Aluminum alloy disc blank for magnetic disc and magnetic disc

Abstract

The present invention relates to an aluminum alloy disc blank for a magnetic disc, characterized by being formed of an aluminum alloy containing Fe: 0.005 to 1.800 mass%, the balance consisting of Al and unavoidable impurities, and a flatness change of the aluminum alloy disc blank for a magnetic disc being 2.0 μm or less when the aluminum alloy disc blank for a magnetic disc is kept in the atmosphere at 50°C or lower for 336 hours.

Description

Technical Field

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

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

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

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

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

[0006] The demands of multimedia applications require large-capacity and high-density hard drives. To further increase capacity, methods are employed to increase the number of drives that can be mounted by thinning the disk. However, this method reduces rigidity as the disk becomes thinner, making it prone to jitter. This is because unstable airflow is generated between the disks when they rotate at high speed, causing disk vibration (jitter). If jitter occurs, the positioning error of the read / write head increases. Therefore, as a jitter countermeasure, filling the hard drive with helium reduces fluid forces. This is because helium has a lower viscosity than air, approximately 1 / 8. By reducing the fluid forces of the gas, the jitter caused by the gas flowing with the hard drive's rotation is reduced. However, the need to seal in helium increases costs. On the other hand, with an atmospheric atmosphere inside the hard drive, there is a tendency to reduce the head lift during read / write operations to further increase capacity. However, if there are protrusions on the disk surface, they can collide with the head, leading to recording errors; therefore, reducing protrusions is required.

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

[0008] (Existing technical literature)

[0009] (Patent Documents)

[0010] Patent Document 1: Japanese Patent Application Publication No. 10-008177 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] According to the method in Patent Document 1, twin-roll continuous casting can increase the cooling rate during solidification of molten metal, resulting in finer intermetallic compounds. However, the method in Patent Document 1 suffers from the problem of difficulty in reducing convex defects in the billet caused by factors other than intermetallic compounds.

[0013] The present invention was made in view of the above-mentioned problems. The inventors discovered that by controlling the flatness variation of the aluminum alloy disk blank for disks, it is possible to obtain an aluminum alloy disk blank for disks with excellent smoothness, thus completing the present invention.

[0014] Methods for solving problems

[0015] One aspect of the present invention is an aluminum alloy disk blank for disks, characterized in that it is formed of an aluminum alloy containing Fe: 0.005 to 1.800% by mass, with the balance consisting of Al and unavoidable impurities, and the flatness of the aluminum alloy disk blank for disks changes to less than 2.0 μm when held at 50°C or below for 336 hours in the atmosphere.

[0016] Another aspect of the present invention is an aluminum alloy blank for a magnetic disk, wherein the aluminum alloy further contains one or more elements selected from the group consisting of Mn: less than 1.80 wt%, Ni: less than 2.50 wt%, Cu: less than 1.00 wt%, Zn: less than 0.70 wt%, Mg: less than 4.50 wt%, Cr: less than 0.30 wt%, Zr: less than 0.15 wt%, Si: less than 14.00 wt%, Be: less than 0.0015 wt%, Sr: less than 0.10 wt%, Na: less than 0.10 wt%, and P: less than 0.10 wt%.

[0017] Another aspect of the present invention is an aluminum alloy disk blank for disks, characterized in that the surface grain size of the aluminum alloy disk blank is less than 18 μm.

[0018] Another aspect of the present invention is an aluminum alloy disk blank for disks, characterized in that the surface grain size of the aluminum alloy disk blank is less than 15 μm.

[0019] Another aspect of the present invention is an aluminum alloy disk blank for disks, characterized in that the surface grain size of the aluminum alloy disk blank is less than 12 μm.

[0020] Another aspect of the present invention is an aluminum alloy disk blank for disks, characterized in that the surface grain size of the aluminum alloy disk blank is less than 11 μm.

[0021] Another aspect of the present invention is an aluminum alloy disk blank for a hard disk, characterized in that the surface grain size of the aluminum alloy disk blank is less than 10 μm.

[0022] Another aspect of the present invention is a disk, characterized in that a Ni-P plating layer and a magnetic layer on the surface of an aluminum alloy substrate formed from an aluminum alloy disk blank are provided.

[0023] Invention Effects

[0024] The aluminum alloy disk blank for disks involved in this invention can control flatness variations and improve smoothness. Attached Figure Description

[0025] Figure 1 This is a graph showing the measurement range of the flatness of aluminum alloy blanks. Detailed Implementation

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

[0027] The present invention relates to an aluminum alloy disk blank (hereinafter sometimes referred to as "aluminum alloy blank"). An aluminum alloy blank is obtained by producing an aluminum alloy sheet using an aluminum alloy with a specified alloy composition and then punching it into a disk shape. The aluminum alloy blank is formed from an aluminum alloy containing Fe: 0.005 to 1.800% by mass, with the balance consisting of Al and unavoidable impurities. The flatness change of the aluminum alloy blank after being held at 50°C or below for 336 hours in atmosphere is less than 2.0 μm. The flatness change is calculated as the absolute value of {(flatness of the aluminum alloy blank before being held at 50°C or below for 336 hours) - (flatness of the aluminum alloy blank after being held at 50°C or below for 336 hours)}. By making this flatness change less than 2.0 μm, residual stress is less likely to be generated during cutting or grinding of the surface of the aluminum alloy blank, and convex defects are less likely to be generated during annealing after processing. As a result, the smoothness of the aluminum alloy blank is improved, which can prevent the generation of convex defects on the disk surface.

