JP2003301231A - Aluminum alloy substrate for magnetic disc - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide at a low cost an aluminum alloy substrate for a magnetic disc which has a desirable, high evenness and smoothness, inhibits generation of fine surface roughness even upon being treated at a relatively high temperature and can realize a high packing density. <P>SOLUTION: The substrate comprises, by mass, 2.0-6.0% Mg, 0.05-0.2% Cr, at least one of Cu and Zn at amounts satisfying the inequality: 0.05%≤3Cu+Zn<0.5%, and the balance being Al and unavoidable impurities. <P>COPYRIGHT: (C)2004,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 in particular, it suppresses the occurrence of minute surface roughness on the surface even if it is processed at a high temperature, and realizes higher recording density and improved reliability. The present invention also relates to an aluminum alloy substrate for a magnetic disk, which has a reduced cost.

[0002]

2. Description of the Related Art A hard disk drive (HD) is one of conventional external recording devices.
D) includes a magnetic disk for recording and reproducing information, and a magnetic head for recording and reproducing information on the magnetic disk. In recent years, these magnetic disks and magnetic heads have made great strides,
It is predicted that the recording density per unit area of the magnetic disk will reach 100 Gb / in ² in the near future. Such a magnetic disk device is mainly used as an external recording device for a personal computer.
Recently, it has been installed in various electric appliances such as television recorders, and further cost reduction has been strongly demanded along with the expansion of such application range.

For the magnetic disk substrate included in the magnetic disk device, an aluminum alloy which is lightweight, non-magnetic and excellent in workability is mainly used. But,
Aluminum alloy has a relatively low hardness, and it is difficult to increase the smoothness of the substrate surface. For this reason, in the coating type that was initially applied to the magnetic disk, it was difficult to fly the magnetic head with a low flying height, and it was difficult to increase the recording density.

That is, in order to increase the recording density of the magnetic disk, it is necessary to stably fly the magnetic disk with a flying height as low as possible. To satisfy this requirement, it is first necessary to increase the smoothness of the magnetic disk substrate. Therefore, in general, a magnetic disk substrate is formed by coating the entire surface of the aluminum alloy substrate with a NiP plating film having a relatively high hardness by electroless plating to a film thickness of about 10 μm. Such an aluminum alloy substrate for a magnetic disk is usually manufactured as follows.

First, a predetermined aluminum alloy seed is melted and cast, and an aluminum alloy substrate adjusted to a desired temper and plate thickness is manufactured through steps such as hot rolling, cold rolling, and if necessary, annealing. To be done. Then, this aluminum alloy substrate is subjected to punching press work to produce a predetermined donut-shaped aluminum alloy substrate. Subsequently, this aluminum alloy substrate is subjected to an O material treatment so as to make the in-plane properties uniform. Subsequently, in order to improve the flatness of the surface of the aluminum alloy substrate, so-called pressure annealing is performed, in which the aluminum alloy substrate is sandwiched by spacers having relatively good flatness and annealed while being pressurized. Generally, the aluminum alloy substrate at the stage of being subjected to the pressure annealing is called a blank material. After that, a predetermined end face processing is applied to the ends of the inner and outer diameters of the blank material.

Further, the aluminum alloy substrate thus end-face-processed on the blank material is subjected to surface smoothing treatment by using, for example, an automatic double-sided grinder for automatically grinding both sides of the substrate. To be done. That is, the aluminum alloy substrate is set inside a pocket of a carrier preset in the automatic double-sided grinder, and the aluminum alloy substrate is ground by a grindstone until the target plate thickness is reached. By such a grinding process, the center line average roughness Ra of the surface of the aluminum alloy substrate is 100.
Å Smoothness can be increased to the level of Å.

However, even with an aluminum alloy substrate whose smoothness is increased to some extent in this way, it was difficult to sufficiently satisfy the smoothness specifications required for a magnetic disk that realizes a higher recording density. Therefore, the NiP plating film is coated on the entire surface of the aluminum alloy substrate whose smoothness is increased as described above by an electroless plating method, and then polishing is performed so that the center line average roughness Ra of this surface is set to 10 Å or less. Only when the smoothness was further increased, an aluminum alloy substrate for a magnetic disk capable of realizing a higher recording density was obtained.

