Disk blank and disk

Abstract

The present invention relates to 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. The present invention also relates to 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.

Description

Technical Field

[0001] The present invention relates to a disk blank and a disk, both of which maintain stable shock resistance even when the thickness is reduced. Background Technology

[0002] Disks used in computer storage devices are manufactured using disk substrates (hereinafter, disk substrates may be simply referred to as "substrate") that have good plating performance as well as excellent mechanical and processing properties. Disk substrates are made from aluminum alloy-based substrates, glass-based substrates, etc. As an aluminum alloy substrate, for example, one known aluminum alloy substrate is made of JIS5086 aluminum alloy (Mg: 3.5% to 4.5% by mass, Fe: 0.50% by mass or less, Si: 0.40% by mass or less, Mn: 0.20% to 0.70% by mass, Cr: 0.05% to 0.25% by mass, Cu: 0.10% by mass or less, Ti: 0.15% by mass or less, Zn: 0.25% by mass or less, with the balance being Al and unavoidable impurities).

[0003] In the manufacturing of a typical hard disk, a ring-shaped aluminum alloy substrate for the disk is first prepared, and then a magnet is attached to the surface of the aluminum alloy substrate. For example, a hard disk using an aluminum alloy substrate made of JIS 5086 alloy is manufactured through the following manufacturing steps.

[0004] First, an aluminum alloy material with a predetermined chemical composition is cast, and the ingot is hot-rolled and then cold-rolled to prepare a rolled material with a predetermined thickness for use as a disk. The rolled material is preferably annealed as needed during cold rolling or similar processes. Next, the rolled material is stamped into a ring shape to obtain a ring-shaped aluminum alloy sheet. Then, to remove strain and other defects generated in the previous manufacturing steps, the ring-shaped aluminum alloy sheet is laminated, and pressure annealing is performed by applying pressure to both the upper and lower surfaces of the sheet while annealing to flatten it. Thus, a ring-shaped disk blank for use with an aluminum alloy is prepared.

[0005] The disk blanks made of aluminum alloy prepared in this way are pretreated by cutting, grinding, degreasing, etching, and zincate treatment (Zn replacement treatment). Next, Ni-P, a hard non-magnetic metal, is electroless plating as a substrate, and the electroless plating surface is polished to manufacture the aluminum alloy substrate for disks.

[0006] Then, magnetic material is sputtered onto the manufactured aluminum alloy substrate for disks to produce a disk made of aluminum alloy. In addition to aluminum alloy, materials such as glass can also be used as the disk substrate.

[0007] In recent years, due to the demands of multimedia and other applications, the need for large capacity and high density disk drives such as HDDs has been continuously increasing. To further increase capacity, the number of disks installed in storage devices is trending upwards, thus creating a demand for thinner disks. Furthermore, to improve the processing speed of disk drives, it is necessary to increase disk rotation speed, and with the increasing demand for high density, disk drives operate at higher temperatures.

[0008] However, this presents several problems: The thinner disk leads to reduced rigidity, potentially degrading its flatness. Furthermore, the increased temperature during disk operation can also worsen flatness. Consequently, the clearance between the read / write head and other components decreases, and when the HDD is subjected to impacts such as drops, the disk may collide with another component, or the read / write head may collide with the disk surface, resulting in reduced shock resistance.

[0009] In addition to the deterioration of disk flatness, there is also the issue of potential deterioration in disk surface roughness. As a result, the read / write head may collide with the disk surface, increasing the likelihood of read / write errors.

[0010] Therefore, in recent years, research has been conducted on improving the impact resistance of disk drives and disk substrates. Since impact resistance may be related to the rigidity of the disk substrate, there are also research examples on improving the rigidity of disk substrates. For example, Patent Document 1 proposes a method for improving the rigidity of an aluminum alloy plate by containing a large amount of Si, which helps to improve rigidity.

[0011] Reference List Patent documents Patent Document 1: WO2016 / 068293 Summary of the Invention

[0012] Technical issues However, while the issue of impact resistance itself has been addressed in the prior art, there are few research examples regarding disk substrates. The method disclosed in Patent Document 1, which involves incorporating a large amount of Si into an aluminum alloy, is effective in improving the rigidity of the aluminum alloy. On the other hand, the disk substrate in Patent Document 1 does not sufficiently improve impact resistance. As mentioned above, in the prior art, impact resistance decreases due to the prolonged operation of the disk device, and it is currently impossible to obtain the desired stable impact resistance. Furthermore, in the prior art, sufficient improvement in surface roughness degradation has not yet been achieved.

[0013] The present invention was made in view of the above circumstances, and the object of the present invention is to provide a disk blank and a disk that still have stable shock resistance even when the thickness is reduced.

[0014] Solution to the problem The inventors conducted in-depth research on the relationship between the impact resistance of disk substrates and the substrate material, discovering that variations in the flatness of the substrate surface have a significant impact on impact resistance. In particular, considering the steps involved in manufacturing the disk substrate, the inventors focused on the flatness of the disk blank after pressure annealing and the flatness of the disk after the magnetic material is adhered. Furthermore, the inventors found that when a disk blank and a disk with a reduced difference in flatness before and after a predetermined heat treatment are obtained, the impact resistance is stabilized. Based on these findings, the inventors completed this invention.

[0015] According to an embodiment of the present invention, the disk blank has a flatness (F2-F1) that satisfies -5 μm ≤ (F2-F1) ≤ 5 μm. (F2-F1) is the difference 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.

[0016] According to an embodiment of the present invention, the disk has (F4-F3) satisfying -5μm≤(F4-F3)≤5μm, where (F4-F3) 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.

[0017] Beneficial effects of the invention The present invention can provide a disk blank and a disk, which still have stable shock resistance even when the thickness is reduced. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating a method for manufacturing an aluminum alloy substrate for a disk according to the present invention, and a method for manufacturing a disk using the aluminum alloy substrate.

[0019] Figure 2 This is a flowchart illustrating a method for manufacturing a glass substrate for a disk according to the present invention, and a method for manufacturing a disk using the glass substrate. Detailed Implementation

[0020] As described above, in this invention, the flatness difference between the disk blank and the disk itself before and after heat treatment at 300°C for 1 hour is -5 μm or greater and 5 μm or less. That is, the absolute value of the flatness difference between the disk blank and the disk after heat treatment at 300°C for 1 hour is 5 μm or less. When the disk blank and the disk have the above configuration, a disk substrate and a disk can be obtained that maintain stable impact resistance even with reduced thickness. Such a disk substrate can be made of aluminum alloy or glass. The materials constituting the disk blank and the disk described in this invention, their manufacturing methods, and their characteristics will be described in detail below.

