JP2003272130A - NiP PLATED ALUMINUM ALLOY SUBSTRATE FOR MAGNETIC DISK - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a NiP plated aluminum alloy substrate for a magnetic disk wherein fine undulation does not occur on the surface of a NiP plated film and the surface having high flatness and high smoothness can be obtained even when a magnetic film is deposited by increasing the temperature of a substrate for enhancing magnetic characteristics and higher recording density can be realized. <P>SOLUTION: A Zn layer, a Cu layer and the NiP plated film are successively formed on the surface of an aluminum alloy substrate and the Cu layer has 0.2 to 4 g/m<SP>2</SP>deposit. The Cu layer is formed by a nonelectrolytic plating method. The aluminum alloy substrate contains 2.0 to 6.0% by mass of Mg and 0.01 to 0.2% by mass of Cr and further contains at least one selected from the group consisting of Cu and Zn so that 3[Cu]+[Zn]=0.2 to 1.5% by mass is satisfied, when the contents of Cu and Zn are defined as [Cu] and [Zn], respectively, and the balance Al and inevitable impurities. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy substrate for a magnetic disk, and more particularly, to forming an electroless NiP plating film on the surface of the aluminum alloy substrate, polishing the film, and then subjecting it to a magnetic disk manufacturing process. Even if the magnetic film is heated to 250 ° C. or higher in a vacuum when the magnetic film is formed by sputtering in the manufacturing process of the magnetic disk, it is possible to prevent the occurrence of fine surface roughness on the surface of the electroless NiP plating film, N for magnetic disk that enables higher recording density
The present invention relates to an iP plated aluminum alloy substrate.

[0002]

The magnetic disk device, such as is one fixed disk device (H ard D isk D rive) BACKGROUND OF THE INVENTION external recording device, and a magnetic disk for recording (storage) of information, the information on the magnetic disk And a magnetic head for writing or reproducing. In recent years, the performance of such magnetic disks and magnetic heads has been greatly improved, and in the near future, an areal recording density of 100 Gb / in ² is about to be achieved.

Conventionally, as a magnetic disk substrate, an aluminum alloy plate which is lightweight and non-magnetic and has excellent workability has been used. However, since the aluminum alloy plate has a low surface hardness, the recording layer is easily destroyed when the magnetic head collides with the magnetic disk. Further, in order to increase the recording density, it is necessary to stably fly the magnetic head with a low flying height, but there is a problem that the high smoothness of the substrate required for that is difficult to obtain with an aluminum alloy alone. Therefore, an aluminum alloy plate having an electroless NiP plating film formed to a thickness of about 10 μm is generally used as a magnetic disk substrate. Such a magnetic disk substrate is manufactured as follows.

First, the desired alloy type by melting and rolling,
An aluminum alloy plate whose temper and thickness have been adjusted is punched into a predetermined ring-shaped substrate by a punching press. Next, in order to remove the processing residual stress in the substrate and improve the flatness, a plurality of punched substrates are stacked between the spacers with high flatness, and the whole is annealed while applying pressure (pressure annealing). . Generally, the one after the annealing is called a blank. Then, predetermined end face processing is performed on the end faces of the inner peripheral edge and the outer peripheral edge of the blank.

After that, the end-faced substrate is set in a pocket of a carrier preset in a double-sided grinder, and is ground by a grindstone until a target plate thickness is reached.
The substrate thus obtained has an extremely smooth surface condition with a center line average roughness Ra of about 100Å. However, even in this state, the required specifications as the magnetic disk cannot be satisfied, and thereafter, the surface of the aluminum alloy plate is further subjected to zincate treatment, an electroless NiP plating film is further formed on the entire surface, and the surface is polished. By
The center line average roughness Ra is polished to 10 Å or less,
It becomes a substrate for magnetic disks.

In a general magnetic disk, the above NiP is used.
On the aluminum alloy substrate on which the plated film is formed, a base film for enhancing magnetic characteristics, a magnetic film made of a Co-based alloy, and a protective film made of C for protecting the magnetic film are formed by sputtering.

