Aluminum alloy blanks for magnetic disks, and aluminum alloy substrates 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 that have good grindability and can suppress thermal deformation during magnetic film sputtering. [Solution] An aluminum blank for magnetic disks containing Mg: 0.1 to 7.0 mass%, Cr: 0.005 to 1.0 mass%, Be: 3 to 100 mass ppm, further containing at least one of Cu: 1.0 mass% or less, and Zn: 1.0 mass% or less, Zr: 100 mass ppm or less, Si: 0.20 mass% or less, and the total of at least one of Fe, Mn, and Ni: 0.05 to 3.0 mass%, with the remainder being Al and impurities, and the area ratio of intermetallic compounds on the surface being 0.10 to 40%, the area ratio being calculated for intermetallic compounds with a maximum length of 0.33 μm or more.

Description

[Technical Field]

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

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

[0003] However, improving rigidity leads to a decrease in grindability, which worsens the processability of aluminum alloy sheets.

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

[0005] 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. For example, Patent Document 3 describes an aluminum alloy plate for magnetic disks that has a specific chemical composition and a compound number gradient in the thickness direction that is greater than or equal to a specific value, and which has excellent flatness.

[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 during magnetic film sputtering. Therefore, in order to produce a magnetic disk with excellent flatness, it is necessary to suppress deformation of the magnetic disk substrate due to thermal distortion.

[0007] From the perspective of suppressing deformation due to thermal strain, for example, Patent Document 5 describes that by using an aluminum alloy plate for caps having a specific chemical composition and a yield strength difference in the direction parallel to rolling before and after heat treatment that is greater than a specific value, excellent stress relaxation resistance can be achieved and thermal deformation can be suppressed. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 7132289 [Patent Document 2] Patent No. 6684139 [Patent Document 3] Japanese Patent Publication No. 2023-004878 [Patent Document 4] Japanese Patent Publication No. 2022-010156 [Patent Document 5] Japanese Patent Publication No. 2021-011621 [Overview of the project] [Problems that the invention aims to solve]

[0009] For aluminum alloy plates for magnetic disks, both good machinability and suppression of thermal deformation are important, but for aluminum alloy plates for magnetic disks that achieve both, There was still room for consideration.

[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 blank for magnetic disks, and an aluminum alloy substrate for magnetic disks that have good grindability and can suppress thermal deformation during magnetic film sputtering. [Means for solving the problem]

[0011] As a result of the inventors' repeated research, it has been found that an aluminum alloy plate for a magnetic disk having good machinability and capable of suppressing thermal deformation during magnetic film sputtering can be obtained by specifying a specific alloy composition and setting the area ratio of intermetallic compounds on the surface to 0.10 to 40%, and the present invention has been created.

[0012] That is, the present invention relates to the following. 〔1〕 Mg: 0.1 to 7.0% by mass, Cr: 0.005 to 1.0% by mass, containing Be: 3 to 100 ppm by mass, Zr: 100 ppm by mass or less, Si: 0.20% by mass or less, and the total of at least one or more of Fe, Mn and Ni: 0.05 to 3.0% by mass, the balance consisting of Al and impurities, the area ratio of intermetallic compounds on the surface being 0.10 to 40%, the aluminum alloy plate for a magnetic disk, wherein the area ratio is calculated for intermetallic compounds having a maximum length of 0.33 μm or more. 〔2〕 the Fe: 0 to 1.00% by mass, the Mn: 0 to 1.0% by mass, and the aluminum alloy plate for a magnetic disk according to 〔1〕, containing at least one or more of the Ni: 0 to 1.0% by mass. 〔3〕<000009​​​​​​​​​​​​A magnetic disk aluminum alloy substrate obtained from the magnetic disk aluminum alloy blank described in [5]. [Effects of the Invention]

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

[0014] [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]

[0015] 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.

[0016] [Aluminum alloy plate for magnetic disks] The aluminum alloy plate for magnetic disks according to this embodiment contains Mg: 0.1 to 7.0 mass%, Cr: 0.005 to 1.0 mass%, Be: 3 to 100 mass ppm, Zr: 100 mass ppm or less, Si: 0.20 mass% or less, and the total amount of at least one of Fe, Mn, and Ni is 0.05 to 3.0 mass%, with the remainder being Al and impurities. The area ratio of intermetallic compounds on the surface is 0.10 to 40%, and this area ratio was calculated for intermetallic compounds with a maximum length of 0.33 μm or more. Here, a maximum length of 0.33 μm or more means that the maximum distance between any two points on the contour line of the intermetallic compound particles is 0.33 μm or more. Furthermore, 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.