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

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

[0030] Fe: 0.005–1.800% by mass

[0031] Fe mainly exists as second-phase particles (Al-Fe intermetallic compounds, etc.), and a portion is dissolved in the matrix. Through the formation of second-phase particles and their dissolution into the matrix, Fe enhances the strength and rigidity of the aluminum alloy blank. However, if the Fe content is less than 0.005% by mass, the strength of the aluminum alloy blank is too low, resulting in deformation during the peeling process after pressure annealing. On the other hand, if the Fe content exceeds 1.800% by mass, large intermetallic compounds are formed, leading to large pits and reduced surface smoothness during etching, zincate treatment, cutting, or grinding. Furthermore, a higher Fe content increases the strength of the aluminum alloy blank, thus increasing the likelihood of cracking during rolling. Therefore, the Fe content in the aluminum alloy is set between 0.005% and 1.800% by mass. It should be noted that, considering the strength, rigidity, and manufacturability of the aluminum alloy blank, the Fe content is preferably set to 0.010–1.500 by mass.

[0032] In one embodiment of the aluminum alloy blank, in addition to Fe, one or more elements selected from Mn (manganese), Ni (nickel), Cu (copper), Zn (zinc), Si (silicon), Be (beryllium), Cr (chromium), Zr (zirconium), Mg (magnesium), Sr (strontium), Na (sodium), and P (phosphorus) may be included as arbitrary components. In this case, an aluminum alloy blank for disk drives can be obtained, characterized in that it is formed of an aluminum alloy containing Fe: 0.005 to 1.800% by mass, and containing one or more elements selected from the group consisting of Mn: less than 1.80% by mass, Ni: less than 2.50% by mass, Cu: less than 1.00% by mass, Zn: less than 0.70% by mass, Mg: less than 4.50% by mass, Cr: less than 0.30% by mass, Zr: less than 0.15% by mass, Si: less than 14.00% by mass, Be: less than 0.0015% by mass, Sr: less than 0.10% by mass, Na: less than 0.10% by mass, and P: less than 0.10% by mass, with the balance consisting of Al and unavoidable impurities. The flatness of the aluminum alloy blank for disk drives, when held at 50°C or below for 336 hours in the atmosphere, changes to less than 2.0 μm.

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

[0034] Mn: less than 1.80% by mass

[0035] In the aforementioned aluminum alloy coil, Mn can be present at a concentration of 1.80% by mass or less as an arbitrary component. Mn mainly exists as second-phase particles (Al-Mn intermetallic compounds, etc.) and is partially dissolved in the matrix. Through the formation of second-phase particles and solid solution into the matrix, Mn enhances the strength and rigidity of the aluminum alloy coil. However, if the Mn content is high, coarse intermetallic compounds are formed, leading to large depressions caused by the detachment of these compounds during etching, zincate treatment, cutting, or grinding of the aluminum alloy coil, potentially reducing surface smoothness. Furthermore, a higher Mn content increases the strength of the aluminum alloy coil, which may cause cracks during rolling. Therefore, the Mn content is preferably set to 1.80% by mass or less. It should be noted that, considering the balance of strength, rigidity, and manufacturability of the aluminum alloy coil, the Mn content is preferably set to 0.01 to 1.50% by mass.

[0036] Ni: less than 2.50% by mass

[0037] In the aforementioned aluminum alloy, Ni can be present as an arbitrary component at 2.50% by mass or less. Ni mainly exists as second-phase particles (Al-Ni intermetallic compounds, etc.) and is partially dissolved in the matrix. Through the formation of second-phase particles and solid solution into the matrix, Ni enhances the strength and rigidity of the aluminum alloy blank. However, if the Ni content is high, coarse intermetallic compounds are formed, leading to large depressions caused by the detachment of these compounds during etching, zincate treatment, cutting, or grinding of the aluminum alloy blank, potentially reducing surface smoothness. Furthermore, a higher Ni content increases the strength of the aluminum alloy blank, which may cause cracking during rolling. Therefore, the Ni content is preferably set to 2.50% by mass or less. It should be noted that, considering the balance of strength, rigidity, and manufacturability of the aluminum alloy blank, the Ni content is preferably set to 0.01 to 2.00% by mass.

