JPH04341535A - Aluminum alloy substrate for high density coating type magnetic disk - Google Patents

Abstract

PURPOSE:To obtain an aluminum alloy suitable for a substrate for high density coating type magnetic disk. CONSTITUTION:The aluminum alloy substrate for high density coating type magnetic disk characterized by having a composition consisting of 3.0-5.5% Mg, 0.05-0.5% Mn, 0.1-0.030% Si, 0.01-0.045% Fe, and the balance Al with inevitable impurities and satisfying 5X(Si%)<=(Mn%) and also having a structure where the size of an Mg-Si compound, the size of an Al-Fe-Mn-Si compound, and crystalline grain size are regulated to <=3mum, <=10mum, and <=40mum, respectively, can be obtained. Accordingly, pitting defect can be reduced when the substrate is ground as magnetic disk and, as a result, the coating type magnetic disk can be made high density.

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 magnetic disks, and more particularly to a high-density coated aluminum alloy substrate for magnetic disks.

0002

2. Description of the Related Art There are three types of aluminum alloy substrates currently used in magnetic disks: (1) chromate-treated aluminum substrates, (2) anodized aluminum substrates, and (3) NiP-plated aluminum substrates. In addition, ceramic substrates are also being developed. Of these, coated magnetic disks using chromate-treated aluminum substrates are most commonly produced today.

Conventionally, materials for magnetic disks have been required to have the following properties, and JIS-A5086 series Al-
A Mg-Mn-Cr alloy substrate is used. (1) Good surface accuracy after precision polishing or cutting. (2) Not only after polishing but also during the subsequent chemical treatment process, protrusions and holes on the substrate surface that cause defects in the magnetic thin film are difficult to form, and even if they are formed, they are small. (3) It has a certain degree of strength and can withstand machining during board production and high-speed rotation during use. (4) It should be lightweight, non-magnetic, and have a certain degree of corrosion resistance. (5) It should not be deformed by heating after applying the medium. Furthermore, with the progress of higher density, coated magnetic disks with core widths of about 10-odd micrometers have come to be manufactured. This is considered to be extremely high performance, close to the limit for coated magnetic disks.

[0004] In general, coated magnetic disk substrates are prepared by melting/casting → homogenization → facing → hot rolling → intermediate annealing → cold rolling → punching → pressure annealing → mirror finishing → pretreatment to activate the surface. Manufactured through the steps of → chromate treatment → media coating. Among these, it is important not to create defects that will cause magnetic recording errors during mirror finishing, pretreatment for activating the surface, and chemical treatment such as chromate treatment. For the above-mentioned high-density coated magnetic disk, since the core width is about 10-odd micrometers, defects caused by particles of about 3 to 4 micrometers in size in the aluminum alloy substrate become a problem.

[0005] Specifically, there are two types of such particles (compounds): nonmetallic inclusions mixed in during casting and intermetallic compounds. The former can be improved by taking equipment measures such as strengthening filters for casting, but the latter intermetallic compounds are generated by impurities such as Si and Fe.

[0006] Furthermore, as an improved JIS-A5086 alloy, an Al-Mg alloy substrate has been proposed in which the contents of Mn, Cr, Fe, Si, and Ti are limited to as small as possible (Japanese Patent Publication No. 48940/1983). ). Furthermore, a method in which the Si content is strictly specified has been proposed (Unexamined Japanese Patent Application Publication No. 2002-2012-
88741).

[0007]

[Problems to be Solved by the Invention] The 5086 alloy conventionally used for magnetic disks is Al-Mg-Mn-
It is a Cr alloy. Therefore, compounds formed by the impurities Si and Fe can be roughly divided into Mg-Si type and Al
-Fe-Mn-Si type.

