JPH01188654A - Manufacture of aluminum alloy sheet for disk excellent in plating suitability and reduced in strain - Google Patents

Abstract

PURPOSE:To obtain an Al alloy sheet for magnetic disk excellent in plating suitability and reduced in strain by applying hot and cold rollings to an Al alloy containing respectively prescribed amounts of Cu and/or Zn together with Mg, blanking the resulting sheet into a disk blank, and subjecting the disk- shaped sheet to holding at a temp. in the prescribed temp. range and then to cooling at a specific cooling velocity. CONSTITUTION:An Al alloy which has a composition containing, by weight, 2-6% Mg and either or both of 0.03-1% Cu and 0.1-2% Zn and further containing, if necessary, 0.05-1.0% Mn and/or 0.03-0.3% Cr is hot-rolled and cold-rolled, and the resulting rolled sheet is formed into disk shape by means of blanking, cutting, etc., and then subjected to stress relief annealing. Subsequently, the disk-shaped Al-alloy sheet after annealing is held at >=280 deg.C, desirably 340-360 deg.C, for 1-10hr, particularly about 2hr, and then cooled down to 120 deg.C at 20-300 deg.C/hr cooling rate. By this method, the Al alloy sheet excellent in surface preparation characteristic and the adhesive strength of a plating film, reduced in strain, and suitable for magnetic disk, optical disk, etc., can be obtained.

