Aluminum alloy sheet for magnetic disk, aluminum alloy blank for magnetic disk, aluminum alloy substrate for magnetic disk, and method for manufacturing aluminum alloy sheet for magnetic disk

Abstract

Provided are an aluminum alloy sheet for a magnetic disk, an aluminum alloy sheet blank for a magnetic disk, and an aluminum alloy sheet substrate for a magnetic disk, which can suppress thermal deformation during sputtering of a magnetic film. An aluminum alloy sheet for a magnetic disk contains Mg: 0.1 to 7.0 mass%, Cr: 0.005 to 1.0 mass%, and Si: 0.20 mass% or less, Ni: 0 to 0.85 mass%, and at least one or more of Fe, Mn, and Ni in a total amount of 0.05 to 3.25 mass%, with the balance including Al and impurities, and has a linear expansion coefficient of 26.0 x 10 －6 (1 / °C) or less, and a stress relaxation rate of 90% or less.

Description

Technical Field

[0001] This invention relates to an aluminum alloy plate for hard disks, an aluminum alloy blank for hard disks, an aluminum alloy substrate for hard disks, and a method for manufacturing an aluminum alloy plate for hard disks. Background Technology

[0002] With the digitization of information and the widespread use of the internet, there is a need to process massive amounts of digital data, thus requiring data centers to focus on increasing the capacity of hard disk drives (HDDs). To achieve this increased capacity, and with the aim of increasing the number of disks in each HDD, the issue of thinner disk walls is being explored.

[0003] However, as shown in Patent Document 1, it is known that in a disk substrate, thermal expansion during magnetic film sputtering causes thermal strain around the clamping portion. The thinner the disk, the greater the thermal strain around the clamping portion.

[0004] In addition, regarding the substrate used for disks, the "flatness" indicator is very important because it largely determines the performance of the hard disk drive (HDD) using the substrate.

[0005] During the substrate manufacturing process, the deformation caused by thermal strain during magnetic film sputtering is a concern. This deformation can adversely affect the flatness of the substrate and become a major cause of non-standard products.

[0006] Currently, from the perspective of resource depletion, the recycling of various items is being promoted, and the recycling of large quantities of consumed metals is also ongoing. The aforementioned non-standard products can also be reused through recycling, but the key is to suppress the occurrence of non-standard products by controlling thermal strain, and this is currently under investigation.

[0007] For example, Patent Document 1 describes the following key point: by achieving an aluminum alloy plate for disks with 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 caused by thermal strain during the sputtering of magnetic films.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2024-059016 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] With the recent demand for thinner films, there is a need for further improvements in the technology used to prevent deformation caused by thermal strain during the sputtering of magnetic films. However, while Patent Document 1 discusses the coefficient of linear expansion, it does not consider stress relaxation resistance.

[0013] Thus, in aluminum alloy plates for hard disks, although both the coefficient of linear expansion and the resistance to stress relaxation are important in order to suppress thermal deformation, there is still room for research on aluminum alloy plates for hard disks that can balance both.

[0014] The present invention addresses the aforementioned problems and aims to provide an aluminum alloy plate for disks, an aluminum alloy blank for disks, an aluminum alloy substrate for disks, and a method for manufacturing the aluminum alloy plate for disks, which can suppress thermal deformation during magnetic film sputtering.

[0015] Problem-solving methods

[0016] Through repeated research, the inventors discovered that by using a specific alloy composition and keeping the coefficient of linear expansion and stress relaxation rate within a specific range, an aluminum alloy plate for disks that can suppress thermal deformation during magnetic film sputtering can be obtained, and thus the present invention was created.

[0017] That is, the present invention relates to the following.

[0018] [1] An aluminum alloy plate for a hard disk, comprising

[0019] Mg: 0.1–7.0% by mass

[0020] Cr: 0.005–1.0% by mass, and

[0021] Si: less than 0.20% by mass

[0022] Ni: 0–0.85% by mass

[0023] The total of at least one of Fe, Mn and Ni: 0.05 to 3.25% by mass.

[0024] The balance includes Al and impurities.

[0025] The coefficient of linear expansion is 26.0 × 10⁻⁶. －6 (1 / ℃) or less,

[0026] The stress relaxation rate is below 90%.

[0027] [2] The aluminum alloy plate for disks according to [1], wherein it contains at least one of the following:

[0028] The Fe content is 0–1.00% by mass, and

[0029] The Mn content is 0–1.4% by mass.

[0030] [3] The aluminum alloy plate for disks according to [1] or [2], wherein it further comprises at least one of the following:

[0031] Be: 3-100 ppm (by weight)

[0032] Cu: less than 1.0% by mass, and

[0033] Zn: less than 1.0% by mass.

