Aluminum alloy plate for magnetic disk and magnetic disk

Abstract

To provide an aluminum alloy plate for magnetic disks and a magnetic disk, exhibiting superior impact resistance and deformation resistance.SOLUTION: An aluminum alloy plate for magnetic disks contains one or more selected from Fe, Mn, and Ni, where the total content of Fe, Mn, and Ni is 0.70 mass% or more and 7.00 mass% or less, the content of Mg is 1.0 mass% or more and less than 5.5 mass%, and the balance consists of aluminum and unavoidable impurities. When the aluminum alloy plate is held under a tensile load of 40 MPa at a temperature of 245 to 250°C for 240 minutes, the elongation of the aluminum alloy plate is 3.7 mm or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aluminum alloy plate for a magnetic disk and a magnetic disk.

Background Art

[0002] A hard disk drive (hereinafter abbreviated as "HDD") is widely used as a storage device in electronic devices such as computers and video recording devices. An HDD incorporates a magnetic disk for recording data. The magnetic disk has an aluminum alloy substrate made of an aluminum alloy and having an annular shape, 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] By the way, in recent years, due to the needs of multimedia and the like, the demand for larger capacity and higher density of magnetic disk devices such as HDDs has been increasing. For further increasing the capacity, the number of magnetic disks mounted in the storage device tends to increase, and accordingly, thinning of the magnetic disk is also required.

[0004] However, there is a problem that when the magnetic disk is thinned, its rigidity and strength decrease. When the rigidity decreases, the impact resistance indicating the degree of difficulty in deforming the magnetic disk decreases. Therefore, improvement of the impact resistance is required for the aluminum alloy plate used as the material of the magnetic disk. In addition, there is also a problem that the aluminum alloy substrate is likely to deform at high temperatures. Therefore, improvement of the deformation resistance is also required for the aluminum alloy plate.

[0005] Under such circumstances, in recent years, the development of an aluminum alloy plate for a magnetic disk having excellent impact resistance and deformation resistance has been studied. For example, Patent Document 1 discloses that in the chemical composition of an aluminum alloy blank, by containing a large amount of elements such as Fe, Mn, and Ni that contribute to the improvement of rigidity, a Young's modulus can be improved, and an aluminum alloy blank for a magnetic disk having high rigidity can be provided.

Prior Art Documents

Patent Document

[0006]

Patent Document 1

[0007] However, in the method of increasing the contents of elements such as Fe, Mn, and Ni disclosed in Patent Document 1 to improve only the rigidity, the target good deformation resistance has not been obtained at present.

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention has been made in view of the above problems, and the inventors have found that by controlling the contents of various additive elements and creep characteristics in an aluminum alloy plate, an aluminum alloy plate for a magnetic disk and a magnetic disk exhibiting good impact resistance and deformation resistance can be obtained, and thus the present invention has been completed.

Means for Solving the Problems

[0009] The aluminum alloy plate for a magnetic disk 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 is 0.70 mass% or more and 7.00 mass% or less, the content of Mg is 1.0 mass% or more and less than 5.5 mass%, the balance is composed of aluminum and unavoidable impurities, and the elongation when the aluminum alloy plate is held at a temperature of 245 to 250 ° C for 240 minutes under a tensile load of 40 MPa is 3.7 mm or less.

Effects of the Invention

[0010] According to the present invention, an aluminum alloy plate for a magnetic disk and a magnetic disk exhibiting good impact resistance and deformation resistance can be obtained.

Modes for Carrying Out the Invention

[0011] Hereinafter, the aluminum alloy plate for magnetic disks and the magnetic disk according to the present embodiment will be described in detail.

[0012] [Aluminum Alloy Plate for Magnetic Disk] The aluminum alloy plate for magnetic disks according to the present invention (hereinafter sometimes referred to as "aluminum alloy plate") will be described. The aluminum alloy plate is obtained by producing an ingot using a raw material of an aluminum alloy having a predetermined alloy composition and subjecting this to a certain rolling process to produce a rolled plate. The aluminum alloy plate contains one or two of Fe, Mn, and Ni, the total content of Fe, Mn, and Ni is 0.70 mass% or more and 7.00 mass% or less, the content of Mg is 1.0 mass% or more and less than 5.5 mass%, the balance is composed of aluminum and inevitable impurities, and the elongation when the aluminum alloy plate is held at a temperature of 245 to 250 °C for 240 minutes under a tensile load of 40 MPa is 3.7 mm or less. In this way, by controlling the content of various additive elements and the creep characteristics of the aluminum alloy plate, it is possible to provide an aluminum alloy plate for magnetic disks and a magnetic disk that exhibit good impact resistance and deformation resistance.

[0013] [Alloy Composition] The alloy composition of the aluminum alloy used for the aluminum alloy plate will be described in detail below.