[0017] (Mg: 0.1 mass% or more and 7.0 mass% or less) Mg is an essential constituent element in the aluminum alloy plate for 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 0.1% by mass, the above effect cannot be obtained. On the other hand, if the Mg content in the aluminum alloy sheet exceeds 7.0% by mass, the rigidity decreases. Therefore, the Mg content should be between 0.1% by mass and 7.0% by mass. Furthermore, the Mg content is 0.5% by mass or more, and 1.0% by mass or more, from the viewpoint of improving yield strength. Preferably, the amount is 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, preferably, the amount is 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 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. If the Cr content in the aluminum alloy sheet is less than 0.005% 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 0.005% by mass and 1.0% by mass. 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, 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, and 0.2% by mass or less.

[0019] (Be: 3 mass ppm or more and 100 mass ppm 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 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. If the Be content is less than 3 ppm by mass, the effects of Be addition cannot be fully obtained. On the other hand, if the Be content exceeds 100 ppm by mass, the Be-containing compound becomes coarse, which can lead to cracking and a decrease in rollability. Therefore, the Be content should be between 3 ppm by mass and 100 ppm by mass. Furthermore, from the viewpoint of fully obtaining the effects of adding Be as described above, the Be content is preferably 4 ppm or more, 5 ppm or more, 8 ppm or more, or 10 ppm or more. Also, from the viewpoint of ensuring rollability, it is preferably 80 ppm or less, 50 ppm or less, 30 ppm or less, or 20 ppm or less.

[0020] (Zr: 100 mass ppm or less) By incorporating a small amount of zinc (Zr) into aluminum alloy sheets, the grain size of the aluminum alloy ingot is refined, thereby improving yield strength. However, if the Zr content exceeds 100 ppm by mass, the intermetallic compounds become coarser, potentially leading to edge cracking and reduced rollability. Therefore, the Zr content should be 100 ppm by mass or less (including 0.00 ppm by mass). Furthermore, from the viewpoint of suppressing a decrease in rollability, the Zr content is preferably 90 ppm by mass or less, 80 ppm by mass or less, 70 ppm by mass or less, 60 ppm by mass or less, 50 ppm by mass or less, 40 ppm by mass or less, and 30 ppm by mass or less. Even if the Zr content is 0 ppm by mass, the properties of the present invention will not be impaired, but if it is included, from the viewpoint of improving yield strength, the Zr content is preferably 5 ppm by mass or more and 10 ppm by mass or more.

[0021] (Si: 0.20% by mass or less) Si is typically incorporated into aluminum alloys as an unavoidable impurity in the base metal, forming elemental Si or Al-Fe-Si intermetallic compounds. If the Si content exceeds 0.20 mass%, the Young's modulus decreases, and the elemental Si and Al-Fe-Si intermetallic compounds become coarser, resulting in reduced rollability. Therefore, the Si content should be 0.20 mass% or less (including 0.00 mass%). Furthermore, from the viewpoint of suppressing a decrease in Young's modulus and rollability, the Si content is preferably 0.18 mass% or less, 0.15 mass% or less, 0.13 mass% or less, 0.10 mass% or less, 0.08 mass% or less, 0.05 mass% or less, 0.04 mass% or less, 0.03 mass% or less, and 0.02 mass% or less. A lower Si content is desirable, and even 0 mass% does not impair the properties of the present invention, but it requires high-purity raw materials (such as Al ingots and intermediate alloy ingots), which increases costs. For this reason, an Si content of 0.004 mass% or more is industrially preferable.

[0022] (Total of Fe, Mn, and Ni: 0.05-3.0% by mass) Fe, Mn, and Ni are components that contribute to improving rigidity and 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 of them, such as 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 0.05 to 3.0 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 rigidity and stress relaxation resistance. On the other hand, if these are included in excess, the area ratio of intermetallic compounds on the surface of the aluminum alloy plate will increase due to the coarsening of intermetallic compounds, which may reduce grindability. For this reason, the total content is preferably 3.0% by mass or less, 2.8% by mass or less, 2.6% by mass or less, 2.4% by mass or less, 2.2% by mass or less, 2.0% by mass or less, 1.8% by mass or less, 1.6% by mass or less, 1.4% by mass or less, and 1.2% by mass or less.

