Aluminum alloy disk material, method for producing aluminum alloy raw material, method for producing aluminum alloy ingot, method for producing aluminum alloy sheet, method for producing aluminum alloy substrate for plating, method for producing aluminum alloy substrate for magnetic disk, method for producing magnetic disk, and magnetic disk

Abstract

The present invention relates to an aluminum alloy disk material (1) having: a peeled surface, which is obtained by peeling a base layer containing Ni from at least one recycled material of an intermediate material or finished product including an aluminum alloy disk and the base layer; and an oxide film (10) on the surface of the peeled surface.

Description

Aluminum alloy disk material, method for manufacturing aluminum alloy raw material, method for manufacturing aluminum alloy ingot, method for manufacturing aluminum alloy plate, method for manufacturing aluminum alloy substrate for plating, method for manufacturing aluminum alloy substrate for magnetic disk, method for manufacturing magnetic disk, and magnetic disk

[0001] The present invention relates to an aluminum alloy disk material, a method for producing an aluminum alloy raw material, a method for producing an aluminum alloy ingot, a method for producing an aluminum alloy plate, a method for producing an aluminum alloy substrate for plating, a method for producing an aluminum alloy substrate for magnetic disks, a method for producing a magnetic disk, and a magnetic disk obtained by the method, all of which are highly recyclable.

[0002] Aluminum alloy magnetic disks used in computer storage devices are manufactured from aluminum alloy substrates based on JIS 5086 series aluminum alloys, which have good plating properties as well as excellent mechanical properties and workability.

[0003] Furthermore, aluminum alloy magnetic disks are manufactured from aluminum alloy substrates in which the content of impurities such as Fe, Si, and Mn in JIS 5086-series aluminum alloys is limited to reduce the size of intermetallic compounds in the matrix, in order to improve pit defects caused by the loss of intermetallic compounds in the plating pretreatment process, or aluminum alloy substrates in which Cu and Zn are intentionally added to JIS 5086-series aluminum alloys in order to improve plating properties.

[0004] In the general manufacturing of aluminum alloy magnetic disks, an aluminum alloy plate is first produced, followed by the production of an annular aluminum alloy disk blank, which is then cut and ground, followed by pressure annealing to produce an aluminum alloy substrate, which is then plated, and a magnetic material is attached to the surface of the aluminum alloy substrate to produce the aluminum alloy magnetic disk.

[0005] For example, an aluminum alloy magnetic disk using a JIS 5086-series aluminum alloy is manufactured by the following manufacturing process. First, an aluminum alloy having a desired alloy composition is cast, and the resulting ingot is hot-rolled and then cold-rolled to produce a rolled material having the thickness required for a magnetic disk. This rolled material is annealed, if necessary, during the cold rolling process. Next, this rolled material is punched into an annular shape, and further, to remove distortion and other defects caused during the manufacturing process, annular aluminum alloy plates are stacked on top of each other, and pressure annealing is performed to flatten the stack while applying pressure from both sides. Through these processes, a disk blank is manufactured.

[0006] The disk blank thus produced is subjected to cutting and grinding as pre-processing, and then heat-treated to remove distortions and other defects caused by the processing steps, thereby producing an aluminum alloy substrate. Next, degreasing, etching, and zincating (Zn substitution) are performed as pre-plating processes, and then Ni-P plating, a hard non-magnetic metal, is applied as a base treatment, and the surface is polished, thereby producing an aluminum alloy substrate for a magnetic disk. Finally, a magnetic material and the like are sputtered to produce an aluminum alloy magnetic disk.

[0007] In recent years, magnetic disks have been required to have larger capacities and higher densities due to needs such as multimedia. To achieve even larger capacities, the number of magnetic disks mounted in storage devices has been increasing, and this has led to a corresponding demand for thinner magnetic disks. However, since thinner aluminum alloy substrates for magnetic disks result in a decrease in their rigidity, aluminum alloy substrates must have higher rigidity. In recent years, high-rigidity materials containing added elements such as Ni have been investigated.

[0008] On the other hand, as the number of magnetic disks mounted increases, the amount of aluminum and other raw materials required for aluminum alloy substrates for magnetic disks is also increasing. However, because these resources are limited, there is a demand to reuse aluminum alloy substrates and magnetic disks with plating or magnetic material attached as part of the raw materials for aluminum alloy materials. For aluminum alloy substrates, those that have developed defects and are unsuitable for use as products are used, and for magnetic disks, those extracted from defective products or used HDDs are used.

[0009] In view of these circumstances, in recent years, there has been a strong demand for and investigation into a method for manufacturing an aluminum alloy ingot with excellent recyclability, a method for manufacturing an aluminum alloy plate using the ingot, a method for manufacturing an aluminum alloy substrate for a magnetic disk using the aluminum alloy plate, and a method for manufacturing a magnetic disk using the aluminum alloy substrate. For example, Patent Document 1 proposes that by adding Ni to an aluminum alloy for a magnetic disk, the aluminum alloy substrate can be reused as a raw material.

[0010] However, in the method disclosed in Patent Document 1, when a large amount of aluminum alloy substrates for magnetic disks is used as a raw material, for example, when the aluminum alloy substrates for magnetic disks account for 50% or more of the raw material by weight, the aluminum alloy raw material may contain 3.0% by mass or more of Ni. Therefore, when producing an aluminum alloy raw material that cannot tolerate a large amount of Ni, only a small amount of aluminum alloy substrates for magnetic disks can be used, which raises concerns about poor recyclability.

[0011] Japanese Patent Application Laid-Open No. 2002-275568

[0012] The present invention has been made in view of the above-mentioned circumstances, and aims to provide an aluminum alloy disk material, a method for manufacturing an aluminum alloy raw material, a method for manufacturing an aluminum alloy ingot, a method for manufacturing an aluminum alloy plate, a method for manufacturing an aluminum alloy substrate for plating, a method for manufacturing an aluminum alloy substrate for magnetic disks, a method for manufacturing a magnetic disk, and a magnetic disk, all of which are highly recyclable.

