Disk blank for magnetic disk and magnetic disk

Abstract

The present invention relates to a disk blank for a magnetic disk, wherein F2-F1, which is the difference between flatness F1 before performing a heat treatment at 300°C for one hour and flatness F2 after performing the heat treatment at 300°C for one hour, satisfies -5 μm ≤ (F2-F1) ≤ 5 μm. The present invention also relates to a magnetic disk wherein F4-F3, which is the difference between flatness F3 before performing the heat treatment at 300°C for one hour and flatness F4 after performing the heat treatment at 300°C for one hour, satisfies -5 μm ≤ (F4-F3) ≤ 5 μm.

Description

Disk blanks for magnetic disks and magnetic disks

[0001] The present invention relates to a disk blank for a magnetic disk, and a magnetic disk, which have stable impact resistance even when the thickness is reduced.

[0002] Magnetic disks used in computer storage devices are manufactured using magnetic disk substrates that have good plating properties as well as excellent mechanical properties and processability (hereinafter, magnetic disk substrates may be simply referred to as "substrates"). These magnetic disk substrates are manufactured from aluminum alloy substrates based on aluminum alloys, glass substrates based on glass, etc. An example of an aluminum alloy substrate is known: a JIS 5086 aluminum alloy (Mg: 3.5 to 4.5 mass%, Fe: 0.50 mass% or less, Si: 0.40 mass% or less, Mn: 0.20 to 0.70 mass%, Cr: 0.05 to 0.25 mass%, Cu: 0.10 mass% or less, Ti: 0.15 mass% or less, Zn: 0.25 mass% or less, the balance being Al and unavoidable impurities).

[0003] In general, magnetic disks are manufactured by first preparing an annular aluminum alloy substrate for a magnetic disk, and then attaching a magnetic material to the surface of the aluminum alloy substrate for a magnetic disk. For example, a magnetic disk using an aluminum alloy substrate for a magnetic disk made of the above-mentioned JIS 5086 alloy is manufactured by the following manufacturing process.

[0004] First, an aluminum alloy material having a predetermined chemical composition is cast, and the resulting ingot is hot-rolled and then cold-rolled to produce a rolled material having a predetermined thickness for a magnetic disk. This rolled material is preferably annealed, if necessary, during the cold rolling process. Next, this rolled material is punched into an annular shape to produce an annular aluminum alloy plate. Then, in order to remove distortions and other problems caused by the manufacturing processes up to this point, the annular aluminum alloy plates are stacked and annealed while applying pressure from both upper and lower surfaces to flatten them, thereby producing an annular aluminum alloy disk blank for a magnetic disk.

[0005] The aluminum alloy magnetic disk blank thus produced is subjected to pre-treatments including cutting, grinding, degreasing, etching, and zincating (Zn substitution treatment), followed by electroless plating of Ni-P, a hard non-magnetic metal, as a base treatment, and polishing the electroless plated surface to produce an aluminum alloy substrate for a magnetic disk.

[0006] The magnetic disk is then manufactured by sputtering a magnetic material onto the aluminum alloy substrate for the magnetic disk. In addition to aluminum alloys, glass and other materials are also used for the magnetic disk substrate.

[0007] In recent years, the demand for larger capacity and higher density for magnetic disk devices such as HDDs has been increasing due to the needs of multimedia and the like. To achieve even greater capacity, the number of magnetic disks installed in storage devices is on the rise, and this has led to a demand for thinner magnetic disks. Furthermore, to improve the processing speed of magnetic disk devices, there is a demand for faster magnetic disk rotation speeds. Along with the demand for higher density, the temperature of magnetic disk devices is becoming higher during operation.

[0008] However, the reduction in rigidity associated with the thinning of magnetic disks has led to a problem in that the flatness of the magnetic disks tends to deteriorate. Furthermore, the rise in temperature during operation of a magnetic disk drive tends to cause the flatness of the magnetic disks to deteriorate. This reduces the gap between the magnetic disks and other components, and when an impact is applied, such as when the HDD is dropped, the magnetic disks tend to collide with other components or the head tends to collide with the magnetic disk surface, resulting in a problem of reduced impact resistance.

[0009] In addition to the deterioration of the flatness of the magnetic disk, the surface roughness of the magnetic disk also tends to increase, which makes it easier for the head to collide with the magnetic disk surface, resulting in an increase in read / write errors.

[0010] Therefore, in recent years, studies have been conducted to improve the impact resistance of magnetic disk devices and magnetic disk substrates. Since impact resistance may be related to the rigidity of magnetic disk substrates, there have been studies on improving the rigidity of magnetic disk substrates. For example, Patent Document 1 proposes a method of increasing the rigidity of an aluminum alloy plate by adding a large amount of Si, which contributes to improving the rigidity of the aluminum alloy plate.

[0011] International Publication No. 2016 / 068293

[0012] However, in the prior art, there are few examples of studies that address the issue of impact resistance itself and apply it to magnetic disk substrates. The technique of increasing the Si content of an aluminum alloy, as described in Patent Document 1, is effective in improving the rigidity of the aluminum alloy. On the other hand, the magnetic disk substrate of Patent Document 1 does not achieve sufficient improvement in impact resistance. Thus, with the prior art, impact resistance decreases with prolonged operation of a magnetic disk device, and the target stable impact resistance has not been achieved. Furthermore, the prior art has not achieved sufficient improvement in terms of the deterioration of surface roughness.

[0013] The present invention has been made in view of the above circumstances, and has as its object to provide a disk blank for a magnetic disk that has stable impact resistance even when the thickness is reduced, and a magnetic disk.

[0014] The present inventors have conducted extensive research into the relationship between the impact resistance of magnetic disk substrates and the substrate material, and have found that changes in the flatness of the substrate surface have a significant effect on impact resistance. In particular, the present inventors have focused on the flatness of magnetic disk blanks after pressure annealing and magnetic disks after magnetic material attachment, taking into account the manufacturing process of magnetic disk substrates. They have found that when a specified heat treatment is performed, the difference in flatness between before and after the heat treatment is reduced, resulting in magnetic disk blanks and magnetic disks with stable impact resistance. The present inventors have completed the present invention based on these findings.

[0015] In the disk blank for a magnetic disk according to an embodiment of the present invention, the difference F2-F1 between the flatness F1 before heat treatment at 300°C for 1 hour and the flatness F2 after heat treatment at 300°C for 1 hour satisfies -5 μm≦(F2-F1)≦5 μm.

[0016] In the magnetic disk according to the embodiment of the present invention, the difference F4-F3 between the flatness F3 before heat treatment at 300°C for 1 hour and the flatness F4 after heat treatment at 300°C for 1 hour satisfies -5 μm≦(F4-F3)≦5 μm.

[0017] According to the present invention, it is possible to provide a disk blank for a magnetic disk that has stable impact resistance even when the thickness is reduced, and a magnetic disk.

[0018] 1 is a flowchart showing a method for manufacturing an aluminum alloy substrate for a magnetic disk according to the present invention, a method for manufacturing a magnetic disk using the same, and a method for manufacturing a glass substrate for a magnetic disk according to the present invention.

[0019] As described above, in the present invention, the difference in flatness between the magnetic disk blank and the magnetic disk before and after heat treatment at 300°C for 1 hour is between -5 μm and 5 μm. That is, the absolute value of the difference between the flatness before and after heat treatment at 300°C for 1 hour is 5 μm or less. By providing the magnetic disk blank and the magnetic disk with the above configuration, a magnetic disk substrate and a magnetic disk can be obtained that have stable and good impact resistance even when thin. Such a magnetic disk substrate can be made of an aluminum alloy or glass. Below, the features of the magnetic disk blank and the magnetic disk according to the present invention will be described in detail, including the materials and manufacturing methods constituting them.

