Aluminum alloy plate for magnetic disks, aluminum alloy blank for magnetic disks, aluminum alloy substrate for magnetic disks, and method for manufacturing aluminum alloy plate for magnetic disks.

Abstract

The present invention provides an aluminum alloy plate for magnetic disks, an aluminum alloy plate blank for magnetic disks, an aluminum alloy plate substrate for magnetic disks, and a method for manufacturing an aluminum alloy plate for magnetic disks, all of which can suppress thermal deformation during magnetic film sputtering. [Solution] An aluminum alloy plate for magnetic disks containing Mg: 2.5 to 7.0 mass%, Cr: 0.01 to 1.0 mass%, Si: 0.20 mass% or less, the total of at least one of Fe, Mn, and Ni: 0.05 to 3.4 mass%, the remainder being Al and impurities, having a thermal conductivity of 152 (W / (m·K)) or less, and a stress relaxation rate of 90% or less.

Description

[Technical Field]

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

[0002] With the digitalization of information and the spread of the internet, large amounts of digital data are being handled, leading to a demand for larger capacity hard disk drives (HDDs), particularly in data centers. To increase HDD capacity, efforts are being made to thin the magnetic disks themselves, with the aim of increasing the number of magnetic disks that can be installed in a single HDD.

[0003] However, as shown in Patent Document 1, it is known that thermal distortion occurs around the gripping portion of a substrate for a magnetic disk due to thermal expansion that occurs during magnetic film sputtering, and the thinner the magnetic disk, the greater the thermal distortion that occurs around the gripping portion.

[0004] Furthermore, regarding substrates for magnetic disks, the "flatness" metric is extremely important because it greatly affects the performance of hard disk drives (HDDs) that use that substrate. During the production process of circuit boards, deformation due to thermal strain that occurs during magnetic film sputtering is a concern. This deformation negatively affects the flatness of the circuit board and can lead to the production of substandard products. Currently, due to concerns about resource depletion, recycling of various materials is progressing, and the recycling of metals, which are consumed in large quantities, has been carried out for some time. While the above-mentioned non-standard products can also be reused through recycling, it is crucial to suppress the generation of non-standard products by controlling thermal distortion, and this is being investigated.

[0005] For example, Patent Document 1 describes that by providing an aluminum alloy plate for magnetic disks having a specific chemical composition and specifying the coefficient of linear expansion and the number density of intermetallic compounds within a specific range, it is possible to achieve excellent plating properties and suppress deformation due to thermal strain during sputtering of the magnetic film. Furthermore, Patent Document 2 describes that by using an aluminum alloy substrate with improved conductivity, i.e., thermal conductivity, the energy required to reach the desired temperature in magnetic film sputtering can be reduced, leading to improved energy efficiency. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2024-059016 [Patent Document 2] Japanese Patent Publication No. 2023-032361 [Overview of the project] [Problems that the invention aims to solve]

[0007] With the recent demand for thinner walls, there is an increasing need for technologies to prevent deformation caused by thermal strain during sputtering of magnetic films. However, Patent Document 1 did not consider improving thermal conductivity or stress relaxation resistance as methods for suppressing thermal strain. Furthermore, while Patent Document 2 considered conductivity from the perspective of energy saving, it did not consider thermal conductivity as a method for suppressing thermal strain. Thus, while both thermal conductivity and stress relaxation resistance are important for suppressing thermal deformation in aluminum alloy plates for magnetic disks, there was still room for investigation into developing an aluminum alloy plate for magnetic disks that could achieve both.

[0008] 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, an aluminum alloy plate substrate for magnetic disks, and a method for manufacturing an aluminum alloy plate for magnetic disks that can suppress thermal deformation during magnetic film sputtering. [Means for solving the problem]

[0009] As a result of extensive research by the inventors, it was discovered that by using a specific alloy composition and setting the thermal conductivity and stress relaxation rate within a specific range, an aluminum alloy plate for magnetic disks that can suppress thermal deformation during magnetic film sputtering can be obtained, thus creating the present invention.

