JPH02159340A - Aluminum alloy sheet for disk having excellent plating characteristics - Google Patents

Abstract

PURPOSE:To provide the alloy sheet with excellent substrate treatability and plating adhesion by specifying the contents of Mg, Cu and Fe and the size of intermetallic compounds in an alloy sheet. CONSTITUTION:As essential components, by weight, 3%<Mg<5.5%, 0.02%<Cu<0.3% and 0.02%<=Fe<=0.06% are incorporated into an Al alloy for a disk. Moreover, the size of intermetallic compounds is regulated to 5mum. The quantity of the intermetallic compounds of 0.5 to <5.5mum is furthermore regulated to 1000pieces/mm<2> and they are preferably dispersed uniformly. The Al alloy sheet has excellent substrate treatability and plating adhesion and has less plating defect such as micropits and nodules, by which a smooth plating surface can be obtd.

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an aluminum alloy plate for disks with excellent plating properties, and more specifically, a plating layer is formed on the surface of an aluminum alloy substrate for disks such as magnetic disks used as storage media in computers. The present invention relates to an aluminum alloy plate for a disk, which has excellent surface treatment properties and plating adhesion when subjected to a step of forming an aluminum alloy plate, and also has fewer nodules and micropits and excellent surface precision after polishing. (Prior Art) In general, a substrate for a disk such as a magnetic disk used as a recording medium for a computer must be lightweight, non-magnetic, and rigid enough to withstand high-speed rotation.
From the viewpoints that good surface precision can be obtained by precision cutting or polishing, and furthermore, it has a certain degree of corrosion resistance, etc.
Aluminum alloy is used. In the past, using a magnetic disk substrate as an example, coating was the main method for forming a magnetic film on an aluminum alloy substrate for magnetic disks, but in recent years, the increasing density of magnetic disks has increased. For this purpose, plating methods and sputtering methods have been developed and are being applied. In the case of magnetic disk substrates made by these plating methods or sputtering methods,
Plating such as N1-P is applied as a base treatment. Conventionally, the aluminum alloy for magnetic disks that undergoes such base plating treatment is AA5086 alloy (Au-
Mg type) is the most commonly used. In some cases, JIS7075 alloy (AQ-Zn-Mg type) is also used. (Problem to be solved by the invention) However, when these conventional aluminum alloys are used as base materials,
AQ-Fe crystallized product (AQ
-Fe, AQ-Fe-Si, AQ-Fe-Mn, etc.),
Since there are many intermetallic compounds such as crystallized substances whose main component is Mg-5i, these coarse intermetallic compounds fall off from the aluminum alloy base during cutting, polishing, or pretreatment for base plating, causing holes. Therefore, there was a drawback that the surface after base plating tends to become rough. In particular, when JIS 7075 alloy (AQ-Zn-Mg series) is used as a base material, since this aluminum alloy contains excessive amounts of Cu and Zn, these coarse intermetallic compounds may also cause the plating surface to deteriorate. Not only will this cause the surface to become rough, but since it is a heat-treated alloy, if the cooling rate is not appropriately adjusted during annealing to remove distortion from a disk punched or machined from a rolled plate, internal stress may occur. There was also the drawback that it occurred. As explained above, conventional aluminum alloys for disks have the disadvantage that the roughness of the disk surface tends to increase, or that plating defects such as pits (small holes) tend to occur due to this. In order to eliminate such drawbacks, a method has been adopted in which the plating film is formed relatively thick, for example, 15 μm or more, and then the surface is polished to remove a layer of 2 μm or more. However, there is a problem in that increasing the thickness of the plating film requires a large amount of cost for plating and polishing. Therefore, in order to reduce costs and improve productivity, it has become an important issue to reduce the thickness of the plating film. Furthermore, apart from the thickness of the plating film, it is also important to reduce the number of pits and to reduce the roughness in the plating pretreatment to improve the efficiency of the plating process. Therefore, for example, purity is 99.9% or 99.99%.
