Recycling method for aluminum alloy substrates, production method for magnetic disk, magnetic disk, and hard disk drive

Abstract

The present invention relates to a recycling method for aluminum alloy substrates that involves a coating film removal step (a) for removing a coating film from a recycling material that includes aluminum alloy substrates and at least one layer of a coating film that is on the aluminum alloy substrates to obtain an aluminum alloy material, a step (b) for using at least a portion of the aluminum alloy material as a starting material to prepare a molten aluminum alloy, a step (c) for heating and holding the prepared molten aluminum alloy, and a step (d) for casting the heated and held molten aluminum alloy to obtain an aluminum alloy ingot.

Description

Aluminum alloy substrate recycling method, magnetic disk manufacturing method, magnetic disk, and hard disk drive

[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.

[0002] Hard disk drives (HDDs) are widely used as storage devices for various electronic devices, including computers and data centers. HDDs store information on magnetic disks, and aluminum alloy substrates for magnetic disks are used as the substrates for these magnetic disks. Aluminum alloy substrates for magnetic disks are made of JIS 5086 alloy (an aluminum alloy containing 3.5% by mass or more and 4.5% by mass or less of Mg, 0.50% by mass or less of Fe, 0.40% by mass or less of Si, 0.20% by mass or more and 0.70% by mass or less of Mn, 0.05% by mass or more and 0.25% by mass or less of Cr, 0.10% by mass or less of Cu, 0.15% by mass or less of Ti, and 0.25% by mass or less of Zn, with the remainder being Al and unavoidable impurities), which has good plating properties and excellent mechanical properties and processability. In one example, the aluminum alloy substrate is manufactured by subjecting the aluminum alloy substrate to electroless Ni-P plating treatment, followed by a process of polishing the surface to a smooth surface.

[0003] For example, an aluminum alloy substrate for a magnetic disk using JIS 5086 alloy is manufactured by the following manufacturing process. First, an aluminum alloy containing the desired chemical composition is cast, and the resulting ingot is homogenized and then hot-rolled. Then, cold-rolled to produce a rolled material of the required thickness for a magnetic disk. This rolled material is preferably annealed, if necessary, during cold-rolling. Next, this rolled material is punched into an annular shape to produce an annular disk blank. To remove distortions and other impurities caused by the manufacturing process, the annular disk blanks are stacked and annealed while applying pressure from both sides to flatten them. The annular disk blanks thus produced are pre-treated with cutting, grinding, degreasing, etching, and zincating (Zn substitution), followed by electroless plating with Ni—P, a hard non-magnetic metal, as a base treatment. The Ni—P-plated surface is then polished, and a magnetic layer is then formed by sputtering a magnetic material, thereby producing 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 high-capacity HDDs have become increasingly common. Given these current circumstances, increasing the capacity of HDDs has become essential. Increasing the capacity of HDDs requires both increasing the number of magnetic disks installed and increasing the capacity per magnetic disk. The former requires reducing the thickness of the magnetic disk, while the latter requires reducing defects on the Ni-P plating surface of the aluminum alloy substrate for magnetic disks. While both of these methods are technically feasible, they result in lower yields in the magnetic disk manufacturing process. Specifically, reducing the thickness of the magnetic disk requires higher processing accuracy during rolling and grinding, while the latter requires a stricter threshold for the number of defects on the Ni-P surface. In other words, the number of defective aluminum alloy substrates for magnetic disks will increase. Considering future demand for magnetic disks, it is easy to predict that the number of defective aluminum alloy substrates for magnetic disks will increase.

[0005] In recent years, growing interest in environmental conservation has made the establishment of metal product recycling technologies essential. It has also become clear that certain types of metals face increasingly significant geopolitical risks. While aluminum is a relatively easy metal to recycle, the difficulty of recycling varies depending on its alloy system. For example, aluminum can materials can be easily recycled by collecting the same alloy. However, aluminum clad materials used in heat exchangers have a multilayer structure of aluminum alloys with different compositions, making it impossible to separate the individual layers. This requires the entire aluminum clad material to be remelted and cast, which alters the original alloy composition, potentially limiting its range of use after recycling.

[0006] On the other hand, aluminum alloys for magnetic disks are high-cost materials that use large amounts of high-purity metal and limit the content of Fe, Si, etc. in order to improve plating defects. Therefore, recycling as much as possible makes it possible to reduce the amount of high-purity metal used. This reduces the amount of high-purity metal produced, which contributes to environmental conservation.

[0007] When an aluminum alloy substrate for magnetic disks is found to be defective because it does not meet the required standards during rolling, grinding, or the like during the manufacturing process, it can be reused as a part of the raw material. However, when a defective aluminum alloy substrate for magnetic disks is produced in a state where the substrate has a coating such as a Ni—P plating layer formed on its surface, its recycling becomes complicated. That is, since the aluminum alloy substrate for magnetic disks is provided with a coating such as a Ni—P plating layer, it can be used as a casting alloy for HDD housings, for example. On the other hand, as mentioned above, reusing an aluminum alloy containing a large amount of high-purity metal as a casting is inefficient in terms of recycling, and therefore it is desirable to reuse it as a rolled material, preferably as an aluminum alloy for magnetic disks again.

[0008] In light of this background, there is a need to establish a technique 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 aluminum alloy substrates with Ni-P plating layers still attached thereto as raw materials for Al-Si alloys. Although this technique makes it possible to reuse aluminum alloy substrates, it is difficult to efficiently utilize aluminum alloy substrates made from high-purity metal.

[0009] Patent Document 2 discloses a method for reusing an aluminum alloy substrate after removing the Ni-P plating layer by returning it to the plating process. This technology makes it possible to reuse the regenerated aluminum alloy substrate. However, recent aluminum alloy substrates for magnetic disks have very strict requirements for preventing defects on the Ni-P plating surface. If an aluminum alloy substrate from which the Ni-P plating layer has been stripped is reused as is, the aluminum alloy substrate will be plated in a damaged state, which may result in frequent defects on the plating surface.

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

[0011] Patent No. 4656194 Japanese Patent Application Laid-open No. 63-282281

[0012] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for recycling aluminum alloy substrates, which has excellent recyclability.

[0013] The present inventors have found that an aluminum alloy plate with excellent recyclability can be obtained by preparing a molten metal, heating and holding the molten metal, and casting the molten metal using, as at least a part of a raw material, an aluminum alloy material obtained by removing a coating from a recycled material having an aluminum alloy substrate and at least one layer of a coating, and have thus completed the present invention.

[0014] A method for recycling an aluminum alloy substrate according to an embodiment of the present invention includes the steps of: obtaining an aluminum alloy material by removing at least one coating from a recycled material having an aluminum alloy substrate and the coating on the aluminum alloy substrate; preparing a molten aluminum alloy using the aluminum alloy material as at least a part of a raw material; heating and holding the prepared molten aluminum; and casting the heated and held molten aluminum to obtain an aluminum alloy ingot.

[0015] According to the present invention, a method for recycling an aluminum alloy substrate with excellent recyclability can be provided.

[0016] 1 is a diagram showing a film removal step in one embodiment of the method for recycling an aluminum alloy substrate according to the present invention. FIG. 2 is a diagram showing the change over time in current density during anodic electrolysis in Example 1B.

[0017] Hereinafter, embodiments of the present invention will be described in detail.

[0018] 1. Method for Recycling Aluminum Alloy Substrates The method for recycling aluminum alloy substrates according to the present invention comprises: (a) a film removing step of obtaining an aluminum alloy material by removing a coating from a recycled material having an aluminum alloy substrate and at least one coating layer on the aluminum alloy substrate; (b) a step of preparing a molten aluminum alloy using the aluminum alloy material as at least a part of a raw material; (c) a step of heating and holding the prepared molten metal; and (d) a step of casting the heated and held molten metal to obtain an aluminum alloy ingot.

