JP3710009B2 - Aluminum alloy plate for magnetic disk substrate and manufacturing method thereof - Google Patents

Description

【００４８】
【表２】

【００４９】
【発明の効果】
このように本発明のアルミニウム合金板を本発明の製造方法により加工することにより、大容量の磁気ディスクで問題となるノジュールやマイクロピットの極めて少ない磁気ディスク基板用アルミニウム合金板を提供することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an aluminum alloy for a magnetic disk substrate, and more particularly to an aluminum alloy for a magnetic disk substrate that has very few pits and nodules in the base treatment and has excellent plating properties, and a method for manufacturing the same.
[0002]
[Prior art]
In recent years, magnetic disks have been increased in capacity and density, and the occupied area per bit of the magnetic disk and the distance between the magnetic head and the magnetic disk have been decreasing.
[0003]
In general, a magnetic disk is formed by grinding an aluminum alloy substrate, electrolessly plating a hard nonmagnetic metal such as amorphous Ni-P as a base treatment for coating the magnetic film, and polishing and then sputtering a magnetic film such as Co. -A Ni-P alloy is coated and manufactured.
Such a magnetic disk substrate is required to have the following characteristics.
[0004]
(1) It is a non-heat treatment type and has sufficient strength to withstand high speed rotation during various processing and use.
(2) Light weight, good mirror surface can be obtained by polishing, and no surface defects such as pits are generated.
(3) Adhesiveness and surface smoothness of electroless plating as a base treatment are excellent, and defects such as pits do not occur after plating.
[0005]
As a magnetic disk substrate satisfying such characteristics, JIS A5086 aluminum alloy (Mg: 3.5 to 4.5 wt%, Fe: ≦ 0.5 wt%, Si: ≦ 0.40 wt%, Mn: 0.2 to Impurities of 0.7 wt%, Cr: 0.05 to 0.25 wt%, Cu: ≦ 0.10 wt%, Ti: ≦ 0.15 wt%, Zn: ≦ 0.25 wt%, balance: A1) and JIS A5086 alloy An alloy is used in which the amount of elements such as Fe and Si is regulated to reduce the intermetallic compound produced in the matrix.
[0006]
However, the substrate made of the JIS A5086 aluminum alloy has a problem that an intermetallic compound in the alloy is dropped during the zincate treatment to generate pits. In the case of conventional electroless plating with a thickness of about 20 μm, this pit did not cause a problem because it often disappeared by subsequent polishing polishing, but the recent plating thickness is, for example, 14 μm, and tends to be thin Therefore, pits remain even after polishing and the surface smoothness of the magnetic disk substrate is impaired.
[0007]
In addition, an aluminum alloy plate is punched to a predetermined size, and thereafter, cutting or grinding is performed. At that time, the intermetallic compound may fall off, resulting in a pit defect.
[0008]
In order to prevent such pit defects, it is desired to reduce the size and size of the intermetallic compound of the aluminum alloy substrate, and various measures have been taken so far.
[0009]
For example, in Japanese Patent Laid-Open No. 2-97639, in order to improve the smoothness of electroless Ni—P alloy plating, the kind and amount of a small amount of additive element in the pretreatment zincate treatment liquid is controlled, and the zincate film is thinned. A method for improving minute defects in a plating film by depositing uniformly and densely is disclosed. In fact, an aluminum alloy for a magnetic disk substrate by this method has been put into practical use and has been highly evaluated.
[0010]
[Problems to be solved by the invention]
However, the magnetic disk substrate by these methods cannot cope with a large-capacity magnetic disk of 2 GB / sheet or more in recent years, and causes the following problems.
[0011]
For one thing, the flying height of the magnetic head has been reduced from 1.5 μ ″ to 1 μ ″ (μ ″: microinch) for the purpose of increasing the capacity. The hemispherical protrusions (nodules) on the disk surface collide with the head and cause a head crash.This is because of light polishing polishing from the viewpoint of economy and to prevent the edge from sagging. However, this is because nodules are likely to remain after polishing.
