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

Abstract

Provided are an aluminum alloy sheet for a magnetic disk, an aluminum alloy blank for a magnetic disk, and an aluminum alloy substrate for a magnetic disk, which have excellent yield strength and Young's modulus and in which cracking during rolling is suppressed. The aluminum alloy sheet, blank, and substrate for a magnetic disk satisfy Mg: 2.1 mass% or more and 4.8 mass% or less, Cu: 1.00 mass% or less, Cr: 0.01 to 0.30 mass%, Si: 0.20 mass% or less, contain one or more of Fe: 0.10 to 1.70 mass%, Mn: 0.06 to 1.50 mass%, and Ni: 0.0001 to 2.70 mass%, and the balance consists of Al and impurities, the total content of Fe, Mn, Ni, and Cr is 1.05 to 2.40 mass%, and the content (mass%) of Mg satisfies the formula: Mg < -2.75 x the total content (mass%) of Fe, Mn, Ni, and Cr + 8.8.

Description

TECHNICAL FIELD

[0001] The present application relates to an aluminum alloy sheet for a magnetic disk, an aluminum alloy blank for a magnetic disk, and an aluminum alloy substrate for a magnetic disk. BACKGROUND

[0002] A magnetic disk used as a recording medium for a computer or the like is formed by forming a magnetic film on a non-magnetic substrate. Generally, the substrate is required to be lightweight and have high rigidity, and to have a smooth surface, and therefore a 5086 alloy (Al-Mg alloy) specified in JIS H 4000:2006 is used.

[0003] Further, the magnetic disk is manufactured by, after the sheet and the blank are manufactured using the alloy, for example, performing mirror processing on the surface, sequentially performing degreasing treatment, acid etching treatment, black film stripping treatment, 1st zincate treatment, nitric acid stripping treatment, 2nd zincate treatment, and non-electrolytic Ni-P plating treatment, and forming a magnetic film on the non-electrolytic Ni-P film.

[0004] Research and development have been conducted on such an aluminum alloy sheet for a magnetic disk, and various kinds of alloy sheets have been proposed.

[0005] For example, in Patent Literature 1, there is described a manufacturing method of a blank material for a magnetic disk composed of an aluminum alloy containing 3.0 to 6.0 mass% of Mg, and the balance being Al and impurities, characterized by having a press annealing step of, while applying a load of 1.5 MPa or more and 4 MPa or less to the blank material for a magnetic disk, annealing at an annealing temperature of 210°C or more and 280°C or less.

[0006] PRIOR ART DOCUMENTS

[0007] PATENT LITERATURE

[0008] Patent Literature 1: Japanese Patent Application Laid-Open No. 2012-123884 SUMMARY

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] In Patent Literature 1, a manufacturing method of a blank material for a magnetic disk is discussed from the viewpoint of yield strength and impact resistance, and it is described that a material of a certain level can be manufactured.

[0011] However, for a sheet for a magnetic disk composed of an aluminum alloy (aluminum alloy sheet, blank, and substrate), the demand for thinning is increasing, and it is necessary to ensure high levels of "yield strength" and "Young's modulus" required for the sheet for thinning.

[0012] Further, with the thinning of the disk material, the probability of occurrence of a rolling crack during manufacture increases, and it is therefore desirable to suppress the occurrence of such a rolling crack as much as possible.

[0013] The present application was made in view of the above problems, and has an object to provide an aluminum alloy sheet for a disk, an aluminum alloy blank for a disk, and an aluminum alloy substrate for a disk, which have excellent yield strength and Young's modulus, and in which the occurrence of a rolling crack during rolling can be suppressed.

[0014] Means for solving the problems

[0015] The present inventors have found as a result of diligent research that, by specifying the alloy composition in detail (particularly, by specifying the "Mg content", the "total content of Fe, Mn, Ni, and Cr", and the "relationship between the Mg content and the total content of Fe, Mn, Ni, and Cr" among the three), not only the "yield strength" and the "Young's modulus" of the disk material are excellent, but also the occurrence of a "rolling crack" can be suppressed.

[0016] Based on the above, the present application was created.

[0017] The aluminum alloy sheet for a disk of the present application satisfies Mg: 2.1 mass% or more and 4.8 mass% or less, Cu: 1.00 mass% or less, Cr: 0.01 mass% or more and 0.30 mass% or less, Si: 0.20 mass% or less, contains one or more of Fe: 0.10 mass% or more and 1.70 mass% or less, Mn: 0.06 mass% or more and 1.50 mass% or less, and Ni: 0.0001 mass% or more and 2.70 mass% or less, the balance being Al and impurities, the total content of Fe, Mn, Ni, and Cr is 1.05 mass% or more and 2.40 mass% or less, and satisfies the formula: Mg content (mass%) < -2.75 x total content of Fe, Mn, Ni, and Cr (mass%) + 8.8.

