Aluminum alloy substrate for magnetic disks

Abstract

This invention provides an aluminum alloy substrate for magnetic disks that is less prone to minute defects such as blistering, has good surface smoothness and flatness, and effectively suppresses the occurrence of head crashes, as well as a method for manufacturing the same and a method for measuring residual stress. [Solution] In crystal orientation analysis by electron backscatter diffraction (EBSD) on the surface, the average KAM value of the aluminum alloy substrate 1 for magnetic disks is 1.0 degrees or less, and it is preferable that the substrate has undergone surface grinding treatment, and that the flatness (PV value) is 20.0 μm or less.

Description

[Technical Field]

[0001] The present invention relates to an aluminum alloy substrate for magnetic disks. More specifically, it relates to an aluminum alloy substrate for magnetic disks that is less prone to minute defects such as blistering, has good surface smoothness and flatness, and can effectively suppress the occurrence of head crashes, a method for measuring residual stress for evaluating the substrate, and a method for manufacturing the substrate. [Background technology]

[0002] Reducing head crashes in hard disk drives (hereinafter sometimes referred to as "HDDs") has long been a critical issue. Physical errors such as crashes can lead to malfunctions such as errors during data reading and writing. In recent years, in order to cope with the rapid spread of cloud computing and other factors, there has been a growing demand for high-capacity HDD devices that can handle the increasing amount of data to be recorded. Against this backdrop, the development of magnetic disk substrates that can further reduce the occurrence of malfunctions such as crashes, suitable for high-capacity HDD devices, is becoming increasingly important.

[0003] The amount of data recorded on an HDD can be increased by thinning the magnetic disk substrate and increasing the number of magnetic disks mounted. Furthermore, by increasing the diameter of the magnetic disk and positioning the data area on the disk surface as close to the outer edge as possible, the data area per magnetic disk can be expanded.

[0004] However, in HDD devices equipped with numerous thin magnetic disks, the spacing between magnetic disks or between magnetic disks and components such as magnetic heads becomes narrower, making contact between magnetic disks or between magnetic disks and magnetic heads more likely. With larger diameter magnetic disks, crashes caused by undulations on the outer edge also become more likely. To prevent such crashes, it is important to improve the surface smoothness and flatness of the magnetic disks.

[0005] As a technology to improve the smoothness and flatness of magnetic disks, for example, Patent Document 1 discloses a magnetic disk substrate in which the amount of height deviation at the outer edge is specified. Patent Document 2 focuses on the arithmetic mean height Sa on the substrate surface, as described below, and discloses a magnetic disk substrate in which the maximum value of Sa in the outer edge region of the disk is 0.50 nm or less and the standard deviation is 0.10 nm or less. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2013-16214 [Patent Document 2] Patent No. 7318146 [Overview of the project] [Problems that the invention aims to solve]

[0007] Conventionally, improvements to the smoothness and flatness of magnetic disks have mainly been attempted by smoothing the magnetic disk substrate. However, even if the surface smoothness and flatness of the magnetic disk substrate are good, minute defects such as blistering may occur when it is processed into a magnetic disk. The substrate studied in Patent Document 1 had a relatively small outer diameter and a thickness exceeding 0.635 mm, so such minute defects were unlikely to be a problem. However, in recent thin-walled, large magnetic disks, even blistering of a few nanometers in height may cause crashes, and further improvements in surface smoothness and flatness are required.

[0008] The magnetic disk substrate described in Patent Document 2 is thin yet suppresses surface waviness, making head crashes less likely even in high-capacity HDD devices. However, considering the increasing capacity of HDD devices in recent years, it is important to further suppress minute defects on the magnetic disk surface.

[0009] The present invention aims to provide an aluminum alloy substrate for magnetic disks that is less prone to minute defects such as blistering, has good surface smoothness and flatness, and can effectively suppress the occurrence of head crashes, a method for measuring residual stress for evaluating the substrate, and a method for manufacturing the substrate. [Means for solving the problem]

[0010] As a result of diligent research, the inventors have discovered that if an aluminum alloy substrate for magnetic disks has an average KAM value of 1.0 degrees or less in crystal orientation analysis by electron backscatter diffraction on the surface, it is less likely to produce minute defects such as blistering during processing into magnetic disks, and as a result, crashes within HDD devices can be suppressed. This led to the completion of the present invention.

[0011] To achieve the above objective, the gist of the present invention is as follows. (1) An aluminum alloy substrate for magnetic disks, wherein the average value of KAM in a specific region is 1.0 degrees or less in crystal orientation analysis by electron backscatter diffraction (EBSD) on the surface. (2) The aluminum alloy substrate is the aluminum alloy substrate for magnetic disks as described in (1) above, which is the substrate after surface grinding treatment. (3) An aluminum alloy substrate for magnetic disks according to (1) or (2) above, wherein the flatness (PV value) is 20.0 μm or less. (4) An aluminum alloy substrate for magnetic disks, any of the above (1) to (3), having a thickness of less than 0.50 mm. (5) A method for measuring residual stress in an aluminum alloy substrate for magnetic disks, characterized in that a measurement area of ​​300 μm × 300 μm is measured on the surface of the aluminum alloy substrate using electron backscatter diffraction (EBSD) with a step size of 0.2 μm. (6) The aluminum alloy substrate is the substrate after surface grinding treatment, and the method for measuring residual stress of the aluminum alloy substrate for magnetic disks as described in (5) above. (7) When manufacturing the aluminum alloy substrate for a magnetic disk according to any one of (1) to (4) above, it has a surface grinding process for grinding the surface of the aluminum alloy substrate, wherein the surface grinding process uses a grinding wheel with a particle size of 800 or more and 4000 or less, and a grinding fluid with a surfactant content of 0.02% by mass or more and 0.2% by mass or less, and the pressure is 50 gf / cm 2 or more and 150 gf / cm 2 or less, the relative speed between the aluminum alloy substrate and the grinding wheel is 10 m / min or more and 300 m / min or less, and the flow rate of the grinding fluid is 100 mL / min or more and 1000 mL / min or less. A method for manufacturing an aluminum alloy substrate for a magnetic disk, characterized in that it is performed under these conditions. (8) A method for manufacturing an aluminum alloy substrate for a magnetic disk according to (7) above, further comprising an annealing process for annealing the aluminum alloy substrate after the surface grinding process at 200°C or more and 300°C or less for 0.1 hour or more and 10.0 hours. A method for manufacturing an aluminum alloy substrate for a magnetic disk.

