阅读说明：本技术 磁盘用铝合金基板及其制造方法、以及使用了该磁盘用铝合金基板的磁盘 (Aluminum alloy substrate for magnetic disk, method for producing same, and magnetic disk using same ) 是由 北脇高太郎 村田拓哉 米光诚 松居悠 藤井康生 坂本辽 中山贤 熊谷航 于 2018-04-09 设计创作，主要内容包括：一种磁盘用铝合金基板及其制造方法、以及使用该磁盘用铝合金基板的磁盘,该磁盘用铝合金基板的特征在于,由含有Fe：0.4～3.0mass％,剩余部分由Al及不可避免的杂质构成的铝合金构成,具有0.5μm以上且小于2.0μm的最长径的第二相粒子以5000个/mm<Sup>2</Sup>以上的分布密度分散。(An aluminum alloy substrate for a magnetic disk, a method for producing the same, and a magnetic disk using the aluminum alloy substrate for a magnetic disk, wherein the aluminum alloy substrate for a magnetic disk is characterized by comprising a base material containing Fe: 0.4 to 3.0 mass% and the balance of Al and inevitable impurities, and has a size of 0.5 μm or more and a small sizeAt a maximum diameter of 2.0 μm, the number of second phase particles is 5000 particles/mm 2 The above distribution density is dispersed.)

1. An aluminum alloy substrate for a magnetic disk, characterized in that,

is prepared from Fe: 0.4 to 3.0 mass% and the balance of Al and inevitable impurities, wherein 5000 pieces/mm of second phase particles having a longest diameter of 0.5 μm or more and less than 2.0 μm²The above distribution density is dispersed.

2. The aluminum alloy substrate for magnetic disk according to claim 1,

the aluminum alloy further includes a transition metal selected from the group consisting of Mn: 0.1 to 3.0 mass%, Si: 0.1 to 0.4 mass%, Ni: 0.1 to 3.0 mass%, Cu: 0.005-1.000 mass%, Mg: 0.1-6.0 mass%, Cr: 0.01 to 1.00 mass% and Zr: 0.01 to 1.00 mass% of 1 or more selected from the group consisting of.

3. The aluminum alloy substrate for magnetic disk according to claim 1 or 2,

the aluminum alloy further contains Zn: 0.005-1.000 mass%.

4. The aluminum alloy substrate for magnetic disks according to any one of claims 1 to 3,

the aluminum alloy further contains 1 or 2 or more selected from the group consisting of Ti, B and V in a total amount of 0.005 to 0.500 mass%.

5. The aluminum alloy substrate for magnetic disks according to any one of claims 1 to 4,

the average crystal grain size in the thickness direction of the cross section is 70 μm or less.

6. The aluminum alloy substrate for magnetic disks according to any one of claims 1 to 5,

the yield strength after heating at 340 ℃ for 3 hours in the atmosphere is 60MPa or more.

7. A magnetic disk, characterized in that,

an aluminum alloy substrate for a magnetic disk as set forth in any one of claims 1 to 6, which is provided on a surface thereof with an electroless Ni-P plating treatment layer and a magnetic body layer thereon.

8. A method for producing an aluminum alloy substrate for a magnetic disk according to any one of claims 1 to 6, comprising:

a continuous casting process of continuously casting a cast sheet using the aluminum alloy,

a cold rolling step of cold rolling the cast sheet,

a disc blank punching step of punching a cold-rolled sheet into a circular shape,

a press annealing step of press annealing the punched disc blank, and

a cutting and grinding step of performing cutting and grinding on the pressure annealed disc blank;

wherein the temperature of the cast slab after 1 minute from the continuous casting step is set to 230 to 350 ℃, and the temperature of the cast slab after 10 minutes from the continuous casting step is set to 150 ℃ or higher and less than 230 ℃.

9. A method for producing an aluminum alloy substrate for a magnetic disk according to any one of claims 1 to 6, comprising:

a continuous casting process of continuously casting a cast sheet using the aluminum alloy,

a homogenization step of homogenizing the cast sheet,

a cold rolling step of cold rolling the homogenized cast sheet,

a disc blank punching step of punching a cold-rolled sheet into a circular shape,

a press annealing step of press annealing the punched disc blank, and

a cutting and grinding step of performing cutting and grinding on the pressure annealed disc blank;

wherein the temperature of the cast slab after the continuous casting step for 1 minute is set to 230 to 350 ℃, and the temperature of the cast slab after the continuous casting step for 10 minutes is set to 150 ℃ or higher and less than 230 ℃;

in the homogenization step, the cast sheet is heat-treated at 300 to 450 ℃ for 0.5 to 24 hours.

10. The method of manufacturing an aluminum alloy substrate for a magnetic disk according to claim 8 or 9,

before or during the cold rolling process, an annealing treatment process for annealing the cast plate or the rolled plate is further included.

Technical Field

The present invention relates to an aluminum alloy substrate for a magnetic disk having high strength and good fluttering (fluttering) characteristics, a method for producing the same, and a magnetic disk using the aluminum alloy substrate for a magnetic disk.