[0014] The aluminum alloy sheet contains one or two of Fe (iron), Mn (manganese), and Ni (nickel), the total content of Fe, Mn, and Ni is 0.70% by mass or more and 7.00% by mass or less, and the content of Mg (magnesium) is 1.0% by mass or more and less than 5.5% by mass. Fe exists mainly as second-phase particles (such as Al-Fe-based intermetallic compounds), and a part of it is dissolved in the matrix, exerting an effect of improving the rigidity (Young's modulus), strength, creep characteristics, etc. of the aluminum alloy sheet. Mn and Ni also exist mainly as second-phase particles (such as Al-Mn-based intermetallic compounds, Al-Ni-based intermetallic compounds), and a part of them is dissolved in the matrix. Due to the formation of second-phase particles and their solid solution in the matrix, Mn and Ni also exert an effect of improving the Young's modulus, strength, etc. of the aluminum alloy sheet.

[0015] (Fe, Mn, and Ni: iron, manganese, and nickel) In an aluminum alloy, when the total content of Fe, Mn, and Ni is 0.70% by mass or more and 7.00% by mass or less, the rigidity and creep characteristics of the aluminum alloy plate are improved, so that good impact resistance and deformation resistance can be imparted. When the total content of Fe, Mn, and Ni is less than 0.70% by mass, the formation of second-phase particles is insufficient, and the impact resistance and deformation resistance decrease. On the other hand, when the total content of Fe, Mn, and Ni exceeds 7.00% by mass, a large number of coarse second-phase particles are generated. Since the second-phase particles are harder than the aluminum matrix, they are difficult to machine. When manufacturing a magnetic disk, it causes a decrease in the grinding rate during grinding, leading to an increase in production costs. In addition, such coarse second-phase particles may fall off during etching, zincate treatment, cutting, or grinding in the manufacturing process of the magnetic disk, resulting in large depressions, and there are concerns about a decrease in the smoothness of the plating surface and plating peeling due to the occurrence of plating pits. Furthermore, since the workability in the rolling process also decreases, the total content of Fe, Mn, and Ni is 0.70% by mass or more and 7.00% by mass or less, preferably 0.90% by mass or more and 6.00% by mass or less, more preferably 1.50% by mass or more and 5.00% by mass or less, and even more preferably 2.00% by mass or more and 4.00% by mass or less.

[0016] (Mg: Magnesium) Mg is contained as an essential component in the aluminum alloy and mainly exists as solid-solution Mg, exerting the effect of improving the strength and creep characteristics of the aluminum alloy plate. Also, when manufacturing a magnetic disk, in order to uniformly, thinly, and densely adhere the zincate film during the zincate treatment, it improves the smoothness of the plating surface made of Ni-P in the plating process, which is the next process after the zincate treatment process.

[0017] In the aluminum alloy, the Mg content is 1.0 mass% or more and less than 5.5 mass%. When the Mg content is 5.5 mass% or more, the Young's modulus decreases, resulting in a decrease in the rigidity of the aluminum alloy plate, and as a result, the impact resistance decreases. Also, when the Mg content is high, in the manufacturing process of the magnetic disk, when pressure annealing of the aluminum alloy disk blank is performed, the adhesion between the aluminum alloy disk blanks or between the aluminum alloy disk blank and the spacer increases, so a large force is required to peel them off, and the aluminum alloy disk blank may be deformed. On the other hand, when the Mg content is less than 1.0 mass%, the effect of improving the rigidity and creep characteristics is insufficient. Therefore, the Mg content is 1.0 mass% or more and less than 5.5 mass%, and from the balance with strength, creep characteristics and manufacturability, it is preferably 1.1 mass% or more and 4.5 mass% or less, more preferably 1.2 mass% or more and 4.5 mass% or less, and even more preferably 1.3 mass% or more and 3.0 mass% or less.

[0018] The aluminum alloy plate may further contain at least one element selected from the group consisting of Cu: 0 mass% or more and 0.40 mass% or less, Zn: 0 mass% or more and 0.70 mass% or less, Cr: 0 mass% or more and 0.40 mass% or less, Zr: 0 mass% or more and 0.30 mass% or less, Si: 0 mass% or more and 0.60 mass% or less, and Be: 0 mass% or more and 0.0020 mass% or less.

[0019] (Cu: Copper) The aluminum alloy may contain 0.40 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 performing a chelate treatment in the manufacturing process of the magnetic disk. When the Cu content is 0.40 mass% or less, in the chelate treatment, a dense, thin and small-thickness-variation Zn film can be deposited on the surface of the aluminum alloy substrate. And by forming such a Zn film, a smooth Ni-P plating layer can be formed by electroless Ni-P plating treatment, which is a subsequent process.

[0020] On the one hand, if the Cu content is too high, the corrosion resistance of the aluminum alloy substrate decreases, and regions where Al is likely to dissolve locally are formed. Therefore, when performing the chelate treatment during the manufacturing process of the magnetic disk, unevenness occurs in the amount of Al dissolved on the surface of the aluminum alloy substrate, and the variation in the thickness of the Zn film tends to increase. As a result, there is a risk of a decrease in the adhesion between the Ni-P plating layer and the aluminum alloy substrate and a decrease in the smoothness of the Ni-P plating layer.

