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

Abstract

The present invention relates to a method for recycling an aluminum alloy substrate, the method comprising: a film removing step (a) of removing a film from one or more recycled materials each including an aluminum alloy substrate and at least one layer of film on the aluminum alloy substrate to obtain an aluminum alloy material; a step (b) of preparing a molten metal of an aluminum alloy using the aluminum alloy material as at least a part of a raw material; a step (c) of heating and holding the prepared molten metal; and a step (d) of casting the heated and held molten metal to obtain an aluminum alloy ingot.

Description

Technical Field

[0001] This invention relates to a method for recycling aluminum alloy substrates, a method for manufacturing disks, disks, and hard disk drives. Background Technology

[0002] Hard disk drives (HDDs) are widely used as storage devices in computers, data centers, and various electronic devices. In an HDD, the disk stores information, and an aluminum alloy substrate is used as the substrate for the disk. As the aluminum alloy substrate for the disk, an aluminum alloy substrate made of JIS 5086 alloy is used. JIS 5086 alloy has good plating ability and excellent mechanical properties and machinability. JIS 5086 alloy is an aluminum alloy containing 3.5% to 4.5% by mass of Mg, 0.50% to 0.40% by mass of Si, 0.20% to 0.70% by mass of Mn, 0.05% to 0.25% by mass of Cr, 0.10% to 0.15% by mass of Ti, and 0.25% to 0.25% by mass of Zn, with the balance being Al and unavoidable impurities. In one embodiment, the aluminum alloy substrate is manufactured by performing a chemical Ni-P plating treatment and then smoothly polishing the surface.

[0003] For example, an aluminum alloy substrate for a hard disk drive using JIS 5086 alloy is manufactured through the following steps. First, an aluminum alloy containing the desired chemical composition is cast, and the ingot is homogenized, then hot-rolled, and then cold-rolled to produce a rolled material with the required thickness for a hard disk drive. If necessary, the rolled material is preferably annealed during cold rolling, etc. Next, the rolled material is stamped into a ring shape to form a ring disk blank, and in order to remove deformations caused by the manufacturing steps, the ring disk blank is stacked and subjected to pressure annealing, in which annealing is performed while pressure is applied from both surfaces to flatten the ring disk blank. The ring disk blank thus manufactured is pretreated by cutting, grinding, degreasing, etching, and zincate treatment (Zn replacement treatment), followed by chemical Ni-P plating of a hard non-magnetic metal as an underlayer treatment, polishing of the Ni-P plating surface, and then sputtering of a magnetic material to form a magnetic material layer to manufacture the aluminum alloy substrate for the hard disk drive.

[0004] In recent years, with the development of cloud services, the construction of new data centers and the replacement of existing data centers with high-capacity HDDs have been actively promoted. Due to this recent trend, increasing HDD capacity is essential. To increase HDD capacity, it is important to increase the number of installed disks and the capacity of each disk. In the former case, it is necessary to reduce the thickness of the disks, and in the latter case, it is necessary to reduce defects on the Ni-P plating surface of the aluminum alloy substrate used for the disks. While both methods are technically feasible, the yield rate in the disk manufacturing process deteriorates when these methods are implemented. Specifically, in the former case, when the disk is thinned, higher processing precision is required in rolling, grinding, etc., and in the latter case, the threshold for the number of defects on the Ni-P surface is more stringent. That is, the number of defective aluminum alloy substrates used for the disks increases, and considering future disk demand, it is easy to expect an increase in the number of defective aluminum alloy substrates used for the disks.

[0005] In recent years, with increased attention to environmental protection, establishing metal product recycling technologies has become crucial. It is clear that geopolitical risks have emerged with respect to certain metal types. While aluminum is a relatively easy metal to recycle, the ease of recycling varies depending on the alloy system. For example, in the case of aluminum can materials, the same alloy can be easily recycled back into aluminum cans because it can be collected as raw material. However, aluminum cladding materials used as heat exchanger materials have a multi-layered structure composed of aluminum alloys with different compositions, and it is impossible to separate each layer. Therefore, the entire aluminum cladding material needs to be remelted and recast, and during remelting and recasting, the alloy composition changes from the original alloy composition, thus limiting the scope of its post-recycling uses.

[0006] Meanwhile, aluminum alloys used in hard disks are high-cost materials, employing large amounts of high-purity base metals to improve plating defects and limiting the content of elements such as Fe and Si. Therefore, by recycling as much as possible, the amount of high-purity base metals used can be reduced. This, in turn, reduces the amount of high-purity base metals required for manufacturing, significantly contributing to environmental protection.

[0007] In the manufacturing process of aluminum alloy substrates for hard disks, when rolling, grinding, etc., fail to meet predetermined standards and the aluminum alloy substrate for hard disks becomes a defective product, the aluminum alloy substrate can be reused as part of the raw materials. However, when a defective product is produced in a state where a film such as a Ni-P coating is formed on the surface of the aluminum alloy substrate for hard disks, its recycling becomes complicated. That is, since a film such as a Ni-P coating is applied to the aluminum alloy substrate for hard disks, the aluminum alloy substrate can be used as a casting alloy for, for example, the casing of an HDD. At the same time, as mentioned above, reusing aluminum alloys, which use a large amount of high-purity base metal, as castings has poor recycling efficiency, and it is desirable to reuse the aluminum alloy as a rolling material, preferably as an aluminum alloy for hard disks.

[0008] Against this backdrop, there is a need for a technique to establish a method for separating films such as Ni-P coatings from aluminum alloys and recycling aluminum alloy substrates. For example, Patent Document 1 discloses a method for reusing aluminum alloy substrates with Ni-P coatings as raw materials for Al-Si alloys. In this technique, although the aluminum alloy substrate can be reused, it is difficult to effectively use aluminum alloy substrates made from high-purity base metals.

[0009] Patent Document 2 discloses a method for returning an aluminum alloy substrate with its Ni-P coating removed to the plating step for reuse. In this technology, the recycled aluminum alloy substrate becomes reusable. However, in recent years, the requirements for defects on the Ni-P plating surface of aluminum alloy substrates used for disks have become extremely stringent, and when aluminum alloy substrates with the Ni-P coating removed are reused as is, plating is performed on the aluminum alloy substrate while the surface is damaged, resulting in frequent defects on the plating surface.

[0010] As mentioned above, in the relevant technologies, it is not possible to use aluminum alloy substrates while maintaining high quality, and it is difficult to use aluminum alloy substrates used for disks and the like, which have been required to maintain high quality in recent years.

[0011] Reference List Patent documents Patent Document 1: JP4656194B Patent Document 2: JPS63-282281A Summary of the Invention

[0012] Technical issues The present invention was made in view of the above circumstances, and its object is to provide a method for recycling aluminum alloy substrates with excellent recyclability.

[0013] Solution to the problem The inventors have discovered that by using aluminum alloy material as at least part of the raw material to prepare molten metal, heating and holding the molten metal, and casting the molten metal, an aluminum alloy plate with excellent recyclability can be obtained. This aluminum alloy material is obtained by removing the film from recycled material having an aluminum alloy substrate and at least one film, thus completing the present invention.

[0014] A method for recycling aluminum alloy substrates according to an embodiment of the present invention includes: A membrane removal step removes a membrane from one or more recycled materials to obtain an aluminum alloy material, each of the one or more recycled materials comprising an aluminum alloy substrate and at least one membrane layer on the aluminum alloy substrate; The step of preparing molten aluminum alloy metal using aluminum alloy materials as at least part of the raw materials; The steps of heating and holding the prepared molten metal at that temperature; and The step of casting heated and held molten metal to obtain aluminum alloy ingots.

[0015] Advantages of the invention According to the present invention, a method for recycling aluminum alloy substrates with excellent recyclability can be provided. Attached Figure Description

[0016] [ Figure 1 ] Figure 1 This is a diagram illustrating the film removal steps of a method for recycling an aluminum alloy substrate according to an embodiment of the present invention.

[0017] [ Figure 2 ] Figure 2 This is a graph showing the change of current density over time during anodic electrolysis in Example 1B. Detailed Implementation

[0018] The embodiments of the present invention will now be described in detail.

[0019] 1. A method for recycling aluminum alloy substrates The method for recycling aluminum alloy substrates according to the present invention includes: (a) A membrane removal step, wherein a membrane is removed from one or more recycled materials, each comprising an aluminum alloy substrate and at least one layer of membrane on the aluminum alloy substrate, to obtain an aluminum alloy material; (b) Step, using aluminum alloy material as at least part of the raw material to prepare molten aluminum alloy metal; (c) Step, heating and holding the prepared molten metal at that temperature; and (d) Step: Casting the heated and held molten metal to obtain an aluminum alloy ingot.

