Aluminum alloy disc blank for magnetic disc and magnetic disc

Abstract

The present invention relates to an aluminum alloy disc blank for a magnetic disc, characterized by being formed of an aluminum alloy containing Mg: 3.40 to 3.90 mass%, the balance consisting of Al and unavoidable impurities, the aluminum alloy disc blank for a magnetic disc having an electrical conductivity of 36.0% IACS or more.

Description

Technical Field

[0001] This invention relates to an aluminum alloy disk blank for disks and a disk using the aluminum alloy disk blank. Background Technology

[0002] Hard disk drives (HDDs) are mostly used as storage devices in electronic devices such as computers or image recording devices. An HDD contains a disk for recording data. The disk has a ring-shaped aluminum alloy substrate, a Ni-P plating layer covering the surface of the aluminum alloy substrate, and a magnetic layer deposited on the Ni-P plating layer.

[0003] In recent years, the amount of information recorded on HDDs has been increasing in various applications, from business uses such as servers or data centers to home uses such as personal computers or video recording devices. To address this, increasing HDD capacity requires improving the recording density of the disks within the HDD. To increase the recording density of the disks, a smooth Ni-P plating layer is formed on an aluminum alloy substrate.

[0004] Disks are typically manufactured using the following method. First, a rolled aluminum alloy sheet is punched into a ring shape to create a disk blank. Next, the disk blank is pressed and heated from both sides along its thickness to reduce warping. Then, the disk blank is machined and ground to form the desired shape, thus obtaining an aluminum alloy substrate. By sequentially performing pretreatment for forming a Ni-P plating layer, electroless Ni-P plating, and sputtering of a magnetic layer on this aluminum alloy substrate, a disk can be manufactured.

[0005] JIS A5086 alloy is often used as the aluminum alloy for aluminum alloy substrates.

[0006] The demands of multimedia applications require large-capacity and high-density hard disks. To further increase capacity, there is a tendency to reduce the head lift during read / write operations. However, if there are protrusions on the disk surface, they can collide with the head, leading to recording errors. Therefore, it is necessary to reduce the presence of protrusions. Furthermore, high yield strength has always been required for aluminum alloy disk blanks to ensure stable processing and use.

[0007] Therefore, various studies have been conducted on techniques to reduce foreign matter such as intermetallic compounds present in aluminum alloy substrates, with the aim of further improving smoothness by reducing convex defects. For example, Patent Document 1 describes a method for reducing Mg2Si compounds and Al-Fe compounds in an aluminum alloy plate for a disk substrate. The aluminum alloy plate for the disk substrate contains 2.0 to 6.0 wt% Mg, 0.05 to 0.15 wt% Cu, 0.10 to 0.30 wt% Zn, 0.05 to 0.12 wt% Zr, and 0.2 wt% or less (including 0 wt%) Sn. The contents of Cu, Zn, Zr, and Sn satisfy the relationship 0.15 wt% ≤ 2Cu + 6Zr - 3Zn - 0.1Sn ≤ 0.32 wt% (where Cu, Zr, Zn, and Sn are their respective weight %). It further contains one or two of Mn (more than 0.01 wt% and less than 0.05 wt%) and Cr (more than 0.01 wt% and less than 0.05 wt%), with the balance consisting of unavoidable impurity elements and Al.

[0008] (Existing technical literature)

[0009] (Patent Documents)

[0010] Patent Document 1: Japanese Patent Application Publication No. 10-008177

[0011] According to the method in Patent Document 1, twin-roll continuous casting can increase the cooling rate during solidification of molten metal, resulting in finer intermetallic compounds. However, the method in Patent Document 1 suffers from the problem of difficulty in reducing convex defects in the billet caused by factors other than intermetallic compounds. Furthermore, the method in Patent Document 1 makes it difficult to sufficiently increase the yield strength of the billet. Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] This invention was made in view of the above-mentioned problems. The inventors discovered that by controlling the Mg content and electrical conductivity of aluminum alloys, it is possible to obtain aluminum alloy blanks for disks that reduce convex defects, improve smoothness, and simultaneously achieve high yield strength, thus completing this invention.

[0014] Means for solving technical problems

[0015] One aspect of the present invention is an aluminum alloy disk blank for disks, characterized in that it is formed of an aluminum alloy containing Mg: 3.40 to 3.90% by mass, with the balance consisting of Al and unavoidable impurities, and the electrical conductivity of the aluminum alloy disk blank for disks is 36.0% IACS or higher.

[0016] Another aspect of the present invention is an aluminum alloy disk blank for a hard disk, characterized in that the aluminum alloy contains Mg: 3.40-3.65% by mass.