[0021] When the Cu content in the aluminum alloy is 0.40 mass% or less, preferably 0.30 mass% or less, the formation of plating pits can be suppressed, and the smoothness of the Ni-P plating layer can be further enhanced. The lower limit of the Cu content is preferably 0.003 mass%, and more preferably 0.010 mass%.

[0022] (Zn: zinc) The aluminum alloy may contain 0.60 mass% or less of Zn as an optional component. Similar to Cu, Zn has the effect of suppressing the elution of Al from the aluminum alloy substrate in the chelate treatment. When the Zn content is 0.60 mass% or less, when performing the chelate treatment during the manufacturing process of the magnetic disk, a dense, thin, and uniform-thickness Zn film can be adhered to the surface of the aluminum alloy substrate. By forming such a Zn film, a smooth Ni-P plating layer can be formed by electroless Ni-P plating in the subsequent process.

[0023] On the other hand, if the Zn content is too high, the corrosion resistance of the aluminum alloy substrate decreases, and regions where Al is likely to dissolve locally are formed. Therefore, when performing the chelate treatment during the manufacturing process of the magnetic disk, unevenness occurs in the amount of Al dissolved on the surface of the aluminum alloy substrate, and the variation in the thickness of the Zn film tends to increase. As a result, there is a risk of a decrease in the adhesion between the Ni-P plating layer and the aluminum alloy substrate and a decrease in the smoothness of the Ni-P plating layer.

[0024] When the Zn content in the aluminum alloy is 0.60 mass% or less, preferably 0.50 mass% or less, the formation of plating pits can be suppressed, and the smoothness of the Ni-P plating layer can be further enhanced. The lower limit of the Zn content is preferably 0.005 mass%, and more preferably 0.01 mass%.

[0025] (Si: Silicon) The aluminum alloy may contain 0.60 mass% or less of Si as an optional component. Si forms a Mg-Si based intermetallic compound with Mg when Mg is contained in the aluminum alloy.

[0026] When such a Mg-Si based intermetallic compound falls off from the surface of the aluminum alloy substrate during the manufacturing process of the magnetic disk, plating pits are likely to be formed in the electroless Ni-P plating process. When the Si content in the aluminum alloy is 0.60 mass% or less, preferably 0.10 mass% or less, and more preferably 0.03 mass% or less, the amount of the above intermetallic compound 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 enhanced.

[0027] In order to suppress the generation of plating pits due to the above intermetallic compound, it is preferable to reduce the Si content. However, Si is contained not only in common purity ingots but also in high purity ingots with an Al purity of 99.9 mass% or more. Therefore, if an attempt is made to produce an aluminum alloy containing almost no Si, special treatment for removing these elements during casting is required, which will lead to an increase in the manufacturing cost of the aluminum alloy plate.

[0028] If the Si content in the aluminum alloy is 0.03 mass% or less, an aluminum alloy plate can be produced without performing special treatment for removing Si. As a result, while avoiding an increase in the manufacturing cost of the aluminum alloy plate, its smoothness can be further enhanced. Further, even if the Si content in the aluminum alloy exceeds 0.03 mass% but is 0.60 mass% or less, an aluminum alloy plate can be produced using a lower-purity ingot. Thereby, the material cost of the aluminum alloy plate can be further reduced.

[0029] (Be: Beryllium) Be is an element added into the molten metal for the purpose of suppressing the oxidation of Mg when casting an aluminum alloy containing Mg. Further, when the Be content contained in the aluminum alloy is 0.0020 mass% or less, the Zn film formed on the surface of the aluminum alloy substrate in the manufacturing process of the magnetic disk can be made denser and the thickness variation can be made smaller. As a result, the smoothness of the Ni-P treatment layer formed on the aluminum alloy substrate can be further enhanced.

[0030] On the other hand, if the Be content in the aluminum alloy is too high, when the aluminum alloy substrate is heated in the manufacturing process of the magnetic disk, Be-based oxides are likely to be formed on the surface of the aluminum alloy substrate. Further, when the aluminum alloy further contains Mg, when the aluminum alloy substrate is heated, Al-Mg-Be-based oxides are likely to be formed on the surface of the aluminum alloy substrate. When the amount of these oxides increases, the thickness variation of the Zn film becomes large, which may cause the occurrence of plating pits.

[0031] When the Be content in the aluminum alloy is 0.0020 mass% or less, preferably 0.0010 mass% or less, the amount of Al-Mg-Be-based oxides is reduced, and the smoothness of the Ni-P plating treatment layer can be further enhanced. Incidentally, when Be is contained in the aluminum alloy, the lower limit of the Be content is preferably 0.0001 mass%.

[0032] (Cr: Chromium) The aluminum alloy may contain Cr of 0.40 mass% or less as an optional component. A part of Cr is dispersed in the aluminum alloy sheet as fine intermetallic compounds generated during casting. Cr that did not form intermetallic compounds during casting is dissolved in the Al matrix and has the effect of improving the strength and creep properties of the aluminum alloy sheet by solid solution strengthening.

