Aluminum alloy plate for magnetic disk, aluminum alloy blank for magnetic disk, and aluminum alloy substrate for magnetic disk

Abstract

To provide an aluminum alloy plate for a magnetic disk, an aluminum alloy plate blank for a magnetic disk, and an aluminum alloy plate substrate for a magnetic disk, which have good grindability and are capable of suppressing thermal deformation during magnetic film sputtering.SOLUTION: An aluminum alloy plate for a magnetic disk contains 0.1-7.0 mass % of Mg, 0.005-1.0 mass % of Cr, 3-100 mass ppm of Be, 100 mass ppm or less of Zr, and 0.20 mass % or less of Si. The total of at least one or more of Fe, Mn, and Ni is 0.05-3.0 mass %, and the remainder comprises Al and impurities. The area ratio of an intermetallic compound on a surface is 0.10-40%, and the area ratio is calculated for an intermetallic compound having a maximum length of 0.33 μm or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aluminum alloy plate for a magnetic disk, an aluminum alloy blank for a magnetic disk, and an aluminum alloy substrate for a magnetic disk. [Background technology]

[0002] Recently, substrates have been made more rigid to suppress vibrations caused by thin magnetic disks during rotation. For example, in Patent Documents 1 and 2, in order to improve the rigidity of the substrate, a chemical composition is adopted in which a specific amount of at least one of Fe, Mn, and Ni is added to an aluminum alloy plate, thereby increasing the rigidity of the magnetic disk substrate itself.

[0003] However, improving the rigidity reduces the grindability, which causes a problem of deterioration in the workability of the aluminum alloy plate.

[0004] Patent Document 2 further describes that good grindability can be obtained by controlling the number density of intermetallic compounds by size on the surface of the aluminum alloy plate.

[0005] Furthermore, with regard to substrates for magnetic disks, the index of "flatness" is a very important index since it greatly affects the performance of hard disk drives (HDDs) using the substrate. For example, Patent Document 3 describes an aluminum alloy plate for magnetic disks that has a specific chemical composition, a gradient in the number of compounds in the plate thickness direction that is equal to or greater than a specific value, and excellent flatness.

[0006] Here, as shown in Patent Document 4, it is known that thermal distortion occurs around the gripping portion of a magnetic disk substrate due to thermal expansion that occurs during magnetic film sputtering. Therefore, to obtain a magnetic disk with excellent flatness, it is necessary to suppress deformation of the magnetic disk substrate due to thermal distortion.

[0007] From the viewpoint of suppressing deformation due to thermal strain, for example, Patent Document 5 describes that an aluminum alloy sheet for a cap having a specific chemical composition and having a difference in proof stress in a direction parallel to rolling before and after heat treatment of a specific value or more can exhibit excellent stress relaxation resistance and suppress thermal deformation. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 7132289 [Patent Document 2] Patent No. 6684139 [Patent Document 3] Japanese Patent Application Publication No. 2023-004878 [Patent Document 4] Japanese Patent Publication No. 2022-010156 [Patent Document 5] Patent Publication No. 2021-011621 Summary of the Invention [Problem to be solved by the invention]

[0009] In an aluminum alloy sheet for a magnetic disk, both good grindability and suppression of thermal deformation are important, but there is still room for further study on an aluminum alloy sheet for a magnetic disk that satisfies both of these requirements.

[0010] The present invention has been made in view of the above-mentioned problems, and aims to provide an aluminum alloy plate for magnetic disks, an aluminum alloy plate blank for magnetic disks, and an aluminum alloy plate substrate for magnetic disks, which have good grindability and can suppress thermal deformation during magnetic film sputtering. [Means for solving the problem]

[0011] As a result of extensive research, the present inventors discovered that by using a specific alloy composition and setting the area ratio of intermetallic compounds on the surface to 0.10 to 40%, an aluminum alloy plate for magnetic disks can be obtained that has good grindability and can suppress thermal deformation during magnetic film sputtering, and thus created the present invention.

[0012] That is, the present invention relates to the following. [1] Mg: 0.1~7.0% by mass, Cr:0.005~1.0% by mass, Be: 3 to 100 mass ppm, Zr: 100 mass ppm or less, Si: 0.20% by mass or less, a total of at least one of Fe, Mn, and Ni: 0.05 to 3.0 mass%; the balance being Al and impurities, The area ratio of the intermetallic compound on the surface is 0.10 to 40%, The area ratio is calculated for intermetallic compounds having a maximum length of 0.33 μm or more. [2] the Fe: 0 to 1.00 mass %; the Mn: 0 to 1.0 mass %, and The aluminum alloy plate for magnetic disks according to [1], containing at least one of the Ni: 0 to 1.0 mass %. [3] The aluminum alloy plate for magnetic disks according to [1] or [2], further containing at least one of Cu: 1.0 mass % or less and Zn: 1.0 mass % or less. [4] The aluminum alloy plate for magnetic disks according to [1] or [2], which has a stress relaxation rate of 90% or less. [5] An aluminum alloy blank for magnetic disks obtained from the aluminum alloy plate for magnetic disks according to [1] or [2]. [6] An aluminum alloy substrate for magnetic disks obtained from the aluminum alloy blank for magnetic disks according to [5]. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide an aluminum alloy plate for magnetic disks, an aluminum alloy plate blank for magnetic disks, and an aluminum alloy plate substrate for magnetic disks, which have good grindability and can suppress thermal deformation during magnetic film sputtering. [Brief explanation of the drawings]

[0014] [Figure 1] 1(a) and 1(b) are diagrams for explaining the measurement of the stress relaxation rate in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0015] An aluminum alloy plate for a magnetic disk, an aluminum alloy blank for a magnetic disk, and an aluminum alloy substrate for a magnetic disk according to one embodiment of the present invention will be described below. In the following description, the aluminum alloy plate for magnetic disk, the aluminum alloy blank for magnetic disk, and the aluminum alloy substrate for magnetic disk according to this embodiment may be simply referred to as the "aluminum alloy plate," the "blank," and the "substrate," respectively.