[0023] 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 1.0 mass%, and Ni: 0 to 1.0 mass%.

[0024] (Fe: 1.00% by mass or less) Fe is included in aluminum alloy sheets to obtain good rigidity and stress relaxation resistance. However, if the Fe content in the aluminum alloy sheet exceeds 1.00 mass%, the grindability may decrease due to the coarsening of intermetallic compounds. Therefore, the Fe content should be 1.00 mass or less (including 0 mass%). Furthermore, from the viewpoint of suppressing a decrease in grindability, the Fe content is preferably 0.90% by mass or less, 0.80% by mass or less, 0.70% by mass or less, 0.60% by mass or less, or 0.50% by mass or less. Furthermore, from the viewpoint of obtaining good rigidity and stress relaxation resistance characteristics, values ​​of 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, and 0.40 mass% or more are preferred.

[0025] (Mn: 1.0% by mass or less) Mn is included in aluminum alloy sheets to obtain good rigidity and stress relaxation resistance. However, if the Mn content in the aluminum alloy sheet exceeds 1.0 mass%, the grindability may decrease due to the coarsening of intermetallic compounds. Therefore, the Mn content should be 1.0 mass or less (including 0 mass%). Furthermore, from the viewpoint of suppressing a decrease in grindability, the Mn content is preferably 0.9% by mass or less, 0.8% by mass or less, 0.7% by mass or less, or 0.6% by mass or less. Also, from the viewpoint of obtaining good rigidity and stress relaxation resistance, it is preferably 0.05% by mass or more, 0.1% by mass or more, or 0.2% by mass or more. Preferably, the amount is 0.3% by mass or more, 0.4% by mass or more, or 0.5% by mass or more.

[0026] (Ni: 1.0% by mass or less) Ni is included in aluminum alloy sheets to obtain good rigidity and stress relaxation resistance. However, if the Ni content in the aluminum alloy sheet exceeds 1.0 mass%, the grindability may decrease due to the coarsening of intermetallic compounds. Therefore, the Ni content should be 1.0 mass or less (including 0 mass%). Furthermore, from the viewpoint of suppressing a decrease in grindability, the Ni content 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, or 0.5% by mass or less. Also, from the viewpoint of obtaining good rigidity and stress relaxation resistance, it is preferably 0.1% by mass or more, 0.2% by mass or more, 0.3% by mass or more, or 0.4% by mass or more.

[0027] (Cu: 1.0 mass% or less, Zn: 1.0 mass% or less) Cu and Zn are components that broaden the solid-liquid coexistence region and contribute to reducing the frequency of molten metal leakage during casting. They are also components that have the effect of uniformly 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. 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.

[0028] (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, V, B, Na, K, Ca, Pb, P, Sn, Ag, Bi, In, Ge, Sr, and Cd. Of these, Ti 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. When each of the elements listed as impurity elements is inevitably present (i.e., is an unavoidable impurity), 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, if the chemical composition does not include the above-mentioned Si, Fe, Mn, Ni, Cu, and Zn, The content of these unavoidable impurities is preferably 0.005% by mass or less for each.

[0029] <Area ratio of intermetallic compounds on the surface of aluminum alloy plate: 0.10~40%> In this embodiment, the aluminum alloy plate for magnetic disks has an area ratio of intermetallic compounds on its surface of 0.10 to 40%, and this area ratio was calculated for intermetallic compounds with a maximum length of 0.33 μm or more. Examples of intermetallic compounds that occupy the surface include Mg-Si intermetallic compounds, Al-Fe intermetallic compounds, Al-Mn intermetallic compounds, Al-Ni intermetallic compounds, Al-Fe-Mn intermetallic compounds, Al-Fe-Ni intermetallic compounds, Al-Mn-Ni intermetallic compounds, Al-Fe-Mn-Ni intermetallic compounds, Al-Cr intermetallic compounds, Al-Ti intermetallic compounds, and Al-Zr intermetallic compounds. In this case, Al-Fe-Cr intermetallic compounds in which a portion of the above Al-Fe intermetallic compounds is substituted, and Al-Mn-Cr intermetallic compounds in which a portion of the Al-Mn intermetallic compounds is substituted are also included. Furthermore, as mentioned above, when Cu and Zn are included in the amounts specified in this invention, examples include Al-Cu intermetallic compounds and Al-Zn intermetallic compounds. In this invention, elemental Si is treated in the same way as intermetallic compounds.