[0021] 1. The disk blank and disk according to the present invention The disk blank according to the present invention has a flatness (F2-F1) satisfying -5 μm ≤ (F2-F1) ≤ 5 μm, where F2-F1 is the difference 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. Preferably, the disk blank has a flatness (H2-H1) satisfying -5 μm ≤ (H2-H1) ≤ 5 μm, where H2-H1 is the difference 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. Furthermore, the disk according to the present invention has a flatness (F4-F3) satisfying -5 μm ≤ (F4-F3) ≤ 5 μm, where F4-F3 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. The disk preferably has a (H4-H3) that satisfies -5 μm ≤ (H4-H3) ≤ 5 μm, where (H4-H3) 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. These characteristics will be described below.

[0022] 1-1. Difference in flatness before and after heat treatment at 300℃ for 1 hour When the disk blank and the disk itself satisfy -5 μm ≤ (F2 - F1) ≤ 5 μm and -5 μm ≤ (F4 - F3) ≤ 5 μm respectively, the stability and impact resistance of the substrate are demonstrated. In the prior art, disk blanks and disks with large differences in flatness before and after heat treatment exhibit large internal strain. In such disk blanks and disks, when the temperature rises during disk device operation, the internal strain is released, and the flatness of the disk deteriorates. Therefore, the gap with other components decreases, and the impact resistance is reduced.

[0023] Conversely, disks with a small difference in flatness before and after heat treatment at 300°C for 1 hour, as described in this invention, have small internal strain, thus suppressing the reduction in shock resistance. That is, when the difference in flatness before and after heat treatment is small, the effect of flatness degradation due to internal strain is small, so even if the disk drive operates for a long time, it can maintain stable shock resistance over a long period of time.

[0024] Based on the above reasons, the disk blank and disk according to the present invention respectively satisfy -5 μm ≤ (F2 - F1) ≤ 5 μm and -5 μm ≤ (F4 - F3) ≤ 5 μm. The disk blank according to the present invention preferably satisfies -3 μm ≤ (F2 - F1) ≤ 3 μm, more preferably -2 μm ≤ (F2 - F1) ≤ 2 μm. The disk according to the present invention preferably satisfies -3 μm ≤ (F4 - F3) ≤ 3 μm, more preferably -2 μm ≤ (F4 - F3) ≤ 2 μm. It should be noted that the heat treatment condition of 1 hour at 300°C used as an indicator in the present invention is determined with reference to the heat treatment conditions in accelerated tests of long-term operation of disk devices such as HDDs.

[0025] It should be noted that in this invention, "flatness" is represented by the difference between the maximum peak height and the maximum valley depth of the entire surface of the disk substrate. Here, the maximum peak height is the maximum value within the measurement range (the disk blank and the entire surface of the disk), and the maximum valley depth is the minimum value within the measurement range (the disk blank and the entire surface of the disk). Flatness can be measured using a disk flatness measuring machine such as the Zygo MESA manufactured by Zygo Corporation, according to the method specified in JIS B0182-1993. Flatness is defined in JIS B 0182-1993 and can be used as an indicator of flatness, which is the same as the flatness described above, and is referred to as "flatness" in this invention. Specifically, a fixture for changing the angle of the measuring surface relative to the flatness measuring machine is fixed to a base mounted in the flatness measuring machine. For example, a fixture including three micrometers can be used, and the angle of the fixture relative to the measuring surface can be adjusted in the θ direction (the direction of tilting from the 0° central angle at an angle θ) and the ψ direction (the diameter direction) using the micrometers. Next, the substrate is placed on the fixture, and the angle can be adjusted so that the substrate is parallel to the measuring surface of the flatness measuring machine in order to measure the flatness.

[0026] 1-2. Difference in root mean square height before and after heat treatment at 300℃ for 1 hour The disk blank according to the present invention preferably has a (H2-H1) that satisfies -5 μm ≤ (H2-H1) ≤ 5 μm, where (H2-H1) is the difference 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. The disk according to the present invention preferably has a (H4-H3) that satisfies -5 μm ≤ (H4-H3) ≤ 5 μm, where (H4-H3) 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. In the disk blank and the disk, when the difference in surface root mean square height before and after heat treatment decreases as described above, a stable surface smoothness effect is achieved in both the disk blank and the disk. In the prior art, disks with a large difference in root mean square height before and after heat treatment have large internal strain. In such substrates, when the temperature rises during disk device operation, the internal strain is released, and the root mean square height of the disk deteriorates. Therefore, the read / write head may collide with the disk surface, increasing the likelihood of read / write errors.

[0027] Conversely, disks with a small difference in root mean square height before and after heat treatment at 300°C for 1 hour, as described in this invention, have small internal strain, thus suppressing the reduction in surface smoothness. That is, when the difference in root mean square height before and after heat treatment is small, the effect of root mean square height degradation caused by internal strain is small, so even if the disk device operates for a long time, it can maintain a stable surface smoothness over a long period of time.

[0028] Based on the above reasons, the disk blank and disk according to the present invention preferably satisfy -5 μm ≤ (H2 - H1) ≤ 5 μm and -5 μm ≤ (H4 - H3) ≤ 5 μm, respectively. The disk blank according to the present invention more preferably satisfies -3 μm ≤ (H2 - H1) ≤ 3 μm, and even more preferably satisfies -2 μm ≤ (H2 - H1) ≤ 2 μm. The disk according to the present invention more preferably satisfies -3 μm ≤ (H4 - H3) ≤ 3 μm, and even more preferably satisfies -2 μm ≤ (H4 - H3) ≤ 2 μm. It should be noted that the heat treatment condition of 1 hour at 300°C, used as an indicator in the present invention, is determined with reference to the heat treatment conditions in accelerated tests of long-term operation of HDDs and other disk devices.

[0029] It should be noted that in this invention, "root mean square height" refers to the root mean square of the reference length of the disk blank and the disk. The "reference length" of the disk blank and the disk is the circumferential length of the middle circumferential portion of the disk (radial position: half of the inner diameter plus half of the difference between the outer diameter and the inner diameter). It should be noted that the root mean square height can be measured using a ZyGO non-contact flatness measuring instrument according to JIS B0601.

[0030] 1-3. Thickness The thickness of the disk blank according to the present invention is preferably 0.49 mm or less, more preferably 0.42 mm or less. As described above, even if the thickness of the disk blank is reduced and the rigidity is decreased, excellent shock resistance can be stably obtained. The thickness of the disk according to the present invention is preferably 0.49 mm or less, more preferably 0.42 mm or less. As described above, even if the thickness of the disk is reduced and the rigidity is decreased, excellent shock resistance can be stably obtained. The outer diameter of the disk is preferably 95 mm or more, more preferably 96 mm or more, and even more preferably 97.2 mm or more. In the prior art, when the outer diameter of the disk is increased as described above, it may collide with another component due to high-speed rotation during use, or the read / write head may collide with the disk surface. Conversely, since the disk according to the present invention stably has excellent shock resistance, it can prevent collisions with other components and read / write heads.

