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

Abstract

The present invention relates to a production method for an aluminum alloy feedstock that involves a separation step in which an aluminum alloy material that is at least partially recycled material that is an intermediate material and / or a finished product that includes an aluminum alloy disk and a base layer is heated to separate the aluminum alloy disk and the base layer. During the separation step, the aluminum alloy material that includes the recycled material is heated to 480°C–590°C and held at that temperature for more than 1 hour.

Description

[Technical Field]

[0001] The present invention relates to a method for producing an aluminum alloy raw material with excellent recyclability, a method for producing an aluminum alloy ingot using the same, a method for producing an aluminum alloy plate using the same, a method for producing an aluminum alloy substrate for plating using the same, a method for producing an aluminum alloy substrate for magnetic disks using the same, a method for producing a magnetic disk using the same, and a magnetic disk obtained by the production methods. [Background technology]

[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, in order to improve pit defects caused by the loss of intermetallic compounds during the plating pretreatment process, aluminum alloy magnetic disks are manufactured from aluminum alloy substrates in which the content of impurities in JIS 5086 aluminum alloys, such as Fe, Si, and Mn, is limited and the size of the intermetallic compounds in the matrix is ​​reduced, or from aluminum alloy substrates in which Cu and Zn are intentionally added to JIS 5086 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 through the following process. First, an aluminum alloy having the desired alloy composition is cast, and the resulting ingot is hot-rolled. The resulting hot-rolled sheet is 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 to remove distortions and other defects caused by the manufacturing process, annular aluminum alloy sheets are stacked, 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 pretreatments, and then heat-treated to remove distortions and other impurities caused by the processing steps, thereby producing an aluminum alloy substrate. The resulting aluminum alloy substrate is then degreased, etched, and zincated (Zn-substitution) as pretreatments for plating, and is then plated with Ni-P, a hard non-magnetic metal, as a base treatment, and polished on the surface to produce an aluminum alloy substrate for a magnetic disk. Finally, a magnetic material or the like is sputtered onto the aluminum alloy to produce a 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 greater capacity, the number of magnetic disks installed 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 have a reduced rigidity, aluminum alloy substrates must have higher rigidity. In recent years, the use of highly rigid materials containing Ni or other additives has been considered.

[0008] Meanwhile, as the number of magnetic disks mounted increases, the amount of aluminum and other raw materials required for the aluminum alloy substrates used in 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 materials 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, while for magnetic disks, defective products and those extracted from 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 producing an aluminum alloy ingot with excellent recyclability, a method for producing an aluminum alloy plate using the ingot, a method for producing an aluminum alloy substrate for magnetic disks using the aluminum alloy plate, and a method for producing a magnetic disk using the aluminum alloy substrate. For example, Patent Document 1 proposes that by adding Ni to an aluminum alloy for magnetic disks, the aluminum alloy substrate for magnetic disks obtained thereafter 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 aluminum alloy substrates for magnetic disks are used in an amount of 50% or more by weight of the raw material, there is a possibility that the aluminum alloy raw material will 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. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-275568 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention has been made in view of the above circumstances, and aims to provide a method for producing an aluminum alloy raw material with excellent recyclability. Another object of the present invention is to provide a method for producing an aluminum alloy ingot, an aluminum alloy sheet, an aluminum alloy substrate for plating, an aluminum alloy substrate for magnetic disks, a magnetic disk, and a magnetic disk, all of which use such an aluminum alloy raw material with excellent recyclability. [Means for solving the problem]

[0013] The present inventors have discovered that an aluminum alloy raw material with excellent recyclability can be obtained by controlling the heating temperature and holding time in the separation process in which an aluminum alloy disk and an underlayer are separated from an intermediate material or a finished product to be recycled, and have completed the present invention.