[0038] Cu: less than 1.00% by mass

[0039] In the aforementioned aluminum alloy, Cu can be present as an arbitrary component of up to 1.00% by mass. Cu mainly exists as second-phase particles (Al-Cu intermetallic compounds, etc.), which improves the strength and Young's modulus of the aluminum alloy blank. Furthermore, it reduces the amount of Al dissolved during the zincate treatment of the aluminum alloy blank. Consequently, it achieves the following effects: during zincate treatment, the zinc coating adheres uniformly, thinly, and densely, and the smoothness is improved in the next process, namely the plating process.

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

[0041] By setting the Cu content in the aforementioned aluminum alloy to preferably 1.00% by mass or less, and more preferably 0.50% by mass or less, the rigidity and strength of the aluminum alloy blank can be further improved, the formation of plating pits can be suppressed, and the smoothness of the Ni-P plating layer can be further improved. It should be noted that the lower limit of the Cu content is preferably 0.005% by mass.

[0042] • Zn: less than 0.70% by mass

[0043] In the aforementioned aluminum alloy, Zn can be present as an arbitrary component up to 0.70% by mass. Zn reduces the amount of Al dissolved during the zincate treatment of the aluminum alloy blank, and has the following effects: it ensures a uniform, thin, and dense zinc coating during zincate treatment, and improves the smoothness and adhesion in the next process, namely the plating process. Furthermore, it forms second-phase particles with other additive elements, thereby increasing Young's modulus and strength.

[0044] However, if the Zn content increases, the corrosion resistance of the aluminum alloy blank decreases, and areas where Al easily dissolves form locally on the aluminum alloy blank. Therefore, during the zincate treatment process in disk manufacturing, variations in the amount of Al dissolved on the surface of the aluminum alloy substrate occur, and the unevenness of the Zn coating thickness tends to increase. This can potentially lead to reduced adhesion between the Ni-P plating layer and the aluminum alloy substrate, and a decrease in the smoothness of the Ni-P plating layer.

[0045] By setting the Zn content in the aforementioned aluminum alloy to preferably 0.70% by mass or less, and more preferably 0.50% by mass or less, the rigidity and strength of the aluminum alloy blank can be further improved, the formation of plating pits can be suppressed, and the smoothness of the Ni-P plating layer can be further improved. It should be noted that the lower limit of the Zn content is preferably 0.10% by mass.

[0046] ·Mg: less than 4.50% by mass

[0047] In the aforementioned aluminum alloys, Mg can be present as an arbitrary component up to 4.50% by mass. Mg mainly exists in solid solution within the matrix, with a portion existing as second-phase particles (Mg-Si intermetallic compounds, etc.). This contributes to improving the strength and rigidity of the aluminum alloy blank.

[0048] However, if the Mg content increases, coarse Al-Mg intermetallic compounds are formed. These compounds then detach during etching, zincate treatment, cutting, or grinding of the aluminum alloy blank, resulting in larger depressions and reduced surface smoothness. Furthermore, a higher Mg content increases strength, thus increasing the likelihood of cracking during rolling.

[0049] By setting the Mg content in the above-mentioned aluminum alloy to preferably 4.50% by mass or less, more preferably 3.50% by mass or less, and even more preferably 3.00% by mass or less, the strength and rigidity of the aluminum alloy blank can be further improved. It should be noted that the lower limit of the Mg content is preferably 1.00% by mass.

[0050] ·Cr: less than 0.30% by mass

[0051] In the aluminum alloy, Cr may be present as an arbitrary component of less than 0.30% by mass. A portion of the Cr is dispersed within the aluminum alloy as fine intermetallic compounds generated during casting, thus increasing the rigidity of the aluminum alloy blank. Cr that does not become intermetallic compounds during the casting of the aluminum alloy dissolves in the Al matrix, thereby increasing the strength of the aluminum alloy blank through solid solution strengthening.

[0052] Furthermore, Cr can further improve the machinability and grindability of aluminum alloy blanks, and can make the recrystallized structure finer. As a result, it can further improve the adhesion between the aluminum alloy substrate and the Ni-P plating layer, and suppress the formation of plating pits.

[0053] However, if the Cr content in the aforementioned aluminum alloy is too high, coarse Al-Cr intermetallic compounds are easily formed in the aluminum alloy blank. When these coarse Al-Cr intermetallic compounds detach from the surface of the aluminum alloy blank, plating pits are easily formed during the subsequent electroless Ni-P plating process.

[0054] By setting the Cr content in the aforementioned aluminum alloy to 0.30% by mass or less, the rigidity and strength of the aluminum alloy blank can be further improved. Furthermore, the formation of plating pits can be more effectively suppressed, further improving the smoothness of the Ni-P plating layer. It should be noted that the lower limit of the Cr content is preferably 0.030% by mass.