[0012]
The other is that the area occupied by one bit is reduced due to the increase in capacity, and small pits (micropits) on the very surface of the magnetic disk substrate after the base plating also cause electrical errors. is there.
The present invention has been made to solve such a problem, and an object of the present invention is to provide an aluminum alloy plate for a magnetic disk substrate and a method for producing the same, which have very few nodules and micropits, which are problematic in a large-capacity magnetic disk. And
[0013]
[Means for Solving the Problems]
As a result of various studies conducted by the present inventors in view of the above-mentioned problems, the generation of nodules and micropits after the base plating is caused by intermetallic compounds in the substrate (Al-Fe series) in the pretreatment etching and zincate treatment. The following findings were obtained by finding that it is closely related to the dissolution reaction of Mg ₂ Si, Al—Cu, Al—Mg—Zn, Mg ₂ Al ₃ ) and the matrix.
[0014]
That is, this dissolution reaction is related to the natural potential difference existing between the matrix and the intermetallic compound. When the compound is noble with respect to the matrix, the matrix around the compound dissolves to form a recess. Moreover, when a compound is base with respect to Matrimas, the compound itself melt | dissolves and forms a recessed part. Examples of the former compound include Al—Fe and Al—Cu, and examples of the latter compound include Al—Mg—Zn and Mg ₂ Al ₃ .
[0015]
In the case of Mg ₂ Si, the surrounding matrix also dissolves, but Mg also dissolves, so that a concave portion in which Si remains is formed inside (since Si is a very inert element). Also, the Si inside may fall off.
[0016]
The nodule generation mechanism is the case where relatively small holes or sharp holes are generated in the pre-treatment on the substrate surface, and when the zincate grows preferentially in the center of the hole during the zincate treatment and becomes nodules, It may remain and have a face on the surface. The former compounds are mainly Al—Mg—Zn and Mg ₂ Al ₃ , and the latter compounds are mainly Al—Fe and Al—Cu.
[0017]
In the pit generation mechanism, a relatively large hole is generated in the pre-treatment on the substrate surface, and it grows along the hole during plating to form a pit. The causative compound is mainly Mg ₂ Si.
[0018]
The major axis of the intermetallic compound of Al—Fe and Mg ₂ Si is larger than that of the intermetallic compound of Al—Cu, Al—Mg—Zn, and Mg ₂ Al ₃ . Therefore, reducing the recesses due to elution of Al—Fe and Mg ₂ Si is effective for reducing large nodules and pits.
[0019]
In addition, since the natural potential of Al-Fe, Mg ₂ Si is more precious than the matrix, reducing the natural potential difference between the matrix and Al-Fe, Mg ₂ Si can also reduce the nodules and pits after the base plating. It is effective to reduce.
[0020]
Based on these findings, the inventors have made the following invention.
The first invention provides an aluminum alloy plate for a magnetic disk substrate having the following component composition (wt%).
Cu: 0.05 to 0.15 wt%, Mg: 2 to 6 wt%, Zn: 0.1 to 0.3 wt%, Zr: 0.05 to 0.12 wt%, and 2Cu + 6Zr-3Zn = 0 15 to 0.32 wt%, and further includes Mn: more than 0.01 and less than 0.05 wt%, Cr: more than 0.01 and less than 0.05 wt%. The impurities are regulated to Si: 0.1 wt% or less, Fe: 0.1 wt% or less, Ti: 0.02 wt% or less, the balance is made of Al and inevitable elements, and the inevitable elements are each 0.02 wt%. It is as follows.
[0021]
According to a second aspect of the present invention, in the surface layer of the aluminum alloy plate of the first aspect, the number of Mg ₂ Si particles having a major axis exceeding 5 μm per unit area is 20 / mm ² or less. An aluminum alloy plate is provided.
[0022]
According to a third invention, in the surface layer of the aluminum alloy plate of the first invention or the second invention, the number of Al—Fe-based intermetallic compounds having a major axis exceeding 5 μm per unit area is 20 pieces / mm ² or less. An aluminum alloy plate for a magnetic disk substrate is provided.