[0013] The present inventors have discovered that when separating an aluminum alloy disk and an underlayer from an intermediate material or a finished product to be recycled, by promoting the formation of an oxide film on the surface of the aluminum alloy disk material obtained by separating the underlayer, an aluminum alloy disk material and an aluminum alloy raw material with excellent recyclability can be obtained, and have completed the present invention.

[0014] The aluminum alloy disk material according to an embodiment of the present invention is an aluminum alloy disk material having a peeled surface formed by peeling off the base layer from at least one of a recycled material of an intermediate material and a finished product, the recycled material comprising an aluminum alloy disk and a base layer containing Ni, and an oxide film on the surface of the peeled surface.

[0015] A method for producing an aluminum alloy raw material according to an embodiment of the present invention includes a separation step in which at least one of an intermediate material and a finished product comprising an aluminum alloy disk and a Ni-containing underlayer is recycled as at least a part of an aluminum alloy raw material, and the aluminum alloy disk and the underlayer are separated by heating or wet treating the aluminum alloy raw material containing the recycled material, and an oxide film is formed on the peeled surface of the aluminum alloy disk material obtained by peeling off the underlayer.

[0016] According to the present invention, it is possible to provide an aluminum alloy disk material, a method for manufacturing an aluminum alloy raw material, a method for manufacturing an aluminum alloy ingot, a method for manufacturing an aluminum alloy plate, a method for manufacturing an aluminum alloy substrate for plating, a method for manufacturing an aluminum alloy substrate for magnetic disks, a method for manufacturing a magnetic disk, and a magnetic disk, all of which are highly recyclable.

[0017] FIG. 1 shows a schematic diagram of an aluminum alloy disk material according to the present invention. FIG. 2 shows a flow chart illustrating the steps from the manufacturing process of an aluminum alloy raw material to the manufacturing process of a magnetic disk according to the present invention. FIG. 3 shows the results of quantitative elemental analysis by GDS for the aluminum alloy disk material produced in Example 1. FIG. 3A shows the results of quantitative elemental analysis with an expanded range of short sputtering time. FIG. 4A shows the results of quantitative elemental analysis with an expanded range of short sputtering time.

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0019] 1. Aluminum Alloy Disk Material As shown in Figure 1, the aluminum alloy disk material 1 of the present invention has a peeled surface formed by peeling the base layer from at least one of an intermediate material and a finished product comprising an aluminum alloy disk and a Ni-containing base layer, and the peeled surface has an oxide film 10. Because the oxide film 10 is formed on the surface of the aluminum alloy disk material 1, when the aluminum alloy disk material 1 is reused to produce an aluminum alloy raw material and a new aluminum alloy ingot is produced using the aluminum alloy raw material, the peeled surface having the oxide film 10 is further melted in the molten metal heating and holding step described below, and the oxide film 10 is partially or entirely peeled off from the aluminum alloy disk material 1 and floats to the surface of the molten metal. By removing the oxide film 10 that has floated to the surface of the molten metal, it is possible to reduce the amount of plating remaining on the surface (peeled surface) of the aluminum alloy disk material 1, thereby obtaining an aluminum alloy disk material with excellent recyclability. The formation of the oxide film 10 can be confirmed, for example, by using glow discharge optical emission spectroscopy (hereinafter referred to as "GDS"), and it can be determined that the oxide film 10 has been formed when a peak in the emission intensity of oxygen (O) is observed.

[0020] The recycled materials used in the present invention are aluminum alloy disks having an underlayer such as a Ni-P plating layer, while the intermediate materials correspond to aluminum alloy substrates for magnetic disks, and the finished products correspond to magnetic disks. These recycled materials include defective products, non-standard products, and, in the case of magnetic disks, used products.

[0021] 2. Recycled Materials First, we will explain aluminum alloy substrates for magnetic disks and magnetic disks as recycled materials used as at least a part of the aluminum alloy material in the production of aluminum alloy raw materials (hereinafter also referred to as "aluminum alloy raw materials" or simply "alloy raw materials"). Furthermore, "at least a part" means that the entire aluminum alloy material may be recycled, or that only a part of the aluminum alloy material may be recycled.

[0022] 2-1. Aluminum Alloy Substrate for Magnetic Disk: (Intermediate Material) A Ni-containing underlayer, such as a Ni—P plating layer, is formed on the surface of an aluminum alloy substrate for magnetic disk. Therefore, in order to incorporate the aluminum alloy substrate for magnetic disk as an intermediate material into at least a portion of an aluminum alloy material that does not contain much Ni, it is important to separate most of the underlayer. The Ni content in the Ni-containing underlayer used in the aluminum alloy substrate for magnetic disk is, for example, 80% by mass or more and 95% by mass or less. Furthermore, when the Ni-containing underlayer 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 underlayer is not particularly limited, but is, for example, 3 μm or more and 25 μm or less, and the thickness of the aluminum alloy substrate for magnetic disk is, for example, 0.3 mm or more and 2.0 mm or less.

[0023] 2-2. Magnetic Disk: (Finished Product) In a magnetic disk, a CoCrPt-based magnetic layer and a protective film made of a carbon-based material or the like are formed on the surface of the above-mentioned aluminum alloy substrate for a magnetic disk. However, since these magnetic layers and protective films are formed on an underlayer, removing the underlayer can remove most of them. Therefore, even a magnetic disk from which the underlayer has been separated can be used with at least a portion of an aluminum alloy material that does not contain large amounts of Ni or P. Note that, like the aluminum alloy substrate for a magnetic disk, when using a magnetic disk as an aluminum alloy material, it is important to remove as much of the underlayer as possible.