Background

Magnetic disks used in computer memory devices are manufactured using a substrate having good platability and excellent mechanical properties and workability. For example, it is produced from a substrate based on JIS5086 aluminum alloy (containing 3.5 to 4.5 mass% of Mg, 0.50 mass% or less of Fe, 0.40 mass% or less of Si, 0.20 to 0.70 mass% of Mn, 0.05 to 0.25 mass% of Cr, 0.10 mass% or less of Cu, 0.15 mass% or less of Ti, and 0.25 mass% or less of Zn, with the remainder being Al and unavoidable impurities).

A general magnetic disk is manufactured as follows: first, an annular aluminum alloy substrate is produced, and the aluminum alloy substrate is plated, and then a magnetic body is attached to the surface of the aluminum alloy substrate.

For example, a magnetic disk made of an aluminum alloy according to the JIS5086 alloy is manufactured by the following manufacturing process. First, an aluminum alloy material of a predetermined chemical composition is cast, a cast slab thereof is hot-rolled, and then, cold-rolled to produce a rolled material having a thickness necessary for a magnetic disk. The rolled material is preferably annealed during cold rolling or the like as necessary. Next, the rolled material is punched out into an annular shape, and in order to remove strain and the like generated in the above-described manufacturing process, aluminum alloy plates formed into an annular shape are laminated, and annealing is performed while applying pressure from both surfaces of both end portions, and pressure annealing for flattening is performed, thereby manufacturing an annular aluminum alloy substrate.

The annular aluminum alloy substrate thus produced was subjected to cutting, grinding, degreasing, etching, and zincing (Zn substitution treatment) as pretreatment, and then, as a base treatment, Ni — P as a hard nonmagnetic metal was electroless-plated, and after the surface of the plating was polished, a magnetic material was sputtered onto the surface of the Ni — P electroless-plated layer, thereby producing an aluminum alloy magnetic disk.

However, in recent years, due to the demand for multimedia and the like, a large capacity and a high density have been demanded for a magnetic disk, and a higher speed has been demanded. In order to increase the capacity, the number of magnetic disks mounted in a storage device increases, and the magnetic disks are required to be thinner. However, when the aluminum alloy substrate for a magnetic disk is thinned, the strength is lowered, and therefore, the aluminum alloy substrate is required to have higher strength.

Further, as the thickness is reduced and the speed is increased, the exciting force is increased along with the reduction of the rigidity and the increase of the fluid force caused by the high-speed rotation, and thus the disk flutter (disk flutterter) is liable to occur. This is because when the magnetic disk is rotated at a high speed, unstable air flow is generated between the disks, and the magnetic disk vibrates (flutters) due to the air flow. This phenomenon is considered to occur for the following reasons: when the rigidity of the substrate is low, the vibration of the magnetic disk becomes large and the magnetic head cannot follow the change. When chattering occurs, a positioning error of a magnetic head as a reading portion increases. Therefore, reduction of disc flutter is strongly demanded.

Further, as the density of magnetic disks increases, the magnetic area per 1 bit is increasingly miniaturized. With this miniaturization, a read error due to a deviation of the positioning error of the magnetic head is likely to occur, and reduction of disk flutter, which is a main cause of the positioning error of the magnetic head, is strongly demanded.

From such a fact, in recent years, aluminum alloy substrates for magnetic disks having high strength and less disk flutter are strongly desired and studied. For example, a proposal has been made to mount an airflow suppressing member having a plate opposed to a disk in a hard disk drive. Patent document 1 proposes a magnetic disk device provided with an air spoiler on the upstream side of an actuator. The air spoiler weakens the air flow blown to the actuator on the disk, thereby reducing turbulent vibration of the magnetic head. In addition, the air spoiler weakens the air flow over the magnetic disk, thereby suppressing disk flutter. Further, patent document 2 proposes a method in which: the strength of the aluminum alloy sheet is improved by containing a large amount of Mg which contributes to the improvement of the strength.

However, in the method disclosed in patent document 1, the flutter suppression effect is different depending on the difference in the distance between the air spoiler and the disk substrate, and high precision of the component is required, which increases the component cost.

Further, although the method of making the aluminum alloy sheet contain a large amount of Mg as shown in patent document 2 is effective for improving the strength, the current situation is that: disc vibration is liable to occur, and a small disc vibration characteristic as a target is not obtained.

[ Prior art documents ]

[ patent document ]

Patent document 1, Japanese patent laid-open publication No. 2002-313061

Patent document 2, Japanese patent laid-open No. 2006-241513

Disclosure of Invention

[ problems to be solved by the invention ]

The present invention has been made in view of the above circumstances, and an object thereof is to provide an aluminum alloy substrate for a magnetic disk having high strength and excellent flutter characteristics of the disk, a method for producing the same, and a magnetic disk using the aluminum alloy substrate for a magnetic disk.

[ means for solving the problems ]

That is, the present invention is as follows in claim 1: an aluminum alloy substrate for a magnetic disk, characterized by comprising, by mass, a composition comprising Fe: 0.4 to 3.0 mass% and the balance of Al and inevitable impurities, wherein 5000 pieces/mm of second phase particles having a longest diameter of 0.5 μm or more and less than 2.0 μm²The above distribution density is dispersed.

