Method for recycling aluminum alloy substrate, method for manufacturing magnetic disk, magnetic disk, and hard disk drive

Abstract

To provide a recycling method for an aluminum alloy substrate having superior recyclability and enabling film removal in a simple and reliable manner.SOLUTION: This recycling method for an aluminum alloy substrate comprises a film removal step of applying physical processing to a recycled material, which has an aluminum alloy substrate and at least one film layer on the aluminum alloy substrate, thereby removing the film from the recycled material to provide an aluminum alloy material.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for recycling an aluminum alloy substrate, a method for manufacturing a magnetic disk, a magnetic disk, and a hard disk drive.

Background Art

[0002] Hard disk drives (HDDs) are widely used as storage devices in various electronic devices, including computers and data centers. In an HDD, a magnetic disk is responsible for storing information, and an aluminum alloy substrate for magnetic disks is used as the substrate of the magnetic disk. As the aluminum alloy substrate for magnetic disks, an aluminum alloy substrate made of JIS 5086 alloy (including 3.5 mass% or more and 4.5 mass% or less of Mg, 0.50 mass% or less of Fe, 0.40 mass% or less of Si, 0.20 mass% or more and 0.70 mass% or less of Mn, 0.05 mass% or more and 0.25 mass% or less of Cr, 0.10 mass% or less of Cu, 0.15 mass% or less of Ti, 0.25 mass% or less of Zn, with the balance being Al and inevitable impurities) having good plating properties and excellent mechanical properties and workability is used. In one example, it is manufactured in a process of subjecting the aluminum alloy substrate to electroless Ni-P plating treatment and then polishing the surface smoothly.

[0003] For example, an aluminum alloy substrate for a magnetic disk using a JIS5086 alloy is manufactured by the following manufacturing process. First, an aluminum alloy containing a desired chemical composition is cast, the ingot is homogenized, then hot-rolled, and then cold-rolled to produce a rolled material with the thickness required for a magnetic disk. It is preferable to anneal this rolled material during the cold rolling process as needed. Next, this rolled material is punched into an annular shape to form an annular disk blank. To remove the strain and the like generated during the manufacturing process, the annular disk blanks are stacked, and pressure annealing is performed while applying pressure from both sides to flatten them. The annular disk blank thus produced is subjected to cutting, grinding, degreasing, etching, and zincate treatment (Zn substitution treatment) as pretreatment, and then Ni-P electroless plating treatment, which is a hard non-magnetic metal, is performed as a base treatment. After polishing the surface subjected to the Ni-P plating treatment, a magnetic material is sputtered to form a magnetic material layer, thereby manufacturing an aluminum alloy substrate for a magnetic disk.

[0004] In recent years, with the development of cloud services, the construction of new data centers and the replacement of existing data centers with large-capacity HDDs have been actively progressing. Given such current circumstances, increasing the capacity of HDDs has become essential. To increase the capacity of HDDs, it is important to increase the number of magnetic disks installed and the capacity per magnetic disk. In the former case, it is necessary to reduce the thickness of the magnetic disk, and in the latter case, it is necessary to reduce the defects on the Ni-P plated surface of the aluminum alloy substrate for the magnetic disk. Although both of the above methods are technically possible, performing these methods will result in a poor yield in the manufacturing process of the magnetic disk. Specifically, for the former, when the magnetic disk is made thinner, higher processing accuracy is required in rolling, grinding, etc., and for the latter, the threshold for the number of defects on the Ni-P surface becomes stricter. That is, the number of defective aluminum alloy substrates for magnetic disks will increase, and it is easily predicted that the number of defective products of aluminum alloy substrates for magnetic disks will increase in consideration of future demand for magnetic disks.

[0005] In recent years, due to the increasing interest in environmental protection, it has become essential to establish recycling technologies for metal products. Also, it has become clear that geopolitical risks are emerging with respect to the types of metals. Although aluminum is a metal that is relatively easy to recycle, the difficulty of recycling varies depending on its alloy system. For example, in the case of aluminum can materials, the same alloy can be collected as raw material, and thus it can be easily made into aluminum can materials again. However, the aluminum clad material used for heat exchanger materials has a multilayer structure of aluminum alloys with different compositions, and it is impossible to separate each layer. For this reason, it is necessary to remelt and cast the entire aluminum clad material, and since it changes from the original alloy composition during remelting and casting, the range of use after recycling may be limited.

[0006] On the other hand, aluminum alloys for magnetic disks are high-cost materials that use a large amount of high-purity ingots for the purpose of improving plating defects and limit the contents of Fe, Si, etc. Therefore, by recycling as much as possible, it becomes possible to reduce the amount of high-purity ingots used. As a result, the amount of high-purity ingots produced can be reduced, which can contribute at least somewhat to environmental protection.

[0007] In the manufacturing process of an aluminum alloy substrate for magnetic disks, if the aluminum alloy substrate for magnetic disks does not meet the predetermined standards due to rolling, grinding, etc. and becomes a defective product, it can be reused as part of the raw material as it is. However, if a defective product occurs in the state of an aluminum alloy substrate for magnetic disks with a film such as a Ni-P plating layer formed on the surface, its recycling becomes complicated. That is, since a film such as a Ni-P plating layer is applied to the aluminum alloy substrate for magnetic disks, for example, it can be used as a casting alloy such as the housing of an HDD. On the other hand, as described above, recycling an aluminum alloy that uses a large amount of high-purity ingots as a casting is not good in terms of recycling efficiency, and it is desired to recycle it as a rolled material, preferably as an aluminum alloy for magnetic disks again.