[0031] 2. The method for manufacturing a disk according to the present invention To achieve the aforementioned standards for disk flatness and root mean square height, it is useful to optimize the conditions in the homogenization and hot rolling processes (more specifically, "holding time at 425°C to 440°C") for disk blanks made of aluminum alloy, and to optimize the conditions in the polishing process (more specifically, the "cooling rate" after heat treatment following surface polishing) for disk substrates made of glass. Detailed explanations will be provided later.

[0032] 3. The aluminum alloy substrate for disks according to the present invention The aluminum alloy substrate for disk drives according to the present invention can be made of aluminum alloy. The alloy composition and manufacturing method of the aluminum alloy substrate for disk drives according to the present invention will be described in detail below.

[0033] 3-1. Alloy Composition of Aluminum Alloys The aluminum alloy used in the disk disk aluminum alloy substrate according to the present invention preferably contains at least one of Fe: 0.01% to 3.00% by mass and Mn: 0.01% to 3.00% by mass as a first selected element (hereinafter, mass% is simply referred to as "%"). When the disk disk aluminum alloy substrate contains an aluminum alloy having the above composition, the vibration resistance, impact resistance and plating performance can be further improved.

[0034] Furthermore, the aluminum alloy constituting the aluminum alloy substrate for disks may further contain one or two or more elements 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%.

[0035] In addition, the aluminum alloy constituting the aluminum alloy substrate for disks may further contain one or two or more elements selected from the group consisting of Ti, B and V as a third optional element, with a total content of 0.005% to 5.000%.

[0036] By appropriately adding the aforementioned selected elements to aluminum alloys, it is possible to obtain aluminum alloy substrates for hard disks with excellent vibration resistance and other properties. The function of these selected elements will be described below.

[0037] Fe: Fe exists primarily as second-phase particles (Al-Fe intermetallic compounds, etc.), with a portion existing as a solid solution in the matrix. Through the formation of second-phase particles and the solid solution within the matrix, Fe enhances the impact resistance of aluminum alloy substrates used in hard disk drives. By increasing the amount of second-phase particles, the strength (Young's modulus or yield stress) of the aluminum alloy is improved through dispersion strengthening. When the Young's modulus and yield stress of the aluminum alloy are increased, the deformation of the substrate caused by vibration during events such as disk drive drops can be kept within the elastic range. Therefore, changes in the flatness of the substrate can be prevented.

[0038] When the Fe content in the aluminum alloy is greater than or equal to 0.01%, the impact resistance, Young's modulus, and strength of the aluminum alloy substrate for disks can be further improved. Furthermore, when the Fe content in the aluminum alloy is 3.00% or lower, the formation of a large number of coarse Al-Fe intermetallic compound particles is suppressed. When these coarse Al-Fe intermetallic compound particles detach during etching, zincate treatment, cutting, or grinding, large depressions are formed on the substrate surface. Suppressing the formation of coarse Al-Fe intermetallic compound particles also suppresses the formation of depressions, further enhancing the surface smoothness achieved through plating. Furthermore, suppressing depressions further suppresses plating peeling. Moreover, suppressing depressions further suppresses the reduction in workability during the rolling process. For the above reasons, the Fe content in the aluminum alloy is preferably in the range of 0.01% to 3.00%. More preferably, it is in the range of 0.03% to 2.40%, and even more preferably, it is in the range of 0.04% to 1.80%.

[0039] Mn: Mn mainly exists in the form of second-phase particles (Al-Mn intermetallic compounds, etc.) and exhibits an effect of improving the impact resistance of aluminum alloy substrates for hard disk drives. By increasing the amount of second-phase particles, the strength of the alloy (Young's modulus or yield stress) is improved through dispersion strengthening. Therefore, changes in the flatness of the aluminum alloy substrate for hard disk drives can be prevented when it vibrates.

[0040] When the Mn content in the aluminum alloy is 0.01% or higher, the impact resistance, Young's modulus, and strength of the aluminum alloy substrate for disks can be further improved. Furthermore, when the Mn content in the aluminum alloy is 3.00% or lower, the formation of a large number of coarse Al-Mn intermetallic compound particles is suppressed. Therefore, the formation of large depressions during etching, zincate treatment, cutting, or grinding is suppressed. In addition, the reduction in the smoothness of the plated surface and the occurrence of plating peeling can be further suppressed. Furthermore, the reduction in workability during the rolling process can be further suppressed. For the above reasons, the Mn content in the aluminum alloy is preferably in the range of 0.01% to 3.00%. More preferably, it is in the range of 0.10% to 1.50%, and even more preferably, it is in the range of 0.40% to 1.20%.

[0041] Mg: Mg mainly exists in the matrix as a solid solution, with a portion existing as second-phase particles (such as Mg-Si intermetallic compounds). Therefore, it exhibits the effect of improving the strength and Young's modulus of the aluminum alloy substrate.

[0042] When the Mg content in the aluminum alloy is 0.100% or higher, the strength and Young's modulus of the aluminum alloy substrate for disks can be further improved. Furthermore, when the Mg content in the aluminum alloy is 6.000% or lower, the reduction in impact resistance can be further suppressed. Therefore, the Mg content in the aluminum alloy is preferably in the range of 0.100% to 6.000%. More preferably, it is in the range of 1.000% to 5.000%, and even more preferably, it is in the range of 2.500% to 4.500%.

[0043] Ni: Ni mainly exists in the form of second-phase particles (Al-Ni intermetallic compounds, etc.) and exhibits the effect of improving the Young's modulus and strength of aluminum alloy substrates for disk drives.

[0044] When the Ni content in the aluminum alloy is 0.100% or higher, the Young's modulus and strength of the aluminum alloy substrate for disks can be further improved. Furthermore, when the Ni content in the aluminum alloy is 5.000% or lower, the formation of a large number of coarse Al-Ni intermetallic compound particles is suppressed. Therefore, the formation of large depressions during etching, zincate treatment, cutting, or grinding is suppressed. Furthermore, the reduction in the smoothness of the plated surface and the occurrence of plating peeling can be further suppressed. In addition, the reduction in workability during the rolling step can be further suppressed. For the above reasons, the Ni content in the aluminum alloy is preferably in the range of 0.100% to 5.000%. The Ni content is more preferably in the range of 0.100% to 2.000%. The lower limit of the Ni content in the aluminum alloy can be 0%.