[0033] In addition, Cr has the effect of further enhancing the machinability and grindability and further refining the recrystallized structure during the manufacturing process of the magnetic disk. As a result, the adhesion between the aluminum alloy substrate and the electroless Ni-P plating layer is further enhanced, and the generation of plating pits is suppressed.

[0034] On the other hand, if the content of Cr in the aluminum alloy is too high, coarse Al-Cr-based intermetallic compounds are likely to be formed in the aluminum alloy substrate. When such coarse Al-Cr-based 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.

[0035] When the content of Cr in the aluminum alloy is 0.40 mass% or less, preferably 0.30 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. Note that the lower limit of the Cr content is not particularly limited and may be 0 mass%.

[0036] (Zr: Zirconium) The aluminum alloy may contain Zr of 0.30 mass% or less as an optional component. A part of Zr is dispersed in the aluminum alloy sheet as fine intermetallic compounds generated during casting. Zr that did not form intermetallic compounds during casting is dissolved in the Al matrix and has the effect of improving the strength and creep properties of the aluminum alloy sheet by solid solution strengthening.

[0037] In addition, Zr has the effect of further enhancing machinability and grindability and further refining the recrystallized structure during the manufacturing process of magnetic disks. As a result, the adhesion between the aluminum alloy substrate and the Ni-P plating layer is further enhanced, and the generation of plating pits is suppressed.

[0038] On the other hand, if the content of Zr in the aluminum alloy is too high, coarse Al-Zr-based intermetallic compounds are likely to be formed in the aluminum alloy substrate. When such coarse Al-Zr-based intermetallic compounds fall off from the surface of the aluminum alloy substrate, plating pits are likely to be formed in the electroless Ni-P plating process in the subsequent process.

[0039] When the content of Zr in the aluminum alloy is 0.30% by mass or less, preferably 0.20% by mass or less, the formation of plating pits can be suppressed, a smooth Ni-P plating layer can be formed, and the strength and creep characteristics of the aluminum alloy substrate can be further improved. Incidentally, the lower limit of the content of Zr is not particularly limited and may be 0% by mass.

[0040] (Other elements) The aluminum alloy may contain elements that are inevitable impurities other than the essential components and optional components described above. Examples of these elements include Ti (titanium), V (vanadium), B (boron), Ga (gallium), etc. As long as the content of each element is 0.10% by mass or less and the total is 0.30% by mass or less, the effects of the present invention are not impaired.

[0041] As described above, in the present invention, Fe, Si, etc. can be positively added, but they may also be inevitable impurities without being positively added. Si is included as an inevitable impurity not only in common purity ingots but also in high-purity ingots with an Al purity of 99.9 mass% or more. Even when included as such an inevitable impurity, as long as it is 0.10% by mass or less, the effects of the present invention are not impaired. Incidentally, when Fe and Si are positively added, from the above viewpoints, the content of Fe in the aluminum alloy is preferably 1.80% by mass or less, and the content of Si is preferably 0.60% by mass or less.

[0042] <Thickness of aluminum alloy plate> From the perspective of the recent trend of thinning 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 with such a thickness, the aluminum alloy plate according to the present invention exhibits good impact resistance and deformation resistance.

[0043] <Second-phase particles> The density of second-phase particles having a major axis length of 5 μm or more and 8 μm or less present in the metal structure of the aluminum alloy plate is preferably 160 particles / mm 2 or more. When the aluminum alloy plate has such a metal structure, it has the effect of improving the creep characteristics of the aluminum alloy plate. When there are few second-phase particles having such a major axis length, grain boundary migration occurs during heating of the aluminum alloy plate, and the deformation of the aluminum alloy plate becomes large. However, when a large number of such second-phase particles are present, grain boundary migration during heating can be pinned, so that deformation of the aluminum alloy plate can be suppressed. Here, the major axis length of the second-phase particles can be measured by particle analysis software using a scanning electron microscope (SEM) photograph, and the density of such second-phase particles can be measured by particle analysis software using an SEM photograph.

[0044] When the major axis length of the second-phase particles present in the metal structure of the aluminum alloy plate is 8 μm or more, the pinning effect of grain boundary migration is small, so the effect of improving deformation suppression becomes small. On the other hand, when the major axis length of the second-phase particles is less than 5 μm, the pinning effect of grain boundary migration is small, so the effect of improving deformation suppression becomes small. Therefore, the major axis length of the second-phase particles present in the metal structure of the aluminum alloy plate is preferably in the range of 5 μm or more and 8 μm or less. Also, the upper limit of the density of the second-phase particles is preferably 3500 particles / mm 2 and more preferably 2500 particles / mm 2 When the density of the second-phase particles exceeds 3500 particles / mm 2 electroless Ni-P plating pits are likely to be formed during the electroless Ni-P plating process in the manufacturing process of the magnetic disk.

