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 rigidity 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, Mn, 100 mass ppm or less of Ti, and 0.20 mass % or less of Si. The total of at least one or more of Fe, Mn, and Ni is 0.03-5.9 mass %, and the remainder comprises Al and impurities. The solid-soluble amount of Mn in an aluminum parent phase is 0.03 mass % 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] With the digitization of information and the spread of the Internet, large amounts of digital data are being handled, which has led to a demand for larger capacity hard disk drives (HDDs), particularly in data centers.To achieve this, thinner magnetic disks are being considered in order to increase the number of magnetic disks per HDD.

[0003] However, when attempting to improve the data transfer rate, particularly at a high rotation speed, during rotation of the magnetic disk, the thinner the magnetic disk, the higher the probability of occurrence of minute vibrations.

[0004] One of the means for suppressing vibrations of such a thinned magnetic disk is to increase the rigidity of the substrate. 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.

[0005] Furthermore, with regard to substrates for magnetic disks, the index of "flatness" is extremely important because it greatly affects the performance of hard disk drives (HDDs) that use the substrate. During the production process of substrates, there is concern about deformation due to thermal strain, which adversely affects the flatness of the substrate and can lead to the production of non-standard products. Currently, in light of resource depletion, recycling of various things is progressing, and recycling of metals, which are consumed in large quantities, has been carried out for some time. The above-mentioned non-standard products can also be reused through recycling, but it is important to suppress the generation of non-standard products by suppressing thermal distortion.

[0006] 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.

[0007] 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.

[0008] 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]

[0009] [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]

[0010] Thus, while good rigidity and suppression of thermal deformation are both important for an aluminum alloy plate for a magnetic disk, there remains room for further study on an aluminum alloy plate for a magnetic disk that satisfies both of these requirements.

[0011] 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 rigidity and can suppress thermal deformation during magnetic film sputtering. [Means for solving the problem]

[0012] As a result of extensive research, the present inventors discovered that by using a specific alloy composition and setting the amount of Mn in solid solution in the aluminum matrix to 0.03 mass % or more, an aluminum alloy plate for magnetic disks can be obtained that has good rigidity and can suppress thermal deformation during magnetic film sputtering, and thus created the present invention.

[0013] 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: 3~100 mass ppm, Contains Mn, Ti: 100 mass ppm or less, Si: 0.20% by mass or less, the total of at least one of Fe, Mn, and Ni: 0.03 to 5.9 mass %, the balance being Al and impurities, An aluminum alloy plate for magnetic disks, having a manganese solid solution content of 0.03 mass % or more in the aluminum matrix. [2] the Fe: 0 to 1.00 mass %; the Mn: 0.03 to 1.4 mass %, and The aluminum alloy plate for magnetic disks according to [1], containing at least one of the Ni: 0 to 3.5 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] [1] or [2], wherein the aluminum alloy plate for magnetic disks has a Young's modulus of 70 GPa or more. [5] The aluminum alloy plate for magnetic disks according to [1] or [2], which has a stress relaxation rate of 90% or less. [6] An aluminum alloy blank for magnetic disks obtained from the aluminum alloy plate for magnetic disks according to [1] or [2]. [7] An aluminum alloy substrate for magnetic disks obtained from the aluminum alloy blank for magnetic disks according to [6]. [Effects of the Invention]

[0014] 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 that have good rigidity and can suppress thermal deformation during magnetic film sputtering. [Brief explanation of the drawings]

[0015] [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

[0016] 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.

[0017] [Aluminum alloy plates for magnetic disks] The aluminum alloy plate 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, Mn, 100 mass ppm or less Ti, 0.20 mass% or less Si, and a total of 0.03 to 5.9 mass% of at least one of Fe, Mn, and Ni, with the remainder being Al and impurities, and the amount of Mn dissolved in the aluminum matrix is ​​0.03 mass% or more. The aluminum alloy plate 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.

[0018] (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.

[0019] (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.

[0020] (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.