[0055] • Zr: less than 0.15% by mass

[0056] In the aforementioned aluminum alloy, Zr can be present as an arbitrary component up to 0.15% by mass. A portion of the Zr is dispersed within the aluminum alloy blank as fine intermetallic compounds generated during the casting process, thus increasing rigidity. Zr that does not become intermetallic compounds during casting remains dissolved in the Al matrix, contributing to increased strength of the aluminum alloy blank through solid solution reinforcement.

[0057] Furthermore, Zr can further improve the machinability and grindability of aluminum alloy blanks, and can make the recrystallized structure finer. As a result, it can further improve the adhesion between the aluminum alloy substrate and the Ni-P plating layer, and can suppress the formation of plating pits.

[0058] However, if the Zr content in the aforementioned aluminum alloy is too high, coarse Al-Zr intermetallic compounds can easily form in the aluminum alloy blank. When these coarse Al-Zr intermetallic compounds detach from the surface of the aluminum alloy blank, plating pits can sometimes form during the subsequent electroless Ni-P plating process.

[0059] By setting the Zr content in the aforementioned aluminum alloy to below 0.15% by mass, the formation of plating pits can be suppressed, a smooth Ni-P plating layer can be formed, and the rigidity and strength of the aluminum alloy blank can be further improved. It should be noted that the lower limit of the Zr content is preferably 0.050% by mass.

[0060] •Si: less than 14.00% by mass

[0061] In the aforementioned aluminum alloys, Si can be present in any composition up to 14.00% by mass. Si mainly exists as second-phase particles (Si particles or Al-Fe-Si intermetallic compounds, etc.), which improve the rigidity and strength of the aluminum alloy blank.

[0062] However, if the Si content in the aforementioned aluminum alloy is too high, coarse particles or intermetallic compounds can easily form in the aluminum alloy blank. When these coarse particles or intermetallic compounds detach from the surface of the aluminum alloy blank, plating pits can sometimes form during the subsequent electroless Ni-P plating process.

[0063] By setting the Si content in the aforementioned aluminum alloy to below 14.00% by mass, the rigidity and strength of the aluminum alloy blank can be further improved. It should be noted that the lower limit of the Si content is preferably 0.10% by mass.

[0064] • Be: less than 0.0015% by mass

[0065] Be is an element added to the molten metal during the casting of Mg-containing aluminum alloys to suppress the oxidation of Mg. Furthermore, by containing less than 0.0015% by mass of Be in the aluminum alloy, the Zn film formed on the surface of the aluminum alloy substrate during disk manufacturing can be made denser, and thickness unevenness can be further reduced. As a result, the smoothness of the Ni-P treatment layer formed on the aluminum alloy substrate can be further improved.

[0066] However, if the Be content in the aforementioned aluminum alloy is excessive, Be-based oxides are easily formed on the surface of the aluminum alloy blank when it is heated during manufacturing. Furthermore, if the aluminum alloy further contains Mg, Al-Mg-Be-based oxides are easily formed on the surface of the blank when heated. If the amount of these oxides increases, the unevenness of the Zn coating thickness becomes greater, potentially leading to plating pits.

[0067] By setting the Be content in the aluminum alloy to preferably 0.0015% by mass or less, and more preferably 0.0010% by mass or less, the amount of Al-Mg-Be oxides can be reduced, thereby further improving the smoothness of the Ni-P plating layer.

[0068] • Sr, Na and P: less than 0.10% by mass

[0069] By including Sr, Na, and P in the aluminum alloy, the second-phase particles (mainly Si particles) in the aluminum alloy blank become finer, thus improving plating performance. Furthermore, it reduces the size inhomogeneity of the second-phase particles in the aluminum alloy blank, thereby reducing the inhomogeneity of the impact resistance properties. Therefore, one or more elements selected from the group consisting of preferably less than 0.10 wt% Sr, preferably less than 0.10 wt% Na, and preferably less than 0.10 wt% P can be selectively added to the aluminum alloy. However, even if the contents of Sr, Na, and P each exceed 0.10 wt%, the effect will saturate, and a more significant improvement cannot be obtained. Moreover, to achieve the above effects, it is more preferable that Sr, Na, and P are each 0.001 wt% or more.

[0070] Other elements

[0071] Aluminum alloys may contain elements that are unavoidable impurities, in addition to the necessary and optional components mentioned above. Examples of such elements include Ti, B, Si, and Ga. As long as their content is 0.05% by mass or less for each element and 0.15% by mass or less in total, the effectiveness of the invention will not be impaired. As described above, in the present invention, Si can be actively added as an optional component, but there are also cases where it is not actively added and is contained as an unavoidable impurity. Si is contained not only as an unavoidable impurity in raw metals of general purity but also as an unavoidable impurity in high-purity raw metals where the purity of Al is 99.9% or more. In the case of unavoidable impurity, as long as it is 0.100% by mass or less, the effectiveness of the invention will not be impaired. It should be noted that when Si is actively added as an optional component, as described above, from the viewpoint of further improving the rigidity and strength of the aluminum alloy blank, the Si content in the aluminum alloy is preferably 14.00% by mass or less.