[0016] [Aluminum alloy plates for magnetic disks] The aluminum alloy sheet for magnetic disks according to this embodiment contains 0.1 to 7.0 mass% Mg, 0.005 to 1.0 mass% Cr, 3 to 100 mass ppm Be, up to 100 mass ppm Zr, up to 0.20 mass% Si, a total of 0.05 to 3.0 mass% of at least one of Fe, Mn, and Ni, with the remainder being Al and impurities. The area fraction of intermetallic compounds on the surface is 0.10 to 40%, and this area fraction is calculated for intermetallic compounds with a maximum length of 0.33 μm or more. Here, a maximum length of 0.33 μm or more means that the maximum distance between any two points on the outline of a particle of the intermetallic compound is 0.33 μm or more. The aluminum alloy sheet for magnetic disks according to this embodiment may also contain Cu and Zn. Hereinafter, each component of the aluminum alloy plate for a magnetic disk according to this embodiment will be described in detail.

[0017] (Mg: 0.1 mass% or more and 7.0 mass% or less) Mg is an essential constituent element in the aluminum alloy plate for a magnetic disk according to this embodiment, and is contained in the aluminum alloy plate in order to obtain good yield strength. If the Mg content in the aluminum alloy sheet is less than 0.1% by mass, the above effect cannot be obtained. On the other hand, if the Mg content in the aluminum alloy sheet exceeds 7.0% by mass, the rigidity decreases. Therefore, the Mg content is set to 0.1% by mass or more and 7.0% by mass or less. From the viewpoint of improving yield strength, the Mg content is preferably 0.5 mass% or more, 1.0 mass% or more, 1.5 mass% or more, 1.7 mass% or more, 2.0 mass% or more, 2.2 mass% or more, or 2.5 mass% or more. From the viewpoint of suppressing a decrease in rigidity, the Mg content is preferably 6.5 mass% or less, 6.0 mass% or less, 5.5 mass% or less, 5.0 mass% or less, 4.5 mass% or less, 4.0 mass% or less, or 3.5 mass% or less.

[0018] (Cr: 0.005 mass% or more and 1.0 mass% or less) Cr is an essential constituent element in the aluminum alloy plate for a magnetic disk according to this embodiment, and is contained in the aluminum alloy plate in order to obtain good yield strength. If the Cr content in the aluminum alloy sheet is less than 0.005% by mass, the above effect cannot be obtained. On the other hand, if the Cr content exceeds 1.0% by mass, the intermetallic compounds become coarse, which may cause edge cracks and reduce rollability. Therefore, the Cr content is set to 0.005% by mass or more and 1.0% by mass or less. From the viewpoint of improving yield strength, the Cr content is preferably 0.01 mass% or more, 0.03 mass% or more, 0.05 mass% or more, 0.08 mass% or more, or 0.1 mass% or more, and from the viewpoint of ensuring rollability, it is preferably 0.9 mass% or less, 0.8 mass% or less, 0.7 mass% or less, 0.6 mass% or less, 0.5 mass% or less, 0.4 mass% or less, 0.3 mass% or less, or 0.2 mass% or less.

[0019] (Be: 3 mass ppm or more and 100 mass ppm or less) Be is an essential element in the aluminum alloy plate for magnetic disks according to this embodiment, and has the effect of forming an oxide film during casting to suppress the formation of Mg oxides. It also has the effect of improving the hot rolling property and formability of the aluminum alloy, and further has the effect of weakening the adhesion between blanks by suppressing oxidation during corrective annealing, thereby suppressing deterioration of flatness due to external force during subsequent peeling, thereby achieving excellent flatness. If the Be content is less than 3 ppm by mass, the effect of adding Be cannot be fully obtained. On the other hand, if the Be content exceeds 100 ppm by mass, Be-containing compounds become coarse, which may cause edge cracks and reduce rollability. Therefore, the Be content is set to 3 ppm by mass or more and 100 ppm by mass or less. The Be content is preferably 4 ppm by mass or more, 5 ppm by mass or more, 8 ppm by mass or more, or 10 ppm by mass or more from the viewpoint of fully obtaining the effects of the addition of Be, and is preferably 80 ppm by mass or less, 50 ppm by mass or less, 30 ppm by mass or less, or 20 ppm by mass or less from the viewpoint of ensuring rollability.