[0021] (Ti: 100 mass ppm or less) By adding a small amount of Ti to an aluminum alloy sheet, the grain size of the aluminum alloy ingot can be refined, thereby obtaining good yield strength. However, if the Ti content exceeds 100 ppm by mass, the intermetallic compounds become coarse, which may cause edge cracks and reduce rollability. Therefore, the Ti 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 Ti 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 Ti content is 0 ppm by mass, when Ti is contained, from the viewpoint of improving proof stress, the Ti content is preferably 5 ppm by mass or more, or 10 ppm by mass or more.

[0022] (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.

[0023] (Total of Fe, Mn, and Ni: 0.03 to 5.9 mass%) Fe, Mn, and Ni are components that contribute to improving rigidity and stress relaxation resistance. Therefore, the aluminum alloy sheet for magnetic disks according to this embodiment contains at least one element selected from the group consisting of Fe, Mn, and Ni in total: 0.03 to 5.9 mass%, and the amount of Mn dissolved in the aluminum matrix is ​​0.03 mass% or more. That is, the aluminum alloy sheet may contain two elements, Fe and Mn, or Mn and Ni, or may contain all of Fe, Mn, and Ni, and there are no particular limitations on the total content thereof as long as it is 0.03 to 5.9 mass%. In order to obtain good rigidity and stress relaxation resistance, the total content of Fe, Mn, and Ni is preferably 0.05% by mass or more, 0.06% by mass or more, 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 compounds may become coarse and the plating properties may be deteriorated. Therefore, the total content is preferably 5.5% by mass or less, 5.0% by mass or less, 4.5% by mass or less, 4.0% by mass or less, 3.5% by mass or less, 3.0% by mass or less, 2.5% by mass or less, 2.0% by mass or less, or 1.5% by mass or less.

[0024] 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: 0.03 to 1.4 mass %, and Ni: 0 to 3.5 mass %.

[0025] (Fe: 1.00% by mass or less) Fe is contained in aluminum alloy sheets 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%, the compounds may become coarse and the platability may be reduced. Therefore, the Fe content is set to 1.00 mass% or less (including 0 mass%). From the viewpoint of suppressing deterioration of plating ability, 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.

[0026] (Mn: 0.03% by mass or more) In the aluminum alloy plate for a magnetic disk according to this embodiment, the amount of Mn dissolved in the aluminum matrix is ​​0.03 mass % or more. 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 is 1.4 mass% or less, it is possible to prevent the compounds from coarsening and reducing the platability. Therefore, the Mn content is preferably 1.4 mass% or less (including 0 mass%). From the viewpoint of suppressing deterioration of plating ability, the Mn content is preferably 1.3 mass% or less, 1.2 mass% or less, 1.1 mass% or less, 1.0 mass% or less, 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 obtaining good rigidity and stress relaxation resistance, the Mn content is preferably 0.06 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.

[0027] (Ni: 3.5% by mass or less) Ni is contained in aluminum alloy sheets to obtain good rigidity and stress relaxation resistance. On the other hand, if the Ni content in the aluminum alloy sheet exceeds 3.5 mass%, the compounds may become coarse and the plating property may be deteriorated. Therefore, the Ni content is set to 3.5 mass% or less (including 0 mass%). From the viewpoint of suppressing deterioration of plating property, the Ni content is preferably 3.0 mass% or less, 2.5 mass% or less, 2.0 mass% or less, 1.5 mass% or less, 1.0 mass% or less, 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 obtaining good rigidity and stress relaxation resistance, the Ni content is preferably 0.1 mass% or more, 0.2 mass% or more, 0.3 mass% or more, or 0.4 mass% or more.

[0028] (Cu: 1.0% by mass or less, Zn: 1.0% by 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.

[0029] (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 Zr, V, B, Na, K, Ca, Pb, P, Sn, Ag, Bi, In, Ge, Sr, and Cd. Among these, Zr 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 impair 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 is such that the above-mentioned Si, Fe, Ni, Cu, and Zn are not added, the content of each of these as unavoidable impurities is preferably 0.005 mass % or less.