[0010] In other words, the present invention relates to the following: [1] Mg: 2.5~7.0% by mass, Contains Cr: 0.01~1.0% by mass, Si: 0.20 mass% or less, The total amount of at least one of Fe, Mn, and Ni is 0.05 to 3.4% by mass. The remainder consists of Al and impurities. The thermal conductivity is 152 (W / (m·K)) or less. An aluminum alloy plate for magnetic disks with a stress relaxation rate of 90% or less. [2] The aforementioned Fe: 0 to 1.00 mass%, The aforementioned Mn: 0 to 1.4 mass%, and An aluminum alloy plate for magnetic disks according to [1], containing at least one of the above Ni: 0 to 1.0 mass%. [3] Furthermore, Be: 3-100 ppm by mass, and Cu: 1.0% by mass or less, An aluminum alloy plate for magnetic disks according to [1] or [2], containing at least one of the following: Zn: 1.0% by mass or less. [4] An aluminum alloy blank for magnetic disks obtained from the aluminum alloy sheet for magnetic disks according to [1] or [2]. [[5]] An aluminum alloy blank for magnetic disks obtained from the aluminum alloy sheet for magnetic disks according to [3]. [[6]] An aluminum alloy substrate for magnetic disks obtained from the aluminum alloy blank for magnetic disks according to [4]. [[7]] Mg: 2.5 to 7.0 mass%, Cr: 0.01 to 1.0 mass%, Si: 0.20 mass% or less, total of at least one selected from the group consisting of Fe, Mn and Ni: 0.05 to 3.4 mass%, a method for producing an aluminum alloy sheet for magnetic disks, with the balance being Al and impurities, the method comprising: a casting step of casting a molten aluminum alloy into an aluminum alloy ingot by a semi-continuous casting method; a homogenization heat treatment step of facing the aluminum alloy ingot and performing homogenization heat treatment thereon; a hot rolling step of hot rolling the homogenization heat-treated aluminum alloy ingot to obtain a hot-rolled sheet; and a cold rolling step of cold rolling the hot-rolled sheet, which are included in this order, wherein the value of the finishing temperature of hot rolling in the hot rolling step and the value of the total content of Cu, Mn, Cr and Ni satisfy the relationship of the following formula (1): 3.8 ≦ T / 100 + C Formula (1) (In formula (1), C is the value of the total content (mass%) of Cu, Mn, Cr and Ni among the components contained in the alloy, and T is the value of the finishing temperature (°C) of hot rolling.) Effects of the Invention

[0011] 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, an aluminum alloy plate substrate for magnetic disks, and a method for manufacturing an aluminum alloy plate for magnetic disks, which can suppress thermal deformation during sputtering of magnetic films. [Brief explanation of the drawing]

[0012] [Figure 1] Figures 1(a) and 1(b) illustrate the measurement of the stress relaxation rate in the embodiment. [Modes for carrying out the invention]

[0013] The following describes an aluminum alloy plate for magnetic disks, an aluminum alloy blank for magnetic disks, and an aluminum alloy substrate for magnetic disks related to one embodiment of the present invention. 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 may be simply referred to as "aluminum alloy plate," "blank," and "substrate," respectively.

[0014] [Aluminum alloy plate for magnetic disks] The aluminum alloy plate for magnetic disks according to this embodiment contains Mg: 2.5 to 7.0 mass%, Cr: 0.01 to 1.0 mass%, Si: 0.20 mass% or less, and the total amount of at least one of Fe, Mn, and Ni is 0.05 to 3.4 mass%, with the remainder being Al and impurities. The aluminum alloy plate for magnetic disks according to this embodiment may also contain Cu and Zn. The components of the aluminum alloy plate for the magnetic disk according to this embodiment will be described in detail below.

[0015] (Mg: 2.5% 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 included in the aluminum alloy plate to obtain good yield strength. If the Mg content in the aluminum alloy sheet is less than 2.5% 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 should be between 2.5% by mass and 7.0% by mass. Furthermore, from the viewpoint of improving yield strength, the Mg content is preferably 2.7% by mass or more, 3.0% by mass or more, 3.2% by mass or more, 3.5% by mass or more, 3.7% by mass or more, 4.0% by mass or more, and 4.2% by mass or more. Also, from the viewpoint of suppressing a decrease in rigidity, it is preferably 6.7% by mass or less, 6.5% by mass or less, 6.2% by mass or less, 6.0% by mass or less, 5.7% by mass or less, 5.5% by mass or less, and 5.2% by mass or less.

[0016] (Cr: 0.01 mass% or more and 1.0 mass% or less) Cr is an essential constituent element in the aluminum alloy plate for magnetic disks according to this embodiment, and is included in the aluminum alloy plate to obtain good yield strength and thermal conductivity. If the Cr content in the aluminum alloy sheet is less than 0.01% by mass, the above effects cannot be obtained. On the other hand, if the Cr content exceeds 1.0% by mass, the intermetallic compounds become coarser, and edge cracking may occur, potentially reducing the rollability. Therefore, the Cr content should be between 0.01% by mass and 1.0% by mass. Furthermore, from the viewpoint of improving yield strength, the Cr content is preferably 0.03% by mass or more, 0.05% by mass or more, 0.08% by mass or more, and 0.1% by mass or more. Also, from the viewpoint of ensuring rollability, it is preferably 0.9% by mass or less, 0.8% by mass or less, 0.7% by mass or less, 0.6% by mass or less, 0.5% by mass or less, 0.4% by mass or less, 0.3% by mass or less, 0.2% by mass or less, and 0.15% by mass or less.

