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

Abstract

The present invention provides 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 are capable of suppressing thermal deformation during magnetic film sputtering. The present invention provides an aluminum alloy plate for magnetic disks, which contains 0.1-7.0 mass % of Mg, 0.005-1.0 mass % of Cr, 3-100 mass ppm of Be, 0.20 mass % or less of Si, and 0.05-5.9 mass % in total of at least one of Fe, Mn, or Ni, with the remainder comprising Al and impurities.

Description

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

[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.

[0002] With the digitization of information and the spread of the Internet, large amounts of digital data are being handled, and this 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 vibration 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 magnetic disk substrates, the index of "flatness" is a very important index because it significantly affects the performance of hard disk drives (HDDs) using the substrate. During the substrate production process, deformation due to thermal distortion is a concern. This deformation adversely affects the flatness of the substrate and can lead to the generation of non-standard products. Currently, in light of resource depletion, recycling of various materials is progressing, and recycling of metals, which are consumed in large quantities, has also been carried out for some time. While the above-mentioned non-standard products can be reused through recycling, it is important to suppress the generation of non-standard products by suppressing thermal distortion. For example, Patent Document 3 describes an aluminum alloy plate for magnetic disks with excellent flatness, which has a specific chemical composition and a compound number gradient in the plate thickness direction equal to or greater than a specific value.

[0006] 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 by using an aluminum alloy sheet for a cap having a specific chemical composition and having a difference in yield strength in a direction parallel to rolling before and after heat treatment of a specific value or more, excellent stress relaxation resistance can be exhibited and thermal deformation can be suppressed.

[0008] Japanese Patent No. 7132289 Japanese Patent No. 6684139 Japanese Patent Application Publication No. 2023-004878 Japanese Patent Application Publication No. 2022-010156 Japanese Patent Application Publication No. 2021-011621

[0009] 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.

[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 rigidity and can suppress thermal deformation during magnetic film sputtering.

[0011] As a result of extensive research, the inventors discovered that by using a specific alloy composition, 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.

[0012] That is, the present invention relates to the following: [1] An aluminum alloy sheet for magnetic disks containing 0.1 to 7.0 mass% Mg, 0.005 to 1.0 mass% Cr, 3 to 100 mass ppm Be, 0.20 mass% or less Si, and a total of 0.05 to 5.9 mass% of at least one of Fe, Mn, and Ni, with the balance being Al and impurities. [2] The aluminum alloy sheet for magnetic disks according to [1], containing at least one of 0 to 1.00 mass% Fe, 0 to 1.4 mass% Mn, and 0 to 3.5 mass% Ni. [3] The aluminum alloy sheet for magnetic disks according to [1] or [2], further containing at least one of 1.0 mass% or less Cu and 1.0 mass% or less Zn. [4] The number density of intermetallic compounds on the surface having a maximum length of 0.05 μm or more and 0.33 μm or less is 1.0 × 10 ６ pieces / mm ２ [5] The aluminum alloy plate for magnetic disks according to [1] or [2], having a Young's modulus of 70 GPa or more. [6] The aluminum alloy plate for magnetic disks according to [1] or [2], having a stress relaxation rate of 90% or less. [7] An aluminum alloy blank for magnetic disks obtained from the aluminum alloy plate for magnetic disks according to [1] or [2]. [8] An aluminum alloy substrate for magnetic disks obtained from the aluminum alloy blank for magnetic disks according to [7].

[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 that have good rigidity and can suppress thermal deformation during magnetic film sputtering.

[0014] Figures 1(a) and 1(b) are diagrams for explaining the measurement of stress relaxation rates in Examples. Figure 2 is a diagram showing a COMPO image (magnification: 10,000x) obtained by photographing an aluminum alloy blank No. 1 in Examples using a scanning electron microscope (FE-SEM). Figure 3 is a diagram showing a COMPO image (magnification: 10,000x) obtained by photographing an aluminum alloy blank No. 3 in Examples using a scanning electron microscope (FE-SEM).

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

[0016] [Aluminum alloy plate 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, 0.20 mass% or less Si, and a total of 0.05 to 5.9 mass% of at least one of Fe, Mn, and Ni, with the balance being Al and impurities. The aluminum alloy plate for magnetic disks according to this embodiment may also contain Cu and Zn. Each component of the aluminum alloy plate for magnetic disks according to this embodiment will be described in detail below.