[0019] In the method for recycling aluminum alloy substrates of the present invention, the aluminum alloy material obtained by removing the coating from the recycled material in the coating removal step is used as at least a part of the raw material, and a molten aluminum alloy is prepared, the molten metal is heated and maintained, and an aluminum alloy ingot is produced from the molten metal. While conventional techniques can reuse Ni-P plated aluminum alloy substrates as raw materials for Al-Si alloys, the applications of the raw material are limited, and efficient recycling of aluminum alloy substrates containing high-purity metals has not yet been achieved. Furthermore, because the aluminum alloy substrate from which the coating has been removed is recycled as is and a coating such as a Ni-P plating layer is formed on the aluminum alloy substrate, defects may occur in the coating on the aluminum alloy substrate.

[0020] In contrast, in the method for recycling aluminum alloy substrates of the present invention, the coating can be effectively removed from the recycled material in the coating removal step. The aluminum alloy material obtained after coating removal can be used as is to prepare a molten aluminum alloy and carry out subsequent steps, thereby producing an aluminum alloy ingot that maintains the alloy composition of the aluminum alloy material. Furthermore, by adding any material, element, aluminum alloy base metal, etc. to the molten aluminum alloy when preparing the molten aluminum alloy, an aluminum alloy ingot with a desired alloy composition can be produced.

[0021] In one embodiment of the method for recycling an aluminum alloy substrate of the present invention, in the coating removal step, a recycled material having an aluminum alloy substrate and at least one Ni-containing coating thereon is immersed in a solution, and an electric current is passed through the recycled material to remove the coating from the recycled material, thereby obtaining an aluminum alloy material. This allows the Ni-containing coating to be effectively removed.

[0022] In one embodiment of the method for recycling an aluminum alloy substrate of the present invention, a physical process is applied to the recycled material in the film removal step, and an aluminum alloy material is produced by removing the film from the recycled material. Because the film is removed by physical processing in this manner, the film can be easily and reliably removed from the aluminum alloy substrate. Furthermore, because the film is completely removed from the aluminum alloy substrate by such physical processing, defects in the film can be suppressed even when a new aluminum alloy plate is manufactured using the resulting aluminum alloy material and a film such as a Ni—P plating layer is formed using this. A method for recycling an aluminum alloy substrate with excellent recyclability can be provided.

[0023] In this way, the present invention can provide a recycling method for aluminum alloy substrates with excellent recyclability. Furthermore, since it is possible to reduce the amount of expensive high-purity aluminum metal used while maintaining the performance of the aluminum alloy plate, costs can be reduced. Furthermore, in one embodiment, the aluminum alloy material obtained after removing the Ni-containing coating is used as a raw material to prepare a molten aluminum alloy and perform subsequent processes, thereby producing an aluminum alloy plate that maintains the alloy composition of the aluminum alloy material. In this embodiment, an aluminum alloy plate with a desired alloy composition can be produced by adding any material, element, aluminum alloy metal, etc. to the molten aluminum alloy during the preparation of the molten aluminum alloy. Furthermore, by setting the conditions for heating and holding the molten aluminum, producing an aluminum alloy ingot from the molten aluminum, homogenizing the aluminum alloy ingot, and rolling the aluminum alloy ingot to predetermined conditions, the properties and characteristics of the aluminum alloy plate after rolling can be set to desired properties and characteristics different from those of recycled materials. Furthermore, in one embodiment, the rolled aluminum alloy plate can have fewer surface defects, and therefore, when a coating is formed on the aluminum alloy plate, defects in the coating can also be reduced.

[0024] (Recycled material) The term "recycled material" used in the present invention refers to a material having an aluminum alloy substrate and a coating on the aluminum alloy substrate. Examples of recycled materials include intermediate materials and finished products generated during the manufacturing process of magnetic disks. An example of an "intermediate material" is an aluminum alloy substrate for magnetic disks, and an example of a "finished product" is a magnetic disk. These recycled materials include defective products, non-standard products, and, in the case of magnetic disks, used products.

[0025] Furthermore, the term "coating" refers to one or more layers formed on an aluminum alloy substrate, and in one embodiment, one or more of the layers contains a layer containing Ni. Such a coating may be composed of a layer containing Ni, or may be composed of a layer containing Ni and a layer not containing Ni. Examples of such coatings include a Ni-P plating layer, a magnetic layer, a protective layer, and a lubricating layer. Of these coatings, for example, in the intermediate material and finished product described below, the coating formed on the aluminum alloy substrate contains a Ni-containing coating, specifically a Ni-P plating layer.

[0026] The shape of the recycled material is not particularly limited, and may be circular, polygonal, or an irregular shape without a specific shape. Because many recycled materials are circular disks, circular recycled material is easy to procure. Furthermore, circular recycled material can be used in a bent, deformed, perforated, or cut state, making it easy to efficiently remove the coating without having to change the processing conditions each time. Therefore, it is preferable that the aluminum alloy substrate constituting the recycled material is circular. In the method for recycling an aluminum alloy substrate of the present invention, the aluminum alloy material obtained by the coating removal step is used as at least a part of the raw material. The aluminum alloy material may be used alone as the raw material, or other materials or elements may be used together with the aluminum alloy material as raw materials.

[0027] (Intermediate Material) An example of an intermediate material is an aluminum alloy substrate for magnetic disks produced during the manufacturing process of a magnetic disk. In one example, a Ni-containing coating, 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 Ni-containing coating used in the aluminum alloy substrate for magnetic disks is, for example, 80% by mass or more and 95% by mass or less. Furthermore, when the Ni-containing coating is a Ni—P plating layer, the P content in the Ni—P plating layer is, for example, 5% by mass or more and 20% by mass or less. Furthermore, the thickness of the Ni-containing coating is not particularly limited, but is, for example, 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.

[0028] (Finished Product) An example of a finished product is a magnetic disk. In one example of a magnetic disk, a Ni—P plating layer, a CoCrPt-based magnetic layer, and a protective layer of a carbon-based material or the like are sequentially formed as coatings on the surface of an aluminum alloy substrate for a magnetic disk. Because these magnetic layers and protective layers are formed on the Ni—P plating layer, removing the Ni—P plating layer also allows these magnetic layers and protective layers to be removed together. Therefore, the aluminum alloy material obtained by removing the coating from the finished magnetic disk can also be used as at least a part of the raw material to prepare a molten aluminum alloy.

[0029] 2. Each step of the method for recycling an aluminum alloy substrate As described above, the method for recycling an aluminum alloy substrate of the present invention comprises steps (a) to (d). Each of steps (a) to (d) will be described in detail below.

[0030] (a) Coating Removal Step In the coating removal step, the coating is removed from the recycled material. The coating removal method is not particularly limited, but examples include chemical treatment, physical treatment, and thermal treatment. Chemical treatment is preferably used in the coating removal step, and it is more preferable to remove the coating from the recycled material by immersing the recycled material in a solution. One example of the recycled material has a Ni—P plating layer as a coating on an aluminum alloy substrate, and the Ni—P plating layer is formed on all surfaces of the aluminum alloy substrate, including both surfaces and the inner and outer diameters. By immersing the recycled material in the solution, the Ni—P plating layer formed as a coating on all surfaces can be effectively removed.

[0031] 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 plating layers can be efficiently removed. Furthermore, because aluminum alloy substrates are corrosion-resistant to acidic solutions containing nitrate ions, the aluminum alloy substrates do not dissolve in the acidic solution. As a result, high-quality aluminum alloy sheets can be obtained. Furthermore, when recycled material having a film such as a Ni—P plating layer is immersed in an alkaline solution, the Ni—P plating layer does not dissolve due to its corrosion resistance to the alkaline solution, making it difficult to remove the film such as the Ni—P plating layer. In contrast, by immersing the recycled material in an acidic solution containing nitrate ions, such a situation can be prevented.

[0032] The acidic solution can be prepared by dissolving nitric acid or a nitrate such as sodium nitrate or potassium nitrate in a solvent such as pure water, industrial water, or tap water, but an aqueous nitric acid solution is preferred. However, when a nitrate is used, it is necessary to further add nitric acid or hydrochloric acid to prepare an acidic solution. Commercially available aqueous nitric acid solutions 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. By having the nitrate ion concentration in the acidic solution within the above range, the coating can be removed efficiently in a short time.