[0024] 2-3. Aluminum alloy material Aluminum alloy materials are general materials adjusted to have a predetermined alloy composition and used as raw materials for producing aluminum alloy ingots. The aluminum alloy raw material produced in the present invention includes an embodiment containing such an aluminum alloy material and an aluminum alloy disk material separated from a recycled material, and an embodiment not containing an aluminum alloy material but being the aluminum alloy disk material itself separated from a recycled material.

[0025] 2-4. Oxide Film The oxide film formed on the surface of the aluminum alloy disk material contains at least one of S (sulfur) and P (phosphorus). Of these elements, S is contained in the oxide film due to the sulfuric acid used in the wet treatment in the separation process, as described below. On the other hand, P is contained in the oxide film due to the plating layer, so an oxide (slag) containing at least one of S (sulfur) and P (phosphorus) is present on the surface (exfoliated surface) of the aluminum alloy disk material. This oxide is formed as an oxide film on the exfoliated surface of the aluminum alloy disk material during the separation process of separating the aluminum alloy disk and the base layer, as described below. The thickness of the oxide film is not particularly limited, but is preferably 0.01 μm to 10 μm, and more preferably 0.02 μm to 5 μm.

[0026] Next, a method for producing an aluminum alloy raw material according to embodiments of the present invention, a method for producing an aluminum alloy ingot using this aluminum alloy raw material, a method for producing an aluminum alloy plate using this aluminum alloy ingot, a method for producing an aluminum alloy substrate for plating using this aluminum alloy plate, a method for producing an aluminum alloy substrate for magnetic disks using this aluminum alloy substrate for plating, a magnetic disk using this aluminum alloy substrate for magnetic disks, and a magnetic disk obtained by the manufacturing methods will be described in detail.

[0027] 3. Manufacturing Method of Aluminum Alloy Raw Material The manufacturing method of the aluminum alloy raw material of the present invention includes a separation step in which at least one of an intermediate material and a finished product comprising an aluminum alloy disk and a Ni-containing underlayer is recycled as a recycled material for at least a part of an aluminum alloy raw material, and the aluminum alloy disk and the underlayer are separated by heating or wet treating the aluminum alloy raw material containing the recycled material. In this separation step, an oxide film is formed on the peeled surface of the aluminum alloy disk material obtained by peeling the underlayer, and in the subsequent molten metal heating and holding step, the underlayer remaining on the peeled surface of the aluminum alloy disk material can be further separated, thereby obtaining an aluminum alloy raw material with excellent recyclability.

[0028] 2 is a flowchart showing each step in the method for producing an aluminum alloy raw material, starting from the manufacturing process for the magnetic disk. As shown in FIG. 2, the aluminum alloy raw material is manufactured through a process for separating the underlayer (step S101). Known methods for separating the underlayer include mechanical processing for physically separating the underlayer, dry processing such as heating, and wet processing such as chemical dissolution. Here, separation by heating and separation by chemical dissolution will be described.

[0029] In step S101, an intermediate material (aluminum alloy substrate for magnetic disk) or a finished product (magnetic disk) is used as at least a part of the aluminum alloy material as the recycled material, and the aluminum alloy disk and the underlayer are separated from the recycled material by heating or wet treatment (step S101).

[0030] In this separation process, when the aluminum alloy disk and the base layer are separated from the recycled material by heating, in step S101, the aluminum alloy material containing the recycled material is preferably heated and held at 480°C or higher and 570°C or lower for more than one hour. Heating causes the Ni-P plating contained in the base layer to react with the aluminum in the aluminum alloy disk, forming a brittle intermediate layer containing Al, Ni, and P between the base layer and the aluminum alloy disk. As a result, thermal stress during cooling after heating causes cracks to form originating from the intermediate layer containing Al, Ni, and P, allowing the base layer to be separated. In the separation process, if the heating temperature is lower than 480°C and / or the holding time is shorter than one hour, the above-mentioned separation effect cannot be achieved. Furthermore, this is insufficient in terms of oxide film formation. On the other hand, if the heating temperature exceeds 570°C, a portion of the aluminum alloy disk melts, making it difficult to peel off the base layer.

[0031] From the viewpoint of separability, the heating temperature is preferably 520°C or higher and 570°C or lower, and the holding time is more preferably 2 hours or longer. By holding the temperature in this manner, it is possible to promote the separation of the aluminum alloy disk and the base layer, and to make the oxide film on the surface thicker. There is no particular upper limit to the holding time, but from an economic viewpoint, it is preferably 30 hours.

[0032] In the separation process, it is preferable to perform a cooling process multiple times, in which the aluminum alloy material containing recycled material is cooled to room temperature after heating. Performing multiple cooling processes can improve separability and form a thicker oxide film on the surface of the aluminum disk material. The cooling process is preferably performed two or more times, more preferably three or more times. Furthermore, in the cooling process, cooling is preferably performed at a cooling rate of 30°C / h or more in the temperature range of 400 to 450°C. As described above, the Ni-P plating contained in the underlayer separates due to thermal stress generated during cooling, which causes cracks to form starting from the intermediate layer containing Al, Ni, and P. However, if the cooling rate in the above temperature range is slow, the thermal stress is small and separation may be insufficient. Therefore, when cooling to room temperature after heating, the cooling rate in the temperature range of 400 to 450°C is preferably 30°C / h or more, more preferably 50°C / h or more, and even more preferably 80°C / h or more. Note that room temperature refers to a range of -10 to 50°C.

[0033] In the cooling step, it is preferable to further apply a physical impact to the aluminum alloy material containing recycled material. By applying an impact to the recycled material, cracks in the intermediate layer containing Al, Ni, and P tend to grow, and the base layer tends to peel off. Methods for applying an impact include dropping the recycled material as the target object, and mechanically moving the target object to contact with another object, but are not limited to these methods, and an impact can be applied to the aluminum alloy material containing recycled material by any method.