[0020] 1. Disk blank for magnetic disk and magnetic disk according to the present invention In the disk blank for magnetic disk according to the present invention, the difference F2-F1 between the flatness F1 before heat treatment at 300°C for 1 hour and the flatness F2 after heat treatment at 300°C for 1 hour satisfies -5 μm≦(F2-F1)≦5 μm. In the disk blank for magnetic disk according to the present invention, the difference H2-H1 between the root-mean-square height H1 before heat treatment at 300°C for 1 hour and the root-mean-square height H2 after heat treatment at 300°C for 1 hour preferably satisfies -5 μm≦(H2-H1)≦5 μm. Furthermore, in the magnetic disk according to the present invention, the difference F4-F3 between the flatness F3 before heat treatment at 300°C for 1 hour and the flatness F4 after heat treatment at 300°C for 1 hour satisfies -5 μm≦(F4-F3)≦5 μm. It is preferable that the difference H4-H3 between the root mean square height H3 before heat treatment at 300° C. for 1 hour and the root mean square height H4 after heat treatment at 300° C. for 1 hour for the magnetic disk satisfies -5 μm≦(H4-H3)≦5 μm. These characteristics will be explained below.

[0021] 1-1. Difference in Flatness Before and After Heat Treatment at 300°C for 1 Hour By satisfying the following for magnetic disk blanks and magnetic disks, respectively: -5 μm≦(F2-F1)≦5 μm, and -5 μm≦(F4-F3)≦5 μm, the impact resistance of the substrate is stabilized. Magnetic disk blanks and magnetic disks with a large difference in flatness before and after conventional heat treatments have a large amount of internal strain. In such magnetic disk blanks and magnetic disks, when the temperature rises during operation of the magnetic disk device, the internal strain is released, deteriorating the flatness of the disk. This reduces the gap with other components, reducing impact resistance.

[0022] In contrast, disks with a small difference in flatness before and after heat treatment at 300°C for one hour, as in the present invention, have little internal strain, and therefore can suppress a decrease in impact resistance. In other words, when the difference in flatness before and after heat treatment is small, the impact of deterioration in flatness due to internal strain is small, and stable impact resistance can be obtained for a long period of time even when the magnetic disk drive is operated for a long period of time.

[0023] For the above reasons, the magnetic disk blank and magnetic disk of the present invention respectively satisfy -5 μm≦(F2−F1)≦5 μm and -5 μm≦(F4−F3)≦5 μm. The magnetic disk blank of the present invention preferably satisfies -3 μm≦(F2−F1)≦3 μm, more preferably -2 μm≦(F2−F1)≦2 μm. The magnetic disk of the present invention preferably satisfies -3 μm≦(F4−F3)≦3 μm, more preferably -2 μm≦(F4−F3)≦2 μm. The heat treatment conditions of 300°C and 1 hour used as an index in the present invention were determined with reference to the heat treatment conditions in accelerated tests for long-term operation of magnetic disk devices such as HDDs.

[0024] In the present invention, "flatness" refers to the difference between the maximum peak height and the maximum valley depth across the entire surface of a magnetic disk substrate. Here, the maximum peak height is the highest value within the measurement range (the entire surface of the magnetic disk blank and the magnetic disk), and the maximum valley depth is the lowest value within the measurement range (the entire surface of the magnetic disk blank and the magnetic disk). Flatness measurement conforms to the method specified in JIS B 0182-1993 and can be performed using a disk flatness measuring instrument such as the Zygo MESA manufactured by Zygo Corporation. JIS B 0182-1993 specifies flatness, which can be evaluated as an index of flatness similar to the above-mentioned flatness and refers to "flatness" in the present invention. Specifically, a jig for changing the angle with respect to the measurement surface of the flatness measuring instrument is fixed to a base installed in the flatness measuring instrument. For example, a jig equipped with three micrometers can be used, and the angle of the jig relative to the measurement surface is adjusted with the micrometers in the θ direction (a direction inclined by an angle θ from a central angle of 0°) and the ψ direction (diameter direction). Then, the substrate is set on the jig, and the angle is adjusted so that the substrate is parallel to the measurement surface of the flatness measuring instrument, thereby measuring flatness.

[0025] 1-2. Difference in root-mean-square height before and after heat treatment at 300°C for 1 hour In the magnetic disk blank according to the present invention, the difference H2-H1 between the root-mean-square height H1 before heat treatment at 300°C for 1 hour and the root-mean-square height H2 after heat treatment at 300°C for 1 hour preferably satisfies -5 μm≦(H2-H1)≦5 μm. In the magnetic disk according to the present invention, the difference H4-H3 between the root-mean-square height H3 before heat treatment at 300°C for 1 hour and the root-mean-square height H4 after heat treatment at 300°C for 1 hour preferably satisfies -5 μm≦(H4-H3)≦5 μm. In the magnetic disk blank and the magnetic disk, by reducing the difference in root-mean-square height of the surface before and after the heat treatment as described above, the effect of stabilizing the surface smoothness of the magnetic disk blank and the magnetic disk is exhibited. Disks with a large difference in root-mean-square height before and after conventional heat treatment have a lot of internal strain. In such substrates, when the temperature rises during operation of a magnetic disk drive, the internal strain is released, causing the root-mean-square height of the disk to deteriorate. This makes it easier for the head to collide with the magnetic disk surface, resulting in an increase in read / write errors.

[0026] In contrast, disks in which the difference in root-mean-square height before and after heat treatment at 300°C for one hour is small, as in the present invention, have little internal strain, and therefore can suppress deterioration in surface smoothness. In other words, when the difference in root-mean-square height before and after heat treatment is small, the impact of internal strain on the deterioration of root-mean-square height is small, and stable surface smoothness can be obtained for a long period of time even when the magnetic disk drive is operated for a long period of time.

[0027] For the above reasons, the magnetic disk blank and magnetic disk of the present invention preferably satisfy the following conditions: -5 μm≦(H2−H1)≦5 μm, and -5 μm≦(H4−H3)≦5 μm, respectively. The magnetic disk blank of the present invention more preferably satisfies the following conditions: -3 μm≦(H2−H1)≦3 μm, and even more preferably -2 μm≦(H2−H1)≦2 μm. The magnetic disk of the present invention more preferably satisfies the following conditions: -3 μm≦(H4−H3)≦3 μm, and even more preferably -2 μm≦(H4−H3)≦2 μm. The heat treatment conditions of 300°C and 1 hour used as an index in the present invention were determined with reference to the heat treatment conditions in accelerated tests for long-term operation of magnetic disk devices such as HDDs.

[0028] In the present invention, the "root mean square height" represents the root mean square of the reference length of the disk blank for a magnetic disk and the magnetic disk. The "reference length" of the disk blank for a magnetic disk and the magnetic disk is the circumferential length of the central portion of the disk (the radial position of the value obtained by calculating half of the difference between half the length of the outer diameter and half the length of the inner diameter, and adding this "half of the difference between half the length of the outer diameter and half the length of the inner diameter" to half the length of the inner diameter). The root mean square height can be measured using a ZyGO non-contact flatness measuring device in accordance with JIS B0601.