[0034] [4] An aluminum alloy blank for disks, which is obtained from the aluminum alloy sheet for disks described in [1] or [2].

[0035] [5] An aluminum alloy blank for disks, which is obtained from the aluminum alloy sheet for disks described in [3].

[0036] [6] An aluminum alloy substrate for a disk, which is obtained from the aluminum alloy blank for a disk described in [4].

[0037] [7] A method for manufacturing an aluminum alloy plate for a hard disk, which is the method for manufacturing an aluminum alloy plate for a hard disk described in [1] or [2], wherein the following steps are included in sequence:

[0038] The casting process uses a semi-continuous casting method to cast molten aluminum alloy into aluminum alloy ingots.

[0039] The homogenization heat treatment process involves surface cutting of the aluminum alloy casting followed by homogenization heat treatment.

[0040] The hot rolling process involves hot rolling an aluminum alloy ingot that has undergone the homogenization heat treatment to obtain a hot-rolled plate;

[0041] The cold rolling process involves cold rolling the hot-rolled plate.

[0042] The value of the initial rolling rate of the cold rolling process and the combined value of Fe, Mn and Ni satisfy the following equation (1).

[0043] 0 < C - R / 100 Equation (1)

[0044] (In formula (1), C is the total mass percentage of Fe, Mn and Ni in the alloy, and R is the initial rolling rate (%) in the cold rolling process.)

[0045] The effects of the invention

[0046] According to the present invention, it is possible to provide an aluminum alloy plate for a magnetic disk, an aluminum alloy blank for a magnetic disk, an aluminum alloy substrate for a magnetic disk, and a method for manufacturing the aluminum alloy plate for a magnetic disk, which can suppress thermal deformation during magnetic film sputtering. Attached Figure Description

[0047] Figure 1 (a) and (b) in the figures are used to illustrate the measurement of stress relaxation rate in the embodiments. Detailed Implementation

[0048] Hereinafter, an aluminum alloy plate for disk, an aluminum alloy blank for disk, and an aluminum alloy substrate for disk according to one embodiment of the present invention will be described.

[0049] Furthermore, in the following description, the aluminum alloy plate for disks, the aluminum alloy blank for disks, and the aluminum alloy substrate for disks in this embodiment are sometimes referred to simply as "aluminum alloy plate," "blank," and "substrate," respectively.

[0050] [Aluminum alloy plate for hard disks]

[0051] The aluminum alloy plate for disks in this embodiment contains Mg: 0.1-7.0% by mass, Cr: 0.005-1.0% by mass, Si: less than 0.20% by mass, Ni: less than 0-0.85% by mass, and the total of at least one of Fe, Mn, and Ni: 0.05-3.25% by mass, with the balance including Al and impurities. Its coefficient of linear expansion is 26.0 × 10⁻⁶. －6 The stress relaxation rate is below 90% (1 / ℃). Additionally, the aluminum alloy plate for disks in this embodiment may also contain Be, Cu, and Zn.

[0052] The following describes in detail the various components of the aluminum alloy plate for disks according to this embodiment.

[0053] (Mg: ≥0.1% by mass and ≤7.0% by mass)

[0054] Mg is an essential constituent element in the aluminum alloy plate for disks in this embodiment, and is contained in the aluminum alloy plate in order to obtain good yield strength.

[0055] If the Mg content in the aluminum alloy sheet is less than 0.1% by mass, the above-mentioned effect cannot be achieved. On the other hand, if the Mg content in the aluminum alloy sheet is higher than 7.0% by mass, the rigidity decreases. Therefore, the Mg content should be between 0.1% by mass and 7.0% by mass.

[0056] Furthermore, 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. Additionally, from the viewpoint of suppressing a decrease in stiffness, the 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.

[0057] (Cr: ≥0.005% by mass and ≤1.0% by mass)

[0058] Cr is an essential constituent element in the aluminum alloy plate for disks in this embodiment, and is contained in the aluminum alloy plate in order to obtain good yield strength.

[0059] If the Cr content in the aluminum alloy sheet is less than 0.005% by mass, the above-mentioned effect cannot be achieved. On the other hand, if the Cr content is higher than 1.0% by mass, the intermetallic compounds coarsen, edge cracks occur, and there is a possibility of reduced rollability. Therefore, the Cr content should be between 0.005% by mass and 1.0% by mass.

[0060] Furthermore, 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. Additionally, 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, or 0.2% by mass or less.