[0017] Another aspect of the present invention is an aluminum alloy disk blank for a hard disk, characterized in that the aluminum alloy contains Mg: 3.40-3.55% by mass.

[0018] Another aspect of the present invention is an aluminum alloy blank for a hard disk, wherein the aluminum alloy further contains one or more elements selected from the group consisting of Cu: less than 0.30 wt%, Zn: less than 0.60 wt%, Fe: less than 0.60 wt%, Si: less than 0.60 wt%, Cr: less than 0.20 wt%, Be: less than 0.0020 wt%, Sr: less than 0.10 wt%, Na: less than 0.10 wt%, and P: less than 0.10 wt%.

[0019] Another aspect of the present invention is a disk, characterized in that a Ni-P plating layer and a magnetic layer on the surface of an aluminum alloy substrate formed from an aluminum alloy disk blank.

[0020] Invention Effects

[0021] The aluminum alloy blank for disks involved in this invention can control the amount of Mg and electrical conductivity to reduce convex defects, improve smoothness, and achieve high yield strength. Attached Figure Description

[0022] Figure 1 This is a graph showing the relationship between the electrical conductivity of an aluminum alloy disk blank and the maximum height of a convex defect.

[0023] Figure 2 It is a graph showing the relationship between the annealing temperature and electrical conductivity of aluminum alloy disk blanks after pressure annealing.

[0024] Figure 3 This is a graph showing the relationship between the Mg content and electrical conductivity of aluminum alloy disk blanks used for hard disks.

[0025] Figure 4 This is a graph showing the relationship between the Mg content and yield strength of aluminum alloy blanks for hard disks. Detailed Implementation

[0026] A-1. Aluminum alloy disk blank for hard disks

[0027] The present invention relates to an aluminum alloy disk blank (hereinafter sometimes referred to as "aluminum alloy blank"). An aluminum alloy blank is obtained by producing an aluminum alloy sheet using an aluminum alloy with a specified alloy composition and then punching it into a disk shape. The aluminum alloy blank is formed from an aluminum alloy containing Mg: 3.40–3.90% by mass, with the balance consisting of Al and unavoidable impurities. The electrical conductivity of the aluminum alloy blank is 36.0% IACS or higher. By ensuring the electrical conductivity of the aluminum alloy blank is 36.0% IACS or higher, the amount of solute atoms (especially Mg) dissolved in the aluminum alloy can be controlled within an appropriate range. As a result, an aluminum alloy blank with reduced convexity defects and excellent smoothness can be produced. It should be noted that an electrical conductivity meter (e.g., "AutoSigma 3000" manufactured by GE Sense & Inspection Technologies Co., Ltd.) can be used for measuring the electrical conductivity. The electrical conductivity of test materials with a thickness of 1 mm or more and 2 mm or less is measured by eddy current method at 25°C. Furthermore, a high yield strength can be achieved by using a Mg content of 3.40–3.90% by mass. The reason is that Mg mainly exists as solid-solution Mg, which enhances strength; therefore, by increasing the Mg content to 3.40–3.90% by mass, the yield strength is improved. As a result, both the improved smoothness due to reduced convex defects and high yield strength can be achieved simultaneously.

[0028] A-1. Alloy composition of aluminum alloys

[0029] The composition of the aluminum alloy used for aluminum alloy blanks and the reasons for its limitations are explained in detail below.

[0030] ·Mg: 3.40–3.90% by mass

[0031] Mg is an essential element contained in aluminum alloys, primarily existing as dissolved Mg, which enhances the strength of the aluminum alloy blank. Furthermore, the zinc coating adheres uniformly, thinly, and densely during the zincate treatment of the aluminum alloy blank, improving the smoothness of the Ni-P plating surface in the subsequent plating process. However, when the Mg content is less than 3.40% by mass (hereinafter sometimes abbreviated as "%)", the strength of the aluminum alloy blank is insufficient, leading to deformation during cutting and grinding. Furthermore, the zinc coating formed by the zincate treatment becomes uneven, reducing the adhesion and smoothness of the plating. On the other hand, if the Mg content exceeds 3.90% by mass, residual stress becomes more easily generated during cutting and grinding. This is because the increased amount of dissolved Mg in the aluminum alloy fixes dislocations that occur during the machining of the aluminum alloy blank. These dislocations do not completely disappear during post-machining annealing, releasing residual stress and creating convex defects, thus reducing smoothness. Therefore, in the aluminum alloy blank of the present invention, the Mg content of the aluminum alloy is specified to be 3.40 to 3.90% by mass. It should be noted that, from the perspective of balancing strength and manufacturability, the Mg content is preferably 3.40 to 3.65% by mass, and more preferably 3.40 to 3.55% by mass.