In this case, it is necessary for the magnetic disk to reduce the medium noise due to the magnetic film. The medium noise is greatly influenced by the crystal grain size of the magnetic film, and the medium noise is reduced. Therefore, it is necessary to make the crystal grains finer. The factor that determines the crystal grain size is the substrate temperature during film formation by sputtering, and increasing the substrate temperature during film formation is an effective means for making the crystal grains finer.

Further, in order to achieve a low flying height of the magnetic head for high recording density, it is required to make the magnetic disk substrate highly flat and smooth. Also, during operation of the magnetic disk device, the magnetic head flies over a magnetic disk that rotates at high speed with an extremely low flying height of several hundred Å or less,
Depending on the recording density, minute waviness on the surface of the magnetic disk with a period of several tens of μm to several mm becomes a problem. When such a minute waviness is large, the floating stability of the magnetic head is impaired, the noise component increases, and a modulation error occurs. Therefore, in some cases, a head crash may occur and the information recorded on the magnetic disk may be destroyed. Therefore, in order to increase the recording density, it is required to reduce minute waviness.

[0009]

However, if the substrate temperature during film formation by sputtering is raised for the purpose of making the crystal grains fine in order to reduce the medium noise, the substrate becomes highly flat and smooth. In addition, it becomes a factor that hinders the prevention of minute undulations, which is a serious problem for higher recording density.

The present invention has been made in view of the above problems, and even when a magnetic film is formed by raising the substrate temperature to improve the magnetic characteristics, minute waviness occurs on the surface of the NiP plated film. Ni for magnetic disks, which can obtain high flatness and high smoothness without increasing the recording density.
It is an object to provide a P-plated aluminum alloy substrate.

[0011]

A NiP plated aluminum alloy substrate for a magnetic disk according to the present invention has a Zn layer, a Cu layer and a NiP layer formed on a surface of the aluminum alloy substrate in this order.
It is characterized in that plated films are sequentially formed.

In this NiP plated aluminum alloy substrate for a magnetic disk, the amount of the Cu layer deposited is, for example, 0.2 to 4 g / m ² . Further, for example, the Cu layer is formed by an electroless plating method. Furthermore,
The aluminum alloy substrate contains, for example, Mg: 2.0 to 6.0% by mass, Cr: 0.01 to 0.2% by mass, and at least one selected from the group consisting of Cu and Zn. The Cu and Zn contents are [Cu]
And [Zn] are contained so that 3 [Cu] + [Zn] = 0.2 to 1.5 mass%, with the balance being Al and unavoidable impurities.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. The inventors of the present invention diligently researched a NiP-plated aluminum alloy substrate whose mechanical properties such as flatness did not change even when the substrate temperature was raised, and a NiP-plated aluminum alloy substrate with a small undulation on the surface of the NiP plated film. I went. Among them, a NiP plating film was formed, the flatness was 5 μm or less, and the center line average roughness Ra was 10Å.
With the surface state of the aluminum alloy substrate polished below,
The relationship with the substrate temperature when performing the heat treatment assuming the substrate heating during sputtering was obtained. As a result, it was confirmed by a differential interference microscope that the surface of the NiP plated film became finely roughened as the substrate temperature increased.
Such a fine surface roughness can not be measured with a contact-type roughness meter having a stylus radius of curvature number μm generally used, the first time an atomic force microscope (A tomic F orce M icroscope) Check It is a fine thing that can be done. According to the atomic force microscope, for example, the width is several tens of μm and the height is 100Å.
In this way, minute parts whose height is 1 / several thousandth of the width are also observed.

Such minute surface roughness will become a serious problem in stable flying under a low flying height of the magnetic head in the future increase in recording density.

Generally, a zincate treatment is carried out as a pretreatment in order to improve the adhesion and smoothness of the NiP plated film, but normally, the zincate treatment is carried out twice. This is because Zn is non-uniform in the first zincate treatment. By performing the second treatment, Zn is uniformly deposited on the surface of the aluminum alloy substrate,
A uniform NiP plating film will be formed.