[0061] (Si: less than 0.20% by mass)

[0062] In the aluminum alloy sheet for disks of this embodiment, Si is an element introduced from the ingot as an impurity. Sometimes it exists in the aluminum alloy sheet as elemental Si, and sometimes it forms Al-Fe-Si intermetallic compounds. If the Si content in the aluminum alloy sheet is higher than 0.20% by mass, the rollability may be reduced due to elemental Si. Therefore, from the viewpoint of suppressing the formation of elemental Si, the Si content in the aluminum alloy sheet is 0.20% by mass or less (including 0.00% by mass).

[0063] Furthermore, from the viewpoint of suppressing the reduction 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.

[0064] However, to reduce the Si content, high-purity raw materials such as Al ingots and master alloy ingots are required, which increases raw material costs. Therefore, the Si content is preferably 0.004% by mass or higher in industrial applications.

[0065] (Ni: 0% by mass or more and 0.85% by mass or less)

[0066] Ni is included in aluminum alloy sheets to obtain good rigidity and resistance to stress relaxation. If the Ni content in the aluminum alloy sheet is higher than 0.85% by mass, the coefficient of linear expansion in the aluminum alloy increases, and the suppression of thermal strain may be insufficient. Therefore, the Ni content is 0.85% by mass or less, preferably 0.80% by mass or less, more preferably 0.75% by mass or less, and even more preferably 0.70% by mass or less. In addition, the amount of Ni added can be 0% by mass, but from the viewpoint of obtaining good resistance to stress relaxation, it can also be 0.01% by mass or more, 0.02% by mass or more, 0.05% by mass or more, 0.10% by mass or more, 0.15% by mass or more, 0.25% by mass or more, 0.30% by mass or more, 0.35% by mass or more, or 0.40% by mass or more.

[0067] (Total of Fe, Mn and Ni: 0.05–3.25% by mass)

[0068] Fe, Mn, and Ni are components that contribute to improving the coefficient of linear expansion and resistance to stress relaxation. Therefore, the aluminum alloy plate for disks in 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 individually, or both Fe and Mn, Mn and Ni, or Ni and Fe may be contained, or all of Fe, Mn, and Ni may be contained, and there is no particular limitation as long as their total content is 0.05 to 3.25% by mass.

[0069] Furthermore, to obtain a good coefficient of linear expansion and resistance to stress relaxation, 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 they are present in excess, the compounds become coarse, which may reduce the plating properties. Therefore, the total content is 3.25% by mass or less, preferably 3.0% by mass or less, 2.5% by mass or less, 2.0% by mass or less, or 1.5% by mass or less.

[0070] Furthermore, the aluminum alloy plate for disks in this embodiment preferably contains at least one of Fe: 0 to 1.00% by mass and Mn: 0 to 1.4% by mass.

[0071] (Fe: less than 1.00% by mass)

[0072] Fe is included in aluminum alloy sheets to obtain a good coefficient of linear expansion and resistance to stress relaxation. On the other hand, if the Fe content in the aluminum alloy sheet exceeds 1.00% by mass, the compound becomes coarser, which may reduce the plating properties. Therefore, the Fe content is 1.00% by mass or less (including 0% by mass).

[0073] Furthermore, from the viewpoint of suppressing the reduction of 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. Additionally, from the viewpoint of obtaining a good coefficient of linear expansion and resistance to stress relaxation, the Fe content is preferably 0.01% by mass or more, 0.02% by mass or more, 0.05% by mass or more, 0.10% by mass or more, 0.15% by mass or more, 0.25% by mass or more, 0.30% by mass or more, 0.35% by mass or more, and 0.40% by mass or more.

[0074] (Mn: less than 1.4% by mass)

[0075] Mn is included in aluminum alloy sheets to obtain a good coefficient of linear expansion and resistance to stress relaxation. On the other hand, if the Mn content in the aluminum alloy sheet exceeds 1.4% by mass, the compound coarsens, which may reduce the plating properties. Therefore, the Mn content is 1.4% by mass or less (including 0% by mass).

[0076] Furthermore, from the viewpoint of suppressing the reduction 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. Additionally, from the viewpoint of obtaining a good coefficient of linear expansion and resistance to stress relaxation, the Mn content 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.

[0077] (Be: 3 ppm or more and 100 ppm or less by mass)

[0078] Be can be contained in the aluminum alloy plate for disks in this embodiment. When Be is contained, it has the effect of inhibiting the formation of Mg oxide by forming an oxide film during casting. In addition, it has the effect of improving the hot rollability and formability of the aluminum alloy. Furthermore, it can reduce the adhesion between blanks caused by oxidation inhibition during straightening annealing, thereby suppressing the deterioration of flatness caused by external forces during subsequent peeling, and thus achieving excellent flatness.

[0079] If the Be content is 3 ppm or more by mass, the effects of adding Be can be fully realized. On the other hand, if the Be content is 100 ppm or less by mass, it can prevent the Be-containing compounds from becoming coarse, suppress the occurrence of edge cracks, and improve rollability.