[0032] In addition to Mg, the aluminum alloy may further contain one or more elements selected from the group consisting of Cu, Zn, Fe, Si, Be, Cr, Sr, Na, and P as further arbitrary components. In this case, an aluminum alloy blank for disk drives can be obtained, characterized in that it is formed from an aluminum alloy containing Mg: 3.40–3.90% by mass, and containing one or more elements selected from the group consisting of Cu: less than 0.30% by mass, Zn: less than 0.60% by mass, Fe: less than 0.60% by mass, Si: less than 0.60% by mass, Cr: less than 0.20% by mass, Be: less than 0.0020% by mass, Sr: less than 0.10% by mass, Na: less than 0.10% by mass, and P: less than 0.10% by mass, with the balance consisting of Al and unavoidable impurities, and the electrical conductivity of the aluminum alloy blank for disk drives is 36.0% IACS or higher.

[0033] The following is a detailed description of each component.

[0034] Cu: less than 0.30% by mass

[0035] In aluminum alloys, Cu can be present as an arbitrary component up to 0.30% by mass. During the zincate treatment process in disk manufacturing, Cu inhibits the leaching of Al from the aluminum alloy. By setting the Cu content to 0.30% by mass or less, a dense, thin, and uniformly thin Zn film can be deposited on the surface of the aluminum alloy substrate during zincate treatment in disk manufacturing. Furthermore, by forming the aforementioned Zn film, a smooth Ni-P plating layer can be formed in subsequent processes, namely, electroless Ni-P plating.

[0036] However, if the Cu content is too high, the corrosion resistance of the aluminum alloy blank decreases, creating localized areas where Al easily dissolves. Therefore, during zincate treatment in disk manufacturing, the amount of Al dissolved on the surface of the aluminum alloy substrate varies, leading to increased unevenness in the Zn coating thickness. This can potentially reduce the adhesion between the Ni-P plating layer and the aluminum alloy substrate, and decrease the smoothness of the Ni-P plating layer.

[0037] By setting the Cu content in the aluminum alloy to 0.30% by mass or less, preferably 0.15% by mass or less, the formation of plating pits can be suppressed, further improving the smoothness of the Ni-P plating layer. It should be noted that the lower limit of the Cu content is preferably set to 0.0050% by mass, more preferably 0.010% by mass.

[0038] • Zn: less than 0.60% by mass

[0039] In aluminum alloys, Zn can be present as an arbitrary component at 0.60% by mass or less. Like Cu, Zn has the function of inhibiting the dissolution of Al from the aluminum alloy during zincate treatment. By setting the Zn content to 0.60% by mass or less, a dense, thin, and uniformly thin Zn film can be deposited on the surface of the aluminum alloy substrate during zincate treatment in disk manufacturing. Furthermore, by forming the aforementioned Zn film, a smooth Ni-P plating layer can be formed in subsequent processes, namely, electroless Ni-P plating.

[0040] However, if the Zn content is too high, the corrosion resistance of the aluminum alloy blank decreases, creating localized areas where Al easily dissolves. Therefore, during the zincate treatment process in disk manufacturing, variations in the amount of Al dissolved on the surface of the aluminum alloy substrate can occur, leading to increased unevenness in the Zn coating thickness. This can potentially reduce the adhesion between the Ni-P plating layer and the aluminum alloy substrate, and decrease the smoothness of the Ni-P plating layer.

[0041] By setting the Zn content in the aluminum alloy to 0.60% by mass or less, preferably 0.50% by mass or less, the formation of plating pits can be suppressed, further improving the smoothness of the Ni-P plating layer. It should be noted that the lower limit of the Zn content is preferably set to 0.10% by mass, more preferably 0.25% by mass.

[0042] Fe, Si: less than 0.60% by mass

[0043] In aluminum alloys, Fe and Si can be present in quantities of less than 0.60% by mass as any component. Fe is almost insoluble in the Al matrix, but rather dispersed within the aluminum alloy blank as an Al-Fe intermetallic compound. In the presence of Mg in the aluminum alloy, Mg-Si intermetallic compounds are formed between Si and Mg.

[0044] When the aforementioned Al-Fe and Mg-Si intermetallic compounds detach from the surface of the aluminum alloy blank, plating pits are easily formed during the subsequent electroless Ni-P plating process. By setting the Fe and Si contents in the aluminum alloy to 0.60% by mass or less, preferably 0.050% by mass or less, and more preferably 0.0010% by mass or less, respectively, the amount of the aforementioned intermetallic compounds present in the aluminum alloy blank can be further reduced. As a result, the formation of plating pits can be suppressed, and the smoothness of the Ni-P plating layer can be further improved.