[0029] 1-3. Plate Thickness The plate thickness of the disk blank for a magnetic disk according to the present invention is preferably 0.49 mm or less, and more preferably 0.42 mm or less. As described above, even when the plate thickness of the disk blank for a magnetic disk is thin and the rigidity is reduced, it can maintain stable and excellent impact resistance. The plate thickness of the magnetic disk according to the present invention is preferably 0.49 mm or less, and more preferably 0.42 mm or less. As described above, even when the plate thickness of the magnetic disk is thin and the rigidity is reduced, it can maintain stable and excellent impact resistance. The outer diameter of the magnetic disk is preferably 95 mm or more, more preferably 96 mm or more, and even more preferably 97.2 mm or more. In conventional technology, when the outer diameter of a magnetic disk is large as described above, the magnetic disk is more likely to collide with other members due to high-speed rotation during use, and the head is more likely to collide with the magnetic disk surface. In contrast, the magnetic disk of the present invention has stable and excellent impact resistance, and therefore can prevent collisions with other members and heads.

[0030] 2. Magnetic Disk Manufacturing Method According to the Present Invention In order to achieve the two standards of flatness and root mean square height described above for magnetic disks, in the manufacturing process, it is useful to optimize the conditions of the homogenization treatment and hot rolling process (more specifically, the "425-440°C residence time") for aluminum alloy magnetic disk blanks, and it is useful to optimize the conditions of the polishing process (more specifically, the "cooling rate" after the heat treatment following surface polishing) for glass disk substrates. A detailed explanation will be given later.

[0031] 3. Aluminum alloy substrate for magnetic disk according to the present invention The aluminum alloy substrate for magnetic disk according to the present invention can be made of an aluminum alloy. The alloy composition of the aluminum alloy substrate for magnetic disk according to the present invention and the method for producing the same will be described in detail below.

[0032] 3-1. Alloy composition of aluminum alloy The aluminum alloy used in the aluminum alloy substrate for magnetic disk according to the present invention preferably contains, as a first selective element, at least one of Fe: 0.01 to 3.00 mass% and Mn: 0.01 to 3.00 mass% (hereinafter, mass% will be simply referred to as "%"). By containing an aluminum alloy of the above composition, the aluminum alloy substrate for magnetic disk can further improve fluttering resistance, impact resistance, and plating ability.

[0033] The aluminum alloy constituting the aluminum alloy substrate for magnetic disks may further contain, as a second selective element, one or more selected from the group consisting of Mg: 0.100 to 6.000%, Ni: 0.100 to 5.000%, Cr: 0.001 to 5.000%, Zr: 0.0001 to 5.000%, Zn: 0.001 to 5.000%, Cu: 0.001 to 5.000%, and Si: 0.01 to 0.40%.

[0034] Furthermore, the aluminum alloy constituting the aluminum alloy substrate for magnetic disk may further contain, as a third selective element, one or more elements selected from the group consisting of Ti, B, and V in a total content of 0.005 to 5.000%.

[0035] By adding the above-mentioned various optional elements to an aluminum alloy in an appropriate amount, it is possible to obtain an aluminum alloy substrate for a magnetic disk having good fluttering resistance, etc. The effects of these optional elements will be explained below.

[0036] Fe: Fe exists mainly as second-phase particles (Al-Fe intermetallic compounds, etc.), with some of it present as solid solution in the matrix. Through the generation of second-phase particles and solid solution in the matrix, Fe exerts the effect of improving the impact resistance of aluminum alloy substrates for magnetic disks. An increase in the number of second-phase particles improves the strength (Young's modulus, yield strength) of the aluminum alloy through dispersion strengthening. When the Young's modulus and yield strength of the aluminum alloy are improved, it becomes possible to keep deformation due to vibration of the substrate within the elastic range when force is applied to the substrate, such as when the magnetic disk device is dropped, causing vibration of the substrate. This makes it possible to prevent changes in the flatness of the substrate.

[0037] By ensuring that the Fe content in the aluminum alloy is 0.01% or more, the impact resistance, Young's modulus, and strength of the aluminum alloy substrate for magnetic disks can be further improved. Furthermore, by ensuring that the Fe content in the aluminum alloy is 3.00% or less, the generation of numerous coarse Al-Fe intermetallic compound particles is suppressed. If coarse Al-Fe intermetallic compound particles fall off during etching, zincating, cutting, or grinding, large pits will form on the substrate surface. By suppressing the generation of coarse Al-Fe intermetallic compound particles, the generation of pits can be suppressed, further enhancing the effect of improving surface smoothness by plating. Furthermore, suppressing pits can further suppress plating peeling. Furthermore, suppressing pits can further suppress deterioration of workability in the rolling process. For these reasons, the Fe content in the aluminum alloy is preferably in the range of 0.01 to 3.00%. The Fe content is more preferably in the range of 0.03 to 2.40%, and even more preferably in the range of 0.04 to 1.80%.

[0038] Mn: Mn exists mainly as second-phase particles (Al-Mn intermetallic compounds, etc.) and has the effect of improving the impact resistance of aluminum alloy substrates for magnetic disks. An increase in the number of second-phase particles improves the strength (Young's modulus and yield strength) of the alloy through dispersion strengthening. This makes it possible to prevent changes in the flatness of the aluminum alloy substrates for magnetic disks when they are vibrated.

[0039] By having the Mn content in the aluminum alloy be 0.01% or more, the impact resistance, Young's modulus, and strength of the aluminum alloy substrate for magnetic disks can be further improved. Furthermore, by having the Mn content in the aluminum alloy be 3.00% or less, the generation of numerous coarse Al-Mn intermetallic compound particles is suppressed. This suppresses the occurrence of large dents during etching, zincating, cutting, and grinding. This further suppresses the decrease in smoothness of the plated surface and the occurrence of plating peeling. Furthermore, it further suppresses the decrease in workability during the rolling process. For these reasons, the Mn content in the aluminum alloy is preferably in the range of 0.01 to 3.00%. The Mn content is more preferably in the range of 0.10 to 1.50%, and even more preferably in the range of 0.40 to 1.20%.

[0040] Mg: Mg exists mainly as a solid solution in the matrix, with a portion existing as second-phase particles (Mg-Si intermetallic compounds, etc.), which has the effect of improving the strength and Young's modulus of the aluminum alloy substrate.

[0041] By setting the Mg content in the aluminum alloy to 0.100% or more, the effect of improving the strength and Young's modulus of the aluminum alloy substrate for magnetic disks can be further enhanced. Furthermore, by setting the Mg content in the aluminum alloy to 6.000% or less, the decrease in impact resistance can be further suppressed. Therefore, the Mg content in the aluminum alloy is preferably set in the range of 0.100 to 6.000%. The Mg content is more preferably set in the range of 1.000 to 5.000%, and even more preferably in the range of 2.500 to 4.500%.

[0042] Ni: Ni exists mainly as second phase particles (Al-Ni based intermetallic compounds, etc.) and exerts the effect of improving the Young's modulus and strength of the aluminum alloy substrate for magnetic disks.