[0023]
4th invention provides the manufacturing method of the aluminum alloy plate (component composition is wt%) for magnetic disc board | substrates characterized by including the following processes.
(A) Cu: 0.05 to 0.15 wt%, Mg: 2 to 6 wt%, Zn: 0.1 to 0.3 wt%, Zr: 0.05 to 0.12 wt%, and 2Cu + 6Zr- 3Zn = 0.15 to 0.32 wt%, Mn: more than 0.01 and less than 0.05 wt%, Cr: more than 0.01 and less than 0.05 wt% 2 types of impurities, Si: 0.1 wt% or less, Fe: 0.1% or less, Ti: 0.02 wt% or less as impurities, the balance is made of Al and inevitable elements, the inevitable elements are A step of melting and casting an aluminum alloy each 0.02 wt% or less to obtain an ingot;
(B) a step of hot rolling the ingot to form a coil;
(C) cold rolling the coil after the hot rolling;
(D) A step of subjecting the coil after the cold rolling to final annealing.
[0024]
As another aspect , during cooling of the coil after hot rolling, between 240 and 150 ° C. is cooled at a cooling rate of 30 to 600 ° C./h, and during cooling after final annealing, between 240 and 150 ° C. is 30. A method for producing an aluminum alloy plate for a magnetic disk substrate, characterized by cooling at a cooling rate of ˜600 ° C./h.
[0025]
According to another aspect of the present invention, there is provided an aluminum alloy plate for a magnetic disk substrate characterized in that cold rolling is performed under a condition that the number of passes with a reduction rate of 20% or more is 3 times or more and the total reduction rate is 60% or more. A manufacturing method is provided.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
First, the significance of the alloy element in the alloy sheet of the present invention and the reason for limiting the alloy composition will be described (hereinafter, wt% of the alloy composition is simply abbreviated as%).
Cu: Since it is an element that makes the natural potential of the matrix noble, pits and nodules are reduced. If it is less than 0.05%, it is not sufficient to make the natural potential of the matrix noble, and if it exceeds 0.15%, the number of Al-Cu folds increases and nodules increase, and unevenness after plating (aggregation of nodules) ) Occurs and the surface becomes non-uniform, so the content is limited to 0.05 to 0.15%.
[0027]
Mg: mainly for obtaining strength. If it is less than 2%, sufficient strength cannot be obtained. If it exceeds 6%, an Al—Mg intermetallic compound is formed and non-metal such as MgO is produced by high-temperature oxidation during melt casting. Since the formation of inclusions becomes significant, the content is limited to 2 to 6%.
[0028]
Zn: Since it is an element that lowers the natural potential of the matrix, it increases pits and nodules. If the content is less than 0.1%, the silicate treatment becomes uneven, unevenness occurs after plating and the surface becomes uneven. If the content exceeds 0.3%, pits and nodules increase. 0.3%.
[0029]
Zr: An element that makes the natural potential of the matrix noble, so pits and nodules are reduced. If it is less than 0.05%, the natural potential of the matrix will not be sufficiently noble, and if it exceeds 0.12%, Al-Zr breakout will occur and pits and nodules are likely to occur. It is limited to 0.05 to 0.12%.
In order to prevent the generation of pits and nodules until a large-capacity magnetic disk substrate can be handled, in addition to the contents of Cu, Zn, and Zr, 2Cu + 6Zr-3Zn = 0.15 It is necessary to satisfy the relationship of 0.32%.
[0030]
Mn, Cr: At the time of homogenization of the ingot and / or during hot rolling and annealing, it breaks out as a fine compound and improves the adhesion of electroless plating to make the recrystallized grains fine, and part of it Since it dissolves in the matrix and improves its strength, it cuts and grinds aluminum alloy substrates.
[0031]
In each case of 0.01% or less, this effect is insufficient, and in the case of 0.05% or more, excess elements in the molten metal are removed by a filter during casting, and a coarse intermetallic compound is generated. Since not only during etching and zincate processing but also when cutting and polishing are performed, pit defects are generated, so the content is limited to more than 0.01 and less than 0.05%. In addition, although the effect is acquired even if it adds Mn and Cr independently, you may add combining.