[0018] Further, the aluminum alloy sheet for a disk of the present application can have Be: 3 ppm or more and 100 ppm or less.

[0019] Further, the aluminum alloy sheet for a disk of the present application can have Sr: 100 ppm or less.

[0020] Further, the aluminum alloy blank for a disk of the present application is formed from the aluminum alloy sheet for a disk.

[0021] Further, the aluminum alloy substrate for a disk of the present application is formed from the aluminum alloy blank for a disk.

[0022] Effects of the Invention

[0023] The aluminum alloy sheet for a magnetic disk, the aluminum alloy blank for a magnetic disk, and the aluminum alloy substrate for a magnetic disk of the present application are excellent in yield strength and Young's modulus, and can suppress occurrence of rolling cracks. DETAILED DESCRIPTION

[0024] Hereinafter, the aluminum alloy sheet for a magnetic disk, the aluminum alloy blank for a magnetic disk, and the aluminum alloy substrate for a magnetic disk of one embodiment of the present application will be described.

[0025] Also, in the following description, the aluminum alloy sheet for a magnetic disk, the aluminum alloy blank for a magnetic disk, and the aluminum alloy substrate for a magnetic disk of the present embodiment are simply referred to as "aluminum alloy sheet" (or "alloy sheet"), "blank", and "substrate", respectively.

[0026] [Aluminum Alloy Sheet]

[0027] The aluminum alloy sheet of the present embodiment is formed of an aluminum alloy in which the contents of Mg, Cu, Cr, and Si are within a prescribed range (or below a prescribed value), one or more of Fe, Mn, and Ni are contained, and the total content of Fe, Mn, Ni, and Cr is within a prescribed range, and the content of Mg and the total content of Fe, Mn, Ni, and Cr satisfy a prescribed formula. Also, the aluminum alloy sheet can further contain Be, and can contain Sr.

[0028] Hereinafter, each component of the aluminum alloy sheet of the present embodiment will be described in detail.

[0029] (Mg: 2.1 mass% or more and 4.8 mass% or less)

[0030] Mg changes the annealing softening behavior, thereby not only increasing the flatness but also contributing to an increase in yield strength. In detail, if the content of Mg is 2.1 mass% or more, the aluminum alloy sheet becomes in a state of O-type tempered material in the annealing temperature region around 320°C, and can exhibit excellent flatness after correction annealing. In addition, if the content of Mg is 2.1 mass% or more, the effect of an increase in yield strength (for example, 110 MPa or more) due to the addition of Mg can be exhibited, and deformation accompanying thinning during processing and use can be suppressed. On the other hand, if the content of Mg is higher than 4.8 mass%, the rollability can decrease (rolling cracks can occur). Therefore, the content of Mg is 2.1 mass% or more and 4.8 mass% or less.

[0031] Also, from the viewpoint of increasing flatness, the content of Mg is preferably 2.3 mass% or more, 2.4 mass% or more, 2.5 mass% or more, 2.6 mass% or more, 2.7 mass% or more, or 2.8 mass% or more. In addition, from the viewpoint of ensuring rollability, the content of Mg is preferably 4.7 mass% or less, 4.6 mass% or less, 4.5 mass% or less, 4.4 mass% or less, or 3.9 mass% or less.

[0032] (Cu: 1.00 mass% or less)

[0033] Cu shows a low equilibrium partition coefficient, greatly reducing the solidus temperature of the aluminum alloy. Therefore, Cu has the effect of expanding the solid-liquid coexistence region on a phase diagram, reducing the frequency of occurrence of casting defects at the time of casting. In addition, Cu also has the effect of uniformly precipitating zinc in zincate treatment. However, if the content of Cu is higher than 1.00 mass%, the solid-liquid coexistence region on the phase diagram is too wide. As a result, intermetallic compounds become coarse, edge cracks occur, and there is a possibility that the rollability decreases. In addition, if the content of Cu is higher than 1.00 mass%, the density increases, and it can interfere with weight reduction. Therefore, the content of Cu is 1.00 mass% or less (including 0.00 mass%).

[0034] Further, from the viewpoint of ensuring the effects brought about by adding Cu, the content of Cu is preferably 0.02 mass% or more, 0.05 mass% or more. In addition, from the viewpoint of ensuring the rollability and the like, the content of Cu is preferably 0.70 mass% or less, 0.60 mass% or less.