[0020] In the method for recycling aluminum alloy substrates according to the present invention, the aluminum alloy material obtained by removing the film from the recycled material in the film removal step is used as at least a portion of the raw material to prepare molten metal for aluminum alloys. The molten metal is heated and held at a certain temperature, and aluminum alloy ingots are manufactured from the molten metal. In related technologies, aluminum alloy substrates subjected to Ni-P plating can be reused as raw materials for Al-Si alloys, but the use of raw materials is limited, and aluminum alloy substrates containing high-purity base metals have not been effectively recycled. Since the aluminum alloy substrate with the film removed is recycled as is, and a film such as a Ni-P plating is formed on the aluminum alloy substrate, defects can occur on the film of the aluminum alloy substrate.

[0021] In contrast, in the method for recycling aluminum alloy substrates according to the present invention, the film can be effectively removed from the recycled material in the film removal step. By using the aluminum alloy material obtained after film removal to prepare molten aluminum alloy and performing subsequent steps, an aluminum alloy ingot maintaining the alloy composition of the aluminum alloy material can be manufactured. When preparing the molten aluminum alloy, an aluminum alloy ingot with a desired alloy composition can also be manufactured by adding any materials, elements, aluminum alloy base metals, etc., to the molten metal.

[0022] In a method for recycling an aluminum alloy substrate according to one aspect of the present invention, in the film removal step, while the recycled material comprising the aluminum alloy substrate and at least one Ni-containing film on the aluminum alloy substrate is immersed in a solution, an electric current is applied to the recycled material to remove the film from the recycled material, thereby obtaining the aluminum alloy material. Therefore, the Ni-containing film can be effectively removed.

[0023] In a method for recycling aluminum alloy substrates according to one aspect of the invention, aluminum alloy material is manufactured by physically processing the recycled material and removing the film from the recycled material in a film removal step. As described above, since the film is removed by physical processing, the film can be easily and reliably removed from the aluminum alloy substrate. Because the film is completely removed from the aluminum alloy substrate by such physical processing, defects on the film can be reduced even if a new aluminum alloy sheet is manufactured using the obtained aluminum alloy material and a film such as a Ni-P coating is formed using the aluminum alloy sheet. A method for recycling aluminum alloy substrates with excellent recyclability can be provided.

[0024] Therefore, the present invention provides a method for recycling aluminum alloy substrates with excellent recyclability. Cost reduction is achieved by reducing the amount of expensive high-purity aluminum base metal used while maintaining the performance of the aluminum alloy sheet. In one aspect, by using the original aluminum alloy material obtained after removing the Ni-containing film as raw material to prepare molten aluminum alloy and performing subsequent steps, an aluminum alloy sheet maintaining the alloy composition of the aluminum alloy material can be manufactured. In this aspect, when preparing the molten aluminum alloy, an aluminum alloy sheet with a desired alloy composition can also be manufactured by adding any materials, elements, aluminum alloy base metals, etc., to the molten metal. By setting conditions for heating and holding the molten metal, manufacturing aluminum alloy ingots from the molten metal, homogenizing the aluminum alloy ingots, and rolling the aluminum alloy ingots to predetermined conditions, the performance and characteristics of the rolled aluminum alloy sheet can be set to desired performance and characteristics different from those of the recycled material. Furthermore, in one aspect, since surface defects in the rolled aluminum alloy sheet can be reduced, film defects can also be reduced when a film is formed on the aluminum alloy sheet.

[0025] (Recycled materials) The "recycled material" used in this invention comprises an aluminum alloy substrate and a film on the aluminum alloy substrate. Examples of recycled materials include intermediate materials and finished products generated during the manufacture of disks. "Intermediate material" corresponds, for example, to the aluminum alloy substrate used for the disk, and "finished product" corresponds, for example, to the disk itself. These recycled materials correspond to defective products, substandard products, used disks, etc.

[0026] The "film" has one or more layers formed on an aluminum alloy substrate, and in one aspect, one or more layers include a Ni-containing layer. Such a film may have a Ni-containing layer, or it may have a Ni-containing layer and a Ni-free layer. Embodiments of the film include a Ni-P plating layer, a magnetic material layer, a protective layer, and a lubricating layer. In such a film, for example in the intermediate materials or finished products described below, the film formed on the aluminum alloy substrate includes a Ni-containing film, and specifically includes a Ni-P plating layer.

[0027] The shape of the recycled material is not particularly limited and can be annular, polygonal, or irregular without a specific shape. Since recycled material is typically in the shape of annular discs, it is easy to procure annular recycled material. Annular recycled material can be used in a bent, deformed, perforated, or cut state, and the film can be effectively removed each time without changing the processing conditions. Therefore, the aluminum alloy substrate constituting the recycled material is preferably annular. In the method for recycling aluminum alloy substrates according to the invention, the aluminum alloy material obtained through the film removal step is used as at least a portion of the raw material, and aluminum alloy material can be used alone as the raw material, or other materials and elements can be used together with the aluminum alloy material as raw materials.

[0028] (Intermediate material) Examples of intermediate materials include aluminum alloy substrates for disks produced during the manufacture of disks. In one embodiment, a Ni-containing film, such as a Ni-P coating, is formed on the surface of the aluminum alloy substrate for the disk. The Ni content in the Ni-containing film used for the aluminum alloy substrate for the disk is, for example, 80% by mass or more and 95% by mass or less. When the Ni-containing film is a Ni-P coating, the P content contained in the Ni-P coating is, for example, 5% by mass or more and 20% by mass or less. The thickness of the Ni-containing film is not particularly limited, and is, for example, 3 μm or more and 25 μm or less, and in this case, the thickness of the aluminum alloy substrate for the disk is, for example, 0.3 mm or more and 2.0 mm or less.

[0029] (Finished product) Examples of finished products include magnetic disks. In one embodiment of the magnetic disk, a Ni-P plating layer, a CoCrPt-type magnetic material layer, and a protective layer of carbon-based materials are sequentially formed as films on the surface of an aluminum alloy substrate used for the magnetic disk. Since the magnetic material layer and the protective layer are formed on the Ni-P plating layer, the magnetic material layer and the protective layer can be removed together by removing the Ni-P plating layer. Therefore, the aluminum alloy material obtained by removing the films from the finished magnetic disk can also be used as at least a portion of the raw material to prepare molten metal for aluminum alloys.

[0030] 2. Steps of a method for recycling aluminum alloy substrates As described above, the method for recycling aluminum alloy substrates according to the present invention includes steps (a) to (d). Each step (a) to (d) will be described in detail below.

[0031] (a) Membrane removal steps In the membrane removal step, the membrane is removed from the recycled material. The treatment method used for membrane removal is not particularly limited, and embodiments include chemical treatment, physical processing, and thermal treatment. Chemical treatment is preferred in the membrane removal step, and more preferably, the membrane is removed from the recycled material by immersing it in a solution. One embodiment of the recycled material has a Ni-P coating as a membrane on an aluminum alloy substrate, and the Ni-P coating is formed on all surfaces of the aluminum alloy substrate, i.e., both surfaces, the inner diameter, and the outer diameter. By immersing the recycled material in a solution, the Ni-P coating formed as a membrane on all surfaces can be effectively removed.

[0032] The solution is preferably an acidic solution containing nitrate ions. By immersing the recycled material in an acidic solution containing nitrate ions, films such as Ni-P coatings can be effectively removed. Since the aluminum alloy substrate is resistant to corrosion by acidic solutions containing nitrate ions, it will not dissolve in the acidic solution. As a result, high-quality aluminum alloy sheets can be obtained. When recycled material with films such as Ni-P coatings is immersed in an alkaline solution, the Ni-P coating does not dissolve due to its resistance to alkaline solutions, making it difficult to remove films such as Ni-P coatings. Conversely, immersing the recycled material in an acidic solution containing nitrate ions prevents this.

[0033] The acidic solution can be prepared by dissolving nitric acid or nitrates such as sodium nitrate or potassium nitrate in a solvent such as pure water, industrial water, or tap water, and is preferably an aqueous solution of nitric acid. When using nitrates, nitric acid or hydrochloric acid needs to be added further to form an acidic solution. Commercially available aqueous solutions of nitric acid can also be used. The nitrate ion concentration in the acidic solution is preferably 25% by mass or more, more preferably 30% by mass or more, and even more preferably 35% by mass or more. The nitrate ion concentration in the acidic solution is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less. When the nitrate ion concentration in the acidic solution is within the above range, the membrane can be effectively removed in a short time.

[0034] In acidic solutions, anions other than nitrate ions, such as chloride ions, sulfate ions, and phosphate ions, may be present. The total concentration of anions other than nitrate ions in the acidic solution is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less. When the total concentration of anions other than nitrate ions in the acidic solution is within the above range, the anions other than nitrate ions do not affect the nitrate ion removal effect on the membrane, and the membrane can be effectively removed. The pH of the acidic solution is preferably -1 to 4, more preferably -1 to 3, and even more preferably -1 to 2. When the pH of the acidic solution is within the above range, the membrane can be effectively removed.