[0043] By setting the Ni content in the aluminum alloy to 0.100% or more, the effect of improving the Young's modulus and strength of the aluminum alloy substrate for magnetic disks can be further enhanced. Furthermore, by setting the Ni content in the aluminum alloy to 5.000% or less, the generation of a large number of coarse Al-Ni intermetallic compound particles is suppressed. This suppresses the occurrence of large depressions during etching, zincating, cutting, and grinding. This further suppresses the decrease in smoothness of the plated surface and the occurrence of plating peeling. Furthermore, it further suppresses the decrease in workability during the rolling process. For these reasons, the Ni content in the aluminum alloy is preferably set in the range of 0.100 to 5.000%. The Ni content is more preferably set in the range of 0.100 to 2.000%. Furthermore, the lower limit of the Ni content in the aluminum alloy may be 0%.

[0044] Cr: Cr exists mainly as second-phase particles (such as Al-Cr intermetallic compounds) and exerts the effect of improving the Young's modulus and strength of an aluminum alloy substrate for a magnetic disk. By setting the Cr content in the aluminum alloy to 0.001% or more, the effect of improving the Young's modulus and strength of an aluminum alloy substrate for a magnetic disk can be further enhanced. Furthermore, by setting the Cr content in the aluminum alloy to 5.000% or less, the generation of numerous coarse Al-Cr intermetallic compound particles is suppressed. This suppresses the occurrence of large depressions during etching, zincating, cutting, and grinding. This further suppresses the decrease in smoothness of the plated surface and the occurrence of plating peeling. Furthermore, it further suppresses the decrease in workability during the rolling process. For these reasons, the Cr content in the aluminum alloy is preferably set to a range of 0.001 to 5.000%. The Cr content is more preferably in the range of 0.010 to 1.000%, and even more preferably in the range of 0.030 to 1.000%.

[0045] Zr: Zr exists mainly as second phase particles (Al-Zr based intermetallic compounds, etc.) and exerts the effect of improving the Young's modulus and strength of the aluminum alloy substrate for magnetic disks.

[0046] By setting the Zr content in the aluminum alloy to 0.0001% or more, the effect of improving the Young's modulus and strength of the aluminum alloy substrate for magnetic disks can be further enhanced. Furthermore, by setting the Zr content in the aluminum alloy to 5.000% or less, the generation of numerous coarse Al-Zr intermetallic compound particles is suppressed. This suppresses the occurrence of large depressions during etching, zincating, cutting, and grinding. This further suppresses the decrease in smoothness of the plated surface and the occurrence of plating peeling. Furthermore, it further suppresses the decrease in workability during the rolling process. For these reasons, the Zr content in the aluminum alloy is preferably set in the range of 0.0001 to 5.000%. The Zr content is more preferably set in the range of 0.0001 to 1.000%. Furthermore, the lower limit of the Zr content in the aluminum alloy may be 0%.

[0047] Zn: Zn reduces the amount of Al dissolved during zincate treatment, and also adheres the zincate film uniformly, thinly, and densely, improving the smoothness and adhesion in the subsequent plating process. Zn also forms second-phase particles with other additive elements, improving the Young's modulus and strength of the aluminum alloy substrate.

[0048] By having the Zn content in the aluminum alloy be 0.001% or more, the amount of Al dissolved during zincate treatment can be reduced, and the zincate film can be uniformly, thinly, and densely adhered, further enhancing the effect of improving the smoothness of the plating. Furthermore, by having the Zn content in the aluminum alloy be 5.000% or less, the zincate film can be made uniform, further preventing a decrease in the smoothness of the plating surface and further preventing plating peeling. Furthermore, a decrease in workability in the rolling process can be further suppressed. For these reasons, the Zn content in the aluminum alloy is preferably in the range of 0.001 to 5.000%. The Zn content is more preferably in the range of 0.060 to 0.700%, and even more preferably in the range of 0.010 to 0.500%.

[0049] Cu: Cu exists mainly as second-phase particles (Al-Cu intermetallic compounds, etc.) and has the effect of improving the strength and Young's modulus of aluminum alloy substrates for magnetic disks. It also reduces the amount of Al dissolved during zincate treatment. Furthermore, it adheres the zincate film uniformly, thinly, and densely, improving the smoothness in the subsequent plating process.

[0050] By having a Cu content of 0.001% or more in the aluminum alloy, the effects of improving the Young's modulus and strength of the aluminum alloy substrate for magnetic disks and the effects of improving smoothness can be further enhanced. Furthermore, by having a Cu content of 5.000% or less in the aluminum alloy, the generation of numerous coarse Al-Cu intermetallic compound particles can be suppressed. This suppresses the occurrence of large depressions during etching, zincating, cutting, and grinding. This further suppresses the decrease in smoothness of the plated surface and the occurrence of plating peeling. Furthermore, it further suppresses the decrease in workability during the rolling process. For these reasons, the Cu content in the aluminum alloy is preferably in the range of 0.001 to 5.000%. The Cu content is more preferably in the range of 0.005 to 1.000%, and even more preferably in the range of 0.015 to 0.500%.

[0051] Si: Si exists mainly as second-phase particles (Si particles, Al-Fe-Si intermetallic compounds, etc.), and an increase in the number of second-phase particles, which have a higher Young's modulus than aluminum, has the effect of improving the impact resistance, Young's modulus, and strength of the aluminum alloy substrate for magnetic disks through dispersion strengthening.

[0052] By having the Si content in the aluminum alloy be 0.01% or more, the effect of improving the impact resistance, Young's modulus, and strength of the aluminum alloy substrate for magnetic disks can be further enhanced. Furthermore, by having the Si content in the aluminum alloy be 0.400% or less, the generation of a large number of coarse Si particles is suppressed. This suppresses the occurrence of large depressions during etching, zincating, cutting, and grinding. This further suppresses the decrease in smoothness of the plated surface and the occurrence of plating peeling. Furthermore, it further suppresses the decrease in workability during the rolling process. For these reasons, the Si content in the aluminum alloy is preferably in the range of 0.01 to 0.400%, more preferably in the range of 0.0150 to 0.350%, and even more preferably in the range of 0.020 to 0.300%.

[0053] Ti, B, V: Ti, B, and V form second phase particles (TiB ２ Borides such as Al ３ The formation of Ti and Ti-V-B particles, etc., which act as crystal grain nuclei, allows for the refinement of crystal grains. As a result, plating properties are improved. Furthermore, the refinement of crystal grains reduces the non-uniformity of the size of second-phase particles, which has the effect of reducing variations in the impact resistance, Young's modulus, and strength of the aluminum alloy substrate for magnetic disks.

[0054] If the total content of Ti, B, and V is less than 0.001%, the above-mentioned effect cannot be obtained. On the other hand, if the total content of Ti, B, and V exceeds 5.000%, the effect saturates and no further significant improvement can be obtained. Therefore, when Ti, B, and V are added, the total content of Ti, B, and V is preferably in the range of 0.001 to 5.000%. The total content of Ti, B, and V is more preferably in the range of 0.005 to 0.500%. Note that the "total amount" refers to the amount of one of Ti, B, and V when only one of them is contained; when two of them are contained, it refers to the total amount of these two; and when all three are contained, it refers to the total amount of these three.

[0055] Other elements: The balance of the aluminum alloy used in the present invention consists of Al and unavoidable impurities. Examples of the unavoidable impurities include Ga, Sn, Sr, P, and Na. The properties of the aluminum alloy substrate obtained in the present invention are not impaired as long as the unavoidable impurity elements are each less than 0.10% and the total amount is less than 0.20%.