[0017] (Si: 0.20% by mass or less) Si is an element that is introduced as an impurity from the base metal in the aluminum alloy sheet for magnetic disks according to this embodiment. It may exist in the aluminum alloy sheet in the form of elemental Si, or it may form Al-Fe-Si intermetallic compounds. If the Si content in the aluminum alloy sheet exceeds 0.20 mass%, the rollability may decrease due to elemental Si. Therefore, from the viewpoint of suppressing the formation of elemental Si, the Si content in the aluminum alloy sheet is set to 0.20 mass% or less (including 0.00 mass%). Furthermore, from the viewpoint of suppressing a decrease in 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, and 0.02% by mass or less. However, reducing the Si content requires the use of high-purity raw materials such as Al ingots and intermediate alloy ingots, which results in higher raw material costs. Therefore, an Si content of 0.004% by mass or higher is industrially preferable.

[0018] (Total of Fe, Mn, and Ni: 0.05-3.4% by mass) Fe, Mn, and Ni are components that contribute to improving stress relaxation resistance. Therefore, the aluminum alloy plate for magnetic disks according to this embodiment contains at least one selected from the group consisting of Fe, Mn, and Ni. That is, it may contain Fe, Mn, or Ni alone, or two types of Fe and Mn, Mn and Ni, or Ni and Fe, or all of Fe, Mn, and Ni, and is not particularly limited as long as the total content is between 0.05 and 3.4% by mass. Furthermore, 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, and 1.0% by mass or more in order to obtain good stress relaxation resistance properties. On the other hand, if these are included in excess, the compound may become coarse and the plating performance may decrease. For this reason, the total content is preferably 3.2% by mass or less, 3.0% by mass or less, 2.7% by mass or less, 2.5% by mass or less, 2.2% by mass or less, 2.0% by mass or less, 1.7% by mass or less, 1.5% by mass or less, and 1.2% by mass or less.

[0019] Furthermore, the aluminum alloy plate for magnetic disks according to this embodiment preferably contains at least one of the following: Fe: 0 to 1.00 mass%, Mn: 0 to 1.4 mass%, and Ni: 0 to 1.0 mass%.

[0020] (Fe: 1.00% by mass or less) Fe is included in aluminum alloy sheets to obtain good stress relaxation resistance. However, if the Fe content in the aluminum alloy sheet exceeds 1.00 mass%, the compound may coarseen, potentially reducing the plating properties. Therefore, the Fe content should be 1.00 mass% or less (including 0 mass%). Furthermore, from the viewpoint of suppressing a decrease in plating properties, 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, and 0.50% by mass or less. Also, from the viewpoint of obtaining good stress relaxation resistance, it 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, and 0.40% by mass or more.

[0021] (Mn: 1.4% by mass or less) Mn is included in aluminum alloy sheets to obtain good thermal conductivity and stress relaxation resistance. However, if the Mn content in the aluminum alloy sheet exceeds 1.4% by mass, the compound may coarseen, potentially reducing the plating properties. Therefore, the Mn content should be 1.4% by mass or less (including 0% by mass). Furthermore, from the viewpoint of suppressing a decrease in plating properties, the Mn content is preferably 1.3% by mass or less, 1.2% by mass or less, 1.1% by mass or less, 1.0% by mass or less, 0.9% by mass or less, 0.8% by mass or less, 0.7% by mass or less, and 0.6% by mass or less. Also, from the viewpoint of obtaining good thermal conductivity and stress relaxation resistance, it is preferably 0.05% by mass or more, 0.1% by mass or more, 0.2% by mass or more, 0.3% by mass or more, 0.4% by mass or more, and 0.5% by mass or more.

[0022] (Ni: 1.0% by mass or less) Ni is included in aluminum alloy sheets to obtain good thermal conductivity and stress relaxation resistance. However, if the Ni content in the aluminum alloy sheet exceeds 1.0 mass%, the compound may coarseen, potentially reducing the plating properties. Therefore, the Ni content should be 1.0 mass or less (including 0 mass%). Furthermore, from the viewpoint of suppressing a decrease in plating performance, the Ni content is preferably 0.9 mass% or less, 0.8 mass% or less, 0.7 mass% or less, 0.6 mass% or less, 0.5 mass% or less, 0.4 mass% or less, 0.3 mass% or less, 0.2 mass% or less, 0.1 mass% or less, and 0.05 mass% or less. Also, from the viewpoint of obtaining good thermal conductivity and stress relaxation resistance, it is preferably 0.01 mass% or more, 0.02 mass% or more, 0.03 mass% or more, and 0.04 mass% or more.