[0014] A method for producing an aluminum alloy raw material according to one embodiment of the present invention is a method for producing an aluminum alloy raw material in which at least one of an intermediate material and a finished product containing an aluminum alloy disk and an underlayer is reused as a recycled material in at least a part of an aluminum alloy raw material, and in a separation step in which the aluminum alloy material containing the recycled material is heated to separate the aluminum alloy disk and the underlayer, the aluminum alloy material containing the recycled material is heated and held at 480°C or higher and 590°C or lower for more than one hour. [Effects of the Invention]

[0015] According to the present invention, a method for producing an aluminum alloy raw material with excellent recyclability can be provided. Furthermore, using such an aluminum alloy raw material with excellent recyclability, a method for producing an aluminum alloy ingot, a method for producing an aluminum alloy sheet, 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 can be provided. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a flow chart showing a process from the production of an aluminum alloy raw material to the production of a magnetic disk according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of the present invention will be described in detail below with reference to FIG. 1. In the present invention, at least one of an intermediate material and a finished product containing an aluminum alloy disk and an underlayer is recycled as at least a portion of an aluminum alloy raw material. The aluminum alloy raw material containing the recycled material is heated to separate the aluminum alloy disk and the underlayer from the intermediate material and the finished product. The heating temperature and holding time in the separation process are controlled. Because the heating temperature and holding time in the separation process have a significant impact on the separability of the underlayer, controlling these factors allows for the production of an aluminum alloy raw material with excellent recyclability. In the present invention, by heating and holding the aluminum alloy raw material containing the recycled material at a temperature of 480°C to 590°C for more than one hour, the separation rate between the aluminum alloy disk and the underlayer after the separation process is 100% or more, enabling complete separation (peeling) of the underlayer. A separation rate of more than 100% indicates that not only the underlayer but also part of the aluminum alloy has been peeled off from the recycled material.

[0018] The recycled material used in the present invention is an aluminum alloy disk having a base layer such as a Ni-P plating layer, an intermediate material is an aluminum alloy substrate for a magnetic disk, and a finished product is a magnetic disk. Examples of the recycled material include defective products, non-standard products, and, in the case of magnetic disks, used magnetic disks.

[0019] 1. Recycled materials First, we will explain the aluminum alloy substrate 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. "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.

[0020] 1-1. Aluminum alloy substrate for magnetic disks (intermediate material) Since an underlayer such as a Ni-P plating layer is formed on the surface of an aluminum alloy substrate for magnetic disks, it is important to separate most of the underlayer in order to reuse the aluminum alloy substrate for magnetic disks as at least a part of an aluminum alloy material that does not contain much Ni or P. The P content in the Ni-P plating layer used for the aluminum alloy substrate for magnetic disks is usually 15% by mass or more and 85% by mass or less. The thickness of the Ni-P plating layer is preferably 5 μm or more and 25 μm or less, and the thickness of the aluminum alloy substrate for magnetic disks is preferably 0.3 mm or more and 2.0 mm or less.

[0021] 1-2. Magnetic disk (finished product) In magnetic disks, a CoCrPt-based magnetic layer and a protective film made of a carbon-based material are formed on the surface of an aluminum alloy substrate for magnetic disks as an intermediate material. However, because these magnetic layers and protective films are formed on an underlayer, removing the underlayer allows most of them to be removed. Therefore, magnetic disks from which the underlayer has been separated can also be reused as at least a portion of an aluminum alloy material that does not contain large amounts of Ni or P. Note that, like aluminum alloy substrates for magnetic disks, when using a magnetic disk as at least a portion of an aluminum alloy material, it is important to remove as much of the underlayer as possible.

[0022] 1-3.Aluminum alloy material The aluminum alloy material is a common material adjusted to have a predetermined alloy composition and used as a raw material for producing aluminum alloy ingots. The aluminum alloy material produced in the present invention includes an embodiment including such an aluminum alloy material and an aluminum alloy disk separated from a recycled material, and an embodiment being the aluminum alloy disk itself separated from a recycled material.

[0023] Next, a detailed description will be given of a method for producing an aluminum alloy raw material according to an embodiment 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.

[0024] 2. Aluminum alloy raw material manufacturing method As shown in FIG. 1, the aluminum alloy raw material is produced through a process of separating the underlayer (step S101).

[0025] In step S101, an intermediate material (aluminum alloy substrate for magnetic disks) or a finished product (magnetic disk) is reused as at least a portion of the aluminum alloy material, and the recycled material is heated and held at 480°C to 590°C for more than one hour to separate the aluminum alloy disk and the underlayer (step S101). The heating temperature is 480°C to 590°C, preferably 520°C to 590°C from the viewpoint of separability, and the holding time is more than one hour, preferably two hours or more, to facilitate separation of the aluminum alloy disk and the underlayer. The Ni-P plating contained in the underlayer reacts with the aluminum in the aluminum alloy disk upon heating, forming a brittle intermediate layer containing Al, Ni, and P between the underlayer and the aluminum alloy disk. Thermal stress during cooling after heating causes cracks to form in the intermediate layer containing Al, Ni, and P, which allows the underlayer to separate.