[0080] From the viewpoint of fully obtaining the aforementioned effects of adding Be, the Be content is preferably 4 ppm or more by mass, 5 ppm or more by mass, 8 ppm or more by mass, or 10 ppm or more by mass. Furthermore, from the viewpoint of ensuring rollability, it is preferably 80 ppm or less by mass, 50 ppm or less by mass, 30 ppm or less by mass, or 20 ppm or less by mass. While it is possible to have no Be, when Be is present, from the viewpoint of reliably obtaining the effects of adding Be, it is preferably 3 ppm or more by mass and 100 ppm or less by mass.

[0081] (Cu: less than 1.0% by mass, Zn: less than 1.0% by mass)

[0082] Cu and Zn are components that expand the solid-liquid coexistence region, helping to reduce the frequency of arcing during casting. Additionally, they are components that promote uniform zinc precipitation during zincate treatment, also contributing to improved coating smoothness. On the other hand, excessive Cu and Zn content may actually negatively affect coating smoothness. Furthermore, the smoothness of the electroless Ni-P coating formed on the surface may be reduced. Therefore, in the aluminum alloy plate for disks of this embodiment, it is preferable to contain at least one of Cu: 1.0% by mass or less and Zn: 1.0% by mass or less. Furthermore, in the aluminum alloy plate for disks of this embodiment, it is preferable to also contain at least one of Be: 3 to 100 ppm by mass, Cu: 1.0% by mass or less, and Zn: 1.0% by mass or less.

[0083] From the viewpoint of suppressing the reduction in coating 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, although Cu may be absent, when present, from the viewpoint of reliably obtaining the effects of Cu addition, a content of 0.005% by mass or more is preferred.

[0084] From the viewpoint of suppressing the reduction in coating 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, or 0.05% by mass or less. Furthermore, although Zn may be absent, when present, from the viewpoint of reliably obtaining the effects of Zn addition, a content of 0.005% by mass or more is preferred.

[0085] (Balance: Al and impurities)

[0086] The aluminum alloy sheet of this embodiment may contain elements other than those mentioned above as impurities, depending on the choice of molten raw materials during the manufacture of the ingot. Specifically, 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 each limited to 0.10% by mass or less, and B, Na, K, Ca, Pb, P, Sn, Ag, Bi, In, Ge, Sr, and Cd are each limited to 0.05% by mass or less. As long as these elements are within these ranges, their presence is not only unavoidable as impurities, but the effectiveness of this embodiment is not hindered even when these elements are intentionally added by increasing the blending ratio of scrap containing these elements.

[0087] When each of the elements shown as impurity elements is unavoidably contained (in other words, when it is an unavoidable impurity), 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.

[0088] Furthermore, when adopting a chemical composition without adding the aforementioned Si, Fe, Mn, Ni, Be, Cu, and Zn, the content of each of these unavoidable impurities is preferably 0.005% by mass or less.

[0089] <Stress relaxation rate: below 90%>

[0090] The inventors have conducted intensive research on the deformation of magnetic films sputtering on aluminum alloy plates for hard disks, and found that deformation can be suppressed by improving the stress relaxation resistance.

[0091] If the stress relaxation rate is 90% or less, deformation can be suppressed even when stress generated by thermal strain during magnetic film sputtering is applied to the thinned substrate. Therefore, the stress relaxation rate of the aluminum alloy plate for disks in this embodiment is preferably 90% or less. From the viewpoint of further suppressing deformation of the thinned substrate, the lower the stress relaxation rate, the better. For example, a stress relaxation rate of 85% or less is more preferred, 80% or less is even more preferred, and 75% or less is particularly preferred.

[0092] Furthermore, although there is no specific lower limit for the stress relaxation rate, it can be, for example, above 0%, above 20%, above 50%, above 60%, or above 70%.

[0093] The stress relaxation rate can be adjusted by setting the contents of Mg, Cr, and Si within a specific range, and by setting the total contents of Fe, Mn, and Ni to the ranges described in this specification. In addition to the aforementioned contents of Fe, Mn, and Ni, the processing conditions in the cold rolling process can also be adjusted by setting them to the ranges described later.

[0094] Stress relaxation rate can be measured in the following manner.

[0095] A test piece measuring 10 mm wide and 60 mm long was cut with the longitudinal direction parallel to the rolling direction. Then, using equations (2) and (3) below, the bending stress in equation (1) below is determined. Figure 1 (a) Span length (x), and conduct the following test.