[0045] The second-phase particles mentioned above refer to precipitates and crystallized substances, specifically, particles such as Al-Fe intermetallic compounds (Al3Fe, Al6Fe, Al6(Fe, Mn), Al-Fe-Si, Al-Fe-Mn-Si, Al-Fe-Ni, Al-Cu-Fe, etc.), Mg-Si intermetallic compounds (Mg2Si, etc.). Other intermetallic compounds include Al-Mn intermetallic compounds (Al6Mn, Al-Mn-Si), Al-Ni intermetallic compounds (Al3Ni, etc.), Al-Cu intermetallic compounds (Al2Cu, etc.), Al-Cr intermetallic compounds (Al7Cr, etc.), Al-Zr intermetallic compounds (Al3Zr, etc.). In addition to these intermetallic compounds, the second-phase particles also include Si particles, etc.

[0046] <Properties of Aluminum Alloy Sheet> (Elongation) When the elongation (deformation amount) of an aluminum alloy plate is 3.7 mm or less when it is held at a temperature of 245 to 250 °C for 240 minutes under a tensile load of 40 MPa, the creep characteristics of the aluminum alloy plate are improved. Therefore, in the manufacturing process of a magnetic disk, deformation of the aluminum alloy substrate during heating can be suppressed. That is, when the aluminum alloy plate exhibits such elongation characteristics, good creep characteristics are imparted, so that an aluminum alloy plate showing good deformation resistance can be provided. The heating here is a heat treatment performed in a process after pressure annealing, for example, a heat treatment such as stress relief heat treatment. The heat treatment is performed by putting an aluminum alloy plate with a sample size of 125 to 130 mm × 12.5 mm in a cassette or the like. However, when the thickness of the aluminum alloy plate becomes thin, the aluminum alloy plate may be deformed due to the stress applied to the contact portion with the cassette. When the elongation of the aluminum alloy plate is 3.7 mm or less when a tensile load of 40 MPa is applied at 245 to 250 °C and held for 240 minutes, deformation of the aluminum alloy plate during heating is suppressed, and an aluminum alloy plate showing good deformation resistance can be obtained, and a magnetic disk showing excellent flatness can be provided. Such elongation is preferably 3.0 mm or less, more preferably 2.5 mm or less, and even more preferably 2.0 mm or less.

[0047] Incidentally, the elongation characteristics can also be measured using an aluminum alloy disk blank after pressure annealing, an aluminum alloy substrate after grinding, an aluminum alloy substrate after plating, or a magnetic disk after sputtering, which will be described later. The sample size at that time is 90 to 95 mm × 12.5 mm. When using an aluminum alloy substrate or a magnetic disk after plating, the plating may be peeled off, and a test piece may be collected from an aluminum alloy substrate whose surface is ground by 10 μm for measurement and evaluation.

[0048] (Young's modulus) By increasing the Young's modulus of the aluminum alloy plate, the effect of improving the impact resistance of the magnetic disk is exerted. Therefore, the Young's modulus of the aluminum alloy plate is preferably 71 GPa or more. When the magnetic disk device drops or the like, the magnetic disk may be deformed, but this deformation is within the elastic range. Therefore, by improving the Young's modulus of the aluminum alloy plate, the impact resistance is improved and such deformation can be suppressed.

[0049] When the Young's modulus of the aluminum alloy plate is less than 71 GPa, the magnetic disk may be greatly deformed when the magnetic disk device drops or the like. If the deformed magnetic disk collides with a large number of other members (such as a ramp load which is a retraction place for other magnetic disks or heads), dust or the like may be generated and cause recording errors. To avoid a decrease in impact resistance, which is a characteristic of the magnetic disk being difficult to deform, the Young's modulus of the aluminum alloy plate is preferably 71 GPa or more, more preferably 72 GPa or more, and even more preferably 73 GPa or more. Incidentally, the upper limit of the Young's modulus of the aluminum alloy plate is not particularly limited, but it varies depending on the material and composition of the aluminum alloy plate and the manufacturing conditions, and is preferably approximately 85 GPa.

[0050] The Young's modulus can be measured by the resonance method. For example, on the surface of an aluminum alloy plate, an arbitrary rectangular region where the rolling direction and the longitudinal direction are parallel can be sampled as a sample, and the Young's modulus can be measured from the sample. Note that the Young's modulus is not limited to the aluminum alloy plate, and it may also be measured using the aluminum alloy disk blank after pressure annealing, the aluminum alloy substrate after grinding, the aluminum alloy substrate after plating, and the magnetic disk after sputtering, which will be described later. When measuring the Young's modulus using the aluminum alloy substrate after plating or the magnetic disk, the plating film including the Ni-P plating layer is peeled off, and a sample can be taken from the aluminum alloy substrate whose surface is ground by 5 to 30 μm, and the Young's modulus can be measured. In addition, the size (length, width, thickness) of the sample required for the measurement can be measured using a micrometer and a caliper, and the weight can be measured using an electronic balance.