[0032]
Fe, Si: Almost no solid solution is present in aluminum but exists as an intermetallic compound. When the amount is large, a large number of coarse intermetallic compounds such as Al—Fe, Mg ₂ Si are formed to cut the substrate. The pit defect is likely to occur at the time of grinding and zincate treatment, so it is limited to 0.1% or less.
[0033]
Further, other unavoidable impurity elements (for example, Ni, V, B, etc.) do not impair the effects of the present invention as long as they are 0.02% or less. Any alloy plate having the above-described composition can be used as a magnetic disk targeted by the present invention. However, this alloy plate can also be manufactured by processing an ingot having the above component composition by a normal rolling method.
[0034]
In the alloy plate, when the number of Mg ₂ Si particles having a major axis exceeding 5 μm per unit area is 20 pieces / mm ² or less, nodules and pits after the base plating can be further reduced. Furthermore, when the number of Al—Fe particles having a major axis exceeding 5 μm per unit area is 20 pieces / mm ² or less, the nodules and pits after the base plating can be significantly reduced.
[0035]
The aluminum alloy plate for a magnetic disk substrate of the present invention can be produced by melting the above-described aluminum alloy having the component composition of the present invention, and performing normal hot rolling, cold rolling and final annealing steps after casting. . However, more desirable quality can be obtained by limiting the conditions such as hot rolling and cold rolling as follows.
[0036]
Moreover, during cooling of the coil after hot rolling, between 240-150 ° C is cooled at a cooling rate of 30-600 ° C / h, and during cooling after final annealing, between 240-150 ° C is 30-600 ° C. When cooling at a cooling rate of / h, the number of Mg ₂ Si particles having a major axis exceeding 5 μm per unit area can be reduced to 20 / mm ² or less respectively, and the nodules and pits after the base plating can be significantly reduced.
[0037]
Further, when the cold rolling is performed under the condition that the number of passes with a reduction rate of 20% or more is 3 times or more and the total reduction rate is 60% or more, the long diameter is larger than 5 μm per unit area of Al—Fe particles. The number can be reduced to 20 pieces / mm ² or less, and the nodules and pits after the base plating can be significantly reduced.
[0038]
【Example】
Commercially available Al ingot with a purity of 99.9% or more is dissolved, and alloy elements are added to it, and an Al alloy having the component composition shown in Table 1 is melted, degassed and settled, and then filtered through a filter. Then, continuous casting was performed to obtain an ingot having a thickness of 350 mm, a width of 1000 mm, and a length of 2000 mm.
[0039]
After chamfering both sides of this ingot by 10 mm and soaking at a temperature of 520 ° C. ± 20 ° C. for about 6 hours, hot rolling (rolling temperature: 520-400 ° C., number of rolling passes: about 20) And a final thickness of about 5.5 mm) and cold rolling (including intermediate annealing, 4 passes) to obtain a plate material having a thickness of 0.82 mm.
[0040]
A doughnut plate having a diameter of 96 mm and an inner diameter of 24 mm was punched from this plate material, annealed at 340 ° C. for 4 hours, and then ground. Thereafter, a plating process was performed under the following conditions to investigate micropits, nodules, and surface roughness.
[0041]
(Processing conditions)
Degreasing: (Uemura Kogyo AD68, 50% 6 minutes)
↓
Etching: (〃 AD101, 10% 2 minutes)
↓
Death Mat: (HNO ₃ 30% 1 minute)
↓
First zincate: (Uemura Kogyo AD301, 30% 6 minutes)
↓
Nitric acid stripping: (HNO ₃ 30% for 1 minute)
↓
Second zincate: (Uemura Kogyo AD301, 30% 20 seconds)
↓
Ni-P plating: (Uemura Kogyo HDX plating thickness 13 μm)
[0042]
Micropits are evaluated by observing a 3 mm ² field of view with an optical microscope, counting the number of less than 2 A, 2 to less than 5 B, and 5 to less than 15 C, 15 or more and less than 25 were D, and 25 or more were E, and the evaluation was performed in a five-step evaluation.