However, as a result of further detailed investigations by the present inventors, the Zn deposition state is different on each crystal grain surface of the aluminum alloy even when the zincate treatment is performed twice, resulting in sputtering. It has been clarified that the surface of the NiP plated film is finely roughened under the condition that the substrate temperature is increased by assuming the substrate heating at the time.

Therefore, as a result of further diligent research conducted by the present inventors, it was found that the above problems can be solved by satisfying the requirements described in the claims of the present invention. That is, according to the present invention, even if a film is formed in a state where the substrate temperature is increased during sputtering, it is possible to prevent the occurrence of fine surface roughness on the surface of the NiP plated film that affects the floating stability of the magnetic head. .

The aluminum alloy sheet used in the present invention is obtained by a general method of melting, casting, rolling and heat treatment. At the time of melting, various elements are added to the aluminum raw material to obtain a magnetic composition having a desired composition. It is an aluminum alloy for disks. Further, the plate thickness, strength, etc. can be changed by adjusting the rolling conditions and the heat treatment conditions when rolling this ingot.

Further, as a method for forming the Zn layer and the Cu layer, there are a sputtering method, an electrolytic plating method and an electroless plating method, and the electroless plating method is more preferable in terms of uniformity of film quality.

Next, the reasons for limiting the amount of the Cu layer deposited on the NiP-plated aluminum alloy substrate of the present invention, the reasons for adding the components, and the reasons for limiting the composition will be described.

Adhesion amount of Cu layer: 0.2 to 4 g / m ^{2 The} Cu layer has excellent adhesion to the Zn layer and the NiP plating film formed by the zincate treatment, and each crystal grain of the aluminum alloy. It is formed uniformly on the substrate surface regardless of the surface.

The adhesion amount of the Cu layer was 0.2 g / m ²
When it is less than 100%, it is difficult to completely cover each crystal grain surface of the aluminum alloy, and when a NiP plated film is formed, the effect of suppressing fine surface roughness of the NiP plated film surface due to substrate heating during sputtering is poor. Also, 4 g / m
^When it is more than ^2, it becomes difficult to obtain a further suppressing effect, and the merit also decreases in terms of cost.
Therefore, it is desirable that the adhesion amount of the Cu layer , which is the second layer, be 0.2 to 4 g / m ² .

Mg: 2.0 to 6.0% by Mass When Mg is less than 2.0% by mass, the strength as a magnetic disk substrate becomes insufficient. In addition, Mg is 6.0 mass%
When it exceeds, the aluminum alloy sheet is likely to be cracked during hot rolling and the workability is deteriorated. Therefore, Mg is
The range of 2.0 to 6.0 mass% is desirable.

Cr: 0.01 to 0.2% by mass When Cr is less than 0.01% by mass, the maximum length is 100 μm.
Coarse crystal grains exceeding m are likely to be generated. Such a non-uniform crystal structure causes non-uniform deposition of Zn in the zincate treatment (zinc substitution treatment, for example, JP-A-6-131659) that is generally performed when forming an electroless NiP plating film. easy. Moreover, Cr is 0.
If it exceeds 2 mass%, a coarse Al—Cr-based intermetallic compound, for example, CrAl _7, is likely to be generated, and when a NiP plated film is formed, defects such as pits are likely to occur on the plated film surface.

3 [Cu] + [Zn] = 0.5 to 1.5
Mass% Cu and Zn influence the precipitation form of Zn in a zincate process. This affects the quality of the surface of the NiP plated film (for example, the generation of pits) and the generation of fine surface roughness on the surface of the NiP plated film due to substrate heating during sputtering. The contents of Cu and Zn are represented by [Cu] and [Zn], respectively.

When the content of 3 [Cu] + [Zn] is less than 0.5% by mass, Zn precipitation during the zincate treatment is likely to be non-uniform on the substrate surface, and the surface of the NiP plated film is finely divided by the substrate heating during sputtering. Rough surface is likely to occur.
Further, when 3 [Cu] + [Zn] exceeds 1.5% by mass, NiP is caused by the pits formed by the zincate treatment.
Pits are easily generated on the surface of the plated film. For this reason,
3 [Cu] + [Zn] is preferably 0.5 to 1.5 mass%. If it is in this range, Cu or Z
n may be added alone.