[0051] <Manufacturing method of aluminum alloy plate> Hereinafter, the manufacturing method of the aluminum alloy plate will be described in detail.

[0052] (Casting process) The raw material of the aluminum material with a predetermined alloy composition is melted, the molten metal is smelted, and then it is cast to produce an ingot. As the casting method, a semi-continuous casting (DC casting) method, a die casting method, a continuous casting (CC casting) method, etc. are used. In the DC casting method, the molten metal poured through the spout is cooled by the bottom block, the wall of the water-cooled mold, and the cooling water directly discharged to the outer peripheral part of the ingot (cast ingot), and is solidified, and is pulled out downward as an ingot. In the die casting method, the molten metal poured into the hollow mold made of cast iron or the like is solidified by having its heat taken away by the wall of the mold, and an ingot is produced. In the CC casting method, the molten metal is supplied through a casting nozzle between a pair of rolls (or a belt caster, a block caster), and a thin plate is directly cast by heat extraction from the rolls.

[0053] In such a casting process, it is preferable to perform a degassing process for reducing the dissolved gas in the molten metal and a filtering process for removing the solid matter in the molten metal in-line.

[0054] As the degassing treatment, for example, a treatment method called the SNIF (Spinning Nozzle Inert Flotation) process, a treatment method called the Alpur process, etc. can be adopted. In these processes, while stirring the molten metal at high speed by a rotating body with blades, a process gas such as argon gas or a mixed gas of argon and chlorine is blown in to form fine bubbles of the process gas in the molten metal. Thereby, hydrogen gas and inclusions dissolved in the molten metal can be removed in a short time. For the degassing treatment, an in-line degassing device can be used.

[0055] As the filtration treatment, for example, a cake filtration method, a filter medium filtration method, etc. can be adopted. Also, for the filtration treatment, for example, filters such as ceramic tube filters, ceramic foam filters, alumina ball filters, etc. can be used.

[0056] (Homogenization treatment process) After producing the ingot and before performing hot rolling, surface machining of the ingot is carried out and homogenization treatment is performed. The homogenization treatment is a heat treatment carried out at 550 to 620 °C for 0.5 to 30 hours. When performing the homogenization treatment, the residence time in the temperature range of 425 to 440 °C is preferably 0.9 hours or less. If the residence time in the temperature range of 425 to 440 °C exceeds 0.9 hours, the number of the above-mentioned second-phase particles may decrease, and as a result, the creep characteristics are likely to deteriorate, so there is a concern about a decrease in the deformation resistance. Also, from the viewpoint of obtaining the above effects, the lower limit of the residence time is preferably 0.1 hours or more. Incidentally, the residence time in the temperature range of 425 to 440 °C includes the time in the treatment steps after the homogenization treatment step, and the residence time is preferably less than 0.5 hours. When 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 is insufficient, and there is a possibility that the variation in impact resistance for each aluminum alloy plate increases. Also, when the heating temperature during the homogenization treatment exceeds 620 °C, there is a possibility that the ingot of the aluminum alloy will melt. Incidentally, even if the heating time during the homogenization treatment exceeds 30 hours, the effect saturates and no further significant improvement effect can be obtained, so the upper limit of the heating time is 30 hours.

[0057] (Hot rolling process) Next, hot rolling is performed on the ingot subjected to the homogenization treatment to produce a hot-rolled plate. 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 ending temperature of the hot rolling is preferably 230 to 400 °C. Also, the thickness of the hot-rolled plate can be appropriately set, for example, from the range of 2.0 to 6.0 mm.

[0058] (Cold rolling process) After performing hot rolling, a cold-rolled plate can be obtained by performing cold rolling of one pass or more on the obtained hot-rolled plate. The total reduction ratio in the cold rolling is preferably, for example, 20 to 95%. Also, the thickness of the cold-rolled plate can be appropriately set from the range of 0.2 to 1.9 mm.

[0059] (Annealing treatment process) In the manufacturing method of the above aspect, annealing treatment may be performed as necessary before the first pass and / or between passes in cold rolling. The annealing treatment may be performed using a batch-type heat treatment furnace. When using a batch-type heat treatment furnace, 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, the workability during cold rolling can be restored. Through the above steps, an aluminum alloy plate is produced.

[0060] <Manufacturing Method of Aluminum Alloy Disk Blank> When manufacturing an aluminum alloy disk blank from the aluminum alloy plate produced through the above steps, for example, the following method can be adopted. First, punching is performed on the aluminum alloy plate to produce an aluminum alloy disk blank having an annular shape. Thereafter, pressure annealing is performed by heating the aluminum alloy disk blank while applying pressure from both sides in the thickness direction, thereby reducing the distortion of the aluminum alloy disk blank and improving the flatness. The holding temperature and pressure in the pressure annealing can be appropriately selected, for example, from the range of 250 to 420 °C and 0.1 to 3 MPa. Also, the holding time in the pressure annealing can be, for example, 30 minutes or more. Through the above steps, an aluminum alloy disk blank is produced.