[0020] (Zr: 100 mass ppm or less) By adding a small amount of Zr to an aluminum alloy sheet, the grain size of the aluminum alloy ingot can be refined, thereby obtaining good yield strength. However, if the Zr content exceeds 100 ppm by mass, the intermetallic compounds become coarse, which may cause edge cracks and reduce rollability. Therefore, the Zr content is set to 100 ppm by mass or less (including 0.00 ppm by mass). From the viewpoint of suppressing a decrease in rollability, the Zr content is preferably 90 ppm by mass or less, 80 ppm by mass or less, 70 ppm by mass or less, 60 ppm by mass or less, 50 ppm by mass or less, 40 ppm by mass or less, or 30 ppm by mass or less. Although the properties of the present invention are not impaired even when the Zr content is 0 ppm by mass, when Zr is contained, from the viewpoint of improving proof stress, the Zr content is preferably 5 ppm by mass or more, or 10 ppm by mass or more.

[0021] (Si: 0.20% by mass or less) Si is usually mixed into aluminum alloys as an unavoidable impurity in base metal, forming elemental Si or Al-Fe-Si intermetallic compounds. If the Si content exceeds 0.20 mass%, the Young's modulus decreases, and the elemental Si and Al-Fe-Si intermetallic compounds become coarse, resulting in poor rollability. Therefore, the Si content is set to 0.20 mass% or less (including 0.00 mass%). In order to prevent a decrease in Young's modulus and rollability, the Si content is preferably 0.18% by mass or less, 0.15% by mass or less, 0.13% by mass or less, 0.10% by mass or less, 0.08% by mass or less, 0.05% by mass or less, 0.04% by mass or less, 0.03% by mass or less, or 0.02% by mass or less. The lower the Si content, the more desirable it is; even a 0% by mass content does not impair the properties of the present invention; however, high-purity raw materials (such as aluminum ingots and intermediate alloy ingots) are required, resulting in higher costs. Therefore, a Si content of 0.004% by mass or more is industrially preferable.

[0022] (Total of Fe, Mn, and Ni: 0.05 to 3.0 mass%) Fe, Mn, and Ni are components that contribute to improving rigidity and stress relaxation resistance. Therefore, the aluminum alloy sheet for a magnetic disk according to this embodiment contains at least one selected from the group consisting of Fe, Mn, and Ni. That is, the aluminum alloy sheet for a magnetic disk according to this embodiment may contain Fe, Mn, or Ni alone, or two of Fe and Mn, Mn and Ni, or Ni and Fe, or may contain all of Fe, Mn, and Ni, and is not particularly limited as long as the total content thereof is 0.05 to 3.0 mass%. In order to obtain good rigidity and stress relaxation resistance, the total content of Fe, Mn, and Ni is preferably 0.10% by mass or more, 0.2% by mass or more, 0.3% by mass or more, 0.5% by mass or more, 0.8% by mass or more, or 1.0% by mass or more. On the other hand, if these elements are contained in excess, the area ratio of the intermetallic compounds on the surface of the aluminum alloy sheet may increase due to coarsening of the intermetallic compounds, which may result in a decrease in grindability. Therefore, the total content is preferably 3.0% by mass or less, 2.8% by mass or less, 2.6% by mass or less, 2.4% by mass or less, 2.2% by mass or less, 2.0% by mass or less, 1.8% by mass or less, 1.6% by mass or less, 1.4% by mass or less, or 1.2% by mass or less.

[0023] The aluminum alloy plate for a magnetic disk according to this embodiment preferably contains at least one of Fe: 0 to 1.00 mass %, Mn: 0 to 1.0 mass %, and Ni: 0 to 1.0 mass %.

[0024] (Fe: 1.00% by mass or less) Fe is contained in the aluminum alloy sheet to obtain good rigidity and stress relaxation resistance. On the other hand, if the Fe content in the aluminum alloy sheet exceeds 1.00 mass%, coarsening of intermetallic compounds may occur, which may result in a decrease in grindability. Therefore, the Fe content is set to 1.00 mass% or less (including 0 mass%). From the viewpoint of suppressing deterioration of grindability, the Fe content is preferably 0.90% by mass or less, 0.80% by mass or less, 0.70% by mass or less, 0.60% by mass or less, or 0.50% by mass or less. From the viewpoint of obtaining good rigidity and stress relaxation resistance, the Fe content is preferably 0.01% by mass or more, 0.02% by mass or more, 0.05% by mass or more, 0.10% by mass or more, 0.15% by mass or more, 0.25% by mass or more, 0.30% by mass or more, 0.35% by mass or more, or 0.40% by mass or more.

[0025] (Mn: 1.0% by mass or less) Mn is contained in the aluminum alloy sheet to obtain good rigidity and stress relaxation resistance. On the other hand, if the Mn content in the aluminum alloy sheet exceeds 1.0 mass%, coarsening of intermetallic compounds may occur, which may result in a decrease in grindability. Therefore, the Mn content is set to 1.0 mass% or less (including 0 mass%). The Mn content is preferably 0.9 mass% or less, 0.8 mass% or less, 0.7 mass% or less, or 0.6 mass% or less from the viewpoint of suppressing deterioration of grindability, and is preferably 0.05 mass% or more, 0.1 mass% or more, 0.2 mass% or more, 0.3 mass% or more, 0.4 mass% or more, or 0.5 mass% or more from the viewpoint of obtaining good rigidity and stress relaxation resistance.

[0026] (Ni: 1.0% by mass or less) Ni is contained in the aluminum alloy sheet to obtain good rigidity and stress relaxation resistance. On the other hand, if the Ni content in the aluminum alloy sheet exceeds 1.0 mass%, coarsening of intermetallic compounds may occur, which may result in a decrease in grindability. Therefore, the Ni content is set to 1.0 mass% or less (including 0 mass%). The Ni content is preferably 0.9 mass% or less, 0.8 mass% or less, 0.7 mass% or less, 0.6 mass% or less, or 0.5 mass% or less from the viewpoint of suppressing deterioration of grindability, and is preferably 0.1 mass% or more, 0.2 mass% or more, 0.3 mass% or more, or 0.4 mass% or more from the viewpoint of obtaining good rigidity and stress relaxation resistance.