[0045] To suppress plating pits caused by the aforementioned intermetallic compounds, it is preferable to reduce the content of Fe and Si. However, these elements are present not only in raw material metals of general purity but also in high-purity raw material metals where Al has a purity of 99.9% by mass or higher. Therefore, if aluminum alloy blanks that are almost free of Fe and Si are to be produced, special treatments for removing these elements are required during casting, leading to increased manufacturing costs for the aluminum alloy blanks.

[0046] Aluminum alloy blanks can be manufactured without special treatments to remove these elements, provided that the Fe and Si contents in the aluminum alloy are both below 0.0010% by mass. This avoids increasing the manufacturing cost of the aluminum alloy blanks and further improves their smoothness. Furthermore, if the Fe and Si contents in the aluminum alloy are greater than 0.0010% by mass but less than 0.60% by mass, lower purity raw material metals can be used to manufacture aluminum alloy blanks. This further reduces the material cost of the aluminum alloy blanks.

[0047] • Be: less than 0.0020% by mass

[0048] Be is an element added to the molten metal during the casting of aluminum alloys containing Mg to suppress the oxidation of Mg. Furthermore, by setting the Be content in the aluminum alloy to 0.0020% by mass or less, the Zn film formed on the surface of the aluminum alloy substrate during disk manufacturing can be made denser, and thickness unevenness can be further reduced. As a result, the smoothness of the Ni-P treatment layer formed on the aluminum alloy substrate can be further improved.

[0049] However, if the Be content in the aluminum alloy is too high, Be-based oxides easily form on the surface of the aluminum alloy blank when it is heated during the manufacturing process. Furthermore, if the aluminum alloy further contains Mg, Al-Mg-Be-based oxides easily form on the surface of the aluminum alloy blank when heated. If the amount of these oxides increases, the unevenness of the Zn coating thickness becomes greater, potentially leading to plating pits.

[0050] By setting the Be content in the aluminum alloy to 0.0020% by mass or less, preferably 0.0010% by mass or less, the amount of Al-Mg-Be oxides can be reduced, further improving the smoothness of the Ni-P plating layer. It should be noted that the lower limit for the Be content can be 0% by mass (0.0000% by mass), but it is preferably set to 0.0002% by mass.

[0051] ·Cr: less than 0.20% by mass

[0052] In aluminum alloys, Cr can be present as an arbitrary component up to 0.20% by mass. A portion of the Cr is dispersed within the aluminum alloy blank as fine intermetallic compounds formed during casting. Cr that does not form intermetallic compounds during casting dissolves in the Al matrix, thus enhancing the strength of the aluminum alloy blank through solid solution strengthening.

[0053] Furthermore, Cr further improves machinability and grindability, and also makes the recrystallized structure finer. As a result, the adhesion between the aluminum alloy substrate and the Ni-P plating layer is further improved, and the formation of plating pits is suppressed.

[0054] However, if the Cr content in the aluminum alloy is too high, coarse Al-Cr intermetallic compounds can easily form in the aluminum alloy substrate. When these coarse Al-Cr intermetallic compounds detach from the surface of the aluminum alloy substrate, plating pits are easily formed during the subsequent electroless Ni-P plating process.

[0055] By setting the Cr content in the aluminum alloy to 0.20% by mass or less, preferably 0.10% by mass or less, the formation of plating pits can be suppressed, a smooth Ni-P plating layer can be formed, and the strength of the aluminum alloy substrate can be further improved. It should be noted that the lower limit of the Cr content is preferably set to 0.030% by mass, more preferably 0.050% by mass.

[0056] • Sr, Na and P: less than 0.10% by mass each

[0057] Sr, Na, and P contribute to the refinement of the second-phase particles (mainly Si particles) in aluminum alloy blanks, thus improving plating properties. They also reduce the size inhomogeneity of the second-phase particles in the aluminum alloy blanks, thereby mitigating uneven impact resistance. Therefore, aluminum alloys can contain less than 0.10% by mass of Sr, Na, and P, respectively.

[0058] However, even with Sr, Na, and P exceeding 0.10% by mass respectively, the above effects will saturate, and no more significant effects can be obtained. Furthermore, to achieve the above effects, it is preferable to set the lower limit values ​​for Sr, Na, and P to 0.0010% by mass.