[0045] Cr: Cr exists primarily as second-phase particles (Al-Cr intermetallic compounds, etc.) and exhibits the effect of improving the Young's modulus and strength of aluminum alloy substrates for disk drives. When the Cr content in the aluminum alloy is 0.001% or higher, the effect of improving the Young's modulus and strength of the aluminum alloy substrate for disk drives can be further enhanced. Furthermore, when the Cr content in the aluminum alloy is 5.000% or lower, the formation of a large number of coarse Al-Cr intermetallic compound particles is suppressed. Therefore, the formation of large depressions during etching, zincate treatment, cutting, or grinding is suppressed. In addition, the reduction in the smoothness of the plated surface and the occurrence of plating peeling can be further suppressed. Furthermore, the reduction in workability during the rolling step can be further suppressed. For the above reasons, the Cr content in the aluminum alloy is preferably in the 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%.

[0046] Zr: Zr mainly exists in the form of second-phase particles (Al-Zr intermetallic compounds, etc.) and exhibits the effect of improving the Young's modulus and strength of aluminum alloy substrates for disk drives.

[0047] When the Zr content in the aluminum alloy is 0.0001% or higher, the Young's modulus and strength of the aluminum alloy substrate for disks can be further improved. Furthermore, when the Zr content in the aluminum alloy is 5.000% or lower, the formation of a large number of coarse Al-Zr intermetallic compound particles is suppressed. Therefore, the formation of large depressions during etching, zincate treatment, cutting, or grinding is suppressed. In addition, the reduction in surface smoothness and plating peeling can be further suppressed. Furthermore, the reduction in workability during the rolling process can be further suppressed. For the above reasons, the Zr content in the aluminum alloy is preferably in the range of 0.0001% to 5.000%. The Zr content is more preferably in the range of 0.0001% to 1.000%. The lower limit of the Zr content in the aluminum alloy can be 0%.

[0048] Zn: Zn reduces the amount of Al dissolved during zincate treatment, forming a uniform, thin, and dense zincate film, and exhibits improved smoothness and adhesion in subsequent plating steps. Furthermore, Zn forms second-phase particles with other additives, demonstrating an effect that improves the Young's modulus and strength of the aluminum alloy substrate.

[0049] When the Zn content in the aluminum alloy is 0.001% or higher, the amount of Al dissolved during the zincate treatment can be reduced, allowing for the formation of a uniform, thin, and dense zincate film, and further improving the smoothness of the coating. Furthermore, when the Zn content in the aluminum alloy is 5.000% or lower, the zincate film is uniform, further suppressing the reduction in the smoothness of the coated surface and further suppressing the occurrence of coating peeling. In addition, it can further suppress the reduction in workability during the rolling process. For the above reasons, the Zn content in the aluminum alloy is preferably in the range of 0.001% to 5.000%. More preferably, it is in the range of 0.060% to 0.700%, and even more preferably, it is in the range of 0.010% to 0.500%.

[0050] Cu: Cu mainly exists in the form of second-phase particles (Al-Cu intermetallic compounds, etc.), and exhibits the effect of improving the strength and Young's modulus of aluminum alloy substrates for disks. Furthermore, the amount of Al dissolved during the zincate treatment is reduced. In addition, the zincate film is formed uniformly, thinly, and densely, and its effect of improving smoothness in subsequent plating steps is further demonstrated.

[0051] When the Cu content in the aluminum alloy is 0.001% or higher, the Young's modulus and strength of the aluminum alloy substrate for disks, as well as the effect on improving smoothness, can be further improved. Furthermore, when the Cu content in the aluminum alloy is 5.000% or lower, the formation of a large number of coarse Al-Cu intermetallic compound particles is suppressed. Therefore, the formation of large depressions during etching, zincate treatment, cutting, or grinding is suppressed. In addition, the reduction in the smoothness of the plated surface and the occurrence of plating peeling can be further suppressed. Furthermore, the reduction in workability during the rolling step can be further suppressed. For the above reasons, the Cu content in the aluminum alloy is preferably in the range of 0.001% to 5.000%. More preferably, the Cu content is in the range of 0.005% to 1.000%, and even more preferably, in the range of 0.015% to 0.500%.

[0052] Si: Si mainly exists in the form of second-phase particles (Si particles, Al-Fe-Si intermetallic compounds, etc.), and by increasing the amount of second-phase particles with a higher Young's modulus than aluminum, it exhibits the effect of improving the impact resistance, Young's modulus and strength of aluminum alloy substrates for disks (through dispersion strengthening).

[0053] When the Si content in the aluminum alloy is 0.01% or higher, the impact resistance, Young's modulus, and strength of the aluminum alloy substrate for disks can be further improved. Furthermore, when the Si content in the aluminum alloy is 0.400% or lower, the formation of a large number of coarse Si particles is suppressed. Therefore, the formation of large depressions during etching, zincate treatment, cutting, or grinding is suppressed. In addition, the reduction in the smoothness of the plated surface and the occurrence of plating peeling can be further suppressed. Furthermore, the reduction in workability during the rolling process can be further suppressed. For the above 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%.

[0054] Ti, B, and V: During the solidification stage of the casting process, Ti, B, and V form second-phase particles (such as borides like TiB2, Al3Ti, and Ti-VB particles). These particles act as grain nuclei, allowing for grain refinement. Therefore, coating performance is improved. Furthermore, due to grain refinement, the inhomogeneity of the second-phase particle size is reduced, resulting in reduced fluctuations in the impact resistance, Young's modulus, and strength of the aluminum alloy substrate used in disks.

[0055] When the total content of Ti, B, and V is less than 0.001%, the above-mentioned effects cannot be obtained. On the other hand, even when the total content of Ti, B, and V is greater than 5.000%, the effect saturates, and no further significant improvement can be obtained. Therefore, when adding Ti, B, and V, 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%. It should be noted that the total content refers to the amount when only one of Ti, B, and V is included, the total amount of the two when two of them are included, and the total amount of all three when all three are included.

[0056] Other elements: The balance of the aluminum alloy used in this invention consists of Al and unavoidable impurities. Examples of unavoidable impurities include Ga, Sn, Sr, P, and Na. As long as each element that is an unavoidable impurity is less than 0.10% and the total amount is less than 0.20%, the properties of the aluminum alloy substrate obtained by this invention will not be impaired.

[0057] It should be noted that, in the above description, intermetallic compounds refer to precipitates or crystallization products, specifically particles of Al-Fe intermetallic compounds (Al3Fe, Al6Fe, Al6(Fe,Mn), Al-Fe-Si, Al-Fe-Mn-Si, Al-Fe-Ni, Al-Cu-Fe, etc.) and Mg-Si intermetallic compounds (Mg2Si, etc.). Examples of other intermetallic compounds include Al-Mn intermetallic compounds (Al6Mn and Al-Mn-Si), Al-Ni intermetallic compounds (Al3Ni, etc.), Al-Cu intermetallic compounds (Al2Cu, etc.), Al-Cr intermetallic compounds (Al7Cr, etc.), and Al-Zr intermetallic compounds (Al3Zr, etc.). It should also be noted that second-phase particles, in addition to intermetallic compounds, also include Si particles, etc.

