Aluminum alloy sheet for magnetic disk and magnetic disk

Abstract

To provide an aluminum alloy sheet for a magnetic disk exhibiting excellent impact resistance and productivity, and a magnetic disk using the same.SOLUTION: The aluminum alloy sheet for a magnetic disk contains one or more of Fe, Mn, and Ni, wherein a total content of Fe, Mn, and Ni is 0.03 mass% or more and 7.00 mass% or less, a content of Mg is 0 mass% or more and less than 4.50 mass%, and a balance is aluminum and inevitable impurities, a complete fracture displacement at shear deformation of the aluminum alloy sheet being 80% or less of a sheet thickness.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aluminum alloy plate for magnetic disks, which has excellent productivity, and a magnetic disk using the aluminum alloy plate for magnetic disks. [Background technology]

[0002] Hard disk drives (hereinafter referred to as "HDDs") are widely used as storage devices in electronic devices such as computers and video recorders, and contain a magnetic disk for recording data. The magnetic disk has a circular aluminum alloy substrate made of an aluminum alloy, a Ni-P plating layer covering the surface of the aluminum alloy substrate, and a magnetic layer laminated on the Ni-P plating layer.

[0003] In recent years, there has been a growing demand for larger capacity and higher density magnetic disk devices such as HDDs due to the needs of multimedia, etc. To achieve even greater capacity, the number of magnetic disks installed in storage devices is on the rise, and this has led to a demand for thinner magnetic disks.

[0004] However, thinning a magnetic disk results in a decrease in rigidity and strength. A decrease in rigidity reduces impact resistance, which indicates the degree to which the substrate is resistant to deformation. Therefore, improved impact resistance is required for the aluminum alloy plates used to make magnetic disks. Furthermore, as the number of magnetic disks required increases, productivity improvements are also required to address this demand. One example of productivity improvements is increasing the number of disks punched per hour during the punching process for disk blanks.

[0005] In light of these circumstances, in recent years, the development of aluminum alloy sheets for magnetic disks that have excellent impact resistance and productivity has been considered. For example, Patent Document 1 proposes a method of increasing Young's modulus and improving rigidity by adding large amounts of elements such as Fe, Mn, and Ni, which contribute to improving rigidity, to the chemical composition of an aluminum alloy blank. Patent Document 2 proposes a method of optimizing a die for a punching press to reduce end face sagging, shorten the time for the subsequent grinding process, and improve productivity. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2017-186597 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-093688

[0007] However, the current situation is that the targeted productivity cannot be achieved by the method disclosed in Patent Document 1, which increases the content of elements such as Fe, Mn, and Ni to improve only the rigidity. Also, the method disclosed in Patent Document 2 is insufficient in improving productivity in terms of the number of sheets punched. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in view of the above problems, and an object of the present invention is to provide an aluminum alloy plate for magnetic disks that exhibits excellent impact resistance and productivity, and a magnetic disk using the same. [Means for solving the problem]

[0009] The present inventors have found that, in an aluminum alloy plate for magnetic disks, it is possible to obtain an aluminum alloy plate for magnetic disks that exhibits excellent impact resistance and productivity even when it is thin, by controlling the contents of various additive elements contained in the aluminum alloy and the complete fracture displacement during shear deformation, and have thus completed the present invention.

[0010] An aluminum alloy plate for magnetic disks according to an embodiment of the present invention contains one or more of Fe, Mn, and Ni, the total content of Fe, Mn, and Ni being 0.03 mass% or more and 7.00 mass% or less, the Mg content being 0 mass% or more and less than 4.50 mass%, with the remainder being aluminum and unavoidable impurities, and the complete fracture displacement during shear deformation of the aluminum alloy plate being 80% or less of the plate thickness. [Effects of the Invention]

[0011] According to the present invention, an aluminum alloy plate for magnetic disks and magnetic disks exhibiting excellent impact resistance and productivity can be obtained. DETAILED DESCRIPTION OF THE INVENTION

[0012] The aluminum alloy plate for a magnetic disk and the magnetic disk according to this embodiment will be described in detail below.

[0013] [Aluminum alloy plates for magnetic disks] The aluminum alloy plate for magnetic disks according to the present invention (hereinafter also referred to as "aluminum alloy plate") is obtained by producing an ingot using an aluminum alloy having a predetermined alloy composition, performing a homogenization treatment, and then performing a predetermined rolling treatment to produce a rolled plate. The aluminum alloy plate contains one or more of Fe, Mn, and Ni, the total content of Fe, Mn, and Ni being 0.03% by mass or more and 7.00% by mass or less, the Mg content being 0% by mass or more and less than 4.50% by mass, with the remainder being aluminum and unavoidable impurities, and the complete fracture displacement during shear deformation of the aluminum alloy plate being 80% or less of the plate thickness. During shear deformation of the aluminum alloy plate, the smaller the fracture displacement (complete fracture displacement) until the aluminum alloy plate completely fractures, the shorter the time until complete fracture, and as a result, the time required for punching an aluminum alloy disk blank in the magnetic disk manufacturing process can be shortened. In this way, by controlling the alloy composition of the aluminum alloy plate and the complete fracture displacement during shear deformation, it is possible to provide an aluminum alloy plate and a magnetic disk that exhibit excellent impact resistance and productivity.