[0059] Other elements

[0060] Aluminum alloys may contain elements that are unavoidable impurities, in addition to the necessary and optional components mentioned above. Examples of such elements include Mn, Zr, Ti, B, Si, and Ga. As long as their content is 0.10% by mass or less for each element and 0.30% by mass or less in total, the effectiveness of the invention will not be impaired. As described above, in the present invention, Si can be actively added as an optional component, but there are also cases where it is not actively added and becomes an unavoidable impurity. Si is an unavoidable impurity not only in raw metals of general purity but also in high-purity raw metals where the purity of Al is 99.9% or more. In the case of its inclusion as an unavoidable impurity, as long as it is 0.10% by mass or less, the effectiveness of the invention will not be impaired. It should be noted that when Si is actively added as an optional component, as described above, from the viewpoint of reducing the amount of intermetallic compounds, the Si content in the aluminum alloy is preferably 0.60% by mass or less.

[0061] Electrical conductivity of aluminum alloy blank: above 36.0% IACS

[0062] A higher electrical conductivity value for the aluminum alloy blank indicates a lower amount of solute atoms dissolved in the aluminum alloy. By setting the electrical conductivity of the aluminum alloy blank within the specific range mentioned above (above 36.0% IACS), the amount of solute atoms (especially Mg) dissolved in the aluminum alloy can be set within an appropriate range. As a result, convex defects can be reduced, resulting in excellent smoothness.

[0063] When the electrical conductivity is below 36.0% IACS, the amount of solute atoms dissolved in the aluminum alloy increases, potentially leading to more convex defects. This is because the increased amount of dissolved Mg in the aluminum alloy fixes dislocations generated during processing. Even during post-processing annealing, these dislocations do not completely disappear, releasing residual stress and resulting in convex defects, thus reducing smoothness. Therefore, the electrical conductivity of the aluminum alloy blank in this invention is specified to be 36.0% IACS or higher. Moreover, the electrical conductivity is preferably 37.0% IACS or higher, and more preferably 38.0% IACS or higher. It should be noted that in aluminum alloys with chemical compositions within the above-mentioned specific range, the upper limit of electrical conductivity is typically around 45.0% IACS. Figure 1 This is a graph showing the relationship between the electrical conductivity of an aluminum alloy blank and the maximum height of a convex defect. Figure 1 The details of the aluminum alloy blank shown are described in later embodiments. Figure 1 As shown, the higher the electrical conductivity, the smaller the maximum height of the convex defect. The convex defect was evaluated according to the following procedure: a micro Vickers hardness tester indented the surface of the aluminum alloy blank under 5 kg conditions, then the surface was machined on a lathe until the indentation disappeared, and annealed at 270°C for 1 hour. The maximum height of the convex defect generated at the indentation site was then measured.

[0064] A-2. Manufacturing methods for aluminum alloy sheets

[0065] (1) Casting process

[0066] Aluminum raw materials with a specified alloy composition are melted and smelted into molten metal, which is then cast to produce ingots. Casting methods include semi-continuous casting (DC casting), metal mold casting, and continuous casting (CC casting). In DC casting, molten metal injected through a spout is cooled by the bottom block, the water-cooled mold walls, and cooling water discharged directly to the outer periphery of the ingot (ingot), solidifying it and pulling it downwards as an ingot. In metal mold casting, molten metal injected into a hollow metal mold made of cast iron or similar materials is cooled by the mold walls, solidifying it into an ingot. In CC casting, molten metal is supplied through a casting nozzle between a pair of rollers (or a belt casting machine, block casting machine) and the rollers absorb heat (cooling) to directly cast thin sheets.

[0067] In the above casting process, it is preferable to perform degassing treatment to reduce dissolved gases in the molten metal and filtration treatment to remove solid substances from the molten metal online.

[0068] For degassing treatment, methods such as SNIF (Spinning Nozzle Inert Flotation) and Alpur (rotating nozzle inert gas flotation) can be used. In these processes, molten metal is stirred at high speed by a bladed rotating body while process gases such as argon or a mixture of argon and chlorine are blown in, forming microbubbles of the process gas within the molten metal. This allows for the removal of dissolved hydrogen or inclusions from the molten metal in a short time. In-line degassing devices can be used in this degassing process.

[0069] For filtration, methods such as cake filtration or filter media filtration can be used. Additionally, filters such as ceramic tube filters, ceramic foam filters, and alumina ball filters can be used in the filtration process.

[0070] (2) Homogenization process

[0071] Between the casting and hot rolling, the casting surface can be milled as needed to perform homogenization. The holding temperature during homogenization can be appropriately set from, for example, a range of 500 to 570°C. Furthermore, the holding time during homogenization can be appropriately set from, for example, a range of 1 to 60 hours.