[0096] Under the condition of load bending stress ( Figure 1 (a) The sample was placed in an atmospheric furnace and subjected to heat treatment simulating magnetic film sputtering (300°C × 1 hour). Afterward, it was removed from the atmospheric furnace, and the deformation *a* before the bending stress was unloaded was measured. Subsequently, the bending stress was released ( Figure 1 (b) shows the state), and the deformation b after the bending stress is unloaded is measured.

[0097] The ratio of the deformation amount b after unloading the bending stress to the deformation amount a before unloading (b / a×100 [%)) is used as the stress relaxation rate.

[0098] σ=M / Z …(1)

[0099] σ: Bending stress [N / mm] 2 ]

[0100] M: Bending moment [N·mm]

[0101] Z: Section modulus (Z [mm]) 3 ] = (w×t 2 ) / 6)

[0102] w: Plate width [mm], t: Plate thickness [mm]

[0103] M = P × x … (2)

[0104] M: Bending moment [N·mm]

[0105] P: Front-end load [N]

[0106] x: Span length [mm]

[0107] P = (3 × E × I × δ) / x 3 …(3)

[0108] P: Front-end load [N]

[0109] E: Young's modulus [N / mm] 2 ]

[0110] I: Second moment of section (I[mm 4 ] = (w×t 3 ) / 12)

[0111] w: Plate width [mm], t: Plate thickness [mm]

[0112] δ: Deflection (2 mm)

[0113] x: Span length [mm]

[0114] [Manufacturing method of aluminum alloy plate for hard disk]

[0115] Next, an example of the manufacturing method of the aluminum alloy plate for disks according to this embodiment will be described.

[0116] The alloy sheet of this embodiment can be manufactured using a manufacturing method and equipment that generally applies to the manufacture of aluminum alloy sheets for magnetic disks, except for certain conditions in the cold rolling process.

[0117] For example, aluminum alloy sheets can be manufactured using a manufacturing method that sequentially includes the following steps: a casting step, in which raw materials are melted and the molten aluminum alloy with a specified chemical composition is cast into an aluminum alloy ingot using a semi-continuous casting method, etc.; a homogenization heat treatment step, in which the cast aluminum alloy ingot is face-cut and subjected to homogenization heat treatment; a hot rolling step, in which the homogenized heat-treated aluminum alloy ingot is hot-rolled to obtain a hot-rolled sheet; and a cold rolling step, in which the hot-rolled sheet is cold-rolled. Additionally, intermediate annealing can be performed before or during the cold rolling step, as needed.

[0118] That is, the manufacturing method of this embodiment is a method for manufacturing an aluminum alloy plate for a hard disk, wherein the following steps are included in sequence:

[0119] The casting process of casting molten aluminum alloy into aluminum alloy ingots using a semi-continuous casting method.

[0120] The aluminum alloy casting is subjected to surface cutting and homogenization heat treatment process.

[0121] The hot rolling process for obtaining hot-rolled plates by hot rolling aluminum alloy castings that have undergone the homogenization heat treatment;

[0122] The cold rolling process for the hot-rolled plate.

[0123] The value of the initial rolling rate of the cold rolling process and the combined value of Fe, Mn and Ni satisfy the following relationship (1).

[0124] 0 < C - R / 100 Equation (1)

[0125] (In formula (1), C is the total mass percentage of Fe, Mn and Ni in the alloy, and R is the initial rolling rate (%) in the cold rolling process.)

[0126] The following is a detailed explanation of each process.

[0127] (Casting process)

[0128] In the casting process, the raw materials are melted at 700–800°C to form a melt of aluminum alloy. Preferably, it is cast into an aluminum alloy ingot at 700–800°C using a known semi-continuous casting method such as DC casting.

[0129] (Homogenization heat treatment process)

[0130] In the homogenization heat treatment process, the cast aluminum alloy ingot undergoes surface cutting and homogenization heat treatment. The surface cutting amount can be, for example, 2 to 40 mm per side.

[0131] The homogenization heat treatment is preferably carried out at a temperature of 400–600°C for 4–50 hours.

[0132] Specifically, by setting the homogenization heat treatment temperature to 400°C or higher and the homogenization heat treatment time to 4 hours or higher, sufficient homogenization of the microstructure can be achieved, reducing deviations in the stress relaxation resistance characteristics 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, surface melting 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. Furthermore, there is no upper limit to the homogenization heat treatment time, but from the viewpoint of manufacturing process economy, 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. Additionally, from the viewpoint of microstructure homogenization, 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.

[0133] (Hot rolling process)

[0134] In the hot rolling process, hot-rolled plates are obtained by hot rolling aluminum alloy castings that have undergone homogenization heat treatment.

[0135] From the viewpoint of adjusting the stress relaxation rate of the aluminum alloy sheet to below 90%, the starting temperature of hot rolling is preferably 490°C or higher. Furthermore, the ending temperature of hot rolling is preferably 300–350°C.