[0008] Against such a background, there is a demand for the establishment of techniques for separating films such as Ni-P plating layers from aluminum alloys and for recovering aluminum alloy substrates. For example, Patent Document 1 discloses a technique for reusing an aluminum alloy substrate with Ni-P plating as a raw material for an Al-Si alloy. Although this technique enables the reuse of the aluminum alloy substrate, it is difficult to efficiently use an aluminum alloy substrate made of high-purity ingot.

[0009] Patent Document 2 discloses a technique for returning a substrate after removing the Ni-P plating layer to the plating process again for reuse. This technique enables the recycled aluminum alloy substrate to be reused. However, in recent years, the requirements for defects on the Ni-P plated surface of aluminum alloy substrates for magnetic disks have become extremely strict. If an aluminum alloy substrate with the Ni-P plating layer peeled off is reused as it is, the plating process is applied to the aluminum alloy substrate in a state where the surface has been damaged, so there is a possibility that defects on the plating surface will occur frequently.

[0010] As described above, in the prior art, it is impossible to reuse the aluminum alloy substrate while maintaining high quality, and it has been difficult to reuse the aluminum alloy substrate for magnetic disks that require high quality in recent years.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0012] The present invention has been made in view of the above circumstances, and an object thereof is to provide a recycling method for an aluminum alloy substrate that is excellent in recyclability and can simply and surely remove a film.

Means for Solving the Problems

[0013] The inventors of the present invention have found that by subjecting a recycling material having an aluminum alloy substrate and at least one layer of film to physical processing, an aluminum alloy substrate with the film completely removed can be obtained, and thus the present invention has been completed.

[0014] The recycling method for an aluminum alloy substrate according to an embodiment of the present invention includes a film removal step of removing a film from a recycling material by subjecting a recycling material having an aluminum alloy substrate and at least one layer of film on the aluminum alloy substrate to physical processing to obtain an aluminum alloy material.

Effects of the Invention

[0015] According to the present invention, it is possible to provide a recycling method for an aluminum alloy substrate that is excellent in recyclability and can simply and surely remove a film.

Modes for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described in detail.

[0017] 1. Recycling Method for Aluminum Alloy Substrate The recycling method for an aluminum alloy substrate in the present invention is (a) including a film removal step of removing a film from a recycling material by subjecting a recycling material having an aluminum alloy substrate and at least one layer of film on the aluminum alloy substrate to physical processing to obtain an aluminum alloy material.

[0018] In the method for recycling an aluminum alloy substrate of the present invention, in the film removal step, the recycling material is physically processed to remove the film from the recycling material, thereby producing an aluminum alloy material. Thus, since the film is removed by physical processing, the film can be easily and surely removed from the aluminum alloy substrate. Further, since the film is completely removed from the aluminum alloy substrate by such physical processing, a method for recycling an aluminum alloy substrate excellent in recyclability can be provided.

[0019] Furthermore, in the prior art, although an aluminum alloy substrate with Ni-P plating can be reused as a raw material for an Al-Si alloy, the use of the raw material is limited, and it has not been possible to efficiently recycle an aluminum alloy substrate containing high-purity ingots. Also, since the aluminum alloy substrate with the film removed is recycled as it is and a film such as a Ni-P plating layer is formed on the aluminum alloy substrate, defects may occur on the film of the aluminum alloy substrate. In contrast, in the method for recycling an aluminum alloy substrate of the present invention, the aluminum alloy material obtained by removing the film is reused, for example, as a raw material for the molten aluminum alloy in the method for manufacturing a magnetic disk described later, and using the molten metal, a new aluminum alloy plate can be manufactured through casting, heat treatment, and rolling processes. Therefore, even if a film such as a Ni-P plating layer is formed using the newly manufactured aluminum alloy plate, defects on the film can be suppressed. Also, since it is possible to reduce the amount of expensive high-purity ingots used while maintaining the performance of the aluminum alloy plate, cost reduction can be achieved.

[0020] (Recycling material) The "recycled material" used in the present invention is a material having an aluminum alloy substrate and a film on the aluminum alloy substrate. Examples of the recycled material include intermediate materials and finished products generated during the manufacturing process of magnetic disks. Examples of the "intermediate material" correspond to an aluminum alloy substrate for magnetic disks, and examples of the "finished product" correspond to magnetic disks. These recycled materials include defective products, out-of-specification products, and used magnetic disks if they are magnetic disks. The "film" is not particularly limited as long as it is one or more layers formed on the aluminum alloy substrate, and examples thereof include Ni-P plating layers, magnetic layers, protective layers, lubricating layers, and the like. Among such films, for example, in the intermediate materials and finished products described later, the film formed on the aluminum alloy substrate includes a film containing Ni, specifically, a Ni-P plating layer.

[0021] The shape of the recycled material is not particularly limited, and it may be an annular shape, a polygonal shape, or an irregular shape without a specific shape. Since there are many annular disks as recycled materials, it is easy to procure annular recycled materials. In addition, the annular recycled material can be used in a bent state, a perforated state, or a cut state, and it is easy to efficiently remove the film without changing the processing conditions each time. Therefore, the aluminum alloy substrate constituting the recycled material is preferably annular. In the method for recycling the aluminum alloy substrate of the present invention, the aluminum alloy material obtained by the film removal step is used as at least part of the raw material, and only the aluminum alloy material may be used as the raw material, or other materials and elements may be used as the raw material together with the aluminum alloy material.