[0033] The acidic solution may contain anions other than nitrate ions, such as chloride ions, sulfate ions, and phosphate ions. 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. By keeping the total concentration of anions other than nitrate ions in the acidic solution within the above range, the anions other than nitrate ions do not affect the film-removing action of nitrate ions, allowing for efficient film removal. Furthermore, the pH of the acidic solution is preferably −1 to 4, more preferably −1 to 3, and even more preferably −1 to 2. By keeping the pH of the acidic solution within the above range, efficient film removal is possible.

[0034] The conditions for immersing the recycled material in the acidic solution can be set to a suitable temperature and time depending on the characteristics of the recycled material. The acidic solution preferably has a temperature of 40 to 60°C, more preferably 45 to 60°C, and even more preferably 50 to 60°C. By keeping the temperature of the acidic solution within the above range, the coating can be efficiently removed in a short time and gas generation due to decomposition of nitric acid can be prevented. The time for immersing the recycled material in the acidic solution is preferably 1 hour or more, more preferably 1 to 3 hours, and even more preferably 1.5 to 2 hours. By keeping the time for immersing the recycled material in the acidic solution within the above range, the coating can be efficiently removed without leaving any residue.

[0035] The rate of film removal depends on the conditions of the film removal process, but in one example, 4 to 7 μm of film is removed in 30 minutes. On the other hand, the thickness of the film on the annular recycled material is, for example, 5 to 10 μm on the surface and 7 to 12 μm on the inner and outer diameters. Therefore, in the above example, by immersing the recycled material in the acidic solution for one hour or more, the film can be effectively and reliably removed from both sides and the entire inner and outer diameters of the aluminum alloy substrate.

[0036] In the coating removal process, one or more sheets of recycled material can be immersed in the solution. When immersing one sheet of recycled material in the solution, the coating can be removed from the recycled material in a short time. When immersing multiple sheets of recycled material in the solution, the coating can be removed from many recycled materials at once, allowing for a larger number of recycled materials to be processed. When immersing multiple sheets of recycled material in the solution, it is preferable to arrange the recycled materials in the solution so that they do not come into contact with each other. By arranging multiple sheets of recycled material in this manner, the solution is less likely to penetrate into the contact areas between the recycled materials, preventing the remaining coating from remaining in parts. Furthermore, this prevents the aluminum alloy in recycled material from which the coating has been removed and the aluminum alloy from which the coating has not been removed from contacting each other, resulting in bimetallic contact and preventing the coating removal from progressing. The spacing between each recycled material in the solution is not particularly limited and can be set as desired depending on the size of the container containing the solution, the number and size of the recycled materials to be immersed in the solution, etc.

[0037] In one embodiment of the coating removal process, the recycled material is immersed in a solution and an electric current is applied to the recycled material to remove the coating from the recycled material, thereby obtaining an aluminum alloy material. Here, "applying an electric current" means passing electricity through the recycled material immersed in the solution. By immersing the recycled material in the solution and applying an electric current to the recycled material, Ni from the Ni-containing coating that constitutes the recycled material becomes Ni ions through chemical and electrical actions and dissolves in the solution. As a result, the Ni-containing coating can be effectively removed. The method of applying an electric current to the recycled material is not particularly limited, but an example is to electrically connect at least the positive electrode of a power source directly to the recycled material.

[0038] Such a solution is preferably an acidic solution containing sulfate ions, and more preferably, the film is removed by performing anodic electrolysis while the recycled material immersed in the acidic solution is electrically connected to a counter electrode. One example of the recycled material has a Ni—P plating layer as a film on an aluminum alloy substrate, and the Ni—P plating layer is formed on both surfaces, the inner diameter, and all surfaces of the aluminum alloy substrate. By passing a current through the recycled material while it is immersed in the acidic solution, the Ni—P plating layer formed as a film on all surfaces can be removed. In particular, performing anodic electrolysis while the recycled material immersed in the acidic solution containing sulfate ions is electrically connected to a counter electrode can effectively remove the Ni—P plating layer.

[0039] Furthermore, an alumite film is formed on the surface of the aluminum alloy substrate exposed by removing the Ni-P plating layer, preventing dissolution of the aluminum alloy substrate and allowing the Ni-P plating layer to be selectively removed. Furthermore, if the recycled material is simply immersed in an alkaline solution without applying current, the corrosion resistance of Ni-containing films such as the Ni-P plating layer to the alkaline solution prevents dissolution of Ni into the solution, making it difficult to remove the film. In contrast, by performing anodic electrolysis while electrically connecting the recycled material immersed in the acidic solution containing sulfate ions as described above to a counter electrode, the Ni-containing film can be effectively and selectively removed while preventing dissolution of the aluminum alloy substrate.

[0040] 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. However, when a sulfate is used, sulfuric acid or nitric acid must be further added to prepare the acidic solution. Alternatively, a commercially available aqueous sulfuric acid solution can 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. By having the sulfate ion concentration in the acidic solution within the above range, the film can be efficiently removed in a short time. Furthermore, the pH of the acidic solution is preferably 0 to 4, more preferably 0 to 3, and even more preferably 1 to 2. By having the pH of the acidic solution within the above range, the film can be efficiently removed.

[0041] When the acidic solution contains sulfate ions, the acidic solution may also contain anions other than sulfate ions, such as chloride ions, nitrate ions, phosphate ions, etc. From the viewpoint of effectively preventing dissolution of aluminum from the aluminum alloy substrate constituting the recycled material, the concentration of anions other than sulfate ions in the acidic solution is preferably 5 mass% or less.

[0042] Conditions for performing anodic electrolysis in a state in which the recycled material immersed in the acidic solution is electrically connected to the counter electrode include the temperature of the acidic solution, the time for anodic electrolysis, the material and size of the counter electrode, and the material and size of the recycled material. The acidic solution preferably has a temperature of 20°C or higher, more preferably 20 to 50°C, and even more preferably 25 to 40°C. By keeping the temperature of the acidic solution within the above range, it is possible to efficiently remove the Ni-containing coating in a short time and save on equipment and energy required to heat the acidic solution.

[0043] The counter electrode used when performing anodic electrolysis while electrically connecting the recycled material immersed in an acidic solution with the counter electrode is electrically connected directly to the negative electrode of a power source and positioned so as to face the recycled material in the acidic solution. A voltage is applied between the recycled material and the counter electrode by the power source. The material of the counter electrode is not particularly limited as long as it can perform anodic electrolysis of the recycled material, but examples of materials that can be used include platinum (Pt), nickel (Ni), aluminum (Al), and carbon (C). The shape of the counter electrode is not particularly limited, but can be, for example, a plate or wire shape. The voltage applied between the recycled 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. By keeping the voltage during anodic electrolysis within the above range, the Ni-containing coating can be efficiently removed in a short time. The recycled material and the counter electrode may each be entirely immersed in the acidic solution, or a portion of each may be exposed to the acidic solution and the remaining portion immersed in the acidic solution.

[0044] 1A and 1B are diagrams illustrating a process of performing anodic electrolysis in a film removal step according to an embodiment. As shown in FIG. 1A, an anodic electrolysis device 1 is configured to ２ SO ４ The apparatus includes a container for containing an acidic solution 6 containing sulfuric acid (H), a recycled material having an aluminum alloy substrate 3 and a Ni—P plating layer (film) 2 formed on the aluminum alloy substrate 3, a counter electrode 4, and a power source 5. ２ SO ４ ) dissociates to form sulfate ions (SO ４ ２－ ) In the acidic solution 6, the recycled material and the counter electrode 4 are arranged so as to face each other, and the positive electrode of the power source 5 is electrically connected directly to the recycled material through a conductor, and the negative electrode of the power source 5 is electrically connected directly to the counter electrode 4 through a conductor. In one example, the recycled material is an annular aluminum alloy substrate for a magnetic disk. When a voltage is applied between the recycled material and the counter electrode 4 from the power source 5, anodic electrolysis of the recycled material occurs, and Ni is released from the Ni-P plating layer 2 into the acidic solution 6. ２＋ begins to dissolve.