In order to impart magnetic characteristics to the aluminum alloy substrate for a magnetic disk thus formed, a magnetic film of, for example, a Co alloy, and a protective film of, for example, C for protecting the magnetic film. Are formed by a sputtering method (physical vapor deposition method) or the like to form a magnetic disk.

In the above magnetic disk, it is necessary to reduce the medium noise generated during operation. It has been clarified that this medium noise originates from the magnetic film, and that the crystal grain size of the magnetic film is particularly related. That is, in order to reduce the medium noise, it is necessary to miniaturize the crystal grains of the magnetic film. The main factor contributing to the crystal grain size of the magnetic film is the substrate temperature during film formation by the sputtering method. Making it higher is an effective means.

Further, it is necessary to reduce the flying height of the magnetic head on the aluminum alloy substrate for magnetic disk in order to realize higher recording density. From this,
The aluminum alloy substrate for magnetic disks is required to have even higher flatness and smoothness.

During operation of the magnetic disk device, the magnetic head is levitated above the magnetic disk rotating at a high speed with a very small flying height of several hundred Å or less. On the surface, several tens of μm
The occurrence of minute surface roughness having a cycle of about several mm is a problem. Such minute surface roughness seriously affects the reliability of the magnetic disk device.

That is, when the surface roughness of the magnetic disk substrate becomes excessive, the floating stability of the magnetic head is impaired and the noise component increases during recording or reproduction of information. May occur. If this modulation error becomes too large, a head crash may occur, resulting in the problem that the information recorded on the magnetic disk is destroyed. Therefore, in order to increase the recording density of the magnetic disk, it is strongly required to suppress the occurrence of minute surface roughness on the surface of the magnetic disk substrate.

[0013]

The above-mentioned magnetic disk device is required to have further improved performance as such an external recording device, but as the range of application to various electric appliances and the like has expanded in recent years, these devices have been developed. There is a strong demand for further cost reduction when it is installed in electrical appliances. Therefore, for example, the recording cost per bit can be further reduced by realizing a higher recording density on the magnetic disk, or the manufacturing cost of the magnetic disk can be reduced by improving the productivity of the aluminum alloy substrate for the magnetic disk. Studies are underway to reduce the number.

Further, for the purpose of miniaturizing the crystal grains of the magnetic film, which is a source of medium noise during operation of the magnetic disk device,
When this magnetic film is formed by the sputtering method, if the substrate temperature during film formation is raised to a certain extent, the flatness and smoothness of the aluminum alloy substrate surface are impaired, that is, minute surface roughness occurs on the substrate surface. It becomes easy and becomes a big problem when the recording density of the magnetic disk is improved.

The present invention has been made in view of the above problems, and an object thereof is to have a desired high flatness and smoothness, and even when processing is performed at a relatively high temperature, minute surface roughness occurs on the surface. An object of the present invention is to provide an aluminum alloy substrate for a magnetic disk that suppresses the generation and can realize a higher recording density at a low cost.

[0016]

In order to solve the above problems, the present inventors (1) suppress changes in mechanical properties such as flatness and smoothness even at high temperatures and coat the surface. The generation of minute surface roughness on the surface of the NiP plated film thus formed is suppressed, and further (2) such aluminum alloy substrate is manufactured by further increasing the grinding speed. I went.

As a result, by controlling the content of the specific component in the aluminum alloy and the average grain size of the crystals, the size of the intermetallic compound which is the origin of the defects of the aluminum alloy is optimized, and the higher grinding speed is obtained. An aluminum alloy substrate for a magnetic disk having desired high flatness and smoothness, and having an effect of suppressing generation of minute surface roughness even at a relatively high temperature even when ground by After discovering this, the present invention was created.

That is, according to the present invention, Mg is added in the range of 2.0-6.
0 mass% and 0.05 to 0.2 mass% of Cr, and at least one of Cu and Zn is 0.0
An aluminum alloy substrate for a magnetic disk is constituted so that the content of 5 ≦ 3Cu + Zn <0.5% by mass is satisfied, and the balance is Al and inevitable impurities (claim 1).