[0023] (Be: 3 mass ppm or more and 100 mass ppm or less) Be may be included in the aluminum alloy plate for magnetic disks according to this embodiment. When Be is included, it has the effect of forming an oxide film during casting and suppressing the formation of Mg oxide. It also has the effect of improving the hot rolling and formability of the aluminum alloy, and furthermore, it can reduce the adhesion between blanks by suppressing oxidation during straightening annealing, and can suppress the deterioration of flatness due to external force during subsequent delamination, thereby achieving excellent flatness. When the Be content is 3 ppm by mass or more, the effects of Be addition can be fully obtained. On the other hand, when the Be content is 100 ppm by mass or less, the rolling properties are improved by preventing the Be-containing compound from becoming coarse and suppressing the occurrence of cracking. From the viewpoint of fully obtaining the above-mentioned effects of Be addition, 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. Furthermore, from the viewpoint of ensuring rolling properties, it 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. Be does not have to be included, but if it is included, from the viewpoint of reliably obtaining the above-mentioned effects of Be addition, it is preferably 3 ppm by mass or more and 100 ppm by mass or less.

[0024] (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 depositing zinc in zincate treatment and contribute to improving the smoothness of the plating. On the other hand, if Cu or Zn is present in excess, the smoothness of the plating may actually be worse. Furthermore, the smoothness of the electroless Ni-P plating film formed on the surface may be reduced. For this reason, it is preferable that the aluminum alloy plate for magnetic disks according to this embodiment further contains at least one of Cu: 1.0 mass% or less and Zn: 1.0 mass% or less. Furthermore, in the aluminum alloy plate for magnetic disks according to this embodiment, it is preferable to further contain at least one of the following: Be: 3 to 100 ppm by mass, 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, and 0.05% by mass or less. Furthermore, Cu may not be included, but if it is included, from the viewpoint of reliably obtaining the effects of adding Cu as described above, 0.005% by mass or more is preferred. From the viewpoint of suppressing a decrease in plating smoothness, 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, and 0.05% by mass or less. Furthermore, Zn may not be included, but if it is included, from the viewpoint of reliably obtaining the effects of adding Zn as described above, it is preferably 0.005% by mass or more.

[0025] (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 raw materials used in the ingot manufacturing process. Specifically, examples of impurity elements include Ti, Zr, V, B, Na, K, Ca, Pb, P, Sn, Ag, Bi, In, Ge, Sr, and Cd. Of these, Ti, Zr, and V are limited to 0.10 mass% or less each, and B, Na, K, Ca, Pb, P, Sn, Ag, Bi, In, Ge, Sr, and Cd are limited to 0.05 mass% or less each. Within this range, these elements will not hinder the effects of this embodiment, whether they are included as unavoidable impurities or actively added, such as by intentionally increasing the proportion of scrap containing these elements. If each of the elements listed as impurity elements is inevitably present (i.e., if they are unavoidable impurities), it is preferable that the content of each element is 0.005% by mass or less, and the total content of each element is 0.015% by mass or less. Furthermore, when the chemical composition does not include the above-mentioned Si, Fe, Mn, Ni, Be, Cu, and Zn, it is preferable that the content of these unavoidable impurities is 0.005% by mass or less for each.

[0026] <Thermal conductivity: 152 (W / (m·K)) or less> The inventors of this invention conducted various studies on conditions that can prevent deformation due to thermal strain when an aluminum alloy plate is used as the substrate for a magnetic disk. As a result, they found that appropriately specifying the thermal conductivity of the aluminum alloy plate is effective. Thermal conductivity is a value that indicates how quickly thermal energy is conducted in a material, and is determined based on thermal diffusivity, density, and specific heat. By controlling the thermal conductivity to a value below a predetermined value, it is possible to reduce the energy imparted to the aluminum alloy plate during magnetic film sputtering, and it is estimated that deformation due to thermal strain during sputtering of the magnetic film can be suppressed. Therefore, the thermal conductivity of the aluminum alloy plate for the magnetic disk according to this embodiment is set to 152 (W / (m·K)) or less. From the viewpoint of further suppressing the deformation of the thinned substrate, a lower thermal conductivity is preferable. For example, a thermal conductivity of 150 (W / (m·K)) or less is more preferable, 147 (W / (m·K)) or less is more preferable, 145 (W / (m·K)) or less is more preferable, 140 (W / (m·K)) or less is more preferable, 135 (W / (m·K)) or less is even more preferable, and 130 (W / (m·K)) or less is particularly preferable. While there is no particular limit to the thermal conductivity, examples include 90 (W / (m·K)) or higher, 100 (W / (m·K)) or higher, 110 (W / (m·K)) or higher, and 120 (W / (m·K)) or higher. The thermal conductivity can be adjusted by setting the content of Mg, Cr, and Si within specific ranges, and the total content of Fe, Mn, and Ni within the ranges described herein. In addition to the above-mentioned content of Fe, Mn, and Ni, the thermal conductivity can also be adjusted by setting the processing conditions in the hot rolling process within the ranges described below.