[0035] (Cr: 0.01 mass% or more and 0.30 mass% or less)

[0036] Cr has the effect of refining primary crystals and uniformly distributing intermetallic compounds, contributing to the improvement of strength and yield strength. If the content of Cr is lower than 0.01 mass%, the primary crystals are not sufficiently refined, and the effects of improving the strength and yield strength brought about by adding Cr cannot be sufficiently obtained. On the other hand, if the content of Cr is higher than 0.30 mass%, intermetallic compounds become coarse, edge cracks occur, and there is a possibility that the rollability decreases. Therefore, the content of Cr is 0.01 mass% or more and 0.30 mass% or less.

[0037] Further, from the viewpoint of improving the strength and yield strength, the content of Cr is preferably 0.05 mass% or more, 0.10 mass% or more, 0.15 mass% or more. In addition, from the viewpoint of ensuring the rollability, the content of Cr is preferably 0.27 mass% or less, 0.25 mass% or less.

[0038] (Si: 0.20 mass% or less)

[0039] Si is usually mixed into the aluminum alloy as an unavoidable impurity in the ingot, forming single Si or Al-Fe-Si intermetallic compounds, and the like. If the content of Si is higher than 0.20 mass%, the Young's modulus decreases, or single Si and Al-Fe-Si intermetallic compounds become coarse, and the rollability decreases. Therefore, the content of Si is 0.20 mass% or less (including 0.00 mass%).

[0040] Further, from the viewpoint of suppressing a decrease in the Young's modulus and the rollability, the content of Si is preferably 0.10% by mass or less, 0.07% by mass or less, 0.04% by mass or less. The lower the content of Si is, the better, and even if it is 0% by mass, the characteristics of the present application are not impaired, but since a raw material (Al ingot and intermediate alloy ingot, etc.) of high purity is required, the cost increases. Therefore, the content of Si is preferably 0.004% by mass or more in industry.

[0041] (Fe: 0.10% by mass or more and 1.70% by mass or less)

[0042] Fe contributes to an increase in strength and the Young's modulus. If the content of Fe is 0.10% by mass or more, an effect of increasing the strength and the Young's modulus based on Fe can be obtained. However, if the content of Fe is more than 1.70% by mass, Al-Fe-Ni intermetallic compounds become coarse, or Al-Mn-Fe intermetallic compounds become coarse, and a crack occurs, so there is a possibility that the rollability decreases. Therefore, when Fe is contained, the content of Fe is 0.10% by mass or more and 1.70% by mass or less.

[0043] Further, from the viewpoint of increasing the rigidity, the content of Fe is more preferably 0.20% by mass or more, 0.30% by mass or more. In addition, from the viewpoint of securing the rollability, the content of Fe is preferably 1.50% by mass or less, 1.40% by mass or less, 1.30% by mass or less, 0.90% by mass or less, 0.50% by mass or less.

[0044] (Mn: 0.06% by mass or more and 1.50% by mass or less)

[0045] Mn contributes to an increase in strength and the Young's modulus. If the content of Mn is 0.06% by mass or more, an effect of increasing the strength and the Young's modulus based on Mn can be obtained. However, if the content of Mn is more than 1.50% by mass, Al-Mn-Fe intermetallic compounds become coarse, and a crack occurs, so there is a possibility that the rollability decreases. Therefore, when Mn is contained, the content of Mn is 0.06% by mass or more and 1.50% by mass or less.

[0046] Further, from the viewpoint of increasing the rigidity, the content of Mn is preferably 0.08% by mass or more, 0.09% by mass or more, 0.10% by mass or more. In addition, from the viewpoint of securing the rollability, the content of Mn is preferably 1.20% by mass or less, 0.90% by mass or less, 0.60% by mass or less, 0.40% by mass or less, 0.30% by mass or less.

[0047] (Ni: 0.0001% by mass or more and 2.70% by mass or less)

[0048] Ni contributes to the increase in strength and Young's modulus. If the content of Ni is 0.0001 mass% or more, the effect of increasing the strength and Young's modulus based on Ni can be obtained. However, if the content of Ni is more than 2.70 mass%, Al-Fe-Ni intermetallic compounds become coarse, edge cracks occur, and there is a possibility that the rollability decreases. Therefore, when Ni is contained, the content of Ni is 0.0001 mass% or more and 2.70 mass% or less.

[0049] Further, from the viewpoint of increasing the rigidity, the content of Ni is 0.40 mass% or more, 0.50 mass% or more, or 0.60 mass% or more. In addition, from the viewpoint of ensuring the rollability, the content of Ni is preferably 2.50 mass% or less, 1.80 mass% or less, or 1.10 mass% or less.