[0035] The conditions for immersing the recycled material in the acidic solution can be set according to the characteristics of the recycled material, including a suitable temperature and immersion time. The acidic solution preferably has a temperature of 40°C to 60°C, more preferably 45°C to 60°C, and even more preferably 50°C to 60°C. When the temperature of the acidic solution is within the above range, the membrane can be effectively removed in a short time, and gas generation due to nitric acid decomposition can be prevented. The immersion time of the recycled material in the acidic solution is preferably 1 hour or more, more preferably 1 hour to 3 hours, and even more preferably 1.5 hours to 2 hours. When the immersion time of the recycled material in the acidic solution is within the above range, the membrane can be effectively removed without leaving any residue.

[0036] The membrane removal rate depends on the conditions of the membrane removal step, and in one embodiment, the membrane removal rate is to remove a membrane of 4 μm to 7 μm within 30 minutes. Meanwhile, the thickness of the membrane in the annular recycled material is, for example, 5 μm to 10 μm on the surface and 7 μm to 12 μm on the inner and outer diameters. Therefore, in the above embodiment, by immersing the recycled material in an acidic solution for more than 1 hour, the membrane on the entire surface of the aluminum alloy substrate, including both surfaces, the inner diameter, and the outer diameter, can be effectively and reliably removed.

[0037] In the membrane removal step, one or more reclaimed materials can be immersed in a solution. When one reclaimed material is immersed in the solution, the membrane can be removed from the reclaimed material in a short time. When multiple reclaimed materials are immersed in the solution, the membrane can be removed from a large amount of reclaimed material at once, thereby increasing the amount of processed reclaimed material. When multiple reclaimed materials are immersed in the solution, it is preferable to arrange the reclaimed materials in the solution so that they do not come into contact with each other. By arranging multiple reclaimed materials in this way, the solution is less likely to enter the contact portions of the reclaimed materials, and it can prevent the membrane from remaining if it is not partially removed. Membrane removal can be prevented from being inhibited by a dissimilar metal contact state, in which the aluminum alloy in the reclaimed material with the membrane removed and the aluminum alloy exposed comes into contact with the membrane in the reclaimed material with the membrane not removed. The spacing between the reclaimed materials in the solution is not particularly limited and can be set to a desired spacing based on the size of the container holding the solution, the quantity and size of the reclaimed materials to be immersed in the solution, etc.

[0038] In one aspect of the membrane removal step, an aluminum alloy material is obtained by removing the membrane from the recycled material while it is immersed in a solution and simultaneously applying an electric current to it. Here, "applying an electric current" means that an electric current flows through the recycled material immersed in the solution. By immersing the recycled material in the solution and applying an electric current to it, Ni from the Ni-containing membrane constituting the recycled material is converted into Ni ions through chemical and electrical reactions and dissolves in the solution. As a result, the Ni-containing membrane can be effectively removed. The method of applying an electric current to the recycled material is not particularly limited, and examples can be given where at least the positive terminal of the power source is electrically directly connected to the recycled material.

[0039] Such a solution is preferably an acidic solution containing sulfate ions, and more preferably, the film is removed by anodic electrolysis while the recovered material is immersed in the acidic solution and electrically connected to the counter electrode. One embodiment of the recovered material has a Ni-P coating as a film on an aluminum alloy substrate, and the Ni-P coating is formed on all surfaces of the aluminum alloy substrate, including two surfaces, an inner diameter, and an outer diameter. By energizing the recovered material while it is immersed in the acidic solution, the Ni-P coating formed as a film on all surfaces in this way can be removed. In particular, the Ni-P coating can be effectively removed when anodic electrolysis is performed while the recovered material is immersed in the acidic solution containing sulfate ions and electrically connected to the counter electrode.

[0040] Because the anodic aluminum oxide film forms on the surface of the aluminum alloy substrate exposed by removing the Ni-P coating, dissolution of the aluminum alloy substrate is prevented, and the Ni-P coating can be selectively removed. When the recycled material is merely immersed in an alkaline solution without electricity, Ni does not dissolve in the solution due to the corrosion resistance of the Ni-containing film, such as the Ni-P coating, to the alkaline solution, and the film is difficult to remove. In contrast, by performing anodic electrolysis as described above with the recycled material immersed in an acidic solution containing sulfate ions and the counter electrode electrically connected to each other, the Ni-containing film can be effectively and selectively removed while preventing dissolution of the aluminum alloy substrate.

[0041] An acidic solution containing sulfate ions can be prepared by dissolving sulfuric acid or a sulfate such as sodium sulfate in a solvent such as pure water, industrial water, or tap water. When using sulfate, sulfuric acid or nitric acid needs to be added further to form an acidic solution. Commercially available aqueous solutions of sulfuric acid can also be used. The sulfate ion concentration in the acidic solution is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 10% by mass or more. When the sulfate ion concentration in the acidic solution is within the above range, the membrane can be effectively removed in a short time. The pH of the acidic solution is preferably 0 to 4, more preferably 0 to 3, and even more preferably 1 to 2. When the pH of the acidic solution is within the above range, the membrane can be effectively removed.

[0042] When an acidic solution contains sulfate ions, anions other than sulfate ions, such as chloride ions, nitrate ions, and phosphate ions, can also be present in the acidic solution. From the viewpoint of effectively preventing aluminum from dissolving from the aluminum alloy substrate constituting the recycled material, the concentration of anions other than sulfate ions in the acidic solution is preferably 5% by mass or less.

[0043] As conditions for anodic electrolysis in which the recovered material is immersed in an acidic solution and the counter electrode is electrically connected to each other, the temperature of the acidic solution, the anodic electrolysis time, the material and size of the counter electrode, and the material and size of the recovered material can be appropriately set. The acidic solution preferably has a temperature of 20°C or higher, more preferably 20°C to 50°C, and even more preferably 25°C to 40°C. When the temperature of the acidic solution is within the above range, Ni-containing films can be effectively removed in a short time, and equipment and energy used to raise the temperature of the acidic solution can be saved.

[0044] When anodic electrolysis is performed while the recovered material and the counter electrode are electrically connected to each other in an acidic solution, the counter electrode is directly connected to the negative terminal of the power supply and faces the recovered material in the acidic solution. A voltage is applied between the recovered material and the counter electrode by the power supply. The material used for the counter electrode is not particularly limited, as long as the anodic electrolysis of the recovered material can be performed, and for example, Pt (platinum), Ni (nickel), Al (aluminum), and C (carbon) can be used. The shape of the counter electrode is not particularly limited and can be, for example, plate-shaped or wire-shaped. The voltage applied between the recovered material and the counter electrode during anodic electrolysis is not particularly limited, but is preferably 2 V or more, more preferably 2.5 V or more, and even more preferably 3 V or more. When the voltage during anodic electrolysis is within the above range, the Ni-containing film can be effectively removed in a short time. The recovered material and the counter electrode can be completely immersed in the acidic solution, or they can be partially exposed above the acidic solution with the remaining portion immersed in the acidic solution.

[0045] Figure 1 This is a diagram illustrating the process of anodic electrolysis in the membrane removal step according to an embodiment. (See diagram for example.) Figure 1 As shown in (a), the anodic electrolysis apparatus 1 includes a container holding an acidic solution 6 containing sulfuric acid (H2SO4), a recovery material having an aluminum alloy substrate 3 and a Ni-P coating (film) 2 formed on the aluminum alloy substrate 3, a counter electrode 4, and a power supply 5. In the acidic solution 6, sulfuric acid (H2SO4) dissociates into sulfate ions (SO42-22-22-3 ... 2-The recycled material and counter electrode 4 face each other in acidic solution 6. The positive terminal of power supply 5 is directly electrically connected to the recycled material via a wire, and the negative terminal of power supply 5 is directly electrically connected to the counter electrode 4 via a wire. In one embodiment, the recycled material is a ring-shaped aluminum alloy substrate for a disk. When a voltage is applied from power supply 5 between the recycled material and counter electrode 4, anodic electrolysis of the recycled material occurs, and Ni... 2+ The solution begins to dissolve from the Ni-P coating 2 into the acidic solution 6.