[0027] (Cu: 1.0 mass% or less, Zn: 1.0 mass% or less) Cu and Zn are components that broaden the solid-liquid coexistence region and contribute to reducing the frequency of molten metal leakage during casting. They are also components that have the effect of uniformly precipitating zinc in zincate treatment, and also contribute to improving plating smoothness. On the other hand, excessive Cu or Zn may actually deteriorate the plating smoothness. Furthermore, the smoothness of the electroless Ni-P plating film formed on the surface may be reduced. Therefore, the aluminum alloy sheet for magnetic disks according to this embodiment preferably further contains at least one of Cu: 1.0% by mass or less and Zn: 1.0% by mass or less. From the viewpoint of suppressing deterioration of plating smoothness, the Cu content is preferably 1.0 mass% or less, 0.75 mass% or less, 0.50 mass% or less, 0.35 mass% or less, 0.25 mass% or less, 0.20 mass% or less, 0.10 mass% or less, or 0.05 mass% or less. Furthermore, Cu does not have to be contained, but if it is contained, from the viewpoint of reliably obtaining the effects of adding Cu, it is preferably 0.005 mass% or more. From the viewpoint of preventing a decrease in plating smoothness, the Zn content is preferably 1.0 mass% or less, 0.75 mass% or less, 0.50 mass% or less, 0.35 mass% or less, 0.25 mass% or less, 0.20 mass% or less, 0.10 mass% or less, or 0.05 mass% or less. Zn does not necessarily have to be contained, but if it is contained, it is preferably 0.005 mass% or more from the viewpoint of reliably obtaining the effects of adding Zn.

[0028] (balance: Al and impurities) The aluminum alloy sheet according to this embodiment may contain elements other than those mentioned above as impurities depending on the selection of the raw materials used for melting during ingot production. Specific examples of impurity elements include Ti, V, B, Na, K, Ca, Pb, P, Sn, Ag, Bi, In, Ge, Sr, and Cd. Among these, Ti and V are restricted to 0.10% by mass or less, and B, Na, K, Ca, Pb, P, Sn, Ag, Bi, In, Ge, Sr, and Cd are restricted to 0.05% by mass or less. Within these ranges, these elements do not interfere with the effects of this embodiment, not only when they are contained as unavoidable impurities, but also when they are intentionally added, for example, by increasing the blending ratio of scrap containing these elements. When each element shown as an impurity element is inevitably contained (i.e., when it is an unavoidable impurity), it is preferable that the content of each element is 0.005 mass% or less, and the total content of each element is 0.015 mass% or less. Furthermore, when the chemical composition does not contain the above-mentioned Si, Fe, Mn, Ni, Cu, and Zn, the content of each of these as unavoidable impurities is preferably 0.005 mass % or less.

[0029] <Area ratio of intermetallic compounds on the surface of aluminum alloy plate: 0.10 to 40%> The aluminum alloy plate for magnetic disk according to this embodiment has an area ratio of intermetallic compounds on the surface of 0.10 to 40%, and this area ratio is calculated for intermetallic compounds with a maximum length of 0.33 μm or more. Examples of intermetallic compounds present on the surface include Mg-Si intermetallic compounds, Al-Fe intermetallic compounds, Al-Mn intermetallic compounds, Al-Ni intermetallic compounds, Al-Fe-Mn intermetallic compounds, Al-Fe-Ni intermetallic compounds, Al-Mn-Ni intermetallic compounds, Al-Fe-Mn-Ni intermetallic compounds, Al-Cr intermetallic compounds, Al-Ti intermetallic compounds, and Al-Zr intermetallic compounds. Also included in this case are Al-Fe-Cr intermetallic compounds in which a portion of the above-mentioned Al-Fe intermetallic compounds is substituted, and Al-Mn-Cr intermetallic compounds in which a portion of the Al-Mn intermetallic compounds is substituted, etc. As described above, when Cu and Zn are contained in the amounts specified in the present invention, examples of the intermetallic compounds include Al-Cu intermetallic compounds, Al-Zn intermetallic compounds, etc. In the present invention, elemental Si is also treated as an intermetallic compound.

[0030] By setting the area ratio of the intermetallic compounds on the surface to 0.10% or more, the stress relaxation resistance of the aluminum alloy sheet can be improved, and the stress relaxation rate can be set to 90% or less. On the other hand, if the area ratio is less than 0.10%, the stress relaxation rate cannot be set to 90% or less. On the other hand, if the area ratio exceeds 40%, good grindability cannot be achieved. Therefore, the area ratio is set to 0.10 to 40%. From the viewpoint of improving the stress relaxation resistance of the aluminum alloy sheet, the area ratio is preferably 0.12% or more, 0.15% or more, 0.20% or more, 0.40% or more, 0.60% or more, 0.80% or more, 1% or more, 2% or more, 4% or more, 6% or more, 8% or more, or 10% or more. Furthermore, from the viewpoint of obtaining good grindability, the area ratio is preferably 35% or less, 30% or less, 25% or less, 20% or less, or 15% or less.