[0014] <Alloy composition> The alloy composition of the aluminum alloy used for the aluminum alloy plate will be described in detail below.

[0015] The aluminum alloy sheet contains one or more of Fe (iron), Mn (manganese), and Ni (nickel), and the total content of Fe, Mn, and Ni is 0.03% by mass or more and 7.00% by mass or less. Fe exists mainly as second-phase particles (Al-Fe intermetallic compounds, etc.), with some present as solid solution in the matrix, and has the effect of improving the rigidity (Young's modulus) and strength of the aluminum alloy sheet and reducing the complete fracture displacement during shear deformation. Mn and Ni also exist mainly as second-phase particles (Al-Mn intermetallic compounds, Al-Ni intermetallic compounds, etc.), with some present as solid solution in the matrix. By generating second-phase particles and dissolving in the matrix, Mn and Ni also have the effect of improving the Young's modulus, strength, etc. of the aluminum alloy disk blank.

[0016] In an aluminum alloy, when the total content of Fe, Mn, and Ni is 0.03% by mass or more and 7.00% by mass or less, the rigidity of the aluminum alloy sheet is improved, thereby imparting excellent impact resistance. Furthermore, the complete fracture displacement during shear deformation of the aluminum alloy sheet is reduced, shortening the time until complete fracture. This shortens the time required for punching aluminum alloy disk blanks in the magnetic disk manufacturing process, resulting in an aluminum alloy sheet with excellent productivity. On the other hand, if the total content of Fe, Mn, and Ni is less than 0.03% by mass, the formation of second-phase particles is insufficient, resulting in reduced impact resistance and productivity. Furthermore, if the total content of Fe, Mn, and Ni exceeds 7.00% by mass, numerous coarse second-phase particles are generated. Because the second-phase particles are harder than the aluminum matrix, they are difficult to grind, which reduces the grinding rate during grinding and increases production costs. Furthermore, these coarse second-phase particles may fall off during etching, zincating, cutting, or grinding, causing large depressions, which may lead to plating pits, resulting in a decrease in the smoothness of the plating surface and plating peeling. Furthermore, this also reduces workability in the rolling process, which may lead to large cracks during rolling. Therefore, the total content of Fe, Mn, and Ni is 0.03% by mass or more and 7.00% by mass or less, preferably 0.05% by mass or more and 6.50% by mass or less, more preferably 0.50% by mass or more and 6.00% by mass or less, and even more preferably 0.80% by mass or more and 5.00% by mass or less.

[0017] (Mg: Magnesium) Mg is an optional component in aluminum alloys, and exists mainly as solid solution Mg, which has the effect of improving the strength of the aluminum alloy sheet. In addition, when manufacturing magnetic disks, Mg helps to deposit a uniform, thin, and dense zincate film during zincate treatment, thereby improving the smoothness of the plated surface made of Ni-P in the plating process that follows the zincate treatment process.

[0018] The Mg content of the aluminum alloy sheet is 0% by mass or more and less than 4.50% by mass. If the Mg content is 4.50% by mass or more, the Young's modulus decreases, resulting in a decrease in the rigidity of the aluminum alloy sheet and, as a result, a decrease in impact resistance. Furthermore, if the Mg content is high, the adhesion between aluminum alloy disk blanks or between an aluminum alloy disk blank and a spacer increases when the aluminum alloy disk blank is subjected to pressure annealing during the magnetic disk manufacturing process. This increases the force required to separate them, which leads to deformation of the aluminum alloy disk blank and reduces productivity. Furthermore, this may increase ductility and increase the complete fracture displacement. In consideration of the balance between strength and productivity, the Mg content is preferably 0.30% by mass or more and 4.30% by mass or less, more preferably 0.50% by mass or more and 4.10% by mass or less, and even more preferably 1.00% by mass or more and 3.90% by mass or less.

[0019] The aluminum alloy plate may further contain at least one element selected from the group consisting of Cu: 0% by mass to 0.40% by mass, Zn: 0% by mass to 0.70% by mass, Cr: 0% by mass to 0.40% by mass, Zr: 0% by mass to 0.30% by mass, Si: 0% by mass to 0.60% by mass, and Be: 0% by mass to 0.0020% by mass.

[0020] (Cu: Copper) The aluminum alloy may contain 0.40% by mass or less of Cu as an optional component. Cu has the effect of suppressing the elution of Al from the aluminum alloy substrate when zincating is performed during the magnetic disk manufacturing process. By ensuring that the Cu content is 0.40% by mass or less, a dense, thin Zn coating with little thickness variation can be adhered to the surface of the aluminum alloy substrate when zincating is performed during the magnetic disk manufacturing process. Furthermore, by forming such a Zn coating, a smooth Ni-P plating layer can be formed in the subsequent electroless Ni-P plating process.