Effect of the Invention

[0012] According to the present invention, there are provided an aluminum alloy substrate for a magnetic disk that is less likely to generate minute defects such as bulges, has good surface smoothness and flatness, and can effectively suppress the occurrence of head crashes, a residual stress measurement method for evaluating the substrate, and a manufacturing method for the substrate.

Brief Description of the Drawings

[0013] [Figure 1] It is a conceptual diagram for explaining the mechanism of bulge generation on the surface when manufacturing a magnetic disk from an aluminum alloy substrate for a magnetic disk. [Figure 2] It is a schematic diagram of a KAM map for the aluminum alloy substrate for a magnetic disk of Example 1 according to the present invention, showing side by side the schematic diagrams of the KAM map before and after heat treatment. [Figure 3]It is a schematic diagram of a KAM map for the aluminum alloy substrate for a magnetic disk of Comparative Example 1, and schematic diagrams of the KAM map before and after heat treatment are shown side by side for two locations that gave typical measurement results. [Figure 4] It is a conceptual diagram for explaining the measurement locations of KAM values in the aluminum alloy substrate for a magnetic disk according to the present invention. [Figure 5] It is a flowchart showing an example of the manufacturing process of the aluminum alloy substrate for a magnetic disk according to the present invention.

Embodiments for Carrying Out the Invention

[0014] Hereinafter, the aluminum alloy substrate for a magnetic disk according to the present invention, its manufacturing method, etc. will be described in detail based on embodiments, but the present invention is not limited to these embodiments.

[0015] ≪Aluminum Alloy Substrate for Magnetic Disk≫ The aluminum alloy substrate for a magnetic disk according to an embodiment of the present invention is an aluminum alloy substrate for a magnetic disk having an average value of KAM of 1.0 degrees or less in crystal orientation analysis by the electron backscatter diffraction (EBSD) method on the surface.

[0016] <Electron Backscatter Diffraction>[ The electron backscatter diffraction (Electron Back Scatter Diffraction Pattern: EBSD) method is an analytical technique for irradiating the surface of a crystalline material inclined at an angle such as 70° with an electron beam and analyzing the obtained diffraction pattern (EBSD pattern). It is possible to determine the crystal orientation and crystal system of the irradiation location, and it is also possible to analyze the internal stress and strain of the sample. In particular, by introducing an EBSD device into an electron microscope (SEM), the crystal orientation in a minute region can be measured with high resolution, so it is widely used as a material evaluation technique.

[0017] (KAM) KAM (Kernel Average Misorientation) is a value that represents the azimuth difference between pixels at a measurement point in EBSD (Evidence-Based Spheroidal Discharge) measurement. For example, if the pixels are square, the KAM value can be calculated by averaging the azimuth differences between a given pixel and four adjacent pixels. Since the KAM value corresponds to the dislocation density, it is used for quantitative evaluation of plastic strain caused by dislocation motion.

[0018] Here, the average value of KAM in this application refers to the KAM value of a specific region (for example, 300 μm × 300 μm) when the KAM values ​​of that region are mapped. The KAM value of that region is expressed as the average of the KAM values ​​of each pixel in that specific region.

[0019] The inventors have found that aluminum alloy substrates for magnetic disks with an average KAM value of 1.0 degrees or less are less prone to developing minute defects such as blistering during processing into magnetic disks. Therefore, they can be processed into magnetic disks with good surface smoothness and flatness, making them less susceptible to head crashes in HDD devices. These effects are particularly pronounced in aluminum alloy substrates for magnetic disks with an average KAM value of 0.8 degrees or less, especially 0.7 degrees or less, and even 0.5 degrees or less. While there are no specific restrictions on the lower limit of the average KAM value, from a practical standpoint, it can be, for example, 0.1 degrees or higher, or 0.2 degrees or higher. For example, any aluminum alloy substrate for magnetic disks with an average KAM value of 0.1 to 1.0 degrees, or 0.2 to 0.5 degrees, would suffice.

[0020] Here, "blistering" refers to a convex, microscopic defect that appears on the surface of the plating layer. The Al alloy composition at the blistered area is the same as or nearly the same as the surrounding area.

[0021] Although this invention is not limited by any particular theory, one possible reason why the aluminum alloy substrate for magnetic disks in this embodiment is less prone to generating minute defects during processing is that internal distortion of the substrate is eliminated or reduced. Even if the surface of an aluminum alloy substrate for magnetic disks is flat, if internal distortion remains, it can be released during processing, causing deformation of the upper layer of the substrate. In the aluminum alloy substrate for magnetic disks in this embodiment, such distortion is absent, which may suppress the generation of minute defects in subsequent processing steps.

[0022] The mechanism by which microscopic defects occur on the surface of a magnetic disk due to internal strain in the substrate is not entirely clear, but it is presumed that microscopic defects occur on the surface through a mechanism such as that shown in Figure 1. Specifically, as shown in Figure 1(a), if foreign matter 2 is present on the surface of the aluminum alloy substrate 1 for magnetic disks, an external force acts on the inside of the substrate through this foreign matter during subsequent processes such as grinding of the substrate surface, causing strain 3 (Figure 1(b)). Since the foreign matter 2 itself is removed in subsequent processes such as grinding and cleaning, the surface of the aluminum alloy substrate 1 for magnetic disks becomes flat, but the internal strain 3 may remain. If a plating layer 4 is formed in this surface state, even if the surface of the plating layer 4 is flat as shown in Figure 1(c), the residual internal strain 3 of the aluminum alloy substrate 1 is released during subsequent heating processes such as heating and annealing, and the effect of the released strain 3 is transferred to the plating layer 4. As a result, it is thought that microscopic defects such as blistering occur on the surface of the plating layer 4 (Figure 1(d)).

[0023] The aluminum alloy substrate for magnetic disks in this embodiment has an average KAM value of 1.0 degrees or less, meaning it contains little to no internal strain. Therefore, even if heat treatment such as annealing is applied during processing into a magnetic disk, it is unlikely to produce minute defects such as blistering. As shown in the examples described later, even when the aluminum alloy substrate for magnetic disks in this embodiment is heated to a temperature of around 260°C, which is a typical annealing condition, no region with an average KAM value of 1.0 degrees or higher appears (Figure 2), and there is almost no change in the crystal orientation analysis results (KAM mapping) (Example 1 described later). In other words, because the aluminum alloy substrate for magnetic disks in this embodiment has little to no internal strain, changes in crystal orientation due to strain release are unlikely to occur when it is processed into a magnetic disk. Therefore, it is considered unlikely that minute defects such as blistering will occur on the surface of the plating layer 4.