[0022] (Intermediate material) Examples of the intermediate material include aluminum alloy substrates for magnetic disks generated during the manufacturing process of magnetic disks. In one example, a film containing Ni such as a Ni-P plating layer is formed on the surface of the aluminum alloy substrate for magnetic disks. The Ni content in the film containing Ni used for the aluminum alloy substrate for magnetic disks is, for example, 80% by mass or more and 95% by mass or less. Further, when the film containing Ni is a Ni-P plating layer, the P content contained in the Ni-P plating layer is, for example, 5% by mass or more and 20% by mass or less. Further, the thickness of the film containing Ni is not particularly limited, but for example, it is 3 μm or more and 25 μm or less. In this case, the thickness of the aluminum alloy substrate for magnetic disks is, for example, 0.3 mm or more and 2.0 mm or less.

[0023] (Finished product) Examples of the finished product include magnetic disks. In one example of a magnetic disk, a Ni-P plating layer, a CoCrPt-based magnetic layer, a protective layer such as a carbon-based material, etc. are sequentially formed as films on the surface of the aluminum alloy substrate for magnetic disks. Since these magnetic layers and protective layers are formed on the Ni-P plating layer, by removing the Ni-P plating layer, these magnetic layers and protective layers can also be removed together. Therefore, the aluminum alloy material obtained by removing the film from the magnetic disk, which is the finished product, can also be used as at least part of the raw material.

[0024] As described above, the method for recycling the aluminum alloy substrate of the present invention has the following step (a) as the film removal step. Hereinafter, step (a) will be described in detail.

[0025] (a) Film removal step In the film removal process, the film is removed from the recycled material. As a treatment method for removing the film, physical processing is performed on the recycled material. As described above, since there are many annular disks in the recycled material, the film formed on the surface of the recycled material of such a shape exists on all surfaces of both sides, the inner diameter, and the outer diameter of the recycled material. In order to surely remove the film formed on the entire surface of the recycled material, physical processing is effective. Also, in the film removal process, the removal of the film from the recycled material is intended to completely remove the film, and partial or incomplete removal of the film is not included.

[0026] Examples of physical processing include a method of cutting the surface and end face of the recycled material using a lathe, or a combination of a method of grinding the surface of the recycled material using a grinding wheel and a method of cutting the end face of the recycled material using a lathe. When the aluminum alloy substrate constituting the recycled material is annular, the surface of the recycled material means both sides (both main surfaces) of the recycled material, and the end face of the recycled material means the side surface on the inner diameter side and the side surface on the outer diameter side. Cutting and grinding are also performed in the process of obtaining the aluminum alloy substrate for plating from the annular disk blank when manufacturing a magnetic disk according to a general manufacturing method. By performing such mechanical processing as physical processing, it is possible to easily remove the film simply without the need to use any particularly new or complicated equipment.

[0027] In cutting, various types of cutting tools can be used, such as a cutting tool in which a cutting edge is formed so as to be able to cut a part of the surface and end face of the recycled material, and a full-profile tool in which a cutting edge is formed along the shape of the end face of the recycled material. The shape of the cutting tool is not particularly limited as long as it is set so as to be able to remove a film having a certain depth.

[0028] In grinding, both sides of the recycled material are sandwiched between grinding wheels, pressure is applied, and they are slid. The grinding wheels can have their roughness selected. Although the grinding speed improves as the roughness increases, the surface roughness of the aluminum alloy material obtained by the grinding process increases. On the other hand, although the grinding speed decreases as the roughness of the grinding wheel decreases, the surface of the aluminum alloy material obtained by the grinding process becomes smoother. In the grinding process, since the surface roughness of the obtained aluminum alloy material is irrelevant and the purpose is to remove the film, the larger the roughness of the grinding wheel, the more efficiently the film can be removed.

[0029] In physical processing, the depth by which the surface and end faces of the recycled material are cut (hereinafter, also referred to as "processing amount") is preferably 1.05 times or more, more preferably 1.1 times or more, the thickness of the film. By making the processing amount 5% or more thicker than the thickness of the film, the film can be completely removed. Incidentally, with respect to the above-mentioned processing amount, if only one of the surface and end faces of the recycled material is satisfied, a part of the film remains in the recycled material, and by satisfying both the surface and end faces of the cycle material, the film is completely removed. For example, when performing cutting as physical processing, the depth of cutting corresponds to the processing amount, and when performing grinding as physical processing, the depth of grinding corresponds to the processing amount. Further, the upper limit of the above-mentioned processing amount is preferably 2.2 times or less, more preferably 2.0 times or less, in order to prevent the surface of the aluminum alloy substrate from being excessively cut.

[0030] 2. Method for manufacturing a magnetic disk The method for manufacturing a magnetic disk of the present invention is (b) A step of preparing a molten aluminum alloy using, as at least a part of the raw material, the aluminum alloy material obtained by the film removal step of the above-described recycling method of the aluminum alloy substrate, (c) A step of heating and holding the prepared molten metal, (d) A step of casting the heated and held molten metal to obtain an aluminum alloy ingot, (e) A step of heating the aluminum alloy ingot to perform a homogenization treatment, (f) A rolling step of rolling a homogenized aluminum alloy ingot into an aluminum alloy plate; (g) A step of pressure flattening the aluminum alloy plate obtained by the rolling step into an annular disk blank; (h) A step of subjecting the pressure-flattened annular disk blank to cutting and grinding to obtain an aluminum alloy substrate for plating; (i) A pre-plating treatment step of subjecting the aluminum alloy substrate for plating to degreasing, etching, and zincate treatment; (j) A step of subjecting the surface of the aluminum alloy substrate subjected to pre-plating treatment to electroless Ni-P plating treatment, and then polishing the surface subjected to Ni-P plating treatment to obtain an aluminum alloy substrate for a magnetic disk; (k) A step of forming a magnetic layer by attaching a magnetic material to the surface of the aluminum alloy substrate for a magnetic disk; It has.