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

[0018] (Cr: 0.005% by mass or more and 1.0% by mass or less) Cr is an essential constituent element in the aluminum alloy plate for magnetic disks according to this embodiment, and is contained in the aluminum alloy plate to obtain good yield strength. If the Cr content in the aluminum alloy plate is less than 0.005% by mass, the above-mentioned effect cannot be obtained. On the other hand, if the Cr content exceeds 1.0% by mass, the intermetallic compounds become coarse, and edge cracks may occur, which may result in a decrease in rollability. Therefore, the Cr content is set to 0.005% by mass or more and 1.0% by mass or less. Note that, from the viewpoint of improving yield strength, the Cr content is preferably 0.01% by mass or more, 0.03% by mass or more, 0.05% by mass or more, 0.08% by mass or more, or 0.1% by mass or more. Furthermore, from the viewpoint of ensuring rollability, the content 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 ppm by mass or more and 100 ppm by mass or less) Be is an essential constituent element in the aluminum alloy plate for magnetic disks according to this embodiment, and has the effect of forming an oxide film during casting and suppressing the formation of Mg oxides. It also has the effect of improving the hot rolling property and formability of the aluminum alloy. Furthermore, it can weaken the adhesion between blanks by suppressing oxidation during corrective annealing, and can also suppress deterioration of flatness due to external forces 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 cracking and reduce rollability. Therefore, the Be content is set to 3 ppm by mass or more and 100 ppm by mass or less. From the viewpoint of fully obtaining the effects of the addition of Be, 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, and from the viewpoint of ensuring rollability, the Be content 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.

[0020] (Si: 0.20% by mass or less) Si is usually mixed into aluminum alloys as an unavoidable impurity in base metal, and forms elements such as elemental Si and Al-Fe-Si intermetallic compounds. If the Si content exceeds 0.20% by 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% by mass or less (including 0.00% by mass). Note that, from the viewpoint of suppressing 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, and even 0% by mass does not impair the characteristics of the present invention, but since high-purity raw materials (such as aluminum ingots and intermediate alloy ingots) are required, the cost increases. Therefore, from an industrial perspective, the Si content is preferably 0.004% by mass or more.

[0021] (Total of Fe, Mn, and Ni: 0.05 to 5.9% by 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 selected from the group consisting of Fe, Mn, and Ni. That is, Fe, Mn, or Ni may be contained alone, or two of Fe and Mn, Mn and Ni, or Ni and Fe may be contained, or all of Fe, Mn, and Ni may be contained. There are no particular limitations on the total content of these elements as long as the total content is 0.05 to 5.9% by 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 compounds may become coarse and the plating ability may be reduced. Therefore, the total content is preferably 5.5 mass% or less, 5.0 mass% or less, 4.5 mass% or less, 4.0 mass% or less, 3.5 mass% or less, 3.0 mass% or less, 2.5 mass% or less, 2.0 mass% or less, or 1.5 mass% or less.

[0022] The aluminum alloy plate for magnetic disks according to this embodiment preferably contains at least one of Fe: 0 to 1.00 mass %, Mn: 0 to 1.4 mass %, and Ni: 0 to 3.5 mass %.

[0023] (Fe: 1.00 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%, the compounds may become coarse and reduce platability. Therefore, the Fe content is set to 1.00 mass% or less (including 0 mass%). Note that, from the viewpoint of suppressing a reduction in platability, the Fe content is preferably 0.90 mass% or less, 0.80 mass% or less, 0.70 mass% or less, 0.60 mass% or less, or 0.50 mass% or less. Furthermore, from the viewpoint of obtaining good rigidity and stress relaxation resistance, the Fe content is preferably 0.01 mass% or more, 0.02 mass% or more, 0.05 mass% or more, 0.10 mass% or more, 0.15 mass% or more, 0.25 mass% or more, 0.30 mass% or more, 0.35 mass% or more, or 0.40 mass% or more.

[0024] (Mn: 1.4 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 1.4 mass%, the compounds may become coarse and reduce platability. Therefore, the Mn content is set to 1.4 mass% or less (including 0 mass%). Note that, from the viewpoint of suppressing a reduction in platability, 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. Furthermore, from the viewpoint of obtaining good rigidity and stress relaxation resistance, the Mn content 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.

[0025] (Ni: 3.5 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 3.5 mass%, the compounds may become coarse and reduce platability. Therefore, the Ni content is set to 3.5 mass% or less (including 0 mass%). Note that, from the viewpoint of suppressing reduction in platability, 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. Furthermore, 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.