[0008] Therefore, in order to cope with higher density, Si,
This problem has been solved by using a high-purity aluminum alloy material with a small amount of Fe and by minimizing the amount of these intermetallic compounds. Furthermore, as shown in Japanese Patent Publication No. 63-48940, Mn, which is an additive element of 5086 alloy, easily forms Al-Mn-Fe-based crystallized compounds during casting due to the presence of a small amount of Fe. Strict regulations have been implemented to limit Mn to 0.01% or less and to limit the amount of impurities. Therefore, in order to apply the material shown in Japanese Patent Publication No. 63-48940 as a high-density coating type magnetic disk substrate, Si should be 0.010% or less and Fe should be 0.0% or less.
There was a problem in that it had to be 10% or less, and only aluminum ingots with a purity of 99.99% or more could be used.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an inexpensive aluminum alloy substrate for a high-density coating type magnetic disk without using a high-purity aluminum alloy material containing small amounts of Si and Fe.

0010

[Means for Solving the Problems] In the course of this process, the present inventors conducted various investigations into the properties of intermetallic compounds after mirror finishing, and found that Mg-Si compounds easily fall off from the matrix; Al-Mn-
It has been found that Fe-based compounds are difficult to fall off and do not form pit defects. Therefore, contrary to the conventional technology, the amount of Mn commensurate with the Si content of the base metal [i.e., 5×(Si%)≦
(Mn%)], Si is absorbed as a harmless Al-Fe-Mn-Si compound, thereby reducing the size of harmful Mg-Si compounds and reducing the amount of crystallization. The present invention has been completed based on the discovery that this can reduce the

That is, the gist of the present invention is to reduce Si to 0 by making an Al-Mg alloy contain Mn commensurate with the Si content and by controlling the Mn content to 0.05 to 0.5%.
．． It is possible to contain Fe up to 0.030% and Fe up to 0.045%, and to eliminate harmful Mg-Si compounds to a thickness of 3 μm or less on the surface of the magnetic disk substrate, Al-Fe-M
The n-Si compound is 10 μm or less and the crystal grain size is 40 μm or less.
This is a high-density coated aluminum alloy substrate for magnetic disks with a thickness of μm or less.

0012

[Operation] The structure and operation of the present invention will be explained. ■Mg [3.0-5.5%] Mg is necessary to increase the strength of the substrate, and is
In order to obtain a strength of 250 MPa or more in the annealed material, it is necessary to contain at least 3% or more. but,
If it exceeds 5.5%, hot workability deteriorates and it reacts with Si contained in the base metal to form an Mg-Si compound, which is not preferable.

■Mn [0.05-0.5%] Mn has conventionally been avoided in magnetic disk substrate materials because it forms Al--Mn compounds. However, the inclusion of a small amount of Mn
By promoting the bonding with Fe and Si during casting, Al-
Mg-, which generates Fe-Mn-Si-based compounds, tends to occur in Al-Mg-based alloys, and is extremely harmful to magnetic disks.
It has been found that the formation of Si-based crystallized substances can be suppressed. In addition, the remaining Mn combined with Fe and Si precipitates as an Al-Mn-based fine compound during the homogenization process, which promotes crystal grain refinement of the substrate, increases strength, and improves the surface quality of the magnetic disk substrate (surface roughness). Therefore, M
The amount of n added should be determined mainly based on the Si content of the base metal, but this effect can be seen at a content of 0.05%.
If it is less than 5×(Si
If the Mn content is less than 0.50%, the effect of detoxifying Si will be insufficient, and if it exceeds 0.50%, the crystallized product will become large, which is not preferable.

■Si [0.010-0.030%]Si
In Al-Mg alloys, Mg-Si crystallized compounds are generated during casting, which crumble during polishing during magnetic disk manufacturing, and dissolve and fall off during subsequent chemical etching. This must be strictly controlled, as it degrades the performance of the magnetic disk. However, as mentioned above, by containing a small amount of Mn, it combines with Fe and Si during casting, resulting in Al-Fe-
It is possible to generate Mn-Si compounds and suppress the generation of Mg-Si crystallized compounds. Therefore, it is preferable to have less Si, but even if Mn is contained in an amount of 0.5%, if it exceeds 0.03%, Mg-Si compounds will be produced, so the Si content must be 0.03% or less. Also,
When it is less than 0.010%, the cost becomes extremely high and it is not practical.