The invention in claim 2 is: the aluminum alloy of claim 1, further comprising an aluminum alloy selected from the group consisting of Mn: 0.1 to 3.0 mass%, Si: 0.1 to 0.4 mass%, Ni: 0.1 to 3.0 mass%, Cu: 0.005-1.000 mass%, Mg: 0.1-6.0 mass%, Cr: 0.01 to 1.00 mass% and Zr: 0.01 to 1.00 mass% of 1 or more selected from the group consisting of.

The invention in claim 3 is: the aluminum alloy according to claim 1 or 2, further containing Zn: 0.005-1.000 mass%.

The invention in claim 4 is: the aluminum alloy according to any one of claims 1 to 3, further comprising 1 or 2 or more selected from the group consisting of Ti, B and V in a total amount of 0.005 to 0.500 mass%.

The invention in claim 5 is: according to any one of claims 1 to 4, the cross section has an average crystal grain size in the plate thickness direction of 70 μm or less.

The invention in claim 6 is: the steel sheet according to any one of claims 1 to 5, wherein the yield strength after heating at 340 ℃ for 3 hours in the atmosphere is 60MPa or more.

The invention in claim 7 is: a magnetic disk, wherein an electroless Ni-P plating treated layer and a magnetic body layer thereon are provided on the surface of the aluminum alloy substrate for magnetic disk according to any one of claims 1 to 6.

The invention in claim 8 is: a method for producing an aluminum alloy substrate for a magnetic disk according to any one of claims 1 to 6, comprising a continuous casting step of continuously casting a cast sheet using the aluminum alloy, a cold rolling step of cold-rolling the cast sheet, a disc blank punching step of punching the cold-rolled sheet into a circular ring shape, a pressure annealing step of pressure annealing the disc blank after punching, and a cutting and grinding step of performing cutting and grinding on the disc blank after pressure annealing; the temperature of the cast slab after the passage of 1 minute after the continuous casting step is set to 230 to 350 ℃, and the temperature of the cast slab after the passage of 10 minutes after the continuous casting step is set to 150 ℃ or higher and less than 230 ℃.

The invention in claim 9 is: a method for producing an aluminum alloy substrate for a magnetic disk according to any one of claims 1 to 6, comprising a continuous casting step of continuously casting a cast plate using the aluminum alloy, a homogenization treatment step of homogenizing the cast plate, a cold rolling step of cold rolling the homogenized cast plate, a disc blank punching step of punching the cold rolled plate into a circular ring shape, a pressure annealing step of pressure annealing the disc blank after punching, and a cutting and grinding step of performing cutting and grinding on the disc blank after pressure annealing; setting the temperature of the cast plate after the continuous casting process for 1 minute to 230-350 ℃, and setting the temperature of the cast plate after the continuous casting process for 10 minutes to be more than 150 ℃ and less than 230 ℃; in the homogenization step, the cast sheet is heat-treated at 300 to 450 ℃ for 0.5 to 24 hours.

The invention in claim 10 is: according to claim 8 or 9, further comprising an annealing treatment process of annealing the cast or rolled sheet before or during the cold rolling process.

[ Effect of the invention ]

According to the present invention, it is possible to provide an aluminum alloy substrate for a magnetic disk having high strength and excellent disk flutter characteristics, a method for producing the same, and a magnetic disk using the aluminum alloy substrate for a magnetic disk.

Drawings

FIG. 1 is a flowchart showing an aluminum alloy substrate for a magnetic disk and a method for manufacturing a magnetic disk according to the present invention.

Detailed Description

The present inventors paid attention to the relationship between the strength and flutter characteristics of the substrate and the material of the substrate, and conducted intensive investigations on the relationship between these characteristics and the characteristics of the substrate (magnetic disk material). As a result, it was found that the Fe content and the distribution of the second phase particles have a large influence on the strength. In addition, it was found that the Fe content and the second phase particles of the aluminum alloy substrate have a large influence on the flutter characteristics of the magnetic disk measured in air or helium. Accordingly, the present inventors have studied the Fe content and the second phase particles having the longest diameter of 0.5 μm or more and less than 2.0 μm in the metal structure, and as a result, have found that: in the second phase particles having a longest diameter of 0.5 μm or more and less than 2.0 μm, the Fe content is in particular 0.4 to 3.0 mass% (hereinafter abbreviated as "%"), and 5000 particles/mm²The above aluminum alloy substrate for a magnetic disk having a dispersed distribution density has improved strength and flutter characteristics, and the present invention has been completed.

A. The invention relates to an aluminum alloy substrate for magnetic disk

The aluminum alloy substrate for magnetic disks according to the present invention (hereinafter, simply referred to as "aluminum alloy substrate according to the present invention" or simply referred to as "aluminum alloy substrate") will be described in detail below.

1. Alloy composition

Next, the aluminum alloy components and the contents thereof constituting the aluminum alloy substrate for magnetic disk using the Al-Fe alloy according to the present invention will be described.