[0034] In the separation step, the rate of temperature rise when heating to a predetermined temperature is not particularly limited, but is preferably 30° C. / h or more, more preferably 50° C. / h or more, and even more preferably 80° C. / h or more. The aluminum alloy material containing the recycled material may be directly charged into a furnace that has been preheated to a predetermined temperature.

[0035] Next, separation by wet processing will be described. When separating the aluminum alloy disk and the underlayer from the recycled material by chemical dissolution, e.g., sulfuric acid electrolysis, in step S101, the aluminum alloy material containing the recycled material is preferably subjected to sulfuric acid electrolysis. The sulfuric acid concentration in the electrolyte used for sulfuric acid electrolysis is preferably 10 g / L to 200 g / L (10 g to 200 g of 98% sulfuric acid per 1 L of water), more preferably 50 g / L to 150 g / L. If the sulfuric acid concentration is less than 10 g / L, dissolution of the underlayer is difficult. On the other hand, if the sulfuric acid concentration exceeds 200 g / L, the viscosity of the electrolyte increases, reducing the dissolution rate and resulting in inefficiency. In addition, the temperature of the electrolyte is preferably 5°C to 50°C. If the temperature is less than 5°C, the current efficiency is low and efficiency decreases, while if the temperature exceeds 50°C, hydrogen generation during electrolysis becomes severe, which is undesirable from a safety standpoint. In addition, the treatment time for sulfuric acid electrolysis is preferably 30 seconds to 1200 seconds. If the treatment time is less than 30 seconds, the formation of an oxide film is insufficient, and if it exceeds 1200 seconds, it is not preferable from the viewpoint of productivity. Furthermore, the voltage applied in sulfuric acid electrolysis is preferably 0.1 V or more and 30 V or less. If the voltage is less than 0.1 V, the dissolution rate becomes slow, and if it exceeds 30 V, hydrogen generation during electrolysis becomes severe, which is not preferable from the viewpoint of safety.

[0036] Furthermore, when quantitative elemental analysis of the aluminum alloy disk obtained after the separation step is performed in the depth direction from the surface of the oxide film by glow discharge optical emission spectroscopy (GD-OES), it is preferable that the time required for the oxygen (O) emission intensity peak to reach half of its peak is 0.1 seconds or longer. Although the above-described separation method can remove a certain amount of the underlayer from the aluminum alloy disk, a portion of the underlayer remains on the surface of the aluminum alloy disk. To further remove this underlayer, it is preferable to thicken the oxide film formed on the surface (exfoliated surface) of the aluminum alloy disk. By thickening the oxide film, the remaining underlayer is more likely to separate from the exfoliated surface of the aluminum alloy disk together with the oxide film. Specifically, in the molten metal holding step described below, the oxide film present on the exfoliated surface is completely separated and floats to the surface of the molten metal, and by removing it, the underlayer can be further removed. Since the time taken for the oxygen (O) emission intensity to reach half of its peak is 0.1 seconds or more, a thick oxide film is formed, which makes it easier for the remaining base layer to separate from the peeled surface of the aluminum alloy disk material together with the oxide film. Furthermore, since this oxide film is partially porous, it tends to float to the surface of the molten metal, but in order to lower the density of the oxide film and make it easier to float to the surface of the molten metal, it is preferable that the oxide film contains at least one of S and P, which have a lower density than Al.

[0037] Through the above steps, an aluminum alloy raw material for magnetic disks is produced.

[0038] 4. Manufacturing Method of Aluminum Alloy Ingot The manufacturing method of an aluminum alloy ingot includes a molten metal preparation step of preparing a molten aluminum alloy using at least a portion of the aluminum alloy raw material obtained by the manufacturing method described above, a molten metal heating and holding step of heating and holding the prepared molten metal, and a casting step of casting the heated and held molten metal. Specifically, as shown in Fig. 2, the aluminum alloy ingot is manufactured through the steps of adjusting the aluminum alloy components, preparing and heating and holding the molten aluminum alloy (step S102), and casting the aluminum alloy (step S103).

[0039] 4-1. Adjustment of Aluminum Alloy Composition and Heating and Holding of Molten Metal (Step S102) In step S102, a molten aluminum alloy having a predetermined alloy composition is prepared by heating and melting the aluminum alloy raw material including the aluminum alloy disk material separated from the recycled material in step S101 in accordance with a conventional method.

[0040] Ni (nickel) content: In the molten metal heating and holding step, 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 the like to form Al-Ni compounds, which cause major defects on the plating surface, so the Ni content needs to be reduced. 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 aluminum alloy composition adjustment step, in which raw materials are heated and melted. For example, the composition of the molten metal is analyzed after the raw materials in the molten metal are completely melted, and if the Ni content is high, aluminum bullion or the like is added to adjust the Ni content to the desired level.

[0041] P (phosphorus) Content: In the molten metal heating and holding process, the P content in the molten aluminum alloy is preferably 0% by mass or more and 0.05% by mass or less. P is present as a plating component partially remaining in recycled materials or contained in aluminum alloy bullion. However, P combines with Mg (magnesium), which is generally contained in the aluminum alloy raw material used for 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. While some of the Mg-P-based oxides can rise to the surface of the molten metal and be removed by heating and holding 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 bullion or the like. However, if adjustment is required, the desired content can be achieved by adding aluminum bullion or the like, as with Ni.

[0042] - Mg (Magnesium) Content In the molten metal heating and holding step, 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 bullion, as with Ni.