[0046] like Figure 1 As shown in (b), when the anodic electrolysis proceeds to a certain extent, a portion of the Ni in the acidic solution 6... 2+ With sulfate ions (SO4) in acidic solution 6 2- ) forms a salt (nickel sulfate; NiSO4), and the remaining Ni 2+ Ni is deposited on counter electrode 4. For example... Figure 1 As shown in (c), when anodic electrolysis proceeds further and the dissolution of Ni into the acidic solution 6 is complete, the Ni-P coating (film) 2 is removed from the surface of the recycled material immersed in the acidic solution 6, and the aluminum alloy substrate 3 is exposed. Since the anodic aluminum oxide film 7 is formed on the surface of the aluminum alloy substrate 3, anodic electrolysis no longer proceeds. As will be discussed later in the reference... Figure 2 As described in the embodiments, in Figure 1 In stage (a), a constant current flows between the recycled material and the counter electrode 4, and a constant current density is observed, but in Figure 1 In stage (b), as the surface area of ​​the exposed aluminum alloy substrate 3 increases, the current flowing between the recycled material and the counter electrode 4 decreases rapidly, and correspondingly, the current density also decreases significantly. Figure 1 In stage (c), the flow between the recycled material and the counter electrode 4 is approximately Figure 1 The constant current in stage (a) is 1 / 10 of the fixed current, and the current density is also significantly smaller than that in stage (a). Figure 1 The constant value of the current density in stage (a). In this way, the change of current or current density during anodic electrolysis is measured, and when the current or current density decreases significantly from the constant current or constant current density in the initial stage of anodic electrolysis and the constant current or constant current density begins to be constant, the Ni-P coating (film) 2 is removed, and the anodic aluminum oxide film 7 is formed on the surface of the aluminum alloy substrate 3, and this time can be determined to be approximately the end time of anodic electrolysis.

[0047] Such a method for recycling aluminum alloy substrates may further include recovering Ni deposited on the surface of the counter electrode during the film removal step and the Ni-containing acidic solution after anodic electrolysis. By recovering Ni deposited on the counter electrode surface and the Ni-containing acidic solution after anodic electrolysis, and separating Ni or using the acidic solution as is, efficient utilization as a resource can be achieved, and recyclability can be further improved. Ni recovered in this way can be used as metallic Ni in various applications, such as adjusting the alloy composition of the molten metal in the preparation of aluminum alloys (described later) to a desired alloy composition, or adjusting the composition of the plating solution used to form a Ni-P coating (film). Products using Ni recovered in this way, as well as Ni-containing acidic solutions (e.g., Ni-containing sulfuric acid solutions), can be provided.

[0048] In one aspect of the membrane removal step, the recycled material is physically processed as a treatment method for removing the membrane. As described above, since the recycled material is typically in the shape of an annular disk, the membrane formed on the surface of the recycled material having this shape exists on all surfaces of the recycled material, including two surfaces, the inner diameter, and the outer diameter. Therefore, physical processing is effective for reliably removing the membrane formed on the entire surface of the recycled material. In the membrane removal step performed by such physical processing, the removal of the membrane from the recycled material aims to completely remove the membrane and does not include partial removal of the membrane.

[0049] Examples of physical processing include methods for cutting the surfaces and end faces of recycled material using a lathe, and combinations of methods for grinding the surfaces of recycled material using a grinding stone and cutting the end faces of recycled material using a lathe. When the aluminum alloy substrate constituting the recycled material is annular, the surfaces of the recycled material refer to the two surfaces (two main surfaces), and the end faces of the recycled material refer to the side surfaces on the inner diameter side and the side surfaces on the outer diameter side. When manufacturing disks according to general manufacturing methods, cutting and grinding are also performed in the step of obtaining the aluminum alloy substrate for plating from the annular disk blank. By performing such machining as physical processing, the film can be removed simply and easily without using special new or complex equipment.

[0050] In cutting, various tools can be used, such as cutting tools and forming tools. Cutting tools are tools shaped to allow the cutting edge to cut a portion of the surface and end face of the recycled material, while forming tools are tools with cutting edges shaped along the end face of the recycled material. The shape of the tool is not particularly limited, as long as the tool can remove a film of a certain depth.

[0051] In grinding, the two surfaces of the recycled material are clamped between a grinding stone, and pressure is applied to cause the recycled material and the grinding stone to slide. The roughness of the grinding stone can be selected, and as the roughness increases, the grinding speed increases, but the surface roughness of the aluminum alloy material obtained by grinding also increases. Conversely, the smaller the roughness of the grinding stone, the slower the grinding speed, but the smoother the surface of the aluminum alloy material obtained by grinding. In grinding, since the surface roughness of the aluminum alloy material to be obtained is irrelevant, and the purpose is to remove the film, the greater the roughness of the grinding stone, the more effectively the film can be removed.

[0052] In physical processing, the depth of cutting the surface and end faces of the recycled material (hereinafter also referred to as "processing amount") is preferably 1.05 times or more the thickness of the film, more preferably 1.1 times or more. When the processing amount is at least 5% greater than the thickness of the film, the film can be completely removed. When the above-mentioned processing amount is sufficient only on one of the surface and end faces of the recycled material, a portion of the film remains in the recycled material, and when the processing amount is sufficient on both the surface and end faces of the recycled material, the film is completely removed. For example, when cutting is performed as physical processing, the cutting depth corresponds to the processing amount, and when grinding is performed as physical processing, the grinding depth corresponds to the processing amount. To prevent the surface of the aluminum alloy substrate from being over-cut, the upper limit of the processing amount is preferably 2.2 times or less, more preferably 2.0 times or less.

[0053] (b) Steps for preparing molten metal of aluminum alloy Next, the aluminum alloy material obtained in the membrane removal step is used as at least a portion of the raw material to prepare molten aluminum alloy. The content of each element in the molten metal prepared in step (b) is as follows.

[0054] • Ni (nickel) content The Ni content in the molten metal of the aluminum alloy is preferably 0% by mass or more and 2.5% by mass or less. Since Ni combines with aluminum (Al) and the like to form Al-Ni compounds, leading to large defects on the plated surface, reducing the Ni content is useful. 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. The Ni content is adjusted in the step of preparing the molten metal of the aluminum alloy by heating and melting the raw materials. For example, after the raw materials in the molten metal are completely melted, the composition of the molten metal is analyzed, and when the Ni content is high, an aluminum alloy base metal or the like is added to adjust the Ni content to the desired Ni content.

[0055] • P (phosphorus) content The phosphorus (P) content in the molten metal of the aluminum alloy is preferably 0% by mass or more and 0.05% by mass or less. P is contained in the aluminum alloy base metal, etc., and combines with Mg (magnesium), which is typically present in the aluminum alloy as a raw material for the molten metal, to form Mg-P oxides. During the plating process, the reaction becomes uneven only in this portion, leading to large defects on the plating surface. As a result, the smoothness of the plating surface is reduced. A portion of the Mg-P oxides can be removed by heating and holding the molten metal to float to the surface of the molten metal, but the content of P itself, which is combined with Mg, is preferably 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 much lower than the Ni content, it is generally not necessary to adjust the P content to the desired level by adding the aluminum alloy base metal, etc. However, when adjustment is required, the aluminum base metal, etc., is added in the same manner as Ni to adjust the content to the desired level.

[0056] • Mg (magnesium) content The Mg content in the molten metal of the aluminum alloy is preferably 0% by mass or more and 6.5% by mass or less. As mentioned above, since Mg combines with P in the molten metal to form Mg-P oxides, the Mg content is preferably low, similar to the case of P. The Mg content in the molten metal is preferably 6.5% by mass or less, and more preferably 4.5% by mass or less. When the Mg content is high, aluminum alloy base metals or the like are added in the same manner as Ni to adjust the Mg content to the desired level.

[0057] • Metallic composition of molten aluminum alloy Regarding the metallic composition of the molten metal in the aluminum alloy, as mentioned above, it is preferable to adjust the content of Ni or P itself and the content of elements such as Mg that form intermetallic compounds with P.

[0058] Meanwhile, elements other than Ni, P, and Mg and their contents are not particularly limited. Examples of alloy compositions contained in the molten metal of the aluminum alloy include the following: The aluminum alloy contains Fe (iron) and optionally Mn (manganese), wherein the total content of Fe and Mn is in the range of 0.005% by mass and 7.00% by mass, and also contains 0.5% by mass and 6.5% by mass of Mg, optionally containing one or more metals selected from the group consisting of 0% by mass and 1.0% by mass of Si (silicon), 0% by mass and 0.7% by mass of Zn (zinc), 0% by mass and 0.30% by mass of Cr (chromium), 0% by mass and 1.0% by mass of Cu (copper), and 0% by mass and 0.20% by mass of Zr (zirconium), with the balance being Al, unavoidable impurities, and other trace components.

[0059] Examples of unavoidable impurities include Ti (titanium) and Ga (gallium) contained in the aluminum alloy, and examples of other trace components include Co (cobalt) and Pt (platinum). The effects of the invention are not impaired when the content of unavoidable impurities and other trace components is less than 0.10% by mass for each element and less than 0.30% by mass in total.