Fe：

Fe is an essential element, and is mainly present as second phase particles (Al — Fe intermetallic compound, etc.) in a solid solution in the matrix, and this has the effect of improving the strength and chatter characteristics of the aluminum alloy substrate. When vibration is applied to such a material, vibration energy is rapidly absorbed due to viscous flow at the interface of the second phase particles and the matrix, and extremely good flutter characteristics are obtained. When the Fe content in the aluminum alloy is less than 0.4%, sufficient strength and chatter characteristics cannot be obtained. On the other hand, when the Fe content exceeds 3.0%, many coarse Al-Fe-based intermetallic compound particles are formed. Such coarse particles of Al-Fe intermetallic compound may be detached during etching, zincing, cutting or grinding to form large pits, thereby reducing the smoothness of the plating surface and causing peeling of the plating. In addition, the workability in the rolling process may also be reduced. Therefore, the Fe content in the aluminum alloy is set to be in the range of 0.4 to 3.0%. The Fe content is preferably 0.6 to 2.0%, more preferably 0.8 to 1.8%.

In order to further improve the strength and flutter characteristics of the aluminum alloy substrate for a magnetic disk, the 1 st selective element may further contain an element selected from the group consisting of Mn: 0.1 to 3.0%, Si: 0.1 to 0.4%, Ni: 0.1 to 3.0%, Cu: 0.005-1.000%, Mg: 0.1-6.0%, Cr: 0.01 to 1.00%, Zr: 0.01 to 1.00% of 1 or more selected from the group consisting of. Further, as the 2 nd selective element, it may be such that it further contains Zn: 0.005-1.000%. Further, the 3 rd selective element may further contain 1 or 2 or more selected from the group consisting of Ti, B and V in a total content of 0.005 to 0.500%. These selection elements will be explained below.

Mn：

Mn exists mainly as second phase particles (Al — Mn-based intermetallic compound, etc.), and exhibits the effect of improving the strength and chatter characteristics of the aluminum alloy substrate. When vibration is applied to such a material, vibration energy is rapidly absorbed due to viscous flow at the interface of the second phase particles and the matrix, and extremely good flutter characteristics are obtained. By setting the Mn content in the aluminum alloy to 0.1% or more, the effect of improving the strength and chatter characteristics of the aluminum alloy substrate can be further improved. Further, when the Mn content in the aluminum alloy is 3.0% or less, the generation of large amounts of coarse Al — Mn intermetallic compound particles is suppressed. Such coarse Al — Mn intermetallic compound particles can be suppressed from falling off and causing large depressions at the time of etching, zincing, cutting or grinding, and further suppressed from causing reduction in the smoothness of the plating surface and peeling of the plating. In addition, the reduction in workability in the rolling step can be further suppressed. Therefore, the Mn content in the aluminum alloy is preferably in the range of 0.1 to 3.0%, more preferably in the range of 0.1 to 1.0%.

Si：

Si exists mainly as second phase particles (Si particles and the like), and exhibits the effect of improving the strength and chatter characteristics of the aluminum alloy substrate. When vibration is applied to such a material, vibration energy is rapidly absorbed due to viscous flow at the interface of the second phase particles and the matrix, and extremely good flutter characteristics are obtained. By setting the Si content in the aluminum alloy to 0.1% or more, the effect of improving the strength and chatter characteristics of the aluminum alloy substrate can be further improved. Further, by making the Si content in the aluminum alloy 0.4% or less, the generation of a large amount of coarse Si particles is suppressed. Such coarse Si particles can be suppressed from falling off and causing large depressions at the time of etching, zincing, cutting or grinding, and further suppressed from causing reduction in the smoothness of the plating surface and peeling of the plating. In addition, the reduction in workability in the rolling step can be further suppressed. Therefore, the Si content in the aluminum alloy is preferably in the range of 0.1 to 0.4%, more preferably in the range of 0.1 to 0.3%.

Ni：

Ni exists mainly as second phase particles (Al — Ni intermetallic compound, etc.), and exerts an effect of improving the strength and chatter characteristics of the aluminum alloy substrate. When vibration is applied to such a material, vibration energy is rapidly absorbed due to viscous flow at the interface of the second phase particles and the matrix, and extremely good flutter characteristics are obtained. By setting the Ni content in the aluminum alloy to 0.1% or more, the effect of improving the strength and chatter characteristics of the aluminum alloy substrate can be further improved. Further, by making the Ni content in the aluminum alloy 3.0% or less, the generation of large amounts of coarse Al — Ni intermetallic compound particles is suppressed. Such coarse Al — Ni intermetallic compound particles can be suppressed from falling off and causing large depressions at the time of etching, zincing, cutting or grinding, and further suppressed from causing reduction in the smoothness of the plating surface and peeling of the plating. In addition, the reduction in workability in the rolling step can be further suppressed. Therefore, the Ni content in the aluminum alloy is preferably in the range of 0.1 to 3.0%, more preferably in the range of 0.1 to 1.0%.