[0030] <Solution amount of Mn in aluminum matrix: 0.03 mass% or more> The greater the amount of Mn dissolved in the aluminum matrix, the better the stress relaxation resistance. If the amount of Mn dissolved in the aluminum matrix is ​​0.03% by mass or more, the better the stress relaxation resistance, and preferably the amount is 0.04% by mass or more, 0.05% by mass or more, 0.06% by mass or more, 0.07% by mass or more, 0.08% by mass or more, 0.09% by mass or more, 0.10% by mass or more, 0.11% by mass or more, 0.12% by mass or more, 0.13% by mass or more, 0.14% by mass or more, 0.15% by mass or more, 0.16% by mass or more, 0.17% by mass or more, 0.18% by mass or more, 0.19% by mass or more, 0.20% by mass or more, 0.21% by mass or more, 0.22% by mass or more, 0.23% by mass or more, 0.24% by mass or more, or 0.25% by mass or more. There is no upper limit to the amount of Mn dissolved in the aluminum matrix, but under normal manufacturing conditions, the upper limit is 0.33 mass % or less.

[0031] The amount of dissolved Mn in the aluminum matrix is ​​measured by using a cold-rolled aluminum alloy sheet as a test material, removing the residue obtained by hot phenol dissolution extraction, and then hot-phenol-dissolving the aluminum alloy sheet. The ratio of the amount of dissolved Mn in the resulting solution to the mass of the aluminum alloy sheet is defined as the amount of dissolved Mn. In other words, assuming that the Mn contained in the aluminum alloy consists of dissolved Mn and intermetallic compounds as second-phase particles, the latter is separated by hot phenol dissolution extraction, and the amount of dissolved Mn analyzed from the solution extracted from the remaining matrix is ​​divided by the mass of the dissolved aluminum alloy sheet to determine the amount of dissolved Mn. The hot phenol dissolution extraction method will be explained. (1) Weigh out 0.1 g of the test material and dissolve it in 25 mL of phenol. (2) After dissolution, the extracted and filtered solution (X [mL]) is subjected to ICP atomic emission spectroscopy to measure the concentration of Mn in the solution (Y [g / mL]). (3) Assuming that all of the dissolved Mn in 0.1 [g] is contained in X [mL], calculate the dissolved Mn concentration [mass%] of the test material using the following formula (I). (Solved Mn concentration [mass%])=(Y[g / mL])×(X[mL]) / (0.1[g])×100...(I)

[0032] In (2), after dissolution, the extracted and filtered solution is adjusted to a constant volume of 50 mL. A portion of the adjusted solution is used to quantitatively analyze the Mn content in the solution by ICP atomic emission spectroscopy. The result is expressed as Y (g / mL). In (3), the amount of solute Mn contained in 50 mL can be calculated from the analysis results obtained in (2). The solute Mn concentration [mass%] in the test material is calculated using the above formula (I).

[0033] More specifically, it can be determined by the method described in the Examples.

[0034] <Young's modulus: 70 GPa or more> Young's modulus is the ratio of stress to strain when a material behaves elastically, and in the present invention, it affects the generation of vibration when a thinned magnetic disk is rotated in an HDD. When the Young's modulus of an aluminum alloy plate is 70 GPa or more, it has high rigidity, and can reliably suppress vibration of the thinned magnetic disk. Therefore, the Young's modulus of the aluminum alloy plate for magnetic disks according to this embodiment is preferably 70 GPa or more. From the viewpoint of further suppressing vibration of the thinned magnetic disk, the higher the Young's modulus, the better. For example, the Young's modulus is preferably 71 GPa or more, more preferably 72 GPa or more, and even more preferably 73 GPa or more. The Young's modulus can be adjusted by adjusting the contents of Mg, Si, Fe, Mn, and Ni to the amounts described in this specification. The Young's modulus can be measured, for example, in accordance with JIS Z 2280:1993 (Testing method for high-temperature Young's modulus of metallic materials) by preparing a test piece measuring 60 mm x 10 mm x 1 mm in thickness, with the longitudinal direction parallel to the rolling direction, and using the test piece. Specifically, in accordance with the method specified in the JIS, the measurement can be performed by the free resonance method in an air atmosphere at room temperature (e.g., 25°C). The test apparatus used is preferably a JE-RT model manufactured by Nippon Technoplus Co., Ltd.