[0043] Metal Components in Molten Aluminum Alloy With regard to the metal components contained in the molten aluminum alloy, in order to effectively remove or reduce the P component derived from the electroless Ni—P plating components contained in the recycled aluminum alloy substrate for magnetic disks and magnetic disks, it is preferable to adjust the content of P itself and elements such as Cu and Mg that form intermetallic compounds with P, as described above.

[0044] On the other hand, elements other than Ni, P, Cu, and Mg and their contents are not particularly limited. Examples of alloy compositions contained in the molten aluminum alloy include the following elements: The aluminum alloy contains the essential element 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), and 0% by mass to 0.20% by mass of Zr (zirconium), with the balance being Al and unavoidable impurities and other trace components.

[0045] Examples of unavoidable impurities include Ti (titanium) and Ga (gallium) contained in aluminum alloys, and other trace components include Co (cobalt) and Pt (platinum), which are components contained in plating and magnetic materials that could not be completely separated from recycled materials. 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.

[0046] 4-2. Heating and Holding of Molten Aluminum Alloy Next, the molten aluminum alloy heating and holding process for heating and holding the molten aluminum alloy will be described. In this process, the molten aluminum alloy is heated and held in a holding furnace under the conditions described below. During this process, it is preferable to remove the oxide film floating on the surface of the molten aluminum alloy outside the furnace. By removing this floating oxide film, etc. by a method such as scooping before casting the aluminum alloy, the Ni and P contents in the molten aluminum alloy can be reduced. Here, since this oxide film contains a part of the base layer that should be removed, leaving the oxide film on the surface of the molten aluminum alloy for a long time may result in the components contained in the base layer being reconstituted into the molten aluminum alloy. Therefore, it is preferable to remove the oxide film outside the furnace as quickly as possible.

[0047] 4-3. Casting of Aluminum Alloy (Step S103) Next, the aluminum alloy casting process will be described. The heated and maintained molten aluminum alloy is 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), or the like, after an in-line degassing treatment or an in-line filtration treatment, as described below, as needed (Step S103). In DC casting, the molten metal poured through a spout loses heat and solidifies by a bottom block, a water-cooled mold wall, and cooling water directly discharged onto the outer periphery of the ingot, and is drawn downward as an ingot. In metal mold casting, the molten metal poured into a hollow mold made of cast iron or the like loses heat and solidifies by the mold wall, producing an ingot. In CC casting, the molten metal is supplied through a casting nozzle between a pair of rolls (or belt casters or block casters), and a thin plate is directly cast by heat removal from the rolls.

[0048] The molten metal heated and held in the molten metal 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 inject argon gas or a mixed gas such as argon and nitrogen into the molten metal while rotating a bladed rotor at high speed to supply the gas as fine bubbles into the molten metal. This allows dehydrogenation gas and inclusion removal 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.

[0049] Through the above steps, an aluminum alloy ingot is produced.

[0050] 5. Manufacturing Method of Aluminum Alloy Plate The manufacturing method of an aluminum alloy plate includes a homogenization step of optionally heat-treating the aluminum alloy ingot obtained by the above-mentioned manufacturing method, a hot rolling step of hot-rolling the optionally homogenized aluminum alloy ingot, and a cold rolling step of cold-rolling the hot-rolled hot-rolled plate. Specifically, the aluminum alloy plate is manufactured through the steps of homogenization treatment (step S104), hot rolling (step S105), and cold rolling (step S106) of the aluminum alloy ingot, as shown in Fig. 2.

[0051] 5-1. Homogenization Treatment (Step S104) The cast aluminum alloy ingot is subjected to a homogenization treatment as needed (Step S104). When the homogenization treatment is performed, 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 on the heating time, if the heating time exceeds 48 hours, the homogenization effect may saturate, resulting in a decrease in productivity.

[0052] 5-2. Hot Rolling (Step S105) Next, the cast aluminum alloy ingot, or the homogenized aluminum alloy ingot if homogenized, is hot rolled to produce a hot-rolled sheet (Step S105). 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 may become coarse, resulting in a decrease in plating adhesion. If the hot rolling end temperature is lower than 260°C, workability by hot rolling cannot be ensured, and if it exceeds 400°C, crystal grains may become coarse, resulting in a decrease in plating adhesion. In hot rolling, the ingot is usually heated and held at the hot rolling starting temperature for 0.5 to 10.0 hours before hot rolling. When homogenization treatment is performed, this heating and holding may be replaced by the homogenization treatment.

[0053] 5-3. Cold Rolling (Step S106) Next, the resulting hot-rolled sheet is cold-rolled to produce a cold-rolled sheet having a thickness of preferably 0.4 mm to 2.0 mm, more preferably 0.6 mm to 2.0 mm (Step S106). That is, after hot rolling, the sheet is finished to the required product thickness by cold rolling. The cold-rolling conditions are not particularly limited and may be determined depending on the required product sheet strength and thickness. 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, as described below, and the adhesion of the plating may be reduced. On the other hand, if the rolling reduction exceeds 90%, the manufacturing time may be extended, which may result in reduced productivity.

[0054] 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, crystal grains may become coarse, resulting in a decrease in plating adhesion. If the annealing time exceeds 10 hours, the manufacturing time may be extended, potentially resulting in a decrease in productivity.

[0055] 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 0 to 60 seconds, and more preferably at an annealing temperature of 450°C or higher and 500°C or lower for a holding time of 0 to 30 seconds. If the annealing temperature is lower than 400°C, a sufficient annealing effect may not be obtained, and if the annealing temperature exceeds 500°C, the crystal grains may become coarse and the plating adhesion may deteriorate. Furthermore, if the holding time exceeds 60 seconds, the crystal grains may become coarse and the plating adhesion may deteriorate. A holding time of 0 seconds means that the material is cooled immediately after reaching the desired annealing temperature.

[0056] Through the above steps, an aluminum alloy plate is produced.