Cu：

Cu exists mainly as second phase particles (Al — Cu-based intermetallic compound, etc.), and exhibits the effect of improving the strength and chatter characteristics of the aluminum alloy substrate. Further, the amount of Al dissolved in the zincating treatment is reduced. Further, the zincating film is uniformly, thinly and densely adhered, and the smoothness in the next plating step is improved. By setting the Cu content in the aluminum alloy to 0.005% or more, the strength of the aluminum alloy substrate, the effect of improving the chatter characteristics, and the effect of improving the smoothness can be further improved. Further, by setting the Cu content in the aluminum alloy to 1.000% or less, the generation of a large amount of coarse Al — Cu intermetallic compound particles is suppressed. Such coarse Al — Cu intermetallic compound particles can be suppressed from falling off and causing large depressions at the time of etching, zincing, cutting or grinding, and the effect of improving the smoothness of the plating surface can be further enhanced, and the occurrence of plating peeling can be further suppressed. In addition, the reduction in workability in the rolling step can be further suppressed. Therefore, the Cu content in the aluminum alloy is preferably in the range of 0.005 to 1.000%, more preferably in the range of 0.005 to 0.400%.

Mg：

Mg exists mainly as second phase particles (Mg — Si based intermetallic compound, etc.), and exerts an effect of improving the strength and chatter characteristics of the aluminum alloy substrate. By setting the Mg content in the aluminum alloy to 0.1% or more, the effect of improving the strength and chatter characteristics of the aluminum alloy substrate can be further improved. Further, by setting the Mg content in the aluminum alloy to 6.0% or less, the generation of large amounts of coarse Mg — Si intermetallic compound particles is suppressed. Such coarse Mg — Si intermetallic compound particles can be prevented from falling off and causing large depressions at the time of etching, zincing, cutting or grinding, and further prevented from causing reduction in the smoothness of the plating surface and peeling of the plating. In addition, the reduction in workability in the rolling step can be further suppressed. Therefore, the Mg content in the aluminum alloy is preferably in the range of 0.1 to 6.0%, more preferably in the range of 0.3% or more and less than 1.0%.

Cr：

Cr is mainly present as second phase particles (Al — Cr-based intermetallic compound, etc.), and exerts an effect of improving the strength and chatter characteristics of the aluminum alloy substrate. By setting the Cr content in the aluminum alloy to 0.01% or more, the effect of improving the strength and chatter characteristics of the aluminum alloy substrate can be further improved. Further, by setting the Cr content in the aluminum alloy to 1.00% or less, the generation of large amounts of coarse Al — Cr intermetallic compound particles is suppressed. Such coarse Al — Cr intermetallic compound particles can be suppressed from falling off and causing large depressions at the time of etching, zincing, cutting or grinding, and further suppressed from causing reduction in the smoothness of the plating surface and peeling of the plating. In addition, the reduction in workability in the rolling step can be further suppressed. Therefore, the Cr content in the aluminum alloy is preferably in the range of 0.01 to 1.00%, more preferably in the range of 0.10 to 0.50%.

Zr：

Zr exists mainly as second phase particles (Al — Zr intermetallic compounds, etc.), and exerts an effect of improving the strength and chatter characteristics of the aluminum alloy substrate. By setting the Zr content in the aluminum alloy to 0.01% or more, the effect of improving the strength and chatter characteristics of the aluminum alloy substrate can be further improved. Further, by setting the Zr content in the aluminum alloy to 1.00% or less, the generation of a large amount of coarse Al — Zr intermetallic compound particles is suppressed. Such coarse particles of the Al-Zr intermetallic compound are prevented from falling off and forming large depressions during etching, zincing, cutting or grinding, and further from lowering the smoothness of the coating surface and peeling off the coating. In addition, the reduction in workability in the rolling step can be further suppressed. Therefore, the Zr content in the aluminum alloy is preferably in the range of 0.01 to 1.00%, more preferably in the range of 0.10 to 0.50%.

Zn：

Zn exerts the following effects: the amount of Al dissolved in the zincate treatment is reduced, so that the zincate coating film is uniformly, thinly and densely adhered, and the smoothness and adhesion in the next plating step are improved. In addition, the second phase particles are formed with other additive elements, and the effect of improving the chatter characteristics is exhibited. By setting the Zn content in the aluminum alloy to 0.005% or more, the amount of Al dissolved during the zincating treatment is reduced, and the zincating film is uniformly, thinly, and densely adhered, whereby the effect of improving the smoothness of plating can be further improved. Further, by setting the Zn content in the aluminum alloy to 1.000% or less, the zinciferous coated film becomes uniform, and the reduction in smoothness of the coating surface can be further suppressed, and the occurrence of coating separation can be further suppressed. Further, the reduction in workability in the rolling step can be further suppressed. Therefore, the Zn content in the aluminum alloy is preferably in the range of 0.005 to 1.000%, more preferably in the range of 0.100 to 0.700.

Ti、B、V：

During the solidification of Ti, B and V during casting, second phase particles (TiB) are formed₂Boride or Al₃Ti, Ti-V-B particles, etc.), since they become grain nuclei, the crystal grains can be made fine. As a result, the plating property is improved. Further, the grain size is made finer, so that the nonuniformity of the second phase particles in size can be reduced, and the effect of reducing the fluctuation of the strength and the chatter characteristics in the aluminum alloy substrate can be exerted. However, when the total content of Ti, B and V is less than 0.005%, the above-mentioned effects are not obtained. On the other hand, even if the total content of Ti, B, and V exceeds 0.500%, the effect is saturated, and a further significant improvement effect is not obtained. Therefore, the total content of Ti, B and V is preferably selected when Ti, B and V are addedThe content is in the range of 0.005 to 0.500%, and more preferably in the range of 0.005 to 0.100%. The total amount means the total amount of 1 kind when only any 1 kind of Ti, B and V is contained, the total amount of 2 kinds when any 2 kinds are contained, and the total amount of 3 kinds when all 3 kinds are contained.