[0021] On the other hand, if the Cu content is too high, the corrosion resistance of the aluminum alloy substrate decreases, and localized areas where Al is easily dissolved are formed. Therefore, when zincating is performed during the manufacturing process of a magnetic disk, the amount of dissolved Al on the surface of the aluminum alloy substrate tends to be uneven, leading to large variations in the thickness of the Zn coating. As a result, there is a risk of a decrease in adhesion between the Ni-P plating layer and the aluminum alloy substrate, and a decrease in the smoothness of the Ni-P plating layer.

[0022] By keeping the Cu content in the aluminum alloy at 0.40% by mass or less, preferably 0.30% by mass or less, the formation of plating pits can be suppressed and the smoothness of the Ni-P plating layer can be further improved. The lower limit of the Cu content is preferably 0.003% by mass, more preferably 0.010% by mass.

[0023] (Zn: Zinc) The aluminum alloy may contain 0.60 mass% or less of Zn as an optional component. Zn, like Cu, has the effect of suppressing Al elution from the aluminum alloy substrate during zincate treatment. By ensuring that the Zn content is 0.60 mass% or less, a dense, thin Zn coating with minimal thickness variation can be adhered to the surface of the aluminum alloy substrate during zincate treatment in the magnetic disk manufacturing process. Furthermore, by forming such a Zn coating, a smooth Ni-P plating layer can be formed in the subsequent electroless Ni-P plating process.

[0024] On the other hand, if the Zn content is too high, the corrosion resistance of the aluminum alloy substrate decreases, and localized areas where Al is easily dissolved are formed. Therefore, when zincating is performed during the manufacturing process of a magnetic disk, unevenness in the amount of Al dissolved on the surface of the aluminum alloy substrate occurs, and the thickness of the Zn film tends to vary greatly. As a result, there is a risk of a decrease in adhesion between the Ni-P plating layer and the aluminum alloy substrate, and a decrease in the smoothness of the Ni-P plating layer.

[0025] By keeping the Zn content in the aluminum alloy at 0.60% by mass or less, preferably 0.50% by mass or less, the formation of plating pits can be suppressed and the smoothness of the Ni-P plating layer can be further improved. The lower limit of the Zn content is preferably 0.005% by mass, more preferably 0.01% by mass.

[0026] (Si: Silicon) The aluminum alloy may contain 0.60 mass % or less of Si as an optional component. When the aluminum alloy contains Mg, Si forms an Mg-Si intermetallic compound with Mg.

[0027] If such Mg-Si intermetallic compounds fall off the surface of the aluminum alloy substrate during the magnetic disk manufacturing process, plating pits are likely to form in the subsequent electroless Ni-P plating process. By keeping the Si content in the aluminum alloy at 0.60 mass% or less, preferably 0.10 mass% or less, and more preferably 0.01 mass% or less, the content of the above intermetallic compounds present in the aluminum alloy substrate 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.

[0028] In order to suppress the occurrence of plating pits due to the intermetallic compounds, it is preferable to reduce the Si content. However, Si is contained not only in general purity ingots but also in high-purity ingots with an Al purity of 99.9% by mass or more. Therefore, if an aluminum alloy containing almost no Si is to be produced, a special process for removing Si during casting is required, which increases the production cost of the aluminum alloy sheet.

[0029] If the Si content in the aluminum alloy is 0.01% by mass or less, the aluminum alloy sheet can be produced without any special treatment for removing Si. As a result, the smoothness of the aluminum alloy sheet can be further improved while avoiding an increase in the production cost of the aluminum alloy sheet. Furthermore, if the Si content in the aluminum alloy is more than 0.01% by mass but is 0.60% by mass or less, the aluminum alloy sheet can be produced using a base metal with a lower purity. This allows for further reduction in the material cost of the aluminum alloy sheet.

[0030] (Be: Beryllium) Be is an element added to the molten metal when casting an aluminum alloy containing Mg to suppress oxidation of Mg. Furthermore, by limiting the Be content in the aluminum alloy to 0.0020 mass% or less, the Zn coating formed on the surface of the aluminum alloy substrate during the magnetic disk manufacturing process can be made denser and the thickness variation can be reduced. As a result, the smoothness of the Ni-P treatment layer formed on the aluminum alloy substrate can be further improved.

[0031] On the other hand, if the Be content in the aluminum alloy is too high, Be-based oxides are likely to form on the surface of the aluminum alloy substrate when the aluminum alloy plate is heated during the magnetic disk manufacturing process. Furthermore, if the aluminum alloy further contains Mg, Al-Mg-Be-based oxides are likely to form on the surface of the aluminum alloy substrate when the aluminum alloy substrate is heated. If the amount of these oxides is too high, the thickness of the Zn coating will vary greatly, which may lead to the occurrence of plating pits.

[0032] By keeping the Be content in the aluminum alloy at 0.0020% by mass or less, preferably 0.0010% by mass or less, the amount of Al-Mg-Be oxides is reduced, and the smoothness of the Ni-P plating layer can be further improved. When Be is contained in the aluminum alloy, the lower limit of the Be content is preferably 0.0001% by mass.