[0050] (Fe, Mn, Ni, and Cr: 1.05 mass% or more and 2.40 mass% or less)

[0051] Fe, Mn, Ni, and Cr have an influence on the strength (yield strength), Young's modulus, and further the occurrence of rolling cracks. Moreover, if the total content of Fe, Mn, Ni, and Cr is less than 1.05 mass%, the yield strength and Young's modulus (particularly, Young's modulus) can not reach a desired value or more. On the other hand, if the total content of Fe, Mn, Ni, and Cr is more than 2.40 mass%, it can be impossible to suppress the occurrence of rolling cracks. Therefore, the total content of Fe, Mn, Ni, and Cr is 1.05 mass% or more and 2.40 mass% or less.

[0052] Further, the total content of Fe, Mn, Ni, and Cr is preferably 1.06 mass% or more, 1.10 mass% or more, 1.15 mass% or more, or 1.20 mass% or more from the viewpoint of increasing the yield strength and Young's modulus. In addition, the total content of Fe, Mn, Ni, and Cr is preferably 2.30 mass% or less, 2.20 mass% or less, or 2.10 mass% or less from the viewpoint of suppressing the occurrence of rolling cracks.

[0053] (Relationship between "the content of Mg" and "the total content of Fe, Mn, Ni, and Cr")

[0054] The present inventors and others have confirmed that the relationship between "the content of Mg" and "the total content of Fe, Mn, Ni, and Cr" in the aluminum alloy sheet has a significant influence on "the yield strength", "Young's modulus", and "the occurrence of rolling cracks" (particularly, "the occurrence of rolling cracks").

[0055] Further, the inventors have found that when the aluminum alloy sheet satisfies the formula "content of Mg (mass %) < -2.75 x total content of Fe, Mn, Ni, and Cr (mass %) + 8.8", both the "yield strength" and the "Young's modulus" can be made excellent, and the occurrence of "rolling cracks" can be suppressed.

[0056] Further, the formula (slope of the formula, intercept of the formula, etc.) is derived based on a large number of experimental results.

[0057] (Be: 3 ppm or more and 100 ppm or less)

[0058] Be exerts an effect of suppressing growth of an oxidation film, and an effect of suppressing formation of Mg oxide at the time of casting. If the content of Be is less than 3 ppm, the effects of suppressing growth of an oxidation film and suppressing formation of Mg oxide brought about by the addition of Be cannot be sufficiently obtained. On the other hand, if the content of Be is more than 100 ppm, Be-containing compounds become coarse, and there is a possibility that coatability is reduced. Therefore, when Be is contained, the content of Be is 3 ppm or more and 100 ppm or less.

[0059] In addition, from the viewpoint of suppressing growth of an oxidation film, the content of Be is preferably 3.5 ppm or more, 4.0 ppm or more, or 4.5 ppm or more. In addition, from the viewpoint of suppressing the coarsening of Be-containing compounds, the content of Be is preferably 20 ppm or less, 10 ppm or less, or 8 ppm or less.

[0060] (Sr: 100 ppm or less)

[0061] Sr promotes branching of dendrites formed at the time of casting, and has an effect of refining crystalline substances. However, if the content of Sr is more than 100 ppm, Al-Sr or the like, which is a Sr-containing compound, becomes coarse, and edge cracks occur, and thus there is a possibility that rollability is reduced. Therefore, when Sr is contained, the content of Sr is 100 ppm or less.

[0062] Further, from the viewpoint of ensuring that the effects brought about by the addition of Sr are obtained, the content of Sr is preferably 3 ppm or more, 10 ppm or more, 20 ppm or more, or 30 ppm or more. In addition, from the viewpoint of suppressing the coarsening of Sr-containing compounds, the content of Sr is preferably 90 ppm or less or 80 ppm or less.

[0063] (balance: Al and impurities)

[0064] The aluminum alloy sheet of the present embodiment can contain elements other than the above as impurities due to the selection of the raw material for melting at the time of ingot production. As the impurity elements, specifically, Zn, Ti, Zr, V, B, Na, K, Ca, Pb, and the like can be listed. Among these, Ti, Zr, and V are each limited to 0.10% by mass or less, Zn is limited to 1.00% by mass or less, and B, Na, K, Ca, and Pb are limited to 0.05% by mass or less. As long as these elements are within these ranges, the effects of the present embodiment are not hindered even if these elements are contained as unavoidable impurities or are actively added by intentionally increasing the blending ratio of scrap containing these elements, and the like.

[0065] When each of the elements shown as the impurity elements is unavoidably contained (in other words, when it is an unavoidable impurity), the content of Zn is 0.25% by mass or less (preferably 0.15% by mass or less, 0.05% by mass or less). The content of each of the elements other than Zn is 0.005% by mass or less, and the total of the elements other than Zn is 0.015% by mass or less.

[0066] In addition, when the above Cu, Fe, Mn, and Ni are not actively added as the chemical composition, the content thereof as an unavoidable impurity is also 0.005% by mass or less.