[0026] In the separation step, if the heating temperature is less than 480°C and / or the holding time is less than 1 hour, the above-mentioned separation effect cannot be obtained. Furthermore, if the heating temperature exceeds 590°C, a portion of the aluminum alloy disk melts, making it difficult to peel off the base layer. While there is no particular upper limit to the holding time, a longer holding time results in a large amount of aluminum peeling off from the aluminum alloy disk, so a holding time of 30 hours is preferred.

[0027] In the separation step, it is preferable to perform a cooling step multiple times to cool the aluminum alloy material containing recycled materials to room temperature after heating. Performing cooling multiple times can improve separability. Furthermore, in the cooling step, the cooling rate in the temperature range of 400°C to 450°C is preferably 30°C / h or higher. 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°C to 450°C is preferably 30°C / h or higher, more preferably 50°C / h or higher, and even more preferably 80°C / h or higher. Note that room temperature refers to a range of -10°C to 50°C.

[0028] 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 aluminum alloy material containing 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 aluminum alloy material containing 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.

[0029] 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.

[0030] Through the above steps, an aluminum alloy raw material, particularly an aluminum alloy raw material for magnetic disks, is produced.

[0031] 3. Manufacturing method of aluminum alloy ingots The method for producing an aluminum alloy ingot includes a molten metal preparation step of melting at least a portion of the aluminum alloy raw material obtained by the above-described production method to prepare a molten aluminum alloy, 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, the aluminum alloy ingot is produced 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 S102), as shown in Fig. 1.

[0032] 3-1. Adjustment of aluminum alloy composition and heating 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 separated from the recycled material in step S101 in accordance with a conventional method.

[0033] 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 combines with aluminum (Al) and other elements to form Al-Ni compounds, which can cause large defects on the plating surface, so the Ni content must 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 the 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.

[0034] ·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 contained as a plating component partially remaining in recycled materials or in aluminum alloy ingots. However, P combines with Mg (magnesium), which is generally contained in the aluminum alloy raw material, 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 float 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, is low. The P content in the molten metal is preferably 0.05% by mass or less, and more preferably 0.01% by mass or less. 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 ingots, etc. However, if adjustment is required, aluminum ingots, etc., can be added to achieve the desired content, as with Ni.

[0035] 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 mentioned above, Mg combines with P in the molten metal to form Mg-P-based oxides, so 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.

[0036] Metallic components in molten aluminum alloys Regarding 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.

[0037] 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 molten aluminum alloys include the following: The aluminum alloy contains, for example, the essential element Fe (iron) and optionally Mn (manganese), with the total content of Fe and Mn ranging from 0.005% to 7.00% by mass, and further contains 0.5% to 6.5% by mass of Mg, and optionally contains one or more metals selected from the group consisting of 0% to 1.0% by mass of Si (silicon), 0% to 0.7% by mass of Zn (zinc), 0% to 0.30% by mass of Cr (chromium), and 0% to 0.20% by mass of Zr (zirconia), with the balance consisting of Al and unavoidable impurities and other trace components.

[0038] 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.

[0039] 3-2. Heating and maintaining molten aluminum alloy Next, the molten metal heating and holding step of heating and holding the molten aluminum alloy will be described. In this step, the molten aluminum alloy is heated and held in a holding furnace under the conditions described below. When the P content is high, the following adjustments are made.

[0040] In order to reduce the P content in the prepared molten aluminum alloy, it is preferable to heat and hold the molten aluminum alloy at a temperature of 700°C or higher and 850°C or lower for 3 hours or longer in the molten metal heating and holding step.

[0041] During the molten metal heating and holding process, some of the P contained in the molten metal is converted into oxides such as Mg-P-based oxides and floats to the surface of the molten metal. The P content in the molten metal can be reduced by removing these floated oxides by methods such as scooping them up before casting. The heating temperature is preferably 700°C or higher and 850°C or lower, and more preferably 700°C or higher and 755°C or lower from the perspective of energy conservation. The holding time is preferably 3 hours or longer, and more preferably 20 hours or longer from the perspective of promoting the formation of Mg-P-based oxides. The holding time is particularly important from the perspective of promoting the formation of Mg-P-based oxides. A heating temperature lower than 700°C and / or a holding time shorter than 3 hours may not be sufficient to promote the formation of Mg-P-based oxides. Furthermore, a heating temperature higher than 850°C may saturate the effect of promoting the formation of Mg-P-based oxides, making it uneconomical. While there is no particular upper limit to the holding time, a holding time longer than 72 hours may saturate the effect of promoting the formation of Mg-P-based oxides, making it uneconomical.