[0035] <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 Fe, Mn, and Ni contents to the ranges described herein. In addition to the Fe, Mn, and Ni contents, 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 amount of Mn dissolved in the aluminum matrix to the ranges described above.

[0036] 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.

[0037] 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]

[0038] M = P × x (2) M: Bending moment [N·mm] P: Tip load [N] x: span length [mm]

[0039] 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]

[0040] [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.

[0041] (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.

[0042] (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. The homogenization heat treatment is preferably carried out at a temperature of 510 to 600°C at a temperature rise rate of 15°C / h or more from room temperature to 510°C, from the viewpoint of adjusting the stress relaxation rate of the aluminum alloy sheet to 90% or less.

[0043] If the heating rate from room temperature to 510°C during homogenization heat treatment is less than 15°C / h, the formation of Mn-containing intermetallic compounds will proceed during the heating process, reducing the amount of Mn dissolved in the structure, making it impossible to obtain sufficient stress relaxation resistance. On the other hand, if the heating rate to 510°C is 15°C / h or higher, homogenization heat treatment can be performed before the formation of Mn-containing intermetallic compounds, thereby achieving the desired amount of Mn dissolved in the structure. Therefore, the heating rate to 510°C is preferably 15°C / h or higher. The heating rate to 510°C is more preferably 18°C / h or higher, or 20°C / h or higher. There is no upper limit to the heating rate to 510°C during homogenization heat treatment, but under normal manufacturing conditions, it is 100°C / h or lower.

[0044] Furthermore, by setting the homogenization heat treatment temperature to 510°C or higher, the structure is homogenized and Mn is sufficiently dissolved, thereby reducing the variation in stress relaxation resistance in the resulting aluminum alloy sheet. In other words, by undergoing the homogenization heat treatment step, the amount of dissolved Mn becomes sufficient and its distribution becomes uniform, and there is no difference in distribution between locations in the subsequent steps. 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, it is possible to prevent the surface of the aluminum alloy ingot from melting. The homogenization heat treatment temperature is more preferably 580°C or lower, and even more preferably 540°C or lower.

[0045] (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.

[0046] (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 or less, 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.

[0047] [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 respective property values ​​of the blank, such as the amount of Mn dissolved in the aluminum matrix, Young's modulus, stress relaxation rate, etc., are equivalent to the respective property values ​​of the aluminum alloy sheet. Therefore, the property values ​​determined for the aluminum alloy sheet can be regarded as the property values ​​of the blank. Conversely, the property values ​​determined for the blank can also be regarded as the property values ​​of the aluminum alloy sheet.

[0048] (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.

[0049] (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.

[0050] 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.

[0051] [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 amount of Mn dissolved in the aluminum matrix, Young's modulus, and stress relaxation rate, are equivalent to the characteristic values ​​of the blank. Therefore, the characteristic values ​​determined for the aluminum alloy sheet or 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 blank.

[0052] 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.

[0053] [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]

[0054] 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.

[0055] (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.

[0056] First, slabs were produced by DC casting of the molten metal in molds with the ingot thickness (500 mm for Nos. 1 and 2, and 535 mm for No. 3). Then, both sides (thickness direction) of the obtained slabs were chamfered by 16 mm. Subsequently, the temperature was increased from room temperature (25°C) to 510°C at the heating rate shown in Table 1, and a homogenization heat treatment was performed by holding at 535°C for 8 hours. Then, Nos. 1 and 3 were hot-rolled (starting temperature: approximately 500°C, finishing temperature: approximately 330°C) to a thickness of 2.3 mm, and No. 2 was hot-rolled to a thickness of 2.0 mm. No. 1 was cold-rolled to a thickness of 0.55 mm, and Nos. 2 and 3 were cold-rolled to a thickness of 0.52 mm, to obtain aluminum alloy sheets of the respective thicknesses. The blanks were then punched out to approximately 98mm diameter using a press, then sandwiched between spacers and subjected to 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.