[0056] In the above description, the intermetallic compound means a precipitate or a crystallized substance, and specifically, an Al-Fe intermetallic compound (Al ３ Fe, Al ６ Fe, Al ６ (Fe, Mn), Al-Fe-Si, Al-Fe-Mn-Si, Al-Fe-Ni, Al-Cu-Fe, etc.), Mg-Si intermetallic compounds (Mg ２ Other intermetallic compounds include Al-Mn based intermetallic compounds (Al ６ Mn, Al-Mn-Si), Al-Ni intermetallic compounds (Al ３ Ni, etc.), Al-Cu intermetallic compounds (Al ２ Cu, etc.), Al-Cr intermetallic compounds (Al ７ Cr, etc.), Al-Zr intermetallic compounds (Al ３ The second phase particles include Si particles and the like in addition to the intermetallic compounds.

[0057] 3-2. Manufacturing Method of Aluminum Substrate for Magnetic Disk According to the Present Invention The following describes in detail each step and process conditions of the manufacturing process of the aluminum alloy substrate for magnetic disk according to this embodiment. FIG. 1 is a flow diagram illustrating the manufacturing method of the aluminum alloy substrate for magnetic disk according to this embodiment and the magnetic disk using the same. In FIG. 1, the aluminum alloy composition adjustment step (step S101), the aluminum alloy casting step (step S102), the homogenization treatment step (step S103), and the hot rolling step (step S104) are performed, and the cold rolling step (step S105) is a process in which an aluminum alloy material is produced by melting and casting, and then this is made into an aluminum alloy plate. Next, a disk-shaped aluminum alloy plate is produced by punching into a disk shape (step S105). Next, a pressure flattening treatment step (step S106) is performed to produce an aluminum alloy disk blank for a magnetic disk. The manufactured magnetic disk blank is then subjected to pretreatments such as a cutting and grinding process (step S107), followed by a heat treatment process (step S108), a zincate treatment process (step S109), and a Ni-P plating process (step S110), followed by surface polishing and heat treatment processes (steps S111 and S112), thereby producing an aluminum alloy substrate for a magnetic disk. The manufactured aluminum alloy substrate for a magnetic disk is then turned into a magnetic disk by a magnetic material attachment process (step S113). The contents of each process will be described in detail below, following the flow of FIG. 1.

[0058] First, a molten aluminum alloy material having the above-mentioned composition is prepared by heating and melting it according to a conventional method (step S101). Next, the prepared molten aluminum alloy material is cast by a semi-continuous casting (DC casting) method, a continuous casting (CC casting) method, or the like to cast an aluminum alloy material (step S102). The production conditions for the aluminum alloy material in the DC casting method and the CC casting method are as follows.

[0059] In DC casting, molten metal poured through a spout loses heat through the bottom block, the water-cooled mold walls, and cooling water that is directly discharged onto the outer periphery of the ingot, solidifies, and is pulled downward as an aluminum alloy ingot.

[0060] On the other hand, in CC casting, molten metal is supplied through a casting nozzle between a pair of rolls (or a belt caster or a block caster), and a thin aluminum alloy plate is directly cast by extracting heat from the rolls.

[0061] The major difference between DC casting and CC casting is the cooling rate during casting. CC casting, which has a high cooling rate, is characterized by smaller second-phase particle size compared to DC casting. In both casting methods, the cooling rate during casting is preferably in the range of 0.1 to 1000°C / s. By setting the cooling rate during casting to 0.1 to 1000°C / s, a large number of second-phase particles are generated, improving the Young's modulus. In addition, the amount of Fe solid solution increases, resulting in an effect of improving strength. If the cooling rate during casting is less than 0.1°C / s, the amount of Fe solid solution decreases, which may result in a decrease in strength. On the other hand, if the cooling rate during casting exceeds 1000°C / s, there is a risk that the number of second-phase particles will decrease, and sufficient impact resistance and Young's modulus may not be obtained.

[0062] The DC-cast aluminum alloy ingot is subjected to a homogenization treatment (step S103). The homogenization treatment involves heat treatment at 540 to 620°C for 0.5 to 30 hours. The 425 to 440°C residence time in the homogenization treatment and hot rolling processes is 0.9 hours or less. If the 425 to 440°C residence time exceeds 0.9 hours, the number of second-phase particles may decrease, which may lead to increased deformation during the pressure annealing process and the presence of significant internal strain. In such magnetic disk blanks and magnetic disks, internal strain may be released when the temperature rises during operation of the magnetic disk device, resulting in deterioration of the flatness and root-mean-square height of the magnetic disk. Note that the "425 to 440°C residence time" refers to the total time the aluminum alloy ingot is held at 425 to 440°C during the homogenization treatment and hot rolling processes. The "425-440°C residence time" in the homogenization treatment step includes the time it takes for the aluminum alloy ingot to reach a predetermined temperature at 425-440°C and the time it takes for the aluminum alloy ingot to cool to 425-440°C before hot rolling. The 425-440°C residence time in the homogenization treatment step and hot rolling step is preferably less than 0.5 hours, more preferably less than 0.4 hours, and even more preferably less than 0.3 hours. If the heating temperature during homogenization treatment is less than 540°C or the heating time is less than 0.5 hours, there is a risk of insufficient homogenization treatment, which may lead to deformation during the pressure annealing step and the presence of significant internal strain. In such magnetic disk blanks and magnetic disks, internal strain may be released when the temperature rises during operation of the magnetic disk device, resulting in a deterioration in the flatness and root-mean-square height of the magnetic disk blanks and magnetic disks. If the heating temperature during the homogenization treatment exceeds 620° C., there is a risk of melting occurring in the aluminum alloy ingot. If the heating time during the homogenization treatment exceeds 30 hours, the effect saturates and no further significant improvement can be obtained.

[0063] Next, the homogenized aluminum alloy ingot (DC cast) is hot rolled to form a plate material (step S104). The conditions for hot rolling are not particularly limited, but the hot rolling start temperature is preferably 450 to 600°C, and the hot rolling end temperature is preferably 230 to 400°C. Note that the "425 to 440°C residence time" in the hot rolling step includes the time during which the aluminum alloy ingot reaches 425 to 440°C during heating to raise the temperature to the hot rolling start temperature.

[0064] Next, the hot-rolled sheet is cold-rolled, and the thickness can be appropriately set within a range of 1.9 mm to 0.20 mm (step S105). The required product thickness is achieved by cold rolling. The cold rolling conditions are not particularly limited and can be determined according to the required product sheet strength and thickness, with a rolling reduction ratio of 10 to 95% being preferred. Annealing may be performed before or during cold rolling to ensure cold rolling workability. When annealing is performed, for example, in the case of batch heating, it is preferable to perform the annealing at 300 to 400°C for 0.1 to 10 hours.

[0065] The aluminum alloy plate obtained by cold rolling is then punched into an annular shape (step S105) to produce an annular aluminum alloy plate. The annular aluminum alloy plate is then subjected to a pressure flattening process (step S106) to produce a disk blank for a magnetic disk. In the pressure flattening process, pressure annealing is performed in air at 250 to 420°C for 0.5 to 10 hours to produce a flattened disk blank for a magnetic disk. When pressure annealing is performed, the internal strain introduced by rolling approaches zero, but does not become completely zero. This is because slight high-temperature deformation occurs after the internal strain is released by pressure annealing, and new internal strain is introduced at that time. This phenomenon becomes more pronounced as the plate thickness becomes thinner and the rigidity becomes lower, but it was not a problem with conventional disk blanks for magnetic disks. Furthermore, if the residence time at 425 to 440°C in the homogenization and hot rolling processes exceeds 0.9 hours and the number of second-phase particles is small, if the temperature in the homogenization process is less than 540°C or more than 620°C, or if the time in the homogenization process is less than 0.5 hours, the magnetic disk blank is prone to deformation at high temperatures and internal strain is easily introduced. Because the internal strain is not large, there is no driving force sufficient to recover it, and even if a subsequent heat treatment is performed, it will not be completely reduced to zero. In a magnetic disk using such a magnetic disk blank, if the temperature rises during operation of the magnetic disk device, the internal strain is released, which may deteriorate the flatness and root-mean-square height of the magnetic disk.