Attempts have been made to improve the quality of the intermetallic compounds by using AQ base metal, but simply increasing the purity of the AM base metal used not only increases the roughness of the plated surface. A problem arises in that the adhesion of the plating layer also decreases. The inventor believes that these causes are due to the precipitation of zinc due to the reduced Fe content in the aluminum material due to the use of high-purity Afl metal during zinc replacement, which is generally used as a pre-plating method for aluminum alloys. It was found that this is due to the roughness and non-uniformity of the grains. Therefore, the inventor of the present invention investigated various problems with conventional aluminum materials as explained above, and as a result of extensive research to satisfy many demands for magnetic disks, the inventors added Cu and Zn as alloying elements. They discovered that plating properties could be improved by doing so, and previously proposed an aluminum alloy for disks (Japanese Patent Publication No. 62-2018). The aluminum alloy for discs according to this proposal has already been put into practical use and has been highly evaluated. However, there is an increasing demand for cost reduction for magnetic disks, and therefore it is important to further reduce the thickness of the base plating and to reduce the polishing allowance during polishing. Therefore, it is necessary to suppress the occurrence of hemispherical protrusions (so-called nodules) that occur on the disk surface after base plating, and how to obtain a smooth plated surface, as well as how to prevent small pits on the extreme surface layer, which have not been a problem in the past. How to reduce the so-called micro pits has become a major development issue. The purpose of the present invention is to satisfy the various requirements for disks such as magnetic disks and optical disks as well as aluminum alloy materials for disks, as described above, to have excellent surface treatment properties and plating adhesion, and to An object of the present invention is to provide an aluminum alloy plate for a disk, which has few plating defects such as pits and nodules and has a smooth plating surface. (Means for Solving the Problem) The present inventors have conducted various studies in view of the above circumstances. First, in addition to a predetermined amount of Mg, Cu was actively added to improve the plating properties by adjusting the composition as essential elements. As a result, the occurrence of nodules and micropits on the plating surface has a strong correlation with the unevenness of the substrate surface after plating pretreatment. It has been found that etching properties are affected by the state of zinc precipitation during zinc substitution treatment, as well as the size of intermetallic compounds in the aluminum alloy. In particular, the size, amount, and distribution state of intermetallic compounds greatly affect micropits, and the maximum amount of intermetallic compounds is 5.
It has been discovered that when the thickness is less than 1 .mu.m, the number of micro pits can be drastically reduced even with a relatively thin plating thickness of about 10 .mu.m and a small polishing stock of 1 .mu.m or less, and the present invention has been developed based on this finding. That is, the present invention has an Mg content of 3% and 5% as an essential element.
．． 5%, 0.02%≦CLI<0.3% and 0°02%
It has a composition containing ≦Fe≦0.06%, and the size of the intermetallic compound is 5 μm or less. It has excellent surface treatment properties and plating adhesion, and has few nodules and micro pits. The gist of this invention is to provide an aluminum alloy plate for disks that has excellent surface precision after polishing. The present invention will be explained in more detail below. (Function) First, the reason for limiting the chemical components in the present invention will be explained. MI: Mg is an element necessary to provide the mechanical strength necessary for the disk base. However, if the content is less than 3%, this effect is insufficient. If it exceeds 5.5%, edge cracking tends to occur during rolling, which reduces productivity, and non-metallic inclusions such as MgO are likely to be generated due to high temperature oxidation during melting and casting, which is undesirable. The amount is in the range of 3%<Mg amount 5.5%. Cu: Cu has the effect of imparting uniform etching properties to the aluminum alloy during pre-plating treatment and making the precipitation of zinc on the substrate surface uniform and fine during zinc replacement treatment. This reduces the roughness of the base plating film surface and contributes to improving the adhesion of the film. However, 0.02%