[0057] 6. Manufacturing Method of Aluminum Alloy Substrate for Plating The manufacturing method of an aluminum alloy substrate for plating includes a processing step of processing the aluminum alloy plate obtained by the above-mentioned manufacturing method into an annular disk blank, a pressure annealing step of pressurizing and flattening the annular disk blank, and a cutting / grinding step of cutting and grinding the pressurized and flattened annular disk blank. Specifically, the aluminum alloy substrate for plating is manufactured through the steps of punching an aluminum alloy plate into an annular disk blank (hereinafter sometimes referred to as a "disk blank") (step S107), pressure flattening and annealing of this disk blank (step S108), subsequent cutting and grinding (step 109: "cutting / grinding step"), and, if necessary, a distortion relief heat treatment (step S110), as shown in FIG.

[0058] 6-1. Production of an annular disk blank (step S107) To process the aluminum alloy plate obtained as described above into an aluminum alloy substrate, first, the aluminum alloy plate is punched into an annular shape to produce an annular disk blank (step S107).

[0059] 6-2. Pressure Annealing (Step 108) Next, the disk blank is subjected to pressure annealing in air at a temperature of 300°C to 450°C for 30 minutes or more, preferably 300°C to 380°C for 60 minutes or more, to produce a flattened disk blank (Step S108). If the pressure annealing 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 and the adhesion of the plating may decrease. There is no particular upper limit to the treatment time, but if it exceeds 24 hours, the manufacturing time may become long, which may result in a decrease in productivity. The pressure used in pressure annealing is usually 0.1 MPa to 3.0 MPa.

[0060] 6-3. Cutting / Grinding (Step S109), Strain Relief Heat Treatment (Step S110) Next, the disk blank flattened in the cutting / grinding process is cut and ground (Step S109). After that, optionally, strain relief heat treatment is performed to remove strain from the disk blank at a temperature of 200°C to 290°C for 0.1 to 10.0 hours (Step S110).

[0061] Through the above steps, an aluminum alloy substrate for plating is produced.

[0062] 7. Manufacturing Method of Aluminum Alloy Substrate for Magnetic Disk The manufacturing method of an aluminum alloy substrate for magnetic disk includes a plating pretreatment step of degreasing, etching, and zincating the aluminum alloy substrate for plating obtained by the manufacturing method described above, and a base plating step of electrolessly plating the surface of the aluminum alloy substrate that has been pretreated with plating with Ni-P and polishing the plated surface. Such an aluminum alloy substrate for magnetic disk is manufactured through the steps of plating pretreatment (step S111) of the aluminum alloy substrate for plating and base (Ni-P) plating (with polishing) (step S112), as shown in Fig. 2.

[0063] 7-1. Plating Pretreatment (Step S111) 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 (Step S111). Degreasing is preferably performed using a commercially available degreasing solution such as AD-68F (manufactured by Uemura Kogyo Co., Ltd.) at a 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 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 smoothness of the surface of the aluminum alloy substrate may decrease, and pits may occur after plating treatment, resulting in a decrease in smoothness.

[0064] 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 may decrease, resulting in the occurrence of pits after plating, resulting in a decrease in smoothness. A conventional desmutting treatment may be performed between the etching treatment and the zincate treatment described below.

[0065] 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.

[0066] 7-2. Base (Ni—P) Plating (with Polishing) (Step 112) Next, the zincate-treated surface of the aluminum alloy substrate for plating is subjected to electroless Ni—P plating as a base treatment, followed by surface polishing (Step S112). The electroless Ni—P plating is preferably carried out using, for example, a commercially available Nimden HDX (Uemura Kogyo Co., Ltd.) plating solution at a 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 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. Plating temperatures below 80°C and / or Ni concentrations below 3 g / L can result in slow plating growth and reduced productivity. Furthermore, if the plating treatment time is less than 30 minutes, numerous defects may occur on the plated surface, resulting in a decrease in the smoothness of the plated surface. On the other hand, if the plating treatment temperature exceeds 95°C and / or the Ni concentration in the plating solution exceeds 10 g / L, the plating may grow unevenly, resulting in a decrease in the smoothness of the plated surface. Furthermore, if the plating treatment time exceeds 180 minutes, the manufacturing time may be extended, which may result in a decrease in productivity. Furthermore, the surface of the base (Ni-P) plated layer is polished.

[0067] An aluminum alloy substrate for a magnetic disk is produced by these pre-plating treatments and the undercoat (Ni-P) plating treatment (with polishing).

[0068] 8. Manufacturing Method of Magnetic Disk The manufacturing method of a magnetic disk includes a magnetization step of adhering a magnetic material to the surface of the aluminum alloy substrate for magnetic disk obtained by the manufacturing method described above to form a magnetic material layer. As shown in Figure 2, such a magnetic disk is produced by adhering a magnetic material to the surface of the aluminum alloy substrate for magnetic disk that has been primed (step S113).

[0069] After the electroless Ni—P plating process, including polishing, a magnetic material is deposited on the Ni—P plating layer by sputtering to form a magnetic layer (step S113). 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.

[0070] By the above steps, a magnetic disk can be produced that has a Ni-P plating layer on the surface of an aluminum alloy substrate for a magnetic disk and a magnetic layer formed on the Ni-P plating layer. The magnetic disk obtained by this magnetic disk manufacturing method is produced using the above-mentioned recycled materials, and is therefore useful as a magnetic disk that is excellent in reducing the environmental load.