[0031] The area ratio of the intermetallic compounds on the surface can be measured as follows: The surface of the blank is cut with a diamond cutting tool to create a mirror surface, and this surface is observed using an FE-SEM (JEOL Ltd. JSM-7001F, accelerating voltage 15 kV) at 1,000x magnification, 50 fields of view, and an observation area of ​​0.54 mm 2 The image is then taken as a composite image, called a COMPO image. From the COMPO image, the matrix portion, i.e., the portion that appears whiter than the parent phase, is considered to be an intermetallic compound, and the area ratio of Al-Fe intermetallic compounds and other compounds can be calculated using the included analysis system "Analysis Station 3,8,0,31" and particle analysis software "EX-351 10 Particle Analysis Software Ver. 3.84." The area ratio of the intermetallic compounds according to this embodiment is calculated for intermetallic compounds having a maximum length of 0.33 μm or more.

[0032] <Stress relaxation rate: 90% or less> The present inventors have conducted extensive research into deformation of aluminum alloy plates for magnetic disks during magnetic film sputtering and have found that deformation can be suppressed by improving stress relaxation resistance. If the stress relaxation rate is 90% or less, deformation can be suppressed even when stress caused by thermal distortion during magnetic film sputtering is applied to the substrate during thinning. Therefore, the stress relaxation rate of the aluminum alloy plate for magnetic disks according to this embodiment is preferably 90% or less. From the viewpoint of further suppressing deformation of the thinned substrate, the lower the stress relaxation rate, the better. For example, the stress relaxation rate is more preferably 85% or less, even more preferably 80% or less, and particularly preferably 75% or less. The lower limit of the stress relaxation rate is not particularly limited, but is, for example, 0% or more, 20% or more, 50% or more, 60% or more, or 70% or more. The stress relaxation rate can be adjusted by adjusting the contents of Fe, Mn, and Ni to those described in this specification. In addition to the above-mentioned contents of Fe, Mn, and Ni, the stress relaxation rate can also be adjusted by adjusting the treatment conditions in the homogenization heat treatment step to the ranges described below and adjusting the area ratio of intermetallic compounds on the surface of the aluminum alloy sheet to the above-mentioned ranges.

[0033] The stress relaxation rate can be measured as follows. A test piece 10 mm wide x 60 mm long is cut out so that the longitudinal direction is parallel to the rolling direction. Then, the span length (x) in Figure 1(a) is determined using the following equations (2) and (3) so that the bending stress in the following equation (1) is constant, and the following test is carried out. The specimen is placed in an atmospheric furnace with a bending stress applied (as shown in Figure 1(a)) and subjected to a heat treatment (300°C x 1 hour) simulating a magnetic film sputtering process. It is then removed from the furnace and the deformation amount a before the bending stress is removed is measured. The bending stress is then removed (as shown in Figure 1(b)) and the deformation amount b after the bending stress is removed is measured. The ratio of the deformation amount b after unloading the bending stress to the deformation amount a before unloading the bending stress (b / a × 100[%]) is defined as the stress relaxation rate.

[0034] σ=M / Z (1) σ: Bending stress [N / mm 2 ] M: Bending moment [N·mm] Z: Section modulus (Z [mm 3 ]=(w×t 2 ) / 6) w: Plate width [mm], t: Plate thickness [mm]

[0035] M = P × x (2) M: Bending moment [N·mm] P: Tip load [N] x: span length [mm]

[0036] P=(3×E×I×δ) / x 3 ···(3) P: Tip load [N] E: Young's modulus [N / mm 2 ] I: Moment of inertia (I [mm 4 ]=(w×t 3 ) / 12) w: Plate width [mm], t: Plate thickness [mm] δ: Deflection (2 [mm]) x: span length [mm]

[0037] <Grindability: Grinding speed 0.5 μm / min or more> The aluminum alloy plate for magnetic disk according to this embodiment preferably has a grinding speed of 0.5 μm / min or more, more preferably 1.0 μm / min or more, 1.5 μm / min or more, 2.0 μm / min or more, or 2.5 μm / min or more, as determined by the following measurement method. The upper limit of the grinding speed is not particularly limited, but is usually 3.0 μm / min or less. The method for measuring the grinding speed is shown below.

[0038] An aluminum alloy plate machined into a circular, i.e., hollow, disk shape is subjected to wet grinding using a machining center equipped with a circular grinding wheel under the following grinding conditions. The grindability of the aluminum alloy plate is evaluated by the value calculated as the grinding speed from the amount of thickness change of the aluminum alloy plate and the grinding time. Note that the C abrasive grains in the grinding wheel refer to black silicon carbide abrasive grains, which are SiC-based.

[0039] Grinding conditions: Aluminum alloy plate size: outer diameter 95mm, inner diameter 43mm Grindstone size: outer diameter 60mm, inner diameter 40mm Grinding pressure 100gf / cm 2 Wheel speed: 1.05 m / s Grinding wheel revolution speed: 100mm / min Grinding fluid: Quaker Chemical Japan KH-8A (registered trademark) 0.5% diluted AION Polyvinyl Alcohol (PVA) Grindstone for Magnetic Disks C abrasive grain #1500

[0040] The grinding speed can be adjusted by adjusting the contents of Fe, Mn, and Ni to the ranges described herein. In addition to the above-mentioned contents of Fe, Mn, and Ni, the grinding speed can also be adjusted by adjusting the treatment conditions in the homogenization heat treatment step to the ranges described below and adjusting the area ratio of intermetallic compounds on the surface of the aluminum alloy sheet to the ranges described above.