[0058] 3-2. The method for manufacturing an aluminum substrate for a hard disk according to the present invention The following will describe in detail the steps and process conditions of the method for manufacturing an aluminum alloy substrate for a disk according to this embodiment. Figure 1 This is a flowchart illustrating a method for manufacturing an aluminum alloy substrate for a hard disk according to this embodiment, and a method for manufacturing a hard disk using the substrate. Figure 1In this process, the aluminum alloy composition adjustment step (step S101), aluminum alloy casting step (step S102), homogenization treatment step (step S103), and hot rolling step (step S104) are performed. The cold rolling step (step S105) is a step of manufacturing aluminum alloy material by melting and casting and forming the aluminum alloy material into an aluminum alloy sheet. Next, the aluminum alloy sheet is stamped into a disc shape to manufacture a disc-shaped aluminum alloy sheet (step S105). Next, the disc-shaped aluminum alloy sheet is subjected to a pressure planarization treatment step (step S106) to manufacture a disk blank made of aluminum alloy. Then, the manufactured disk blank is subjected to pretreatment steps such as cutting and grinding (step S107), heat treatment step (step S108), zincate treatment step (step S109), and Ni-P plating treatment step (step S110), and then surface polishing and heat treatment steps (steps S111 and S112) to manufacture an aluminum alloy substrate for disks. A magnetic attachment step (step S113) is performed on the manufactured aluminum alloy substrate for the disk to form a disk. The following will be performed according to... Figure 1 The process is described in detail for each step.

[0059] First, according to conventional methods, a molten aluminum alloy material with the above-mentioned composition is prepared by heating and melting (step S101). Next, the prepared molten aluminum alloy material is cast using methods such as semi-continuous casting (DC casting) or continuous casting (CC casting) to produce an aluminum alloy material (step S102). The production conditions for the aluminum alloy material in the DC casting and CC casting methods are as follows.

[0060] In DC casting, molten aluminum alloy material injected through the spout has its heat removed by cooling water sprayed directly onto the bottom block, water-cooled mold walls, and the outer periphery of the ingot. After cooling and solidification, it is pulled down to form an aluminum alloy ingot.

[0061] On the other hand, in the CC casting method, molten aluminum alloy material is supplied through a casting nozzle between a pair of rolls (or a belt casting machine and a block casting machine), and the aluminum alloy sheet is directly cast by dissipating heat from the rolls.

[0062] A significant difference between DC casting and CC casting lies in the cooling rate during casting. CC casting, characterized by its high cooling rate, results in smaller second-phase particles compared to those in DC casting. In both casting methods, the cooling rate during casting is preferably in the range of 0.1 °C / s to 1000 °C / s. When the cooling rate is between 0.1 °C / s and 1000 °C / s, a large number of second-phase particles are generated, and Young's modulus is increased. Furthermore, the amount of Fe dissolved in the solid solution increases, leading to improved strength. When the cooling rate is less than 0.1 °C / s, the amount of Fe dissolved in the solid solution may decrease, potentially reducing strength. Conversely, when the cooling rate is greater than 1000 °C / s, the number of second-phase particles may decrease, potentially resulting in insufficient impact resistance and Young's modulus.

[0063] The aluminum alloy ingots cast by DC are subjected to a homogenization treatment (step S103). The homogenization treatment is a heat treatment at 540°C to 620°C for 0.5 hours to 30 hours. The holding time at 425°C to 440°C in both the homogenization treatment and hot rolling steps is 0.9 hours or less. When the holding time at 425°C to 440°C is longer than 0.9 hours, the number of second-phase particles may decrease, and therefore deformation may occur during the pressure annealing step, potentially resulting in large internal strain. In such disk blanks and disks, when the temperature rises during disk device operation, the internal strain is released, and the flatness and root mean square height of the disk may deteriorate. It should be noted that "the holding time at 425°C to 440°C" refers to the total time the aluminum alloy ingot is held at 425°C to 440°C during the homogenization treatment and hot rolling steps. The "holding time at 425°C to 440°C" in the homogenization process includes the time required to reach 425°C to 440°C during the heating of the aluminum alloy ingot to a predetermined temperature, and the time required to reach 425°C to 440°C during the cooling of the aluminum alloy ingot until hot rolling. The holding time at 425°C to 440°C in both the homogenization and hot rolling processes is preferably less than 0.5 hours, more preferably less than 0.4 hours, and even more preferably less than 0.3 hours. When the heating temperature during homogenization is below 540°C or the heating time is less than 0.5 hours, the homogenization process may be insufficient, and deformation may occur during the pressure annealing step, potentially resulting in large internal strain. In such disk blanks and disks, the internal strain is released as the temperature rises during disk device operation, and the flatness and root mean square height of the disk blanks and disks may deteriorate. When the heating temperature during homogenization is above 620°C, the aluminum alloy ingot may melt. Even when the heating time during homogenization exceeds 30 hours, the effect becomes saturated and no further significant improvement can be achieved.

[0064] Next, the homogenized aluminum alloy ingot (DC casting) is hot-rolled to produce sheet metal (step S104). There are no particular limitations on the hot rolling conditions; the preferred starting temperature is 450°C to 600°C, and the preferred ending temperature is 230°C to 400°C. It should be noted that the "holding time at 425°C to 440°C" in the hot rolling step includes the time required for the temperature to reach 425°C to 440°C during the process of heating the aluminum alloy ingot to the starting temperature of hot rolling.

[0065] Next, the hot-rolled sheet can be cold-rolled to appropriately set its thickness within the range of 1.9 mm to 0.20 mm (step S105). Cold rolling is performed to obtain the target thickness of the product sheet. There are no particular limitations on the conditions during cold rolling, which can be determined according to the required strength and thickness of the product sheet; the rolling rate is preferably 10% to 95%. Annealing can be performed before or during cold rolling to ensure cold-rolled processability. When annealing is performed, for example, in the case of batch heating, the annealing is preferably carried out at 300°C to 400°C for 0.1 hours to 10 hours.

[0066] Then, the cold-rolled aluminum alloy sheet is stamped into a ring shape (step S105) to obtain a ring-shaped aluminum alloy sheet. The ring-shaped aluminum alloy sheet is then subjected to a pressure planarization process (step S106) to manufacture a disk blank. In the pressure planarization process, pressure annealing is performed in air at 250°C to 420°C for 0.5 to 10 hours to prepare a planarized disk blank. During pressure annealing, the internal strain introduced by rolling is close to zero, but not entirely zero. This is because after the internal strain is released during pressure annealing, the ring-shaped aluminum alloy sheet undergoes slight deformation at high temperatures, which introduces new internal strain. This phenomenon is more pronounced when the thickness is thinner and the rigidity is lower, which is not a problem for disk blanks in the prior art. Furthermore, when the holding time at 425°C to 440°C in the homogenization and hot rolling steps exceeds 0.9 hours and the number of second-phase particles is small, when the temperature in the homogenization step is below 540°C or above 620°C, or when the time in the homogenization step is less than 0.5 hours, the disk blank may deform at high temperatures, potentially introducing internal strain. Since this internal strain is small, there is no driving force for recovery, and even with subsequent heat treatment, the internal strain will not be completely zero. In disks using such disk blanks, when the temperature rises during disk device operation, the internal strain is released, and the flatness and root mean square height of the disk may deteriorate.