[0024] Figure 3 shows representative examples of KAM maps obtained by crystal orientation analysis before and after heating for a typical aluminum alloy substrate for magnetic disks (Comparative Example 1, described later). Unlike Figure 2, which analyzes the aluminum alloy substrate for magnetic disks of this embodiment, Figure 3 shows regions where the average KAM value is 1.0 degrees or higher (actually greater than 1.0 degrees). In addition, in typical aluminum alloy substrates for magnetic disks, there are also areas where the KAM map changes significantly before and after heating. Thus, aluminum alloy substrates for magnetic disks that have regions where the average KAM value is greater than 1.0 degrees carry the risk of developing minute defects such as blistering on the surface during processing into magnetic disks.

[0025] (Measurement of KAM value) The KAM value can be determined through crystal orientation analysis using the EBSD method, but there are no particular restrictions on the method of crystal orientation analysis. Furthermore, it is preferable to analyze the Nearest neighbor, which represents the adjacent range for determining the crystal orientation difference, using the 3rd method.

[0026] There are no particular restrictions on the conditions for EBSD measurement. For example, the measurement may be performed by irradiating the sample with an electron beam at an inclination angle of about 70°. The measurement is preferably performed in a measurement area of, for example, 300 μm × 300 μm with a step size of 0.2 μm, particularly about 0.1 μm. It is also preferable to use an EBSD device incorporated into an electron microscope such as an FE-SEM. By using it in combination with an SEM, it becomes easier to perform crystal orientation analysis in even smaller areas with even higher resolution.

[0027] EBSD measurement may be performed on at least one surface of the aluminum alloy substrate for magnetic disks, preferably at one or more locations on both surfaces. For example, measurements may be taken on a 300 μm × 300 μm measurement area on the surface of the aluminum alloy substrate for magnetic disks, preferably 500 μm × 500 μm, more preferably a square area of ​​about 1 mm × 1 mm, or a hexagonal area.

[0028] There are no particular restrictions on the number of EBSD measurement points; measurement can be performed at any single point on the substrate surface. From the standpoint of ensuring accuracy, it is preferable to have two or more measurement points, particularly three or more. From the standpoint of ease of operation, for example, there may be 16 points or less, preferably 12 points or less, and more preferably 8 points or less. Specifically, as shown in Figure 4, for example, a virtual circle 12 is assumed to be a concentric circle with radius r12 of about 2 / 3 to 4 / 5 of the outer edge 11 (radius r11) of the aluminum alloy substrate 10 for magnetic disks. One example is to measure the KAM value at four measurement points 13 that are tangent to the inside of this virtual circle 12 and are positioned at equal intervals (90 degrees in Figure 4), and then calculate the average value.

[0029] Prior to EBSD measurement, analysis using differential interferometry, Raman mapping, polarizing microscopes, phase-contrast microscopes, etc., may be performed. Raman spectral peaks are useful for detecting residual stress and strain because their wavenumber may shift when stress is applied to the sample. Polarizing microscopes and phase-contrast microscopes can also rapidly detect minute foreign matter. These analytical techniques have a wide measurement area and can be used to pinpoint areas where strain may be occurring. Therefore, by analyzing the surface of the aluminum alloy substrate for magnetic disks using these techniques, and then focusing EBSD measurements on areas where signs of strain or foreign matter are detected, it becomes possible to efficiently identify areas where the KAM value exceeds 1.0. As a result, it becomes possible to more reliably exclude aluminum alloy substrates for magnetic disks that are at risk of developing blistering or other defects.

[0030] Furthermore, internal strain in the aluminum alloy substrate for magnetic disks occurs, as described above, for example, during the surface grinding process of the substrate. Therefore, it is preferable to measure the KAM value on the aluminum alloy substrate for magnetic disks at the point when the surface grinding process has been completed. In one embodiment of the present invention, the aluminum alloy substrate includes the above-mentioned aluminum alloy substrate, which is the substrate at the point when the surface grinding process has been completed. Specific manufacturing methods for the aluminum alloy substrate for magnetic disks, such as surface grinding, will be described later.

[0031] If an aluminum alloy substrate for magnetic disks has an average KAM value of 1.0 degree or less, as described above, it is less likely to produce minute defects such as blistering during processing of the magnetic disk, and as a result, head crashes can be suppressed. Below, the material, shape, etc. of the substrate that makes up such an aluminum alloy substrate for magnetic disks will be described.

[0032] <Aluminum alloy substrate> The aluminum alloy substrate in this embodiment can be any substrate made of aluminum alloy, and various known types can be used. Aluminum alloy substrates are suitable as substrates for magnetic disks because they are less prone to defects, have good mechanical properties and processability, and are low cost.

[0033] (Material of the circuit board) There are no particular restrictions on the material of the aluminum alloy substrate. For example, conventionally used alloys include those containing elements such as magnesium (Mg), copper (Cu), zinc (Zn), and chromium (Cr), but are not limited to these. It may also be a material mainly composed of aluminum (Al) rather than an alloy. Furthermore, from the viewpoint of improving rigidity, it may be an alloy containing elements such as iron (Fe), manganese (Mn), and nickel (Ni).

[0034] Examples of aluminum alloy compositions include compositions where Al is the main component, and one or more components selected from the group consisting of 10% or less Mg, 0.300% or less Cu, 0.60% or less Zn, 0.0020% or less Be, 0.30% or less (especially 0.20% or less Cr), 1.70% or less Mn, 0.600% or less Fe, 0.20% or less Ti, 0.20% or less Zr, 0.10% or less Sr, 0.10% or less Na, 0.600% or less Si, and 0.10% or less P, along with unavoidable impurities. With aluminum alloys of such compositions, aluminum alloy substrates for magnetic disks with an average KAM value of 1.0 or less can be prepared more easily. Note that in the compositions above and below, "%" all mean "mass%".

[0035] Examples of specific compositions for the above-mentioned aluminum alloy include, for example, a composition containing Mg: 2.0-6.0%, Cu: 0.005-0.150%, Zn: 0.05-0.60%, Cr: 0.01-0.30%, Fe: 0.001-0.030%, and Si: 0.001-0.030%, with the remainder being Al and unavoidable impurities. Furthermore, other components may be included, for example, at a concentration of 0.1% or less for each element and 0.3% or less in total.