[0043]
The nodule was evaluated in the same manner, and those exceeding 10 μm were less than 2 A, 2 to 5 less than B, 5 to less than 15 C, 15 to less than 25 The evaluation was performed in a five-step evaluation, with D as the object and E as 25 or more.
[0044]
The surface roughness was measured with a universal surface roughness meter SE-3H (manufactured by Kosaka Laboratories), the centerline roughness Ra (μm) defined in JIS B0601 was measured at four points, and the average value was evaluated. .
[0045]
The measurement results are shown in Table 1. As is clear from Table 1, it can be seen that the examples of the present invention are excellent in terms of micropits, nodules, and surface roughness. On the other hand, it can be seen that a comparative example out of the composition range of the present invention is inferior in any of micropits, nodules, and surface roughness.
[0046]
As for the production conditions, No. for the alloy of the present invention. No. 5 is used, and the comparative alloy is No. 15 alloys were manufactured under the conditions shown in Table 2, and micropits and nodules were evaluated in the same manner as described above. In Table 2, the cooling rate of hot rolling (° C./h) is the rate of cooling between 240 ° C. and 150 ° C. after hot rolling, the total reduction rate is the total reduction rate, and the single reduction rate Denotes the reduction rate per pass, and the cooling rate of the final annealing refers to the rate of cooling between 240 ° C. and 150 ° C. after the final annealing. As is apparent from Table 2, it can be seen that the micropits and nodules can be significantly reduced if the alloy of the present invention is produced under the conditions of the present invention.
[0047]
[Table 1]

[0048]
[Table 2]

[0049]
【The invention's effect】
As described above, by processing the aluminum alloy plate of the present invention by the manufacturing method of the present invention, it is possible to provide an aluminum alloy plate for a magnetic disk substrate that has very few nodules and micropits that are problematic in a large-capacity magnetic disk. .

Claims (4)

An aluminum alloy plate for a magnetic disk substrate having the following component composition (wt%).
Cu: 0.05 to 0.15 wt%, Mg: 2 to 6 wt%, Zn: 0.1 to 0.3 wt%, Zr: 0.05 to 0.12 wt%, and 2Cu + 6Zr-3Zn = 0 Further, Mn: more than 0.01 and less than 0.05 wt%, Cr: more than 0.01 and less than 0.05 wt%. The impurities are regulated to Si: 0.1 wt% or less, Fe: 0.1 wt% or less, Ti: 0.02 wt% or less, the balance is made of Al and inevitable elements, and the inevitable elements are each 0.02 wt%. It is as follows. 2. The aluminum alloy plate for a magnetic disk substrate according to claim 1, wherein the number of Mg ₂ Si particles having a major axis exceeding 5 μm per unit area in the surface layer of the aluminum alloy plate is 20 / mm ² or less. . ^3. The number of Al—Fe intermetallic compounds having a major axis exceeding 5 μm per unit area in the surface layer of the aluminum alloy plate is 20 pieces / mm ² or less, according to claim 1 or 2. Aluminum alloy plate for magnetic disk substrate. A method for producing an aluminum alloy plate for a magnetic disk substrate (component composition is wt%), comprising the following steps.
(A) Cu: 0.05 to 0.15 wt%, Mg: 2 to 6 wt%, Zn: 0.1 to 0.3 wt%, Zr: 0.05 to 0.12 wt%, and 2Cu + 6Zr- 3Zn = 0.15 to 0.32 wt%, Mn: more than 0.01 and less than 0.05 wt%, Cr: more than 0.01 and less than 0.05 wt% 2 types of impurities, Si: 0.1 wt% or less, Fe: 0.1% or less, Ti: 0.02 wt% or less as impurities, the balance is made of Al and inevitable elements, the inevitable elements are (B) a step of hot rolling the ingot to form a coil; and (c) a step after the hot rolling. A step of cold rolling the coil; and (d) final firing of the coil after the cold rolling. The step of.