[0031] As described above, the method for manufacturing a magnetic disk of the present invention has steps (b) to (k). Hereinafter, each of steps (b) to (k) will be described in detail.

[0032] (b) A step of preparing a molten aluminum alloy Next, a molten aluminum alloy is prepared using at least a part of the aluminum alloy material obtained in the film removal step as a raw material. The content of each element in the molten metal prepared in step (b) is described below.

[0033] · Ni (nickel) content The Ni content in the molten aluminum alloy is preferably 0% by mass or more and 2.5% by mass or less. Since Ni combines with aluminum (Al) etc. to form an Al-Ni based compound and causes large defects on the plating surface, it is useful to reduce the Ni content. The Ni content in the molten metal is preferably 2.5% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less. Adjustment of the Ni content is carried out in the process of preparing the molten aluminum alloy by heating and melting the raw materials. For example, after the raw materials in the molten metal are completely melted, the components of the molten metal are analyzed, and when the Ni content is high, an aluminum alloy ingot etc. is added to adjust to the desired Ni content.

[0034] ·P (phosphorus) content The P content in the molten aluminum alloy is preferably 0% by mass or more and 0.05% by mass or less. P is contained in aluminum alloy ingots etc., but it combines with Mg (magnesium) generally contained in the aluminum alloy of the molten metal raw materials to form an Mg-P based oxide, and during the plating process, the reaction becomes non-uniform only in that part, and large defects may occur on the plating surface. As a result, the smoothness of the plating surface decreases. Although a part of the Mg-P based oxide can be removed by floating on the surface of the molten metal by heating and holding the molten metal, it is preferable that the content of P itself that combines with Mg is low. The P content in the molten metal is preferably 0.05% by mass or less, and more preferably 0.01% by mass or less. Since the P content in the molten metal is extremely small compared to the Ni content, it is generally not necessary to add an aluminum alloy ingot etc. to adjust to the desired content. However, when adjustment is necessary, like Ni, an aluminum ingot etc. is added to adjust to the desired content.

[0035] ·Mg (magnesium) content The Mg content in the molten aluminum alloy is preferably 0 mass% or more and 6.5 mass% or less. As described above, since Mg combines with P in the molten metal to form Mg-P-based oxides, it is preferable that the content thereof is low as with P. The Mg content in the molten metal is preferably 6.5 mass% or less, more preferably 4.5 mass% or less. When the Mg content is high, aluminum alloy ingots or the like are added as with Ni and adjusted to a desired content.

[0036] · Metal components in the molten aluminum alloy Regarding the metal components contained in the molten aluminum alloy, as described above, it is preferable to adjust the contents of Ni, P itself, and elements such as Mg that form intermetallic compounds with P.

[0037] On the other hand, elements other than Ni, P, and Mg and their contents are not particularly limited. Examples of the alloy composition contained in the molten aluminum alloy include the following. The aluminum alloy contains Fe (iron) and optionally Mn (manganese), and the total content of these Fe and Mn is in the range of 0.005 mass% or more and 7.00 mass% or less. Further, it contains 0.5 mass% or more and 6.5 mass% or less of Mg, and optionally, 0 mass% or more and 1.0 mass% or less of Si (silicon), 0 mass% or more and 0.7 mass% or less of Zn (zinc), 0 mass% or more and 0.30 mass% or less of Cr (chromium), 0 mass% or more and 1.0 mass% or less of Cu (copper), and 0 mass or more and 0.20 mass% or less of Zr (zirconia). It contains one or more metals selected from the group consisting of, and the balance consists of Al, inevitable impurities, and other trace components.

[0038] Examples of inevitable impurities include Ti (titanium), Ga (gallium), etc. contained in the aluminum alloy, and examples of other trace components include Co (cobalt), Pt (platinum), etc. As long as the contents of these inevitable impurities and other trace components are 0.10 mass% or less for each element and 0.30 mass% or less in total, the effects of the present invention are not impaired.

[0039] (c) Step of heating and holding the molten metal Next, the molten metal of the aluminum alloy is heated and held. In this step, the molten metal of the aluminum alloy is heated and held by a holding furnace. At this time, it is preferable to remove the oxide film floating on the surface of the molten metal outside the furnace. By removing this floating oxide film by means such as skimming before casting the aluminum alloy, the contents of Ni and P in the molten metal can be reduced. At that time, it is preferable to remove the oxide film outside the furnace as quickly as possible.

[0040] (d) Step of casting the molten metal to obtain an aluminum alloy ingot Next, the molten metal is cast to obtain an aluminum alloy ingot. The molten metal of the aluminum alloy that has been heated and held is cast into an aluminum alloy ingot by a semi - continuous casting method (DC casting method), die casting method, continuous casting method (CC method), etc. after in - line degassing treatment and in - line filtration treatment described later as necessary. In the DC casting method, the molten metal poured through the spout is deprived of heat 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), solidifies, and is pulled downward as a cast ingot. In the die casting method, the molten metal poured into a hollow mold made of cast iron or the like is deprived of heat by the wall of the mold and solidifies to produce a cast ingot. In the CC casting method, the molten metal is supplied through a casting nozzle between a pair of rolls (or a belt caster, block caster), and a thin plate is directly cast by heat extraction from the rolls.