[0042] 3-3. Casting aluminum alloy (step S103) Next, the aluminum alloy casting process will be described. The heated and maintained molten aluminum alloy is subjected to in-line degassing treatment or in-line filtration treatment, as necessary, and then cast into an aluminum alloy ingot by a semi-continuous casting method (DC casting), a permanent mold casting method, a continuous casting method (CC casting), or the like (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 permanent 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 removing heat from the rolls.

[0043] The molten metal heated and held in the molten metal heating and holding process is preferably subjected to in-line degassing or in-line filtration according to conventional methods before being subjected to the casting process. Commercially available degassing devices, such as those sold under the trademarks SNIF and ALPUR, can be used as in-line degassing devices. These in-line degassing 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.

[0044] Through the above steps, an aluminum alloy ingot, particularly an aluminum alloy ingot for magnetic disks, is produced.

[0045] 4. Manufacturing method of aluminum alloy plate The method for producing an aluminum alloy sheet includes a homogenization step of optionally heat-treating the aluminum alloy ingot obtained by the above-mentioned production 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 sheet obtained by hot rolling. Specifically, the aluminum alloy sheet is produced 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. 1.

[0046] 4-1. Homogenization process (step S104) The cast aluminum alloy ingot is subjected to a homogenization treatment, if necessary (step S104). When the homogenization treatment is performed, the heat treatment is preferably performed at a heating temperature of 480°C to 560°C for at least 1 hour, and more preferably at a heating 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.

[0047] 4-2. 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. If the hot-rolling end temperature is higher than 500°C, crystal grains may become coarse, resulting in poor plating adhesion. If the hot-rolling end temperature is lower than 260°C, workability by hot rolling cannot be ensured. If the hot-rolling end temperature is higher than 400°C, crystal grains may become coarse, resulting in poor 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.

[0048] 4-3. Cold rolling (step S106) Next, the resulting hot-rolled sheet is 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 (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 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, which may result in reduced plating adhesion. On the other hand, if the rolling reduction exceeds 90%, the manufacturing time may be extended, potentially resulting in reduced productivity.

[0049] 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, the annealing 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, 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.

[0050] On the other hand, continuous annealing is preferably performed at an annealing temperature of 400°C or higher and 500°C or lower, with holding time of 0 to 60 seconds, and more preferably at an annealing temperature of 450°C or higher and 500°C or lower, with 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 coating adhesion may deteriorate. Furthermore, if the annealing time exceeds 60 seconds, the crystal grains may become coarse and the coating adhesion may deteriorate. A holding time of 0 seconds means that the steel is cooled immediately after reaching the desired annealing temperature.

[0051] Through the above steps, an aluminum alloy plate, particularly an aluminum alloy plate for a magnetic disk, is produced.

[0052] 5. Manufacturing method of aluminum alloy substrate for plating The method for producing an aluminum alloy substrate for plating includes a processing step of processing the aluminum alloy sheet obtained by the above-mentioned production method 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. Specifically, the aluminum alloy substrate for plating is produced through the steps of punching an aluminum alloy sheet 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 S109: "cutting and grinding step"), and, if necessary, a stress relief heat treatment (step S110).

[0053] 5-1. Fabrication of an annular disc 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).

[0054] 5-2. Pressure annealing (step S108) 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. 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.

[0055] 5-3. Cutting and grinding (step S109), distortion removal heat treatment (step S110) Next, the disk blank flattened in the cutting and grinding process is cut and ground (step S109), and then optionally subjected to a distortion relief heat treatment at a temperature of 200°C to 290°C for 0.1 to 10.0 hours (step S110) to remove distortion from the disk blank.

[0056] Through the above steps, an aluminum alloy substrate for plating is produced.

[0057] 6. Manufacturing method of aluminum alloy substrate for magnetic disk The method for producing an aluminum alloy substrate for magnetic disks includes a pre-plating step of degreasing, etching, and zincating the aluminum alloy substrate for plating obtained by the above-mentioned production method, and a base plating step of electrolessly plating Ni-P on the surface of the pre-plated aluminum alloy substrate and polishing the plated surface. As shown in Fig. 1, such an aluminum alloy substrate for magnetic disks is produced through the steps of pre-plating (step S111) of the aluminum alloy substrate for plating and base (Ni-P) plating (with polishing) (step S112).