[0067] [Method for manufacturing aluminum alloy sheet]

[0068] The aluminum alloy sheet of the present embodiment can be manufactured using a manufacturing method and equipment under general conditions for manufacturing a substrate for a magnetic disk. For example, the aluminum alloy sheet can be manufactured by a manufacturing method including the following steps in order: a casting step of casting molten metal adjusted to a prescribed chemical composition into an ingot as a raw material for melting; a homogenization heat treatment step of performing homogenization heat treatment on the cast ingot; a hot rolling step of hot-rolling the cast ingot subjected to the homogenization heat treatment to obtain a hot-rolled sheet; and a cold rolling step of cold-rolling the hot-rolled sheet to obtain a cold-rolled sheet. Also, intermediate annealing can be performed as needed before or during the cold rolling step.

[0069] (Casting step)

[0070] In the casting step, the raw material is melted at 700 to 800°C, and casting is performed by a known semi-continuous casting method such as a DC casting method. Furthermore, the casting speed in the casting step is not particularly limited, and for example, is 100 mm / minute or less, 80 mm / minute or less, or 70 mm / minute or less. Also, regarding the thickness of the slab in the casting step, for example, it is 400 mm or more and 650 mm or less.

[0071] In addition, the cast ingot is preferably subjected to surface cutting, and the amount of surface cutting can be performed, for example, at 2 to 40 mm per single side.

[0072] (homogenizing heat treatment step)

[0073] The homogenizing heat treatment step, for example, can be performed at a temperature of 400 to 600°C for 4 to 48 hours.

[0074] (rolling step)

[0075] The rolling step, for example, can be performed at a starting temperature of 490°C or higher. In addition, the rolling step can be performed at an ending temperature of 300 to 350°C. The rolling from 520°C to 400°C is preferably completed within 30 minutes, and more preferably completed within 15 minutes. In addition, the thickness of the hot-rolled sheet obtained by the rolling step, for example, can be 3 mm or less.

[0076] (cold rolling step)

[0077] In the cold rolling step, the thickness of the cold-rolled sheet obtained by the cold rolling step, for example, is preferably 0.5 to 1.3 mm, and more preferably 0.7 mm or less.

[0078] [blank]

[0079] The blank of the present embodiment is formed of the aluminum alloy sheet of the present embodiment. Furthermore, the blank of the present embodiment is a punched disc (annular disc) formed by punching the aluminum alloy sheet of the present embodiment, and is subjected to a correction annealing. The chemical composition of the blank is not changed from that of the aluminum alloy sheet, in other words, is the same as that of the aluminum alloy sheet.

[0080] Further, the characteristic values such as the yield strength and the Young's modulus of the blank of the present embodiment are values measured for the blank subjected to the correction annealing step described later or the aluminum alloy sheet subjected to a heat treatment under the same conditions as the correction annealing step described later.

[0081] (yield strength)

[0082] The yield strength of the blank is preferably 110 MPa or higher. From the viewpoint of further improving the mechanical properties of the disc, the yield strength of the blank is more preferably 115 MPa or higher, and 120 MPa or higher. Further, the upper limit of the yield strength is not particularly specified, and for example, is 220 MPa, or 200 MPa or lower.

[0083] The yield strength, for example, can be measured by preparing a JIS No. 5 test piece with the rolling direction as the longitudinal direction in accordance with JIS Z 2241:2011 (Metallic materials - Tensile testing method) and performing a tensile test. Further, a test piece similar to the JIS No. 5 test piece, but with a reduced size, can also be used for the measurement.

[0084] (Young's modulus)

[0085] The Young's modulus of the blank is preferably 71.0 GPa or more. If the Young's modulus is 71.0 GPa or more, the material itself has high rigidity, and thus, even if the blank is not made thick, the vibration during the operation of the magnetic disk can be sufficiently reduced. From the viewpoint of suppressing the vibration during the operation of the magnetic disk, the Young's modulus of the blank is preferably 71.2 GPa or more.

[0086] The Young's modulus can be measured, for example, in accordance with JIS Z 2280: 1993 (Test method for high temperature Young's modulus of metallic materials) by preparing a test piece of 60 mm x 10 mm x about 0.55 mm thick with the rolling direction as the longitudinal direction, using this test piece, and measuring at room temperature in an atmospheric atmosphere by a free resonance method. As a test device, for example, JE-RT manufactured by Techno-Plus Co., Ltd., Japan can be used.

[0087] [Method for manufacturing blank]

[0088] The blank of the present embodiment can be manufactured by a manufacturing method and equipment using general conditions for manufacturing a substrate for a magnetic disk. For example, the blank can be manufactured by a manufacturing method including, in order, a punching step of punching an aluminum alloy sheet obtained by cold rolling into a circular ring shape, and a correction annealing step of performing correction annealing on the punched substrate.