If it is less than 0.3%, the above effects cannot be obtained, and if it is more than 0.3%, a large number of nodules will be generated, or the etching property of grain boundaries will be excessive, resulting in the smoothness of the plated surface. It is not desirable because it impairs the sex. Therefore, the amount of Cu is in the range of 0.02%≦Cu<0.3%, and more preferably in the range of 0.03<0.2% of Cu. Fe: Fe produces AQ-Fe-based intermetallic compounds (Aρ-Fe-Si-based when containing Sl or Mn as impurities. AQ-Fe-Mn-based, etc. also exist), and is used as a substrate for disks. It is preferable because it may cause depressions due to protrusions or falling off during processing such as cutting, polishing, and grinding during processing (so-called substrate processing), and may fall off or melt during the plating pretreatment process, causing pits on the plated surface. do not have. However, at the same time, it becomes the core of film formation during plating pretreatment and plating treatment, and it has been found that uniformly and finely dispersing it is effective in improving the uniformity of the film. In order for this intermetallic compound to exhibit a sufficient effect as a nucleus, the amount of Fe is required to be 0.02% or more. In addition, in order to prevent defects on the plating surface, the size must be 5 μm or less, and furthermore, the amount of intermetallic compounds with a size of 0.5 μm or more and less than 5.5 μm, especially AQ-Fe-based intermetallic compounds, is 1000 μm or less. It is preferable that the size and amount of these intermetallic compounds be uniformly dispersed with at least 100% Fe/+u++". The size and amount of these intermetallic compounds are greatly influenced by the Fe content in the material, but depending on the casting conditions and soaking treatment. The influence of (soaking) conditions is also large, and can be reduced by, for example, increasing the pouring temperature during casting and increasing the cooling rate during solidification.However,
In order to reduce the size of the intermetallic compound to 5 μm or less, in the case of a normal semi-continuous casting method in which the ingot is cast to a thickness of 300 to 400 mm or more, a raw material with Fe≦0601%, that is, is used. It is necessary to use a high-purity base metal with a purity of 99.98% or 99.99% or more, which is disadvantageous from the viewpoint of plating performance and economic efficiency. In order to satisfy all of these requirements, the thickness of the cast plate must be reduced by θ to increase the cooling rate during solidification, and Fe50.
It is necessary to set it to 0.6%. Therefore, the amount of Fe is 0.0
The range is 2≦Fe≦0.06%. In addition, 0.03≦
When Fe<0.04%, the size of the intermetallic compound is 4μ.
In the case of 0.02%≦Fe<0.03%, it is possible to reduce the pupil to 3μ or less. Furthermore, when reducing the plating thickness or polishing method, it is desirable to reduce the amount of Fe as necessary. In addition, in order to provide plating adhesion, the amounts of Fe and Cu should be 0.
It is desirable that the relationship be 0.04%≦Fe+Cu<0.3%. Note that impurities are inevitably mixed into the aluminum alloy, but it is desirable to control them as follows. Since Si tends to form Mg-8i-based intermetallic compounds and easily falls off during pre-plating treatment, it is desirable that si<o and o5%. Mn, Cr, Zr, Zn, Ti, etc. other than Si have the effect of refining recrystallized grains, preventing grain gloss during high-temperature heat treatment, and refining the casting structure, so JI
M may be included within the range allowed by the S5086 alloy, but it may cause coarsening of the above-mentioned intermetallic compounds or cause inclusions.
nS2.4%, Cr≦0.1%, ZrS2.1%, Zn
<0.1%, preferably TiS2.1%. More preferably, MnS2.35%, Cr≦0.08%, ZrS2.
05%, ZnS 3.05%, and TiS 2.05%. Further, although elements such as B and Be are often added during melting and casting, it is desirable that the amount of each element be 1100 pp or less. Next, a method for manufacturing an aluminum alloy plate for a disk according to the present invention will be explained. Casting methods include a semi-continuous casting method and a thin plate continuous casting method, but the thin plate continuous casting method, which allows the above-mentioned intermetallic compounds to be made finer, is preferable. However, in the case of the thin plate continuous casting method, the plate thickness at the time of casting is set to 1211111 or less in order to obtain a sufficient effect of refining the intermetallic compound by rapid cooling. Since it is desirable to perform cold rolling of 30% or more from the viewpoint of accuracy of processing, etc., the thickness is set to 3 mm or more. After casting, rolling is performed by a conventional method in the case of a continuously cast thin sheet coil, but only cold rolling may be used. In that case, if the plate thickness is relatively thick, hot rolling may be performed subsequent to casting, or in the case of semi-continuously cast ingots, soaking treatment may be performed after face side.
Performs hot rolling and cold rolling. In the cold rolling process, annealing is preferably performed as necessary. By annealing before and during rolling,
Effects such as removal of segregation and improvement of rolling properties can be obtained. After forming this rolled plate into a disk shape by punching, cutting, etc., annealing is performed to remove distortion if necessary. At this time, applying a load to the disk surface has a large distortion correction effect. Next, a normal rolled plate has a roughness of 1, for example, Ra=0.