[0026] (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 are effective in 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 a decrease in plating smoothness, the Cu content is preferably 1.0% by mass or less, 0.75% by mass or less, 0.50% by mass or less, 0.35% by mass or less, 0.25% by mass or less, 0.20% by mass or less, 0.10% by mass or less, or 0.05% by mass or less. Furthermore, Cu may not be contained, but if it is contained, it is preferably 0.005% by mass or more from the viewpoint of reliably obtaining the effects of adding Cu. The Zn content is preferably 1.0% by mass or less, 0.75% by mass or less, 0.50% by mass or less, 0.35% by mass or less, 0.25% by mass or less, 0.20% by mass or less, 0.10% by mass or less, or 0.05% by mass or less from the viewpoint of suppressing a decrease in plating smoothness. Furthermore, Zn may not be contained, but if it is contained, it is preferably 0.005% by mass or more from the viewpoint of reliably obtaining the effects of adding Zn.

[0027] (Remainder: 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 melting raw materials used in producing the ingot. Specific examples of impurity elements include Ti, Zr, V, B, Na, K, Ca, Pb, P, Sn, Ag, Bi, In, Ge, Sr, and Cd. Among these, Ti, Zr, and V are restricted to 0.10 mass% or less, and B, Na, K, Ca, Pb, P, Sn, Ag, Bi, In, Ge, Sr, and Cd are restricted to 0.05 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 the elements shown as impurity elements are inevitably contained (i.e., when they are unavoidable impurities), the content of each element is preferably 0.005% by mass or less, and the total content of each element is preferably 0.015% by 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 unavoidable impurities is preferably 0.005% by mass or less.

[0028] <Young's modulus: 70 GPa or more> Young's modulus is the ratio of stress to strain when a material behaves elastically. In the present invention, it affects the generation of vibration when a thinned magnetic disk is rotated in a 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, a higher Young's modulus is preferable. 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 as described herein. 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 thick with the longitudinal direction parallel to the rolling direction and using the test piece. Specifically, the measurement can be carried out in accordance with the JIS standard by a free resonance method in an air atmosphere at room temperature (for example, 25° C.) It is preferable to use a test device such as the JE-RT model manufactured by Nippon Technoplus Co., Ltd.

[0029] <Stress Relaxation Rate: 90% or Less> After extensive research into the deformation of an aluminum alloy plate for magnetic disks during magnetic film sputtering, the inventors discovered that deformation can be suppressed by improving stress relaxation resistance. A stress relaxation rate of 90% or less can suppress deformation even when stress caused by thermal distortion during magnetic film sputtering is applied to the thinned substrate. 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, a lower stress relaxation rate is preferable. 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 may be, 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 as described herein. In addition to the above-described contents of Fe, Mn, and Ni, the content can be adjusted by setting the treatment conditions in the homogenization heat treatment step within the ranges described below and setting the number density of intermetallic compounds having a maximum length of 0.05 μm or more and 0.33 μm or less within the ranges described below.

[0030] The stress relaxation rate can be measured as follows. A test piece measuring 10 mm wide and 60 mm long is cut out so that the longitudinal direction is parallel to the rolling direction. The span length (x) in FIG. 1(a) is determined using the following formulas (2) and (3) so that the bending stress in the following formula (1) is constant, and the following test is performed. The test piece is placed in an atmospheric furnace with a bending stress applied (the state shown in FIG. 1(a)), and subjected to a heat treatment (300°C x 1 hour) simulating a magnetic film sputtering process. The test piece 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 (the state shown in FIG. 1(b)), and the deformation amount b after the bending stress is removed is measured. The ratio of the deformation amount b after the bending stress removal to the deformation amount a before the bending stress removal (b / a x 100 [%]) is defined as the stress relaxation rate.

[0031] 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]

[0032] M = P x x (2) M: bending moment [N mm] P: tip load [N] x: span length [mm]

[0033] 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 amount (2 [mm]) x: span length [mm]