The unavoidable impurities include, for example, F
e, Si, Mn, and the like, which form an intermetallic compound with Al and Mg which are essential elements, and NiP
Since it causes the formation of pits or nodules during the formation of the plated film, it is preferably 0.1% by mass or less, and more preferably 0.02% by mass or less.

[0028]

EXAMPLES The effects of the examples satisfying the claims of the present invention will be described below in comparison with comparative examples outside the scope of the claims. Using the aluminum alloys shown in Table 1 below, a 3.5-inch type aluminum alloy substrate for a magnetic disk having a plate thickness of 1.27 mm was manufactured by the following manufacturing process.

[0029]

[Table 1]

After melting these aluminum alloys having a predetermined composition, casting them to a plate thickness of 50 mm, chamfering them, and 540
Heated at 8 ℃ for 8 hours and homogenized, then hot rolled to a final plate thickness of 3 mm, and then a final plate thickness of 1.3 mm.
Cold-rolled so that Next, from the obtained aluminum alloy plate, circular disk blanks having an outer diameter of 95 mm and an inner diameter of 25 mm were punched out, a predetermined number of the blanks were stacked, and then pressure annealed at 340 ° C. Further, the end face of the blank was processed and ground so that the final plate thickness was 1.27 mm.

The characteristics of the obtained aluminum alloy plate were evaluated for the following evaluation items. 1. Tensile Strength After cold rolling an aluminum alloy plate at 340 ° C. into an O material, the tensile direction should be parallel to the rolling direction J
A tensile test piece according to IS5 was produced. Then JIS
A tensile test was carried out according to Z2241 to determine the tensile strength. 2. Observation of Zn layer surface Regarding an aluminum alloy substrate that has undergone the following treatment steps,
The SEM observation of the surface of the Zn layer which is the first layer was performed. <Treatment process> Alkaline degreasing (60 ° C x 2 minutes) → water washing → acid etching (65 ° C x 2 minutes) → water washing → nitric acid desmut (room temperature x 1 minute) → water washing → primary zincate → drying → surface observation (SEM ( S canning E lectro
n M icroscope) 3. ) . N before and after heat treatment assuming substrate heating during sputtering
Observation of iP plated film surface A NiP plated film was formed on an aluminum alloy substrate that had been subjected to the following treatment steps, and surface polishing was further performed by a double-sided polishing machine so that the center line average roughness Ra was 10 Å or less.
After that, assuming heating of the substrate during sputtering film formation, in vacuum,
A heat treatment of heating at 280 ° C. for 1 hour was performed. At this time, the center line average roughness Ra of the NiP plated aluminum alloy substrate before and after the heat treatment was measured by an atomic force microscope.

At this time, various materials having different Cu adhesion amounts were prepared by adjusting the plating time during electroless Cu plating. The method of forming each layer is as follows. <Treatment process> Alkaline degreasing (60 ° C x 2 minutes) → water washing → acid etching (65 ° C x 2 minutes) → water washing → nitric acid desmut (room temperature x 1 minute) → water washing → primary zincate → water washing → electroless Cu plating → Washing with water → Electroless NiP plating

The above evaluation results are shown in Tables 2 to 5 below.