■Fe[0.010~0.045%]Al
-Fe-Mn-Si compounds do not fall off during polishing or chemical treatment during the manufacture of magnetic disk substrates, so the severity is not as severe, but coarse compounds such as 1
If it exceeds 0 μm, the compound will easily create scratches during polishing, and there is a risk of falling off due to unstable factors during chemical processing. It is necessary to Also, 0.
If it is less than 0.010%, the cost will be extremely high, similar to Si, and it will not be practical.

■Cr, Zr, V each [0.05 to 0.20
%] Cr, Zr, and V do not crystallize compounds during casting, so
It is effective in making crystal grains finer and improving strength and surface quality after etching without causing pit defects. However, if it is less than 0.05%, it will not have this effect, and if it is more than 0.20%, a coarse intermetallic compound will be formed during casting, making it impossible to use it as a magnetic disk substrate.

■Mg-Si compound [≦3 μm] Mg-
The Si-based compound is produced by combining Si mixed from the base metal of the aluminum raw material with Mg, which is the main component of the aluminum alloy used in the present invention, and the smaller the amount, the better. This crumbles during polishing during the manufacturing of the magnetic disk, or dissolves and falls off during etching during the subsequent chemical treatment, resulting in depressions and deteriorating the performance of the magnetic disk. For this reason, even if this is contained, it is necessary to make the size fine and to make the depressions smaller, so the size needs to be 3 μm or less.

■Al-Fe-Mn-Si compound [≦1
0 μm] In an Al-Fe-Mn-Si-based compound, Fe mixed from the base metal of the aluminum raw material is combined with Al, and when Mn and Si coexist, it crystallizes as a compound incorporating them. It is also partially formed during the homogenization process. but,
Unlike Mg-Si compounds, it does not fall off during polishing or chemical processing, so it is not as severe. Due to the risk of falling off, it is preferable to suppress the size to 10 μm or less. The thickness of 10 μm or less can be achieved by reducing the Fe content to 0.045% or less, as described above.

■Crystal grains [≦40 μm] Crystal grains have the effect of ensuring the strength of the material, but in the case of magnetic disks, if the crystal grains are coarse, the surface quality will deteriorate,
If it exceeds μm, it is not preferable. In order to obtain a material with crystal grains of 40 μm or less, Mn dissolved in solid solution during casting must be at least 0.
．． 0.05% or more is required.

[0020]

[Example] An example of the present invention will be explained. An aluminum alloy having the composition shown in Table 1 was continuously cast into an ingot with a thickness of 450 mm, homogenized at 520°C for 8 hours, the segregation layer near the casting surface was cut off, heated to 450°C, and then hot rolled. (Hot working degree: 98%) A plate with a thickness of 6 mm was prepared. Thereafter, a plate with a thickness of 2 mm was formed by cold working (degree of cold working: 67%), punched into a donut shape, and then pressure annealed at 360° C. for 1 hour to obtain an aluminum alloy substrate of O material.

[0021]

[Table 1]

It is said that the occurrence of a magnetic recording error in a magnetic disk is a fatal defect. In order to predict this in advance, Mg-Si compounds and Al-Fe-Mn
- The shape and distribution of the Si-based compound and the size of the crystal grain size were measured, and the size of the Mg-Si-based compound was 3 μm or less, and the size of the Al
-The size of the Fe-Mn-Si compound is 10 μm or less,
The material of the present invention has a crystal grain size of 40 μm or less. In addition, the material has a yield strength of 118M, which reduces "wobble" due to deformation when rotating as a magnetic disk.
The present invention is a material that can obtain Pa or more.