[0060] (c) The step of heating and holding the molten metal at that temperature Next, the molten aluminum alloy is heated and held at that temperature. In this step, the molten aluminum alloy is heated and held at that temperature in a holding furnace. At this time, it is preferable to remove the oxide film floating on the surface of the molten metal out of the furnace. By removing the floating oxide film before casting the aluminum alloy using methods such as skimming, the Ni or P content in the molten metal can be reduced. It is preferable to remove the oxide film out of the furnace as quickly as possible.

[0061] (d) The step of casting molten metal to obtain aluminum alloy ingots. Next, the molten metal is cast to obtain aluminum alloy ingots. After online degassing or online filtration, as described later as needed, the heated and held molten metal of the aluminum alloy is cast into aluminum alloy ingots using semi-continuous casting methods (DC casting method), mold casting method, continuous casting method (CC method), etc. In the DC casting method, the molten metal injected via the runner is cooled by cooling water directly discharged to the bottom block, the walls of the water-cooled mold, and the outer periphery of the ingot, solidifies, and is pulled downwards as an ingot. In the mold casting method, the molten metal injected into a hollow mold made of cast iron or the like is cooled by the walls of the mold and solidifies to create an ingot. In the CC casting method, the molten metal is supplied through a casting nozzle between a pair of rolls (or a belt casting machine and a block casting machine), and thin sheets are directly cast by deheating from the rolls.

[0062] Before the casting step, it is preferable to perform online degassing or online filtration on the molten metal that has been heated and held at a certain temperature during the heating and holding process, according to conventional methods. As an online degassing device, commercially available degassing devices under trademarks such as SNIF or ALPUR can be used. In these online degassing devices, a bladed rotating body rotates at high speed while argon or a mixture of argon and nitrogen is blown into the molten metal, supplying the gas as fine bubbles. Therefore, dehydrogenated gases and inclusions can be removed online in a short time. As an online filtration process, ceramic tube filters, ceramic foam filters, alumina ball filters, etc., are used, and inclusions are removed through filter cake filtration mechanisms, filter media filtration mechanisms, etc.

[0063] In the above steps, when preparing molten aluminum alloy metal, aluminum alloy sheets with a desired alloy composition can be manufactured by adding arbitrary materials, elements, aluminum alloy base metals, etc., to the molten metal. By setting conditions for heating and holding the molten metal to manufacture aluminum alloy ingots from the molten metal, and as described below, homogenizing the aluminum alloy ingots and rolling them 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.

[0064] 3. Methods for manufacturing disks The method for manufacturing a disk according to the present invention includes the following steps: (e) Heating the aluminum alloy ingot obtained by the method used for recycling aluminum alloy substrates to perform homogenization treatment; (f) Rolling step: Rolling the aluminum alloy ingot that has undergone homogenization treatment to obtain an aluminum alloy sheet; (g) The aluminum alloy sheet obtained in the rolling step is flattened under pressure into an annular disc; (h) The pressurized and flattened annular disc blank is cut and ground to obtain an aluminum alloy substrate for plating; (i) Pre-plating treatment step, in which the aluminum alloy substrate to be plated is degreased, etched and zincated; (j) Performing a chemical Ni-P plating treatment on the surface of an aluminum alloy substrate that has undergone pre-plating, followed by polishing the Ni-P plating treated surface to obtain an aluminum alloy substrate for disks; and (k) Attach magnetic material to the surface of an aluminum alloy substrate for a disk to form a magnetic material layer.

[0065] The following will describe each step (e) to step (k) in detail.

[0066] (e) Heating the aluminum alloy ingot for homogenization. The aluminum alloy ingot obtained as described above is heated and subjected to a homogenization treatment. During the homogenization treatment, the aluminum alloy ingot is preferably heated at a heating temperature of 480°C to 560°C for at least 1 hour, more preferably at a heating temperature of 500°C to 550°C for at least 2 hours. Sufficient homogenization cannot be obtained when the heating temperature is below 480°C or the heating time is less than 1 hour. When the heating temperature exceeds 560°C, the aluminum alloy ingot will melt. There is no particular upper limit to the heating time, but when the heating time exceeds 48 hours, the homogenization effect saturates, and productivity decreases.

[0067] (f) Rolling steps Next, in the rolling step, the homogenized aluminum alloy ingot is rolled to obtain an aluminum alloy sheet. In this rolling step, rolling can be performed once or multiple times, and both cold rolling and hot rolling can be performed. In one embodiment, the homogenized aluminum alloy ingot is hot-rolled to produce a hot-rolled sheet. The hot rolling conditions are not particularly limited, and 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. The hot rolling finish temperature is preferably 260°C or higher and 400°C or lower, and more preferably 280°C or higher and 380°C or lower. When the hot rolling start temperature is below 300°C, the processability obtained by hot rolling cannot be guaranteed, and when the hot rolling start temperature exceeds 500°C, the grains coarsen, and the adhesion of the Ni-P coating formed in the steps described later decreases. When the hot rolling finish temperature is below 260°C, the processability obtained through hot rolling cannot be guaranteed, and when the hot rolling finish temperature exceeds 400°C, the grains become coarser, and the adhesion of the Ni-P coating formed in the steps described later decreases. In hot rolling, aluminum alloy ingots are typically heated at the hot rolling start temperature and held for more than 0.5 hours and less than 10.0 hours before hot rolling.

[0068] In one embodiment, the obtained hot-rolled sheet is then cold-rolled to produce a cold-rolled sheet preferably having a thickness of 0.4 mm or more and 2.0 mm or less, more preferably having a thickness of 0.6 mm or more and 2.0 mm or less. That is, cold rolling is performed after hot rolling to obtain the desired product thickness. The conditions for cold rolling are not particularly limited and can be determined based on the required sheet strength and thickness of the aluminum alloy sheet, and the rolling rate is preferably 20% or more and 90% or less, more preferably 20% or more and 80% or less. When the rolling rate is less than 20%, the grains coarsen during the pressure flattening annealing of the coil, described later, and the adhesion of the Ni-P coating formed in the steps described later decreases. Meanwhile, when the rolling rate exceeds 90%, the manufacturing time increases and the productivity decreases.

[0069] To ensure good cold-rolling workability, annealing can be performed freely before or during cold rolling. When annealing is performed, for example, intermittent annealing for 0.1 hours to 10 hours is preferred at an annealing temperature of 300°C to 450°C, and more preferably intermittent annealing for 1 hour to 5 hours at an annealing temperature of 300°C to 380°C. When the annealing temperature is below 300°C and / or the annealing time is less than 0.1 hours, sufficient annealing effect cannot be obtained. When the annealing temperature exceeds 450°C, the grains become coarser, and the adhesion of the Ni-P coating formed in the steps described later decreases. Furthermore, when the annealing time exceeds 10 hours, the manufacturing time increases, and the productivity decreases.

[0070] Simultaneously, continuous annealing is preferably performed at an annealing temperature of 400°C to 500°C with a holding time of 60 seconds or less, and more preferably at an annealing temperature of 450°C to 500°C with a holding time of 30 seconds or less. When the annealing temperature is below 400°C, sufficient annealing effect cannot be obtained, and when the annealing temperature is above 500°C, the grains become coarser, and the adhesion of the Ni-P coating formed in the steps described later decreases. When the holding time exceeds 60 seconds, the grains become coarser, and the adhesion of the Ni-P coating formed in the steps described later decreases. Cooling can begin immediately after reaching the desired annealing temperature.

[0071] The aluminum alloy sheet is manufactured through the above steps. Next, the following steps are performed on the manufactured aluminum alloy sheet to manufacture the hard disk.

[0072] (g) Flatten the aluminum alloy sheet under pressure into a ring-shaped disc. The aluminum alloy sheet obtained through the rolling steps described above is stamped into an annular shape to manufacture an annular disc. In one embodiment, the annular disc is subjected to pressure annealing in atmospheric conditions at a temperature of 300°C to 450°C for at least 30 minutes, and preferably at a temperature of 300°C to 380°C for at least 60 minutes, to manufacture a flattened annular disc. When the pressure annealing temperature is below 300°C and / or the processing time is less than 30 minutes, a sufficient flattening effect cannot be obtained. When the processing temperature exceeds 450°C, the grains coarsen, and the adhesion of the Ni-P coating formed in the steps described later decreases. There is no particular upper limit to the processing time, but when the upper limit exceeds 24 hours, the manufacturing time increases and the productivity decreases. The pressure in the pressure annealing is typically 0.1 MPa to 3.0 MPa.

[0073] (h) The annular disc blank is cut and ground to obtain an aluminum alloy substrate for plating. Next, the annular disc blank, which has been flattened in cutting and grinding, is cut and ground to prepare the shape and surface of the annular disc blank as a whole. Then, a strain removal heat treatment is performed at a temperature of 200°C to 290°C for 0.1 hours to 10.0 hours to remove the strain of the annular disc blank.