[0072] Flatness variation of aluminum alloy blank

[0073] The flatness change (the absolute value of the difference between the flatness before and after holding) of the aluminum alloy blank according to the present invention when held at 50°C or below in the atmosphere for 336 hours is set to be 2.0 μm or less. By reducing the flatness change to 2.0 μm or less, convex defects can be reduced, and the surface smoothness can be improved. Aluminum alloy blanks with a flatness change exceeding 2.0 μm are prone to residual stress during surface cutting or grinding. Even during annealing after processing, the residual stress does not completely disappear. During sputtering, the residual stress is released, resulting in convex defects and reduced smoothness. Therefore, the flatness change of the aluminum alloy blank according to the present invention when held at 50°C or below in the atmosphere for 336 hours is 2.0 μm or less. It should be noted that the flatness change of the aluminum alloy blank is preferably 1.0 μm or less, more preferably 0.9 μm or less, and even more preferably 0.8 μm or less.

[0074] It should be noted that, in this invention, flatness is expressed as the difference between the maximum peak height and the maximum valley depth of the entire surface of the aluminum alloy blank. Here, the maximum peak height is the difference between the average line of the contour curve within the measurement range and the highest value within the measurement range, and the maximum valley depth is the difference between the average line and the lowest value within the measurement range. Figure 1 This is a graph showing the flatness of the aluminum alloy blank 2 within the aforementioned measurement range. (See figure.) Figure 1As shown, let Rx (mm) be the radius from the center 1 of the aluminum alloy blank 2 to its inner diameter, and Ry (mm) be the radius from the center 1 of the aluminum alloy blank 2 to its outer diameter. The area enclosed by the circles Rx+1 (mm) and Ry-1 (mm) is the measurement range. The aluminum alloy blanks used for flatness measurement are those obtained by storing each aluminum alloy blank at 0–50°C for less than one hour after peeling following pressure annealing. It should be noted that preliminary tests have confirmed that if the blanks are stored at 0–50°C for less than one hour after peeling following pressure annealing, the flatness change of the same aluminum alloy blanks held below 50°C for 336 hours is unaffected by temperature and shows the same value.

[0075] Crystal grain size

[0076] The surface grain size of the aluminum alloy blank involved in this invention is preferably 18 μm or less, more preferably 15 μm or less, even more preferably 12 μm or less, particularly preferably 11 μm or less, and even more preferably 10 μm or less. By reducing the grain size as described above, convex defects can be reduced. More specifically, aluminum alloy blanks with such small grain sizes as described above have increased deformation resistance due to increased grain boundaries, thus suppressing flatness variations. As a result, residual stress is less likely to be generated during surface cutting or grinding, and residual stress is also effectively reduced during post-processing annealing. During sputtering, convex defects are less likely to occur, and smoothness is improved. Therefore, the grain size is preferably 18 μm or less, more preferably 15 μm or less, even more preferably 12 μm or less, particularly preferably 11 μm or less, and even more preferably 10 μm or less.

[0077] A-2. Manufacturing methods for aluminum alloy sheets

[0078] (1) Casting process

[0079] Aluminum raw materials with a specified alloy composition are melted and smelted into molten metal, which is then cast to produce ingots. Casting methods include semi-continuous casting (DC casting), metal mold casting, and continuous casting (CC casting). In DC casting, molten metal injected through a spout is cooled by the bottom block, the water-cooled mold walls, and cooling water discharged directly to the outer periphery of the ingot (ingot), solidifying it and pulling it downwards as an ingot. In metal mold casting, molten metal injected into a hollow metal mold made of cast iron or similar materials is cooled by the mold walls, solidifying it into an ingot. In CC casting, molten metal is supplied through a casting nozzle between a pair of rollers (or a belt casting machine, block casting machine) and the rollers absorb heat (cooling) to directly cast thin sheets.

[0080] In the above casting process, it is preferable to perform degassing treatment to reduce dissolved gases in the molten metal and filtration treatment to remove solid substances from the molten metal online.

[0081] For degassing treatment, methods such as SNIF (Spinning Nozzle Inert Flotation) and Alpur (rotating nozzle inert gas flotation) can be used. In these processes, molten metal is stirred at high speed by a bladed rotating body while process gases such as argon or a mixture of argon and chlorine are blown in, forming microbubbles of the process gas within the molten metal. This allows for the removal of dissolved hydrogen or inclusions from the molten metal in a short time. In-line degassing devices can be used in this degassing process.

[0082] For filtration, methods such as cake filtration or filter media filtration can be used. Additionally, filters such as ceramic tube filters, ceramic foam filters, and alumina ball filters can be used in the filtration process.

[0083] (2) Homogenization process

[0084] Between the casting and hot rolling, the casting surface can be milled as needed to perform homogenization. The holding temperature during homogenization can be appropriately set from, for example, a range of 500 to 570°C. Furthermore, the holding time during homogenization can be appropriately set from, for example, a range of 1 to 60 hours.