[0041] In the step of heating and holding the molten metal, it is preferable that the molten metal heated and held is subjected to in-line degassing treatment and in-line filtration treatment according to a conventional method before being subjected to the casting process. As the in-line degassing treatment device, commercially available degassing devices under trademarks such as SNIF and ALPUR can be used. These in-line degassing treatment devices rotate a rotator with blades at high speed while blowing argon gas or a mixed gas of argon and nitrogen etc. into the molten metal to supply the gas into the molten metal as fine bubbles. Thereby, dehydrogen gas and inclusions can be removed in-line in a short time. As the in-line filtration treatment, a ceramic tube filter, a ceramic foam filter, an alumina ball filter etc. are used, and inclusions are removed by a cake filtration mechanism, a filter medium filtration mechanism etc.

[0042] (e) Step of heating the aluminum alloy ingot to perform homogenization treatment Next, the aluminum alloy ingot obtained as described above is heated to perform homogenization treatment. In the homogenization treatment, the aluminum alloy ingot is preferably heated under the conditions of a heating temperature of 480 °C or higher and 560 °C or lower for 1 hour or longer, more preferably a heating temperature of 500 °C or higher and 550 °C or lower for 2 hours or longer. When the heating temperature is less than 480 °C or the heating time is less than 1 hour, a sufficient homogenization effect may not be obtained. Also, at a heating temperature exceeding 560 °C, the aluminum alloy ingot may melt. Also, the upper limit of the heating time is not particularly limited, but even if it exceeds 48 hours, the homogenization effect may saturate and there is a risk of causing a decrease in productivity.

[0043] (f) Rolling process Next, in the rolling process, the homogenized aluminum alloy ingot is rolled into an aluminum alloy plate. In the rolling process, rolling can be performed once or multiple times, and cold rolling and hot rolling can be carried out as the rolling treatment. In one example, the homogenized aluminum alloy ingot is used to produce a hot-rolled plate by hot rolling. The conditions for hot rolling are not particularly limited, but the hot rolling start temperature is preferably 300°C or higher and 500°C or lower, and more preferably 320°C or higher and 480°C or lower. Also, the hot rolling end temperature is preferably 260°C or higher and 400°C or lower, and more preferably 280°C or higher and 380°C or lower. If the hot rolling start temperature is less than 300°C, the workability by hot rolling cannot be ensured. If it exceeds 500°C, the crystal grains become coarser, and the adhesion of the Ni-P plating layer formed in the subsequent process may decrease. Also, if the hot rolling end temperature is less than 260°C, the workability by hot rolling cannot be ensured. If it exceeds 400°C, the crystal grains become coarser, and the adhesion of the Ni-P plating layer formed in the subsequent process may decrease. In hot rolling, usually, the ingot is heated and held at the hot rolling start temperature for 0.5 hours or more and 10.0 hours or less, and then hot rolling is performed.

[0044] In one example, next, the obtained hot-rolled plate is cold-rolled to produce a cold-rolled plate preferably having a thickness of 0.4 mm or more and 2.0 mm or less, more preferably 0.6 mm or more and 2.0 mm or less. That is, after the hot rolling is completed, it is finished to the required product plate thickness by cold rolling. The conditions for cold rolling are not particularly limited, but they may be determined according to the required plate strength and plate thickness of the aluminum alloy plate. The rolling ratio is preferably 20% or more and 90% or less, and more preferably 20% or more and 80% or less. If this rolling ratio is less than 20%, the crystal grains become coarser in the pressure flattening annealing of the disk blank described later, and the adhesion of the Ni-P plating layer formed in the subsequent process may decrease. On the other hand, if this rolling ratio exceeds 90%, the manufacturing time becomes long, and there is a risk of reducing productivity.

[0045] In order to ensure good cold rolling workability, annealing may be optionally performed before or during cold rolling. When annealing is performed, for example, in batch annealing, it is preferably carried out under the conditions of an annealing temperature of 300°C or higher and 450°C or lower for 0.1 hour or more and 10 hours or less, and more preferably under the conditions of an annealing temperature of 300°C or higher and 380°C or lower for 1 hour or more and 5 hours or less. If the annealing temperature is less than 300°C and / or the annealing time is less than 0.1 hour, a sufficient annealing effect may not be obtained. Further, when the annealing temperature exceeds 450°C, the crystal grains may coarsen and the adhesion of the Ni-P plating layer formed in the subsequent process may decrease. When the annealing time exceeds 10 hours, the manufacturing time may become long and there is a risk of causing a decrease in productivity.

[0046] On the other hand, in continuous annealing, it is preferably carried out under the conditions of an annealing temperature of 400°C or higher and 500°C or lower and a holding time of 60 seconds or less, and more preferably under the conditions of an annealing temperature of 450°C or higher and 500°C or lower and a holding time of 30 seconds or less. If the annealing temperature is less than 400°C, a sufficient annealing effect may not be obtained. When the annealing temperature exceeds 500°C, the crystal grains may coarsen and the adhesion of the Ni-P plating layer formed in the subsequent process may decrease. Further, when the holding time exceeds 60 seconds, the crystal grains may coarsen and the adhesion of the Ni-P plating layer formed in the subsequent process may decrease. Incidentally, cooling may be started immediately after reaching the desired annealing temperature.

[0047] An aluminum alloy sheet is produced by the above respective steps.