[0058] 6-1. 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 degreasing solution, such as a commercially available 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, and 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 surface smoothness of the aluminum alloy substrate may decrease, and pits may occur after plating, resulting in a decrease in smoothness.

[0059] Etching is preferably performed using an etching solution such as commercially available AD-107F (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 results 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 formation 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.

[0060] The zincate treatment is preferably carried out using a zincate treatment solution, such as the commercially available AD-301F-3X (manufactured by Uemura Kogyo Co., Ltd.), at a temperature of 10°C to 35°C, for a period of 0.1 to 5 minutes, and with a concentration of the zincate treatment solution of 100 mL / L to 500 mL / L, and more preferably at a temperature of 15°C to 30°C, for a period of 0.1 to 2 minutes, and with a concentration of the zincate treatment solution 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 concentration of the zincate treatment solution is less than 100 mL / L, the zincate coating may become nonuniform, resulting in pits and reduced smoothness after plating. 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.

[0061] 6-2. Base (Ni-P) plating treatment (with polishing) (Step S112) Next, the zincate-treated surface of the aluminum alloy substrate for plating is subjected to electroless Ni-P plating as a surface preparation, followed by polishing of the surface (step S112). The electroless Ni-P plating is preferably performed using a plating solution, such as commercially available Nimuden HDX (manufactured by Uemura Kogyo Co., Ltd.), 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. More preferably, the plating temperature is 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 may result in slow plating growth and reduced productivity. Plating times of less than 30 minutes may result in numerous defects on the plating surface, reducing 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 unevenly, resulting in a decrease in plating smoothness. Furthermore, if the plating time exceeds 180 minutes, the manufacturing time may become longer, which may result in a decrease in productivity. Furthermore, the surface of the base (Ni-P) plating is polished.

[0062] An aluminum alloy substrate for a magnetic disk is produced by these pre-plating treatments and the undercoat (Ni-P) plating treatment (with polishing).

[0063] 7. Magnetic Disk Manufacturing Method The method for manufacturing a magnetic disk includes a magnetization step of forming a magnetic layer by adhering a magnetic material to the surface of the aluminum alloy substrate for a magnetic disk obtained by the above-mentioned manufacturing method. Such a magnetic disk is produced by adhering a magnetic material to the surface of the aluminum alloy substrate for a magnetic disk that has been subjected to a surface treatment, as shown in Figure 1 (step S113).

[0064] 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 layer may be formed by applying a lubricating oil to the protective layer.

[0065] By the above steps, a magnetic disk can be produced which 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 production method is produced using the above-mentioned recycled materials, and is therefore useful as a magnetic disk which is excellent in reducing the environmental load.

[0066] The methods for producing an aluminum alloy raw material, an aluminum alloy ingot, an aluminum alloy plate, an aluminum alloy substrate for plating, an aluminum alloy substrate for magnetic disks, and a magnetic disk according to the present embodiments have been described above, but the present invention is not limited to the above-described embodiments, and various modifications and variations are possible based on the technical concept of the present invention.

[0067] Based on the above embodiments, the present invention relates to the following [1] to

[13] . [1] A method for producing an aluminum alloy raw material, comprising: reusing at least one of an intermediate material and a finished product, each containing an aluminum alloy disk and an underlayer, as a recycled material for at least a part of an aluminum alloy raw material; and heating and holding the aluminum alloy raw material containing the recycled material at a temperature of 480°C or higher and 590°C or lower for more than one hour in a separation step of heating the aluminum alloy raw material containing the recycled material to separate the aluminum alloy disk and the underlayer. [2] The method for producing an aluminum alloy raw material according to [1] above, wherein in the separating step, a cooling step of cooling the aluminum alloy material containing the recycled material to room temperature after heating is performed multiple times. [3] The method for producing an aluminum alloy raw material according to [2] above, wherein in the cooling step, the cooling rate in a temperature range of 400°C or higher and 450°C or lower is 30°C / h or higher. [4] The method for producing an aluminum alloy raw material according to the above [2] or [3], wherein in the cooling step, a physical impact is further applied to the aluminum alloy material containing the recycled material. [5] A method for producing an aluminum alloy ingot, comprising: a molten metal preparation step of preparing a molten aluminum alloy by melting at least a part of an aluminum alloy raw material obtained by the production method according to any one of the above [1] to [4]; 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. [6] The method for producing an aluminum alloy ingot according to [5] above, wherein in the molten metal heating and holding step, the Ni content in the molten aluminum alloy is 2.5 mass % or less. [7] 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 the above-mentioned [5] or [6]; 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 obtained by the hot rolling. [8] A method for producing an aluminum alloy substrate for plating, comprising: a processing step of processing the aluminum alloy plate obtained by the manufacturing method described in [7] above 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. [9] A method for producing an aluminum alloy substrate for magnetic disks, comprising: a pre-plating step of degreasing, etching and zincating the aluminum alloy substrate for plating obtained by the production method described in [8] above; and a base plating step of electrolessly plating the surface of the pre-plating treated aluminum alloy substrate with Ni-P, and polishing the plated surface.