[0074] (i) Pre-plating treatment steps The aluminum alloy substrate manufactured as described above for plating undergoes degreasing, etching, and zincate treatment (Zn replacement treatment) as a pre-plating process. Degreasing is preferably performed using, for example, a commercially available AD-68F degreasing solution (manufactured by Uemura Kogyo) under the following conditions: a degreasing temperature of 40°C or higher and 70°C or lower, a degreasing time of 3 minutes or higher and 10 minutes or lower, and a degreasing solution concentration of 200 mL / L or higher and 800 mL / L or lower. More preferably, the degreasing temperature is 45°C or higher and 65°C or lower, the degreasing time is 4 minutes or higher and 8 minutes or lower, and the degreasing solution concentration is 300 mL / L or higher and 700 mL / L or lower. Sufficient degreasing effect cannot be obtained when the degreasing temperature is below 40°C, the degreasing time is less than 3 minutes, and / or the degreasing solution concentration is less than 200 mL / L. When the degreasing temperature is higher than 70°C, the degreasing time is longer than 10 minutes, and / or the concentration of the degreasing solution is greater than 800 mL / L, the smoothness of the surface of the aluminum alloy substrate used for plating decreases, pits are formed after plating, and the smoothness is reduced.

[0075] Etching is preferably performed using, for example, a commercially available AD-107F etching solution (manufactured by Uemura Kogyo) under the following conditions: an etching temperature of 50°C or higher and 75°C or lower, an etching time of 0.5 minutes or higher and 5 minutes or lower, and an etching solution concentration of 20 mL / L or higher and 100 mL / L or lower. More preferably, the etching is performed under the following conditions: an etching temperature of 55°C or higher and 70°C or lower, an etching time of 0.5 minutes or higher and 3 minutes or lower, and an etching solution concentration of 40 mL / L or higher and 100 mL / L or lower. When the etching temperature is below 50°C, the etching time is less than 0.5 minutes, and / or the etching solution concentration is less than 20 mL / L, sufficient etching effect cannot be obtained. When the etching temperature exceeds 75°C, the etching time exceeds 5 minutes, and / or the etching solution concentration exceeds 100 mL / L, the surface smoothness of the aluminum alloy substrate used for plating decreases, pits are formed after plating, and the smoothness is reduced. A routine cleaning process can be performed between the etching process and the zincate process described later.

[0076] Zincate treatment is preferably performed using, for example, a commercially available zincate treatment solution, AD-301F-3X (manufactured by Uemura Kogyo Co., Ltd.), under the following conditions: a zincate treatment temperature of 10°C or higher and 35°C or lower, a zincate treatment time of 0.1 minutes or higher and 5 minutes or lower, and a zincate treatment solution concentration of 100 mL / L or higher and 500 mL / L or lower. More preferably, the zincate treatment temperature is 15°C or higher and 30°C or lower, a zincate treatment time of 0.1 minutes or higher and 2 minutes or lower, and a zincate treatment solution concentration of 200 mL / L or higher and 400 mL / L or lower. When the zincate treatment temperature is below 10°C, the zincate treatment time is less than 0.1 minutes, and / or the zincate treatment solution concentration is less than 100 mL / L, the zincate film becomes uneven, pits are formed after the coating treatment, and the smoothness is reduced. When 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 uneven, pits are formed after the coating treatment, and the smoothness is reduced.

[0077] (j) Steps for obtaining an aluminum alloy substrate for a disk Next, the surface of the zincate-treated aluminum alloy substrate for plating is subjected to a chemical Ni-P plating treatment as an undercoat, followed by surface polishing. The chemical Ni-P plating treatment is preferably performed using, for example, a commercially available Nimden HDX plating solution (manufactured by Uemura Kogyo Co., Ltd.) under the following conditions: a plating temperature of 80°C or higher and 95°C or lower, a plating time of 30 minutes or higher and 180 minutes or lower, and a Ni concentration in the plating solution of 3 g / L or higher and 10 g / L or lower. More preferably, it is performed under the following conditions: a plating temperature of 85°C or higher and 95°C or lower, a plating time of 60 minutes or higher and 120 minutes or lower, and a Ni concentration in the plating solution of 4 g / L or higher and 9 g / L or lower. In the film removal step according to one aspect, Ni deposited on the counter electrode surface and the Ni-containing acidic solution after anodic electrolysis can be recovered, and the Ni and the Ni-containing acidic solution can be added to the plating solution. When the plating temperature is below 80°C and / or the Ni concentration in the plating solution is less than 3 g / L, the plating growth rate is slow, leading to reduced productivity. When the plating time is less than 30 minutes, numerous defects occur on the plating surface, and the smoothness of the plating surface decreases. Simultaneously, when the plating temperature exceeds 95°C and / or the Ni concentration in the plating solution exceeds 10 g / L, uneven plating growth occurs, further reducing plating smoothness. When the plating time exceeds 180 minutes, manufacturing time increases, and productivity decreases. Furthermore, the substrate (Ni-P) plating surface is polished. Aluminum alloy substrates for disks are manufactured through pre-plating and under-plating (Ni-P) plating (with polishing).

[0078] (k) Steps for forming a magnetic material layer Following a chemical Ni-P plating process that includes polishing, a magnetic material is attached to the Ni-P plating by sputtering to form a magnetic material layer. This magnetic material layer can be a single layer or formed from multiple layers with different compositions. After sputtering, a protective layer made of carbon-based material can be formed on the magnetic material layer by CVD, or a lubricating oil can be applied to the protective layer to form a lubricating layer, if desired.

[0079] 4. Disk The disk according to the invention can be manufactured using the methods described above for manufacturing disks. The disk according to the invention comprises an aluminum alloy substrate for the disk, a Ni-P plating layer on the surface of the aluminum alloy substrate for the disk, and a magnetic material layer formed on the Ni-P plating layer. A protective layer or lubricating layer may be formed on the magnetic material layer. Since such a disk according to the invention is manufactured using the aforementioned recycled materials, it is useful as a disk that excels in reducing environmental impact.

[0080] 5. Hard drive The hard disk drive according to the invention includes one or more of the aforementioned disks, a spindle motor for rotating the disks, a clamping member for fixing the inner diameter side portion of the disks, a read / write head for processing data on the disks, an actuator for movably supporting the read / write head relative to the disks, and a pivot arm for pivoting and positioning the actuator. Since such a hard disk drive according to the invention is manufactured using the aforementioned recycled materials, it is excellent in reducing environmental impact. In particular, hard disk drives for data centers, etc., comprise a large number of disks to process large amounts of data. By using recycled materials to manufacture many of the disks in such a hard disk drive, disks that are particularly excellent in reducing environmental impact can be provided.

[0081] Based on the above embodiments, the present invention relates to the following [1] to

[18] . [1] A method for recycling aluminum alloy substrates includes: The membrane removal step (a) removes the membrane from one or more recycled materials, each comprising an aluminum alloy substrate and at least one layer of membrane on the aluminum alloy substrate, to obtain aluminum alloy material; Step (b): Use aluminum alloy material as at least part of the raw material to prepare molten aluminum alloy metal; Step (c) involves heating and holding the prepared molten metal at that temperature; and Step (d) involves casting the heated and held molten metal to obtain an aluminum alloy ingot. [2] According to the method for recycling aluminum alloy substrates [1], wherein, The membrane contains Ni. [3] According to the method for recycling aluminum alloy substrates in [1] or [2], wherein, In membrane removal step (a), the membrane is removed from the recycled material by immersing the recycled material in a solution. [4] According to the method for recycling aluminum alloy substrates in [3], wherein, The solution is an acidic solution containing nitrate ions. [5] According to the method for recycling aluminum alloy substrates in [4], wherein, The acidic solution has a temperature of 40°C to 60°C and a nitrate ion concentration of more than 25% by mass, and In the membrane removal step (a), the recovered material is immersed in an acidic solution for more than 1 hour. [6] According to the method for recycling aluminum alloy substrates in [4] or [5], wherein, The total concentration of anions other than nitrate ions in the acidic solution is less than 5% by mass. [7] According to any one of [3] to [6], a method for recycling aluminum alloy substrates, wherein, In the membrane removal step (a), multiple recycled materials are immersed in a solution such that the recycled materials do not come into contact with each other. [8] According to the method for recycling aluminum alloy substrates in [1] or [2], wherein, In membrane removal step (a), the membrane is removed from the recycled material by physically processing the recycled material. [9] According to the method for recycling aluminum alloy substrates in [8], wherein, Physical processing is a method of cutting the surface and end faces of recycled materials using a lathe, or a combination of grinding the surface of recycled materials with a grinding stone and cutting the end faces of recycled materials using a lathe.