According to this structure, the size and number of the intermetallic compounds in the aluminum alloy substrate for the magnetic disk are optimized so that even if the compound is ground at a higher grinding speed, a desired high flatness and smoothness can be obtained. And an aluminum alloy substrate for a magnetic disk which suppresses the occurrence of minute surface roughness on the surface of the NiP plating film, which is a problem even under the condition of higher recording density even when processed at a relatively high temperature. To be realized.

Further, in the present invention, it is preferable that the average grain size of the crystal grains in the aluminum alloy is regulated to 50 μm or less (claim 2). According to this structure, the size of the aluminum alloy crystal grains is further optimized, and the above effect is further enhanced.

It is more preferable that the present invention contains Fe and Si in an amount of 0.05% by mass or less and the ratio of Fe and Si contents (Fe / Si) is 1.5 or more ( Claim 3). According to this structure, the size and number of the intermetallic compounds can be suppressed,
The above effect is further enhanced.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below. As the aluminum alloy used in the present invention, for example, a 5000 series aluminum alloy defined in JIS H4000 can be applied. The aluminum alloy substrate for a magnetic disk according to the present invention can be manufactured as follows.

That is, a general method is carried out in which an ingot is prepared by melting and casting an aluminum alloy containing a predetermined component whose content is regulated in the present invention, and the ingot is subjected to rolling and heat treatment. Manufactured by. Then, when the aluminum alloy is melted, various elements are added to aluminum to obtain an aluminum alloy for a magnetic disk having a desired composition. Further, by controlling the rolling conditions and the heat treatment conditions when rolling this ingot, the plate thickness, strength and the like can be appropriately adjusted. The reason why the content of each component is numerically limited in the aluminum alloy substrate for a magnetic disk according to the present invention is as follows.

[Mg content: 2.0 to 6.0 mass%]
Mg is an element that contributes to the strength of the aluminum alloy.
That is, when the content of Mg is less than 2.0% by mass, the strength of the aluminum alloy is lowered and the strength as a magnetic disk substrate is insufficient. Further, when the content of Mg exceeds 6.0 mass%, the aluminum alloy substrate is cracked during hot rolling and the workability is deteriorated. Therefore, in the present invention, the content of Mg is restricted to the range of 2.0 to 6.0 mass%.

[Cr Content: 0.05 to 0.2% by Mass] Cr is an element that contributes to the size of crystal grains in the aluminum alloy. That is, the content of Cr is 0.05
If it is less than mass%, the maximum length of aluminum alloy is 5
Coarse crystal grains exceeding 0 μm are likely to be generated.
Such a non-uniform crystal structure is a zincate treatment (a treatment for replacing the surface of the aluminum alloy substrate with Zn, which is a pretreatment generally performed when the NiP plated film is formed by the electroless plating method. JP-A-6-13
1659. It is inconvenient to evenly precipitate Zn by). Further, the content of Cr is 0.
If it exceeds 2% by mass, a coarse Al—Cr intermetallic compound, for example, CrAl _7, is generated. Therefore, when a NiP plated film is formed, pit-like defects are likely to occur on the surface of the NiP plated film. . Therefore, in the present invention, the Cr content is restricted to the range of 0.05 to 0.2 mass%.

[3Cu + Zn: 0.05 to 0.5 mass%
Less than] Cu and Zn are elements that influence the form of Zn deposited on the surface of the aluminum alloy in the zincate treatment. That is, the contents of Cu and Zn are N-based on the aluminum alloy substrate by electroless plating.
Pit that occurs in the surface layer when forming the iP plated film, or minute surface roughness that occurs on the surface of the NiP plated film due to substrate heating when forming the magnetic film on the NiP plated film by the sputtering method. , And influence the surface microstructure that determines the surface texture of the aluminum alloy substrate.