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

[0031] The area ratio of intermetallic compounds on the surface can be measured as follows: The surface of the blank is cut to a mirror finish with a diamond cutting tool, and this surface is then scanned using a FE-SEM (JEOL Ltd. JSM-7001F, acceleration voltage 15kV) at 1,000x magnification, with 50 fields of view and an observation area of ​​0.54 mm². 2 The image is then captured to obtain a compositional image called a COMPO image. From the captured COMPO image, the matrix portion, i.e., the part that appears whiter than the matrix phase, is considered to be intermetallic compounds. Using the attached analysis system "Analysis Station 3,8,0,31" and particle analysis software "EX-351 10 Particle Analysis Software Ver.3.84", the area fraction of Al-Fe intermetallic compounds and other compounds can be calculated. The area ratio of intermetallic compounds according to this embodiment was calculated for intermetallic compounds with a maximum length of 0.33 μm or more.

[0032] <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. The lower limit of the stress relaxation rate is not particularly limited, but for example, it could be 0% or more, 20% or more, These are 50% or more, 60% or more, and 70% or more. The stress relaxation rate can be adjusted by setting the content of Fe, Mn, and Ni to the levels 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 treatment conditions in the homogenization heat treatment process to the range described later and the area ratio of intermetallic compounds on the surface of the aluminum alloy plate to the range described above.

[0033] 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). Afterward, 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)), 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 [%]).

[0034] σ = M / Z ... (1) σ: Bending stress [N / mm] 2 ] M: Bending moment [N·mm] Z: Section modulus (Z[mm 3 ]=(w×t2 ) / 6) w: Plate width [mm], t: Plate thickness [mm]

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

[0036] P = (3 × E × I × δ) / x 3 ...(3) P: Tip load [N] E: Young's modulus [N / 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]

[0037] <Grinding performance: Grinding speed of 0.5 μm / min or higher> The aluminum alloy plate for magnetic disks according to this embodiment preferably has a grinding speed of 0.5 μm / min or more, determined by the measurement method described below, and more preferably 1.0 μm / min or more, 1.5 μm / min or more, 2.0 μm / min or more, or 2.5 μm / min or more. Furthermore, there is no particular upper limit to the grinding speed, but it is usually 3.0 μm / min or less. The method for measuring grinding speed is shown below.

[0038] A circular, or hollow, disc-shaped, aluminum alloy plate is subjected to wet grinding using a machining center equipped with a circular grinding wheel under the following grinding conditions. The grindability of the aluminum alloy plate is evaluated by the grinding speed, which is determined from the change in the thickness of the aluminum alloy plate and the grinding time. Note that "C abrasive grains" in the grinding wheel refer to black silicon carbide (SiC) abrasive grains.

[0039] Grinding conditions: Size of aluminum alloy plate: outer diameter 95 mm, inner diameter 43 mm Size of grinding wheel: outer diameter 60 mm, inner diameter 40 mm Grinding pressure: 100 gf / cm 2 Peripheral speed of grinding wheel: 1.05 m / s Revolution speed of grinding wheel: 100 mm / min Grinding fluid: KH-8A (registered trademark) manufactured by Nippon Quaker Chemical Co., Ltd., 0.5% dilution Grinding wheel: PVA grinding wheel for magnetic disk manufactured by AION Co., Ltd. C abrasive grain #1500

[0040] The grinding speed can be adjusted by setting the contents of Fe, Mn, and Ni as described in this specification. Further, in addition to the above contents of Fe, Mn, and Ni, the processing conditions in the homogenization heat treatment process are set within the range described below, and the area ratio of the intermetallic compound on the surface of the aluminum alloy plate is set within the above range, whereby the grinding speed can be adjusted.