[0045] As shown in FIG. 1(b), when the anodic electrolysis progresses to a certain extent, Ni in the acid solution 6 ２＋ A part of the sulfate ions (SO ４ ２－ ) and salt (nickel sulfate; NiSO ４ ) and the remaining Ni ２＋ is deposited as Ni on the counter electrode 4. As shown in FIG. 1(c), as anodic electrolysis progresses further, when dissolution of Ni into the acidic solution 6 is completed, the Ni-P plating layer (film) 2 is removed from the surface of the recycled material immersed in the acidic solution 6, exposing the aluminum alloy substrate 3. An anodized aluminum film 7 is formed on the surface of the aluminum alloy substrate 3, preventing further anodic electrolysis. As will be described later with reference to FIG. 2 in the Examples, at the stage shown in FIG. 1(a), a constant current flows between the recycled material and the counter electrode 4, resulting in a constant current density. However, at the stage shown in FIG. 1(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 rapidly decreases, resulting in a significant decrease in current density. Finally, at the stage shown in FIG. 1(c), a constant current, approximately 1 / 10 of the constant current flowing at the stage shown in FIG. 1(a), flows between the recycled material and the counter electrode 4, and the current density also becomes a constant value significantly lower than the current density at the stage shown in FIG. 1(a). In this way, the change in the current or current density of the anodic electrolysis is measured, and when the current or current density is significantly reduced from the constant current or constant current density at the beginning of the anodic electrolysis and begins to become a constant constant current or constant current density, it can be determined that the Ni-P plating layer (film) 2 has been removed and the anodized aluminum film 7 has been formed on the surface of the aluminum alloy substrate 3, and that this is essentially the end of the anodic electrolysis.

[0046] This method for recycling an aluminum alloy substrate can further include a step of recovering the Ni deposited on the surface of the counter electrode in the coating removal step and the acidic solution containing Ni after anodic electrolysis. By recovering the Ni deposited on the surface of the counter electrode and the acidic solution containing Ni after anodic electrolysis in this way and isolating the Ni or using the acidic solution as is, the Ni can be effectively utilized as a resource, further improving recyclability. The Ni recovered in this way can be used for various purposes as metallic Ni, or can be used to adjust the alloy composition of the molten aluminum alloy in the step of preparing the molten aluminum alloy described below, or can be used to adjust the composition of the plating solution that forms the Ni-P plating layer (coating). Furthermore, products can be provided that use the recovered Ni and the acidic solution containing Ni (e.g., a sulfuric acid solution containing Ni).

[0047] In one embodiment of the coating removal process, the recycled material is subjected to physical processing as a processing method for removing the coating. As described above, recycled materials are often circular disks, and therefore the coating formed on the surface of recycled materials of this shape is present on both sides, the inner diameter, and all surfaces of the outer diameter of the recycled material. Therefore, physical processing is effective in reliably removing the coating formed on the entire surface of the recycled material. In such a coating removal process using physical processing, the removal of the coating from the recycled material is intended to completely remove the coating, and does not include partial or partial removal of the coating.

[0048] Examples of physical processing include 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 using a grinding wheel and a method of cutting the end faces of the recycled material using a lathe. When the aluminum alloy substrate constituting the recycled material is annular, the surface of the recycled material refers to both surfaces (both main surfaces) of the recycled material, and the end faces of the recycled material refer to the inner diameter side and the outer diameter side. Cutting and grinding are also performed in the process of obtaining an aluminum alloy substrate for plating from an annular disk blank when producing a magnetic disk according to a general manufacturing method. By performing such mechanical processing as physical processing, the coating can be removed simply and easily without the need for any particularly new or complicated equipment.

[0049] In the cutting process, various cutting tools can be used, such as a cutting tool with a cutting blade formed so that it can cut part of the surface and end face of the recycled material, a formed tool with a cutting blade formed to fit the shape of the end face of the recycled material, etc. The shape of the cutting tool is not particularly limited, as long as it is set so that it can remove a coating to a certain depth.

[0050] In grinding, both sides of the recycled material are sandwiched between grinding stones and slid under pressure. The roughness of the grinding stone can be selected, and the greater the roughness, the faster the grinding speed, but the rougher the surface of the aluminum alloy material obtained by grinding. On the other hand, 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, the roughness of the surface of the aluminum alloy material obtained is irrelevant, and the purpose is to remove the coating, so the rougher the grinding stone, the more efficiently the coating can be removed.

[0051] In physical processing, the depth to which the surface and end face of the recycled material are removed (hereinafter also referred to as the "processing amount") is preferably 1.05 times or more the thickness of the coating, and more preferably 1.1 times or more. When the processing amount is 5% or more thicker than the thickness of the coating, the coating can be completely removed. Note that if the processing amount only fills one of the surface and end face of the recycled material, part of the coating will remain on the recycled material. When both the surface and end face of the recycled material are filled, the coating is completely removed. For example, when cutting is performed as the physical processing, the cutting depth corresponds to the processing amount, and when grinding is performed as the physical processing, the grinding depth corresponds to the processing amount. Furthermore, the upper limit of the processing amount is preferably 2.2 times or less, and more preferably 2.0 times or less, in order to prevent excessive removal of the surface of the aluminum alloy substrate.

[0052] (b) Step of preparing a molten aluminum alloy Next, a molten aluminum alloy is prepared using the aluminum alloy material obtained in the coating removal step as at least a part of the raw material. The contents of each element in the molten aluminum alloy prepared in step (b) are described below.

[0053] 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. Ni bonds with aluminum (Al) and other elements to form Al-Ni compounds, which can cause major defects on the plating surface, so it is useful to reduce the Ni content. The Ni content in the molten aluminum alloy 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 process of preparing the molten aluminum alloy by heating and melting the raw materials. For example, the composition of the molten aluminum alloy is analyzed after the raw materials in the molten aluminum alloy are completely melted, and if the Ni content is high, aluminum alloy or other raw materials are added to adjust the Ni content to the desired level.

[0054] 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, which is contained in aluminum alloy base metals and the like, combines with Mg (magnesium), which is commonly contained in the aluminum alloy raw material of the molten metal, to form Mg-P-based oxides. This can cause uneven reactions in that area during the plating process, potentially resulting in significant defects on the plated surface. As a result, the smoothness of the plated surface is reduced. Although some of the Mg-P-based oxides can rise to the surface of the molten metal and be removed by heating the molten metal, it is preferable that the content of P itself, which bonds with Mg, be 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. Because 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 aluminum alloy base metals or the like. However, if adjustment is required, the desired content can be achieved by adding aluminum base metals or the like, as with Ni.

[0055] - Mg (Magnesium) Content The Mg content in the molten aluminum alloy is preferably 0% by mass or more and 6.5% by mass or less. As described above, Mg combines with P in the molten metal to form Mg-P-based oxides, and therefore, like P, its content is preferably low. The Mg content in the molten metal is preferably 6.5% by mass or less, and more preferably 4.5% by mass or less. If the Mg content is high, it is adjusted to the desired content by adding aluminum alloy base metal, etc., as with Ni.

[0056] Metal Components in the Molten Aluminum Alloy As for the metal components contained in the molten aluminum alloy, as described above, it is preferable to adjust the contents of Ni and P themselves, as well as elements such as Mg that form intermetallic compounds with P.

[0057] On the other hand, elements other than Ni, P, and Mg and their contents are not particularly limited. Examples of alloy compositions contained in the molten aluminum alloy include the following: The aluminum alloy contains Fe (iron) and, optionally, Mn (manganese), with the total content of Fe and Mn being in the range of 0.005% by mass to 7.00% by mass, and further contains 0.5% by mass to 6.5% by mass of Mg, and optionally contains one or more metals selected from the group consisting of 0% by mass to 1.0% by mass of Si (silicon), 0% by mass to 0.7% by mass of Zn (zinc), 0% by mass to 0.30% by mass of Cr (chromium), 0% by mass to 1.0% by mass of Cu (copper), and 0% by mass to 0.20% by mass of Zr (zirconia), with the balance being Al and unavoidable impurities and other trace components.