The inventors of the present invention have investigated the surface properties of aluminum alloy substrates obtained by variously changing the Cu and Zn contents in the aluminum alloy, and have obtained the following findings. That is, when (3Cu + Zn) is less than 0.05% by mass, Z in the zincate treatment is
The precipitation distribution of n becomes non-uniform on the substrate surface, and as a result, minute surface roughness is likely to occur on the NiP plated film surface due to substrate heating during film formation by the sputtering method. In addition, (3C
If (u + Zn) exceeds 0.5% by mass, pits are likely to occur in the surface layer of the NiP plating film due to the pits generated by the zincate treatment. Therefore, in the present invention, (3Cu + Zn) is regulated within the range of 0.05 to 0.5 mass%.

At this time, when the content of Zn is large, the precipitation form of Zn in the zincate treatment tends to be from a particle form to a relatively uniform film form, and a minute surface roughness occurs on the NiP plated film surface. Is suppressed. Further, in the present invention, if the content of (3Cu + Zn) is within the above range, Cu or Zn may be added alone.

[Average grain size of aluminum alloy crystal grains: 5
0 μm or less] The above zincate treatment is applied to the aluminum alloy substrate according to the present invention, a NiP plating film is subsequently formed by an electroless plating method, and a magnetic film is further formed thereon by a sputtering method. After heating, minute surface roughness easily occurs on the surface of the NiP plated film.

Generally, each crystal grain of an aluminum alloy is
It is said to have different potentials depending on the plane orientation. As a result of investigations by the present inventors, it was revealed that the zincate treatment causes different Zn precipitation morphology and precipitation amount for each crystal grain. Therefore, the present inventors considered that the morphology and the amount of Zn deposited in each crystal grain are related to the morphology of the crystal grain, and conducted various experiments. As a result, it was found that the occurrence of such minute surface roughness on the surface of the NiP plated film depends on the size of the aluminum alloy crystal grains.

Furthermore, the inventors of the present invention set the crystal grain size in an appropriate range, that is, if the crystal grain size is 50 μm or less in average grain size, the surface of the aluminum alloy substrate is treated by the zincate treatment. Since the Zn deposited on the surface of the aluminum alloy film is uniformly formed, Ni
Even if a P-plated film is formed and treated at a relatively high temperature,
It was clarified that the generation of minute surface roughness on the surface of the NiP plated film is suppressed.

That is, since the aluminum alloy has a different potential depending on the plane orientation of each crystal grain, it is possible to form a uniform zincate film by minimizing the influence of the potential difference between the crystal grains. Therefore, in the aluminum alloy substrate for a magnetic disk according to the present invention, it is more desirable to regulate the average grain size of the aluminum alloy crystal grains to 50 μm or less.

[Fe content: 0.05 mass% or less] F
e is an element that forms an intermetallic compound together with Al and Mg in the aluminum alloy and greatly contributes to the formation of defects in the NiP plated film. That is, the content of Fe is
If it exceeds 0.05% by mass, intermetallic compounds will fall off during the zincate treatment, and large pits will be easily formed on the surface, which will cause defects in the NiP plated film, and the magnetic film etc. will be formed by the sputtering method. When the film is formed, after the substrate is heated, a slight surface roughness occurs on the surface of the NiP plated film, which leads to a decrease in the smoothness of the aluminum alloy substrate. Therefore, in the present invention, it is desirable to regulate the Fe content to 0.05 mass% or less.

[Si: 0.05% by mass or less] Si is Al and M in the aluminum alloy, like the above-mentioned Fe.
It is an element that forms an intermetallic compound together with g and is greatly involved in the formation of defects in the NiP plated film. That is, Si
When the content of Al exceeds 0.05 mass%, a large intermetallic compound is generated, and large pits are formed on the surface of the aluminum alloy substrate after the zincate treatment. Therefore, in the present invention, it is desirable to regulate the Si content to 0.05% or less.