[0041] [Manufacturing method of aluminum alloy plate for magnetic disk] Next, an example of the manufacturing method of the aluminum alloy plate for magnetic disk according to the present embodiment will be described. The aluminum alloy plate according to the present embodiment can be manufactured by a manufacturing method and equipment under general conditions for manufacturing an aluminum alloy plate for magnetic disk, except for some conditions in the homogenization heat treatment process and the hot rolling process. For example, a casting process in which a raw material is melted and a molten aluminum alloy adjusted to a predetermined chemical composition is cast into an aluminum alloy ingot by a semi-continuous casting method or the like, a homogenization heat treatment process in which the cast aluminum alloy ingot is face-milled and subjected to homogenization heat treatment, a hot rolling process in which the aluminum alloy ingot subjected to homogenization heat treatment is hot-rolled to obtain a hot-rolled plate, and a cold rolling process in which the hot-rolled plate is cold-rolled. The aluminum alloy plate can be manufactured by a manufacturing method including these steps in this order. Note that, if necessary, intermediate annealing may be performed before the cold rolling process or during the cold rolling process. Hereinafter, each step will be described in detail.

[0042] (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.

[0043] (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. From the viewpoint of achieving an area ratio of intermetallic compounds on the surface of the aluminum alloy plate of 0.10 to 40%, the homogenization heat treatment is preferably carried out at a temperature of 510 to 600°C, and the time during which it is held at 510°C or higher is preferably 48 hours or less.

[0044] By setting the homogenization heat treatment temperature to 510°C or higher, the formation of intermetallic compounds in the aluminum alloy is promoted during the homogenization heat treatment, increasing the area ratio of intermetallic compounds on the surface of the aluminum alloy plate, resulting in good stress relaxation resistance and enabling the homogenization of the structure. The homogenization heat treatment temperature is more preferably 515°C or higher, and even more preferably 520°C or higher. On the other hand, by setting the homogenization heat treatment temperature to 600°C or lower, it is possible to prevent the surface of the aluminum alloy ingot from melting. The homogenization heat treatment temperature is more preferably 580°C or lower, and even more preferably 540°C or lower.

[0045] If the homogenization heat treatment is held at a temperature of 510°C or higher for longer than 48 hours, excessive intermetallic compound formation occurs, causing the area ratio of intermetallic compounds on the surface of the aluminum alloy plate to exceed a predetermined value, which reduces grindability. Therefore, the holding time at a temperature of 510°C or higher is preferably 48 hours or less, more preferably 40 hours or less, 35 hours or less, 30 hours or less, 25 hours or less, 20 hours or less, 15 hours or less, or 10 hours or less. From the viewpoint of homogenizing the structure, the lower limit of the holding time at 510°C or higher during the homogenization heat treatment can be, for example, 4 hours.

[0046] (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 480°C or higher. Furthermore, the ending temperature for hot rolling is preferably 300 to 350°C. 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. Furthermore, the thickness of the hot-rolled sheet obtained by hot rolling can be, for example, 3 mm or less.

[0047] (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.

[0048] [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 the area ratio of intermetallic compounds on the surface, stress relaxation rate, and grindability, 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.

[0049] (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.

[0050] (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 faster than 1000°C / hour. Cooling can be done, for example, by opening the door of the annealing furnace.

[0051] 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.

[0052] [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 the area ratio of intermetallic compounds on the surface, stress relaxation rate, and grindability, 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.

[0053] 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.

[0054] [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]

[0055] 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.

[0056] (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.

[0057] First, molten metal was used to create slabs using DC casting in molds with ingot thicknesses (500 mm for No. 1 and 2, and 535 mm for No. 3). Then, both sides (in the thickness direction) of the obtained slabs were machined by 16 mm each. After that, a homogenization heat treatment was performed, held at 535°C for the holding time specified in Table 1. Next, No. 1 and 3 were hot-rolled to a thickness of 2.3 mm, and No. 2 to a thickness of 2.0 mm (starting temperature: approximately 500°C, ending temperature: approximately 330°C). No. 1 was then cold-rolled to a thickness of 0.55 mm, and No. 2 and 3 to a thickness of 0.52 mm. After that, The blanks (O-tempered material) of various thicknesses were produced by punching out ring-shaped sections using a press machine, with an outer diameter of approximately 98 mm and an inner diameter of approximately 24 mm. These blanks were then sandwiched between spacers and subjected to corrective annealing (heating to 200-280°C at a heating rate of 50°C / h or higher, followed by holding at 300-400°C for no more than 7 hours).