[0033] (Cr: chromium) The aluminum alloy may contain 0.40 mass% or less of Cr as an optional component. Part of the Cr is dispersed in the aluminum alloy sheet as fine intermetallic compounds formed during casting. Cr that does not form intermetallic compounds during casting dissolves in the Al matrix and has the effect of improving the strength of the aluminum alloy sheet through solid solution strengthening.

[0034] Furthermore, Cr improves the machinability and grindability of the magnetic disk during manufacturing, and also refines the recrystallized structure, thereby improving the adhesion between the aluminum alloy substrate and the Ni-P plating layer and suppressing the occurrence of plating pits.

[0035] On the other hand, if the Cr content in the aluminum alloy is too high, coarse Al-Cr intermetallic compounds are likely to be formed in the aluminum alloy substrate, and if such coarse Al-Cr intermetallic compounds fall off from the surface of the aluminum alloy substrate, plating pits are likely to be formed in the subsequent electroless Ni-P plating process.

[0036] By keeping the Cr content in the aluminum alloy at 0.40 mass% or less, preferably 0.30 mass% or less, it is possible to suppress the formation of plating pits, form a smooth Ni-P plating layer, and further improve the strength of the aluminum alloy substrate. Note that there is no particular lower limit for the Cr content, and it may be 0 mass%.

[0037] (Zr: zirconium) The aluminum alloy may contain 0.30 mass% or less of Zr as an optional component. Some of the Zr is dispersed in the aluminum alloy sheet as fine intermetallic compounds formed during casting. Zr that does not form intermetallic compounds during casting dissolves in the Al matrix and has the effect of improving the strength of the aluminum alloy sheet through solid solution strengthening.

[0038] Furthermore, Zr enhances the machinability and grindability of the magnetic disk during manufacturing, and also refines the recrystallized structure, thereby improving the adhesion between the aluminum alloy substrate and the Ni-P plating layer and suppressing the occurrence of plating pits.

[0039] On the other hand, if the Zr content in the aluminum alloy is too high, coarse Al-Zr intermetallic compounds are likely to be formed in the aluminum alloy substrate, and if such coarse Al-Zr intermetallic compounds fall off from the surface of the aluminum alloy substrate, plating pits are likely to be formed in the subsequent electroless Ni-P plating process.

[0040] By keeping the Zr content in the aluminum alloy at 0.30% by mass or less, preferably 0.20% by mass or less, it is possible to suppress the formation of plating pits, form a smooth Ni-P plating layer, and further improve the strength of the aluminum alloy substrate. The lower limit of the Zr content is not particularly limited, and may be 0% by mass.

[0041] (Other elements) The aluminum alloy may contain elements that act as unavoidable impurities in addition to the various atoms described above. These elements include Ti (titanium), V (vanadium), B (boron), Ga (gallium), etc., and the effects of the present invention are not impaired as long as the content of each element is 0.10% by mass or less, and the total content is 0.30% by mass or less.

[0042] As described above, in the present invention, Fe, Si, etc. can be actively added, but there are also cases where they are not actively added and become unavoidable impurities. Si is contained as an unavoidable impurity not only in ingots of ordinary purity but also in high-purity ingots with an Al purity of 99.9 mass% or more. Even when contained as an unavoidable impurity in this way, the effects of the present invention are not impaired as long as the content is 0.10 mass% or less. Furthermore, when Fe or Si is actively added, from the above-mentioned viewpoint, it is preferable that the Fe content in the aluminum alloy be 1.80 mass% or less and the Si content be 0.60 mass% or less.

[0043] <Thickness of aluminum alloy plate> In view of the recent trend toward thinner magnetic disks, the thickness of the aluminum alloy plate is preferably 0.48 mm or less, and more preferably 0.42 mm or less. Even at such a thickness, the aluminum alloy plate according to the present invention exhibits excellent impact resistance and productivity.

[0044] (2nd phase particles) The second-phase particles mentioned above refer to precipitates or crystallized substances, and specifically refer to particles of Al-Fe-based intermetallic compounds (Al3Fe, Al6Fe, Al6(Fe, Mn), Al-Fe-Si, Al-Fe-Mn-Si, Al-Fe-Ni, Al-Cu-Fe, etc.), Mg-Si-based intermetallic compounds (Mg2Si, etc.), etc. Other intermetallic compounds include Al-Mn-based intermetallic compounds (Al6Mn, Al-Mn-Si), Al-Ni-based intermetallic compounds (Al3Ni, etc.), Al-Cu-based intermetallic compounds (Al2Cu, etc.), Al-Cr-based intermetallic compounds (Al7Cr, etc.), and Al-Zr-based intermetallic compounds (Al3Zr, etc.). In addition to these intermetallic compounds, the second-phase particles also include Si particles, etc.