[0089] The punching step is a step of punching an aluminum alloy sheet into a desired shape, and for example, the punching treatment can be performed in a manner applicable to a substrate for a 3.5-inch HDD having an inner diameter of 24 mm and an outer diameter of 96 mm, or a substrate for a 2.5-inch HDD having an inner diameter of 19 mm and an outer diameter of 66 mm, or the like.

[0090] In the correction annealing step, it is preferable to stack the substrates with a spacer having high flatness interposed therebetween, and to perform annealing while applying a load to the substrates. The annealing temperature is 250 to 500°C, and the holding time can be, for example, about 3 to 5 hours. The temperature increase rate of the correction annealing is, for example, about 70 to 150°C / hour, and the average is 80°C / hour (Max. 150°C / hour), and in the temperature decrease, for example, the door of the annealing furnace can be opened to perform the temperature decrease (cooling). In addition, with respect to the temperature increase of the correction annealing, even if the temperature increase is performed in stages, the effect of the present embodiment is not impaired. For example, as described in paragraphs 0068 to 0069 of Japanese Patent No. 5815153, the temperature increase rate in a specific temperature range can be made a predetermined rate (or more), and the temperature increase rate outside the specific temperature range can be made another temperature increase rate, and the temperature increase can be performed at a plurality of temperature increase rates (temperature increase in stages).

[0091] [Substrate]

[0092] The substrate of the present embodiment is formed from the blank of the present embodiment. Furthermore, the substrate of the present embodiment is one in which the end surface of the blank of the present embodiment has been subjected to cutting processing and the main surface has been subjected to grinding processing, and the chemical composition has not changed from that of the blank and the aluminum alloy plate, in other words, is the same as that of the blank and the aluminum alloy plate.

[0093] In addition, the substrate of the present embodiment, because it is manufactured by subjecting the blank to the processing of the surfaces (end surface and main surface) described later, the yield strength and Young's modulus of the substrate do not change from those of the blank, and are the same as those of the blank.

[0094] (Substrate: Thickness of Oxidation Coating Film)

[0095] The substrate of the present embodiment, if containing Be, can suppress the growth of the oxidation coating film.

[0096] Furthermore, because the thickness of the substrate of the present embodiment (thickness of each surface) is thin, it is not necessary to perform a long or strong acid etching treatment, and thus it is possible to suppress etching damage to the surface of the substrate. Finally, the occurrence of unevenness after the electroless Ni-P plating treatment based on surface etching damage is reduced, and the possibility of obtaining a smooth plated surface after polishing the surface is increased.

[0097] On the other hand, the thickness of the oxidation coating film of the substrate of the present embodiment is preferably 1 nm or more depending on the relationship of the composition.

[0098] Therefore, the thickness of the oxidation coating film of the substrate of the present embodiment is preferably 1 nm or more and less than 6.5 nm.

[0099] Further, from the viewpoint of making the effects more definite, the thickness of the oxidation coating film of the substrate is more preferably 6.0 nm or less, and 5.7 nm or less. In addition, the thickness of the oxidation coating film of the substrate is more preferably 3 nm or more, and 4 nm or more.

[0100] [Method of Manufacturing Substrate]

[0101] The substrate of the present embodiment can be manufactured using a manufacturing method and apparatus under general conditions for manufacturing a substrate for a magnetic disk. For example, the substrate can be manufactured by a manufacturing method including the following steps in order: an end surface processing step of cutting processing the end surface of the blank; and a grinding processing step of grinding processing the main surface of the blank.

[0102] [Method of Manufacturing Magnetic Disk]

[0103] The magnetic disk can be manufactured using a manufacturing method and apparatus under general conditions for manufacturing a magnetic disk. For example, after performing acid etching processing on the surface of the substrate and forming an electroless Ni-P film, the surface of the electroless Ni-P film is polished. Subsequently, on the surface of the substrate, a bottom layer, a magnetic layer, a protective film, and the like are formed, and thus a magnetic disk can be manufactured.

[0104] Further, details of the manufacturing conditions of the blank, the substrate, etc. are described in, for example, Japanese Patent No. 3471557 and Japanese Patent No. 5199714. The manufacturing of the blank, the substrate, etc. can be performed with reference to these documents.

[0105] Example

[0106] Hereinafter, an example of the present application is shown to specifically explain the present application. However, the technical scope of the present application is not limited by the example.

[0107] (Factory trial: preparation of test materials)

[0108] The test materials of Nos. 1 to 4 were manufactured using aluminum alloys having the chemical compositions shown in Table 1, based on the following conditions.