Other elements:

the balance of the aluminum alloy used in the present invention is composed of Al and inevitable impurities. Here, as the inevitable impurities, Ga, Sn and the like are cited, and if the respective contents are less than 0.1% and the total content is less than 0.2%, the characteristics of the aluminum alloy substrate obtained in the present invention are not impaired.

2. Distribution state of second phase particles

Next, the distribution state of the second phase particles in the aluminum alloy substrate for a magnetic disk of the present invention will be described.

In the aluminum alloy substrate of the present invention, the number of second phase particles having a longest diameter of 0.5 μm or more and less than 2.0 μm in the metal structure is 5000/mm²The above distribution density is dispersed.

The second phase particles mean precipitates or crystals, specifically, an Al-Fe intermetallic compound (Al)₃Fe、Al₆Fe、Al₆(Fe, Mn), Al-Fe-Si, Al-Fe-Mn-Si, Al-Fe-Ni, Al-Cu-Fe, etc.), Al-Mn based intermetallic compound (Al₆Mn, Al-Mn-Si), Si particles, Al-Ni based intermetallic compound (Al)₃Ni, etc.), Al-Cu based intermetallic compound (Al)₂Cu, etc.), Mg-Si based intermetallic compound (Mg)₂Si, etc.), Al-Cr based intermetallic compound (Al₇Cr, etc.), and Al-Zr based intermetallic compounds (Al₃Zr, etc.) and the like.

In the microstructure of the aluminum alloy substrate of the present invention, the number of second phase particles having a longest diameter of 0.5 μm or more and less than 2.0 μm is 5000 particles/mm²In the above case, the aluminum alloy substrate can be maintained with high strength. Generally, aluminum alloy substrates are produced by grain boundary migration during press annealingThe strength is greatly reduced. However, when the number of second phase particles is 5000/mm²If the amount of the above is large, grain boundary migration during pressure annealing is prevented (ピ ン to め), and high strength can be maintained.

When the longest diameter of the second phase particles present in the microstructure of the aluminum alloy substrate of the present invention is 2.0 μm or more, the second phase particles are unevenly deformed around them during rolling such as cold rolling, and recrystallization is likely to occur during pressure annealing, so that the effect of maintaining high strength is insufficient. On the other hand, when the longest diameter of the second phase particles is less than 0.5 μm, the longest diameter of the second phase particles is small and the effect of preventing grain boundary migration is difficult to obtain, and thus the effect of maintaining high strength is insufficient. Therefore, the longest diameter of the second phase particles present in the metal structure of the aluminum alloy substrate is set to be in the range of 0.5 μm or more and less than 2.0 μm. The longest diameter of the second phase particles is preferably less than 0.5 to 1.5 μm.

In the metal structure of the aluminum alloy substrate of the present invention, the number of second phase particles having a longest diameter of 0.5 μm or more and less than 2.0 μm is less than 5000 particles/mm²In the case of (2), the second phase particles having the longest diameter of 0.5 μm or more and less than 2.0 μm, which are subjected to the effect of preventing the grain boundary migration, are less, and the effect of maintaining the high strength is insufficient. Therefore, in the microstructure of the aluminum alloy substrate of the present invention, the number of second phase particles having a longest diameter of 0.5 μm or more and less than 2.0 μm is 5000/mm²The above distribution density is dispersed. Further, the distribution density is preferably 10000 pieces/mm from the viewpoint of improving the strength²The above range is more preferably 30000 pieces/mm²The above range. The upper limit of the distribution density is not particularly limited, and is naturally determined depending on the composition and production method of the aluminum alloy to be used, and is 200000 pieces/mm in the present invention²Left and right.

In the present invention, the longest diameter means that, in a plane image of the second phase particles observed by an optical microscope, the maximum value of the distance between one point on the contour line and another point on the contour line is first measured, then the maximum value is measured for all the points on the contour line, and finally the maximum value is selected from all the maximum values.

3. Flutter characteristic

The flutter characteristics are also affected by the motor characteristics of the hard disk drive. In the present invention, the flutter characteristic is preferably 50nm or less, more preferably 30nm or less in air. It is judged that the thickness is50 nm or less, which is resistant to the use of general HDDs. If the wavelength exceeds 50nm, a positioning error of the magnetic head as a reading unit increases.

Further, the flutter characteristics are preferably 30nm or less, more preferably 20nm or less in helium gas. If the thickness is 30nm or less, it is judged that the HDD can be used for a higher density recording capacity. If the wavelength exceeds 30nm, a positioning error of the magnetic head as a reading unit increases.

Here, since the required chatter characteristics vary depending on the hard disk drive used, it is preferable to appropriately determine the distribution state of the second phase particles in accordance with the chatter characteristics. They are obtained by: the casting method including the content of the additive elements and the cooling rate at the time of casting, and the thermal history and the working history of the subsequent heat treatment and working are appropriately adjusted.