[0071] Based on the above embodiments, the present invention relates to the following [1] to

[13] . [1] An aluminum alloy disk material having a peeled surface formed by peeling off the underlayer from at least one of a recycled material, an intermediate material and a finished product, comprising an aluminum alloy disk and a Ni-containing underlayer, wherein the aluminum alloy disk material is characterized in that an oxide film is formed on the peeled surface. [2] The aluminum alloy disk material according to [1] above, wherein the oxide film contains at least one of S and P. [3] The aluminum alloy disk material according to [1] or [2] above, wherein the underlayer includes a Ni-P plating layer. [4] A method for producing an aluminum alloy raw material, comprising: reusing at least one of a recycled material, an intermediate material and a finished product, comprising an aluminum alloy disk and a Ni-containing underlayer, as at least a part of an aluminum alloy raw material; and separating the aluminum alloy disk and the underlayer by heating or wet treating the aluminum alloy raw material containing the recycled material, wherein the aluminum alloy disk material obtained by peeling off the underlayer has an oxide film formed on the peeled surface. [5] A method for producing an aluminum alloy raw material according to [4] above, wherein, when quantitative elemental analysis is performed in the depth direction from the surface of the oxide film by glow discharge optical emission spectroscopy, the time required for the oxygen (O) emission intensity to reach half of its peak is 0.1 seconds or more. [6] A method for producing an aluminum alloy raw material according to [4] or [5] above, wherein the oxide film contains at least one of S and P. [7] A method for producing an aluminum alloy ingot, comprising: a molten metal preparation step of preparing a molten aluminum alloy using at least a part of the aluminum alloy raw material obtained by the production method according to [4] to [6] above, a molten metal heating and holding step of heating and holding the prepared molten metal, and a casting step of casting the heated and held molten metal. [8] A method for producing an aluminum alloy ingot according to [7] above, wherein oxides present on the surface of the molten aluminum alloy are removed in the molten metal heating and holding step.[9] A method for producing an aluminum alloy plate, comprising: a homogenization step of optionally heat-treating an aluminum alloy ingot obtained by the production method described in [7] or [8] above; a hot-rolling step of hot-rolling the optionally homogenized aluminum alloy ingot; and a cold-rolling step of cold-rolling the hot-rolled plate.

[10] A method for producing an aluminum alloy substrate for plating, comprising: a processing step of processing the aluminum alloy plate obtained by the production method described in [9] above into an annular disk blank, a pressure annealing step of press-flattening the annular disk blank, and a cutting / grinding step of cutting and grinding the press-flattened annular disk blank.

[11] A method for producing an aluminum alloy substrate for magnetic disks, comprising: a plating pretreatment step of degreasing, etching, and zincating the aluminum alloy substrate for plating obtained by the production method described in

[10] above; and a primer plating step of electrolessly plating the surface of the pre-plated aluminum alloy substrate and polishing the plated surface.

[12] A method for manufacturing a magnetic disk, comprising a magnetism imparting step of adhering a magnetic material to the surface of the aluminum alloy substrate for magnetic disk obtained by the manufacturing method described in

[11] above to form a magnetic material layer.

[13] A magnetic disk obtained by the manufacturing method described in

[12] above.

[0072] The aluminum alloy disk material, the method for manufacturing an aluminum alloy raw material, the method for manufacturing an aluminum alloy ingot, the method for manufacturing an aluminum alloy plate, the method for manufacturing an aluminum alloy substrate for plating, the method for manufacturing an aluminum alloy substrate for magnetic disks, the method for manufacturing a magnetic disk, and the magnetic disk according to the present embodiments have been described above, but the present invention is not limited to the above-mentioned embodiments, and various modifications and changes are possible based on the technical concept of the present invention.

[0073] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0074] Aluminum alloy substrates for magnetic disks (hereinafter referred to as "aluminum alloy substrates") were used as recycled materials, and these were heated and cooled or subjected to sulfuric acid electrolysis under the conditions shown in Table 1 to separate the underlayers and produce aluminum alloy raw materials (aluminum alloy disk materials). The sulfuric acid electrolysis was carried out using sulfuric acid with a concentration of 100 g / L under conditions of a temperature of 25°C, a treatment time of 4 minutes, and an applied voltage of 2 V.

[0075] The P content in the Ni-P plating layer adhered to the aluminum alloy substrate used as the recycled material was about 12 mass% relative to the total mass of the aluminum alloy substrate. The aluminum alloy used for the aluminum alloy substrate had an alloy composition in which the total content of Fe and Mn was 0.015 mass% to 0.030 mass%, 3.8 mass% to 4.5 mass% of Mg, 0.005 mass% or less of Ni, and one or more metals selected from the group consisting of 0.03 mass% or less of Si, 0.30 mass% to 0.40 mass% of Zn, 0.04 mass% to 0.06 mass% of Cr, and 0.005 mass% to 0.025 mass% of Cu, with the balance consisting of Al, unavoidable impurities, and trace components.

[0076] To evaluate the separability, the aluminum alloy disk material after separation by heating or wet treatment was melted and cast, and the Ni content (Na) [mass %] of the ingot was measured, and the separation ratio (Ns = (1 - Na / Nd) x 100) was calculated from the Ni content (Nd) [mass %] of the entire aluminum alloy disk material before separation of the base layer. Note that 3.9 mass % was used as a representative value for the Ni content (Nd).

[0077] The presence or absence of an oxide film on the peeled surface of the aluminum alloy disk material after separation by heating or wet processing was determined using GDS. Quantitative elemental analysis using GDS was performed from the surface of the peeled surface in the depth direction. If a peak in the oxygen (O) emission intensity was observed, it was determined that an oxide film had been formed. If an oxide film had been formed, the time when the peak O emission intensity was reduced to half and the presence or absence of P and S in the oxide film were determined by measuring the O, P, and S emission intensities using a GDS ("JY5000RF" manufactured by HORIBA) at a gas pressure of 400 Pa and an output of 30 W for a sputtering time of 15 seconds. From the data after measurement, the time when the peak O emission intensity was reduced to half was calculated using the following formula, and the presence or absence of P and S in the oxide film was also determined. Examples of the results are shown in Figures 3A-B and 4A-B.