[0066] Before zincate treatment, the magnetic disk blank undergoes a cutting and grinding process (step S107) and a heat treatment process (step S108). In the heat treatment process, the magnetic disk blank is held, for example, at a temperature in the range of 130 to 280°C for 0.5 to 10.0 hours. This heat treatment makes it possible to suppress the reduction of dislocations and improve impact resistance. If the heat treatment temperature exceeds 280°C or the heat treatment time exceeds 10.0 hours, dislocations may be reduced, resulting in a decrease in impact resistance. On the other hand, if the heat treatment temperature is less than 130°C or the heat treatment time is less than 0.5 hours, the strain introduced by processing may not be sufficiently removed, resulting in a deterioration in the flatness of the magnetic disk blank and magnetic disk due to changes over time. For these reasons, it is preferable to hold the magnetic disk blank after cutting and grinding at a temperature in the range of 130 to 280°C for 0.5 to 10.0 hours.

[0067] Next, the surface of the disk blank for the magnetic disk is degreased, etched, and subjected to a zincate treatment (Zn substitution treatment) (step S109). In the zincate treatment, a zincate film is formed on the surface of the disk blank for the magnetic disk. A commercially available zincate treatment solution can be used for the zincate treatment, and it is preferable to perform the treatment under conditions of a temperature of 10 to 35°C, a treatment time of 0.1 to 5 minutes, and a concentration of 100 to 500 mL / L. The zincate treatment is performed at least once, and may be performed two or more times. By performing the zincate treatment multiple times, fine Zn can be precipitated to form a uniform zincate film. When performing the zincate treatment two or more times, a Zn stripping treatment may be performed between the treatments. The Zn stripping treatment is performed using HNO ３ It is preferable to use a solution and perform the treatment under conditions of a temperature of 15 to 40°C, a treatment time of 10 to 120 seconds, and a concentration of 10 to 60%. It is also preferable that the second and subsequent zincate treatments be performed under the same conditions as the first zincate treatment.

[0068] Furthermore, the zincate-treated surface of the magnetic disk blank is subjected to an electroless Ni—P plating process (step S110) as a base treatment for magnetic material adhesion. The electroless Ni—P plating process preferably uses a commercially available plating solution or the like, and is performed under conditions of a temperature of 80 to 95° C., a treatment time of 30 to 180 minutes, and a Ni concentration of 3 to 10 g / L.

[0069] The plated surface after electroless Ni—P plating is polished for smoothness as needed (step S111). This polishing step preferably involves multiple stages of polishing, with the diameter of the polishing abrasive grains adjusted accordingly. For example, the main surface is polished using a polishing solution containing large-diameter abrasive grains with a particle size of 0.1 to 1.0 μm and a hard or soft polishing pad. Next, the surface is polished using a polishing solution containing small-diameter abrasive grains with a particle size of approximately 0.01 to 0.1 μm and a soft polishing pad, followed by a heat treatment step as needed (step S112) to obtain an aluminum alloy substrate for a magnetic disk. The magnetic disk blank is preferably heat-treated at a temperature of 100 to 250° C. for a treatment time of 30 minutes or less.

[0070] Finally, a magnetic material is attached to the electroless Ni-P plated surface of the aluminum alloy substrate for magnetic disk by sputtering (step S113), thereby producing an aluminum alloy magnetic disk.

[0071] 4. Magnetic Disk Glass Substrate According to the Present Invention The magnetic disk substrate according to the present invention may be made of a glass material. Hereinafter, the glass material to be used and the method for manufacturing the substrate will be described in detail for the magnetic disk glass substrate according to the present invention.

[0072] 4-1. Glass Material Glass ceramics such as amorphous glass and crystallized glass can be used as the glass material. From the viewpoint of formability and processability, amorphous glass is preferably used. For example, aluminosilicate glass, soda-lime glass, soda-aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, etc. are preferably used.

[0073] Specific glass components include SiO ２ : 55 to 75% as the main component, Al ２ O ３ Preferably, the glass contains 0.3 to 25% of Li and 0 to 20% of CaO. ２ O: 0.01-6%, Na ２ O: 0.7-12%, K ２ O: 0-8%, MgO: 0-7%, ZrO ２ : 0 to 10% and TiO ２ : Glass containing 0 to 1% of one or more of these added is preferred.

[0074] SiO ２ The content of 55 to 75% has the effect of increasing the f (frequency) of the glass substrate. ２ The content is preferably in the range of 55 to 75%, more preferably 60 to 75%. ２ O ３ The content of Al in the glass is 0.3 to 25%, which has the effect of increasing the ρ of the glass substrate. ２ O ３ The content of CaO is preferably in the range of 0.3 to 25%, and more preferably 1.0 to 25%. When the CaO content is 0 to 20%, the effect of increasing f and ρ (density) of the glass substrate is exhibited. The content of CaO in the glass is preferably in the range of 0 to 20%, and more preferably 1 to 20%.

[0075] The glass contains B, which reduces viscosity and improves solubility and clarity. ２ O ３ (Contained as an essential component in aluminoborosilicate glass and borosilicate glass), SrO and BaO reduce high-temperature viscosity, improve melting, clarity and formability, and also have the effect of improving Young's modulus, ZnO improves ion exchange performance and reduces high-temperature viscosity without reducing low-temperature viscosity, and SnO improves clarity and ion exchange performance. ２ , Fe as a colorant ２ O ３ In addition to the above, As is used as a fining agent. ２ O ３ and Sb ２ O ３Furthermore, trace elements such as oxides of La, P, Ce, Sb, Hf, Rb, and Y may be contained. These elements may be contained in an amount of 15% or less.

[0076] 4-2. Manufacturing Method of Magnetic Disk Glass Substrate According to the Present Invention Next, an example of a manufacturing method of a magnetic disk glass substrate according to this embodiment will be described. Figure 2 is a flow diagram showing an example of a manufacturing method of a magnetic disk glass substrate according to this embodiment and a magnetic disk using the same. Below, the contents of each step will be described according to the flow of Figure 2.

[0077] First, a glass plate is manufactured as a raw material (step S201). Next, the glass plate manufactured in step S201 is cored to form a doughnut-shaped glass substrate (step S202).

[0078] Next, chamfered surfaces are formed on the inner and outer peripheral end surfaces of the formed doughnut-shaped glass substrate (step S203). After the inner and outer peripheral end surfaces of the doughnut-shaped glass substrate with the chamfered surfaces are polished, surface polishing is performed. This polishing process comprises rough polishing (step S204) and precision polishing (step S205). In the rough polishing (step S204) process, the main surfaces are polished using a polishing solution containing large-diameter abrasive grains, e.g., with a particle size of 0.1 to 1.0 μm, and a hard or soft polishing pad. In the subsequent precision polishing (step S205) process, the main surfaces of the roughly polished doughnut-shaped glass substrate are further polished with precision using a polishing solution containing small-diameter abrasive grains, e.g., with a particle size of approximately 0.01 to 0.1 μm, and a soft polishing pad.