[0036] Other specific examples of aluminum alloy compositions include those containing Mg: 1.0-6.5%, Cu: 0-0.070%, Zn: 0-0.60%, Fe: 0-0.50%, Si: 0-0.50%, Cr: 0-0.20%, Mn: 0-0.50%, Zr: 0-0.20%, and Be: 0-0.0020%, with the remainder being Al and unavoidable impurities.

[0037] As the aluminum alloy, alloys in the A5,000 series or A8,000 series, particularly A5086, may be used. Such alloys are less prone to defects in the substrate and can provide sufficient mechanical properties. A5086 contains Mg: 3.5-4.5%, Fe: 0.50% or less, Si: 0.40% or less, Mn: 0.20-0.7%, Cr: 0.05-0.25%, Cu: 0.10% or less, Ti: 0.15% or less, and Zn: 0.25% or less, with the remainder being Al and unavoidable impurities.

[0038] As the aluminum alloy, an aluminum-iron alloy can also be used. Aluminum-iron alloys are generally alloys that contain Fe, an essential element, and one or two of the optional elements Mn and Ni. More preferably, the total content of Fe, Mn, and Ni is 1.00 to 7.00 mass%, and particularly preferably, the alloy further contains one or more of the following elements: Si: 14.0 mass% or less, Zn: 0.7 mass% or less, Cu: 1.0 mass% or less, Mg: 3.5 mass% or less, Cr: 0.30 mass% or less, and Zr: 0.20 mass% or less, with the remainder being aluminum and unavoidable impurities and other trace elements. These aluminum-iron alloys are highly rigid and resistant to deformation, making them useful as substrates for magnetic disks in this embodiment.

[0039] (Flatness of the substrate) The aluminum alloy substrate for magnetic disks in this embodiment preferably possesses good surface smoothness and flatness. For example, if the flatness PV value of the magnetic disk is 20.0 μm or less, particularly 15.0 μm or less, and especially 10.0 μm or less, the risk of crashing is low and physical errors are less likely to occur even when many disks are mounted in an HDD device. As one embodiment of the present invention, the above-mentioned aluminum alloy substrate for magnetic disks has a flatness (PV value) of 20.0 μm or less.

[0040] Here, flatness PV is the difference between the highest point (P) and the lowest point (V) when the height (roughness) of the main surface of the substrate is measured across the entire surface, after determining a plane that fits differentially to the main surface of the substrate using the least squares method. Flatness PV represents the flatness of the entire substrate, including not only the surface roughness but also the waviness and unevenness of the substrate itself. Here, flatness may be measured on both main surfaces, and the higher value may be used as the flatness of the measured substrate.

[0041] Furthermore, a small PV value is preferable for aluminum alloy substrates for magnetic disks, etc., from the viewpoint of shape evaluation. If the flatness PV is large, when measuring the surface shape of the substrate with an optical inspection device, in the optical system where the measurement light emitted from the inspection device is reflected off the substrate surface and returned to the sensor of the inspection device, some of the reflected measurement light may not return to the sensor of the inspection device, making it impossible to evaluate the surface shape of the desired area. On the other hand, if the PV is small, for example, 20.0 μm or less, the surface shape can be evaluated without problems using an optical inspection device. Also, if the PV is small, such as 20.0 μm or less, errors such as head crashes in HDDs can be suppressed. Although there is no lower limit to the PV, 0.1 μm or 0.2 μm is preferable from a manufacturing standpoint.

[0042] Flatness can also be evaluated by the arithmetic mean height Sa. Sa is the arithmetic mean of the absolute difference in height between each point on the substrate surface relative to the mean plane, i.e., the arithmetic mean height in three dimensions. In this embodiment, the aluminum alloy substrate for magnetic disks preferably has a maximum value of 0.50 nm or less, particularly 0.40 nm or less, when the arithmetic mean height Sa, as defined in ISO 25178, is measured in the mid-wavelength region using scanning optical interferometry through a Gaussian filter with a cutoff wavelength of 1.0 mm in multiple viewing regions located in the outer peripheral region of at least one side. The lower limit of Sa is not limited, but from a manufacturing standpoint, 0.05 μm, 0.1 μm, or 0.2 μm is preferred.

[0043] Furthermore, the contour curve of the substrate surface can be divided into a waviness curve consisting of long wavelengths and a roughness curve consisting of short wavelengths. The wavelength at which it is suitable to detect (extract) only the contour curve (e.g., waviness curve) in the wavelength range to be detected, and to not detect other contour curves (e.g., roughness curve), is the "cutoff wavelength" mentioned above. For example, by using a Gaussian filter to remove the roughness components on the shorter wavelength side and the larger waviness components on the longer wavelength side that are far from the cutoff wavelength, that is, by measuring in the medium wavelength region centered on the cutoff wavelength of 1.0 mm, it is possible to evaluate only minute waviness components. Also, the "outer edge region" refers to the area enclosed by the outer edge of the substrate and a virtual circle defined a few mm inward from that outer edge (for example, virtual circle 12 in Figure 4).

[0044] (Circuit board size) As described above, the aluminum alloy substrate for magnetic disks of this embodiment is less prone to minute defects such as blistering, and has good surface smoothness and flatness. Therefore, magnetic disks based on the aluminum alloy substrate for magnetic disks of this embodiment are less likely to crash even when many are mounted in an HDD device. This effect is particularly noticeable in magnetic disks with a thickness of 0.60 mm or less or 0.50 mm or less, and especially in thin-walled magnetic disks with a thickness of less than 0.5 mm, for example, 0.48 mm or less, and even 0.38 mm or less. This is because such thin-walled substrates are more susceptible to the effects of residual strain. For similar reasons, the effect of this embodiment is particularly noticeable in magnetic disks with an outer diameter of, for example, 65 mm or more, especially 80 mm or more, and especially 95 mm or more. As one embodiment of the present invention, the aluminum alloy substrate for magnetic disks has a thickness of less than 0.50 mm, and furthermore, the aluminum alloy substrate for magnetic disks has an outer diameter of 80 mm or more.