[0045] <Characteristics of aluminum alloy sheets> (Young's modulus) Increasing the Young's modulus of the aluminum alloy plate has the effect of improving the impact resistance of the magnetic disk. Therefore, the Young's modulus of the aluminum alloy plate is preferably 70 GPa or more. Although the magnetic disk may be deformed when the magnetic disk device is dropped, this deformation is within the elastic range. Therefore, by improving the Young's modulus of the aluminum alloy plate, the impact resistance can be improved and such deformation can be suppressed.

[0046] If the Young's modulus of the aluminum alloy plate is less than 70 GPa, the magnetic disk may be significantly deformed when the magnetic disk device is dropped, and if the deformed magnetic disk collides with other components (such as other magnetic disks or ramp roads where the head is retracted), dust may be generated, which may cause recording errors. To avoid a decrease in the impact resistance of the magnetic disk, which is a characteristic of the magnetic disk being less likely to deform, the Young's modulus of the aluminum alloy plate is preferably 70 GPa or more, more preferably 71 GPa or more, and even more preferably 72 GPa or more. The upper limit of the Young's modulus of the aluminum alloy plate is not particularly limited, but varies depending on the material and composition of the aluminum alloy disk blank and the manufacturing conditions, and is preferably 80 GPa or less.

[0047] Young's modulus can be measured by a resonance method. For example, a rectangular area on the surface of an aluminum alloy sheet, the longitudinal direction of which is parallel to the rolling direction, can be taken as a sample, and the Young's modulus can be measured from the sample. It should be noted that the Young's modulus can be measured not only from aluminum alloy sheets, but also from aluminum alloy disk blanks after pressure annealing (described later), aluminum alloy substrates after grinding, aluminum alloy substrates after plating, and magnetic disks after sputtering. When measuring the Young's modulus using aluminum alloy substrates and magnetic disks after plating, the plating film including the Ni-P plating layer can be peeled off, and the surface can be ground 5 to 30 μm to obtain a sample, and the Young's modulus can be measured. The size (length, width, thickness) of the sample required for measurement can be measured using a micrometer and vernier calipers, and the weight can be measured using an electronic balance.

[0048] (Complete fracture displacement during shear deformation of aluminum alloy plate relative to plate thickness) In the present invention, the complete fracture displacement during shear deformation of the aluminum alloy plate is 80% or less of the plate thickness. This allows the aluminum alloy disk blank to fracture in a short time during punching when manufacturing a magnetic disk, thereby improving productivity. The small complete fracture displacement during shear deformation allows the punch stroke during punching to be reduced, thereby enabling punching to be completed in a short time and improving productivity.

[0049] If the complete fracture displacement during shear deformation of an aluminum alloy plate exceeds 80% of the plate thickness, the punch stroke will also increase, which may result in a decrease in productivity. Therefore, the complete fracture displacement is 80% or less, and preferably 60% or less. The lower limit of the complete fracture displacement is not particularly limited, but is approximately 20%.

[0050] (Elongation of aluminum alloy plate) In the present invention, the elongation of the aluminum alloy plate, specifically, the fracture elongation measured on a JIS No. 5 test piece in accordance with the provisions of JIS Z2241:2011, is preferably 5% or less. A small fracture elongation tends to reduce the complete fracture displacement during shear deformation, allowing the punch stroke to be reduced when punching an aluminum alloy disk blank. As a result, punching can be completed in a short time, improving productivity. A fracture elongation of 3% or less is more preferable.

[0051] <Method of manufacturing aluminum alloy sheets for magnetic disks> The method for producing an aluminum alloy sheet will be described in detail below.

[0052] (Casting process) Aluminum raw materials with a specified alloy composition are melted to produce molten metal, which is then cast to produce ingots. Casting methods include semi-continuous casting (DC casting), permanent mold casting, and continuous casting (CC casting). In DC casting, molten metal poured through a spout solidifies by absorbing heat from the bottom block, the water-cooled mold walls, and cooling water directly discharged onto the outer periphery of the ingot, and is then drawn downward as an ingot. In permanent mold casting, molten metal poured into a hollow mold made of cast iron or other material solidifies by absorbing heat from the mold walls to produce an ingot. In CC casting, molten metal is supplied through a casting nozzle between a pair of rolls (or belt casters or block casters), and thin plates are directly cast by removing heat from the rolls.

[0053] In such a casting process, it is preferable to carry out in-line a degassing treatment to reduce the amount of gas dissolved in the molten metal and a filtration treatment to remove solids from the molten metal.

[0054] For example, the degassing process can be performed using a process known as the SNIF (Spinning Nozzle Inert Flotation) process or the Alpur process. In these processes, a process gas such as argon gas or a mixture of argon and chlorine is blown into the molten metal while stirring the molten metal at high speed using a rotor with blades, forming fine bubbles of the process gas into the molten metal. This allows hydrogen gas and inclusions dissolved in the molten metal to be removed in a short period of time. An in-line degassing device can be used for the degassing process.

[0055] For example, a cake filtration method, a filter medium filtration method, etc. may be used for the filtration. For example, a ceramic tube filter, a ceramic foam filter, an alumina ball filter, etc. may be used for the filtration.