[0085] (3) Hot rolling process

[0086] Next, the ingot is hot-rolled to produce a hot-rolled plate. There are no particular limitations on the hot rolling conditions, but for example, the starting temperature can be set in the range of 400 to 550°C and the ending temperature can be set in the range of 260 to 380°C.

[0087] (4) Cold rolling process

[0088] After hot rolling, a cold-rolled sheet can be obtained by cold rolling the hot-rolled sheet in one or more passes. The higher the total reduction rate of cold rolling, the smaller the crystal grain size; therefore, the total reduction rate of cold rolling is preferably set to 70% or more, more preferably 80% or more. There is no specific upper limit set for the total reduction rate of cold rolling; however, if the total reduction rate is too high, the cold rolling time becomes longer and the cost increases, so it is set to around 95%. Furthermore, the thickness of the cold-rolled sheet can be appropriately set, for example, from a range of 0.2 to 1.9 mm.

[0089] (5) Annealing process

[0090] In the manufacturing method described above, annealing can be performed as needed, either before the first cold rolling or between two cold rolling passes. Annealing can be performed using either a batch heat treatment furnace or a continuous heat treatment furnace. When using a batch heat treatment furnace, it is preferable to set the holding temperature during annealing to 250–430°C and the holding time to the range of 0.1–10 hours. Conversely, when using a continuous heat treatment furnace, it is preferable to set the furnace dwell time to within 60 seconds and the furnace temperature to 400–500°C. Annealing under these conditions restores the workability acquired during cold rolling.

[0091] The aluminum alloy sheet is produced through the above processes.

[0092] A-3. Manufacturing method of aluminum alloy substrate

[0093] The aforementioned aluminum alloy sheet is punched to produce a ring-shaped aluminum alloy blank. Subsequently, the aluminum alloy blank is subjected to pressure annealing by simultaneously heating and pressing it from both sides along its thickness direction. This reduces deformation and improves flatness. The holding temperature and pressure during pressure annealing can be appropriately selected from, for example, a range of 250–430°C and 1.0–3.0 MPa. Furthermore, the holding time during pressure annealing can be set to, for example, 30 minutes or more.

[0094] After pressure annealing, the individual aluminum alloy blanks are peeled off and then preferably stored in the atmosphere at a temperature range below -10°C. By storing them below -10°C before cutting and grinding, flatness variations in the blanks can be suppressed. By reducing flatness variations as described above, convex defects in the aluminum alloy blanks can be reduced, and surface smoothness can be improved. Aluminum alloy blanks with flatness variations greater than 2.0 μm are prone to generating residual stress during surface cutting or grinding. Even during annealing after processing, the residual stress does not completely disappear. When sputtering is performed, the residual stress is released, resulting in convex defects and reduced smoothness. Therefore, after peeling off the aluminum alloy blanks after pressure annealing, it is preferable to store them in the atmosphere at a temperature range below -10°C, more preferably below -20°C, and even more preferably below -25°C. There is no particular setting for the lower limit of the storage temperature; however, if the temperature is too low, the cost increases, so it is preferable to store them at -40°C or higher, more preferably at -38°C or higher, and even more preferably at -35°C or higher. It should be noted that the above-mentioned preservation process is different from the preservation of aluminum alloy blanks at 0-50°C for less than 1 hour during flatness measurement.

[0095] Next, the aluminum alloy blank is sequentially machined and ground to produce an aluminum alloy substrate with the desired shape. After these processes, a deformation-eliminating heat treatment is performed at 150–350°C for 0.1–10.0 hours to remove the deformation caused during processing.

[0096] The aluminum alloy substrate is produced through the above processes.

[0097] B. Disk

[0098] B-1. The Composition of a Disk

[0099] A disk having the aforementioned aluminum alloy substrate has, for example, the following configuration: The disk has an aluminum alloy substrate formed from an aluminum alloy blank, a Ni-P plating layer covering the surface of the aluminum alloy substrate, and a magnetic layer deposited on the Ni-P plating layer. It should be noted that the Ni-P plating layer is preferably an electroless Ni-P plating layer formed by an electroless plating process.

[0100] The disk may also have a protective layer formed of carbon-based materials such as diamond-like carbon and deposited on the magnetic layer, and a lubricating layer formed of lubricating oil and coated on the protective layer.

[0101] B-2. Disk Manufacturing Methods

[0102] When manufacturing disks from aluminum alloy substrates, the following method can be used, for example. First, the aluminum alloy substrate is degreased and cleaned to remove processing oils and other oils adhering to its surface. After degreasing and cleaning, the aluminum alloy substrate can be etched with acid if necessary. When etching is performed, it is preferable to perform a decontamination treatment to remove the stains generated by etching from the aluminum alloy substrate after etching. The processing conditions for these treatments can be appropriately set depending on the type of processing solution.