[0027] <Stress relaxation rate: 90% or less> The inventors of this invention have diligently studied the deformation of aluminum alloy plates for magnetic disks during magnetic film sputtering and have found that deformation can be suppressed by improving the stress relaxation resistance characteristics. A stress relaxation rate of 90% or less suppresses deformation even when stress caused by thermal strain during magnetic film sputtering is applied to the substrate during thinning. Therefore, a stress relaxation rate of 90% or less is preferred for the aluminum alloy plate for magnetic disks according to this embodiment. From the viewpoint of further suppressing deformation of the thinned substrate, a lower stress relaxation rate is preferable. For example, a stress relaxation rate of 85% or less is more preferable, 80% or less is even more preferable, and 75% or less is particularly preferable. While there are no particular limitations on the lower limit of the stress relaxation rate, examples include 0% or more, 20% or more, 50% or more, 60% or more, and 70% or more. The stress relaxation rate can be adjusted by setting the content of Mg, Cr, and Si within a specific range, and the total content of Fe, Mn, and Ni within the range described herein. In addition to the above-mentioned content of Fe, Mn, and Ni, the stress relaxation rate can also be adjusted by setting the processing conditions in the hot rolling process within the range described below.

[0028] The stress relaxation rate can be measured as follows. A test specimen measuring 10 mm in width and 60 mm in length is cut out so that its longitudinal direction is parallel to the rolling direction. Then, the span length (x) in Figure 1(a) is determined using equations (2) and (3) below so that the bending stress in equation (1) below is constant, and the following test is performed. The sample is placed in an atmospheric furnace under a bending stress (as shown in Figure 1(a)) and subjected to a heat treatment simulating magnetic film sputtering (300°C for 1 hour). After that, it is removed from the atmospheric furnace and the deformation amount a before bending stress removal is measured. Then, the bending stress is removed (as shown in Figure 1(b)) and the deformation amount b after bending stress removal is measured. The stress relaxation rate is defined as the ratio of the deformation amount b after unloading to the deformation amount a before unloading (b / a × 100 [%]).

[0029] 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]

[0030] M = P × x ... (2) M: Bending moment [N·mm] P: Tip load [N] x: Span length [mm]

[0031] P = (3 × E × I × δ) / x 3 ...(3) P: Tip load [N] E: Young's modulus [N / mm²] 2 ] I: Second moment of area (I[mm[mm] 4 ]=(w×t 3 ) / 12) w: Plate width [mm], t: Plate thickness [mm] δ: Deflection (2 [mm]) x: Span length [mm]

[0032] [Manufacturing method for aluminum alloy plates for magnetic disks] Next, an example of a method for manufacturing an aluminum alloy plate for magnetic disks according to this embodiment will be described. The alloy sheet according to this embodiment can be manufactured using manufacturing methods and equipment that are typical for manufacturing aluminum alloy sheets for magnetic disks, with the exception of some conditions in the hot rolling process. For example, an aluminum alloy sheet can be manufactured by a manufacturing method that includes, in this order: a casting step of melting raw materials and adjusting the molten aluminum alloy to a predetermined chemical composition, and then casting it into an aluminum alloy ingot using a semi-continuous casting method or the like; a homogenization heat treatment step of surface machining the cast aluminum alloy ingot and subjecting it to homogenization heat treatment; a hot rolling step of hot rolling the homogenized aluminum alloy ingot to obtain a hot-rolled sheet; and a cold rolling step of cold rolling the hot-rolled sheet. If necessary, intermediate annealing may be performed before the cold rolling step or during the cold rolling step.

[0033] In contrast, the manufacturing method according to this embodiment is Mg: 2.5~7.0% by mass, Cr:0.01~1.0% by mass It contains, Si: 0.20 mass% or less, The total amount of at least one of Fe, Mn, and Ni is 0.05 to 3.4% by mass. A method for manufacturing an aluminum alloy plate for magnetic disks, the remainder of which consists of Al and impurities, A casting process in which molten aluminum alloy is cast into an aluminum alloy ingot using a semi-continuous casting method, The process involves surface machining the aluminum alloy ingot and then subjecting it to a homogenization heat treatment, A hot rolling process to obtain a hot-rolled plate by hot-rolling the aluminum alloy ingot that has undergone the homogenization heat treatment, The process includes, in this order, a cold rolling step in which the hot-rolled sheet is cold-rolled, The method for manufacturing an aluminum alloy sheet for a magnetic disk is such that the value of the end temperature of the hot rolling process and the value of the total amount of Cu, Mn, Cr, and Ni satisfy the following equation (1). 3.8 ≦ T / 100 + C Equation (1) (In formula (1), C is the total amount (mass%) of Cu, Mn, Cr, and Ni among the components contained in the alloy, and T is the value of the end temperature (°C) of the hot rolling process.)

[0034] The following provides a detailed explanation of each step.

[0035] (Casting process) In the casting process, the raw materials are melted at 700-800°C to obtain molten aluminum alloy. It is preferable to cast this molten aluminum alloy ingot at 700-800°C using a known semi-continuous casting method such as DC casting.