[0061] <Manufacturing Method of Aluminum Alloy Substrate for Magnetic Disk> It is preferable to perform annealing on the pressure-annealed aluminum alloy disk blank 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. Also, 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 the annealing treatment under such conditions, solid-solution Mg etc. precipitate, and as a result, the conductivity of the aluminum alloy disk blank can be increased.

[0062] After annealing, cutting and grinding are sequentially performed on the aluminum alloy disk blank to produce an aluminum alloy substrate having a desired shape. After these processes, if necessary, a stress-relieving heat treatment for removing the strain during processing may be performed under the conditions of 150 to 350 °C for 0.1 to 10.0 hours. Through the above steps, an aluminum alloy substrate is produced.

[0063] <Magnetic Disk> The magnetic disk according to the present invention includes an aluminum alloy substrate formed using the above-described aluminum alloy plate, 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. Note that the Ni-P plating layer is preferably an electroless Ni-P plating layer formed by electroless plating.

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

[0065] From the perspective of the recent thinning of magnetic disks, the thickness of the magnetic disk is preferably 0.48 mm or less, and more preferably 0.42 mm or less. Even with such a thickness, the magnetic disk according to the present invention exhibits good impact resistance and deformation resistance.

[0066] <Method for Manufacturing Magnetic Disk> When manufacturing a magnetic disk from an aluminum alloy substrate, for example, the following method can be adopted. First, as a pre-plating treatment, degreasing and cleaning are performed on the aluminum alloy substrate to remove oil such as processing oil adhering to the surface of the aluminum alloy substrate. After degreasing and cleaning, if necessary, the aluminum alloy substrate may be etched using an acid. When etching is performed, after etching, it is preferable to perform a desmatt treatment to remove the smut generated by etching from the aluminum alloy substrate. The treatment conditions in these treatments can be appropriately set according to the type of treatment liquid.

[0067] After performing these pre-plating treatments, a zincate treatment for forming a Zn film on the surface of the aluminum alloy substrate is performed. In the zincate treatment, a Zn film can be formed by performing zinc replacement plating in which Al is replaced with Zn. As the zincate treatment, it is preferable to adopt a so-called double zincate method in which after performing the first zinc replacement plating, the Zn film formed on the surface of the aluminum alloy substrate is once peeled off, and zinc replacement plating is performed again 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 the Zn film formed only by the first zinc replacement plating. As a result, defects in the electroless Ni-P plating layer can be reduced in the subsequent electroless Ni-P plating process.

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

[0069] When the thickness of the Ni-P plating layer is increased, the plating pits tend to decrease, and a smooth Ni-P plating layer can be formed. Therefore, the thickness (plating thickness) of the Ni-P plating layer is preferably 7 μm or more, more preferably 18 μm or more, and even more preferably 25 μm or more. In practical use, the upper limit value of the plating thickness is about 40 μm.

[0070] After electroless Ni-P plating, by polishing the Ni-P plating layer, the smoothness of the surface of the Ni-P plating layer can be further enhanced.

[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 be composed of a single layer or may be composed of a plurality of layers having different compositions. Conventional methods are applied to the temperature and the like of sputtering. However, when the temperature of sputtering is particularly 100 °C or lower, when the conductivity of the aluminum alloy substrate is high, an energy-saving effect is exhibited. After sputtering, a protective layer made of a carbon-based material is formed on the magnetic layer by CVD (Chemical Vapor Deposition). Next, a lubricating oil is applied on the protective layer to form a lubricating layer. Through the above steps, a magnetic disk is manufactured.

[0072] Based on the above embodiments, the present invention relates to the following [1] to [5]. [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 0.70% by mass or more and 7.00% by mass or less, the content of Mg is 1.0% by mass or more and less than 5.5% by mass, and the balance is composed of aluminum and inevitable impurities, The aluminum alloy plate for a magnetic disk is characterized in that the elongation when the aluminum alloy plate is held at a temperature of 245 to 250 °C for 240 minutes under a tensile load of 40 MPa is 3.7 mm or less. [2] An aluminum alloy sheet for a magnetic disk according to [1] above, further containing at least one element selected from the group consisting of Cu: 0 mass% or more and 0.40 mass% or less, Zn: 0 mass% or more and 0.70 mass% or less, Cr: 0 mass% or more and 0.40 mass% or less, Zr: 0 mass% or more and 0.30 mass% or less, Si: 0 mass% or more and 0.60 mass% or less, and Be: 0 mass% or more and 0.0020 mass% or less. [3] An aluminum alloy sheet for a magnetic disk according to [1] or [2] above, having a thickness of 0.48 mm or less. [4] An aluminum alloy sheet for a magnetic disk according to [1] or [2] above, having a thickness of 0.42 mm or less. [5] A magnetic disk including an aluminum alloy substrate formed using the aluminum alloy sheet for a magnetic disk according to [1] to [4] 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.