[0079] The magnetic disk glass substrate according to the present invention is subjected to a heat treatment at 270 to 350° C. after polishing by the above precision polishing, and the cooling rate to 200° C. after heating is less than 5° C. / h (step S206).

[0080] In this way, by performing a heat treatment at 270 to 350°C after surface polishing of the doughnut-shaped glass substrate and cooling it to 200°C at a cooling rate of less than 5°C / h after heating, internal strain in the doughnut-shaped glass substrate is released, making it possible to suppress changes in flatness and root-mean-square height during operation of the magnetic disk drive, and stabilizing impact resistance. Although the heat treatment can release strain, if the subsequent cooling rate is too fast, thermal stress will be generated and new strain will be introduced. Therefore, the cooling rate is preferably less than 5°C / h, and 3°C / h or less.

[0081] The reason why the heat treatment temperature is set to 270 to 350° C. is that if the heating temperature exceeds 350° C., the flatness deteriorates, resulting in a decrease in impact resistance. On the other hand, if the heat treatment temperature is less than 270° C., the strain introduced by polishing is not sufficiently removed, resulting in a deterioration in the flatness of the glass magnetic disk due to changes over time during long-term operation of the magnetic disk device, and a decrease in impact resistance.

[0082] The heat treatment time is not limited, but is preferably set to 0.6 to 3 hours, since too long a treatment time will increase costs.

[0083] The magnetic disk glass substrate according to the present invention is manufactured by the heat treatment after the surface polishing described above. Finally, a magnetic material is attached to the polished surface of the magnetic disk glass substrate by sputtering (step S207). This completes the manufacturing of a glass magnetic disk.

[0084] Based on the above embodiments, the present invention relates to the following [1] to

[10] . [1] A disk blank for a magnetic disk, in which the difference F2-F1 between the flatness F1 before heat treatment at 300°C for 1 hour and the flatness F2 after heat treatment at 300°C for 1 hour satisfies -5 μm≦(F2-F1)≦5 μm. [2] A disk blank for a magnetic disk according to [1] above, in which the difference H2-H1 between the root-mean-square height H1 before heat treatment at 300°C for 1 hour and the root-mean-square height H2 after heat treatment at 300°C for 1 hour satisfies -5 μm≦(H2-H1)≦5 μm. [3] A disk blank for a magnetic disk according to [1] or [2] above, in which the thickness is 0.49 mm or less. [4] A disk blank for a magnetic disk according to [1] or [2] above, in which the thickness is 0.42 mm or less. [5] A magnetic disk, wherein F4-F3, which is the difference between the flatness F3 before heat treatment at 300°C for 1 hour and the flatness F4 after heat treatment at 300°C for 1 hour, satisfies -5 μm≦(F4-F3)≦5 μm. [6] The magnetic disk according to [5] above, wherein H4-H3, which is the difference between the root-mean-square height H3 before heat treatment at 300°C for 1 hour and the root-mean-square height H4 after heat treatment at 300°C for 1 hour, satisfies -5 μm≦(H4-H3)≦5 μm. [7] The magnetic disk according to [5] or [6] above, wherein the thickness is 0.49 mm or less. [8] The magnetic disk according to [5] or [6] above, wherein the thickness is 0.42 mm or less. [9] The magnetic disk according to any one of [5] to [8] above, wherein the outer diameter is 95 mm or more.

[10] The disk blank for a magnetic disk according to any one of the above [1] to [4], wherein the absolute value E of the difference C between the sum A of the residual stresses at each measurement point in the region from the center of the thickness to the surface in the thickness direction of the disk blank for a magnetic disk and the sum B of the residual stresses at each measurement point in the region from the center of the thickness to the back surface in the thickness direction of the disk blank for a magnetic disk is divided by the average value D of A and B (C / D) is 4.0 or less.

[0085] The present invention will be described in more detail below based on examples, but the present invention is not limited to these. In these examples, aluminum alloy substrates for magnetic disks and glass substrates for magnetic disks were manufactured as magnetic disk substrates, and the characteristics of the disk blanks for magnetic disks and the magnetic disks were evaluated.

[0086] A. Manufacturing of Aluminum Alloy Magnetic Disks (Examples 1 to 4, Comparative Examples 1 and 2) First, each alloy material having the composition shown in Table 1 was melted in a conventional manner to produce a molten aluminum alloy (step S101). In Table 1, "-" indicates a value below the measurement limit.

[0087]

[0088] Next, the molten aluminum alloy was cast by DC casting to produce an ingot (step S102). Before the homogenization treatment, both surfaces of the ingot were chamfered.

[0089] Next, the homogenization treatment was carried out under the conditions shown in Table 2 (step S103). Next, hot rolling was carried out to obtain a hot-rolled sheet (step S104).

[0090] After the hot rolling, the aluminum alloy plate was cold-rolled to obtain an aluminum alloy plate (step S105). The aluminum alloy plate was punched into an annular shape having an outer diameter of 98 mm and an inner diameter of 24 mm (step S105), thereby producing an annular aluminum alloy plate.

[0091] The annular aluminum alloy plate thus produced was subjected to pressure annealing (pressure flattening treatment) for 3 hours at the temperature shown in Table 2 to produce a disk blank for a magnetic disk (step S106). In Example 4 and Comparative Example 2, the disk blank for a magnetic disk was further subjected to end face processing (cutting) to obtain an outer diameter of 97 mm and an inner diameter of 25 mm, and then grinding (surface grinding to 25 μm) (step S107). Thereafter, heat treatment, zincate treatment, Ni—P electroless plating, heat treatment, and sputtering (adhesion of magnetic material) were performed by conventional methods (steps S108 to S110, S112 to S113) to produce an aluminum alloy magnetic disk.

[0092] B. Manufacturing of Magnetic Disks Made of Glass Substrate (Example 5, Comparative Example 3) Magnetic disks made of aluminosilicate glass manufactured under the conditions shown in Table 2 were used. The magnetic disks had a plate thickness of 0.49 mm, an outer diameter of 97 mm, and a circular hole with an inner diameter of 25 mm. In Example 5, after the polishing step, a heat treatment and a cooling treatment (cooling rate 4.5°C / h) were performed under the conditions shown in Table 2. In Comparative Example 3, the magnetic disk after polishing was not subjected to a heat treatment.

[0093] C. Evaluation of characteristics of manufactured magnetic disk blanks or magnetic disks The magnetic disk blanks or magnetic disks manufactured under the conditions shown in Table 2 were evaluated for flatness and root mean square height (before heat treatment and after heat treatment at 300°C for 1 hour) by the following method.

[0094] [Flatness] First, the flatness F1 and root-mean-square height H1 were measured for the magnetic disk blanks (Examples 1 to 3, Comparative Example 1). The flatness F3 and root-mean-square height H3 were measured for the magnetic disks (Examples 4 to 5, Comparative Examples 2 to 3). The magnetic disk blanks (Examples 1 to 3, Comparative Example 1) were then subjected to a heat treatment at 300°C for 1 hour, and the flatness F2 and root-mean-square height H2 after the heat treatment were measured. The magnetic disks (Examples 4 to 5, Comparative Examples 2 to 3) were also subjected to a heat treatment at 300°C for 1 hour, and the flatness F4 and root-mean-square height H4 after the heat treatment were measured. Next, the differences between the flatness and root-mean-square height before and after the heat treatment, i.e., (F2 - F1), (F4 - F3), (H2 - H1), and (H4 - H3), were calculated. Flatness and root mean square height measurements were performed using a ZyGO non-contact flatness measuring instrument.