[0041] [Method of manufacturing aluminum alloy sheets for magnetic disks] Next, an example of a method for manufacturing an aluminum alloy plate for a magnetic disk according to this embodiment will be described. The alloy sheet according to this embodiment can be manufactured using manufacturing methods and equipment under conditions generally used for manufacturing aluminum alloy sheets for magnetic disks, with the exception of some conditions in the homogenization heat treatment and hot rolling processes. For example, the aluminum alloy sheet can be manufactured using a manufacturing method including, in this order, a casting process in which raw materials are melted and the resulting molten aluminum alloy, adjusted to a predetermined chemical composition, is cast into an aluminum alloy ingot by semi-continuous casting or the like; a homogenization heat treatment process in which the cast aluminum alloy ingot is chamfered and subjected to homogenization heat treatment; a hot rolling process in which the homogenized heat-treated aluminum alloy ingot is hot-rolled to obtain a hot-rolled sheet; and a cold rolling process in which the hot-rolled sheet is cold-rolled. If necessary, intermediate annealing may be performed before or during the cold rolling process. Each step will be described in detail below.

[0042] (Casting process) In the casting step, the raw materials are melted at 700 to 800° C. to produce a molten aluminum alloy, which is then preferably cast into an aluminum alloy ingot at 700 to 800° C. by a known semi-continuous casting method such as DC casting.

[0043] (Homogenization heat treatment process) In the homogenization heat treatment step, the cast aluminum alloy ingot is subjected to surface grinding and then subjected to homogenization heat treatment. The amount of surface grinding can be, for example, 2 to 40 mm per side. From the viewpoint of setting the area ratio of intermetallic compounds on the surface of the aluminum alloy sheet to 0.10 to 40%, the homogenization heat treatment is preferably carried out at a temperature of 510 to 600°C, and the time for which the temperature is maintained at 510°C or higher is preferably 48 hours or less.

[0044] By setting the homogenization heat treatment temperature to 510°C or higher, the formation of intermetallic compounds in the aluminum alloy is promoted during the homogenization treatment, the area ratio of intermetallic compounds on the surface of the aluminum alloy sheet is increased, and good stress relaxation resistance properties are obtained, while the structure can be homogenized. The homogenization heat treatment temperature is more preferably 515°C or higher, and even more preferably 520°C or higher. On the other hand, by setting the homogenization heat treatment temperature to 600°C or lower, melting of the surface of the aluminum alloy ingot can be prevented. The homogenization heat treatment temperature is more preferably 580°C or lower, and even more preferably 540°C or lower.

[0045] If the homogenization heat treatment is performed at a temperature of 510°C or higher for longer than 48 hours, the generation of intermetallic compounds will be excessive, causing the area ratio of intermetallic compounds on the surface of the aluminum alloy sheet to exceed a predetermined value, resulting in a decrease in grindability. Therefore, the time for which the temperature is maintained at 510°C or higher is preferably 48 hours or less, and more preferably 40 hours or less, 35 hours or less, 30 hours or less, 25 hours or less, 20 hours or less, 15 hours or less, or 10 hours or less. The lower limit of the time for which the temperature is maintained at 510°C or higher during the homogenization heat treatment can be, for example, 4 hours, from the viewpoint of homogenizing the structure.

[0046] (Hot rolling process) In the hot rolling step, the aluminum alloy ingot that has been subjected to the homogenization heat treatment is hot rolled to obtain a hot rolled sheet. The starting temperature of the hot rolling is preferably 490°C or higher from the viewpoint of adjusting the stress relaxation rate of the aluminum alloy sheet to 90% or less, and the finishing temperature of the hot rolling is preferably 300 to 350°C. Specifically, by setting the starting temperature of hot rolling to 480°C or higher, the rolling load during hot rolling can be reduced, and an increase in the number of hot rolling passes can be suppressed. The starting temperature of hot rolling is more preferably 490°C or higher, and even more preferably 500°C or higher. On the other hand, from the viewpoint of suppressing cracking during hot rolling, the starting temperature of hot rolling is preferably 550°C or lower, and more preferably 520°C or lower. Furthermore, the thickness of the hot-rolled sheet obtained by hot rolling can be set to, for example, 3 mm or less.

[0047] (Cold rolling process) In the cold rolling step, the obtained hot-rolled sheet is cold-rolled to obtain a cold-rolled sheet. The thickness of the cold-rolled sheet is, for example, preferably 0.3 to 1.3 mm, and more preferably 0.70 mm or less, 0.69 mm, 0.65 mm or less, 0.60 mm or less, 0.55 mm or less, 0.50 mm or less, 0.45 mm or less, 0.40 mm or less, or 0.35 mm. By undergoing these steps in order, the aluminum alloy plate according to this embodiment can be obtained.