At 1 to 0.5 μm, it is large for a disk substrate, and
Since it is necessary to further reduce the distortion, the disk surface is removed by cutting or polishing. In this case, deleting the surface of less than 10 μm is not enough to remove the strain, and deleting the surface of more than 500 μm satisfies the performance of the disk, but it is wasteful from an economic point of view such as productivity and cost. As for the disk substrate, the thickness of the surface to be removed is preferably 10 to 500 μm. In this processing step, annealing is performed if necessary to remove processing strain. Next, pretreatment such as degreasing, pickling, and Zn substitution treatment is performed,
A non-magnetic plating film such as N1-P is formed thereon. The etching in the pretreatment may be mild etching (etching amount 3 to 10 mg/dm'') or strong etching (etching amount 11 mg/dm'' or more). According to the present invention, strong etching is possible, and even if the final polishing allowance is reduced, excellent post-polishing surface precision with few pits can be obtained. Pickling is preferable for etching, which is superior to conventional aluminum alloys for disks in which only weak etching can be applied. If the plating film thickness is less than 3 μm, the roughness of the disk surface will be large due to the influence of pretreatment, and pits will easily remain.Furthermore, the amount of finish polishing will inevitably be small, resulting in uniform plating with small roughness. Since it is difficult to obtain a film, it is better to set the thickness to 3 μm or more, and from the viewpoint of the surface strength of the disk base, 5 μm is recommended.
The thickness of the plating film is preferably 20 μm or more.Although the performance does not particularly deteriorate even if the thickness of the plating film is increased, it is economically disadvantageous to make it too thick, so it is preferable to set the thickness to 20 μm or more. do not have. After the plated disk thus manufactured is finished polished, a magnetic film is further formed by plating or sputtering, and the disk is used as a magnetic disk. Finish polishing allowance can be reduced to 0.2~2μ
m is desirable; even in this case, a smooth surface with few micro pits and excellent surface precision can be obtained after polishing. Next, examples of the present invention will be shown. (Example) Alloys 1 to 5 (inventive examples) and Nα6 to Nα1.2 (comparative examples) having the chemical components shown in Table 1 were dissolved in a conventional manner, and after filtering, It was cast using the casting method shown below. In the case of normal semi-continuous casting materials, after ingot making 1. A slab having a thickness of 400 m+a, a width of 1000 mm, and a length of 3500 m+s was subjected to soaking treatment under the conditions shown in Table 1, and then hot rolled and cold rolled to a thickness of 2 mm. In the case of thin plate continuous cast material, 6■ thickness x 800mm width (x length)
It was cast into a coil shape, annealed at a temperature of 450°C for 5 hours, and then cold rolled to a thickness of 2IIIm. Next, after punching these plates, they were subjected to strain relief annealing to obtain hollow disks with an outer diameter of 130+am and an inner diameter of 40 mm. Furthermore, by cutting the surface of the disk, Rmaxo, 1μ,
After manufacturing an aluminum alloy substrate for magnetic disks with a plate thickness of 1,89 auw, the substrate was treated under the following conditions to investigate the size and amount of crystallized substances1 distribution, as well as the surface treatment properties and plating adhesion. In addition, the plated surface was polished and its surface precision (micro pit occurrence) was investigated. The results are shown in Tables 1 to 3. (Processing conditions) Degreasing (U-Cleaner UA-68, 5%, Uzai Kogyo Co., Ltd.
0℃, 5 minutes, immersion) ↓ Pickling (Jozai Kogyo 19AD-101, 10%) (Note) ↓ Zinc replacement (Jozai Kogyo AD-301, R, T, 1 minute,
↓ Nitric acid peeling (50% nitric acid, R, T, 1 minute, immersion) ↓ Zinc replacement (Jozai Kogyo AD-301, R, T, 30 seconds, immersion) ↓ N1-P plating (upper material Industrial Nimuden HDX. 90℃, immersion, plating thickness 7.5μm) (Note) 65℃× for mild etching by pickling.