[0109] First, a slab was produced by DC casting of molten metal in a mold having a block thickness of 500 mm. Then, each of the two surfaces (thickness direction) of the obtained slab was surface cut by 16 mm. Subsequently, homogenization heat treatment was performed at 540°C for 8 hours. Then, hot rolling (start temperature: about 500°C, end temperature: about 330°C) was performed until the thickness reached 2.3 mm, and cold rolling was performed until the thickness reached 0.55 mm. Thereafter, punching processing was performed to 96 to 98 φ using a press, and correction annealing was performed with a spacer interposed (heating rate: about 70 to 140°C / hour (average about 110°C / hour), annealing temperature: about 320°C, holding time: about 3 hours) to manufacture a blank (O-tempered material) having a plate thickness of 0.55 mm.

[0110] Thereafter, mirror surface processing of 30 μm was performed on each surface of the blank, and a substrate was manufactured.

[0111] (Laboratory trial: preparation of test materials)

[0112] The test materials of Nos. 5 to 8 were manufactured using aluminum alloys having the chemical compositions shown in Table 2, based on the following conditions.

[0113] First, a slab was produced by book mold casting of molten metal in a mold having a thickness of 35 mm, a width of 145 mm, and a length of 250 mm. Then, each of the two surfaces (thickness direction) of the obtained slab was surface cut by 2.5 mm. Subsequently, homogenization heat treatment was performed at 535°C for 8 hours. Then, hot rolling was performed until the thickness reached 3.4 mm, and cold rolling was performed until the thickness reached 0.55 mm. Thereafter, punching processing was performed to 96 φ using a press, and correction annealing was performed with a spacer interposed (heating rate: about 70 to 140°C / hour (average about 80°C / hour), annealing temperature: about 320°C, holding time: about 3 hours) to manufacture a blank (O-tempered material) having a plate thickness of 0.55 mm.

[0114] For each of the test materials manufactured, the yield strength, Young's modulus, thickness of the oxidation film, and occurrence of rolling cracks were measured or confirmed in the following manner.

[0115] (Yield strength)

[0116] The yield strength was measured in accordance with JIS Z 2241:2011 (Metallic materials - Tensile testing method) from the ingots No. 1 to 4 to produce 13B test pieces with the rolling direction as the longitudinal direction, and by performing a tensile test, the 0.2% yield strength was measured. The evaluation was "pass" when the 0.2% yield strength was 110 MPa or more, and was "fail" when it was less than 110 MPa.

[0117] (Young's modulus)

[0118] The Young's modulus was measured in accordance with JIS Z 2280:1993 (Metallic materials - High temperature Young's modulus testing method) from the ingots No. 1 to 4 to produce 60 mm x 10 mm x about 0.55 mm thick test pieces with the rolling direction as the longitudinal direction, and using the test pieces, the measurement was performed in the atmospheric air at room temperature by the free resonance method. As the test device, JE-RT manufactured by Techno-Plus Co., Ltd., was used. The evaluation was "pass" when the Young's modulus was 71.0 GPa or more, and was "fail" when it was less than 71.0 GPa.

[0119] (Thickness of oxidation film)

[0120] A Mark's high frequency glow discharge optical emission surface analysis device JY5000RF manufactured by Horiba, Ltd. was used to analyze the surface of the ingots No. 1 to 3 at a sputtering speed of 0.236 μm / min, a sputtering rate of 0.011 g / m 2 / s, and an analysis time of 2 minutes. From the analysis results, the depth at which the light emission intensity of oxygen O was half of the maximum value was defined as the oxidation film thickness. For each of the test materials, the measurement was performed three times, and the average value calculated was used as the analysis value. Also, if the ingot to be measured is described in detail, it is the ingot on which mirror surface processing of 30 μm was performed on each surface, and after the surface was cleaned with a fluorine-based solvent (AMOLEA (registered trademark) AS-300 manufactured by DKS Co., Ltd.), it was stored under the prescribed conditions (room temperature 25°C, daily average humidity 72%, daily minimum humidity 51%), and the ingot within 8 hours from the mirror surface processing was used.

[0121] (Occurrence of rolling cracks: No. 1 to 4)

[0122] For the cold-rolled sheet (No. 1 to 4) having a thickness of 0.55 mm and a width of 1250 mm, the left and right ends (both ends in the width direction) with respect to the rolling direction of about 2000 to 3000 m in length were visually confirmed, and it was determined whether or not a rolling crack had occurred.

[0123] (occurrence of a rolling crack: No. 5 to 8)

[0124] For the cold-rolled sheet (No. 5 to 8) having a thickness of 0.55 mm, a width of 145 mm, and a length of 1400 mm, the upper layer 10 points of the depth of a crack (a cold-rolled crack) occurring in the left and right ends with respect to the rolling direction of the sheet due to rolling were calculated. If the calculated average value was lower than 4.0 mm, it was determined as "O" (if it was a factory material, it was a level that could be determined that no cold-rolled crack had occurred), and if the calculated average value was 4.0 mm or more, it was determined as "X" (if it was a factory material, it was a level that could be determined that a cold-rolled crack had occurred).