[0067] Before zincate treatment or similar processes, the disk blank undergoes a cutting and grinding step (step S107) and a heat treatment step (step S108). In the heat treatment step, the disk blank is held, for example, at a temperature between 130°C and 280°C for 0.5 hours to 10.0 hours. This heat treatment suppresses dislocation reduction and improves impact resistance. When the heat treatment temperature is above 280°C, or when the heat treatment time is longer than 10.0 hours, dislocations decrease, thus reducing impact resistance. On the other hand, when the heat treatment temperature is below 130°C, or when the heat treatment time is less than 0.5 hours, the strain introduced by machining is not sufficiently removed, which may cause the flatness of the disk blank and the disk to deteriorate over time. For these reasons, the heat treatment of the disk blank after cutting and grinding is preferably performed at a temperature between 130°C and 280°C for 0.5 hours to 10.0 hours.

[0068] Next, the surface of the disk blank is degreased and etched to perform a zincate treatment (Zn replacement treatment) (step S109). In the zincate treatment, a zincate film is formed on the surface of the disk blank. The zincate treatment can be performed using a commercially available zincate treatment solution, preferably at a temperature of 10°C to 35°C, a treatment time of 0.1 minutes to 5 minutes, and a concentration of 100 mL / L to 500 mL / L. The zincate treatment can be performed at least once, or two or more times. By performing multiple zincate treatments, fine Zn particles precipitate out to form a uniform zincate film. When performing two or more zincate treatments, a Zn stripping treatment can be performed between zincate treatments. The Zn stripping treatment is preferably performed using an HNO3 solution at a temperature of 15°C to 40°C, a treatment time of 10 seconds to 120 seconds, and a concentration of 10% to 60%. The second and subsequent zincate treatments are preferably performed under the same conditions as the first zincate treatment.

[0069] In addition, the surface of the zincate-treated disk blank undergoes an electroless Ni-P plating treatment step (step S110) as a substrate treatment for magnetic attachment. In the electroless Ni-P plating treatment step, it is preferable to use a commercially available plating solution or the like and perform the plating treatment at a temperature of 80°C to 95°C, a treatment time of 30 minutes to 180 minutes, and a Ni concentration of 3 g / L to 10 g / L.

[0070] The plated surface after electroless Ni-P plating is polished to make it smooth as needed (step S111). In this polishing step, it is preferable to perform polishing in multiple stages, and adjust the diameter of the polishing particles in each stage. For example, the main surface is polished using a polishing slurry containing large-diameter polishing abrasive grains with a particle size of 0.1 μm to 1.0 μm and a hard or soft polishing pad. Next, the surface is polished using a polishing slurry containing small-diameter polishing abrasive grains with a particle size of about 0.01 μm to 0.1 μm and a soft polishing pad, and then a heat treatment step is performed as needed (step S112) to obtain an aluminum alloy substrate for disks. The heat treatment of the disk blank is preferably performed at a heat treatment step temperature of 100°C to 250°C and a treatment time of 30 minutes or less.

[0071] Finally, the magnetic material is attached to the electroless Ni-P plating surface of the aluminum alloy substrate for the disk by sputtering (step S113). Thus, a disk made of aluminum alloy is manufactured.

[0072] 4. The glass substrate for disks according to the present invention The disk substrate according to the present invention can be made of glass material. The glass material used in the disk glass substrate according to the present invention and the method of manufacturing the substrate will be described in detail below.

[0073] 4-1. Glass Materials Glass ceramics (such as amorphous glass or crystalline glass) can be used as glass materials. It should be noted that, from the viewpoint of formability and processability, amorphous glass is preferred. For example, aluminosilicate glass, soda-lime glass, sodium-aluminosilicate glass, aluminoborosilicate glass, or borosilicate glass are preferred.

[0074] As a specific glass composition, it is preferred to have 55% to 75% SiO2 as the main component, and to add 0.3% to 25% Al2O3 and 0% to 20% CaO. Furthermore, it is preferred to have one or more of the following: 0.01% to 6% Li2O, 0.7% to 12% Na2O, 0% to 8% K2O, 0% to 7% MgO, 0% to 10% ZrO2, and 0% to 1% TiO2.

[0075] When the SiO2 content is 55% to 75%, the effect of increasing the frequency (f) of the glass substrate is observed. The SiO2 content in the glass is preferably in the range of 55% to 75%, more preferably 60% to 75%. When the Al2O3 content is 0.3% to 25%, the effect of increasing the density (ρ) of the glass substrate is observed. The Al2O3 content in the glass is preferably in the range of 0.3% to 25%, more preferably 1.0% to 25%. When the CaO content is 0% to 20%, the effect of increasing both the f and ρ (density) of the glass substrate is observed. The CaO content in the glass is preferably in the range of 0% to 20%, more preferably 1% to 20%.

[0076] It should be noted that the glass may contain B2O3 (an essential component in aluminoborosilicate or borosilicate glass), which reduces viscosity and improves solubility and clarity; SrO or BaO, which reduces viscosity at high temperatures, improves solubility, clarity, and formability, and also increases Young's modulus; ZnO, which improves ion exchange performance and reduces viscosity at high temperatures without reducing viscosity at low temperatures; SnO2, which improves clarity and ion exchange performance; Fe2O3 as a colorant; and As2O3 or Sb2O3 as a clarifying agent. In addition, it may contain oxides of elements such as La, P, Ce, Sb, Hf, Rb, and Y as trace elements. The content of these components may be 15% or less.

[0077] 4-2. Method for manufacturing glass substrate for disks according to the present invention Next, an example of a method for manufacturing a glass substrate for a disk according to this embodiment will be described. Figure 2 This is a flowchart illustrating an example of a method for manufacturing a glass substrate for a disk according to this embodiment, and a method for manufacturing a disk using the substrate. The following will be in accordance with... Figure 2 The process description covers the content of each step.

[0078] First, a glass plate is manufactured as raw material (step S201). Next, the glass plate manufactured in step S201 is cored to form a doughnut-shaped glass substrate (step S202).