[0095] Table 2 shows the evaluation results of the various properties of the magnetic disk blanks and magnetic disks manufactured in this example. In Table 2, "plate thickness" in the "cold rolling or polishing" step refers to the plate thickness of the aluminum alloy plate after cold rolling in Examples 1 to 4 and Comparative Examples 1 and 2, refers to the plate thickness of the magnetic disk after polishing, heating, and cooling in Example 5, and refers to the plate thickness of the magnetic disk after polishing in Comparative Example 3. "Cooling rate after heating" in Table 2 refers to the cooling rate when the magnetic disk made of aluminosilicate glass is polished, heated to 300°C, and then cooled to 200°C in Example 5. "425-440°C residence time" in the homogenization treatment and hot rolling steps in Table 2 refers to the total time of the following (a) to (c). (a) the time it takes for the temperature of the aluminum alloy ingot to reach 425 to 440°C during heating to a predetermined temperature in the homogenization treatment step; (b) the time it takes for the temperature of the aluminum alloy ingot to reach 425 to 440°C during cooling after the homogenization treatment step and before hot rolling; (c) the time it takes for the temperature of the aluminum alloy ingot to reach 425 to 440°C during heating to a hot rolling starting temperature in the hot rolling step.

[0096] As shown in Table 2, in Examples 1 to 4, the residence time at 425 to 440°C in the homogenization treatment and hot rolling process was 0.9 hours or less, the homogenization treatment process was carried out under conditions of 540 to 620°C for 0.5 to 30 hours, and in Example 5, the cooling rate to 200°C after heating was less than 5°C / h. Therefore, in all of Examples 1 to 5, the difference in flatness and the difference from the root mean square height, (F2-F1) in Examples 1 to 3, (F4-F3) in Examples 4 to 5, (H2-H1) in Examples 1 to 3, and (H4-H3) in Examples 4 to 5, were small, and it was determined that stable impact resistance and stable surface smoothness could be obtained.

[0097] In contrast, as shown in Table 2, in Comparative Example 1, the homogenization treatment step was carried out at a temperature of less than 540°C, in Comparative Example 2, the residence time at 425 to 440°C in the homogenization treatment and hot rolling step was more than 0.9 hours, and in Comparative Example 3, the magnetic disk after polishing was not subjected to a heating treatment or a cooling treatment. For this reason, in Comparative Examples 1 to 3, the difference in flatness and the difference from the root mean square height, namely (F2-F1) in Comparative Example 1, (F4-F3) in Comparative Examples 2 to 3, (H2-H1) in Comparative Example 1, and (H4-H3) in Comparative Examples 2 to 3, were poor, and it was therefore determined that stable impact resistance and stable surface smoothness could not be obtained.

[0098] To investigate the effect of internal strain on the flatness, a multi-axis diffractometer manufactured by HUBER Corporation installed on the bending magnet beamline BL19B2 of SPring-8 (Super Photon Ring 8 GeV, High-Brilliance Synchrotron Radiation Facility) was used to investigate the residual stress caused by internal strain in aluminum alloy magnetic disk blanks by X-ray diffraction. As the magnetic disk blanks, magnetic disk blanks M1 and M2 were used, in which the difference F2-F1 between the flatness F1 before heat treatment at 300°C for 1 hour and the flatness F2 after heat treatment at 300°C for 1 hour satisfies -5 μm≦(F2-F1)≦5 μm. Residual stress was measured using the following method: Reference: "Stress Measurement of Coarse-Grained Materials by Double Exposure Method," Materials, Vol. 68 (2019), p. 312-313. This measurement was carried out under SPring-8 Project No. 2023B1568. The size of the magnetic disk blank was 98 mm in outer diameter, 24 mm in inner diameter, and 0.52 mm in thickness. The measurement area was 37 mm in the radial direction from the inner periphery to the outer periphery, and ±5 mm (10 mm wide) in the direction perpendicular to the radial direction, with measurements carried out at 1 mm pitch in both the radial direction and the perpendicular direction. The test piece was a sample cut in the radial direction at a location 8 mm or more away from the measurement area. The X-ray energy was 20 keV, and the entrance slit dimensions were 0.5 x 0.2 mm. ２The analysis was performed using the {420} diffraction of aluminum. After calculating the residual stress, the difference C between the sum A of the residual stresses at each measurement point in the region from the center of the plate thickness to the surface in the plate thickness direction and the sum B of the residual stresses at each measurement point in the region from the center of the plate thickness to the back surface in the plate thickness direction was divided by the average value D of A and B (C / D), and the absolute value E of this difference was calculated. Note that tensile residual stress is defined as +, and compressive residual stress is defined as -. Residual stress is defined as 30 MPa or less. The E of the magnetic disk blank M1 was 3.6, and the E of the magnetic disk blank M2 was 4.7. It is believed that a large E indicates a large difference in residual stress between the front and back surfaces, i.e., large internal strain and large changes in flatness. Therefore, E is preferably 4.0 or less, and more preferably 3.8 or less.

[0099] According to the present invention, a disk blank for a magnetic disk, which has stable impact resistance even when the thickness is reduced, and a magnetic disk can be obtained.

Claims

1. A disk blank for a magnetic disk, wherein the difference F2 - F1 between the flatness F1 before heat treatment at 300°C for 1 hour and the flatness F2 after heat treatment at 300°C for 1 hour satisfies -5 μm ≤ (F2 - F1) ≤ 5 μm.

2. The disk blank for a magnetic disk according to claim 1, wherein the difference H2 - H1 between the root mean square height H1 before heat treatment at 300°C for 1 hour and the root mean square height H2 after heat treatment at 300°C for 1 hour satisfies -5 μm ≤ (H2 - H1) ≤ 5 μm.

3. The disk blank for a magnetic disk according to claim 1 or 2, wherein the plate thickness is 0.49 mm or less.

4. The disk blank for a magnetic disk according to claim 1 or 2, wherein the plate thickness is 0.42 mm or less.

5. A magnetic disk, wherein the difference F4 - F3 between the flatness F3 before heat treatment at 300°C for 1 hour and the flatness F4 after heat treatment at 300°C for 1 hour satisfies -5 μm ≤ (F4 - F3) ≤ 5 μm.

6. The magnetic disk according to claim 5, wherein the difference H4 - H3 between the root mean square height H3 before heat treatment at 300°C for 1 hour and the root mean square height H4 after heat treatment at 300°C for 1 hour satisfies -5 μm ≤ (H4 - H3) ≤ 5 μm.

7. The magnetic disk according to claim 5 or 6, wherein the plate thickness is 0.49 mm or less.

8. The magnetic disk according to claim 5 or 6, wherein the plate thickness is 0.42 mm or less.

9. The magnetic disk according to claim 5 or 6, wherein the outer diameter is 95 mm or more.

10. The magnetic disk according to claim 7, wherein the outer diameter is 95 mm or more.

11. For the disk blank for a magnetic disk, the absolute value E of the value (C / D) obtained by dividing the difference C between the sum A of the residual stresses at each measurement point in the region from the center of the plate thickness to the surface and the sum B of the residual stresses at each measurement point in the region from the center of the plate thickness to the back surface in the plate thickness direction by the average value D of A and B is 4.0 or less. The disk blank for a magnetic disk according to claim 1 or 2.

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