[0048] In the above steps (b) to (f), when preparing the molten aluminum alloy, by adding an arbitrary material, element, aluminum alloy ingot, etc. into the molten metal, an aluminum alloy sheet having a desired alloy composition can be manufactured. Further, by setting the conditions for heating and holding the molten metal, manufacturing the aluminum alloy ingot from the molten metal, homogenizing the aluminum alloy ingot, and rolling the aluminum alloy ingot to predetermined conditions, the properties and characteristics of the rolled aluminum alloy sheet can be set to desired properties and characteristics different from those of recycled materials.

[0049] (g) Step of pressure flattening an aluminum alloy plate into an annular disk blank The aluminum alloy plate obtained by the rolling step of the recycling method of the aluminum alloy substrate as described above is punched into an annular shape to produce an annular disk blank. In one example, the annular disk blank is subjected to pressure annealing at a temperature of 300°C or higher and 450°C or lower for 30 minutes or longer, preferably at a temperature of 300°C or higher and 380°C or lower for 60 minutes or longer in the atmosphere to produce a flattened annular disk blank. If the treatment temperature of the pressure annealing is less than 300°C and / or the treatment time is less than 30 minutes, the flattening effect may not be sufficiently obtained. Further, if the treatment temperature exceeds 450°C, the crystal grains may coarsen, and the adhesion of the Ni-P plating layer formed in the subsequent process may decrease. The upper limit of the treatment time is not particularly limited, but if it exceeds 24 hours, the manufacturing time may become long, leading to a decrease in productivity. Incidentally, the pressure in the pressure annealing is usually 0.1 MPa or higher and 3.0 MPa or lower.

[0050] (h) Step of subjecting the annular disk blank to cutting and grinding to obtain an aluminum alloy substrate for plating Next, the flattened annular disk blank in the cutting and grinding process is subjected to cutting and grinding to prepare the shape and surface of the annular disk blank as a whole. Then, optionally, stress relief heat treatment for relieving the stress of the annular disk blank is performed at a temperature of 200°C or higher and 290°C or lower for 0.1 hour or longer and 10.0 hours or shorter.

[0051] (i) Pretreatment step before plating The aluminum alloy substrate for plating produced as described above is subjected to degreasing, etching, and zincate treatment (Zn substitution treatment) as pre-plating treatments. For degreasing, for example, a commercially available degreasing solution such as AD-68F (manufactured by Uemura Kogyo Co., Ltd.) is used, and it is preferably carried out under the conditions of a degreasing temperature of 40°C or higher and 70°C or lower, a degreasing time of 3 minutes or longer and 10 minutes or shorter, and a concentration of the degreasing solution of 200 mL / L or higher and 800 mL / L or lower. More preferably, it is carried out under the conditions of a degreasing temperature of 45°C or higher and 65°C or lower, a degreasing time of 4 minutes or longer and 8 minutes or shorter, and a concentration of the degreasing solution of 300 mL / L or higher and 700 mL / L or lower. If the degreasing temperature is less than 40°C, the degreasing time is less than 3 minutes, and / or the concentration of the degreasing solution is less than 200 mL / L, a sufficient degreasing effect may not be obtained. Also, if the degreasing temperature exceeds 70°C, the degreasing time exceeds 10 minutes, and / or the concentration of the degreasing solution exceeds 800 mL / L, the smoothness of the surface of the aluminum alloy substrate for plating may decrease, and pits may occur after the plating process, resulting in a decrease in smoothness.

[0052] For etching, for example, a commercially available etching solution such as AD-107F (manufactured by Uemura Kogyo Co., Ltd.) is used, and it is preferably carried out under the conditions of an etching temperature of 50°C or higher and 75°C or lower, an etching time of 0.5 minutes or longer and 5 minutes or shorter, and a concentration of the etching solution of 20 mL / L or higher and 100 mL / L or lower. More preferably, it is carried out under the conditions of an etching temperature of 55°C or higher and 70°C or lower, an etching time of 0.5 minutes or longer and 3 minutes or shorter, and a concentration of the etching solution of 40 mL / L or higher and 100 mL / L or lower. If the etching temperature is less than 50°C, the etching time is less than 0.5 minutes, and / or the concentration of the etching solution is less than 20 mL / L, a sufficient etching effect may not be obtained. Also, if the etching temperature exceeds 75°C, the etching time exceeds 5 minutes, and / or the concentration of the etching solution exceeds 100 mL / L, the smoothness of the surface of the aluminum alloy substrate for plating may decrease, and pits may occur after the plating process, resulting in a decrease in smoothness. Incidentally, a normal desmatt treatment may be carried out between the etching treatment and the zincate treatment described below.

[0053] The zincate treatment is preferably carried out using, for example, a commercially available zincate treatment solution such as AD-301F-3X (manufactured by Kamimura Kogyo Co., Ltd.) under the conditions of a zincate treatment temperature of 10°C or higher and 35°C or lower, a zincate treatment time of 0.1 minute or longer and 5 minutes or shorter, and a concentration of the zincate treatment solution of 100 mL / L or higher and 500 mL / L or lower. More preferably, it is carried out under the conditions of a zincate treatment temperature of 15°C or higher and 30°C or lower, a zincate treatment time of 0.1 minute or longer and 2 minutes or shorter, and a concentration of the zincate treatment solution of 200 mL / L or higher and 400 mL / L or lower. If the zincate treatment temperature is less than 10°C, the zincate treatment time is less than 0.1 minute, and / or the concentration of the zincate treatment solution is less than 100 mL / L, the zincate film becomes non-uniform, and pits may occur after the plating treatment, resulting in a decrease in smoothness. Also, if the zincate treatment temperature exceeds 35°C, the zincate treatment time exceeds 5 minutes, and / or the concentration of the zincate treatment solution exceeds 500 mL / L, the zincate film becomes non-uniform, and pits may occur after the plating treatment, resulting in a decrease in smoothness.