[0034] <Number density of intermetallic compounds having a maximum length of 0.05 μm or more and 0.33 μm or less: 1.0 × 10 ６ pieces / mm ２ The greater the number density of intermetallic compounds in the aluminum alloy having a maximum length of 0.05 μm or more and 0.33 μm or less, the better the stress relaxation resistance properties that can be obtained. Intermetallic compounds having a maximum length of less than 0.05 μm or more than 0.33 μm do not have an effect on the stress relaxation resistance properties. The number density of intermetallic compounds having a maximum length of 0.05 μm or more and 0.33 μm or less on the surface of the aluminum alloy plate for a magnetic disk according to this embodiment is 1.0×10 ６ pieces / mm ２ More than 1.5 × 10 is preferable. ６ pieces / mm ２ More preferably, 2.0 × 10 ６ pieces / mm ２ More preferably, 2.5 × 10 ６ pieces / mm ２ More preferably, 3.0 × 10 ６ pieces / mm ２ More preferably, 3.5×10 ６ pieces / mm ２ The upper limit is not particularly limited, but for example, 1.0 × 10 ８ pieces / mm ２ Below, 1.0 x 10 ７ pieces / mm ２ The following is the result.

[0035] Examples of intermetallic compounds 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 Al-Fe intermetallic compounds is substituted, and Al-Mn-Cr intermetallic compounds in which a portion of the Al-Mn intermetallic compounds is substituted. Furthermore, when Cu and Zn are contained in the amounts specified in the present invention, examples of the intermetallic compounds include Al-Cu intermetallic compounds and Al-Zn intermetallic compounds.

[0036] The maximum length and number density of intermetallic compounds can be measured as follows: The surface of the measurement sample is cut with a diamond cutting tool to make it a mirror surface, and this surface is observed at a magnification of 10,000 times with 6 fields of view and an observation area of ​​0.0006 mm using an FE-SEM (JSM-7001F manufactured by JEOL Ltd., accelerating voltage 5 kV). ２ The image is photographed as a COMPO image, and a composition image called a COMPO image is obtained. From the photographed COMPO image, the matrix portion, i.e., the portion that appears whiter than the parent phase, is considered to be an intermetallic compound, and their maximum length is measured using particle analysis software ImageJ (ver. 1.53q). The maximum length of an intermetallic compound refers to the maximum value of the distance between any two points on the outline of an intermetallic compound particle. Then, the number of intermetallic compounds with a maximum length of 0.05 μm or more and 0.33 μm or less is counted using the particle analysis software, and the number density per unit area is calculated.

[0037] [Manufacturing Method of Aluminum Alloy Sheet for Magnetic Disk] Next, an example of a manufacturing method of an aluminum alloy sheet for 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, except for some conditions in the homogenization heat treatment and hot rolling processes. For example, an 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. Note that, if necessary, intermediate annealing may be performed before the cold rolling process or during the cold rolling process. Each process will be described in detail below.

[0038] (Casting Step) In the casting step, 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.

[0039] (Homogenization Heat Treatment Step) In the homogenization heat treatment step, the cast aluminum alloy ingot is chamfered and subjected to homogenization heat treatment. The chamfering amount can be, for example, 2 to 40 mm per side. From the viewpoint of adjusting the stress relaxation rate of the aluminum alloy sheet to 90% or less, the homogenization heat treatment is preferably performed by holding the aluminum alloy sheet at a temperature of 400 to 600°C for 4 to 50 hours. Specifically, by setting the homogenization heat treatment temperature to 400°C or higher and the homogenization heat treatment time to 4 hours or longer, the generation of intermetallic compounds in the aluminum alloy generated in the homogenization treatment having a size of 0.05 μm to 0.33 μm is promoted, thereby obtaining good stress relaxation resistance properties and enabling sufficient homogenization of the structure, thereby reducing the variation in the stress relaxation resistance properties of the resulting aluminum alloy sheet. The homogenization heat treatment temperature is preferably 420°C or higher, 440°C or higher, 450°C or higher, 460°C or higher, 480°C or higher, 500°C or higher, or 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. In addition, there is no upper limit to the homogenization heat treatment time, but from the viewpoint of economic efficiency in the manufacturing process, it is preferably 48 hours or lower, more preferably 30 hours or lower, even more preferably 24 hours or lower, and particularly preferably 18 hours or lower. In addition, from the viewpoint of promoting the formation of intermetallic compounds, the lower limit of the homogenization heat treatment time is preferably 6 hours or higher, more preferably 8 hours or higher, and even more preferably 10 hours or higher.

[0040] (Hot Rolling Step) In the hot rolling step, the aluminum alloy ingot subjected to the homogenization heat treatment is hot rolled to obtain a hot rolled sheet. The starting temperature of the hot rolling is preferably 480°C or higher from the viewpoint of adjusting the stress relaxation rate of the aluminum alloy sheet to 90% or less. The ending temperature of the hot rolling is preferably 300 to 350°C. Specifically, by setting the starting temperature of the hot rolling to 480°C or higher, the rolling load during the hot rolling can be reduced, and an increase in the number of hot rolling passes can be suppressed. The starting temperature of the 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 the hot rolling, the starting temperature of the hot rolling is preferably 550°C or lower, and more preferably 520°C or lower. The thickness of the hot rolled sheet obtained by hot rolling can be, for example, 3 mm or lower.