[0072] (3) Hot rolling process

[0073] Next, the ingot is hot-rolled to produce a hot-rolled plate. There are no particular limitations on the hot rolling conditions, but for example, the starting temperature can be set in the range of 400 to 550°C and the ending temperature can be set in the range of 260 to 380°C.

[0074] (4) Cold rolling process

[0075] After hot rolling, the resulting hot-rolled sheet can be cold-rolled in one or more passes to obtain a cold-rolled sheet. There are no particular limitations on the cold rolling conditions; they can be appropriately set according to the desired thickness and strength of the aluminum alloy coil. For example, the total reduction rate of the cold rolling can be set to 20%–95%. Furthermore, the thickness of the cold-rolled sheet can be appropriately set, for example, from 0.2 to 1.9 mm.

[0076] (5) Annealing process

[0077] In the manufacturing method described above, annealing can be performed as needed, either before the first cold rolling or between two cold rolling passes. Annealing can be performed using either a batch heat treatment furnace or a continuous heat treatment furnace. When using a batch heat treatment furnace, it is preferable to set the holding temperature during annealing to 250–430°C and the holding time to the range of 0.1–10 hours. Conversely, when using a continuous heat treatment furnace, it is preferable to set the furnace dwell time to within 60 seconds and the furnace temperature to 400–500°C. Annealing under these conditions restores the workability acquired during cold rolling.

[0078] The aluminum alloy sheet is produced through the above processes.

[0079] A-3. Manufacturing method of aluminum alloy substrate

[0080] When manufacturing an aluminum alloy substrate from the aforementioned aluminum alloy sheet, the following method can be used, for example. First, the aluminum alloy sheet is punched to produce a circular aluminum alloy blank. Then, the aluminum alloy blank is subjected to pressure annealing by simultaneously heating and pressing it from both sides in the thickness direction, thereby reducing deformation and improving flatness. The holding temperature and pressure during pressure annealing can be appropriately selected from, for example, a range of 250–430°C and 1.0–3.0 MPa. Furthermore, the holding time during pressure annealing can be set to, for example, 30 minutes or more.

[0081] After pressure annealing, annealing is preferably performed before cutting and grinding. The holding temperature during annealing is preferably set to 190–260°C, and the holding time is set to the range of 0.1–10 hours. Furthermore, the holding temperature during annealing is more preferably 190–240°C, and even more preferably 190–220°C. The holding time during annealing is more preferably 0.5–10 hours, and even more preferably 1–10 hours. Annealing under the above conditions improves electrical conductivity. This is mainly due to the precipitation of dissolved Mg, which reduces residual stress during machining. Figure 2 It is a graph showing the relationship between the annealing temperature and electrical conductivity of an aluminum alloy blank after pressure annealing. Figure 2 The details of the aluminum alloy blank shown are described in the later embodiments. For example... Figure 2 As shown, annealing at around 190–260°C increases electrical conductivity.

[0082] After annealing, the aluminum alloy blank is sequentially machined and ground to produce an aluminum alloy substrate with the desired shape. After these processes, a deformation-eliminating heat treatment can be performed at 150–350°C for 0.1–10.0 hours, as needed, to remove the deformation caused during processing.

[0083] The aluminum alloy substrate is produced through the above processes.

[0084] B. Disk

[0085] B-1. The Composition of a Disk

[0086] A disk having the aforementioned aluminum alloy substrate has, for example, the following configuration: The disk has an aluminum alloy substrate, a Ni-P plating layer covering the surface of the aluminum alloy substrate, and a magnetic layer deposited on the Ni-P plating layer. It should be noted that the Ni-P plating layer is preferably an electroless Ni-P plating layer formed by an electroless plating process.

[0087] The disk may also have a protective layer formed of carbon-based materials such as diamond-like carbon and deposited on the magnetic layer, and a lubricating layer formed of lubricating oil and coated on the protective layer.

[0088] B-2. Disk Manufacturing Methods

[0089] When manufacturing disks using aluminum alloy substrates, the following methods can be employed, for example. First, the aluminum alloy substrate is degreased and cleaned to remove processing oils and other oils adhering to its surface. After degreasing and cleaning, the aluminum alloy substrate can be etched using acid, if necessary. When etching is performed, it is preferable to perform a decontamination treatment after etching to remove stains generated during etching from the aluminum alloy substrate. The processing conditions for these treatments can be appropriately set depending on the type of processing solution.