[0054] (j) Step of obtaining an aluminum alloy substrate for magnetic disk Next, electroless Ni-P plating treatment is performed on the surface of the zincated aluminum alloy substrate for plating as a pretreatment, and then the surface is polished. The electroless Ni-P plating treatment is preferably carried out, for example, using a commercially available Nimden HDX (manufactured by Uemura Kogyo Co., Ltd.) plating solution, etc., under the conditions of a plating treatment temperature of 80°C or higher and 95°C or lower, a plating treatment time of 30 minutes or longer and 180 minutes or shorter, and a Ni concentration in the plating solution of 3 g / L or higher and 10 g / L or lower. More preferably, it is carried out under the conditions of a plating treatment temperature of 85°C or higher and 95°C or lower, a plating treatment time of 60 minutes or longer and 120 minutes or shorter, and a Ni concentration in the plating solution of 4 g / L or higher and 9 g / L or lower. If the plating treatment temperature is less than 80°C and / or the Ni concentration in the plating solution is less than 3 g / L, the growth rate of the plating is slow, which may lead to a decrease in productivity. Also, if the plating treatment time is less than 30 minutes, a large number of defects may occur on the plating surface, and the smoothness of the plating surface may decrease. On the other hand, if the plating treatment temperature exceeds 95°C and / or the Ni concentration in the plating solution exceeds 10 g / L, the plating grows unevenly, and the smoothness of the plating may decrease. Also, if the plating treatment time exceeds 180 minutes, the manufacturing time becomes long, which may lead to a decrease in productivity. Further, the surface of the underlying (Ni-P) plated layer is subjected to a polishing treatment. Through these pre-plating treatments and the underlying (Ni-P) plating treatment (with polishing), an aluminum alloy substrate for a magnetic disk is produced.

[0055] (k) Step of forming a magnetic layer After the electroless Ni-P plating treatment including the polishing treatment, a magnetic material is deposited on the Ni-P plating layer by sputtering to form a magnetic layer. The magnetic layer may be a single layer or may be formed from a plurality of layers having different compositions from each other. After sputtering, if necessary, a protective layer made of a carbon-based material may be formed on the magnetic layer by CVD, and a lubricating layer may be formed by applying a lubricating oil on the protective layer.

[0056] 3. Magnetic Disk By the method for manufacturing the magnetic disk described above, the magnetic disk of the present invention can be produced. The magnetic disk of the present invention has an aluminum alloy substrate for a magnetic disk, a Ni-P plating layer on the surface of the aluminum alloy substrate for the magnetic disk, and a magnetic layer formed on the Ni-P plating layer. Further, a protective layer or a lubricating layer may be formed on the magnetic layer. Since such a magnetic disk of the present invention is produced using the above-described recycled material, it is beneficial as a magnetic disk excellent in reducing environmental load.

[0057] 4. Hard Disk Drive The hard disk drive of the present invention includes one or more of the above-described magnetic disks, a spindle motor for rotating the magnetic disk, a clamp member for fixing the inner diameter side portion of the magnetic disk, a magnetic head for performing data processing on the magnetic disk, an actuator for movably supporting the magnetic head with respect to the magnetic disk, and a swing arm for rotating and positioning the actuator. Since such a hard disk drive of the present invention is produced using the above-described recycled material, it is excellent in reducing environmental load. In particular, a hard disk drive used in a data center or the like performs a large amount of data processing, and thus includes a large number of magnetic disks. By making many of the magnetic disks in such a hard disk drive using the recycled material, it can be made particularly excellent in reducing environmental load.

[0058] Based on the above embodiments, the present invention relates to the following [1] to [8]. [1] A method for recycling an aluminum alloy substrate, including a film removing step of obtaining an aluminum alloy material by removing a film from the recycled material by subjecting the recycled material having an aluminum alloy substrate and at least one layer of film on the aluminum alloy substrate to physical processing. [2] The recycling method of the aluminum alloy substrate according to [1] above, wherein the physical processing is a method of cutting the surface and end face of the recycled material using a lathe, or a combination of a method of grinding the surface of the recycled material using a grinding wheel and a method of cutting the end face of the recycled material using a lathe. [3] The recycling method of the aluminum alloy substrate according to [1] or [2] above, wherein in the physical processing, the depth at which the surface and end face of the recycled material are cut is 1.05 times or more the thickness of the film. [4] The recycling method of the aluminum alloy substrate according to any one of [1] to [3] above, wherein the film contains Ni. [5] The recycling method of the aluminum alloy substrate according to any one of [1] to [4] above, wherein the aluminum alloy substrate constituting the recycled material is annular. [6] A step of preparing a molten aluminum alloy using, as at least part of the raw materials, the aluminum alloy material obtained by the film removal step of the recycling method of the aluminum alloy substrate according to any one of [1] to [5] above, A step of heating and holding the prepared molten metal, A step of casting the heated and held molten metal to obtain an aluminum alloy ingot, A step of heating the aluminum alloy ingot to perform a homogenization treatment, A rolling step of rolling the homogenized aluminum alloy ingot into an aluminum alloy plate, A step of pressure-flattening the aluminum alloy plate obtained by the rolling step into an annular disk blank, A step of subjecting the pressure-flattened annular disk blank to cutting and grinding to obtain an aluminum alloy substrate for plating, A pre-plating treatment step of subjecting the aluminum alloy substrate for plating to degreasing, etching, and zincate treatment, A step of performing electroless Ni-P plating treatment on the surface of an aluminum alloy substrate subjected to plating pretreatment, and then polishing the surface subjected to the Ni-P plating treatment to obtain an aluminum alloy substrate for a magnetic disk; A method for manufacturing a magnetic disk, comprising: a step of forming a magnetic layer by attaching a magnetic material to the surface of the aluminum alloy substrate for a magnetic disk. [7] A magnetic disk obtained by the method for manufacturing a magnetic disk according to [6] above. [8] A hard disk drive including the magnetic disk according to [7] above.