[0136] Specifically, by setting the starting temperature of 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 of hot rolling is more preferably 490°C or higher, and even more preferably 500°C or higher. On the other hand, from the viewpoint of suppressing cracks during hot rolling, the starting temperature of hot rolling is preferably 550°C or lower, and more preferably 520°C or lower.

[0137] In addition, the thickness of the hot-rolled sheet obtained by hot rolling can be, for example, less than 3 mm.

[0138] (Cold rolling process)

[0139] 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 0.3 to 1.3 mm, 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.

[0140] The thickness of the cold-rolled sheet after cold rolling is determined according to the desired thickness as an alloy sheet, billet, or substrate. Cold rolling can be repeated multiple times to achieve the target thickness. In order to obtain a good coefficient of linear expansion, it is preferable that the composition contained in the alloy and the rolling rate of the initial rolling process in the cold rolling process are related by the following formula (1).

[0141] In the method for manufacturing aluminum alloy plates for disks according to this embodiment, the value of the initial rolling rate of the cold rolling process and the value of the sum of Fe, Mn and Ni satisfy the following relationship (1).

[0142] 0 < C - R / 100 Equation (1)

[0143] (In formula (1), C is the total mass percentage of Fe, Mn and Ni in the alloy, and R is the initial rolling rate (%) in the cold rolling process.)

[0144] In the method for manufacturing aluminum alloy plates for disks according to this embodiment, a good coefficient of linear expansion can be obtained by satisfying the relationship between the initial rolling rate of the cold rolling process and the sum of Fe, Mn and Ni as expressed in the above formula (1).

[0145] This means that the higher the total mass percentage (mass%) of Fe, Mn, and Ni in the alloy, the better the coefficient of linear expansion can be obtained. On the other hand, if the initial rolling rate (%) in the cold rolling process is large, a good coefficient of linear expansion cannot be obtained.

[0146] When the initial rolling rate is high, the amount of strain accumulated in the alloy sheet increases, making it impossible to achieve sufficient strain removal during subsequent straightening annealing. If the strain removal after straightening annealing is insufficient, the strain will be released when the alloy sheet is heated, causing the alloy sheet to expand and potentially failing to achieve the specified coefficient of linear expansion.

[0147] On the other hand, even with a large initial rolling rate, a good coefficient of linear expansion can be obtained if the total amount of Fe, Mn, and Ni in the alloy is sufficiently large. Therefore, to obtain a good coefficient of linear expansion, it is preferable to satisfy the above formula.

[0148] [Aluminum alloy blank for hard disk]

[0149] The aluminum alloy blank for disks in this embodiment is obtained from the aforementioned aluminum alloy sheet for disks. Specifically, the blank can be manufactured by further performing the following steps in sequence: a punching process, in which the aluminum alloy sheet obtained after the cold rolling process is punched into a ring shape; and a straightening annealing process, in which the ring-shaped substrate obtained by the punching process is subjected to straightening annealing, for example, by applying a load while annealing to make it flattened.

[0150] The chemical composition of the obtained blank is unchanged compared to the aluminum alloy plate mentioned above; it is the same composition.

[0151] Furthermore, the linear expansion coefficient, stress relaxation rate, and other characteristic values ​​of the billet are equivalent to those of the aluminum alloy sheet. Therefore, the characteristic values ​​required for the aluminum alloy sheet can be considered as characteristic values ​​for the billet. Conversely, the characteristic values ​​required for the billet can also be considered as characteristic values ​​for the aluminum alloy sheet.

[0152] (Punching process)

[0153] In the punching process, the aluminum alloy plate is tempered and then punched into a ring shape as needed, so that it can be used, for example, as a substrate for a 3.5-inch HDD with an inner diameter of 24mm and an outer diameter of 96mm, or a substrate for a 2.5-inch HDD with an inner diameter of 19mm and an outer diameter of 66mm.

[0154] (Corrective annealing process)

[0155] In the straightening annealing process, it is preferable to stack the annular substrates by clamping them with, for example, partitions with high flatness, and to anneal them while applying a load to achieve planarization. The annealing temperature is 250–500°C, and the holding time can be, for example, about 3–5 hours.

[0156] The heating rate for corrective annealing can be, for example, around 80°C / hour on average, preferably below 1000°C / hour. Cooling can be achieved, for example, by opening the furnace door of the annealing furnace.

[0157] Regarding the heating during corrective annealing, the effect of this embodiment is not compromised even if the heating is performed in stages. For example, as described in paragraphs 0068 and 0069 of Japanese Patent No. 5815153, the heating rate within a specific temperature range can be a predetermined rate or higher, and different heating rates can be applied outside that specific temperature range. In this way, heating is performed at multiple heating rates, i.e., staged heating is implemented.