[0090] After these pre-plating treatments, a zincate treatment is performed to form a Zn film on the surface of the aluminum alloy substrate. In the zincate treatment, a Zn film is formed by zinc displacement plating, which replaces Al with Zn. Preferably, a double zincate method is used, where after the first zinc displacement plating, the Zn film formed on the surface of the aluminum alloy substrate is temporarily peeled off, and a second zinc displacement plating is performed to form a Zn film. According to the double zincate method, a denser Zn film can be formed on the surface of the aluminum alloy substrate compared to a Zn film formed solely by the first zinc displacement plating. As a result, defects in the Ni-P plating layer can be reduced in the subsequent electroless Ni-P plating process.

[0091] After forming a Zn film on the surface of an aluminum alloy substrate through zincate treatment, an electroless Ni-P plating process is performed, thereby replacing the Zn film with a Ni-P plating layer. As described above, if coarse Si-KO and Ti-B particles can be reduced on the surface of the aluminum alloy substrate, a dense, thin, and uniform Zn film can be formed on the surface of the zincate-treated aluminum alloy substrate. Furthermore, by replacing such a Zn film with a Ni-P plating layer during the electroless Ni-P plating process, a smooth Ni-P plating layer with fewer plating pits can be formed.

[0092] Increasing the thickness of the Ni-P plating layer tends to reduce plating pits, resulting in a smoother Ni-P plating layer. Therefore, the plating thickness is preferably 7 μm or more, more preferably 18 μm or more, and even more preferably 25 μm or more. It should be noted that in practical applications, the upper limit of the plating thickness is approximately 40 μm.

[0093] After electroless Ni-P plating, polishing the Ni-P plating layer can further improve the surface smoothness of the Ni-P plating layer.

[0094] Following electroless Ni-P plating (including polishing), a magnetic material is attached to the Ni-P plating layer by sputtering to form a magnetic material layer. This magnetic material layer can consist of a single layer or multiple layers with different compositions. After sputtering, a protective layer of carbon-based material is formed on the magnetic material layer using CVD. Next, lubricant is applied to the protective layer to form a lubricating layer. Through these steps, a hard disk is obtained.

[0095] (Example)

[0096] An example of an aluminum alloy sheet, its manufacturing method, and an aluminum alloy blank made from the sheet is described.

[0097] The specific manner in which these aluminum alloy plates and their manufacturing methods, as well as the aluminum alloy blanks made from these aluminum alloy plates and their manufacturing methods, are not limited to the embodiments shown below. Without prejudice to the spirit of the present invention, appropriate modifications may be made to the configuration according to the embodiments.

[0098] (1) Fabrication of aluminum alloy sheets

[0099] The aluminum alloy sheet used for evaluation in this embodiment was produced using the following method. First, molten metal having the chemical composition shown in Table 1 was prepared in a furnace.

[0100] Table 1

[0101]

[0102] Next, the molten metal in the furnace is transferred to form an ingot using the casting method shown in Table 2. The surface of the ingot is then milled to remove the segregation layer present on the surface. After milling, the ingot is homogenized by heat treatment under the conditions shown in Table 2. Hot rolling is then performed to obtain a hot-rolled sheet. Finally, cold rolling is performed under the conditions shown in Table 2 to obtain a cold-rolled sheet.

[0103] (2) Fabrication of aluminum alloy blanks

[0104] The aforementioned aluminum alloy sheet was punched to obtain a ring-shaped aluminum alloy blank with an outer diameter of 98 mm and an inner diameter of 24 mm. Next, the obtained aluminum alloy blank was subjected to pressure annealing by applying pressure from both sides along its thickness direction and holding it at the temperatures shown in Table 2 for 3 hours. Then, it was annealed again at the temperatures shown in Table 2 for 3 hours. It should be noted that "-" in Table 2 indicates that annealing was not performed. Through the above operations, experimental material for producing aluminum alloy blanks was prepared.

[0105] • Measurement of electrical conductivity

[0106] The conductivity (%IACS) of the test material was measured using an aluminum alloy blank or an annealed aluminum alloy blank via the eddy current method using a conductivity meter (GE Sense & Inspection Technologies Co., Ltd. "AutoSigma 3000"). It should be noted that the conductivity measurement was performed at 25°C. Furthermore, when the sheet thickness was less than 1 mm, two or more blanks were overlapped to achieve a thickness of 1 mm or more but less than 2 mm before measurement.