[0045] <Magnetic disk> As another embodiment of the present invention, the present invention also includes a magnetic disk based on the aluminum alloy substrate for magnetic disks of the above embodiment. Such a magnetic disk can be used as a magnetic disk for any recording method. For example, perpendicular magnetic recording (PMR) and surface magnetic recording (SMR) are preferably used as high-capacity magnetic disks for data centers. To achieve even higher capacities, energy-assisted magnetic recording technologies such as heat-assisted magnetic recording (HAMR) and microwave-assisted magnetic recording (MAMR) have been developed, and research is also underway on using bit pattern media to further increase the recording density on the surface. The magnetic disk of this embodiment is suitable for these applications.

[0046] ≪Method for measuring residual stress≫ The following describes a method for measuring residual stress in an aluminum alloy substrate or magnetic disk for a magnetic disk according to the above-described embodiment, based on a typical embodiment.

[0047] Another embodiment of the present invention is a method for measuring residual stress in an aluminum alloy substrate for magnetic disks, characterized in that a measurement area of ​​300 μm × 300 μm is measured on the surface of the aluminum alloy substrate using electron backscatter diffraction (EBSD) with a step size of 0.2 μm.

[0048] The conditions for EBSD measurement and the like in this embodiment are the same as those described for the embodiment of the aluminum alloy substrate for magnetic disks. In the residual stress measurement method of this embodiment, it is preferable that the aluminum alloy substrate to be measured is the substrate at the point when surface grinding treatment has been performed.

[0049] The residual stress measurement method of this embodiment allows for the selection of aluminum alloy substrates for magnetic disks that are less prone to developing minute defects such as blistering in subsequent processes, prior to processing into magnetic disks. This selection method can also be applied to substrates other than aluminum alloys for magnetic disks, such as metals, glass, ceramics, and resins.

[0050] (Application to glass substrates) Glass substrates are suitable for use as substrates for magnetic disks because they are less prone to defects, have good mechanical properties and processability, and are also resistant to plastic deformation. When applying the residual stress measurement method of this embodiment to a glass substrate for magnetic disks, it is preferable to select substrates with an average KAM value of 1 degree or less, and especially 0.5 degrees or less.

[0051] There are no particular restrictions on the material of the glass substrate. Examples include aluminosilicate glass, soda-lime glass, soda-aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, and even physically strengthened glass or chemically strengthened glass that has undergone treatment such as air cooling or liquid cooling. However, it is not limited to these. Among these, aluminosilicate glass is preferred. Substrates made of such materials are excellent in terms of flatness and strength, and can also have good long-term reliability.

[0052] ≪Manufacturing method for aluminum alloy substrates for magnetic disks≫ Below, we will again describe the manufacturing method of an aluminum alloy substrate for magnetic disks based on an embodiment. Figure 5 shows a flowchart of a typical embodiment of the manufacturing method of an aluminum alloy substrate for magnetic disks.

[0053] In Figure 5, the steps of preparing the aluminum alloy components (step S101), casting the aluminum alloy (step S102), homogenization treatment (step S103), hot rolling (step S104), and cold rolling (step S105) are processes for manufacturing an aluminum alloy material by melting and casting, and then forming it into an aluminum alloy sheet. Next, a disk blank made of aluminum alloy is manufactured by blanking and pressure flattening treatment (step S106). Then, pre-treatment such as cutting and grinding (step S107) is performed on the manufactured disk blank to produce an annular aluminum alloy sheet. In the above embodiment, it is preferable to measure the residual stress on the substrate after the grinding (surface grinding) process has been completed.

[0054] Next, this substrate (G-sub) is subjected to zincate treatment (step S108) and electroless Ni-P plating (step S109). The resulting aluminum alloy substrate for magnetic disks (also called a "blank substrate") is subjected to rough polishing (step S110) and precision polishing (step S111), and becomes a magnetic disk by adhesion of a magnetic material (step S112). Either rough polishing (step S110) or precision polishing (step S111) may be used. In addition, it is common to subject the substrate to heat treatment such as annealing between precision polishing (step S111) and adhesion of the magnetic material (step S112).

[0055] The following will explain the details of each step, following the flow chart in Figure 5.

[0056] First, a molten aluminum alloy material having the above-mentioned component 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, continuous casting (CC casting) method, etc. (Step S102). Vertical semi-continuous casting is particularly preferred. The manufacturing conditions for the aluminum alloy material in the DC casting method and the CC casting method are as follows.

[0057] In DC casting, molten metal poured through a spout loses heat to the bottom block, the water-cooled mold walls, and the cooling water directly discharged around the outer circumference of the ingot, causing it to solidify and be drawn downward as an aluminum alloy ingot.

[0058] On the other hand, in the CC casting method, molten metal is supplied through a casting nozzle between a pair of rolls (or belt casters, block casters), and thin sheets of aluminum alloy are directly cast by heat dissipation from the rolls.

[0059] The main difference between DC casting and CC casting lies in the cooling rate during casting. CC casting, with its higher cooling rate, is characterized by smaller second-phase particle size compared to DC casting.

[0060] For DC-cast aluminum alloy ingots, homogenization treatment is performed as necessary (step S103). When performing homogenization treatment, it is preferable to perform heat treatment at 280 to 620°C for 0.5 to 30 hours, and more preferably at 300 to 620°C for 1 to 24 hours. If the heating temperature during homogenization treatment is less than 280°C or the heating time is less than 0.5 hours, the homogenization treatment may be insufficient, and there is a risk that the variation in the loss coefficient for each aluminum alloy sheet will be large. If the heating temperature during homogenization treatment exceeds 620°C, there is a risk that melting will occur in the aluminum alloy ingot. Even if the heating time during homogenization treatment exceeds 30 hours, the effect will saturate, and no further significant improvement effect can be obtained.

[0061] Next, the aluminum alloy ingot (DC casting), which has been homogenized as needed, or which has not been homogenized, is hot-rolled to form a sheet material (step S104). The conditions for hot rolling are not particularly limited, but the starting temperature for hot rolling is preferably 250 to 600°C, and the ending temperature for hot rolling is preferably 230 to 450°C.

[0062] Next, the hot-rolled sheet or the cast sheet cast by the CC casting method is cold-rolled to obtain an aluminum alloy sheet of, for example, 0.30 to 0.60 mm thickness (step S105). The cold-rolling conditions are not particularly limited and can be determined according to the required product sheet strength and thickness (thickness dimension), with a rolling ratio of 10 to 95% being preferable.