[0078] <Presence or absence of a peak in O emission intensity> When the ratio (average value of O emission intensity up to a sputtering time of less than 1.0 second) / (average value of O emission intensity up to a sputtering time of 7.0 seconds or more and less than 8.0 seconds) was 1 or more, it was determined that an oxide film was formed.

[0079] <Time at which the peak O emission intensity is halved> (O emission intensity at each sputtering time) - (average O emission intensity for sputtering times 7-10 seconds) - ((maximum O emission intensity) - (average O emission intensity for sputtering times 7-10 seconds)) / 2 was calculated, and the sputtering time immediately before this value became negative was regarded as the time at which the peak O emission intensity was halved. Note that if the oxide film was thick and a sputtering time of 15 seconds was insufficient, the sputtering time was increased, and in that case, the (average O emission intensity for sputtering times 7-10 seconds) was calculated as the average value for the sputtering time multiplied by the value of (new sputtering time / 15), rather than the sputtering time of 7-10 seconds.

[0080] <Presence or Absence of P> When the ratio (average value of P emission intensity up to a sputtering time of less than 0.1 seconds) / (average value of P emission intensity up to a sputtering time of 0.3 seconds or more but less than 0.5 seconds) was 2 or more, it was determined that the oxide film contained P.

[0081] <Presence or Absence of S Content> When the ratio (average value of S emission intensity up to a sputtering time of less than 0.1 seconds) / (average value of S emission intensity up to a sputtering time of 0.3 seconds or more but less than 0.5 seconds) was 3 or more, it was determined that the oxide film contained P.

[0082]

[0083] As shown in Table 1, the separation ratio was 98% or more in Examples 1 to 5, and excellent recyclability was obtained. In particular, Examples 2 to 4, in which the time it took for the peak of the O emission intensity to reach half its peak was long, and Example 1, in which both P and S were contained in the oxide film, showed a high separation ratio and excellent recyclability.

[0084] On the other hand, in Comparative Example 1, a part of the aluminum alloy disk melted, making it difficult to peel off the base layer, which made it difficult to analyze by GDS and prevented confirmation of the oxide film. Furthermore, the peeling rate was less than 60%, resulting in poor recyclability.

[0085] The present invention can provide an aluminum alloy disk material, a method for producing an aluminum alloy raw material, a method for producing an aluminum alloy ingot, a method for producing an aluminum alloy plate, a method for producing an aluminum alloy substrate for plating, a method for producing an aluminum alloy substrate for magnetic disks, a method for producing a magnetic disk, and a magnetic disk, all of which are highly recyclable.

Claims

1. An aluminum alloy disk material having a peeled surface formed by peeling off the base layer from at least one of a recycled material of an intermediate material and a finished product comprising an aluminum alloy disk and a base layer containing Ni, the aluminum alloy disk material being characterized in that the peeled surface has an oxide film on its surface.

2. The aluminum alloy disk material according to claim 1, wherein the oxide film contains at least one of S and P.

3. The aluminum alloy disk material according to claim 1 or 2, wherein the underlayer includes a Ni-P plating layer.

4. A method for producing an aluminum alloy raw material, comprising a separation step of reusing at least one of an intermediate material and a finished product comprising an aluminum alloy disk and a Ni-containing underlayer as a recycled material for at least a part of an aluminum alloy raw material, and separating the aluminum alloy disk and the underlayer by heating or wet treating the aluminum alloy raw material containing the recycled material, characterized in that an oxide film is formed on the peeled surface of the aluminum alloy disk material obtained by peeling off the underlayer.

5. The method for producing an aluminum alloy raw material according to claim 4, wherein, when a quantitative elemental analysis is performed in the depth direction from the surface of the oxide film by glow discharge optical emission spectroscopy, the time required for the peak of the emission intensity of oxygen (O) to reach half is 0.1 seconds or more.

6. The method for producing an aluminum alloy raw material according to claim 4 or 5, wherein the oxide film contains at least one of S and P.

7. A method for producing aluminum alloy ingots, comprising: a molten metal preparation step of preparing a molten aluminum alloy using at least a portion of the aluminum alloy raw material obtained by the production method described in claim 4 or 5; a molten metal heating and holding step of heating and holding the prepared molten metal; and a casting step of casting the heated and held molten metal.

8. The method for producing an aluminum alloy ingot according to claim 7, wherein an oxide film present on the surface of the molten aluminum alloy is removed in the molten metal heating and holding step.

9. A method for producing an aluminum alloy sheet, comprising: a homogenization step of optionally heat-treating an aluminum alloy ingot obtained by the production method according to claim 7; a hot rolling step of hot-rolling the optionally homogenized aluminum alloy ingot; and a cold rolling step of cold-rolling the hot-rolled sheet.

10. A method for producing an aluminum alloy substrate for plating, comprising the steps of: a processing step of processing an aluminum alloy plate obtained by the manufacturing method described in claim 9 into an annular disk blank; a pressure annealing step of pressurizing and flattening the annular disk blank; and a cutting and grinding step of cutting and grinding the pressurized and flattened annular disk blank.

11. A method for producing an aluminum alloy substrate for magnetic disks, comprising the steps of: a pre-plating step of subjecting the aluminum alloy substrate for plating obtained by the method according to claim 10 to degreasing, etching and zincating; and a base plating step of subjecting the surface of the pre-plating treated aluminum alloy substrate to electroless Ni-P plating and polishing the plated surface.

12. A method for producing a magnetic disk, comprising a magnetic layer forming step of adhering a magnetic material to the surface of an aluminum alloy substrate for a magnetic disk obtained by the method according to claim 11.

13. A magnetic disk obtained by the manufacturing method according to claim 12.

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