[10] According to the method for recycling aluminum alloy substrates in [8] or [9], wherein, In physical processing, the depth of cutting on the surface and end faces of the recycled material is more than 1.05 times the thickness of the film.

[11] According to the method for recycling aluminum alloy substrates in [2], wherein, In membrane removal step (a), the membrane is removed from the recycled material by energizing the recycled material while it is immersed in the solution.

[12] According to the method for recycling aluminum alloy substrates in

[11] , wherein, The solution is an acidic solution containing sulfate ions.

[13] According to the method for recycling aluminum alloy substrates

[12] , wherein, The acidic solution has a temperature above 20°C and a sulfate ion concentration of above 5% by mass, and In membrane removal step (a), the membrane is removed by anodic electrolysis while the recovered material and the counter electrode immersed in the acidic solution are electrically connected to each other.

[14] The method for recycling aluminum alloy substrates according to

[13] also includes: The step of recovering Ni deposited on the surface of the counter electrode in the membrane removal step (a) and the Ni-containing acidic solution after anodic electrolysis.

[15] A method for recycling aluminum alloy substrates according to any one of [1] to

[14] , wherein, The aluminum alloy substrate that constitutes the recycled material has a ring shape.

[16] A method for manufacturing a hard disk includes: Step (e) involves heating the aluminum alloy ingot obtained by the method for recycling aluminum alloy substrates according to any one of [1] to

[15] to perform homogenization treatment; Rolling step (f) involves rolling an aluminum alloy ingot that has undergone homogenization treatment to obtain an aluminum alloy sheet; Step (g) involves pressing and flattening the aluminum alloy sheet obtained in rolling step (f) into an annular disc. Step (h) involves cutting and grinding the pressurized and flattened annular disc blank to obtain an aluminum alloy substrate for plating; The pre-plating process (i) involves degreasing, etching, and zincate treatment of the aluminum alloy substrate to be plated. Step (j) involves chemically depositing Ni-P onto the surface of the pre-plated aluminum alloy substrate, followed by polishing the Ni-P-plated surface to obtain the aluminum alloy substrate for the disk; and Step (k) involves attaching magnetic material to the surface of an aluminum alloy substrate for a disk to form a magnetic material layer.

[17] A disk obtained by means of a method for manufacturing a disk according to

[16] .

[18] A hard disk drive, comprising: According to

[17] disk.

[0100] Although the method for recycling aluminum alloy substrates, the method for manufacturing disks, the disks, and the hard disk drives according to this embodiment have been described above, the present invention is not limited to the above embodiments, and various modifications and changes can be made based on the technical concept of the present invention.

[0101] Example The present invention will now be described in more detail based on embodiments, but the invention is not limited thereto.

[0102] (Examples 1A to 4A, and Comparative Examples 1A and 2A) As the recycling material, an aluminum alloy substrate used for disks (hereinafter referred to as the "sample"; outer diameter: 95 mm, inner diameter: 25 mm, total thickness: 1.3 mm) was used, which had an aluminum alloy substrate made of JIS 5086 alloy (Al-Mg alloy) and a Ni-P coating (film) with a thickness of 10 μm formed on the aluminum alloy substrate by chemical Ni-P plating. The samples in each embodiment were immersed in an acidic solution under the conditions shown in Table 1. The acidic solution in each embodiment consisted of an acid component and water, which was a mixture of nitric acid, hydrochloric acid and sulfuric acid, and the total content of the acid component and water was 100% by mass.

[0103] The aluminum alloy used for the aluminum alloy substrate contains 0.02% by mass Fe, 0.018% by mass Si, 4.02% by mass Mg, 0.35% by mass Zn and 0.052% by mass Cr, with the balance being Al, unavoidable impurities and trace elements.

[0104] [Table 1]

[0105] The measurement of “sample thinning amount” and “membrane removal assessment” described in Table 1 were performed as follows.

[0106] (Measurement of sample thinning amount) The mass of the sample before immersion in the acidic solution was measured. Next, the sample immersed in the acidic solution was washed with pure water, dried with a hot air dryer, and its mass was measured again. Then, the thickness reduction of the sample was calculated as {(mass of the sample before immersion in the acidic solution) - (mass of the sample after immersion in the acidic solution)} / (specific gravity of the Ni-P coating × total surface area of ​​the sample) to measure the thickness reduction of each sample surface. The specific gravity of the Ni-P coating was 7.6 g / m². 3 .

[0107] (Membrane removal assessment) Visually inspect the appearance of the entire sample, including the outer periphery, after immersion in the acidic solution. Cases where no Ni-P coating is detected and the Ni-P coating is completely removed are evaluated as "◎", and cases where residual Ni-P coating is detected are evaluated as "×".

[0108] (Recovery assessment) A 1 kg sample was obtained, comprising multiple samples from which the Ni-P coating had been removed under the conditions of Example 1A. Six samples were freely selected from the multiple samples from which the Ni-P coating had been removed, and the composition of the aluminum alloy in each sample was analyzed by a first spark discharge emission spectrometry (SESES), and the average value of the detected elements was calculated. Subsequently, all 1 kg samples were dissolved to prepare molten metal, and after the molten metal was heated and held at a certain temperature, it was poured into a mold and cast to obtain an aluminum alloy ingot. The cast aluminum alloy ingot was cut into arbitrary sizes, and the composition of the aluminum alloy was analyzed by a method similar to that of the first spark discharge emission spectrometry (a second spark discharge emission spectrometry). Furthermore, the following calculation was made: {(content of each element obtained by the second spark discharge emission spectrometry) - (content of each element obtained by the first spark discharge emission spectrometry)} / (content of each element obtained by the first spark discharge emission spectrometry) × 100 (%) (described as “variable” in Table 2). The results of the spark discharge emission spectrometry are shown in Table 2.

[0109] [Table 2]

[0110] In each embodiment, the sample film used was a Ni-P coating with a thickness of 10 μm. As shown in Table 1, it was confirmed that in Examples 1A to 4A, the Ni-P coating could be effectively removed because the sample thinning amount was 10 μm or more. As indicated by "◎" in Table 1, visual observation confirmed that the Ni-P coating was completely removed in the samples of Examples 1A to 4A. Meanwhile, as shown in Table 1, in Comparative Examples 1A and 2A, the sample thinning amount was 0 μm, and the Ni-P coating could not be removed. As indicated by "×" in Table 1, visual observation confirmed that Ni-P coating residue remained in the samples of Comparative Examples 1A and 2A.

[0111] As shown in Table 2, the variations in Fe, Si, Mg, Zn, and Cr are less than ±4.19% by mass. This variation is acceptable and confirms that the composition of the aluminum alloy remains substantially unchanged after the removal of the Ni-P coating and before the preparation of the molten metal, as well as during the preparation of the molten metal, heating and holding, and after casting.

[0112] (Examples 1B to 3B) As the recycling material, an aluminum alloy substrate (outer diameter: 95 mm, inner diameter: 25 mm, total thickness: 1.3 mm) used for hard disks was used as the test material. This aluminum alloy substrate for hard disks has an aluminum alloy substrate made of JIS 5086 alloy (Al-Mg alloy) and a Ni-P coating (film) formed on the aluminum alloy substrate by chemical Ni-P plating. Samples in each embodiment were obtained by cutting the test material into 20 mm × 45 mm dimensions, leaving a clamping allowance at the top of the test material and a 10 mm × 10 mm allowance at the bottom as the target area for peeling, while masking the test material.

[0113] The aluminum alloy used for the aluminum alloy substrate contains 0.02% by mass Fe, 0.018% by mass Si, 4.02% by mass Mg, 0.35% by mass Zn and 0.052% by mass Cr, with the balance being Al, unavoidable impurities and trace elements.

[0114] In each embodiment, the sample is electrically connected to the positive terminal of the power supply, the Pt wire is used as the counter electrode, the negative terminal of the power supply is electrically connected to the counter electrode, and the sample and counter electrode are immersed in an acidic solution to manufacture as described above. Figure 1 The anodic electrolysis apparatus is shown. During anodic electrolysis, the composition of the acidic solution and the voltage applied between the sample and the counter electrode are set as shown in Table 3 below. The acidic solution contains sulfuric acid and pure water, with the pure water content being 90% by mass. Preliminary tests have confirmed that during anodic electrolysis, the change in current density flowing between the sample and the counter electrode over time is measured. (1) In the initial stage of anodic electrolysis, the current density is constant. (2) As the removal of the Ni-P coating (film) proceeds, the current density decreases rapidly. (3) When the removal of the Ni-P coating (film) is complete, and the aluminum alloy substrate is exposed and an anodic aluminum oxide film is formed on the aluminum alloy substrate, the current density is significantly lower than the constant current in the initial stage of anodic electrolysis. Therefore, in each embodiment, the change in current density flowing between the sample and the counter electrode over time during anodic electrolysis is measured, and the time when the state of (3) is first observed is measured as the "peel-off time" when the removal of the film is complete.