[0058] Examples of unavoidable impurities include Ti (titanium), Ga (gallium), etc. contained in aluminum alloys, and examples of other trace components include Co (cobalt), Pt (platinum), etc. The effects of the present invention are not impaired as long as the content of these unavoidable impurities and other trace components is 0.10% by mass or less for each element and 0.30% by mass or less in total.

[0059] (c) Step of Heating and Holding the Molten Metal Next, the molten aluminum alloy is heated and held. In this step, the molten aluminum alloy is heated and held in a holding furnace. At this time, it is preferable to remove the oxide film floating on the surface of the molten metal to the outside of the furnace. By removing this floating oxide film by a method such as scooping before casting the aluminum alloy, the contents of Ni and P in the molten metal can be reduced. At this time, it is preferable to remove the oxide film to the outside of the furnace as quickly as possible.

[0060] (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 heated and maintained molten aluminum alloy is subjected to in-line degassing or in-line filtration, as necessary, and then cast into an aluminum alloy ingot by a semi-continuous casting method (DC casting), a metal mold casting method, a continuous casting method (CC casting method), or the like. In the DC casting method, the molten metal poured through a spout loses heat by the bottom block, the water-cooled mold wall, and cooling water directly discharged onto the outer periphery of the ingot, solidifies, and is drawn downward as an ingot. In the metal mold casting method, the molten metal poured into a hollow mold made of cast iron or the like loses heat by the mold wall, solidifies, and an ingot is produced. In the CC casting method, the molten metal is supplied through a casting nozzle between a pair of rolls (or belt casters, block casters), and a thin plate is directly cast by removing heat from the rolls.

[0061] The molten metal heated and held in the heating and holding step is preferably subjected to in-line degassing treatment or in-line filtration treatment according to conventional methods before being subjected to the casting process. Commercially available degassing devices, such as those sold under trademarks like SNIF and ALPUR, can be used as in-line degassing treatment devices. These in-line degassing treatment devices rotate a bladed rotor at high speed while blowing argon gas or a mixed gas such as argon and nitrogen into the molten metal, supplying the gas into the molten metal as fine bubbles. This allows dehydrogenation gas and inclusion removal to be performed in-line in a short time. For in-line filtration, ceramic tube filters, ceramic foam filters, alumina ball filters, etc. are used, and inclusions are removed using a cake filtration mechanism, a filter media filtration mechanism, etc.

[0062] In the above process, when preparing a molten aluminum alloy, an aluminum alloy plate having a desired alloy composition can be produced by adding any material, element, aluminum alloy base metal, etc. to the molten aluminum alloy. Furthermore, by setting predetermined conditions for heating and maintaining the molten aluminum alloy, producing an aluminum alloy ingot from the molten aluminum alloy, and further for homogenizing the aluminum alloy ingot (described later) and rolling the aluminum alloy ingot, the properties and characteristics of the aluminum alloy plate after rolling can be set to desired properties and characteristics different from those of recycled materials.

[0063] 3. Method for Manufacturing a Magnetic Disk The method for manufacturing a magnetic disk of the present invention comprises: (e) a step of heating and homogenizing an aluminum alloy ingot obtained by the above-described method for recycling an aluminum alloy substrate; (f) a rolling step of rolling the homogenized aluminum alloy ingot to form an aluminum alloy plate; (g) a step of pressurizing and flattening the aluminum alloy plate obtained by the rolling step into an annular disk blank; (h) a step of cutting and grinding the pressurized and flattened annular disk blank to obtain an aluminum alloy substrate for plating; (i) a plating pretreatment step of degreasing, etching, and zincating the aluminum alloy substrate for plating; (j) a step of electrolessly plating the surface of the pre-plated aluminum alloy substrate with Ni—P and then polishing the Ni—P plated surface to obtain an aluminum alloy substrate for magnetic disks; and (k) a step of adhering a magnetic material to the surface of the aluminum alloy substrate for magnetic disks to form a magnetic material layer. Each of steps (e) to (k) is described in detail below.

[0064] (e) Step of Heating Aluminum Alloy Ingot for Homogenization The aluminum alloy ingot obtained as described above is heated for homogenization. In the homogenization, the aluminum alloy ingot is heated at a temperature of preferably 480°C to 560°C for at least 1 hour, and more preferably at a temperature of 500°C to 550°C for at least 2 hours. If 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. Furthermore, if the heating temperature exceeds 560°C, the aluminum alloy ingot may melt. Furthermore, although there is no particular upper limit to the heating time, if the heating time exceeds 48 hours, the homogenization effect may saturate, resulting in a decrease in productivity.

[0065] (f) Rolling Step Next, in the rolling step, the homogenized aluminum alloy ingot is rolled to form an aluminum alloy plate. In the rolling step, rolling is performed once or multiple times, and the rolling process can be cold rolling or hot rolling. In one example, the homogenized aluminum alloy ingot is hot rolled to produce a hot-rolled plate. The hot rolling conditions 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. 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 lower than 300°C, workability by hot rolling cannot be ensured, and if it exceeds 500°C, crystal grains become coarse, which may reduce the adhesion of the Ni—P plating layer formed in the process described below. Furthermore, if the hot rolling finishing temperature is less than 260°C, workability by hot rolling cannot be ensured, and if it exceeds 400°C, the crystal grains become coarse, which may reduce the adhesion of the Ni-P plating layer formed in a step described later. In hot rolling, the aluminum alloy ingot is usually heated and held at the hot rolling starting temperature for 0.5 to 10.0 hours, and then hot rolling is carried out.

[0066] In one example, the resulting hot-rolled sheet is then cold-rolled to produce a cold-rolled sheet preferably having a thickness of 0.4 mm to 2.0 mm, more preferably 0.6 mm to 2.0 mm. That is, after hot rolling, the product is finished to the required thickness by cold rolling. The cold-rolling conditions are not particularly limited, but may be determined depending on the required sheet strength and thickness of the aluminum alloy sheet. The rolling reduction is preferably 20% to 90%, more preferably 20% to 80%. If the rolling reduction is less than 20%, the crystal grains may become coarse during the pressure flattening annealing of the disk blank, which will be described later, and the adhesion of the Ni—P plating layer formed in the process described later may be reduced. On the other hand, if the rolling reduction exceeds 90%, the manufacturing time may be extended, which may result in a decrease in productivity.

[0067] 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 performed at an annealing temperature of 300°C to 450°C for 0.1 to 10 hours, and more preferably at an annealing temperature of 300°C to 380°C for 1 to 5 hours. If the annealing temperature is less than 300°C and / or the annealing time is less than 0.1 hours, a sufficient annealing effect may not be obtained. Furthermore, if the annealing temperature exceeds 450°C, the crystal grains may become coarse, which may reduce the adhesion of the Ni—P plating layer formed in the process described below. If the annealing time exceeds 10 hours, the manufacturing time may be extended, which may result in reduced productivity.

[0068] On the other hand, continuous annealing is preferably performed at an annealing temperature of 400°C or higher and 500°C or lower for a holding time of 60 seconds or less, and more preferably at an annealing temperature of 450°C or higher and 500°C or lower for a holding time of 30 seconds or less. If the annealing temperature is lower than 400°C, a sufficient annealing effect may not be obtained. If the annealing temperature exceeds 500°C, the crystal grains may become coarse, which may reduce the adhesion of the Ni-P plating layer formed in the process described below. Furthermore, if the holding time exceeds 60 seconds, the crystal grains may become coarse, which may reduce the adhesion of the Ni-P plating layer formed in the process described below. Note that cooling may be started immediately after the desired annealing temperature is reached.

[0069] An aluminum alloy plate is produced through the above steps. The produced aluminum alloy plate is then subjected to the following steps to produce a magnetic disk.

[0070] (g) A step of pressurizing and flattening the aluminum alloy sheet into an annular disk blank. The aluminum alloy sheet obtained by the rolling step 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 in air at a temperature of 300°C to 450°C for 30 minutes or more, preferably at a temperature of 300°C to 380°C for 60 minutes or more, to produce a flattened annular disk blank. If the pressure annealing treatment temperature is less than 300°C and / or the treatment time is less than 30 minutes, the flattening effect may not be sufficient. Furthermore, if the treatment temperature exceeds 450°C, the crystal grains may become coarse, which may reduce the adhesion of the Ni-P plating layer formed in the later step. The upper limit of the treatment time is not particularly limited, but if it exceeds 24 hours, the production time may be extended, which may result in a decrease in productivity. The pressure used in the pressure annealing is usually 0.1 MPa to 3.0 MPa.