[0058] For each test material manufactured, the surface area ratio of intermetallic compounds, grindability, and stress relaxation rate were evaluated as follows.

[0059] (Percentage of intermetallic compound area on the surface) The area ratio of intermetallic compounds on the surface was measured as follows: The blank surface was cut to a mirror finish with a diamond cutting tool, and this surface was scanned using a FE-SEM (JEOL Ltd. JSM-7001F, acceleration voltage 15kV) at 1,000x magnification, with 50 fields of view and an observation area of ​​0.54 mm². 2 The image was taken as a composite image, and a compositional image called a COMPO image was obtained. From the captured COMPO image, the matrix portion, that is, the part that appears whiter than the matrix, was considered to be the intermetallic compound, and the attached analysis system "Analysis Station 3,8,0,31" was used to analyze it. Using the particle analysis software "EX-35110 Particle Analysis Software Ver.3.84," the area fraction of Al-Fe intermetallic compounds with a maximum length of 0.33 μm or more was calculated.

[0060] (Grinding speed) The blank was machined to the specified size by altering its outer and inner diameters, and wet grinding was performed using a machining center equipped with an annular grinding wheel under the following grinding conditions. The grindability of the test material was evaluated by determining the grinding speed from the change in the thickness of the test material and the grinding time. In the context of the grinding wheel, "C abrasive grains" refers to black silicon carbide (SiC) abrasive grains. Grinding speeds of 0.5 μm / min or higher were rated "○", and those less than 0.5 μm / min were rated "×".

[0061] Grinding conditions: Size of the test specimen: Outer diameter 95 mm, inner diameter 43 mm Grinding wheel dimensions: Outer diameter 60mm, Inner diameter 40mm Grinding pressure: 100 gf / cm² 2 Grinding wheel peripheral speed: 1.05 m / sec Grinding wheel rotation speed: 100 mm / min Grinding fluid: Quaker Chemical Japan KH-8A (registered trademark), 0.5% dilution. Grinding stone, manufactured by AION, made of polyvinyl alcohol (PVA) for magnetic disks. C abrasive #1500

[0062] (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 (as shown in Figure 1(a)) and subjected to a heat treatment simulating magnetic film sputtering (300°C for 1 hour). After removal from the atmospheric furnace, the deformation amount a before bending stress removal was measured. Subsequently, the bending stress was removed (as shown in Figure 1(b)), and the deformation amount b after bending stress removal was measured. The stress relaxation rate was defined as the ratio of the deformation amount b after unloading to the deformation amount a before unloading (b / a × 100 [%]). Materials with a stress relaxation rate of 90% or less were evaluated as "○" indicating excellent deformation suppression during magnetic film sputtering, while those exceeding 90% were evaluated as "×" indicating poor deformation suppression during magnetic film sputtering.

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

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

[0065] P = (3 × E × I × δ) / x 3 ...(3) P: Tip load [N] E: Young's modulus [N / 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]

[0066] Table 1 shows the alloy composition (chemical composition), surface area ratio of intermetallic compounds, and other details for each test material. The results of the evaluation of grindability and stress relaxation rate are shown. Underlined text in the table indicates that the specific features of the present invention are not met.

[0067] [Table 1]

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

Claims

1. Mg: 0.1 to 7.0% by mass, Cr: 0.005 to 1.0% by mass, Be: Contains 3 to 100 ppm by mass, Furthermore, it contains at least one of the following: Cu: 1.0% by mass or less, and Zn: 1.0% by mass or less. Zr: 100 mass ppm or less, Si: 0.20% by mass or less, The total amount of at least one of Fe, Mn, and Ni is 0.05 to 3.0% by mass. The remainder consists of Al and impurities. The area ratio of intermetallic compounds on the surface is 0.10 to 40%. The aforementioned area ratio was calculated for intermetallic compounds with a maximum length of 0.33 μm or more, in an aluminum alloy blank for magnetic disks.

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

3. An aluminum alloy blank for a magnetic disk according to claim 1 or 2, wherein the stress relaxation rate is 90% or less.

4. An aluminum alloy substrate for magnetic disks obtained from an aluminum alloy blank for magnetic disks according to claim 1 or 2.

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

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