[0103] After these pre-plating treatments, a zincate treatment is performed to form a Zn film on the surface of the aluminum alloy substrate. In the zincate treatment, a Zn film is formed by zinc displacement plating, which replaces Al with Zn. Preferably, a double zincate method is used, where after the first zinc displacement plating, the Zn film formed on the surface of the aluminum alloy substrate is temporarily peeled off, and a second zinc displacement plating is performed to form a Zn film. According to the double zincate method, a denser Zn film can be formed on the surface of the aluminum alloy substrate compared to a Zn film formed solely by the first zinc displacement plating. As a result, defects in the Ni-P plating layer can be reduced in the subsequent electroless Ni-P plating process.

[0104] After forming a Zn film on the surface of an aluminum alloy substrate through zincate treatment, an electroless Ni-P plating process is performed, thereby replacing the Zn film with the Ni-P plating layer. Moreover, by replacing such a Zn film with a Ni-P plating layer in the electroless Ni-P plating process, a smooth Ni-P plating layer with fewer plating pits can be formed.

[0105] Increasing the thickness of the Ni-P plating layer tends to reduce plating pits, resulting in a smoother Ni-P plating layer. Therefore, the 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. It should be noted that in practical applications, the upper limit of the Ni-P plating layer thickness is approximately 40 μm.

[0106] After electroless Ni-P plating, polishing the Ni-P plating layer can further improve the surface smoothness of the Ni-P plating layer.

[0107] Following electroless Ni-P plating (including polishing), a magnetic material is attached to the Ni-P plating layer by sputtering to form a magnetic material layer. This magnetic material layer can consist of a single layer or multiple layers with different compositions. After sputtering, a protective layer made of a carbon-based material is formed on the magnetic material layer using CVD, if necessary. Next, a lubricating oil is applied to the protective layer to form a lubricating layer. Through these steps, a hard disk can be obtained.

[0108] Example

[0109] An aluminum alloy sheet, its manufacturing method, and examples of aluminum alloy coils made from the aluminum alloy sheet are described. It should be noted that the specific manner in which the aluminum alloy sheet, its manufacturing method, the aluminum alloy coil, and its manufacturing method are involved in this invention are not limited to the embodiments shown below. Without departing from the spirit of the invention, appropriate modifications can be made to the configuration based on the embodiments.

[0110] (1) Fabrication of aluminum alloy sheets

[0111] The aluminum alloy sheets used for evaluation in each example were produced using the following method. First, molten metal with the chemical composition shown in Table 1 was prepared in a furnace.

[0112] Next, the molten metal in the furnace is transferred to form an ingot using the casting method shown in Table 2. The surface of the ingot is then milled to remove the segregation layer present on the surface. After milling, the ingot is homogenized by heat treatment under the conditions shown in Table 2. Next, hot rolling is performed under the conditions shown in Table 2 to obtain a hot-rolled sheet. Finally, cold rolling is performed under the conditions shown in Table 2 to obtain an aluminum alloy sheet.

[0113] (2) Fabrication of aluminum alloy blanks

[0114] The aforementioned aluminum alloy sheet was punched to obtain a ring-shaped aluminum alloy blank with an outer diameter of 98 mm and an inner diameter of 24 mm. Next, the obtained aluminum alloy blank was subjected to pressure annealing by applying pressure from both sides in the thickness direction and holding it at the temperatures shown in Table 2 for 3 hours. Then, the aluminum alloy blank was stored under the conditions shown in Table 2. Test materials for various examples of aluminum alloy blanks were prepared as described above.

[0115] The evaluation methods for each test material are described below. It should be noted that B3, due to its low Fe content and low strength, is prone to deformation during peeling after pressure annealing and cannot be used as an aluminum alloy coil; therefore, it was not evaluated. Additionally, B4, due to its high Fe content and high strength, develops cracks during rolling and cannot be used as an aluminum alloy coil; therefore, it was not evaluated.

[0116] Methods for determining crystal grain size

[0117] First, for grain size analysis, a glow discharge spectrophotometer (GDS, JY5000RF, HORIBA) was used to sputter the rolled surface of the aluminum alloy billet used for microstructure observation for 60 seconds at a gas pressure of 400 Pa and an output power of 30 W. On the sputtered surface, the orientation information of the texture was obtained by measuring the electron backscatter diffraction (SEM-EBSD) on the attached scanning electron microscope. The measurement area of ​​the sample was set to 1000 μm × 1000 μm. For the measurement step interval, a step interval of 3 μm was set for grain sizes above 12 μm, a step interval of 2 μm was set for grain sizes above 8 μm but less than 12 μm, and a step interval of approximately 1 / 4 was set for grain sizes less than 8 μm.

[0118] Based on the obtained orientation data, the grain size was determined using EBSD analysis software ("OIM Analysis" manufactured by TSL Corporation). At this point, grain boundaries with an orientation difference (misorientation) of 5° or more were considered grain boundaries, and the diameter calculated as the equivalent circle was set as the grain size.