[0056] (Homogenization process) After the ingot is produced, it is subjected to facing and homogenization treatment before hot rolling. The homogenization treatment is a heat treatment at 550 to 620°C for 0.5 to 30 hours. The residence time at 425 to 440°C during the homogenization treatment is preferably 0.9 hours or less. If the residence time at 425 to 440°C exceeds 0.9 hours, the number of second-phase particles described above may decrease, which may increase the complete fracture displacement during shear deformation, resulting in a decrease in productivity. In order to achieve the above effects, the lower limit of the residence time is preferably 0.1 hours or more. The residence time in the temperature range of 425 to 440°C includes the time in treatment steps subsequent to the homogenization treatment step, and is preferably less than 0.5 hours. If the heating temperature during the homogenization treatment is less than 550°C or the heating time is less than 0.5 hours, the homogenization treatment may be insufficient, resulting in a large variation in impact resistance among individual aluminum alloy sheets. Furthermore, if the heating temperature during the homogenization treatment exceeds 620°C, there is a risk that the aluminum alloy ingot will melt. Note that if the heating time during the homogenization treatment exceeds 30 hours, the effect saturates and no further significant improvement can be obtained, so the upper limit of the heating time is 30 hours.

[0057] (Hot rolling process) Next, the homogenized ingot is hot rolled to produce a hot rolled sheet. The rolling conditions for the hot rolling are not particularly limited, but the starting temperature of the hot rolling is preferably 450 to 600°C, and the finishing temperature of the hot rolling is preferably 230 to 400°C. The thickness of the hot rolled sheet can be appropriately set, for example, within the range of 2.0 to 6.0 mm.

[0058] (Cold rolling process) After hot rolling, the resulting hot-rolled sheet can be subjected to one or more passes of cold rolling to obtain a cold-rolled sheet. The total reduction in cold rolling is preferably, for example, 20 to 95%. The thickness of the cold-rolled sheet can be appropriately set within the range of 0.2 to 1.9 mm.

[0059] (Annealing process) In the manufacturing method of the above embodiment, annealing may be performed, if necessary, at least either before the first pass of cold rolling or between passes. The annealing may be performed using a batch-type heat treatment furnace. When a batch-type heat treatment furnace is used, the holding temperature during annealing is preferably in the range of 300 to 400°C, and the holding time is preferably in the range of 0.1 to 10 hours. By performing the annealing treatment under such conditions, it is possible to restore the workability during cold rolling. An aluminum alloy sheet is produced by the above steps.

[0060] <Method of manufacturing an aluminum alloy substrate for magnetic disks> When an aluminum alloy substrate is produced from the aluminum alloy plate produced through the above steps, for example, the following method can be used. First, the aluminum alloy plate is punched to produce an aluminum alloy disk blank having a circular ring shape. Then, the aluminum alloy disk blank is subjected to pressure annealing by heating while being pressed from both sides in the thickness direction, thereby reducing distortion of the aluminum alloy disk blank and improving flatness. The holding temperature and pressure in the pressure annealing can be appropriately selected, for example, from the ranges of 250 to 420°C and 0.1 to 3 MPa. The holding time in the pressure annealing can be, for example, 30 minutes or more.

[0061] After pressure annealing, annealing is preferably performed before cutting and grinding. The holding temperature during annealing is preferably 190 to 260°C, more preferably 190 to 240°C, and even more preferably 190 to 220°C. The holding time during annealing is preferably 0.1 to 10 hours, more preferably 0.5 to 10 hours, and even more preferably 1 to 10 hours. By performing annealing treatment under these conditions, solute Mg and the like are precipitated, and as a result, the electrical conductivity of the aluminum alloy disk blank can be increased.

[0062] After annealing, the aluminum alloy disk blank is sequentially subjected to cutting and grinding to produce an aluminum alloy substrate having a desired shape. After these processes, if necessary, a stress relief heat treatment may be performed at 150 to 350°C for 0.1 to 10.0 hours to remove strain caused during processing. Through these steps, an aluminum alloy substrate is produced.

[0063] <Magnetic disk> The magnetic disk according to the present invention comprises an aluminum alloy substrate formed using the above-mentioned aluminum alloy plate, a Ni-P plating layer formed on the surface of the aluminum alloy substrate, and a magnetic layer formed on the Ni-P plating layer. The Ni-P plating layer is preferably an electroless Ni-P plating layer formed by electroless plating.

[0064] The magnetic disk may further have a protective layer made of a carbonaceous material such as diamond-like carbon and laminated on the magnetic layer, or may have a lubricating layer coated with lubricating oil on the protective layer.

[0065] In view of the recent trend toward thinner magnetic disks, the thickness of the magnetic disk is preferably 0.48 mm or less, and more preferably 0.42 mm or less. Even at such a thickness, the magnetic disk according to the present invention exhibits excellent impact resistance.