[0073] As described above, the aluminum alloy sheet and the magnetic disk according to the present invention have been described. However, the present invention is not limited to the above-described embodiments, and various modifications and changes are possible based on the technical idea of the present invention.

Examples

[0074] Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited thereto. Also, room temperature is defined as a range of 20°C ± 15°C.

[0075] <Production of Aluminum Alloy Sheet> An aluminum alloy sheet was produced by the following method. First, in a melting furnace, a molten metal having the chemical components shown in Table 1 was prepared.

[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 machined to remove the segregation layer present on the ingot surface. After machining, the ingot was heat-treated under the conditions shown in Table 2 to perform homogenization treatment. Thereafter, hot rolling was carried out to obtain a hot-rolled sheet. Further, cold rolling was carried out under the conditions shown in Table 2 to produce an aluminum alloy sheet.

[0078] (Volume fraction of second-phase particles) The perimeter and the longest diameter of the second-phase particles were calculated by combining SEM and particle analysis software. The SEM observation was performed using a scanning electron microscope ("FlexSEM 1000" manufactured by Hitachi High-Tech Corporation, Operation Ver. 1.9) under the conditions of acceleration voltage: 15 kV, magnification: 1000 times, scan resolution: 1024 pixels, scan dwell time: 35 μs, and field area: 0.07 mm2 or more. The particle analysis software used was "AZtec" (Ver. 3.3 SP1) manufactured by Oxford Instruments. Each second-phase particle with a higher or lower contrast than the matrix was analyzed one by one by EDS (energy-dispersive X-ray analysis) to obtain the perimeter (mm / mm 2 ) and the longest diameter (number / mm 2 ). The analysis time by EDS for each detected second-phase particle was set to 2 seconds. The results are shown in Table 2.

[0079] (Elongation) A sample of 129×12.5 mm was taken from the cold-rolled aluminum alloy sheet, heat-treated at a holding temperature of 320 °C and a holding time of 3 hours, and the elongation was measured. Using a creep tester, after the sample reached a temperature of 245 - 250 °C, a tensile load of 40 MPa was applied and held for 240 minutes, and then the elongation (deformation amount) was measured. When the deformation amount was 3.7 mm or less, it was evaluated that the deformation resistance was good, and when the deformation amount exceeded 3.7 mm, it was evaluated that the deformation resistance was inferior. The results are shown in Table 2.

[0080] (Young's modulus) From the surface of the aluminum alloy plate after cold rolling, a 60 mm × 8 mm sample was wire-cut from an arbitrary region where the rolling direction and the longitudinal direction were parallel, and the Young's modulus was measured. Since it may not be possible to measure accurately if the plate thickness is too thin, some samples were measured with a plate thickness of 0.5 mm or more. The Young's modulus was measured at room temperature by the resonance method using a JE-RT type device manufactured by Nippon Technoplus Co., Ltd. The size (length, width, thickness) of the sample required for the measurement was measured using a micrometer and a caliper, and the weight was measured using an electronic balance. When the Young's modulus was 71 GPa or more, it was evaluated that the impact resistance was good, and when it was less than 71 GPa, it was evaluated that the impact resistance was inferior. The results are shown in Table 2.

[0081]

Table 2

[0082] As shown in Tables 1 and 2, in the aluminum alloy plate having a predetermined alloy composition, Examples 1 to 4 in which the elongation (deformation amount) shown by the aluminum alloy plate was 3.7 mm or less showed a high Young's modulus and improved creep characteristics, and good impact resistance and deformation resistance could be achieved.

[0083] On the other hand, in Comparative Examples 1 and 2, since both the alloy composition and the creep characteristics (elongation) were outside the ranges defined in the present invention, the results were inferior in impact resistance and deformation resistance.

Industrial Applicability

[0084] The aluminum alloy plate according to the present invention has a specific alloy composition and creep characteristics, so that even if the thickness of the aluminum alloy plate is thin, it exhibits good impact resistance and deformation resistance. Further, by using such an aluminum alloy plate, a magnetic disk having good impact resistance and deformation resistance can be provided.

Claims

1. An aluminum alloy sheet for magnetic disks, containing one or more of Fe, Mn, and Ni, wherein the total content of Fe, Mn, and Ni is 0.70% by mass or more and 7.00% by mass or less, the content of Mg is 1.0% by mass or more and less than 5.5% by mass, and the balance consists of aluminum and inevitable impurities, wherein the elongation when the aluminum alloy sheet is held at a temperature of 245 to 250 °C for 240 minutes under a tensile load of 40 MPa is 3.7 mm or less.

2. The aluminum alloy sheet 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.

3. The aluminum alloy sheet for magnetic disks according to Claim 1 or 2, having a thickness of 0.48 mm or less.

4. The aluminum alloy sheet for magnetic disks according to Claim 1 or 2, having a thickness of 0.42 mm or less.

5. A magnetic disk comprising an aluminum alloy substrate formed using the aluminum alloy sheet for magnetic disks according to Claim 1 or 2, 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.

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