[10] A method for manufacturing a magnetic disk, comprising a magnetic imparting step of adhering a magnetic material to the surface of an aluminum alloy substrate for a magnetic disk obtained by the manufacturing method described in [9] above to form a magnetic material layer.

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

[10] above.

[12] a separation step of reusing at least one of an intermediate material and a finished product including the aluminum alloy disk and the underlayer as a recycled material for at least a part of an aluminum alloy material, and heating the aluminum alloy material including the recycled material to separate the aluminum alloy disk from the underlayer; a molten metal preparation step of melting at least a portion of the aluminum alloy raw material obtained in the separation step to prepare a molten aluminum alloy; a molten metal heating and holding step of heating and holding the prepared molten metal; a casting step of casting the heated and held molten metal into an aluminum alloy ingot; a homogenization treatment step in which the obtained aluminum alloy ingot is optionally heat-treated; 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 obtained by hot rolling, A method for producing an aluminum alloy plate, comprising heating and holding the aluminum alloy material containing the recycled material at a temperature of 480°C or higher and 590°C or lower for more than one hour.

[13] a separation step of reusing at least one of an intermediate material and a finished product including the aluminum alloy disk and the underlayer as a recycled material for at least a part of an aluminum alloy material, and heating the aluminum alloy material including the recycled material to separate the aluminum alloy disk from the underlayer; a molten metal preparation step of melting at least a portion of the aluminum alloy raw material obtained in the separation step to prepare a molten aluminum alloy; a molten metal heating and holding step of heating and holding the prepared molten metal; a casting step of casting the heated and held molten metal into an aluminum alloy ingot; a homogenization treatment step in which the obtained aluminum alloy ingot is optionally heat-treated; 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 obtained by hot rolling, A method for producing an aluminum alloy plate, wherein the separation rate between the aluminum alloy disk and the underlayer after the separation step is 100% or more.

[14] A processing step of processing the aluminum alloy plate obtained by the manufacturing method according to

[12] or

[13] above into an annular disk blank; a pressure annealing step of pressurizing and flattening the annular disk blank; a cutting and grinding process for producing an aluminum alloy substrate for plating by performing cutting and grinding processes on the pressurized and flattened annular disk blank; a plating pretreatment step of subjecting the obtained aluminum alloy substrate for plating to degreasing, etching and zincate treatment; a base plating process in which an electroless Ni-P plating process is performed on the surface of the aluminum alloy substrate that has been subjected to pre-plating treatment, and the plated surface is polished; A method of manufacturing a magnetic disk, comprising a magnetic imparting step of adhering a magnetic material to the surface of an aluminum alloy substrate for a magnetic disk obtained by undercoating treatment to form a magnetic material layer. [Example]

[0068] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0069] An aluminum alloy substrate for magnetic disks (hereinafter referred to as "aluminum alloy substrate") was used as the recycled material, and was heated, held, and cooled under the conditions shown in Table 1 to separate the underlayer and produce an aluminum alloy raw material (aluminum alloy disk). In Table 1, "temperature" and "time" represent the "heating time" and "holding time," respectively, in the separation process, "cooling cycles" represent the number of times the aluminum alloy substrate was cooled to room temperature (25°C) after heating in the cooling process, and "cooling rate" represents the cooling rate in the temperature range of 400°C to 450°C. In addition, physical impact was applied by dropping the object (aluminum alloy substrate) from a height of 1 m in the cooling process.