[Fe / Si: 1.5 or More] In the present invention, Fe, which is an element effective for improving the grindability of an aluminum alloy substrate, and Si, which is an element contributing to formability,
By optimizing the ratio of the aluminum alloy substrate and the aluminum alloy substrate, it is possible to improve the grindability of the aluminum alloy substrate and obtain an aluminum alloy substrate having high flatness and smoothness even if the grinding speed is increased. That is, it is the ratio of the contents of Fe and Si (Fe
/ Si) is less than 1.5, the aluminum alloy substrate has poor grindability and formability, and it becomes difficult to obtain desired high flatness and smoothness when the grinding speed is increased, and Grinding at a low grinding speed to obtain desired high flatness and smoothness hinders the productivity of aluminum alloy substrates for magnetic disks. Therefore, in the present invention, it is the ratio of the contents of Fe and Si (F
It is desirable to regulate e / Si) to 1.5 or more.

Among the components contained in the aluminum alloy substrate for a magnetic disk according to the present invention, the important elements include Mn, in addition to Mg, Cr, Fe and Si described above.
Ti is mentioned. The Mn and Ti are Al and Mg.
Since it causes the formation of intermetallic compounds and pits or nodules when the NiP plated film is formed, it is preferable to regulate the content of each of them to 0.05 mass% or less.

[0037]

EXAMPLES The present invention will be specifically described below by comparing Examples according to the present invention with Comparative Examples which do not satisfy the requirements of the present invention. Example No. 1 according to the present invention was manufactured using the aluminum alloys having the compositions shown in Table 1 through the following manufacturing steps. 1 to 15 and Comparative Example Nos. That do not satisfy the requirements of the present invention. 16-22 aluminum alloy substrates were produced.

[0038]

[Table 1]

[Manufacturing Process] First, each aluminum alloy having the composition shown in Table 1 is melted and cast to have a thickness of 50 m.
m ingot was produced. Next, the ingot was subjected to chamfering, then homogenized at 540 ° C. for 8 hours, and further hot-rolled to produce a hot-rolled plate having a final thickness of 3 mm. Subsequently, this hot rolled plate was cold rolled to produce a cold rolled plate having a final plate thickness of 1.3 mm. Then, this cold-rolled sheet was punched to produce a 3.5 inch size (95 mmφ outer diameter, 25 mmφ inner diameter) aluminum alloy substrate. Then, this aluminum alloy substrate was subjected to pressure annealing treatment at 340 ° C. for 3 hours, and then the surface was ground to give Example No. 1 having a final thickness of 1.25 mm according to the present invention. Comparative Examples Nos. 1 to 15 which do not satisfy the requirements of the present invention. 16 to 22 aluminum alloy substrates were obtained.

By adjusting the cold working rate during the cold rolling, the size of the aluminum alloy crystal grains was appropriately changed to produce each of the aluminum alloy substrates. The average grain size of the aluminum alloy crystal grains was determined by the cutting method performed as follows. (1) First, the surface of the aluminum alloy substrate is observed with an optical microscope (magnification: 200), and a photograph is taken. (2) Next, a straight line is drawn at an arbitrary position of this optical micrograph (for example, a line passing through the center, a line connecting left and right, or a diagonal line). (3) Then, the numerical value obtained by dividing the length of the straight line by the number of aluminum alloy crystal grains crossing this straight line is taken as the average grain size of the aluminum alloy crystal grains (for example, in the above-mentioned optical micrograph). A line connecting the top and bottom, left and right passing through the center,
Alternatively, the average grain size of the aluminum alloy crystal grains may be calculated on the diagonal line, and the average value of these average grain sizes may be determined. In addition, the example No. 1
.About.15 and Comparative Example Nos. That do not satisfy the requirements of the present invention. 1
Evaluation was performed on 6 to 22.

[Evaluation Method] 1. Tensile strength Tensile strength is the same as that of the above-mentioned Example No. 1 to 15 and Comparative Example No. The aluminum alloy plates after cold rolling in 16 to 22 were subjected to O treatment at 340 ° C., and then tensile test pieces according to JIS No. 5 were prepared so that the tensile direction was parallel to the rolling direction. Then, a tensile test was conducted on this tensile test piece to determine the tensile strength. The tensile strength is 230 N /
If the aluminum alloy plate has a size of mm ² or more, the aluminum alloy substrate for a magnetic disk has no problem in strength.