[0115] Figure 2 This is a graph showing the change in current density over time during anodic electrolysis in Example 1B. Figure 2 In this case, the start time of anodic electrolysis is 0 seconds. For example... Figure 2 As shown, in Example 1B, the current density begins to decrease approximately 80 seconds after the start of anodic electrolysis, and after 125 seconds, the current density becomes low and constant. Therefore, the stripping time is set to 125 seconds. The "stripping time" measured in each example is shown in Table 3.

[0116] (Comparative Example 1B and Comparative Example 2B) The composition of the acidic solution is shown in Table 3 below. The samples were immersed in the acidic solution without anodic electrolysis. The acidic solution contained sulfuric acid or hydrochloric acid and pure water, with the pure water content being 90% by mass. In Comparative Examples 1B and 2B, since no voltage was applied to the samples, it was visually confirmed whether the Ni-P coating (film) had been removed. In Comparative Examples 1B and 2B, it was confirmed that the Ni-P coating (film) remained even after immersing the samples in the acidic solution for 60 minutes. Therefore, in Table 3 below, the peeling time in Comparative Examples 1B and 2B is indicated as "-".

[0117] [Table 3]

[0118] As shown in Examples 1B to 3B in Table 3, the stripping time was shortest in Example 1B, where the voltage during anodic electrolysis was the highest, and longest in Example 3B, where the voltage during anodic electrolysis was the lowest. This indicates that the film removal effect is high when the voltage during anodic electrolysis is 2 V. In Comparative Examples 1B and 2B, the Ni-P coating (film) could not be removed because anodic electrolysis was not performed. As described above, it has been confirmed that the method of the present invention for recycling aluminum alloy substrates can effectively remove Ni-P coatings (films), and that the recycling method is excellent in terms of recyclability.

[0119] (Examples 1C to 6C and Comparative Examples 1C to 4C) As the recycled material, an aluminum alloy substrate used for hard disk drives (hereinafter referred to as the "sample"; outer diameter: 95 mm, inner diameter: 25 mm, total thickness: 1.3 mm) was used. This sample had an aluminum alloy substrate made of JIS5086 alloy (Al-Mg alloy) and a Ni-P coating (film) formed on the aluminum alloy substrate by chemical Ni-P plating. The film formed on the aluminum alloy substrate had a surface thickness (both main surfaces) of 10 μm and an end-face thickness (the side surface on the inner diameter side and the side surface on the outer diameter side) of 11 μm. The samples in each embodiment were cut under the conditions shown in Table 4. The "cutting amount" in Table 4 refers to the depth to which the surface and end-face of the sample were cut.

[0120] The aluminum alloy used for the aluminum alloy substrate has a composition of 4% by mass Mg, 0.025% by mass Fe, 0.025% by mass Si, 0.3% by mass Zn and 0.05% by mass Cu, with the balance being Al, unavoidable impurities and trace elements.

[0121] (Recovery assessment) Recyclability was assessed based on the residual state of the removed film by observing the appearance of the sample's surface and end faces after cutting. No Ni-P coating was detected, and residual Ni-P coating was detected, which was assessed as "×". Good recyclability was indicated when both the sample's surface and end faces were assessed as "○".

[0122] [Table 4]

[0123] As shown in Table 4, in Examples 1C to 6C, when both the surface and end face of the sample were evaluated as "○", it was confirmed that the Ni-P coating was completely removed. Meanwhile, in Comparative Examples 1C and 3C, both the surface and end face of the sample were evaluated as "×", and the Ni-P coating remained overall. In Comparative Examples 2C and 4C, either the surface or end face of the sample was evaluated as "×", and the Ni-P coating remained locally.

[0124] Industrial applicability According to the present invention, a method for recycling aluminum alloy substrates with excellent recyclability can be provided. Since disks can be manufactured by reusing the aluminum alloy sheets obtained by such recycling method, the amount of expensive high-purity base metal to be used can be reduced, thereby reducing costs and being advantageous from an environmental protection perspective.

[0125] List of reference numerals 1: Anode electrolysis device 2: Ni-P coating (film) 3: Aluminum alloy substrate 4: Counter electrode 5: Power supply 6: Acid solution 7: Anodized aluminum film.

Claims

1. A method for recycling aluminum alloy substrates, comprising: The membrane removal step (a) involves removing the membrane from one or more recycled materials, each comprising the aluminum alloy substrate and at least one layer of membrane on the aluminum alloy substrate, to obtain aluminum alloy material; Step (b): Use the aluminum alloy material as at least part of the raw material to prepare molten aluminum alloy metal; Step (c) involves heating and holding the prepared molten metal at that temperature. as well as Step (d) involves casting the heated and held molten metal to obtain an aluminum alloy ingot.

2. The method for recycling aluminum alloy substrates according to claim 1, wherein, The membrane contains Ni.

3. The method for recycling aluminum alloy substrates according to claim 1, wherein, In the membrane removal step (a), the membrane is removed from the recycled material by immersing the recycled material in a solution.

4. The method for recycling aluminum alloy substrates according to claim 3, wherein, The solution is an acidic solution containing nitrate ions.

5. The method for recycling aluminum alloy substrates according to claim 4, wherein, The acidic solution has a temperature of 40°C to 60°C and a nitrate ion concentration of more than 25% by mass, and In the membrane removal step (a), the recovered material is immersed in the acidic solution for more than 1 hour.

6. The method for recycling aluminum alloy substrates according to claim 5, wherein, The total concentration of anions other than nitrate ions in the acidic solution is less than 5% by mass.

7. The method for recycling aluminum alloy substrates according to claim 3, wherein, In the membrane removal step (a), a plurality of the recovered materials are immersed in a solution such that the recovered materials do not come into contact with each other.

8. The method for recycling aluminum alloy substrates according to claim 1, wherein, In the membrane removal step (a), the membrane is removed from the recycled material by physically processing the recycled material.

9. The method for recycling aluminum alloy substrates according to claim 8, wherein, The physical processing is a method of cutting the surface and end faces of the recycled material using a lathe, or a combination of a method of grinding the surface of the recycled material with a grinding stone and a method of cutting the end faces of the recycled material using a lathe.

10. The method for recycling aluminum alloy substrates according to claim 8, wherein, In the physical processing, the depth of cutting on the surface and end face of the recycled material is more than 1.05 times the thickness of the film.

11. The method for recycling aluminum alloy substrates according to claim 2, wherein, In the membrane removal step (a), the membrane is removed from the recycled material by energizing the recycled material while it is immersed in a solution.

12. The method for recycling aluminum alloy substrates according to claim 11, wherein, The solution is an acidic solution containing sulfate ions.

13. The method for recycling aluminum alloy substrates according to claim 12, wherein, The acidic solution has a temperature above 20°C and a sulfate ion concentration of above 5% by mass, and In the membrane removal step (a), the membrane is removed by anodic electrolysis while the recovered material immersed in the acidic solution and the counter electrode are electrically connected to each other.

14. The method for recycling aluminum alloy substrates according to claim 13, further comprising: The step of recovering Ni deposited on the surface of the counter electrode in the membrane removal step (a) and the Ni-containing acidic solution after the anodic electrolysis.

15. The method for recycling aluminum alloy substrates according to claim 1 or 2, wherein, The aluminum alloy substrate constituting the recycled material has an annular shape.

16. A method for manufacturing a disk, comprising: Step (e) involves heating the aluminum alloy ingot obtained by the method for recycling aluminum alloy substrates according to claim 1 or 2 to perform homogenization treatment; Rolling step (f) involves rolling the aluminum alloy ingot that has undergone the homogenization treatment to obtain an aluminum alloy sheet; Step (g) involves flattening the aluminum alloy sheet obtained in the rolling step (f) into an annular disc. Step (h) involves cutting and grinding the pressurized and flattened annular disc blank to obtain an aluminum alloy substrate for plating; The pre-plating process (i) involves degreasing, etching, and zincate treatment of the aluminum alloy substrate to be plated. Step (j): Perform chemical Ni-P plating on the surface of the aluminum alloy substrate that has undergone the pre-plating treatment, and then polish the surface that has undergone the Ni-P plating treatment to obtain an aluminum alloy substrate for disk. as well as Step (k) involves attaching magnetic material to the surface of the aluminum alloy substrate for the disk to form a magnetic material layer.

17. A disk obtained by the method for manufacturing a disk according to claim 16.

18. A hard disk drive, comprising: The disk according to claim 17.

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