[0079] Next, chamfered surfaces are formed on the inner and outer peripheral end faces of the formed annular glass substrate (step S203). Then, the inner and outer peripheral end faces of the annular glass substrate with the chamfered surfaces are polished, followed by surface polishing. This polishing step includes rough polishing (step S204) and fine polishing (step S205). In the rough polishing step (step S204), for example, a polishing slurry containing large-diameter polishing abrasive grains with a particle size of 0.1 μm to 1.0 μm and a hard or soft polishing pad are used to perform a rough polishing step on the main surface. In the subsequent fine polishing step (step S205), for example, a polishing slurry containing small-diameter polishing abrasive grains with a particle size of approximately 0.01 μm to 0.1 μm and a soft polishing pad are used to further refine the main surface of the rough-polished annular glass substrate.

[0080] Then, the glass substrate for disks according to the present invention is subjected to heat treatment at 270°C to 350°C after fine polishing, and the cooling rate after heating is set to less than 5°C / h, and cooled to 200°C (step S206).

[0081] In this manner, after polishing the surface of the annular glass substrate, heat treatment at 270°C to 350°C is performed, and the cooling rate after heating is set to less than 5°C / h, cooling to 200°C. This releases the internal strain in the annular glass substrate, suppresses flatness variations and root-mean-square height during disk drive operation, and stabilizes impact resistance. Although heat treatment releases strain, subsequent cooling, if at a high rate, can generate thermal stress and introduce new strain. Therefore, the cooling rate is less than 5°C / h, preferably 3°C / h or lower.

[0082] Furthermore, the reason for setting the heat treatment temperature to 270°C to 350°C is that when the heating temperature is higher than 350°C, the flatness deteriorates, thus reducing the impact resistance. On the other hand, when the heat treatment temperature is lower than 270°C, the strain introduced by polishing is not sufficiently removed. Therefore, the flatness of the glass-based disk deteriorates due to time variations during the long-term operation of the disk device, and the impact resistance also deteriorates.

[0083] It should be noted that there is no limit to the heat treatment time. However, if the treatment time is too long, the cost will increase, so the preferred treatment time is 0.6 hours to 3 hours.

[0084] By performing the heat treatment following surface polishing as described above, a glass substrate for a disk according to the present invention is manufactured. Finally, a magnetic material is adhered to the polished surface of the glass substrate for the disk by sputtering (step S207). Thus, a glass disk is manufactured.

[0085] Based on the above embodiments, the present invention relates to the following [1] to

[10] . [1] A disk blank for a hard disk, wherein (F2-F1) satisfies -5 μm ≤ (F2-F1) ≤ 5 μm, and (F2-F1) is the difference between the flatness F1 before heat treatment at 300℃ for 1 hour and the flatness F2 after heat treatment at 300℃ for 1 hour. [2] According to the disk blank described above [1], its (H2-H1) satisfies -5 μm≤(H2-H1)≤5 μm, and (H2-H1) is the difference between the root mean square height H1 before heat treatment at 300℃ for 1 hour and the root mean square height H2 after heat treatment at 300℃ for 1 hour. [3] The disk blank described in [1] or [2] above has a thickness of 0.49 mm or less. [4] The disk blank described in [1] or [2] above has a thickness of 0.42 mm or less. [5] A disk having (F4-F3) satisfying -5 μm ≤ (F4-F3) ≤ 5 μm, where (F4-F3) 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. [6] According to the disk described above [5], its (H4-H3) satisfies -5 μm≤(H4-H3)≤5 μm, and (H4-H3) is the difference between the root mean square height H3 before heat treatment at 300℃ for 1 hour and the root mean square height H4 after heat treatment at 300℃ for 1 hour. [7] The disk described in [5] or [6] above has a thickness of 0.49 mm or less. [8] The disk described in [5] or [6] above has a thickness of 0.42 mm or less. [9] The disk according to any one of [5] to [8] above has an outer diameter of 95 mm or greater.

[10] According to any one of [1] to [4] above, the absolute value E of the disk blank (C / D) is 4.0 or less, and the value (C / D) is obtained by dividing C by the average value D of A and B, where A is the sum of residual stresses at multiple measurement points in the region from the center of the thickness to the front surface in the thickness direction of the disk blank, B is the sum of residual stresses at multiple measurement points in the region from the center of the thickness to the back surface in the thickness direction of the disk blank, and C is the difference between the sum A and the sum B.

[0096] Example The present invention will now be described in more detail with reference to embodiments, but the invention is not limited thereto. In the examples, an aluminum alloy substrate for disks and a glass substrate for disks were manufactured as disk substrates, and the characteristics of the disk blank or disk were evaluated.

[0097] A. Manufacturing of aluminum alloy disks (Examples 1 to 4 and Comparative Examples 1 and 2) First, according to conventional methods, the alloy materials having the compositions shown in Table 1 are melted to prepare molten aluminum alloys (step S101). In Table 1, "-" indicates values ​​less than the measurement limit.

[0098] [Table 1]

[0099] Next, molten aluminum alloy is cast using DC casting to prepare an ingot (step S102). Both surfaces of the ingot are milled prior to homogenization.

[0100] Next, homogenization is performed under the conditions shown in Table 2 (step S103). Next, hot rolling is performed to obtain a hot-rolled sheet (step S104).

[0101] After hot rolling, cold rolling is performed to obtain an aluminum alloy sheet (step S105). The aluminum alloy sheet is then stamped into a ring shape with an outer diameter of 98 mm and an inner diameter of 24 mm (step S105) to prepare a ring-shaped aluminum alloy sheet.

[0102] The annular aluminum alloy sheet thus prepared was subjected to pressure annealing (pressure planarization treatment) at the temperature shown in Table 2 for 3 hours to obtain a disk blank (step S106). In Example 4 and Comparative Example 2, the disk blank was further face-machined (cut) to make its outer diameter 97 mm and inner diameter 25 mm, and then ground (ground to a surface roughness of 25 μm) (step S107). Subsequently, heat treatment, zincate treatment, electroless Ni-P plating, heat treatment, and sputtering treatment (magnetic body adhesion) were performed by conventional methods (steps S108 to S110 and S112 to S113) to obtain an aluminum alloy disk.

[0103] B. Manufacturing of glass-based disks (Example 5 and Comparative Example 3) Each disk was made of aluminosilicate glass manufactured under the conditions shown in Table 2. The disk thickness was 0.49 mm, the outer diameter was 97 mm, and the inner diameter of the circular hole was 25 mm. It should be noted that in Example 5, after the polishing step, heat treatment and cooling treatment were performed under the conditions shown in Table 2 (cooling rate: 4.5°C / h). In Comparative Example 3, the polished disk was not subjected to heat treatment.

[0104] C. Evaluation of the characteristics of the manufactured disk blanks or disks. The flatness and root mean square height (before and after 1 hour of heat treatment at 300°C) of the blanks or disks manufactured under the conditions shown in Table 2 were evaluated using the following methods.