[0036] (Homogenization heat treatment process) The homogenization heat treatment process involves surface machining of the cast aluminum alloy ingot and then applying the homogenization heat treatment. The amount of surface machining can be, for example, 2 to 40 mm per side. Homogenization heat treatment is preferably carried out by holding the material 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 more, it is possible to sufficiently homogenize the structure, thereby reducing the variation in stress relaxation resistance characteristics of the resulting aluminum alloy sheet. Preferred homogenization heat treatment temperatures are 420°C or higher, 440°C or higher, 450°C or higher, 460°C or higher, 480°C or higher, 500°C or higher, and 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. More preferably, the homogenization heat treatment temperature is 580°C or lower, and even more preferably 540°C or lower. Furthermore, there is no upper limit to the time of the homogenization heat treatment, but from the viewpoint of economic efficiency in the manufacturing process, it is preferable to have 48 hours or less, more preferably 30 hours or less, even more preferably 24 hours or less, and particularly preferable to have 18 hours or less. Furthermore, from the viewpoint of structural homogenization, the lower limit of the homogenization heat treatment time is preferably 6 hours or more, more preferably 8 hours or more, and even more preferably 10 hours or more.

[0037] (Hot rolling process) In the hot rolling process, an aluminum alloy ingot that has undergone homogenization heat treatment is hot-rolled to obtain a hot-rolled sheet. From the viewpoint of adjusting the stress relaxation rate of the aluminum alloy sheet to 90% or less, the starting temperature for hot rolling is preferably 490°C or higher. Specifically, by setting the starting temperature for hot rolling to 480°C or higher, the rolling load during hot rolling can be reduced, and the increase in the number of hot rolling passes can be suppressed. The starting temperature for 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 for hot rolling is preferably 550°C or lower, and more preferably 520°C or lower.

[0038] In the method for manufacturing an aluminum alloy plate for magnetic disks according to this embodiment, the value of the end temperature of the hot rolling process and the value of the total amount of Cu, Mn, Cr, and Ni satisfy the following relationship (1). 3.8 ≦ T / 100 + C Equation (1) (In formula (1), C is the total amount (mass%) of Cu, Mn, Cr, and Ni among the components contained in the alloy, and T is the value of the end temperature (°C) of the hot rolling process.)

[0039] In the method for manufacturing an aluminum alloy plate for magnetic disks according to this embodiment, a good thermal conductivity can be obtained when the value of the end temperature of the hot rolling process and the total amount of Cu, Mn, Cr, and Ni satisfy the relationship of formula (1) above.

[0040] This indicates that a higher total amount of Cu, Mn, Cr, and Ni, which are mainly present as solid solution elements in the alloy, results in better thermal conductivity, while a lower end temperature for hot rolling does not result in good thermal conductivity. If the hot rolling termination temperature is low, sufficient solid solution elements cannot be dissolved in the alloy at the end of the hot rolling process, resulting in poor thermal conductivity. On the other hand, even if the hot rolling termination temperature is low, good thermal conductivity can be obtained if the total amount of Cu, Mn, Cr, and Ni in the alloy is sufficiently large. Therefore, it is preferable to satisfy the above equation in order to obtain good thermal conductivity. Furthermore, the thickness of the hot-rolled sheet obtained by hot rolling can be, for example, 3 mm or less.

[0041] (Cold rolling process) In the cold rolling process, 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, and 0.35 mm or less. By following these steps in order, an aluminum alloy sheet according to this embodiment can be obtained.

[0042] [Aluminum alloy blank for magnetic disks] The aluminum alloy blank for magnetic disks according to this embodiment is obtained from the above-mentioned aluminum alloy sheet for magnetic disks. Specifically, the blank can be manufactured by further following these steps in order: a punching step in which the aluminum alloy sheet obtained after the cold rolling step is punched out in an annular shape, and a straightening annealing step in which the annular substrate obtained in the punching step is subjected to straightening annealing, for example, by applying a load while annealing to flatten it. The chemical composition of the resulting blank will not change from that of the aluminum alloy plate described above, and will be the same. Furthermore, the characteristic values ​​of the blank, such as thermal conductivity and stress relaxation rate, are equivalent to those of the aluminum alloy sheet. Therefore, the characteristic values ​​obtained for the aluminum alloy sheet can be considered as characteristic values ​​for the blank. Conversely, the characteristic values ​​obtained for the blank can also be considered as characteristic values ​​for the aluminum alloy sheet.

[0043] (punching process) In the punching process, the aluminum alloy sheet is tempered as needed, and then punched into an annular shape so that it can be used, for example, as 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.

[0044] (Corrective annealing process) In the straightening annealing process, it is preferable to stack annular substrates sandwiched between spacers having high flatness, for example, and then anneal them while applying a load to flatten them. The annealing temperature can be 250 to 500°C, and the holding time can be, for example, 3 to 5 hours. The heating rate in straightening annealing can be, for example, an average of about 80°C / hour, and preferably no more than 1000°C / hour at the fastest. Cooling can be done, for example, by opening the door of the annealing furnace.