[0063] Furthermore, it is preferable to perform annealing treatment before or during cold rolling to ensure cold rolling workability. The temperature during annealing treatment is preferably 250 to 500°C, particularly 300 to 450°C. By performing annealing treatment under these conditions, deformation becomes less likely to occur even during long-term use, and good flatness can be maintained. More specific annealing conditions include, for example, holding at 300 to 450°C for 0.1 to 10 hours for batch heating, or holding at 400 to 500°C for 0 to 60 seconds for continuous heating. Here, a holding time of 0 seconds means that cooling occurs immediately after reaching the desired holding temperature.

[0064] Then, the aluminum alloy sheet obtained by cold rolling is punched into a ring shape to form an annular aluminum alloy sheet. Preferably, the annular aluminum alloy sheet is made into a disk blank by blanking and pressure flattening treatment (step S106). The blanking and pressure flattening treatment is performed at a temperature above the recrystallization temperature of the aluminum alloy at 30-60 kg / cm². 2 It is preferable to perform this process under a certain amount of pressure. For example, a flattened blank can be produced by holding it in air at a temperature of 250-500°C, particularly 300-400°C, for 0.5-10 hours, especially 1-5 hours.

[0065] Prior to the subsequent zincate treatment, the disk blank is subjected to cutting and grinding (step S107) and, if necessary, heat treatment (annealing). Here, the grinding of the surface of the aluminum alloy substrate is important for manufacturing an aluminum alloy substrate for magnetic disks that is less prone to minute defects such as blistering in subsequent processes, so this process will be described separately in detail along with the polishing process. It is preferable to clean the aluminum alloy substrate prior to grinding. Water, organic solvents, etc. may be used for cleaning.

[0066] Next, the disk blank surface is degreased, etched, and subjected to zincate treatment (Zn substitution treatment) (step S108). Degreasing can be performed using a commercially available degreasing solution such as AD-68F (manufactured by Uemura Kogyo Co., Ltd.) at a concentration of 200-800 mL / L, a temperature of 40-70°C, and a processing time of 3-10 min. Etching can also be performed by acid etching using a commercially available etching solution such as AD-107F (manufactured by Uemura Kogyo Co., Ltd.) at a concentration of 20-100 mL / L, a temperature of 50-75°C, and a processing time of 0.5-5 min.

[0067] In zincate treatment, a zincate film is formed on the surface of the disk blank. The zincate treatment can be performed using commercially available zincate solutions, preferably at a concentration of 100-500 mL / L, a temperature of 10-35°C, and a treatment time of 0.1-5 minutes. 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 particles can be deposited, forming a uniform zincate film.

[0068] If zincate treatment is performed two or more times, a zinc stripping treatment may be performed in between. The zinc stripping treatment is preferably performed using an HNO3 solution at a concentration of 10-60%, at a temperature of 15-40°C, and for a treatment time of 10-120 seconds (therefore, it is also called "nitric acid stripping treatment"). Furthermore, it is preferable to perform the second and subsequent zincate treatments under the same conditions as the first zincate treatment.

[0069] Furthermore, the zincate-treated disk blank surface is subjected to a pre-treatment for magnetic material adhesion, such as electroless Ni-P plating (step S109). The electroless Ni-P plating is preferably performed using a commercially available plating solution, such as Nimden® HDX manufactured by Uemura Kogyo Co., Ltd., under conditions of Ni concentration: 3-10 g / L, temperature: 80-95°C, and processing time: 30-180 minutes.

[0070] After electroless Ni-P plating, the plated surface is subjected to polishing as described below (steps S110-S111) to create a substrate for magnetic disks. A magnetic material is attached to this substrate (step S112), and if desired, it is laminated to manufacture magnetic disks such as hard disks. The magnetic material can be attached by sputtering, for example.

[0071] As described above, it is common to include an annealing step between step S111 and step S112. Annealing has advantages such as releasing processing stress during the polishing process and suppressing deformation of the substrate in subsequent processes. Annealing is generally performed at a temperature of 150 to 300°C, especially around 250 to 300°C, for 1 to 60 minutes, especially around 10 to 30 minutes.

[0072] <Grinding process> There are no particular limitations on the grinding method in this embodiment, and it can be carried out by various known methods. For example, using a grinding wheel with a grit size of 800 to 4000, particularly 3000 to 4000, and a grinding fluid with a surfactant content of 0.02% to 0.2% by mass, particularly 0.10% to 0.15% by mass, and a pressurized pressure of 50 gf / cm² 2 More than 150gf / cm 2 The following, in particular, 60 gf / cm³ 2 More than 100gf / cm 2The following conditions apply: the relative speed between the aluminum alloy substrate and the grinding wheel is 10 m / min to 300 m / min, particularly 100 m / min to 200 m / min; the flow rate of the grinding fluid is 100 mL / min to 1000 mL / min, particularly 200 mL / min to 600 mL / min; the process should be carried out for, for example, 1 to 10 minutes. A general-purpose double-sided or single-sided grinding machine can be used for grinding.

[0073] (Annealing treatment) As described above, it is preferable to further anneal the aluminum alloy substrate after surface grinding. Annealing can be carried out, for example, at a temperature of 200°C to 300°C for 0.1 hours to 10.0 hours, and particularly at a temperature of 220 to 280°C for 0.5 to 5.0 hours.

[0074] <Polishing process> Aluminum alloy substrates for magnetic disks are generally subjected to a polishing process for flattening before magnetic material is attached. In this polishing process, it is preferable to perform polishing in multiple stages with adjusted abrasive particle diameters. Generally, it is preferable to perform rough polishing and precision polishing using a double-sided simultaneous polishing machine, and this can be done using a commercially available batch-type double-sided simultaneous polishing machine. It is also preferable to perform dummy polishing prior to rough polishing to control the surface of the polishing pad.

[0075] (Double-sided polishing machine) A double-sided simultaneous polishing machine typically comprises an upper and lower platen made of cast iron, a carrier that holds multiple substrates between the upper and lower plates, and polishing pads attached to the substrate contact surfaces of the upper and lower plates. In the polishing process, the carrier typically holds multiple substrates between the upper and lower plates, and each substrate is clamped between the upper and lower plates with a predetermined processing pressure. As a result, each substrate is simultaneously clamped from above and below by the polishing pads. Next, while supplying a predetermined amount of polishing fluid between the polishing pads and each substrate, the upper and lower plates are rotated in opposite directions. At this time, the carrier also rotates on its own axis by a sun gear, causing the substrates to undergo planetary motion. This causes the substrates to slide against the surface of the polishing pads, and both surfaces are polished simultaneously.