[0023] For the compound distribution, an O material plate was cut into 5 mm square pieces, filled with resin, and finished by emery polishing and buff polishing so that a position at a depth of about 100 μm from the surface layer was exposed. The position 100 μm from the surface layer corresponds to the position after mirror finishing, that is, the surface used as a magnetic disk. During buffing, depending on the composition of the polishing agent, Mg-Si compounds and Al
Since there is a difference in the degree of coloring of the -Fe-Mn-Si based compounds, both were measured as equivalent circle diameters using an image analyzer. The measurement was performed using a microscope with a magnification of 400 times and a total measurement area of 1 mm2. These results are shown in Table 2.

[0024]

[Table 2]

Conventional material No. 1 has very good performance as a magnetic disk, but it requires the use of 99.99% high-purity aluminum base metal.
This is not preferable due to high cost.

Invention material No. 2 to 13 are all within the component range of the present invention, and the compound distribution is 3 μm or less for Mg-Si compounds and 10 μm for Al-Fe-Mn-Si compounds.
µm or less, crystal grain size is 40 µm or less, yield strength 118
MPa or more can be obtained, which is satisfactory as a substrate for a magnetic disk.

On the other hand, comparative material No. No. 14 has a high Fe content of 0.048%. No. 15 has a Si content of 0.
034%, high Fe content of 0.055%, 10 μm
The presence of the above Al-Fe-Mn-Si compounds poses a risk of generating scratches during mirror polishing of the magnetic disk substrate. Further, since there are nine Mg-Si compounds having a diameter of 3 to 5 μm or more, holes are formed during polishing or various chemical treatments, which is not preferable.

[0028]No. No. 16 has a high Si content of 0.035%, and there are nine Mg-Si compounds with a diameter of 3 μm or more, which is not preferable.

[0029]No. No. 17 has a high Mn content of 0.64%, and there are 12 Al-Fe-Mn-Si compounds with a diameter of 10 μm or more, which is not preferable.

[0030]No. Test No. 18 had a high Mg content of 5.94%, and large cracks were detected at a degree of hot working of 50%, so the test was discontinued.

[0031]No. 19 has a Cr content of 0.49%, N
o. 20 has a Zr content of 0.30% and a V content of 0.
．． The test was discontinued because a huge intermetallic compound was generated during casting, which was as high as 25%.

[0032]No. No. 21 has a low Mn content of 0.02%, contains Mg-Si compounds with a diameter of 3 μm or more, and has a large crystal grain size of 45 μm, which is not preferable.

[0033]No. No. 22 has a low Mg content of 2.68% and a low yield strength of 64 MPa, which is not preferable.

[0034]

Effects of the Invention As explained above, the present invention provides an aluminum alloy containing 0.05 to 0.5% of Mn to an aluminum alloy containing 3 to 5.5% of Mg as a substrate for a magnetic disk.
By adjusting the Mn content to match the i content and controlling the size and distribution of the intermetallic compound, it is possible to reduce pitting defects when polished as a magnetic disk, making it possible to increase the density of coated magnetic disks. It is extremely useful industrially.

Claims (2)

[Claims] [Claim 1] Mg: 3.0 to 5.5%, Mn: 0.
05-0.5%, Si: 0.010-0.030%, F
e: 0.010 to 0.045%, and 5×(S
i%)≦(Mn%), the balance is Al and unavoidable impurities, the size of the Mg-Si compound is 3 μm or less, and the Al-F
An aluminum alloy substrate for a high-density coated magnetic disk, characterized in that the size of the e-Mn-Si-based compound is 10 μm or less and the crystal grain size is 40 μm or less. Claim 2: Further Cr: 0.05 to 0.20%,
Zr: 0.05-0.20%, V: 0.05-0.20
The aluminum alloy substrate for a high-density coated magnetic disk according to claim 1, containing one or more of the following.