[0119] • Investigation of flatness changes

[0120] First, for aluminum alloy blanks that underwent pressure annealing as described above and were stored as appropriate, flatness was measured within one hour after peeling. Then, the aluminum alloy blanks were placed flat on a platform or similar surface and placed at the temperatures and times shown in Table 2. Flatness was measured again, and the absolute value of the difference in flatness before and after placement, i.e., {(flatness before placement below 50°C for 336 hours) - (flatness after placement below 50°C for 336 hours)}, was calculated as the flatness change. It should be noted that the meaning of flatness is as described above. Furthermore, flatness was measured using a flatness measuring machine (MESA) manufactured by ZyGO Corporation. When the flatness change was less than 2 μm, the vibration evaluation was A (excellent); when it exceeded 2 μm, the vibration evaluation was D (poor). The results are shown in Table 2. It should be noted that "-" in Table 2 indicates that no treatment or evaluation was performed.

[0121] Table 1

[0122]

[0123] Table 2

[0124]

[0125] As shown in Tables 1 and 2, test materials A1 to A12 have the chemical composition of the present invention, and the flatness change of the blank when the blank is kept at 50°C or below for 336 hours in the atmosphere is less than 2.0 μm. Therefore, these test materials can improve surface smoothness.

[0126] For test materials B1 and B2, the flatness change of the coils after being kept at below 50°C for 336 hours in the atmosphere exceeded 2.0 μm. Therefore, convex defects are easily generated, and the smoothness is reduced.

[0127] Symbol Explanation

[0128] 1. Center of aluminum alloy blank

[0129] 2 aluminum alloy blanks

Claims

1. An aluminum alloy disc blank for magnetic discs, characterized by comprising, in mass %, The aluminum alloy contains one or two or more elements selected from the group consisting of Mn: 0.01 mass% or more and 1.80 mass% or less, Ni: 0.01 mass% or more and 2.50 mass% or less, Cu: 0.005 mass% or more and 1.00 mass% or less, Zn: 0.10 mass% or more and 0.70 mass% or less, Mg: 1.00 mass% or more and 4.50 mass% or less, Cr: 0.030 mass% or more and 0.30 mass% or less, Zr: 0.050 mass% or more and 0.15 mass% or less, Si: 0.10 mass% or more and 14.00 mass% or less, Be: 0.0015 mass% or less, Sr: 0.001 mass% or more and 0.10 mass% or less, Na: 0.001 mass% or more and 0.10 mass% or less, and P: 0.001 mass% or more and 0.10 mass% or less, with the balance consisting of Al and unavoidable impurities.

2. The aluminum alloy disc blank for magnetic discs according to claim 1, wherein, The aluminum alloy contains one or two or more elements selected from the group consisting of Mn: 0.01 mass% or more and 1.80 mass% or less, Ni: 0.01 mass% or more and 2.50 mass% or less, Cu: 0.005 mass% or more and 1.00 mass% or less, Zn: 0.10 mass% or more and 0.70 mass% or less, Mg: 1.00 mass% or more and 4.50 mass% or less, Cr: 0.030 mass% or more and 0.30 mass% or less, Zr: 0.050 mass% or more and 0.15 mass% or less, Si: 0.10 mass% or more and 14.00 mass% or less, Be: 0.0015 mass% or less, Sr: 0.001 mass% or more and 0.10 mass% or less, Na: 0.001 mass% or more and 0.10 mass% or less, and P: 0.001 mass% or more and 0.10 mass% or less.

3. The aluminum alloy disc blank for magnetic discs according to claim 1 or 2, characterized by The crystal grain size of the surface of the aluminum alloy substrate formed from the aluminum alloy disk blank of any one of claims 1 to 7 is 18 μm or less.

4. The aluminum alloy disc blank for magnetic discs according to claim 1 or 2, characterized by The crystal grain size of the surface of the aluminum alloy substrate formed from the aluminum alloy disk blank of any one of claims 1 to 7 is 15 μm or less.

5. The aluminum alloy disc blank for magnetic discs according to claim 1 or 2, characterized by The crystal grain size of the surface of the aluminum alloy substrate formed from the aluminum alloy disk blank of any one of claims 1 to 7 is 12 μm or less.

6. The aluminum alloy disc blank for magnetic discs according to claim 1 or 2, characterized by The crystal grain size of the surface of the aluminum alloy substrate formed from the aluminum alloy disk blank of any one of claims 1 to 7 is 11 μm or less.

7. The aluminum alloy disc blank for magnetic discs according to claim 1 or 2, characterized by The crystal grain size of the surface of the aluminum alloy substrate formed from the aluminum alloy disk blank of any one of claims 1 to 7 is 10 μm or less.

8. A magnetic disc, characterized by The surface of an aluminum alloy substrate formed from the aluminum alloy disk blank of any one of claims 1 to 7 has a Ni-P plating treatment layer and a magnetic body layer on the Ni-P plating treatment layer.

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