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to the production of an aluminum alloy plate for disks that has excellent plating properties and less distortion. (Prior Art) In general, disk substrates such as magnetic disks, optical disks, and magneto-optical disks are required to have various characteristics.
For example, the following (1) to (
8) are required. (1) The substrate must be non-magnetic since the surface is coated with a magnetic medium to record and reproduce information. (2) It must have mechanical strength and rigidity that can withstand high-speed rotation. (3) The number of protrusions and pits that cause defects in the magnetic medium coated on the surface of the substrate is small and few. (4) Since the flying height of the recording/reproducing magnetic head from the disk surface is 1 μm or less, the surface accuracy and flatness must be sufficient for stable flying. (5) It must have sufficient heat resistance to withstand high-temperature environments such as when coating magnetic media and forming a protective film. (6) It must have good surface treatment properties (plating, alumite, etc.) associated with coating magnetic media. (7) It has a certain degree of corrosion resistance, and its shape accuracy and dimensional accuracy are stable over a long period of time. (8) Light weight due to the trend toward smaller drive motors. (Problems to be Solved by the Invention) Conventionally, as a magnetic disk substrate to meet such requirements, a plated aluminum alloy such as AA5086 or JIS7075 has been used. However, these conventional materials are suitable for use on the surface of aluminum alloy plates (AQ-Fe series, AQ-Mn-F
e type) and precipitated phases (especially A in JI87075 alloy)
Q-Cu7Mg series) etc. fall off during polishing or dissolve and fall off during plating pretreatment (alkali etching, acid etching), resulting in a disadvantage that the surface tends to become rough. In addition, since JIS 7075 alloy is a heat-treated alloy, internal stress may occur or coarse precipitation may occur if the cooling rate is not appropriately adjusted during strain relief annealing of disks made by punching or cutting from rolled plates. There was a drawback that objects appeared. In this way, because the roughness of the disk surface tends to increase, or because of this, pits (small holes) tend to occur in the plating film, conventional materials have a plating film with a diameter of about 30 to 50 μm, for example. The method used was to form a relatively thick film and then finish it by polishing. Therefore, reducing the thickness of the plating film has become an important issue in order to improve productivity and reduce the number of pits. Improve processing efficiency by reducing roughness in
It is also an important issue to make the Therefore, for example, attempts have been made to improve the quality by using 99.9% or 99.99% AQ metal and making the crystallized substances and precipitates finer. alone,
On the contrary, the substitution of Zn during the zincate treatment is not performed uniformly, causing problems such as not only increasing the roughness of the plated surface but also reducing the adhesion of the plated layer. The present invention has been made to solve the above-mentioned problems, and provides a magnetic disk, an optical disk, or an optical disk with excellent plating properties, especially the adhesion of the Nj-P plating film, and less distortion.
The object of the present invention is to provide a method for manufacturing an aluminum alloy plate for disks such as magnetic disks. (Means for Solving the Problems) In view of the above circumstances, the present inventors have conducted extensive research on improving the plating properties of aluminum alloys, and as a result, they first added a small amount of Cu and Zn simultaneously. proposed an aluminum alloy plate with excellent plating properties (Special Publication No. 201.8/1982), but as a result of subsequent research, it was found that the adhesion of the plating film could be improved by adding Cu or Zn alone. Zn does not reduce the properties of the
In addition to gaining the knowledge that the substitution can be performed thinner and more uniformly,
We have discovered that by maintaining an appropriate cooling rate after strain relief annealing, it is possible to prevent coarsening of precipitates and to produce a disk base with little distortion, and have thus completed the present invention. (Means for Solving the Problems) That is, the method for manufacturing an aluminum alloy plate for disks with excellent plating properties and low distortion according to the present invention is as follows: Mg: 2-
6%, Cu:0.03-1% and Zn:0.
Mn: 0.05-1.0% and Cr: 0.03-0.03%.
An aluminum alloy containing at least one of 0.3% and the remainder consisting of AQ and impurities is heated to a temperature of at least 280'C or higher after hot rolling and cold rolling and punching a disk blank. It is characterized by being held for 1 hour or more and less than 10 hours, and then cooling to 120°C at a rate of 20°C/hr or more and 300°C/hr or less. The present invention will be explained in more detail below. First, the reason for limiting the chemical components in the present invention will be explained. Mg: Mg is an element necessary to provide mechanical strength necessary for a disk base. However, if the content is less than 2%, the necessary strength as a disk base cannot be obtained, and if the content is less than 2%,
If it exceeds the above range, edge cracking tends to occur during rolling, productivity decreases, and AQ-Mg intermetallic compounds are generated.
Non-metallic inclusions such as MgO are likely to be generated due to high temperature oxidation during melting and casting. Therefore, the Mg content is set in the range of 2 to 6%. Cu, Zn: Cu and Zn are each dissolved uniformly in an aluminum alloy, and are expected to form a nucleus at the start of the zinc substitution reaction in zincate treatment.By uniformly distributing Cu or Zn, a thin and uniform A dense zinc-substituted coating is obtained. This reduces the roughness of the N1-P plating film and suppresses the occurrence of pits after polishing. However, Cu
If the Zn content is less than 0.03% or the Zn content is less than 0.1%, the above effects cannot be obtained. Further, if the Cu content exceeds 1%, excessive zinc substitution occurs, and not only a thin and uniform zinc substitution film cannot be obtained, but also the corrosion resistance of the material decreases. Furthermore, if the Zn content exceeds 2%, corrosion resistance and mechanical strength will decrease, and grain boundary precipitation will occur during annealing, making it unsuitable as a plated disk material. Therefore, the Cu content is 0.03 to 1%, and the Zn content is 0.
．． If the range is 1 to 2%, and considering the amount added and its effect, the Cu content is 0.03 to 0.4%, and the Zn content is 0.
．． A range of 1 to 1.5% is preferred. However, it is sufficient to contain at least one of Cu and Zn. Note that when Cu and Zn are added at the same time as proposed above, a synergistic effect of the two elements occurs, so it is sufficient to add a smaller amount within the above range. The above elements are essential components, but if necessary, Mn
and Cr. Mn near - Mn is expected to improve mechanical strength by forming fine intermetallic compounds and suppress coarsening of crystal grains, so the amount of Mg can be suppressed to a relatively low concentration and mechanical It is added as necessary when it is required to maintain appropriate physical strength or when there is a risk of coarsening of crystal grains during the manufacturing process up to the final product (media). However, if the Mn content is less than 0.05%, the above effects cannot be obtained, and if it exceeds 1.0%, AQ-Mn, AQ
This is not preferable because giant intermetallic compounds such as -Mn-Fe crystallize and deteriorate plating properties. Therefore, the Mn content is in the range of 0.05 to 1.0%. Cr: Similar to Mn, Cr is expected to have the effect of grain refinement, but this effect is not observed at less than 0.03%;
．． If it exceeds 3%, huge intermetallic compounds will crystallize. Therefore, the Cr content is set in the range of 0.03% to 0.3%. Note that the aluminum alloy having the above composition may be accompanied by impurities, but it is desirable to suppress these to as low a level as possible. In particular, Fe and Si are mixed as base metal impurities, but these are He-Fe series, Afl-Fe-8i series,
Generates intermetallic compounds such as Mg-8i. Since these are harder than the AQ matrix, they may cause protrusions or fall-off dents during cutting or polishing, and Mg-8
The i-series dissolves and falls off during the plating pretreatment, causing pits on the plating surface. Therefore, it is desirable that these intermetallic compounds be small and few in number, and desirably have a size of 10 μm or less. Fe content is 0.4%, Si content is 0