[0034]

[Table 2]

[0035]

[Table 3]

[0036]

[Table 4]

[0037]

[Table 5]

However, in these tables, in the case of the comparative example in which the Cu adhesion amount was 0, each layer was formed by the following processing steps. Further, in this treatment step, the secondary zincate treatment was omitted in Comparative Example 17. <Treatment process> Alkaline degreasing (60 ° C x 2 minutes) → water washing → acid etching (65 ° C x 2 minutes) → water washing → nitric acid desmut (room temperature x 1 minute) → water washing → primary zincate → water washing → nitric acid peeling → secondary Zincate →
Washing with water → Electroless NiP plating

In Tables 2 to 5, the column "Observation of Zn layer surface" shows the case where Zn is uniformly deposited, the triangle is where pits are generated, and the case where Zn is not deposited uniformly. In addition, in the “Ra change amount before and after heat treatment” column, Cu
The amount of change in the center line average roughness Ra before and after heat treatment when the amount of adhesion is 0, 0.3, 2.0 and 5.0 g / m ² is shown. The case where the Cu adhesion amount is 0 g / m ² is a comparative example, and the cases where the Cu adhesion amount is 0.3, 2.0 and 5.0 g / m ² are examples.

As shown in Tables 2 to 5, in the examples of the present invention, the center line average roughness before and after the heat treatment was also included, including the examples 43 to 48 in which Zn was unevenly deposited. The change in Ra was extremely small, and no fine surface roughness was observed on the NiP plated film surface even after the heat treatment.

However, in the case of Comparative Examples 1 to 17 having no Cu layer, the center line average roughness Ra before and after the heat treatment is not changed even if the components of the aluminum alloy substrate are within the range specified in claim 4 of the present invention. The amount of change is extremely large.
The surface of the P-plated film was slightly roughened.

In Examples 1 to 24 and Examples 37 to 42 in which the composition of the aluminum alloy substrate satisfies the range defined in claim 4 of the present application, the Zn layer was formed uniformly and The change in the line average roughness Ra is also extremely small. Further, when the Cu adhesion amount satisfies the range of 0.2 to 4 g / m ² defined in claim 2 of the present application, the change in the center line average roughness Ra before and after the heat treatment is smaller, and even after the heat treatment. A better NiP plated film surface was obtained.

Further, the magnetic disk N obtained in the embodiment is used.
A magnetic disk was manufactured using an iP-plated aluminum alloy substrate, and the floating stability of the magnetic head was evaluated. It was found that the magnetic head floated stably and an excellent flat surface was obtained. However, the magnetic head obtained in the comparative example showed unstable flying of the magnetic head, increased noise, and many modulation errors.

In the above, the board size is 1.27.
Although the mm, 3.5 inch type has been described, the same effect as described above can be obtained with other sizes.

[0045]

As described in detail above, according to the present invention,
In the process of manufacturing a magnetic disk, even if a magnetic film is formed by raising the substrate temperature in order to improve the magnetic characteristics, the NiP
It is possible to obtain a NiP plated aluminum alloy substrate for a magnetic disk capable of obtaining a high flatness and a high smoothness surface without generation of micro-roughness on the surface of the plating film and achieving a high recording density.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Sei Okamoto             15 Kinugaoka, Moka City, Tochigi Prefecture God Inc.             Inside the Tooka Works Moka Works F-term (reference) 4K022 AA02 AA44 BA08 BA14 BA16                       BA25 BA31 BA32 CA11 CA28                       DA01 DB29                 5D006 CB04 CB06 CB08

Claims (4)

[Claims] 1. Zn on the surface of an aluminum alloy substrate
A NiP-plated aluminum alloy substrate for a magnetic disk, in which a layer, a Cu layer, and a NiP-plated film are sequentially formed. 2. The amount of the Cu layer deposited is 0.2 to 4 g.
/ M ^{2 The} NiP-plated aluminum alloy substrate for a magnetic disk according to claim 1, wherein 3. The NiP plated aluminum alloy substrate for a magnetic disk according to claim 1, wherein the Cu layer is formed by an electroless plating method. 4. The aluminum alloy substrate comprises Mg:
2.0 to 6.0% by mass, Cr: 0.01 to 0.2% by mass, and at least one selected from the group consisting of Cu and Zn with Cu and Zn contents, respectively. As [Cu] and [Zn], 3 [Cu] + [Zn] =
The content is 0.2 to 1.5% by mass, and the balance is A
4. The NiP-plated aluminum alloy substrate for a magnetic disk according to claim 1, wherein the NiP-plated aluminum alloy substrate has a composition of 1 and unavoidable impurities.