In the embodiment of the present invention, it is preferable that the aluminum alloy plate has a thickness of 0.45mm or more. When the thickness of the aluminum alloy plate is less than 0.45mm, the substrate may be deformed by an acceleration force due to a drop or the like occurring at the time of mounting a hard disk drive or the like. However, the present invention is not limited to this, as long as the deformation can be suppressed by further increasing the yield strength. Further, when the thickness of the aluminum alloy plate exceeds 1.30mm, the flutter characteristics are improved, but the number of disks that can be mounted in the hard disk is reduced, which is not preferable. Therefore, the thickness of the aluminum alloy plate is more preferably 0.45 to 1.30mm, and still more preferably 0.50 to 1.00 mm.

In addition, the fluid force can be reduced by filling the hard disk with helium gas. This is because the gas viscosity of helium is small compared to air, about 1/8. By reducing the fluid force of the gas, chatter vibration generated by the gas flow accompanying the rotation of the hard disk can be reduced.

4. Crystal size

Next, the average crystal grain size in the thickness direction of the cross section of the aluminum alloy substrate of the present invention will be described.

The average crystal grain size in the thickness direction of the cross section of the aluminum alloy substrate of the present invention is preferably 70 μm or less. When the average crystal grain size is 70 μm or less, the strength of the aluminum alloy substrate is further improved. Here, the cross section indicates an L-ST cross section (a cross section formed in the rolling direction and the plate thickness direction). Since the crystal grains extend in the rolling direction of the plate material in the rolling step, the crystal grain size in the plate thickness direction after the rolling process is smaller than the crystal grain size in the rolling direction or in the direction orthogonal thereto (also orthogonal to the plate thickness direction). Here, in the pressure annealing step performed after the rolling process, the grain size increases when the recrystallized grains are formed.

When the average grain size exceeds 70 μm, the strength may be reduced by coarsening of crystal grains. When the strength of the aluminum alloy substrate is lowered, there is a risk that the aluminum alloy substrate may be deformed by an external force or the like applied thereto at the time of transportation, installation, or the like, and therefore the average grain size of the aluminum alloy substrate is preferably 70 μm or less, more preferably 50 μm or less. The lower limit of the average grain size is not particularly limited, but is naturally determined depending on the composition of the aluminum alloy used and the production method, and is about 1 μm in the present invention.

The average crystal grain size in the thickness direction of the cross section of the aluminum alloy substrate of the present invention is measured as follows. For the section (L-ST section) of the aluminum alloy substrate after the grinding process (step S107), Barker etching was performed using a Barker reagent, and 1 field of view was photographed at a magnification of 200 times with a polarization microscope so that the entire thickness entered the field of view. The measurement of the crystal grain size was carried out by the intersection method, in which the number of crystal grains present between the entire plate thickness along the plate thickness direction and intersecting a straight line drawn is counted, and 5 straight lines of 1000 μm are drawn in the ST direction. The arithmetic mean of these measurements was taken as the average crystal size.

5. Yield strength

Next, the yield strength of the aluminum alloy substrate of the present invention will be described.

In the aluminum alloy substrate of the present invention, the yield strength after heating at 340 ℃ for 3 hours in the atmosphere is preferably 60MPa or more. In this case, the effect of further suppressing the deformation of the substrate during the production of the magnetic disk can be exhibited. If the yield strength of the aluminum alloy substrate is reduced, there is a risk that the aluminum alloy substrate is deformed by an external force or the like applied thereto during transportation, mounting, or the like. Therefore, the yield strength of the aluminum alloy substrate after heating at 340 ℃ for 3 hours in the atmosphere is preferably 60MPa or more, more preferably 75MPa or more. The maximum heat treatment performed in the steps from the production of the magnetic disk substrate (step S107 in fig. 1) to the attachment of the magnet (step S110 in fig. 1) is less than 350 ℃, and therefore the yield strength when heating at 340 ℃ is defined. The upper limit of the yield strength is not particularly limited, and is naturally determined depending on the alloy composition and the production conditions, and in the present invention, is about 250 MPa.

B. The method for producing an aluminum alloy substrate of the present invention

The respective steps and process conditions of the aluminum alloy substrate production step of the present invention will be described in detail below.

The method for manufacturing an aluminum alloy substrate according to the present invention will be described with reference to the flow shown in fig. 1. Here, the preparation of the aluminum alloy component (step S101) to the cold rolling (step S104) are steps of producing an aluminum alloy substrate, and the production of a disk blank (step S105) to the attachment of a magnet (step S110) are steps of producing a magnetic disk from the produced aluminum alloy substrate.

6. Preparation and casting of aluminium alloy compositions

First, a melt of an aluminum alloy material having the above-described composition is heated and melted by a conventional method to prepare (step S101). Then, a thin plate of an aluminum alloy of about 2.0 to 10.0mm is cast from the prepared molten aluminum alloy material by a continuous casting method (CC method) (step S102).

In the CC method, a molten metal is supplied between a pair of rolls (or a belt caster or a block caster) through a casting nozzle, and a cast slab of an aluminum alloy is directly cast by heat extraction from the rolls.