[0041] (Cold rolling step) 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 preferably, for example, 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 or less. By sequentially undergoing these steps, the aluminum alloy sheet according to this embodiment can be obtained.

[0042] [Aluminum Alloy Blank for Magnetic Disk] The aluminum alloy blank for magnetic disk according to this embodiment is obtained from the aluminum alloy plate for magnetic disk described above. Specifically, the blank can be manufactured by further performing, in this order, a punching process in which the aluminum alloy plate obtained after the cold rolling process is punched into a circular shape, and a correction annealing process in which the circular substrate obtained in the punching process is subjected to correction annealing, for example, by annealing while applying a load to flatten it. The chemical composition of the obtained blank remains unchanged from that of the aluminum alloy plate described above, and is the same composition. Furthermore, the characteristic values ​​of the blank, such as Young's modulus, stress relaxation rate, and number density of intermetallic compounds, are equivalent to those of the aluminum alloy plate. Therefore, the characteristic values ​​determined for the aluminum alloy plate 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 plate.

[0043] (Punching Process) In the punching process, the aluminum alloy plate may be tempered as necessary, and then punched into a ring shape so that the plate can be used as a substrate for a 3.5-inch HDD having an inner diameter of 24 mm and an outer diameter of 96 mm, or a substrate for a 2.5-inch HDD having an inner diameter of 19 mm and an outer diameter of 66 mm.

[0044] (Straightening Annealing Process) In the straightening annealing process, it is preferable to stack the annular substrates, for example, sandwiched between spacers with high flatness, and anneal the substrates while applying a load to flatten them. The annealing temperature can be 250 to 500°C, and the holding time can be, for example, about 3 to 5 hours. The temperature rise rate in straightening 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.

[0045] Regarding the temperature rise in corrective annealing, even if the temperature is raised in stages, 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 multiple temperature rise rates, i.e., staged, such that the temperature rise rate in a specific temperature range is a predetermined rate or a predetermined rate or higher, and a different temperature rise rate is used outside the specific temperature range. Note that in this embodiment, the annealing temperature in corrective annealing is assumed to be in the practical temperature range of 250 to 400°C, within the general annealing temperature range described above. By sequentially going through these steps, a blank according to this embodiment can be obtained.

[0046] [Aluminum Alloy Substrate for Magnetic Disk] The aluminum alloy substrate for magnetic disk according to this embodiment is obtained from the aluminum alloy blank for magnetic disk described above. Specifically, the substrate can be manufactured by performing 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 obtained substrate remains the same as that of the blank described above. Furthermore, the characteristic values ​​of the substrate, such as Young's modulus, stress relaxation rate, and number density of intermetallic compounds, are equivalent to those of the blank. Therefore, the characteristic values ​​determined for the aluminum alloy plate 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 plate or blank.

[0047] 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.

[0048] [Magnetic Disk Manufacturing Method] Magnetic disks can be manufactured using manufacturing methods and equipment under typical conditions 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 the like are formed on the surface of the substrate, thereby manufacturing a magnetic disk.

[0049] 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.

[0050] (Preparation of Test Materials) Test materials Nos. 1 to 3 were manufactured using aluminum alloys having the chemical compositions shown in Table 1 under the following conditions.

[0051] 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 8 hours. 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 to a thickness of 2.0 mm. No. 1 was 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 a diameter of approximately 98 mm, 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 7 hours or less) to produce blanks (O-tempered materials) of the respective thicknesses.

[0052] For each of the produced test materials, the number density, Young's modulus, and stress relaxation rate of the intermetallic compounds having a maximum length of 0.05 μm or more and 0.33 μm or less were evaluated as follows.