The immersion was performed for 3 minutes (etching amount: 8 mg/da"), and in the case of strong etching, the immersion was performed at 75° C. for 5 minutes (etching amount: 23 mg/da"). The size, amount, and distribution of intermetallic compounds can be determined by measuring the surface area of the aluminum alloy substrate for magnetic disks using a scanning electron microscope at a magnification of 1000x.
was measured and evaluated. Regarding surface treatment properties, the surface after the second zinc replacement was inspected w4, and the precipitates were uniform and even, ○, the precipitates were rough, grainy, and uneven, ×, and the intermediate values were Δ
And so. Regarding the adhesion of the plating, a case where the plating did not peel off when bent by 90° was rated 0, and a case where the plating peeled off even partially was rated x. Regarding the surface accuracy after final polishing, after mirror polishing the plated surface using alumina powder, the surface was inspected at 640x magnification.
00 locations and no pits with a maximum diameter of 2 μm or more
was set as 0, those with 1 to 4 pits were set as Δ, and those with at least one pit of 5 or more or 8μ1 or larger were set as ×. Note that the polishing method was set to 0.5μ. From Table 1, in the examples of the present invention, the size of the crystallized particles is 5 μm or less, and the crystallized particles with a size of 0.5 μm or more and less than 5.5 μm are 10
00 pieces/■2 or more and uniformly distributed. However, Comparative Example Na1O, which has an aluminum alloy composition within the range of the present invention, has small crystallized substances and has no problems in terms of amount and distribution, but is inferior in terms of surface treatment properties, plating adhesion, surface nodules, and micro pits. . Also, among the comparative examples whose aluminum alloy composition is outside the scope of the present invention, there are examples with small crystallized substances (&6 to 7, Nα11 to Nα12), but Nα6 has a small amount of crystallized substances, and has a small amount of surface nodules and economical Nα7 also has problems in terms of crystallization, surface nodules, and economic efficiency, as well as poor surface treatment, plating adhesion, and surface accuracy after polishing. In addition, Nα11 has surface nodules and poor surface precision after polishing, and Nα12 has segregation in the crystallized material distribution.
The surface precision is poor after polishing. On the other hand, as is clear from Tables 2 and 3, Example 1 of the present invention is excellent in all of the surface treatment properties, plating adhesion, surface nodules, and surface precision after polishing, and is also excellent in economy.

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Table 3 (Wtl cleaning conditions: Strong etching = 75°C x 5 minutes) (Effects of the invention) As detailed above, according to the present invention, Cu and F
By including e as an essential element and regulating the size of the intermetallic compound, or regulating its size, amount, and distribution, it has excellent surface treatment properties and plating adhesion, and is free from micropits, nodules, etc. It is possible to obtain an aluminum alloy for disks that has few plating defects and allows a smooth plating surface. Furthermore, it is possible to perform a base treatment of 1 strength etching, to reduce the plating thickness, and to reduce the amount of polishing of the plating surface, and since there is no need to use high-purity base metal, products such as magnetic disks can be provided at low cost. It is particularly suitable as a material for magnetic disks, optical disks, etc. 9 Patent applicant Hisashi Nakamura, Patent attorney representing Kobe Steel, Ltd.

Claims (5)

[Claims] (1) 3% by weight (the same applies hereinafter) as essential elements
<Mg≦5.5%, 0.02%≦Cu<0.3% and 0
．． It has a composition containing 0.02%≦Fe≦0.06%, and the size of the intermetallic compound is 5μm or less.It has excellent surface treatment properties and plating adhesion. Aluminum alloy plate for discs with excellent surface precision after polishing. (2) The aluminum alloy plate for a disk according to claim 1, wherein the amount of the intermetallic compound having a size of 0.5 μm or more and less than 5.5 μm is 1000 pieces/mm^2 or more and is uniformly dispersed. (3) The aluminum alloy plate for a disk according to claim 1, wherein the Fe is contained in a range of 0.04≦Fe≦0.06%, and the size of the intermetallic compound is 5 μm or less. (4) The aluminum alloy plate for a disk according to claim 1, wherein the Fe is contained in a range of 0.03≦Fe<0.04%, and the size of the intermetallic compound is 4 μm or less. (5) The aluminum alloy plate for a disk according to claim 1, wherein the Fe is contained in a range of 0.02≦Fe<0.03%, and the size of the intermetallic compound is 3 μm or less.