．． If it exceeds 25%, the crystallization of intermetallic compounds of 10 μm or more cannot be ignored, so the Fe content is 0.40%.
It is desirable to suppress the Si content to 0.25% or less. The size of these crystallized substances is greatly influenced by the casting method (especially the cooling rate), and the so-called
When using semi-continuous casting method, the Fe content is 0.1
5% or less, Si content is preferably 0.1% or less, more preferably Fe content is 0.1% or less, Si content is 0.07%.
It is as follows. Furthermore, impurities such as No. 1 and B do not have any influence on the aluminum alloy plate for disks obtained according to the present invention even if they are contained within the range contained in the JIS5086 alloy. Next, manufacturing of the aluminum alloy plate for disks having the above composition will be explained. The above aluminum alloy is melted and cast using a conventional method, and the ingot (or thin continuous cast coil) is soaked and rolled. Note that this soaking treatment is usually performed by maintaining the temperature at 4 oo'c or higher for 48 hours or less. In the rolling process, large ingots are hot-rolled and cold-rolled from the viewpoint of productivity, and thin continuous cast coils may only be cold-rolled, and if the plate thickness is relatively thick, hot-rolling is performed. It may also be carried out subsequent to casting. In this case, it is best to perform annealing as necessary during the cold rolling process, and in the case of thin continuous cast coils, annealing is performed before and during rolling to remove segregation and improve rollability. effective. Next, this rolled plate is punched out, cut, etc. into a disk shape, and annealed to remove strain. Usually, a disk blank is manufactured by punching a coil, but the punched disk has distortions such as warping of about 100 μm. This strain is removed by annealing. In the present invention, it is important to perform annealing under the following conditions in order to obtain a disk substrate with little distortion. especially,
At this time, it was found that it is preferable to recrystallize the material to obtain an O material. ■ Annealing temperature: 300°C in order to complete recrystallization within several hours of holding time.
A high temperature of around 10°C is required, but since the above aluminum alloy recrystallizes at 280°C, a temperature of 280°C or higher is required. When considering retention time, desirably 340
℃ or higher. ■ When annealing at a holding time of 280°C, there is a possibility that the entire disk will not recrystallize if the holding time is less than 1 hour.
Considering productivity, it is not preferable to hold the heat for too long. Therefore, the heating time should be 1 hour or more and 10 hours or less. The annealing temperature and holding time are preferably 34o'c.
It takes about 2 hours at ~360°C. ■ Cooling rate The cooling process affects the final amount of strain and precipitates. When kept at a temperature of 150°C to 200°C for a long time during cooling, AQ-Mg, AQ-Cu, AQ-
Since compounds such as Mn precipitate and deteriorate plating pretreatment properties, it is necessary to cool to 120°C at a rate of 20'C/hr or more. 15 for cooling rates slower than 20°C/hr
The time required to pass through the temperature range of 0° C. to 200° C. is also increased, which is undesirable because the deposits have an adverse effect on the plating properties. On the other hand, a cooling rate of 300'C/hr or more is not preferable because the temperature distribution and internal stress within the disk and annealing jig will increase the final strain.For the above reasons, the cooling rate of 20'C/hr or more is undesirable. 3
Cooling is performed at a rate of 00°C/hr or less. When considering productivity at an industrial level, it is preferable to perform annealing under load, and the cooling rate is 40°C/hr or more.
Desirably 0°C/hr or less. Note that the roughness of a normal rolled plate is, for example, Ra=0.1~
Since it is 0.5 μm, which is large for a disk substrate, and it is necessary to further reduce distortion, the disk surface is removed by cutting or polishing. In this case, surface deletion of less than 10 μm is not enough to remove distortion, and surface deletion of more than 500 μm, although the disk performance is satisfactory, is wasteful from an economic point of view such as productivity and cost.
For a disk base made of an aluminum alloy plate, 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. This annealing is also performed under the above cooling conditions. Next, pre-treatments such as degreasing, etching, Zn substitution, Sn substitution, etc. are repeatedly performed by conventional methods, and a non-magnetic plating film such as N1-P is formed thereon. In addition, before forming a non-magnetic plating film such as N1-P, Cu
Strike plating may also be applied. If the thickness of this plating film is less than 3 μm, the disk surface will be rough due to the influence of pretreatment, and pits will easily remain.
Furthermore, the number of final polishing methods is inevitably reduced, and it is not possible to obtain a uniform plating film with small roughness, so it is better to form a plating film with a thickness of 3 μm or more, and from the viewpoint of the strength of the plating film. is preferably 5 μm or more. Further, even if the thickness of the plating film is increased, the performance does not particularly deteriorate, but it is economically disadvantageous to make the plating film too thick, so it is preferably 20 μm or less. After final polishing the disk manufactured by plating in this manner, a magnetic film is further formed by plating or sputtering, and the disk is used as a magnetic disk. (Example) Next, the present invention will be explained in detail. Example 1 An aluminum alloy having the chemical components shown in Table 1 was melted, filtered, agglomerated, and solidified on both sides.
It was made into an ingot with dimensions of m x 1000 mm x 3500 mm. Next, after performing homogenization treatment at a temperature of 530°C for 12 hours, hot rolling was performed to obtain a plate thickness of 5 mm, and then a plate thickness of 2 mm.
Cold rolling was performed to a thickness of mm. Next, the obtained plate material was punched to an outer diameter of 130 m.
It was a hollow disk with an inner diameter of 40 mm and an inner diameter of 40 mm. After cutting the surface of this disk to give Rmaxo of 08 μm,
, subjected to strain relief annealing by holding for 2 hours, and heated to 45℃ up to 120℃.
It was cooled at a rate of .degree. C./hr to obtain an aluminum alloy substrate for a magnetic disk. The base thus obtained was degreased (trichloroethane) → alkaline etched (5% NaOH at 125°C, 30°C).
2 seconds, immersion) → Neutralization (30% HNO, 25℃, 10 seconds,
Soaking) → Pickling (HNO3: HF:'H20=3:
1: 2.25℃, 30 seconds, immersion) → Zinc replacement (1
(120g/QNaOH120g/QZnO12
g/fl FeCR3・6H20, 50g/flKNa
C4H40G・4H20, Ig/QNaNO,,25-
15 = °C, 30 seconds, immersion) → Pickling (20% HNO3, 25 °C,
10 seconds, immersion) → Zinc replacement (second time) (processing solution and conditions are the same as the first time) → N1-P plating (Nippon Kanigen Blue Shuma, 90°C, immersion, plating thickness 5 μm and 1
0 μm). Table 3 shows the results of investigating the surface treatment properties, plating adhesion, and the surface of the plated surface after polishing. The surface treatment property was determined by observing the surface after the second zinc substitution. If the precipitate was uniform and even, it would be marked O. If the precipitate was coarse and uneven, it would be marked x. thing Δ
It was evaluated by marking it. Plating adhesion was evaluated by marking O if the plating did not peel off after 900 bends, and marking X if it peeled off even partially. Regarding the polished surface of the plated surface, the plated surface was mirror polished using aluminum oxide powder, and then the surface was observed and investigated. Note that the polishing method was set to 2 μm. For evaluation, observe 50 locations using a microscope at 400x magnification, and mark O if there are no pits with a maximum diameter of 2 μm or more, mark Δ if there are 1 to 4 pits, and mark X if there are 5 or more pits. Attached. As is clear from Table 2, the inventive examples ■, ■, ■, ■, whose compositions were appropriately adjusted, compared with the comparative examples ■, ■, ■, ■,
Excellent in surface treatment properties, plating film adhesion, etc.
In particular, it can be seen that good results are obtained even when the plating thickness is reduced. Note that all of the discs obtained had a distortion of 1
It was 0 μm or less.