[0053] (Number density of intermetallic compounds having a maximum length of 0.05 μm or more and 0.33 μm or less) The surface of the test material was cut with a diamond bite to form a mirror surface, and this surface was observed at a magnification of 10,000 times with 6 fields of view and an observation area of ​​0.0006 mm using an FE-SEM (JSM-7001F manufactured by JEOL Ltd., accelerating voltage 5 kV).２ The image was photographed as a COMPO image, and a composition image called a COMPO image was obtained. From the photographed COMPO image, the matrix portion, i.e., the portion appearing whiter than the parent phase, was considered to be an intermetallic compound, and their maximum length was measured using particle analysis software ImageJ (ver. 1.53q). Then, the number of intermetallic compounds having a maximum length of 0.05 μm or more and 0.33 μm or less was counted using the particle analysis software, and the number density per unit area was calculated.

[0054] (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 of the test material were cut out from the test material, with the rolling direction parallel to the longitudinal direction, and the test pieces were used for measurement. The thickness of test piece No. 1 was 0.55 mm, and Nos. 2 and 3 were 0.52 mm. Measurements were performed using a JE-RT model tester manufactured by Nippon Technoplus Co., Ltd. in an air atmosphere at room temperature (25°C) by a free resonance method. Young's modulus of 70 GPa or more was evaluated as "○", and that of less than 70 GPa was evaluated as "×". ○ was a pass, and × was a fail.

[0055] (Stress Relaxation Rate) Test pieces measuring 10 mm wide and 60 mm long were cut from the test material so that the longitudinal direction was parallel to the rolling direction. The span length (x) in FIG. 1(a) was determined for each test material using the following formulas (2) and (3) so that the bending stress in the following formula (1) was constant, and the following test was performed. The test pieces were placed in an atmospheric furnace with a bending stress applied (the state shown in FIG. 1(a)) and subjected to a heat treatment (300°C x 1 hour) simulating a magnetic film sputtering process. The test pieces were then removed from the atmospheric furnace, and the deformation amount a before the bending stress was removed was measured. The bending stress was then removed (the state shown in FIG. 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 x 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, and samples with a stress relaxation rate of more than 90% were evaluated as "Poor" indicating poor deformation suppression during magnetic film sputtering.

[0056] σ=M / Z...(1) σ: Bending stress [N / mm２ ] M: Bending moment [N mm] Z: Section modulus (Z [mm ３ ]=(w×t ２ ) / 6) w: Plate width [mm], t: Plate thickness [mm]

[0057] M = P x x (2) M: bending moment [N mm] P: tip load [N] x: span length [mm]

[0058] 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 amount (2 [mm]) x: span length [mm]

[0059] The results of evaluation of the alloy composition (chemical composition), number density of intermetallic compounds, Young's modulus, and stress relaxation rate for 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.

[0060]

[0061] As is clear from the results in Table 1, Nos. 1 and 2, which satisfied the requirements of the present invention, were able to obtain aluminum alloy sheets and blanks having good rigidity and excellent stress relaxation resistance, and capable of suppressing thermal deformation during magnetic film sputtering. On the other hand, No. 3, whose total of Fe, Mn, and Ni did not satisfy the requirements of the present invention, was inferior to Nos. 1 and 2 in rigidity and stress relaxation resistance.

[0062] 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.

[0063] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on Japanese patent applications filed on June 26, 2023 (Patent Application No. 2023-104342) and February 19, 2024 (Patent Application No. 2024-023206), the contents of which are incorporated herein by reference.

Claims

1. An aluminum alloy plate for magnetic disks, comprising: 0.1-7.0 mass% Mg, 0.005-1.0 mass% Cr, 3-100 mass ppm Be, 0.20 mass% or less Si, 0.05-5.9 mass% in total of at least one of Fe, Mn and Ni, with the remainder being Al and impurities.

2. The aluminum alloy plate for magnetic disks according to claim 1, containing at least one of the following: Fe: 0 to 1.00 mass %, Mn: 0 to 1.4 mass %, and Ni: 0 to 3.5 mass %.

3. The aluminum alloy plate for magnetic disks according to claim 1 or 2, further comprising at least one of Cu: 1.0 mass% or less and Zn: 1.0 mass% or less.

4. The number density of intermetallic compounds on the surface having a maximum length of 0.05 μm or more and 0.33 μm or less is 1.0 × 10 ６ pieces / mm ２ 3. The aluminum alloy sheet for magnetic disks according to claim 1 or 2.

5. The aluminum alloy sheet for magnetic disks according to claim 1 or 2, which has a Young's modulus of 70 GPa or more.

6. The aluminum alloy sheet for magnetic disks according to claim 1 or 2, which has a stress relaxation rate of 90% or less.

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

8. An aluminum alloy substrate for magnetic disks obtained from the aluminum alloy blank for magnetic disks according to claim 7.

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