[0048] [Aluminum alloy blanks for magnetic disks] The aluminum alloy blank for a magnetic disk according to this embodiment is obtained from the aluminum alloy plate for a magnetic disk. Specifically, the blank can be manufactured by further undergoing, in this order, a punching step in which the aluminum alloy plate obtained after the cold rolling step is punched into a circular shape, and a correction annealing step in which the circular substrate obtained in the punching step is subjected to correction annealing, for example, by annealing while applying a load to flatten it. The chemical composition of the resulting blank will not change from the aluminum alloy plate described above and will have the same composition. Furthermore, the characteristic values ​​of the blank, such as the area ratio of intermetallic compounds on the surface, the stress relaxation rate, and the grindability, are equivalent to the characteristic values ​​of the aluminum alloy sheet. Therefore, the characteristic values ​​determined for the aluminum alloy sheet can be regarded as the characteristic values ​​of the blank. Conversely, the characteristic values ​​determined for the blank can also be regarded as the characteristic values ​​of the aluminum alloy sheet.

[0049] (Punching process) In the punching process, the aluminum alloy plate is tempered as necessary, and then punched into a ring shape so that it can be used for, for example, a substrate for a 3.5-inch HDD with an inner diameter of 24 mm and an outer diameter of 96 mm, or a substrate for a 2.5-inch HDD with an inner diameter of 19 mm and an outer diameter of 66 mm.

[0050] (Straightening annealing process) In the correction annealing step, the annular substrates are preferably stacked, sandwiched between spacers having high flatness, and annealed while applying a load to the substrates to flatten them. The annealing temperature is 250 to 500°C, and the holding time can be, for example, about 3 to 5 hours. The temperature rising rate in the corrective annealing can be, for example, about 80°C / hour on average, and is preferably 1000°C / hour or less at the fastest. The temperature can be lowered (cooled) by, for example, opening the door of the annealing furnace.

[0051] Regarding the temperature rise in the corrective annealing, even if the temperature is raised stepwise, the effect of this embodiment is not impaired. For example, as described in paragraphs 0068 and 0069 of Japanese Patent No. 5815153, the temperature may be raised at a plurality of temperature rise rates, i.e., stepwise, so that the temperature rise rate in a specific temperature range is a predetermined rate or a predetermined rate or more, and the temperature rise rate outside the specific temperature range is a different rate. In this embodiment, the annealing temperature for the corrective annealing is assumed to be in the practical temperature range of 250 to 400° C., within the above-mentioned range of general annealing temperatures. By going through these steps in order, the blank according to this embodiment can be obtained.

[0052] [Aluminum alloy substrates for magnetic disks] The aluminum alloy substrate for magnetic disk according to this embodiment is obtained from the aluminum alloy blank for magnetic disk. Specifically, the substrate can be manufactured by carrying out a cutting process (end surface processing) to cut the end faces of the blank and a grinding process (mirror finish) to grind the surface (main surface) of the blank. The chemical composition of the resulting substrate will not change from the blank described above and will have the same composition. Furthermore, the characteristic values ​​of the substrate, such as the area ratio of intermetallic compounds on the surface, stress relaxation rate, grindability, etc., are equivalent to the characteristic values ​​of the blank. Therefore, the characteristic values ​​determined for the aluminum alloy sheet or the blank can be regarded as the characteristic values ​​of the substrate. Conversely, the characteristic values ​​determined for the substrate can also be regarded as the characteristic values ​​of the aluminum alloy sheet or the blank.

[0053] The aluminum alloy plate, blank, and substrate according to this embodiment can be obtained by the above-mentioned methods, but other processes may be performed between or before or after each process, as long as they do not adversely affect each process.

[0054] [Magnetic disk manufacturing method] The magnetic disk can be manufactured using manufacturing methods and equipment generally used for manufacturing magnetic disks. For example, the surface of a substrate is acid-etched to form an electroless Ni-P plating film, and the surface of the electroless Ni-P plating film is then polished. Next, an underlayer, a magnetic layer, a protective film, and other layers are formed on the surface of the substrate, thereby manufacturing the magnetic disk. [Example]

[0055] The present invention will be specifically described below with reference to examples of the present invention, but the technical scope of the present invention is not limited thereto.

[0056] (Preparation of test materials) The test materials Nos. 1 to 3 were manufactured using aluminum alloys having the chemical compositions shown in Table 1 under the following conditions.

[0057] First, slabs were produced by DC casting using a mold with the same thickness as the ingot (500 mm for Nos. 1 and 2, and 535 mm for No. 3). Both sides of the resulting slabs (thickness direction) were then chamfered by 16 mm. They were then subjected to a homogenization heat treatment at 535°C for the holding time listed in Table 1. Nos. 1 and 3 were then hot-rolled (starting temperature: approximately 500°C, finishing temperature: approximately 330°C) to a thickness of 2.3 mm, and No. 2 to a thickness of 2.0 mm. No. 1 was then cold-rolled to a thickness of 0.55 mm, and Nos. 2 and 3 to a thickness of 0.52 mm. The blanks were then punched using a press to form circular rings with an outer diameter of approximately 98 mm and an inner diameter of approximately 24 mm, and then sandwiched between spacers for corrective annealing (heating to 200-280°C at a rate of 50°C / h or more, followed by holding at 300-400°C for no more than 7 hours) to produce blanks (O-tempered material) of the respective thicknesses.

[0058] The area ratio of intermetallic compounds on the surface, grindability, and stress relaxation rate of each of the produced test materials were evaluated as follows.