[0066] <Magnetic Disk Manufacturing Method> When manufacturing a magnetic disk from an aluminum alloy substrate, for example, the following method can be used. First, as a pre-plating treatment, the aluminum alloy substrate is degreased and cleaned to remove oils such as processing oils adhering to the surface of the aluminum alloy substrate. After degreased and cleaned, the aluminum alloy substrate may be etched using an acid, if necessary. If etching is performed, it is preferable to perform a desmutting treatment after etching to remove smut generated by etching from the aluminum alloy substrate. The treatment conditions for these treatments can be appropriately set depending on the type of treatment solution.

[0067] After these pre-plating treatments, a zincate treatment is performed to form a Zn coating on the surface of the aluminum alloy substrate. In the zincate treatment, a zinc coating can be formed by zinc immersion plating, which replaces Al with Zn. A preferred zincate treatment is the so-called double zincate method, in which the Zn coating formed on the surface of the aluminum alloy substrate after the first zinc immersion plating is once stripped off and another zinc immersion plating is performed to form a Zn coating. The double zincate method allows a denser Zn coating to be formed on the surface of the aluminum alloy substrate compared to the Zn coating formed by only the first zinc immersion plating. As a result, defects in the Ni-P plating layer can be reduced in the subsequent electroless Ni-P plating process.

[0068] After forming a Zn coating on the surface of an aluminum alloy substrate by zincate treatment, the Zn coating can be replaced with a Ni-P plating layer by performing electroless Ni-P plating at around 90° C. Then, by replacing such a Zn coating with a Ni-P plating layer in the electroless Ni-P plating, a smooth Ni-P plating layer with few plating pits can be formed.

[0069] Increasing the thickness of the Ni-P plating layer tends to reduce plating pits, allowing for the formation of a smooth Ni-P plating layer. Therefore, the thickness of the Ni-P plating layer (plating thickness) is preferably 7 μm or more, more preferably 18 μm or more, and even more preferably 25 μm or more. In practice, the upper limit of the plating thickness is approximately 40 μm.

[0070] By polishing the Ni-P plated layer after the electroless Ni-P plating process, the smoothness of the surface of the Ni-P plated layer can be further improved.

[0071] After electroless Ni-P plating or polishing, a magnetic material is deposited on the Ni-P plating layer by sputtering to form a magnetic layer. The magnetic layer may consist of a single layer or multiple layers with different compositions. Conventional sputtering temperatures are used, but high electrical conductivity of the aluminum alloy substrate, particularly at sputtering temperatures of 100°C or less, can provide energy savings. After sputtering, a protective layer made of a carbon-based material is formed on the magnetic layer by chemical vapor deposition (CVD). Next, a lubricating oil is applied to the protective layer to form a lubricating layer. This completes the magnetic disk production process.

[0072] The aluminum alloy plate and magnetic disk according to the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications and changes are possible based on the technical concept of the present invention.

[0073] Based on the above embodiments, the present invention relates to the following [1] to [6]. [1] An aluminum alloy plate for a magnetic disk, containing one or more of Fe, Mn, and Ni, wherein the total content of Fe, Mn, and Ni is 0.03% by mass or more and 7.00% by mass or less, the content of Mg is 0% by mass or more and less than 4.50% by mass, and the balance is aluminum and unavoidable impurities, An aluminum alloy plate for magnetic disks, wherein the complete fracture displacement during shear deformation of the aluminum alloy plate is 80% or less of the plate thickness. [2] The aluminum alloy plate for magnetic disks according to the above [1], wherein the breaking elongation measured on a JIS No. 5 test piece in accordance with the provisions of JIS Z2241:2011 is 5% or less. [3] The aluminum alloy plate for magnetic disks according to the above [1] or [2], further containing at least one element selected from the group consisting of Cu: 0% by mass or more and 0.40% by mass or less, Zn: 0% by mass or more and 0.70% by mass or less, Cr: 0% by mass or more and 0.40% by mass or less, Zr: 0% by mass or more and 0.30% by mass or less, Si: 0% by mass or more and 0.60% by mass or less, and Be: 0% by mass or more and 0.0020% by mass or less. [4] The aluminum alloy plate for magnetic disks according to any one of [1] to [3] above, having a plate thickness of 0.48 mm or less. [5] The aluminum alloy plate for magnetic disks according to any one of [1] to [3] above, which has a plate thickness of 0.42 mm or less. [6] A magnetic disk comprising an aluminum alloy substrate formed using the aluminum alloy plate for magnetic disks according to any one of [1] to [5] above, a Ni-P plating layer provided on the surface of the aluminum alloy substrate, and a magnetic layer provided on the Ni-P plating layer. [Example]

[0074] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these. Room temperature is defined as the range of 20°C ± 15°C.

[0075] <Production of aluminum alloy plate> An aluminum alloy plate was produced by the following method: First, a molten metal having the chemical composition shown in Table 1 was prepared in a melting furnace.

[0076] [Table 1]

[0077] Next, the molten metal in the melting furnace was transferred, and an ingot was produced by the casting method shown in Table 2. Next, the surface of the ingot was chamfered to remove the segregation layer present on the ingot surface. After the chamfering, the ingot was subjected to a homogenization treatment by heat treatment under the conditions shown in Table 2. Thereafter, hot rolling was carried out to obtain a hot-rolled sheet. Furthermore, cold rolling was carried out under the conditions shown in Table 2 to produce an aluminum alloy sheet.