[Left below]

-191 Example 2 Aluminum alloy Na having the chemical components shown in Table 1
] to 4, aluminum alloy substrates for magnetic disks were obtained using the same steps and conditions as in Example 1. However, cooling after heating during strain relief annealing was performed at various cooling rates shown in Table 3. The total weight and pretreatment properties of the obtained substrate were examined. The results are also listed in Table 3.The total weight was calculated using a strain measuring device using laser interference (-
The evaluation was made based on the average value of 10 sheets measured by a method (manufactured by Dick). In addition, the pretreatment property was determined by measuring the surface roughness after degreasing → alkali etching → neutralization → pickling in Example 1 three times using a stylus-type roughness meter (scanning distance 4 mm), and Ra (human roughness) without drift. ) was evaluated based on the average value. As is clear from Table 3, according to the cooling conditions within the range of the present invention, both the overall weight and the surface roughness after plating pretreatment are small.

[Left below]

(Effects of the Invention) As detailed above, according to the present invention, since the composition of the aluminum alloy is appropriately adjusted and the strain relief annealing conditions are particularly regulated, the surface treatment property and the adhesion of the plating film are excellent.
Moreover, an aluminum alloy plate suitable for magnetic disks, optical disks, etc. with small distortion can be obtained. Patent applicant Hisashi Nakamura, patent attorney representing Kobe Steel, Ltd.

Claims (1)

[Claims] In terms of weight% (the same applies hereinafter), it contains Mg: 2 to 6% and also contains at least one of Cu: 0.03 to 1% and Zn: 0.1 to 2%, and further, if necessary, Mn: 0.
An aluminum alloy containing at least one of 05 to 1.0% Cr and 0.03 to 0.3% Cr, with the remainder consisting of Al and impurities is hot rolled and cold rolled to produce a disk blank. At least 280℃ after punching
Maintain at the above temperature for 1 hour or more but less than 10 hours, then 2
A method for producing an aluminum alloy plate for disks with excellent plating properties and low distortion, characterized by cooling to 120°C at a rate of 0°C/hr or more and 300°C/hr or less.