[0059] (area ratio of intermetallic compounds on the surface) The area ratio of the intermetallic compounds on the surface was measured as follows: The surface of the blank was cut with a diamond cutting tool to create a mirror surface, and this surface was observed using an FE-SEM (JSM-7001F manufactured by JEOL Ltd., accelerating voltage 15 kV) at 1,000x magnification, 50 fields of view, and an observation area of ​​0.54 mm 2 The image was then taken as a composite image, which was called a COMPO image. From the COMPO image, the matrix portion, i.e., the portion that appeared whiter than the parent phase, was deemed to be an intermetallic compound, and the area ratio of Al-Fe intermetallic compounds with a maximum length of 0.33 μm or more was calculated using the attached analysis system "Analysis Station 3,8,0,31" and particle analysis software "EX-35110 Particle Analysis Software Ver. 3.84."

[0060] (grinding speed) The outer and inner diameters of the blank were machined to the specified size of the test material, and wet grinding was carried out using a machining center equipped with a circular grinding wheel under the following grinding conditions. The grindability of the test material was evaluated by the grinding speed calculated from the amount of change in thickness of the test material and the grinding time. Note that the C abrasive grains in the grinding wheel refer to black silicon carbide abrasive grains, which are SiC-based. A grinding speed of 0.5 μm / min or more was evaluated as "good", and a grinding speed of less than 0.5 μm / min was evaluated as "poor".

[0061] Grinding conditions: Size of the test piece: outer diameter 95mm, inner diameter 43mm Grindstone size: outer diameter 60mm, inner diameter 40mm Grinding pressure 100gf / cm 2 Wheel speed: 1.05 m / s Grinding wheel revolution speed: 100mm / min Grinding fluid: Quaker Chemical Japan KH-8A (registered trademark) 0.5% diluted AION Polyvinyl Alcohol (PVA) Grindstone for Magnetic Disks C abrasive grain #1500

[0062] (Stress relaxation rate) Test pieces measuring 10 mm wide and 60 mm long were cut out from the test material so that the longitudinal direction was parallel to the rolling direction. The span length (x) in Figure 1(a) was determined for each test material using the following equations (2) and (3) so that the bending stress in the following equation (1) would be constant, and the following test was carried out. The specimen was placed in an atmospheric furnace with a bending stress applied (as shown in Figure 1(a)), and subjected to a heat treatment (300°C x 1 hour) simulating a magnetic film sputtering process. After that, it was removed from the furnace, and the deformation amount a before the bending stress was removed was measured. After that, the bending stress was removed (as shown in Figure 1(b)), and the deformation amount b after the bending stress was removed was measured. The ratio of the deformation amount b after unloading the bending stress to the deformation amount a before unloading the bending stress (b / a × 100[%]) was taken as the stress relaxation rate, and samples with a stress relaxation rate of 90% or less were evaluated as "Good" indicating excellent deformation suppression during magnetic film sputtering, while samples with a stress relaxation rate of more than 90% were evaluated as "Poor" indicating poor deformation suppression during magnetic film sputtering.

[0063] σ=M / Z (1) σ: Bending stress [N / mm 2 ] M: Bending moment [N·mm] Z: Section modulus (Z [mm 3 ]=(w×t 2 ) / 6) w: Plate width [mm], t: Plate thickness [mm]

[0064] M = P × x (2) M: Bending moment [N·mm] P: Tip load [N] x: span length [mm]

[0065] P=(3×E×I×δ) / x 3 ···(3) P: Tip load [N] E: Young's modulus [N / mm 2 ] I: Moment of inertia (I [mm 4 ]=(w×t 3 ) / 12) w: Plate width [mm], t: Plate thickness [mm] δ: Deflection (2 [mm]) x: span length [mm]

[0066] The alloy composition (chemical composition), surface area ratio of intermetallic compounds, grindability, and stress relaxation rate of each test material are shown in Table 1. Note that underlines in the table indicate that the specific features of the present invention are not met.

[0067] [Table 1]

[0068] As is clear from the results in Table 1, Nos. 1 and 2, which satisfy the requirements of the present invention, have good grindability, and have excellent stress relaxation resistance, and aluminum alloy plates and blanks that can suppress thermal deformation during magnetic film sputtering were obtained. On the other hand, No. 3, in which the total amount of Fe, Mn, and Ni did not satisfy the requirements of the present invention and the area ratio of the intermetallic compounds on the surface did not satisfy the requirements of the present invention, had inferior stress relaxation resistance compared to Nos. 1 and 2.

Claims

1. Mg: 0.1 to 7.0% by mass, Cr: 0.005 to 1.0% by mass, Be: 3 to 100 mass ppm; Zr: 100 mass ppm or less, Si: 0.20% by mass or less, The total content of at least one of Fe, Mn, and Ni: 0.05 to 3.0 mass%; the balance being Al and impurities; the area ratio of the intermetallic compound on the surface is 0.10 to 40%; The area ratio is calculated for intermetallic compounds having a maximum length of 0.33 μm or more.

2. The Fe: 0 to 1.00 mass% Mn: 0 to 1.0 mass %, and 2. The aluminum alloy plate for magnetic disks according to claim 1, further comprising at least one of the Ni: 0 to 1.0 mass %.

3. 3. The aluminum alloy plate for magnetic disks according to claim 1, further comprising at least one of Cu: 1.0% by mass or less and Zn: 1.0% by mass or less.

4. 3. The aluminum alloy sheet for magnetic disks according to claim 1, wherein the stress relaxation rate is 90% or less.

5. An aluminum alloy blank for magnetic disks obtained from the aluminum alloy plate for magnetic disks according to claim 1 or 2.

6. An aluminum alloy substrate for a magnetic disk obtained from the aluminum alloy blank for a magnetic disk according to claim 5.

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