[0045] Regarding the heating of the straightening annealing, the effects of this embodiment can be impaired even if the heating is increased in stages. For example, as described in paragraphs 0068 and 0069 of Japanese Patent Publication No. 5815153, heating may be increased at multiple heating rates, i.e., in stages, by setting the heating rate in a specific temperature range to a predetermined rate or higher, and using a different heating rate for temperatures outside that specific temperature range. In this embodiment, the annealing temperature for straightening is assumed to be within the practical temperature range of 250 to 400°C, within the general annealing temperature range described above. By following these steps in order, a blank according to this embodiment can be obtained.

[0046] [Aluminum alloy substrate for magnetic disks] The aluminum alloy substrate for magnetic disks according to this embodiment is obtained from the above-mentioned aluminum alloy blank for magnetic disks. Specifically, the substrate can be manufactured by performing cutting (end face machining) on ​​the end face of the blank and grinding (mirror finish) on the surface (main surface) of the blank. The chemical composition of the resulting substrate will not change from the blank described above and will be the same. Furthermore, the characteristic values ​​of the substrate, such as thermal conductivity and stress relaxation rate, are equivalent to those of the blank. Therefore, characteristic values ​​obtained for aluminum alloy sheets and blanks can be considered as characteristic values ​​for the substrate. Conversely, characteristic values ​​obtained for the substrate can also be considered as characteristic values ​​for aluminum alloy sheets and blanks.

[0047] The aluminum alloy plate, blank, and substrate according to this embodiment can each be obtained by the method described above, but other processes may be carried out between or before / after each process, as long as they do not adversely affect each process.

[0048] [Manufacturing method for magnetic disks] Magnetic disks can be manufactured using manufacturing methods and equipment that meet general conditions for manufacturing magnetic disks. For example, the surface of a substrate can be acid-etched to form an electroless Ni-P plating film, and then the surface of the electroless Ni-P plating film can be polished. Subsequently, a base layer, a magnetic layer, a protective film, etc., can be formed on the surface of the substrate to manufacture a magnetic disk. [Examples]

[0049] The present invention will be specifically described below with reference to examples of the present invention. However, the technical scope of the present invention is not limited thereto.

[0050] (Preparation of test materials) The test materials for Nos. 1 to 3 were manufactured using aluminum alloys with the chemical compositions shown in Table 1, under the following conditions.

[0051] First, molten metal was used to create slabs using DC casting in molds of different ingot thicknesses (500 mm for No. 1 and 2, and 530 mm for No. 3). Then, both sides (in the thickness direction) of the obtained slabs were machined by 16 mm. After that, a homogenization heat treatment was performed, held at 535°C for 8 hours. Next, No. 1 and 3 were hot-rolled (starting temperature: approximately 500°C) until they reached a thickness of 2.3 mm, and No. 2 until it reached a thickness of 2.0 mm. No. 1 was then cold-rolled until it reached a thickness of 0.55 mm, and No. 2 and 3 until they reached a thickness of 0.52 mm. After that, the slabs were punched out to a diameter of approximately 98 mm using a press, and then subjected to straightening annealing (heated at 200-280°C at a heating rate of 50°C / h or more, followed by holding at 300-400°C for 7 hours or less) while sandwiched with spacers, to produce blanks (O-tempered material) of each thickness.

[0052] The thermal conductivity and stress relaxation rate of each test material manufactured were evaluated as follows.

[0053] (Thermal conductivity) The thermal conductivity was calculated using the following formula based on the thermal diffusivity, room temperature density, and specific heat. Thermal conductivity = Thermal diffusivity × Room temperature density × Specific heat The measurement method for each item will be explained in detail. The thermal diffusivity was measured using a flash method with a thermomechanical analyzer (NETZSCH LFA467) on a test specimen of approximately Φ10 mm taken from the obtained blank. The measurement conditions were a nitrogen gas atmosphere and a measurement temperature of 300°C. The room-temperature density was measured by taking a test specimen of approximately 60 mm x 10 mm from the obtained blank and using the water displacement method at room temperature. The specific heat was measured by the DSC method using a thermomechanical analyzer (NETZSCH DSC404F3) on a test specimen of approximately Φ5.5 mm taken from the obtained blank. The measurement conditions were an argon gas atmosphere and a measurement temperature of 25 to 300°C. The thickness of each test specimen is 0.55 mm for test specimen No. 1, and 0.52 mm for Nos. 2 and 3. The thermal conductivity measured by the method described above can be considered as the thermal conductivity of the blank at 300°C, and if this value is 152 (W / (m·K)) or less, it can be determined that it has the effect of suppressing deformation due to thermal strain that occurs during sputtering of the magnetic film. Furthermore, thermal conductivity values ​​exceeding 145 (W / (m·K)) and 152 (W / (m·K)) or less were evaluated as "〇" indicating excellent deformation suppression, values ​​of 145 (W / (m·K)) or less were evaluated as "◎" indicating particularly excellent deformation suppression, and values ​​exceeding 152 (W / (m·K)) were evaluated as "×" indicating poor deformation suppression during magnetic film sputtering.