[0125] The alloy composition and the test results of the test materials (factory materials) manufactured in the factory are shown in Table 1, the alloy composition and the test results of the test materials (laboratory materials) manufactured in the laboratory are shown in Table 2, and the results of the thickness of the oxidation coating of the test materials (part of them) manufactured in the factory are shown in Table 3.

[0126] The so-called "thickness of the oxidation coating" of Table 3 is the thickness of the oxidation coating formed on one side of the substrate.

[0127] In addition, the so-called "difference in the thickness of the oxidation coating" of Table 3 is a value calculated by "thickness of the oxidation coating of No. 3 - thickness of the oxidation coating of No. 1" (put No. 1 in No. V of the table) in the case of the substrate of No. 1, for example, based on No. 3 which does not contain Be.

[0128] In addition, the so-called "reduction rate of the thickness of the oxidation coating" of Table 3 is a value calculated by [("thickness of the oxidation coating of No. 3" - "thickness of the oxidation coating of No. 1") / "thickness of the oxidation coating of No. 3" x 100] (put No. 1 in No. V of the table) in the case of the substrate of No. 1, for example, based on No. 3 which does not contain Be.

[0129] [Table 1]

[0130]

[0131] [Table 2]

[0132]

[0133] [Table 3]

[0134] [Table 3]

[0135]

[0136] According to the results of No. 1 to 4 of Table 1, since the alloy components satisfy the requirements prescribed in the present application (particularly, since the content of Mg, the total content of Fe, Mn, Ni and Cr, and the prescribed relational expression are satisfied), it was confirmed that the yield strength was above the prescribed value, the Young's modulus was above the prescribed value, and in addition, the occurrence of rolling cracks was suppressed.

[0137] In addition, according to the results of No. 5 of Table 2, since the alloy components satisfy the requirements prescribed in the present application (particularly, since the content of Mg, the total content of Fe, Mn, Ni and Cr, and the relational expression of the content of Mg and the total content of Fe, Mn, Ni and Cr are satisfied), it was judged that the rolling crack depth was short as a laboratory material, and the occurrence of rolling cracks could be suppressed as a plant material.

[0138] On the other hand, according to the results of No. 6 and 7 of Table 2, since the prescribed relational expression (the relational expression of the content of Mg and the total content of Fe, Mn, Ni and Cr) was not satisfied, it was judged that the rolling crack depth was long as a laboratory material, and the occurrence of rolling cracks could not be suppressed as a plant material.

[0139] In addition, according to the results of No. 8 of Table 2, since the content of Mg was higher than the prescribed value, it was judged that the rolling crack depth was long as a laboratory material, and the occurrence of rolling cracks could not be suppressed as a plant material.

[0140] According to the results of No. 1 to 3 of Table 3, it was confirmed that No. 1 and 2 containing Be could make the thickness of the oxidation coating film thinner by about 20% compared to No. 3 not containing Be.

[0141] As a result, it was presumed that No. 1 and 2 containing Be could suppress the occurrence of etching damage on the surface of the substrate without a long time or strong acid etching treatment. Furthermore, the occurrence of unevenness after the electroless Ni-P plating treatment based on the etching damage on the surface was reduced, and the possibility of obtaining a smooth plated surface after surface polishing was improved.

Claims

1. An aluminum alloy plate for a hard disk, wherein, Mg: ≥2.6% by mass and ≤3.9% by mass Cu: less than 1.00% by mass Cr: ≥0.01% by mass and ≤0.30% by mass Si: less than 0.20% by mass Fe: ≥0.10% by mass and ≤0.50% by mass Mn: ≥0.06% by mass and ≤1.50% by mass Ni: ≥0.40% by mass and ≤2.70% by mass, and Be: 3 ppm or more and 100 ppm or less The balance includes Al and impurities. The combined content of Fe, Mn, Ni, and Cr is 1.20% by mass or more and 2.10% by mass or less. The formula satisfies the condition that the content of Mg (by mass%) is < -2.75 × the total content of Fe, Mn, Ni and Cr (by mass%) + 8.

8.

2. The aluminum alloy plate for disks according to claim 1, wherein, Sr: below 100ppm.

3. An aluminum alloy blank for a hard disk, formed from an aluminum alloy sheet for a hard disk as described in claim 1 or claim 2.

4. An aluminum alloy substrate for a hard disk, formed from the aluminum alloy blank for a hard disk as described in claim 3.

Images