[0071] (h) A step of subjecting the annular disk blank to cutting and grinding to obtain an aluminum alloy substrate for plating: Next, the annular disk blank flattened in the cutting and grinding step is cut and ground to adjust the overall shape and surface of the annular disk blank, and then optionally, a distortion relief heat treatment is performed to remove distortion from the annular disk blank at a temperature of 200°C to 290°C for 0.1 to 10.0 hours.

[0072] (i) Plating Pretreatment Step The aluminum alloy substrate for plating prepared as described above is subjected to degreasing, etching, and zincate treatment (Zn substitution treatment) as pretreatment for plating. Degreasing is preferably carried out using, for example, a commercially available degreasing solution such as AD-68F (manufactured by Uemura Kogyo Co., Ltd.) at a degreasing temperature of 40°C to 70°C, for a degreasing time of 3 to 10 minutes, and with a degreasing solution concentration of 200 mL / L to 800 mL / L, or more preferably at a degreasing temperature of 45°C to 65°C, for a degreasing time of 4 to 8 minutes, and with a degreasing solution concentration of 300 mL / L to 700 mL / L. If the degreasing temperature is less than 40°C, the degreasing time is less than 3 minutes, and / or the degreasing solution concentration is less than 200 mL / L, sufficient degreasing effect may not be obtained. Furthermore, 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 surface smoothness of the aluminum alloy substrate for plating may decrease, and pits may occur after plating, resulting in a decrease in smoothness.

[0073] Etching is preferably performed using, for example, a commercially available etching solution such as AD-107F (manufactured by Uemura Kogyo Co., Ltd.) at an etching temperature of 50°C to 75°C, for an etching time of 0.5 to 5 minutes, and with an etching solution concentration of 20 mL / L to 100 mL / L. More preferably, etching is performed at a temperature of 55°C to 70°C, for an etching time of 0.5 to 3 minutes, and with an etching solution concentration of 40 mL / L to 100 mL / L. If the etching temperature is less than 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 effects may not be obtained. Furthermore, if 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 for plating may decrease, resulting in the occurrence of pits after plating, thereby reducing smoothness. A conventional desmutting treatment may be performed between the etching treatment and the zincate treatment described below.

[0074] The zincate treatment is preferably carried out using, for example, a commercially available zincate treatment solution such as AD-301F-3X (manufactured by Uemura Kogyo Co., Ltd.) at a zincate treatment temperature of 10°C to 35°C, for a zincate treatment time of 0.1 to 5 minutes, and with a zincate treatment solution concentration of 100 mL / L to 500 mL / L, and more preferably at a zincate treatment temperature of 15°C to 30°C, for a zincate treatment time of 0.1 to 2 minutes, and with a zincate treatment solution concentration of 200 mL / L to 400 mL / L. If the zincate treatment temperature is less than 10°C, the zincate treatment time is less than 0.1 minute, and / or the zincate treatment solution concentration is less than 100 mL / L, the zincate coating may become non-uniform, causing pits after plating and reducing smoothness. Furthermore, 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 coating may become non-uniform, causing pits after plating treatment and reducing smoothness.

[0075] (j) Step of Obtaining an Aluminum Alloy Substrate for Magnetic Disks Next, the zincate-treated surface of the aluminum alloy substrate for plating is subjected to electroless Ni—P plating as a base treatment, and then the surface is polished. The electroless Ni—P plating is preferably performed using, for example, a commercially available Nimden HDX (manufactured by Uemura Kogyo Co., Ltd.) plating solution at a plating temperature of 80°C to 95°C, for a plating time of 30 to 180 minutes, and with a Ni concentration in the plating solution of 3 g / L to 10 g / L, or more preferably at a plating temperature of 85°C to 95°C, for a plating time of 60 to 120 minutes, and with a Ni concentration in the plating solution of 4 g / L to 9 g / L. In the film removal step according to one embodiment described above, the Ni deposited on the surface of the counter electrode and the acidic solution containing Ni after anodic electrolysis may be recovered, and these Ni and the acidic solution containing Ni may be added to the plating solution. If the plating temperature is less than 80°C and / or the Ni concentration in the plating solution is less than 3 g / L, the plating growth rate will be slow, which may result in a decrease in productivity. Furthermore, if the plating time is less than 30 minutes, numerous defects may occur on the plating surface, resulting in a decrease in the smoothness of the plating surface. On the other hand, if the plating temperature exceeds 95°C and / or the Ni concentration in the plating solution exceeds 10 g / L, the plating may grow non-uniformly, resulting in a decrease in the smoothness of the plating. Furthermore, if the plating time exceeds 180 minutes, the manufacturing time will be long, which may result in a decrease in productivity. Furthermore, the surface of the base (Ni-P) plated substrate is polished. An aluminum alloy substrate for a magnetic disk is produced by these pre-plating treatments and the base (Ni-P) plating treatment (with polishing).

[0076] (k) Step of forming a magnetic layer After the electroless Ni-P plating process including the polishing process, a magnetic material is attached to 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 multiple layers having different compositions. After sputtering, if necessary, a protective layer made of a carbon-based material may be formed on the magnetic layer by CVD, or a lubricating oil may be applied to the protective layer to form a lubricating layer.

[0077] 4. Magnetic Disk The magnetic disk of the present invention can be produced by the above-described magnetic disk manufacturing method. The magnetic disk of the present invention comprises an aluminum alloy substrate for magnetic disks, a Ni-P plating layer on the surface of the aluminum alloy substrate for magnetic disks, and a magnetic layer formed on the Ni-P plating layer. A protective layer and a lubricating layer may also be formed on the magnetic layer. Because such a magnetic disk of the present invention is produced using the recycled materials described above, it is useful as a magnetic disk that excels in reducing environmental impact.

[0078] 5. Hard Disk Drive The hard disk drive of the present invention comprises one or more of the above-described magnetic disks, a spindle motor for rotating the magnetic disks, a clamping member for fixing the inner diameter side of the magnetic disks, a magnetic head for processing data on the magnetic disks, an actuator for supporting the magnetic head movably relative to the magnetic disks, and a swing arm for rotating and positioning the actuator. Because such a hard disk drive of the present invention is manufactured using the above-described recycled materials, it excels in reducing the environmental impact. In particular, hard disk drives used in data centers and the like are equipped with a large number of magnetic disks to process large amounts of data. By manufacturing many of the magnetic disks in such a hard disk drive using recycled materials, it is possible to provide magnetic disks that are particularly excellent at reducing the environmental impact.

[0079] Based on the above embodiments, the present invention relates to the following [1] to

[18] . [1] A method for recycling an aluminum alloy substrate, comprising: a coating removal step (a) of obtaining an aluminum alloy material by removing at least one coating from a recycled material having an aluminum alloy substrate and the aluminum alloy substrate and the coating being formed thereon; a step (b) of preparing a molten 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. [2] The method for recycling an aluminum alloy substrate according to the above [1], wherein the coating contains Ni. [3] The method for recycling an aluminum alloy substrate according to the above [1] or [2], wherein the coating is removed from the recycled material by immersing the recycled material in a solution in the coating removal step (a). [4] The method for recycling an aluminum alloy substrate according to the above [3], wherein the solution is an acidic solution containing nitrate ions. [5] The method for recycling an aluminum alloy substrate according to [4] above, wherein the acidic solution has a temperature of 40 to 60°C and a nitrate ion concentration of 25 mass% or more, and wherein, in the film removing step (a), the recycled material is immersed in the acidic solution for 1 hour or more. [6] The method for recycling an aluminum alloy substrate according to [4] or [5] above, wherein a total concentration of anions other than nitrate ions in the acidic solution is 5 mass% or less. [7] The method for recycling an aluminum alloy substrate according to any one of [3] to [6] above, wherein, in the film removing step (a), a plurality of the recycled materials are immersed in the solution so that the recycled materials do not come into contact with each other. [8] The method for recycling an aluminum alloy substrate according to [1] or [2] above, wherein, in the film removing step (a), the film is removed from the recycled material by subjecting the recycled material to physical processing. [9] The method for recycling aluminum alloy substrates according to the above [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 using a grinding wheel and a method of cutting the end faces of the recycled material using a lathe.