2. Grinding speed Grinding was performed by punching each of the cold-rolled sheets in the above-described Examples and Comparative Examples to produce a 3.5-inch size aluminum alloy substrate, and then performing edge-face processing to produce a blank material. Each blank was dressed with a # 600 ring dresser using a double-sided grinder (-18B manufactured by Speedfam), and then ground under the following conditions.

<Grinding conditions> Nippon Tokken Kenzo Co., Ltd .- # 400
0 grindstone, Cosmo-AD3118 coolant was used to grind for 30 seconds at a primary pressure of 24 g / cm ² and a secondary pressure of 90 g / cm ² until the final plate thickness reached 1.25 mm. Grinding was performed. Then, as the grinding speed, the time from the start to the final plate thickness of 1.25 mm was measured when grinding was performed with the secondary pressure, and the grinding amount per minute was obtained.

3. Precipitation Form and Precipitation Amount of Zn by Zincate Treatment Furthermore, regarding the aluminum alloy substrate that was subjected to the following treatment steps, the precipitation form and the amount of Zn deposit by the zincate treatment were investigated.

<Process of Zincate Treatment> First, a degreasing agent (made by Federity Co., Ltd. 315) was applied to each of the aluminum alloy substrates of the above-mentioned Examples and Comparative Examples as an alkaline degreasing treatment.
It was immersed in 2) at 60 ° C. for 2 minutes and then washed with water. next,
As the acid etching treatment, it was immersed in an etching solution (3133 manufactured by Federity Co., Ltd.) at 65 ° C. for 2 minutes and then washed with water. Subsequently, as a nitric acid desmutting treatment, it was immersed in 30% nitric acid (special grade manufactured by Wako Pure Chemical Industries, Ltd.) at room temperature for 1 minute, and then washed with water. Then, as the primary zincate treatment, 20
Zincate solution (311 manufactured by Fedity) at 30 ° C for 30 seconds.
The aluminum alloy substrate was immersed in 6) and then washed with water. Furthermore, as nitric acid peeling, 30% nitric acid at 20 ° C for 30
After dipping for a second, it was washed with water. Then, as a secondary zincate treatment, after dipping at 20 ° C. for 30 seconds, it was washed with water and dried.

<Formation of Zn Precipitation> Subsequently, the magnetic disk substrates of the above-mentioned examples and comparative examples thus treated with zincate were observed by SEM (scanning electron microscope), and aluminum after zincate treatment was performed. The Zn deposition morphology on the surface of the alloy substrate and the occurrence of pits on the aluminum alloy substrate surface were observed.

<Amount of Zn Deposited> Further, the amount of Zn deposited was determined from the mass difference before and after the Zn removal by dipping in nitric acid with respect to the zincate-treated aluminum alloy substrate.

4. Observation of the surface of the NiP plated film after electroless plating and the surface of the NiP plated film after heat treatment assuming substrate heating when forming a film by a sputtering method Each of the aluminum alloy substrates of the above-mentioned Examples and Comparative Examples was subjected to zincate treatment. After that, electroless plating was performed by a usual method to form a NiP plated film of about 10 μm.
This surface was observed with an optical microscope, and the generation states of pits and nodules were compared between the aluminum alloy substrates.

After that, surface polishing was carried out by a double-sided polishing machine (-18B manufactured by Speed Fam Co.), and the center line average roughness Ra of the surface measured by a three-dimensional shape measuring instrument (trade name: WYKO) was 10 Å or less. So that Subsequently, assuming the conditions for forming a magnetic film by the sputtering method, heat treatment is performed in vacuum at 285 ° C. for 30 minutes, and the obtained aluminum alloy substrate is subjected to the three-dimensional shape measurement as before the heat treatment. The surface roughness was measured using a measuring instrument, and the amount of change in the center line average roughness Ra of the surface before and after the heat treatment was determined. Table 2 shows the results of the above evaluations.

[0050]

[Table 2]

The following are clear from Tables 1 and 2. Example No. 1 according to the present invention. The aluminum alloy substrates Nos. 1 to 15 could realize desired high flatness and smoothness even if they were ground at a higher grinding speed. That is, Example No. 1 according to the present invention. 1 to 15 are all
The zinc morphology by the zincate treatment was a film-like uniform deposition, the number of pits on the zincate treated surface was small, and the surface condition of the NiP plated film was good. Further, even if a heat treatment is applied after polishing, the change in the center line average roughness Ra of the surface is small, and no minute surface roughness of the surface, which is a problem when realizing a higher recording density, was not observed.