[0076] There are no particular restrictions on the type and structure details of the double-sided polishing machine, and any commercially available device may be used. Here, it is preferable that the thickness dimension of the carrier for holding the substrate in the double-sided polishing machine is 0.05 to 0.15 mm smaller than the thickness dimension of the substrate, and more preferably 0.07 to 0.12 mm smaller. With such a carrier, an aluminum alloy substrate for a magnetic disk with good surface smoothness and flatness can be more reliably manufactured in the outer peripheral region.

[0077] (Rough polishing) There are no particular restrictions on the method of the rough polishing process, and it can be carried out under any conditions according to the material of the substrate. For example, rough polishing can be performed using a polishing liquid containing alumina with a particle size of 0.1 to 1.0 μm and a polishing pad made of hard or soft polyurethane or the like. However, the conditions of the rough polishing process are not limited to these, and desired ones can be selected from known polishing process conditions. For example, instead of the above alumina, abrasive grains such as silica, cerium oxide, zirconium oxide, SiC, diamond, etc. with a desired particle size may be used. Here, "hard" refers to those with a hardness (Asker C) of 85 or more measured by the measurement method defined in the Japan Rubber Association Standard Specification (standard compliance: SRIS0101), and "soft" refers to those with a hardness of 60 to 80.

[0078] Specific rough polishing conditions are also affected by the material of the substrate used and the processes (for example, steps S101 to S109) until rough polishing is performed, and it is difficult to uniquely determine them. Also, it is not limited to specific conditions. For example, the polishing time can be 2 to 5 minutes, the rotation speed of the polishing platen can be 10 to 35 rpm, the rotation speed of the sun gear can be 5 to 15 rpm, the polishing liquid supply rate can be 1000 to 5000 mL / min, and the processing pressure can be 20 to 250 g / cm 2 , preferably 20 to 150 g / cm 2 , more preferably 60 to 120 g / cm 2 , and the polishing amount can be set to conditions of 2.5 to 3.5 μm.

[0079] (Dummy polishing) When performing the polishing process, it is preferable to perform dummy polishing to control the surface of the polishing pad prior to the rough polishing described above. Generally, the dummy polishing process is carried out using a dummy substrate and under the same conditions as the rough polishing process, preferably the same conditions. There are no particular restrictions on the dummy substrate used, but it is preferable to use a blank substrate of the same type as the blank substrate of the product, and especially a blank substrate manufactured under the same conditions as the blank substrate of the product.

[0080] This dummy polishing process allows the surface of the polishing pad used in the rough polishing step described above to be adjusted to a suitable state. Note that dummy polishing is an optional step and can be omitted if the polishing pad surface is adjusted and controlled. For example, dummy polishing can be performed prior to the start of the rough polishing batch, and then the adjusted polishing pad can be used to repeat the rough polishing of product blank substrates in multiple batches.

[0081] (Precision polishing) There are no particular restrictions on the method of precision polishing, and it can be carried out using various known methods. For example, it can be done using a polishing solution containing colloidal silica with a particle size of about 0.01 to 0.10 μm and a soft polishing pad. Of course, the conditions for precision polishing are not limited to these. Abrasive grains such as cerium oxide, zirconium oxide, SiC, and diamond of a desired particle size may also be used. Furthermore, through this process, the main surface of the substrate is polished to a mirror finish, and a substrate for magnetic disks is manufactured. It is preferable to wash the polished substrate with a neutral detergent, pure water, IPA, etc.

[0082] The specific conditions for precision polishing are difficult to determine uniquely, as they are influenced by the material of the substrate used and the processes up to rough polishing, and are not limited to specific conditions. For example, a polishing time of 2-5 minutes, a polishing platen rotation speed of 10-35 rpm, a sun gear rotation speed of 5-15 rpm, a polishing fluid supply rate of 1000-5000 mL / min, and a processing pressure of, for example, 10-200 g / cm². 2 Preferably 20-120 g / cm³ 2 Especially 50-100 g / cm³ 2 The polishing amount can be set to 1.0 to 1.5 μm.

[0083] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and includes all aspects included in the concept and claims of the present invention, and can be modified in various ways within the scope of the present invention. [Examples]

[0084] The present invention will be described in more detail below based on examples, but the present invention is not limited thereto.

[0085] [Example 1] Using A5086 alloy (aluminum alloy A), a donut-shaped blank material with an outer diameter (diameter) of 98 mm and an inner diameter of 24 mm was prepared according to the conventional method described above. Furthermore, the inner and outer circumferences were machined, and chamfering was performed on the inner and outer end faces at the same time. Foreign matter of about 20-40 μm in size was intentionally attached to this blank material, and it was annealed at 300°C for 30 minutes (annealing-1).

[0086] Next, after removing any foreign matter that had adhered to the substrate, grinding was performed under the following conditions, followed by further cleaning to obtain a substrate with a thickness of 0.46 mm. • Sharpening stone: #4000 grit silicon carbide (SiC) sharpening stone • Processing pressure: 100 gf / cm² 2 • Grinding plate rotation speed: 30 rpm Coolant (grinding fluid) flow rate: 200 mL / min • Grinding time: 5 minutes

[0087] The cleaned substrate was further annealed at 300°C for 30 minutes (annealing-2), and then at 250°C for 30 minutes (annealing-3). Next, the annealed substrate was subjected to crystal orientation analysis by EBSD, and the first KAM value was measured. The EBSD measurement was performed using a TSL MSC-2200, at the measurement locations shown in Figure 4 (four measurement locations 13 tangent to a virtual circle 10 mm inward from the outer edge, spaced 90 degrees apart from each other; measurement area: 300 × 300 μm), with a measurement step of 1 μm. A schematic diagram of a representative KAM mapping obtained is shown in Figure 2(a). The average value of the first KAM was 0.367 degrees.

[0088] Next, the substrate after measurement was subjected to annealing under general annealing conditions of 260°C for 30 minutes (annealing-4), and after cooling, its appearance was observed using an optical microscope (blister test). In addition, the KAM value was measured a second time to measure the residual strain after annealing-4, and a KAM map and its schematic diagram were created to confirm whether there were any regions where the KAM value had changed from the first KAM map. The results are shown in Table 1 and Figure 2(b) below. No minute defects were observed on the surface during the optical microscope observation in the blister test (〇).