[10] The method for recycling an aluminum alloy substrate according to [8] or [9] above, wherein the depth to which the surface and edge faces of the recycled material are removed in the physical processing is 1.05 times or more the thickness of the coating.

[11] The method for recycling an aluminum alloy substrate according to [2] above, wherein in the coating removal step (a), the coating is removed from the recycled material by passing an electric current through the recycled material while the recycled material is immersed in a solution.

[12] The method for recycling an aluminum alloy substrate according to

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

[13] The method for recycling an aluminum alloy substrate according to

[12] above, wherein the acidic solution has a temperature of 20°C or higher and a sulfate ion concentration of 5 mass% or higher, and wherein in the coating removal step (a), the coating is removed by anodic electrolysis while the recycled material is electrically connected to a counter electrode immersed in the acidic solution.

[14] The method for recycling an aluminum alloy substrate according to the above

[13] , further comprising a step of recovering Ni deposited on the surface of the counter electrode in the film removing step (a) and an acidic solution containing Ni after anodic electrolysis.

[15] The method for recycling an aluminum alloy substrate according to any one of the above [1] to

[14] , wherein the aluminum alloy substrate constituting the recycled material is annular.

[16] A method for manufacturing a magnetic disk, comprising: a step (e) of heating and homogenizing an aluminum alloy ingot obtained by the method for recycling an aluminum alloy substrate according to any one of the above [1] to

[15] ; a rolling step (f) of rolling the homogenized aluminum alloy ingot to form an aluminum alloy plate; a step (g) of pressurizing and flattening the aluminum alloy plate obtained by the rolling step (f) into an annular disk blank; a step (h) of cutting and grinding the pressurized and flattened annular disk blank to obtain an aluminum alloy substrate for plating; a plating pretreatment step (i) of degreasing, etching, and zincating the aluminum alloy substrate for plating; a step (j) of electrolessly plating the surface of the pre-plated aluminum alloy substrate and then polishing the Ni-P plated surface to obtain an aluminum alloy substrate for magnetic disk; and a step (k) of adhering a magnetic material to the surface of the aluminum alloy substrate for magnetic disk to form a magnetic material layer.

[17] A magnetic disk obtained by the method for manufacturing a magnetic disk according to

[16] above.

[18] A hard disk drive equipped with the magnetic disk according to

[17] above.

[0080] The above has described the method for recycling an aluminum alloy substrate, the method for manufacturing a magnetic disk, the magnetic disk, and the hard disk drive according to the present embodiment, but the present invention is not limited to the above embodiment, and various modifications and changes are possible based on the technical concept of the present invention.

[0081] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0082] (Examples 1A to 4A, Comparative Examples 1A to 2A) As recycled materials, aluminum alloy substrates for magnetic disks (hereinafter referred to as "samples"; outer diameter 95 mm, inner diameter 25 mm, total thickness 1.3 mm) were used, each having an aluminum alloy substrate made of JIS 5086 alloy (Al-Mg alloy) and a 10 μm thick Ni-P plating layer (film) formed on the aluminum alloy substrate by electroless Ni-P plating treatment. The samples of each example were immersed in an acidic solution under the conditions shown in Table 1. The acidic solution of each example consisted of an acid component, which was a mixture of nitric acid, hydrochloric acid, and sulfuric acid, and water, with the total content of the acid component and water being 100% by mass.

[0083] The aluminum alloy used for the aluminum alloy substrate had a composition containing 0.02 mass% Fe, 0.018 mass% Si, 4.02 mass% Mg, 0.35 mass% Zn, 0.052 mass% Cr, and the remainder consisting of Al, unavoidable impurities, and trace components.

[0084]

[0085] The measurement of "amount of thinning of sample" and "evaluation of coating removal" shown in Table 1 above were carried out as follows.

[0086] (Measurement of the amount of thinning of the sample) The mass of the sample before immersion in the acidic solution was measured in advance. Next, the sample after immersion in the acidic solution was washed with pure water, dried in a hot air dryer, and the mass was measured again. Thereafter, the amount of thinning of the sample was measured as the amount of thinning per one side of the sample by calculating {(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 plating layer x total surface area of ​​the sample). The specific gravity of the Ni-P plating layer was 7.6 g / m ３ was used.

[0087] (Evaluation of Coating Removal) After immersion in the acidic solution, the overall appearance of the sample, including the outer periphery, was visually observed. A case in which the Ni—P plating layer was not observed and the Ni—P plating layer was completely removed was evaluated as "◎", and a case in which the Ni—P plating layer was observed to remain was evaluated as "×".

[0088] (Recyclability Evaluation) 1 kg of samples were obtained from multiple samples in which the Ni—P plating layer had been removed under the conditions of Example 1A. Six samples were randomly selected from the multiple samples in which the Ni—P plating layer had been removed. The aluminum alloy composition of each sample was analyzed by a first spark discharge optical emission spectroscopy (SEA) analysis, and the average value of each detected element was calculated. Subsequently, all 1 kg of sample was melted to prepare a molten metal, which was then heated and held. The molten metal was then poured into a mold and cast to obtain an aluminum alloy ingot. The aluminum alloy ingot obtained after casting was cut to a desired size, and the aluminum alloy composition was analyzed using the same method as the first SEA analysis (a second SEA analysis). The formula {(content of each element obtained by the second SEA analysis) - (content of each element obtained by the first SEA analysis)} / (content of each element obtained by the first SEA analysis) × 100 (%) (referred to as "change" in Table 2) was also calculated. The results of the SEA analysis are shown in Table 2.

[0089]

[0090] The coating of the samples used in each example was a 10 μm thick Ni—P plating layer, and as shown in Table 1, in Examples 1A to 4A, the amount of thinning of the samples was 10 μm or more, confirming that the Ni—P plating layer was effectively removed. Furthermore, as indicated by "◎" in Table 1, visual observation also confirmed that the Ni—P plating layer was completely removed in the samples of Examples 1A to 4A. On the other hand, as shown in Table 1, the amount of thinning of the samples of Comparative Examples 1A to 2A was 0 μm, meaning that the Ni—P plating layer could not be removed. Furthermore, as indicated by "×" in Table 1, visual observation also confirmed that the Ni—P plating layer remained in the samples of Comparative Examples 1A to 2A.

[0091] As shown in Table 2, the amount of change in each of the elements Fe, Si, Mg, Zn, and Cr was ±4.19% by mass or less. This amount of change is acceptable, and it was confirmed that there was almost no change in composition between the aluminum alloy before the preparation of the molten metal after the Ni—P plating layer was removed and the aluminum alloy after the preparation of the molten metal, heating and holding, and casting.

[0092] (Examples 1B to 3B) A recycled material was used as a test material: an aluminum alloy substrate for magnetic disks (outer diameter 95 mm, inner diameter 25 mm, total thickness 1.3 mm) having an aluminum alloy substrate made of JIS 5086 alloy (Al-Mg alloy) and a Ni-P plating layer (film) formed on the aluminum alloy substrate by electroless Ni-P plating treatment. A piece measuring 20 mm x 45 mm was cut out from the test material, and masked, leaving an upper clip gripping margin and a lower 10 mm x 10 mm area to be peeled, to prepare a sample for each example.

[0093] The aluminum alloy used for the aluminum alloy substrate had a composition containing 0.02 mass% Fe, 0.018 mass% Si, 4.02 mass% Mg, 0.35 mass% Zn, 0.052 mass% Cr, and the remainder consisting of Al, unavoidable impurities, and trace components.