In the casting of a thin aluminum alloy plate by the CC process, the temperature of the cast plate after 1 minute from the casting is set to 230 to 350 ℃, preferably 240 to 340 ℃. Further, the temperature of the cast plate after 10 minutes from the casting is set to 150 ℃ or more and less than 230 ℃, preferably 160 to 220 ℃. In this way, the strength can be improved by setting the temperature of the cast sheet after 1 minute after casting to 230 to 350 ℃ and setting the temperature of the cast sheet after 10 minutes after casting to 150 ℃ or higher and less than 230 ℃ and distributing a large number of fine second phase particles (mainly, Al — Fe-based compound) therein.

In the CC method, the cooling rate at the time of solidification is significantly increased compared to the DC casting method, and the amount of solid solution of an additive element such as Fe increases. Therefore, in the process of cooling the cast sheet from a high temperature of about 600 ℃ to room temperature after the cast sheet is cast by the CC method, the precipitated second phase particles may be coarsened at a relatively low temperature in a short time.

When the temperature of the cast sheet exceeds 350 ℃ after 1 minute from the casting, the second phase particles coarsen and the strength decreases. On the other hand, when the temperature of the cast slab is less than 230 ℃ after 1 minute has passed after casting, the cooling rate is too high, and therefore precipitation of second phase particles having a longest diameter of 0.5 μm or more and less than 2.0 μm is reduced, and the strength is lowered.

When the temperature of the cast sheet is 230 ℃ or higher 10 minutes after casting, the second phase particles coarsen and the strength decreases. In addition, when the temperature of the cast sheet is less than 150 ℃ after 10 minutes has elapsed after casting, the precipitation of second phase particles having a longest diameter of 0.5 μm or more and less than 2.0 μm is reduced, and the strength is lowered.

In the CC method, as a method for cooling the cast slab, for example, fan air cooling, spray cooling, shower cooling, water cooling, or the like can be used.

7. Homogenization treatment

Next, the cast sheet is homogenized as necessary (step S103). The heat treatment conditions for the homogenization treatment are 300 to 450 ℃ for 0.5 to 24 hours, preferably 310 to 440 ℃ for 0.5 to 20 hours. By setting the heat treatment conditions for the homogenization treatment to 300 to 450 ℃ for 0.5 to 24 hours in this way, the effects of reducing the size unevenness of the second phase particles and reducing the variation in the strength and chatter characteristics of the aluminum alloy substrate can be obtained. When the temperature of the homogenization treatment is less than 300 ℃, the above-mentioned effects cannot be obtained, and when the temperature exceeds 450 ℃, the second phase particles are coarsened, and the strength may be lowered. Further, the above-described effect cannot be obtained when the time for the homogenization treatment is less than 0.5 hour, and the strength may be reduced because the second phase particles are coarsened when the time exceeds 24 hours. In addition, compared with the case of cooling from high temperature to 300-450 ℃, a lot of fine second phase particles exist when the temperature is raised from the vicinity of room temperature to 300-450 ℃, and coarsening of the second phase particles can be suppressed if the temperature is heated at 300-450 ℃ for 24 hours or less.

8. Cold rolling

Next, the sheet material is cold rolled into an aluminum alloy sheet of about 1.8mm to 0.45mm (step S104). The steel sheet is processed into a required product thickness by cold rolling. The conditions for cold rolling are not particularly limited, and may be determined according to the required product sheet strength or sheet thickness, and the rolling reduction is preferably 10 to 95%. Before or during the cold rolling, annealing treatment may be performed to ensure cold rolling workability. When the annealing treatment is performed, for example, the annealing treatment is preferably performed under a condition of 200 ℃ or higher and 380 ℃ or lower for 0.1 to 10 hours in the case of batch heating, and is preferably performed under a condition of 250 ℃ or higher and 400 ℃ or lower for 0 to 60 seconds in the case of continuous heating. Here, the treatment time of 0 second in the continuous system means that heating is stopped immediately after the treatment temperature is reached.

When an aluminum alloy plate is processed for a magnetic disk, the aluminum alloy plate is punched out into a circular ring shape to produce a disk blank (step S105). Then, the disc blank is subjected to pressure annealing at 100 ℃ or higher and less than 350 ℃ for 30 minutes or longer in the atmosphere to produce a flattened blank (step S106). Next, the blank is subjected to cutting and grinding to produce an aluminum alloy substrate (step S107). Subsequently, degreasing, etching, and zincing (Zn substitution treatment) are performed on the surface of the aluminum alloy substrate (step S108). Next, the zincated surface is subjected to Ni — P plating treatment as a base treatment (step S109). Finally, the magnet is attached to the Ni — P plating surface by sputtering to form a magnetic disk (step S110).

In addition, after the aluminum alloy substrate is formed in step S107, the aluminum alloy substrate is not exposed to the sun at a temperature of 350 ℃ or higher, and thus the kind of intermetallic compound constituting the second phase particles or the distribution thereof is not changed. Therefore, the kind of intermetallic compound constituting the second phase particles and the distribution thereof can be evaluated by using the aluminum alloy substrate or the magnetic disk after the step of Ni — P plating treatment (step S109) instead of the aluminum alloy substrate produced in step S107.