[0054] (Stress relaxation rate) A test specimen measuring 10 mm in width and 60 mm in length was cut from the test material so that its longitudinal direction was parallel to the rolling direction. Then, the span length (x) in Figure 1(a) was determined for each test material using equations (2) and (3) below, so that the bending stress in equation (1) below was constant, and the following test was carried out. The sample was placed in an atmospheric furnace under a bending stress load (the state shown in Fig. 1(a)), and subjected to heat treatment (300°C × 1 hour) simulating magnetic film sputtering treatment. Thereafter, the sample was taken out from the atmospheric furnace, and the deformation amount a before unloading the bending stress was measured. Thereafter, the bending stress was unloaded (the state shown in Fig. 1(b)), and the deformation amount b after unloading the bending stress was measured. The ratio of the deformation amount b after unloading to the deformation amount a before unloading the bending stress (b / a × 100 [%]) is defined as the stress relaxation rate. Samples with a stress relaxation rate of 90% or less were evaluated as "○", which are excellent in deformation suppression during magnetic film sputtering, and samples with a stress relaxation rate exceeding 90% were evaluated as "×", which are inferior in deformation suppression during magnetic film sputtering.

[0055] 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]

[0056] M=P×x···(2) M: bending moment [N·mm] P: tip load [N] x: span length [mm]

[0057] P=(3×E×I×δ) / x 3 ···(3) P: tip load [N] E: Young's modulus [N / mm 2 I: second moment of area (I [mm 4 =(w×t 3 ) / 12) w: plate width [mm], t: plate thickness [mm] δ: deflection amount (2 [mm]) x: span length [mm]

[0058] Table 1 shows the evaluation results of alloy composition (chemical composition), thermal conductivity, and stress relaxation rate for each test sample.

[0059] ​​ [Table 1]

[0060] As is clear from the results in Table 1, Nos. 1 and 2, which satisfy the provisions of the present invention, yielded aluminum alloy plates and blanks that have good thermal conductivity, excellent stress relaxation resistance, and can suppress thermal deformation during magnetic film sputtering. On the other hand, in No. 3, the value of the hot rolling completion temperature in the hot rolling process and the value of the total amount of Cu, Mn, Cr, and Ni did not satisfy the relationship in equation (1), and the total amount of Fe, Mn, and Ni did not satisfy the provisions of the present invention. As a result, both the thermal conductivity and stress relaxation rate did not satisfy the provisions of the present invention, and there was a risk of deformation due to thermal strain occurring during sputtering of the magnetic film.

Claims

1. Mg: 2.5 to 7.0% by mass, Contains Cr: 0.01 to 1.0% by mass, Si: 0.20% by mass or less, The Fe content is 0 to 1.00% by mass. The Mn content is 0.4 to 1.4% by mass. The Ni content is 0 to 0.3% by mass. The total amount of Fe, Mn, and Ni is 0.4 to 1.5% by mass. Furthermore, it contains at least one of the following: Be: 3 to 100 ppm by mass, Cu: 1.0% by mass or less, and Zn: 1.0% by mass or less. The remainder consists of Al and impurities. The thermal conductivity is 152 (W / (m·K)) or less. An aluminum alloy plate for magnetic disks with a stress relaxation rate of 90% or less.

2. An aluminum alloy blank for a magnetic disk obtained from an aluminum alloy plate for a magnetic disk as described in claim 1.

3. An aluminum alloy substrate for magnetic disks obtained from an aluminum alloy blank for magnetic disks as described in claim 2.

4. A method for manufacturing an aluminum alloy plate for a magnetic disk according to claim 1, A casting process in which molten aluminum alloy is cast into an aluminum alloy ingot using a semi-continuous casting method, The process involves surface machining the aluminum alloy ingot and then subjecting it to a homogenization heat treatment, A hot rolling process to obtain a hot-rolled plate by hot-rolling the aluminum alloy ingot that has undergone the homogenization heat treatment, The process includes, in this order, a cold rolling step in which the hot-rolled sheet is cold-rolled, A method for manufacturing an aluminum alloy plate for a magnetic disk, wherein the value of the end temperature of the hot rolling process in the hot rolling step and the total amount of Cu, Mn, Cr, and Ni satisfy the relationship shown in formula (1) below. 3.8 ≦ T / 100 + C Formula (1) (In formula (1), C is the total amount (mass%) of Cu, Mn, Cr, and Ni among the components contained in the alloy, and T is the value of the end temperature (°C) of the hot rolling process.)

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