[0094] An anodic electrolysis apparatus as shown in FIG. 1 was fabricated by electrically connecting each sample to the positive electrode of a power supply, electrically connecting a platinum wire as a counter electrode to the negative electrode of the power supply, and immersing the sample and counter electrode in an acidic solution. The composition of the acidic solution and the voltage applied between the sample and counter electrode during anodic electrolysis were set as shown in Table 3 below. The acidic solution was composed of sulfuric acid and pure water, with the pure water content being 90% by mass. Furthermore, preliminary tests were conducted to measure the change over time in the current density flowing between the sample and counter electrode during anodic electrolysis. The results confirmed that (1) a constant current density was observed at the beginning of anodic electrolysis, (2) the current density rapidly decreased as the removal of the Ni—P plating layer (film) progressed, and (3) when the removal of the Ni—P plating layer (film) was completed, the aluminum alloy substrate was exposed, and an anodized aluminum coating was formed on the aluminum alloy substrate, the current density became constant and significantly lower than the constant current at the beginning of anodic electrolysis. For this reason, in each example, the change over time in the current density flowing between the sample and the counter electrode during anodic electrolysis was measured, and the time when the above-mentioned state (3) first appeared was measured as the "peeling time," which is the time when removal of the coating was completed.

[0095] Figure 2 is a graph showing the change in current density over time during anodic electrolysis in Example 1B. In Figure 2, the start of anodic electrolysis is set to 0 seconds. As shown in Figure 2, in Example 1B, the current density began to decrease approximately 80 seconds after the start of anodic electrolysis and reached a low, constant current density after 125 seconds. For this reason, the peeling time was set to 125 seconds. The "peeling times" measured in each example are shown in Table 3 below.

[0096] (Comparative Examples 1B and 2B) The composition of the acidic solution was as shown in Table 3 below, and the sample was immersed in the acidic solution without anodic electrolysis. The acidic solution consisted of sulfuric acid or hydrochloric acid and pure water, with the pure water content being 90 mass%. In Comparative Examples 1B and 2B, no voltage was applied to the sample, so whether or not the Ni-P plating layer (film) had been removed was confirmed visually. In Comparative Examples 1B and 2B, it was confirmed that the Ni-P plating layer (film) remained even 60 minutes after the sample was immersed in the acidic solution. Therefore, the peeling times for Comparative Examples 1B and 2B are indicated by "-" in Table 3 below.

[0097]

[0098] As shown in Examples 1B to 3B in Table 3, Example 1B, which had the highest voltage during anodic electrolysis, had the shortest stripping time, and Example 3B, which had the lowest voltage during anodic electrolysis, had the longest stripping time. This shows that a high film removal effect is achieved when the voltage during anodic electrolysis is 2 V. Furthermore, in Comparative Examples 1B and 2B, anodic electrolysis was not performed, and therefore the Ni-P plating layer (film) could not be removed. As described above, the aluminum alloy substrate recycling method of the present invention was able to efficiently remove the Ni-P plating layer (film), confirming that the recycling method has excellent recyclability.

[0099] (Examples 1C to 6C, Comparative Examples 1C to 4C) As recycled materials, aluminum alloy substrates for magnetic disks (hereinafter referred to as "samples"; outer diameter 95 mm, inner diameter 25 mm, total thickness 1.3 mm) were used, which had an aluminum alloy substrate made of JIS 5086 alloy (Al-Mg alloy) and a Ni-P plating layer (film) formed on the aluminum alloy substrate by electroless Ni-P plating treatment. The film formed on the aluminum alloy substrate had a thickness of 10 μm on the surface (both main surfaces) and 11 μm on the end faces (side surfaces on the inner diameter side and side surfaces on the outer diameter side). The samples of each example were machined under the conditions shown in Table 4. The "cutting amount" in Table 4 refers to the depth to which the surface and end faces of the sample were machined.

[0100] The aluminum alloy used for the aluminum alloy substrate had a composition containing 4 mass% Mg, 0.025 mass% Fe, 0.025 mass% Si, 0.3 mass% Zn, and 0.05 mass% Cu, with the remainder being Al, unavoidable impurities, and trace components.

[0101] (Evaluation of recyclability) Recyclability was evaluated by observing the appearance of the surface and end face of the sample after cutting, based on the state of remaining removed coating. When no Ni-P plating layer was observed, it was evaluated as "Good", and when the Ni-P plating layer was observed to remain, it was evaluated as "Poor". If both the surface and end face of the sample were evaluated as "Good", the recyclability was deemed good.

[0102]

[0103] As shown in Table 4, in Examples 1C to 6C, if both the surface and end face of the sample were evaluated as "good," it was confirmed that the Ni-P plating layer was completely removed. On the other hand, in Comparative Examples 1C and 3C, both the surface and end face of the sample were evaluated as "poor," meaning that the Ni-P plating layer remained entirely. Furthermore, in Comparative Examples 2C and 4C, either the surface or end face of the sample was evaluated as "poor," meaning that the Ni-P plating layer remained locally.

[0104] The present invention provides a method for recycling aluminum alloy substrates with excellent recyclability. Furthermore, since the aluminum alloy plate obtained by this recycling method can be reused to manufacture magnetic disks, the amount of expensive high-purity ingots used can be reduced, leading to cost savings and also being beneficial from the standpoint of environmental conservation.

[0105] REFERENCE SIGNS LIST 1 Anode electrolysis device 2 Ni-P plating layer (film) 3 Aluminum alloy substrate 4 Counter electrode 5 Power source 6 Acid solution 7 Anodized aluminum film

Claims

1. A method for recycling aluminum alloy substrates, comprising: a coating removal step (a) of obtaining an aluminum alloy material by removing a coating from a recycled material having an aluminum alloy substrate and at least one layer of a coating on the aluminum alloy substrate; a step (b) of preparing a molten 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.

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

3. The method for recycling an aluminum alloy substrate according to claim 1, wherein in the film removing step (a), the film is removed from the recycled material by immersing the recycled material in a solution.

4. The method for recycling an aluminum alloy substrate 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 to 60°C and a nitrate ion concentration of 25 mass% or more, and in the film removal step (a), the recycled material is immersed in the acidic solution for one hour or more.

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

7. The method for recycling aluminum alloy substrates according to claim 3, wherein in the film removing step (a), a plurality of the recycled materials are immersed in the solution so that the recycled materials are not in contact with each other.

8. The method for recycling an aluminum alloy substrate according to claim 1, wherein in the film removing step (a), the film is removed from the recycled material by subjecting the recycled material to a physical process.

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 using a grinding wheel 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 the depth to which the surface and end faces of the recycled material are cut in the physical processing is 1.05 times or more the thickness of the coating.

11. The method for recycling aluminum alloy substrates according to claim 2, wherein in the coating removal step (a), the coating is removed from the recycled material by passing an electric current through the recycled material while the recycled material is immersed in a solution.

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

13. A method for recycling an aluminum alloy substrate as described in claim 12, wherein the acidic solution has a temperature of 20°C or higher and a sulfate ion concentration of 5 mass% or higher, and in the film removal step (a), the film is removed by performing anodic electrolysis in a state where the recycled material is electrically connected to a counter electrode immersed in the acidic solution.

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

15. A method for recycling aluminum alloy substrates according to claim 1 or 2, wherein the aluminum alloy substrate constituting the recycled material is annular.

16. A method for manufacturing a magnetic disk, comprising: a step (e) of heating and homogenizing the aluminum alloy ingot obtained by the method for recycling an aluminum alloy substrate according to claim 1 or 2; a rolling step (f) of rolling the homogenized aluminum alloy ingot to form an aluminum alloy plate; a step (g) of pressing and flattening the aluminum alloy plate obtained by the rolling step (f) into an annular disk blank; a step (h) of cutting and grinding the pressed and flattened annular disk blank to obtain an aluminum alloy substrate for plating; a plating pretreatment step (i) of degreasing, etching and zincating the aluminum alloy substrate for plating; a step (j) of electrolessly plating the surface of the aluminum alloy substrate that has been pretreated for plating with Ni-P and then polishing the Ni-P plated surface to obtain an aluminum alloy substrate for magnetic disks; and a step (k) of adhering a magnetic material to the surface of the aluminum alloy substrate for magnetic disks to form a magnetic material layer.

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

18. A hard disk drive comprising the magnetic disk according to claim 17.

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