[0059] As described above, the recycling method of the aluminum alloy substrate, the manufacturing method of the magnetic disk, the magnetic disk, and the hard disk drive according to the present embodiment have been described. However, the present invention is not limited to the above embodiments, and various modifications and changes are possible based on the technical idea of the present invention.

Example

[0060] Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.

[0061] As a recycled material, an aluminum alloy substrate made of JIS5086 alloy (Al-Mg alloy) and a Ni-P plating layer (film) formed on the aluminum alloy substrate by electroless Ni-P plating treatment were used for an aluminum alloy substrate for a magnetic disk (hereinafter referred to as "sample"; outer diameter 95 mm, inner diameter 25 mm, overall thickness 1.3 mm). In the film formed on the aluminum alloy substrate, the thickness of the surface (both main surfaces) was 10 μm, and the thickness of the end surfaces (inner diameter side surface and outer diameter side surface) was 11 μm. The samples of each example were subjected to cutting under the conditions shown in Table 1. In Table 1, the "cutting amount" means the depth at which the surface and end surfaces of the sample are cut.

[0062] The composition of the aluminum alloy used for the aluminum alloy substrate consisted of 4% by mass of Mg, 0.025% by mass of Fe, 0.025% by mass of Si, 0.3% by mass of Zn, 0.05% by mass of Cu, with the balance being Al, inevitable impurities, and trace components.

[0063] (Evaluation of recyclability) Recyclability was evaluated by observing the appearance of the surface and end faces of the samples after cutting, based on the remaining situation of the film removal. When the Ni-P plating layer was not confirmed, it was evaluated as "〇", and when the remaining Ni-P plating layer was confirmed, it was evaluated as "×". If the evaluations of both the surface and end faces of the sample were "〇", the recyclability was considered good.

[0064] [Table 1]

[0065] As shown in Table 1, in Examples 1 to 6, it was confirmed that the Ni-P plating layer was completely removed if the evaluations of both the surface and end faces of the sample were "〇". On the other hand, in Comparative Examples 1 and 4, the evaluations of both the surface and end faces of the sample were "×", and the Ni-P plating layer remained entirely. Also, in Comparative Examples 2 and 4, the evaluation of either the surface or end face of the sample was "×", and the Ni-P plating layer remained locally. [Industrial applicability]

[0066] According to the present invention, it is possible to provide a recycling method for an aluminum alloy substrate that is excellent in recyclability and enables the removal of the film simply and surely. In addition, since it is possible to manufacture a magnetic disk by reusing the aluminum alloy plate obtained by such a recycling method, the amount of expensive high-purity ingot used can be reduced, the cost can be lowered, and it is also beneficial from the viewpoint of environmental protection.

Claims

1. A method for recycling an aluminum alloy substrate, comprising a film removal step of obtaining an aluminum alloy material by physically processing a recycled material having an aluminum alloy substrate and at least one layer of film on the aluminum alloy substrate to remove the film from the recycled material.

2. The method for recycling an aluminum alloy substrate according to claim 1, wherein the physical processing is a method of cutting the surface and end face of the recycled material using a lathe, or a combination of a method of grinding the surface of the recycled material using a grindstone and a method of cutting the end face of the recycled material using a lathe.

3. The method for recycling an aluminum alloy substrate according to claim 1 or 2, wherein in the physical processing, the depth at which the surface and end face of the recycled material are cut is 1.05 times or more the thickness of the film.

4. The method for recycling an aluminum alloy substrate according to claim 1 or 2, wherein the film contains Ni.

5. The method for recycling an aluminum alloy substrate according to claim 1 or 2, wherein the aluminum alloy substrate constituting the recycled material is annular.

6. A step of preparing a molten aluminum alloy using, as at least part of the raw material, the aluminum alloy material obtained by the film removal step of the recycling method according to claim 1 or 2; A step of heating and holding the prepared molten metal; A step of casting the heated and held molten metal to obtain an aluminum alloy ingot; A step of heating the aluminum alloy ingot to perform a homogenization treatment; A rolling step of rolling the homogenized aluminum alloy ingot into an aluminum alloy plate; A step of pressurizing and flattening the aluminum alloy plate obtained by the rolling step into an annular disk blank; A step of subjecting the annular disk blank that has been pressure-flattened to cutting and grinding processes to obtain an aluminum alloy substrate for plating; A pre-plating treatment step of subjecting the aluminum alloy substrate for plating to degreasing, etching, and zincate treatment; A step of subjecting the surface of the aluminum alloy substrate that has undergone pre-plating treatment to electroless Ni-P plating treatment, and then polishing the surface that has undergone Ni-P plating treatment to obtain an aluminum alloy substrate for a magnetic disk; A method for manufacturing a magnetic disk, comprising a step of attaching a magnetic material to the surface of the aluminum alloy substrate for a magnetic disk to form a magnetic material layer.

7. A magnetic disk obtained by the method for manufacturing a magnetic disk according to Claim 6.

8. A hard disk drive comprising the magnetic disk according to Claim 7.

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