[0078] (Young's modulus) A 60 mm x 8 mm sample was taken from the surface of the resulting aluminum alloy sheet in a random region parallel to the rolling direction and longitudinal direction using wire cutting. The sample was heat-treated at 320°C for 3 hours, and the Young's modulus was measured. Young's modulus measurements were performed at room temperature using a JE-RT type device manufactured by Nippon Technoplus Co., Ltd., using the resonance method. The sample size (length, width, and thickness) required for measurement was measured using a micrometer and calipers, and the weight was measured using an electronic balance. A Young's modulus of 70 GPa or higher was considered to have excellent impact resistance, and a Young's modulus of less than 70 GPa was considered to have poor impact resistance. The results are shown in Table 2.

[0079] (Complete fracture displacement during shear deformation) The resulting aluminum alloy plates were heat-treated at 320°C for 3 hours. 50 x 50 mm samples were cut and a φ11 mm hole was drilled in the center of each sample. The shear deformation test was performed by punching the sample with a punch (φ25.37 mm) that had a slight clearance with the die inner diameter (φ25.40 mm). The shear deformation test measured the complete fracture displacement during shear deformation. The punch was inserted into the center hole of the sample and tightened with a screw. The punch containing the sample was then inserted into the die, the upper plate was attached, and the screws on all four sides were tightened. The sample was then placed in the testing machine and subjected to excessive compression to induce shear fracture. During the test, the displacement (fracture displacement) and load were measured at 0.1 second intervals. The load increased with time up to a certain displacement, but after reaching a maximum load, the load decreased with time at fracture. Using the load at each time, the load at a certain time (P1) and the load 0.1 seconds before that load (P0), the value calculated at each time by [(P0-P1) / P0] x 100 was obtained, and the displacement when this value exceeded 1 was defined as the complete fracture displacement during shear deformation. The results are shown in Table 2.

[0080] (Elongation at break) The cold-rolled aluminum alloy sheets were subjected to heat treatment at a holding temperature of 320°C for 3 hours, and JIS No. 5 specimens were taken in accordance with the provisions of JIS Z2241:2011 to perform a tensile test and measure the breaking elongation. The results are shown in Table 2.

[0081] [Table 2]

[0082] As shown in Tables 1 and 2, in the aluminum alloy sheets having the predetermined alloy composition, Examples 1 to 4 in which the complete fracture displacement during shear deformation was 80% or less of the sheet thickness all showed a high Young's modulus of 70 GPa or more, and excellent impact resistance and productivity were achieved.

[0083] On the other hand, in Comparative Examples 1 and 2, the complete fracture displacement during rupture deformation of the aluminum alloy plate exceeded 80% of the plate thickness, resulting in poor productivity. In addition, the Young's modulus was less than 70 GPa, resulting in poor impact resistance. [Industrial Applicability]

[0084] The aluminum alloy sheet according to the present invention has a specific alloy composition and a predetermined thickness, and thus exhibits excellent impact resistance and productivity due to its complete fracture displacement during shear deformation. Furthermore, by using such an aluminum alloy sheet, it is possible to provide a magnetic disk having excellent impact resistance while improving productivity.

Claims

1. An aluminum alloy plate for a magnetic disk, comprising one or more of Fe, Mn, and Ni, the total content of Fe, Mn, and Ni being 0.03% by mass or more and 7.00% by mass or less, the content of Mg being 0% by mass or more and less than 4.50% by mass, and the balance being aluminum and unavoidable impurities, An aluminum alloy plate for magnetic disks, wherein the displacement at complete fracture during shear deformation of said aluminum alloy plate is 80% or less of the plate thickness.

2. 2. The aluminum alloy plate for magnetic disks according to claim 1, wherein the breaking elongation measured on a JIS No. 5 test piece in accordance with JIS Z2241:2011 is 5% or less.

3. 3. The aluminum alloy plate for magnetic disks according to claim 1, further containing at least one element selected from the group consisting of Cu: 0% by mass or more and 0.40% by mass or less, Zn: 0% by mass or more and 0.70% by mass or less, Cr: 0% by mass or more and 0.40% by mass or less, Zr: 0% by mass or more and 0.30% by mass or less, Si: 0% by mass or more and 0.60% by mass or less, and Be: 0% by mass or more and 0.0020% by mass or less.

4. 3. The aluminum alloy sheet for magnetic disks according to claim 1, having a thickness of 0.48 mm or less.

5. 3. The aluminum alloy sheet for magnetic disks according to claim 1, having a thickness of 0.42 mm or less.

6. 3. A magnetic disk comprising: an aluminum alloy substrate formed using the aluminum alloy plate for magnetic disks according to claim 1; a Ni-P plating layer provided on the surface of the aluminum alloy substrate; and a magnetic layer provided on the Ni-P plating layer.

Images