On the other hand, Comparative Example No. 3 in which the amount of (3Cu + Zn) exceeds the upper limit of the range regulated by the present invention. 16, 1
In Nos. 7 and 18, relatively many pits were generated after the zincate treatment, and relatively many pits were also observed on the surface of the NiP plated film. Further, Comparative Example No. 1 in which Mg is less than the lower limit value of the range regulated by the present invention. No. 19 did not have the tensile strength required in the magnetic disk substrate.

Further, in Comparative Example No. 7 in which Mg exceeds the upper limit of the range regulated by the present invention. Sample No. 20 was satisfactory in the Zn precipitation morphology, pit generation state, and Zn precipitation amount, but was difficult to roll due to excessively high tensile strength and was inferior in productivity. Further, Comparative Example No. 3 in which the content of Cr is less than the lower limit value of the range regulated by the present invention. In No. 21, the aluminum alloy crystal grains were coarsened, and thus Zn was precipitated in a granular form by the zincate treatment, and the change in the center line average roughness Ra of the surface before and after the heat treatment was also large and the smoothness was deteriorated. It was

Comparative Example No. 3 in which the Cr content exceeds the upper limit of the range regulated by the present invention. In No. 22, since a coarse Cr-based intermetallic compound is formed, the peripheral portion of the intermetallic compound is dissolved by the zincate treatment, the intermetallic compound is removed and a large pit is formed, and the surface characteristics after NiP plating are performed. However, the change in the center line average roughness Ra of the surface before and after the heat treatment was large, and the smoothness was deteriorated.

[0055]

According to the present invention constructed as described above, the following effects can be obtained. That is, according to claim 1 of the present invention, Mg and Cr in the aluminum alloy are
Since the content of Cu and the content ratio of Cu and Zn are regulated, the desired flatness and smoothness can be obtained even if the grinding is performed at a higher grinding speed, and the fineness on the surface can be maintained even at a relatively high temperature. It is possible to provide an aluminum alloy substrate for a magnetic disk in which the occurrence of surface roughness is suppressed.

Further, according to the invention of claim 2, since the size of the aluminum alloy crystal grain is regulated, the size of the crystal grain is further optimized, and the grindability is further improved. Is further enhanced, and the above-mentioned effect is obtained. According to the invention of claim 3, Fe and Si
Since the content of Fe and the value of Fe / Si are regulated, the size and the number of the intermetallic compounds can be suppressed, and the above effects can be further enhanced.

As a result, according to the aluminum alloy substrate for a magnetic disk of the present invention, even when heated at a relatively high temperature when forming a magnetic film by the sputtering method,
It is possible to suppress the occurrence of minute surface roughness on the surface, which is a problem when realizing a high recording density on the surface of the NiP plated film. Moreover, since the aluminum alloy substrate for magnetic disk according to the present invention can obtain the desired high flatness and smoothness as described above even if it is ground at a relatively high grinding speed, the productivity is improved and the cost is reduced. Can be achieved.

Claims (3)

[Claims] 1. In addition to containing 2.0 to 6.0 mass% of Mg and 0.05 to 0.2 mass% of Cr, Cu and Z are contained.
At least one of n is 0.05 mass% ≦ 3Cu
+ Zn <0.5% by mass, so as to satisfy the relationship:
An aluminum alloy substrate for a magnetic disk, characterized in that the balance is composed of Al and unavoidable impurities. 2. The average grain size of aluminum alloy crystal grains is 5.
The aluminum alloy substrate for a magnetic disk according to claim 1, wherein the aluminum alloy substrate has a thickness of 0 μm or less. 3. Fe and Si in an amount of 0.05 mass% or less, respectively, and the ratio of the Fe and Si contents (Fe / S
The aluminum alloy substrate for a magnetic disk according to claim 1 or 2, wherein i) is configured to be 1.5 or more.