[0057] The amount of Mn dissolved in the aluminum matrix, Young's modulus, and stress relaxation rate of each of the produced test materials were evaluated as follows.

[0058] (Mn solid solution amount in aluminum matrix) The amount of dissolved Mn in the aluminum matrix was measured by using a blank after corrective annealing as a test material, removing the residue obtained by hot phenol dissolution extraction, and then hot phenol dissolving the blank. The ratio of the amount of dissolved Mn in the solution to the mass of the blank was determined as the amount of dissolved Mn. In other words, assuming that the Mn contained in the aluminum alloy consists of dissolved Mn and intermetallic compounds as second-phase particles, the latter was separated by hot phenol dissolution extraction, and the amount of dissolved Mn analyzed from the solution extracted from the remaining matrix was divided by the mass of the dissolved blank to determine the amount of dissolved Mn. For the test specimens, small pieces were cut from the blank after the straightening annealing and weighed to a total of 0.1 g. Next, a beaker containing 25 mL of phenol was placed on a hot plate, and the phenol was heated to a set temperature of 250 °C. The test specimens were then added and dissolved. Next, benzyl alcohol was added to the solution. Next, the solution to which the benzyl alcohol had been added was filtered through a polytetrafluoroethylene membrane filter (pore size 0.1 μm) to remove the second-phase particles as residue. The solution from which the second-phase particles had been removed was quantitatively analyzed by inductively coupled plasma emission spectroscopy (ICP). The amount of Mn thus obtained was divided by the mass of the dissolved blank (0.1 g) to determine the amount of Mn in solid solution.

[0059] (Young's modulus) Young's modulus was measured in accordance with JIS Z 2280:1993 (Testing method for high-temperature Young's modulus of metallic materials). Test pieces measuring 60 mm x 10 mm x thickness mm were cut out from the test material (blank) with the longitudinal direction parallel to the rolling direction. The thickness of test piece No. 1 was 0.55 mm, and Nos. 2 and 3 were 0.52 mm. The measurements were carried out using a test device, model JE-RT, manufactured by Nippon Technoplus Co., Ltd., in an air atmosphere at room temperature (25°C) by the free resonance method. Those with a Young's modulus of 70 GPa or more were evaluated as "○", and those with a Young's modulus of less than 70 GPa were evaluated as "×". ○ indicates pass, and × indicates fail.

[0060] (Stress relaxation rate) Test pieces measuring 10 mm wide and 60 mm long were cut out from the test material (blank) 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.

[0061] 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]

[0062] M = P × x (2) M: Bending moment [N·mm] P: Tip load [N] x: span length [mm]

[0063] 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]

[0064] Table 1 shows the evaluation results of the alloy composition (chemical composition), Young's modulus, and stress relaxation rate for each test material (blank), as well as the measurement results of the amount of Mn dissolved in the aluminum matrix for each test material (blank). Note that underlines in the table indicate that the specific features of the present invention are not met.

[0065] [Table 1]

[0066] As is clear from the results in Table 1, Nos. 1 and 2, which satisfy the specifications of the present invention, have good rigidity, excellent stress relaxation resistance, and are capable of suppressing thermal deformation during magnetic film sputtering. 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 amount of Mn dissolved in the aluminum matrix did not satisfy the requirements of the present invention, was inferior to Nos. 1 and 2 in rigidity and stress relaxation resistance.

Claims

1. Mg: 0.1 to 7.0% by mass, Cr: 0.005 to 1.0% by mass, Be: 3 to 100 mass ppm, Contains Mn, Ti: 100 mass ppm or less, Si: 0.20% by mass or less, a total of at least one of Fe, Mn, and Ni: 0.03 to 5.9 mass%; the balance being Al and impurities; An aluminum alloy plate for magnetic disks, having an Mn solid solution content of 0.03 mass % or more in an aluminum matrix.

2. The Fe: 0 to 1.00 mass% Mn: 0.03 to 1.4 mass%, and 2. The aluminum alloy plate for magnetic disks according to claim 1, further comprising at least one of the following: Ni: 0 to 3.5 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 Young's modulus is 70 GPa or more.

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

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

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

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