[0107] • Determination of the maximum height of convex defects

[0108] Using an aluminum alloy blank or an annealed aluminum alloy blank, an indentation is made into the surface using a micro Vickers hardness tester under a 5 kg load. The surface is then machined on a lathe until the indentation disappears, followed by annealing at 270°C for 1 hour. The maximum height of the convex defect generated at the indentation site is measured. The maximum height is measured using a flatness measuring machine (MESA) manufactured by ZyGO. In this invention, the maximum height is expressed as the difference between the maximum peak height and the maximum valley depth on the surface of the aluminum alloy blank, within a circle with a radius of 5 mm from the center of the indentation before cutting. Here, the maximum peak height is the difference between the average line of the profile curve within the measurement range and the highest value within the measurement range, and the maximum valley depth is the difference between the average line and the lowest value within the measurement range. Regarding the evaluation of the maximum height of the convex defect, cases with a maximum height of 0.750 μm or less are designated as A (Excellent), those exceeding 0.750 μm but below 0.760 μm are designated as B (Good), and those exceeding 0.760 μm are designated as C (Poor).

[0109] • Determination of yield strength

[0110] According to JIS Z2241, after annealing the cold-rolled aluminum alloy coil at 320℃ for 3 hours (simulated heating under pressure), JIS No. 5 test pieces were taken along the rolling direction and measured with n=1. In the strength evaluation, the case with a yield strength of 90MPa or above was set as A (excellent), and the case with a yield strength of less than 90MPa was set as C (poor).

[0111] The results are shown in Table 2.

[0112] Table 2

[0113]

[0114] As shown in Tables 1 and 2, Examples 1 to 6 have the specific alloy compositions specified in the claims and an electrical conductivity of 36.0% IACS or higher. Therefore, in these examples, the formation of convex defects can be suppressed, smoothness can be improved, and a high yield strength of 90 MPa or higher can be obtained.

[0115] On the other hand, in Comparative Examples 1 to 9, due to any deviation of the alloy composition or electrical conductivity from the claims, convex defects are formed, resulting in low smoothness or low yield strength.

[0116] Figures 1-4 The results of some or all of the embodiments are shown in the figures. It should be noted that... Figures 1-4 The diagrams also show some results other than those from the examples. More specifically, Figure 1 This is a graph showing the relationship between the electrical conductivity of an aluminum alloy blank and the maximum height of a convex defect. It shows that within the range of data shown in the graph, the relationship ["maximum height of convex defect" = -0.0281 × "electrical conductivity" + 1.7712] is satisfied. The result is derived from... Figure 1 It can be seen that if the electrical conductivity increases, the maximum height of the convex defect decreases.

[0117] Figure 2 This is a graph showing the relationship between the annealing temperature and electrical conductivity of aluminum alloy blanks after pressure annealing. It can be seen that by annealing the temperature in the range of 190 to 260°C after pressure annealing, the electrical conductivity is above 36.0% IACS.

[0118] Figure 3 This is a graph showing the relationship between Mg content and electrical conductivity of aluminum alloy blanks. It shows that within the range of data shown in the graph, the relationship ["Electrical conductivity" = -7.6977 × "Mg content" + 64.317] is satisfied. The result is derived from... Figure 3 It can be seen that if the Mg content increases, the conductivity decreases.

[0119] Figure 4 This is a graph showing the relationship between the Mg content and yield strength of aluminum alloy blanks. It shows that within the range of data shown in the graph, the relationship ["Yield Strength" = 21.702 × "Mg Content" + 18.749] is satisfied. The result is derived from... Figure 4 It can be seen that if the Mg content increases, the yield strength increases.

[0120] Industrial availability

[0121] According to the present invention, by having a specific alloy composition and electrical conductivity, it is possible to provide an aluminum alloy disk blank for disks that suppresses the formation of convex defects, improves smoothness, and has high yield strength.

Claims

1. An aluminum alloy disk blank for hard disks, characterized in that, It is formed of an aluminum alloy containing Mg: 3.40 to 3.90% by mass, with the balance consisting of Al and unavoidable impurities, and the electrical conductivity of the aluminum alloy blank for the disk is above 36.0% IACS.

2. The aluminum alloy disk blank for disks according to claim 1, characterized in that, The aluminum alloy contains Mg: 3.40-3.65% by mass.

3. The aluminum alloy disk blank for disks according to claim 1, characterized in that, The aluminum alloy contains Mg: 3.40-3.55% by mass.

4. The aluminum alloy disk blank for a hard disk according to any one of claims 1 to 3, wherein, The aluminum alloy further contains one or more elements selected from the group consisting of Cu: less than 0.30 wt%, Zn: less than 0.60 wt%, Fe: less than 0.60 wt%, Si: less than 0.60 wt%, Cr: less than 0.20 wt%, Be: less than 0.0020 wt%, Sr: less than 0.10 wt%, Na: less than 0.10 wt%, and P: less than 0.10 wt%.

5. A disk, characterized in that, The surface of the aluminum alloy substrate formed from the aluminum alloy blank for disks according to any one of claims 1 to 4 has a Ni-P plating layer and a magnetic layer on the Ni-P plating layer.

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