 2 hours.
Strain relief annealing was performed for a period of time. Further, after the surface of the disk was cut to form a substrate, a plating test was conducted.
The plating process is shown in Table 2.

The results of these plating tests and the mechanical properties are shown in Table 3. However, no investigation was conducted on cracks that occurred during hot rolling. The plating test was evaluated by observing 66 surfaces at 640 magnification with an optical microscope, and the diameter was 10 μm.
The measurement was performed by counting the above nodules and the number of pits having a diameter of 1 μm or more. The number of nodules is 5
mm ² or less ◎, 10 / mm ² or less ○, 20
The number of pits / mm ² or less is indicated as △, and the number of pits of 30 / mm ² or more is indicated as ×, and the number of pits is 0 / mm ² ○, 5 / m
Those with m ² or less are shown as Δ, and those with more than m ² are shown as ×. Comprehensive evaluation: ○ If the yield strength, which indicates the deformation resistance during handling, is 150 N / mm ² or more and there are no plating pits, ○; if the yield strength is high but the plating pits are produced, △; Even if no defect occurred, it was rated as x.

As is clear from Table 3, each of the examples of the present invention has excellent strength and good plating property.

[0061]

[Table 1]

[0062]

[Table 2]

[0063]

[Table 3]

[0064]

Example 2 An aluminum alloy having the chemical composition shown in Table 4 was wrought and then face-polished to obtain 50 mm × 220 mm × 250 mm.
mm ingot was used. Then, soaking was performed at 530 ° C., and then hot rolling was performed. The hot rolling was performed at a working rate of 3% with water containing oil until the surface temperature reached 450 ° C. The finished plate thickness in hot rolling was set to 6 mm, and then cold rolling was performed to 0.9 mm. After this rolled plate was made into an O material at 340 ° C., it was processed into 0.9 mm × 10 mm × 200 mm and subjected to a bending test and a drop test.

The bending test was carried out by fixing one end in the length direction of the plate and applying a load of 85 N to the other end, and measuring the amount of deformation at this time (see FIG. 1). Here, the smaller the numerical value of the material, the better the handling resistance. The drop test was performed using a DuPont test machine (see FIG. 2). In the same test, a test piece was dropped from a punch height of 50 mm of 163 g, and the amount of deformation of the test piece at that time was measured. In this test, the smaller the value of the material, the better the handling resistance.

The test results are shown in Table 5. As can be seen from this table, the examples of the present invention are much more excellent in handling resistance than the conventional alloys.

[0067]

[Table 4]

[0068]

[Table 5]

[0069]

Example 3

Aluminum alloys having the chemical composition shown in Table 6 were ingot-cast by a thin plate continuous casting method to a thickness of 7 mm, and soaking was carried out at 510 ° C. Then, cold rolling was performed to 0.9 mm.
Further, a heat treatment was performed at 350 ° C., and mechanical properties and hardness were measured. As for the strength evaluation, those with a proof stress of 160 N / mm ² or more and a hardness of 80 MHv or more are ◎, and a proof stress is 130 N / m.
Those having m ² or more and hardness of 70 MHv or more were evaluated as ◯, and other materials were evaluated as x. The results are shown in Table 7.

The cold-rolled sheet was punched into a disk, subjected to sub-processing, and then N-plated using a commercially available plating solution.
The i-P plating was performed and the plating defect was evaluated. As an evaluation standard, there are no nodules of 10 μm or more and no pits ◎ 10 nodules of 10 μm or more / mm ² or less without pits ○ 10 nodules of 10 μm or more / mm ² or more, Or, those with pits were marked with x. The results are shown in Table 7.

As is clear from Table 7, all the examples of the present invention have excellent strength and plating property.

[0073]

[Table 6]

[0074]

[Table 7]

[0075]

Example 4

Aluminum alloys having the chemical composition shown in Table 8 were ingot-cast by a thin plate continuous casting method so that the thickness of the ingot was 5 to 100 mm, followed by heat treatment at 350 ° C. for 3 hours, and then the crystallized product A distribution survey was conducted. As a result, as shown in Table 9, it can be seen that when the cast plate thickness is 8 mm or less, the crystallized substances of 6 μm or less can be completely eliminated.

[0077]

[Table 8]

[0078]

[Table 9]

[0079]

Example 5

In order to investigate the influence of hot rolling, aluminum alloys having the chemical composition shown in Table 10 were formed by thin plate continuous casting.
It was cast to a thickness of mm, then soaked at 520 ° C., and then hot-rolled to obtain a plate having a thickness of 4 mm. This plate was polished and the distribution of crystallized substances was investigated. As a result, as shown in Table 11, it can be seen that the crystallized product becomes coarser at any temperature when hot rolling is performed.

[0081]

[Table 10]

[0082]

[Table 11]

[0083]

As described in detail above, according to the present invention,
It is possible to provide an aluminum alloy plate for thin-walled discs that has high strength and is excellent in plating properties and handling resistance. Particularly, the effect of completely eliminating plating defects and being able to sufficiently cope with thinning is extremely large.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the procedure of a bending test.

FIG. 2 is a schematic diagram showing a procedure of a drop test.

Claims (7)

[Claims] 1. The composition contains Mg: 5.5 to 7.5% as an essential element in weight% (hereinafter the same), and further contains Cu: 0.03 to
0.3%, Mn: 0.1 to 0.5%, the balance consisting of Al and impurities, of which Fe and Si are F
Aluminum for thin-walled discs to which DC casting method is applied, characterized in that e ≦ 0.1% and Si ≦ 0.1%, and the ratio of Mn amount to Fe amount (Mn / Fe) is 3 or more. Alloy plate. 2. The aluminum alloy plate according to claim 1, further containing Zn: 0.3% or less. 3. The aluminum alloy having the chemical composition according to claim 1 or 2, after soaking the ingot by the DC casting method at a high temperature of 510 ° C. or higher, only the surface is cooled, and the surface temperature becomes 450 ° C. A method for producing an aluminum alloy sheet for thin-walled disks, which comprises performing hot rolling at a rolling rate of 5% or less or performing hot rolling after the surface temperature reaches 450 ° C. or less. 4. The method according to claim 3, wherein water containing oil or the like is used for cooling only the surface. 5. An essential element containing Mg: 5.5 to 8.0%, Cu: 0.03 to 0.3%, Mn: 0.1 to 0.5%.
%, With the balance being Al and impurities, of which Fe and Si are Fe ≦ 0.1% and Si ≦ 0.1%, respectively.
Aluminum alloy plate for thin-walled discs, which is produced by the continuous thin plate casting method, characterized in that 6. The aluminum alloy plate according to claim 5, further containing Zn: 0.5% or less. 7. An aluminum alloy having the chemical composition according to claim 5 or 6, which has a thickness of 8 by a thin plate continuous casting method.
A method for manufacturing an aluminum alloy plate for a thin-walled disc, which comprises casting to a thickness of not more than mm and then omitting the hot rolling step and cold rolling.