[0070] The P content in the Ni-P plating layer attached to the aluminum alloy substrate used as the recycled material was approximately 12% by mass relative to the total mass of the aluminum alloy substrate. The aluminum alloy used for the aluminum alloy substrate for magnetic disks had an alloy composition in which the total content of Fe and Mn was 0.015% to 0.030% by mass, 3.8% to 4.5% by mass of Mg, 0.01% by mass or less of Ni, and one or more metals selected from the group consisting of 0.03% by mass or less of Si, 0.30% by mass to 0.40% by mass of Zn, 0.04% by mass to 0.06% by mass of Cr, and 0.005% by mass to 0.025% by mass of Cu, with the balance consisting of Al, unavoidable impurities, and trace elements.

[0071] To evaluate separability, the weight of the aluminum alloy disk (Ws) after heating was measured, and the difference (S1 = Ws - Wa) between the calculated weight of the aluminum alloy portion of the aluminum alloy substrate before heating (Wa) was calculated. This difference (S2 = Wp - S1) was then calculated. The difference between this weight and the calculated weight of the base layer (Wp) of the aluminum alloy substrate before heating (S2 = Wp - S1) was then divided by Wp (S2 / Wp), and multiplied by 100 to calculate the separation rate (%). The results are shown in Table 1. Although chamfers were present on the outer and inner peripheries of the aluminum alloy substrate, their impact on the overall weight was small, so the chamfers were considered to be absent in the calculations. Furthermore, a separation rate exceeding 100% indicates that not only the base layer but also some of the aluminum alloy had peeled off from the recycled material. However, since this was only a small portion of the entire aluminum alloy disk, the peeled base layer was evaluated as indicating excellent recyclability.

[0072] [Table 1]

[0073] As shown in Table 1, in Examples 1 to 13, the separation rate was 100% or more, and excellent results were obtained in terms of recyclability. In particular, the longer the heating time and holding time, the higher the separation rate and the better the recyclability. Furthermore, by setting the cooling rate to 30°C / h or more in the temperature range of 400°C or more and 450°C or less, the separation rate increased and the recyclability improved. Furthermore, even when the aluminum alloy substrate was subjected to a physical impact during the cooling process, the separation rate increased and the recyclability improved.

[0074] In contrast, in Comparative Examples 1 to 4, the heating temperature was too low or the holding time was insufficient, resulting in a separation rate of less than 100%, and poor recyclability. In particular, in Comparative Example 1, the heating temperature was too low, so the underlayer could not be separated. [Industrial Applicability]

[0075] The present invention can provide an aluminum alloy raw material with excellent recyclability. Furthermore, by using such an aluminum alloy raw material with excellent recyclability, it is possible to provide an aluminum alloy ingot, an aluminum alloy plate, an aluminum alloy substrate for plating, an aluminum alloy substrate for magnetic disks, and a magnetic disk, all of which have excellent recyclability.

Claims

1. At least one of an intermediate material and a finished product including an aluminum alloy disk and an underlayer is reused as a recycled material for at least a part of an aluminum alloy material, the aluminum alloy material including the recycled material is heated to separate the aluminum alloy disk and the underlayer, and in a separation step of separating and removing the underlayer, the aluminum alloy material including the recycled material is heated and held at 480°C or higher and 590°C or lower for 2 hours or more, and then cooled, the underlayer includes a Ni—P plating layer, the intermediate material includes an aluminum alloy substrate for a magnetic disk; The method for producing an aluminum alloy raw material, wherein the finished product includes a magnetic disk.

2. 2. The method for producing an aluminum alloy raw material according to claim 1, wherein in the separating step, a cooling step of cooling the aluminum alloy material containing the recycled material to room temperature after the heating and holding step is performed a plurality of times.

3. 3. The method for producing an aluminum alloy raw material according to claim 2, wherein in the cooling step, a cooling rate in a temperature range of 400°C or higher and 450°C or lower is 30°C / h or higher.

4. The method for producing an aluminum alloy raw material according to claim 2, wherein a physical impact is further applied to the aluminum alloy material containing the recycled material in the cooling step.

5. 5. A method for producing an aluminum alloy ingot, comprising: a molten metal preparing step of preparing a molten aluminum alloy by melting at least a part of an aluminum alloy raw material obtained by the production method according to any one of claims 1 to 4; 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.