[0105] [flatness] First, the flatness F1 and root mean square height H1 of the disk blanks (Examples 1 to 3 and Comparative Example 1) were measured. Furthermore, the flatness F3 and root mean square height H3 of the disks (Examples 4 and 5 and Comparative Examples 2 and 3) were measured. Next, the disk blanks (Examples 1 to 3 and Comparative Example 1) were heat-treated at 300°C for 1 hour, and the flatness F2 and root mean square height H2 after heat treatment were measured. Furthermore, the disks (Examples 4 and 5 and Comparative Examples 2 and 3) were heat-treated at 300°C for 1 hour, and the flatness F4 and root mean square height H4 after heat treatment were measured. Then, the differences in flatness and root mean square height before and after heat treatment were calculated, namely (F2 - F1), (F4 - F3), (H2 - H1), and (H4 - H3). Flatness and root mean square height were measured using a ZyGO non-contact flatness measuring instrument.

[0106] Table 2 shows the performance evaluation results of the disk blanks or disks manufactured in the examples.

[0107] [Table 2]

[0108] It should be noted that the "thickness" in the "cold rolling or polishing" step in Table 2 refers to: the thickness of the aluminum alloy sheet after cold rolling in Examples 1 to 4 and Comparative Examples 1 and 2; the thickness of the disk after polishing, heating and cooling in Example 5; and the thickness of the disk after polishing in Comparative Example 3.

[0109] The “cooling rate after heating” in Table 2 refers to the cooling rate at which the aluminosilicate glass disk is polished, heated to 300°C, and then cooled to 200°C in Example 5.

[0110] In Table 2, the "holding time at 425°C to 440°C" in the homogenization and hot rolling steps represents the total time for (a) to (c) below.

[0111] (a) The time during which the temperature of the aluminum alloy ingot reaches 425°C to 440°C during the homogenization process, when the temperature is raised to a predetermined temperature. (b) The time after the homogenization step for cooling the aluminum alloy ingot until the temperature reaches 425°C to 440°C during hot rolling, and (c) The time during which the temperature of the aluminum alloy ingot reaches 425°C to 440°C during the hot rolling process.

[0112] As shown in Table 2, in Examples 1 to 4, the holding time at 425°C to 440°C in the homogenization and hot rolling steps is 0.9 hours or less, and the homogenization step is carried out under the condition of holding at 540°C to 620°C for 0.5 hours to 30 hours. In Example 5, the cooling rate to 200°C after heating is less than 5°C / h. Therefore, in Examples 1 to 5, the differences in flatness and root mean square height, namely (F2-F1) in Examples 1 to 3, (F4-F3) in Examples 4 and 5, (H2-H1) in Examples 1 to 3, and (H4-H3) in Examples 4 and 5, are all small, and it is determined that stable impact resistance and stable surface smoothness can be obtained.

[0113] Conversely, as shown in Table 2, in Comparative Example 1, the homogenization process was carried out at a temperature below 540°C; in Comparative Example 2, the holding time at 425°C to 440°C in both the homogenization and hot rolling processes was longer than 0.9 hours; and in Comparative Example 3, the polished disks were not subjected to heat treatment or cooling. Therefore, in Comparative Examples 1 to 3, since the differences in flatness and root mean square height—(F2–F1) in Comparative Example 1, (F4–F3) in Comparative Examples 2 and 3, (H2–H1) in Comparative Example 1, and (H4–H3) in Comparative Examples 2 and 3—were all poor, it was determined that stable impact resistance and stable surface smoothness could not be obtained.

[0114] To investigate the effect of flatness degradation caused by internal strain, the residual stress induced by internal strain in disk blanks made of aluminum alloy was studied by X-ray diffraction using a HUBER multiaxial diffractometer mounted on the deflection electromagnet beamline BL19B2 of SPring-8 (Super Photon Ring, 8 GeV, High Brightness Radiation Facility). For the disk blanks used, disk blank M1 was used where the difference between its flatness F1 before and after heat treatment at 300°C for 1 hour (F2 - F1) satisfied -5 μm ≤ (F2 - F1) ≤ 5 μm, and disk blank M2 was used where (F2 - F1) did not satisfy -5 μm ≤ (F2 - F1) ≤ 5 μm. The residual stress was calculated using the double-exposure method described in the reference: “Double-Exposure Method for Measuring Coarse-Grained Stress,” Materials, Vol. 68 (2019), pp. 312-313. It should be noted that this measurement was performed under project number 2023B1568 of SPring-8. The disk blank had an outer diameter of 98 mm, an inner diameter of 24 mm, and a thickness of 0.52 mm. The measurement area was a radial region of 37 mm from the inner circumference to the outer circumference, and a region ±5 mm (10 mm wide) in a direction orthogonal to the radial direction, with measurements taken at 1 mm intervals in both the radial and orthogonal directions. It should be noted that a sample radially cut at least 8 mm from the measurement area was used as the test piece. The X-ray energy was 20 keV, and the entrance slit size was 0.5 × 0.2 mm. 2 Analysis was performed using {420} diffraction of aluminum. After calculating the residual stress, the absolute value E of the value (C / D) was calculated. This value (C / D) is the difference C between the sum of residual stresses A at multiple measurement points in the region from the center of the thickness to the front surface and the sum of residual stresses B at multiple measurement points in the region from the center of the thickness to the back surface, divided by the average value D of A and B. It should be noted that tensile residual stress is represented by "+", and compressive residual stress is represented by "-". The residual stress is 30 MPa or lower. The E for disk blank M1 is 3.6, and the E for disk blank M2 is 4.7. It can be considered that when E is larger, the difference in residual stress between the front and back surfaces is larger, that is, the internal strain is larger, and the flatness variation is larger. Therefore, E is preferably 4.0 or smaller, more preferably 3.8 or smaller.

[0115] Industrial applicability According to the present invention, even when the thickness is reduced, disk blanks and disks with stable impact resistance can be obtained.

Claims

1. A disk blank for a hard disk, wherein (F2-F1) satisfies -5 μm ≤ (F2-F1) ≤ 5 μm, and (F2-F1) is the difference 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.

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

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

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

5. A disk having (F4-F3) satisfying -5 μm ≤ (F4-F3) ≤ 5 μm, where (F4-F3) 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.

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

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

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

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

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

11. The disk blank according to claim 1 or 2, wherein the absolute value E of its value (C / D) is 4.0 or less, said value (C / D) is obtained by dividing C by the average value D of A and B, where A is the sum of residual stresses at a plurality of measurement points in the region from the center of the thickness to the front surface in the thickness direction of the disk blank, B is the sum of residual stresses at a plurality of measurement points in the region from the center of the thickness to the back surface in the thickness direction of the disk blank, and C is the difference between the sum A and the sum B.

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