[0089] [Comparative Example 1] The procedure was the same as in Example 1, except that grinding was performed without removing foreign matter after annealing-1. After grinding, the foreign matter had fallen off. The measurement and visual observation results are shown in Table 1 and Figure 3 (schematic diagrams of two representative locations before and after the blister test).

[0090] [Example 2] The procedure was the same as in Example 1, except that Ni-P plating was formed and then rough and fine polishing was performed between annealing-2 and annealing-3. The measurement and visual observation results are shown in Table 1 below. In addition to visual observation, a differential interferometer was used to evaluate for any minute defects that could potentially cause blistering, and it was confirmed that there were no such minute defects.

[0091] Furthermore, Ni-P plating was performed after annealing-2 and subjecting the substrate to conventional degreasing, acid etching, and zincate treatment. The Ni-P plating treatment was carried out using Nimden® HDX electroless plating solution manufactured by Uemura Kogyo Co., Ltd., under the conditions of Ni concentration: 6 g / L, temperature: 88°C, and treatment time: 130 minutes, forming an electroless Ni-P plating film with a thickness of 10 μm on each side.

[0092] Next, both sides (front and back) of the substrate, which had undergone electroless Ni-P plating and annealing, were subjected to rough polishing. The rough polishing was performed on both sides under the following conditions. (rough polishing) • Abrasive grains: Alumina abrasive grains with a particle size of 0.4 μm • Polishing pad: Hard urethane polishing pad with a hardness of 87 • Processing pressure: 100g / cm² 2 • Grinding plate rotation speed: 30 rpm Sun gear rotation speed: 10 rpm ·Polishing liquid supply rate: 3.5L / min • Grinding time: 5 minutes

[0093] After rough polishing, the substrate was washed with pure water and then precision polished to produce a substrate for magnetic disks. Precision polishing was performed on both sides under the following conditions. (Precision polishing) • Abrasive grains: Colloidal silica abrasive grains with a particle size of 0.08 μm • Polishing pad: Foamed urethane polishing pad with a hardness of 76 • Processing pressure: 100g / cm² 2 • Grinding plate rotation speed: 30 rpm Sun gear rotation speed: 10 rpm ·Polishing liquid supply rate: 3.5L / min • Grinding time: 3 minutes

[0094] A differential interferometer was used to check for blistering on the magnetic disk substrate after precision polishing. No blistering was observed.

[0095] [Examples 3-7, Comparative Examples 2-4] Except for changing the manufacturing lot of the aluminum alloy substrate, the procedure in Example 1 was repeated for Examples 3 to 7, and the procedure in Comparative Examples 2 to 4 was repeated for Comparative Example 1. The average values ​​of the G sub-surface KAM and the results of the visual inspection after heat treatment for each example and comparative example are shown in Table 1.

[0096] [Table 1]

[0097] In Example 1 of the present invention, no minute defects were observed on the surface of the aluminum alloy substrate for magnetic disks, even after annealing-4. KAM mapping also showed almost no change in the crystal orientation before and after heating. In Example 2, it was confirmed that no blistering or minute defects occurred after Ni-P plating. Similar results were obtained in Examples 3 to 7 as in Example 1. It was shown that in aluminum alloy substrates for magnetic disks with an average KAM value of 1.0 degrees or less according to the present invention, the crystal orientation hardly changes even after general annealing, and no minute defects such as blistering occur on the surface.

[0098] On the other hand, in Comparative Example 1, where the first KAM value exceeded 1, the crystal orientation state changed slightly before and after heating in the KAM mapping (Figures 3(c)-(d)). Similar results were obtained in Comparative Examples 2-4. This suggests that substrates ground with foreign matter remaining are more likely to release strain during the annealing process, making them prone to blistering.

[0099] Furthermore, the aluminum alloy substrates for magnetic disks in Comparative Examples 1-4 also had flat surfaces after grinding, and no minute defects were observed. This demonstrates the importance of keeping the average KAM value of the aluminum alloy substrate for magnetic disks below 1.0 degrees in order to obtain a magnetic disk free from surface defects such as blistering, and therefore with a reduced risk of head crash. [Explanation of Symbols]

[0100] 1. Aluminum alloy substrate for magnetic disks 2 Foreign object 3. Distortion generation region 4 Plating layer 10. Aluminum alloy substrate for magnetic disks 11 Outer edge 12 virtual yen 13 measurement points r11 Radius of the outer edge 11 r12 is the radius of the virtual circle 12.

Claims

1. An aluminum alloy substrate for magnetic disks, wherein the average value of the KAM in a specific region is 1.0 degree or less, as determined by crystal orientation analysis using electron backscatter diffraction (EBSD) on the surface.

2. The aluminum alloy substrate for a magnetic disk according to claim 1, wherein the aluminum alloy substrate is the substrate after surface grinding treatment.

3. The aluminum alloy substrate for magnetic disks according to claim 1, wherein the flatness (PV value) is 20.0 μm or less.

4. An aluminum alloy substrate for a magnetic disk according to claim 1, wherein the thickness dimension is less than 0.50 mm.

5. A method for measuring residual stress in an aluminum alloy substrate for magnetic disks, characterized in that a measurement area of ​​300 μm × 300 μm on the surface of the aluminum alloy substrate is measured with a step size of 0.2 μm using electron backscatter diffraction (EBSD).

6. The method for measuring residual stress in an aluminum alloy substrate for a magnetic disk according to claim 5, wherein the aluminum alloy substrate is the substrate at the point in time after surface grinding treatment.

7. In manufacturing an aluminum alloy substrate for a magnetic disk according to any one of claims 1 to 4, It has a surface grinding process for grinding the surface of an aluminum alloy substrate, The surface grinding process involves using a grinding wheel with a grit size of 800 to 4000 and a grinding fluid with a surfactant content of 0.02% to 0.2% by mass, with a pressurized pressure of 50 gf / cm². ２ More than 150gf / cm ２ The method for manufacturing an aluminum alloy substrate for a magnetic disk is characterized in that the relative speed between the aluminum alloy substrate and the grinding wheel is 10 m / min or more and 300 m / min or less, and the flow rate of the grinding fluid is 100 mL / min or more and 1000 mL / min or less.

8. A method for manufacturing an aluminum alloy substrate for a magnetic disk according to claim 7, A method for manufacturing an aluminum alloy substrate for a magnetic disk, further comprising an annealing step of annealing the aluminum alloy substrate after the surface grinding step at a temperature of 200°C to 300°C for 0.1 hours to 10.0 hours.

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