6. 6. The method for producing an aluminum alloy ingot according to claim 5, wherein the molten aluminum alloy has a Ni content of 2.5 mass% or less in the molten aluminum alloy heating and holding step.

7. 6. A method for producing an aluminum alloy plate, comprising: a homogenization treatment step of optionally heat-treating an aluminum alloy ingot obtained by the production method according to claim 5; a hot rolling step of hot-rolling the homogenized aluminum alloy ingot or the aluminum alloy ingot that has been subjected to no homogenization treatment; and a cold rolling step of cold-rolling the hot-rolled plate obtained by the hot rolling.

8. 8. A method for producing an aluminum alloy substrate for plating, comprising: a processing step of processing an aluminum alloy plate obtained by the manufacturing method according to claim 7 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.

9. 9. A method for producing an aluminum alloy substrate for magnetic disks, comprising: a pre-plating step of subjecting the aluminum alloy substrate for plating obtained by the method of claim 8 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.

10. 10. A method for producing a magnetic disk, comprising a magnetism imparting step of adhering a magnetic material to the surface of an aluminum alloy substrate for a magnetic disk obtained by the method of claim 9 to form a magnetic material layer.

11. a separation step of reusing at least one of an intermediate material and a finished product containing the aluminum alloy disk and the underlayer as a recycled material for at least a part of an aluminum alloy material, heating the aluminum alloy material containing the recycled material to separate the aluminum alloy disk and the underlayer, and separating and removing the underlayer; a molten metal preparation step of melting at least a portion of the aluminum alloy raw material obtained in the separation step to prepare a molten aluminum alloy; a molten metal heating and holding step of heating and holding the prepared molten metal; a casting step of casting the heated and held molten metal into an aluminum alloy ingot; a homogenization treatment step in which the obtained aluminum alloy ingot is optionally heat-treated; a hot rolling step of hot rolling an aluminum alloy ingot that has been homogenized or that has been omited from the homogenization treatment; and a cold rolling step of cold rolling the hot-rolled sheet obtained by hot rolling, The aluminum alloy material containing the recycled material is heated and held at 480°C or higher and 590°C or lower for 2 hours or longer, and then cooled; the underlayer includes a Ni—P plating layer, the intermediate material includes an aluminum alloy substrate for a magnetic disk; The method for manufacturing an aluminum alloy plate, wherein the finished product includes a magnetic disk.

12. a separation step of reusing at least one of an intermediate material and a finished product containing the aluminum alloy disk and the underlayer as a recycled material for at least a part of an aluminum alloy material, heating the aluminum alloy material containing the recycled material to separate the aluminum alloy disk and the underlayer, and separating and removing the underlayer; a molten metal preparation step of melting at least a portion of the aluminum alloy raw material obtained in the separation step to prepare a molten aluminum alloy; a molten metal heating and holding step of heating and holding the prepared molten metal; a casting step of casting the heated and held molten metal into an aluminum alloy ingot; a homogenization treatment step in which the obtained aluminum alloy ingot is optionally heat-treated; a hot rolling step of hot rolling an aluminum alloy ingot that has been homogenized or that has been omited from the homogenization treatment; and a cold rolling step of cold rolling the hot-rolled sheet obtained by hot rolling, The aluminum alloy material containing the recycled material is heated and held at 480°C or higher and 590°C or lower for 2 hours or longer, and then cooled; the separation rate between the aluminum alloy disk and the underlayer after the separation step is 100% or more; the underlayer includes a Ni—P plating layer, the intermediate material includes an aluminum alloy substrate for a magnetic disk; The method for manufacturing an aluminum alloy plate, wherein the finished product includes a magnetic disk.

13. a processing step of processing the aluminum alloy plate obtained by the manufacturing method according to claim 11 or 12 into an annular disk blank; a pressure annealing step of pressurizing and flattening the annular disk blank; a cutting and grinding process step of subjecting the pressurized flattened annular disk blank to cutting and grinding processes to produce an aluminum alloy substrate for plating; a plating pretreatment step of subjecting the obtained aluminum alloy substrate for plating to degreasing, etching and zincate treatment; a base plating process in which an electroless Ni-P plating process is performed on the surface of the aluminum alloy substrate that has been subjected to pre-plating treatment, and the plated surface is polished; A method of manufacturing a magnetic disk, comprising a magnetic imparting step of adhering a magnetic material to the surface of an aluminum alloy substrate for a magnetic disk obtained by undercoating treatment to form a magnetic material layer.

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