[0158] Furthermore, in this embodiment, the annealing temperature for corrective annealing is assumed to be 250–400°C, even within the range of the usual annealing temperatures described above.

[0159] By going through these processes sequentially, the blank of this embodiment can be obtained.

[0160] [Aluminum alloy substrate for hard disks]

[0161] The aluminum alloy substrate for disk drives in this embodiment is obtained from the aforementioned aluminum alloy blank for disk drives. Specifically, the substrate can be manufactured by performing the following processes: cutting the end face of the blank (end face machining); and grinding the surface (main face) of the blank (mirror finish machining).

[0162] The chemical composition of the obtained substrate is unchanged from that of the aforementioned preform, and is the same.

[0163] Furthermore, the characteristic values ​​of the substrate, such as the coefficient of linear expansion and stress relaxation rate, are equivalent to those of the billet. Therefore, the characteristic values ​​required for the aluminum alloy sheet and the billet can be considered as characteristic values ​​for the substrate. Conversely, the characteristic values ​​required for the substrate can also be considered as characteristic values ​​for the aluminum alloy sheet and the billet.

[0164] The aluminum alloy plate, blank, and substrate of this embodiment can be obtained by the methods described above, but other processes can be performed between or before and after each process without causing adverse effects on each process.

[0165] [Disk manufacturing method]

[0166] Disks can be manufactured using methods and equipment typically employed in disk manufacturing. For example, after acid etching to form an electroless Ni-P coating on the surface of a substrate, the surface of the electroless Ni-P coating is ground. Then, an underlayer, a magnetic layer, a protective film, etc., are formed on the surface of the substrate, thereby enabling the manufacture of a disk.

[0167] Example

[0168] The following describes embodiments of the present invention in detail. However, the scope of the present invention is not limited thereto.

[0169] (Preparation of test materials)

[0170] Test materials No. 1 to 4 were manufactured using aluminum alloys with the chemical composition shown in Table 1, under the following conditions.

[0171] First, slabs are produced by DC casting using molds with individual casting thicknesses (500 mm for No. 1 and 3, and 530 mm for No. 2 and 4). Then, 16 mm face cuttings are performed on both sides (thickness direction) of the resulting slabs. Next, a homogenization heat treatment is performed at 535°C for 8 hours. Following this, hot rolling (starting temperature: approximately 500°C, ending temperature: approximately 330°C) is carried out until No. 1 reaches a thickness of 2.0 mm, and No. 2, 3, and 4 reach a thickness of 2.3 mm. Cold rolling is then performed until No. 1 and 4 reach a thickness of 0.52 mm, No. 2 reaches a thickness of 0.53 mm, and No. 3 reaches a thickness of 0.55 mm. Subsequently, the blanks (O-type tempered materials) of various thicknesses are manufactured by punching with a stamping press to achieve a diameter of approximately 98 oz, and then straightening annealing is performed by clamping them with a partition (heating at a rate of 50 oz / h or higher at 200–280 ℃, and then holding at 300–400 ℃ for no more than 7 hours).

[0172] For each manufactured test material, the coefficient of linear expansion and stress relaxation rate are evaluated as follows.

[0173] (Stress relaxation rate)

[0174] A test piece measuring 10 mm wide and 60 mm long was cut from the test material with its longitudinal direction parallel to the rolling direction. Then, using equations (2) and (3) below, the bending stress was determined for each test material in a manner consistent with equation (1) below. Figure 1 For the span length (x) in (a), the following test is conducted.

[0175] Under the condition of bending stress under load ( Figure 1The sample was placed in an atmospheric furnace in the state shown in (a) and subjected to heat treatment simulating magnetic film sputtering (300°C × 1 hour). Afterward, it was removed from the atmospheric furnace, and the deformation 'a' before the bending stress was unloaded was measured. Subsequently, the bending stress was released ( Figure 1 (b) shows the state), and the deformation b after the bending stress is unloaded is measured.

[0176] The ratio of the deformation amount b after bending stress unloading to the deformation amount a before unloading (b / a×100 [%)) is used as the stress relaxation rate. If the stress relaxation rate is below 90%, it is evaluated as excellent deformation suppression during magnetic film sputtering "〇"; if it is above 90%, it is evaluated as poor deformation suppression during magnetic film sputtering "×".

[0177] σ=M / Z…(1)

[0178] σ: Bending stress [N / mm] 2 ]

[0179] M: Bending moment [N·mm]

[0180] Z: Section modulus (Z [mm]) 3 ] = (w×t 2 ) / 6)

[0181] w: Plate width [mm], t: Plate thickness [mm]

[0182] M = P × x … (2)

[0183] M: Bending moment [N·mm]

[0184] P: Front-end load [N]

[0185] x: Span length [mm]

[0186] P = (3 × E × I × δ) / x 3 …(3)

[0187] P: Front-end load [N]

[0188] E: Young's modulus [N / mm] 2 ]

[0189] I: Second moment of section (I[mm 4 ] = (w×t 3 ) / 12)

[0190] w: Plate width [mm], t: Plate thickness [mm]

[0191] δ: Deflection (2 mm)

[0192] x: Span length [mm]

[0193] (Coefficient of linear expansion)

[0194] The coefficient of linear expansion was measured using a thermomechanical analysis apparatus (NETZSCH TMA402F1 (free expansion method)) via thermomechanical analysis (TMA). Measurement conditions included a load of 5 gf, a heating rate of 5 °C / min, and a measurement temperature range from room temperature to 300 °C. Considering measurement stability, the coefficient of linear expansion was calculated as the average coefficient of linear expansion between 25 °C and 300 °C. 4 mm × 19 mm test pieces were extracted from the obtained blanks for measurement using the tensile method. The sheet thicknesses of the test pieces are as follows: Test piece No. 1: 0.52 mm; Test piece No. 2: 0.53 mm; Test piece No. 3: 0.55 mm; Test piece No. 4: 0.52 mm.

[0195] If the coefficient of linear expansion is 26.0 × 10 －6 If the coefficient of thermal expansion is below 1 / ℃, it can be determined that it has the effect of suppressing deformation caused by thermal strain. Additionally, if the coefficient of linear expansion is 25.7 × 10⁻⁶... －6 If the value is below 1 / ℃, it can be determined that the deformation suppression effect is more excellent.

[0196] Table 1 shows the evaluation results for the alloy composition (chemical composition), coefficient of linear expansion, and stress relaxation rate of each test material.

[0197] Table 1

[0198]

[0199] As shown in Table 1, No.1, which meets the requirements of this invention, has a good coefficient of linear expansion and excellent stress relaxation resistance, and can produce aluminum alloy plates and blanks that can suppress thermal deformation during magnetic film sputtering.

[0200] On the other hand, No. 2, which has a high initial rolling ratio in the cold rolling process, and No. 3, which does not meet the requirements of this invention regarding Ni content, and whose coefficient of linear expansion does not meet the requirements of this invention, may deform due to thermal strain generated during the sputtering of the magnetic film. The combined content of Fe, Mn, and Ni does not meet the requirements of this invention regarding No. 4, and its stress relaxation resistance is worse than No. 1.

Claims

1. An aluminum alloy plate for hard disks, comprising... Mg: 0.1–7.0% by mass Cr: 0.005–1.0% by mass, and, Si: less than 0.20% by mass Ni: 0–0.85% by mass The total of at least one of Fe, Mn and Ni: 0.05 to 3.25% by mass. The balance contains Al and impurities. The coefficient of linear expansion is 26.0 × 10⁻⁶. －6 The following units are in 1 / ℃. The stress relaxation rate is below 90%.

2. The aluminum alloy plate for disks according to claim 1, wherein, It contains at least one of the following: Fe: 0-1.00% by mass and Mn: 0-1.4% by mass.

3. The aluminum alloy plate for disks according to claim 1 or 2, wherein, It also contains at least one of the following: Be: 3 to 100 ppm by mass, Cu: less than 1.0% by mass, and Zn: less than 1.0% by mass.

4. An aluminum alloy blank for disk drives, obtained from the aluminum alloy sheet for disk drives as described in claim 1 or 2.

5. An aluminum alloy blank for a hard disk, obtained from the aluminum alloy sheet for a hard disk as described in claim 3.

6. An aluminum alloy substrate for a hard disk, obtained from the aluminum alloy blank for a hard disk as described in claim 4.

7. A method for manufacturing an aluminum alloy plate for a hard disk, as described in claim 1 or 2, wherein, The process includes the following steps in sequence: The casting process uses a semi-continuous casting method to cast molten aluminum alloy into aluminum alloy ingots. The homogenization heat treatment process involves surface cutting of the aluminum alloy casting followed by homogenization heat treatment. The hot rolling process involves hot rolling an aluminum alloy ingot that has undergone the homogenization heat treatment to obtain a hot-rolled plate; The cold rolling process involves cold rolling the hot-rolled plate. The initial rolling rate of the cold rolling process and the combined values ​​of Fe, Mn and Ni satisfy the following equation (1). 0 < C - R / 100 Equation (1) In formula (1), C is the total mass percentage of Fe, Mn and Ni in the alloy, and R is the initial rolling percentage in the cold rolling process.

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