Aluminum secondary alloy, aluminum substrate for magnetic disk, and method for producing aluminum secondary alloy

Abstract

To provide an aluminum secondary alloy capable of yielding a magnetic disk substrate with high recyclability; an aluminum substrate for magnetic disks obtained by using the same; and a method for producing an aluminum secondary alloy.SOLUTION: Provided is an aluminum secondary alloy which contains aluminum scrap as at least part of the raw material, and contains Mg, Fe, Zn, Ni, and P, wherein the Mg content is 3.0 mass% to 15 mass%, and the P content is 0.1 mass ppm to 25 mass ppm.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an aluminum secondary alloy, an aluminum substrate for a magnetic disk, and a method for producing the aluminum secondary alloy. [Background technology]

[0002] Aluminum is considered a metal material with excellent recyclability, and many aluminum products made of aluminum wrought materials, including aluminum cans and die-cast products, are remelted after disposal and recycled into new products. However, since impurities remain attached to discarded aluminum products and the concentration of impurity elements gradually increases with repeated recycling, it is common for aluminum products to be cascade-recycled into products with looser component standards.

[0003] The same is true for hard disk substrate materials, whose surfaces are treated with zinc and Ni-P plating after use. Since it is generally difficult to remove these individually, it is assumed that they are cascade recycled, just like the above examples.

[0004] In addition, with the expansion of applications for aluminum products, new alloys not currently specified by JIS standards are being developed. For disk materials, materials have also been developed that actively add transition metal elements (Fe, Mn, Ni, Cr, etc.) to impart rigidity (Patent Document 1). These have a high impurity concentration, so there is hope that scrap can be used, but if undesigned elements are mixed in due to scrap, it will have a negative effect on quality. For example, in JIS AC3A alloy, if the melting raw material contains a high concentration of P, the eutectic Si phase becomes coarse, coarsening the iron-based compounds and also degrading the mechanical properties (Non-Patent Document 1). Therefore, strict management of the melting raw material components is important to maintain high quality.

[0005] Most aluminum substrates for magnetic disks are based on JIS5086 alloy, but the surfaces of waste disk substrates are Ni-P plated, which means they contain high concentrations of P. If these are mixed as recycled materials as is, there is a risk that the P will cause the transition metal compounds containing Fe etc. to coarsen and reduce the mechanical properties, or that compounds containing P will become suspended as inclusions. For this reason, there is a problem that the recovered waste disk substrates cannot be used as raw materials as is.

[0006] As a method for removing impurities from molten aluminum, for example, Patent Document 2 describes a method for removing P and / or Sb by adding Mg and blowing chlorine gas into molten aluminum containing P and / or Sb at a molten aluminum temperature of 650 to 850°C. Patent Document 3 describes a method for removing impurities, comprising the steps of: adding Mg or an Mg alloy to molten aluminum or an aluminum alloy containing impurities; holding the molten metal after the adding step at a temperature in the range of 470° C. or higher and 50° C. or lower; and separating the intermetallic compound produced in the holding step from the molten metal. Patent Document 4 describes a method for removing phosphorus from a molten aluminum alloy for casting using a dephosphorization flux. Patent Document 5 describes a method of removing phosphorus by maintaining the molten metal at 700 to 850° C. for three hours or more. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 7132289 [Patent Document 2] Patent No. 3524519 [Patent Document 3] JP 2019-183265 A [Patent Document 4] JP 2020-007630 A [Patent Document 5] JP 2023-032363 A [Non-patent literature]

[0008] [Non-Patent Document 1] Oshiro et al., Light Metals, 47(1997), 341. Summary of the Invention [Problem to be solved by the invention]

[0009] However, the method of Patent Document 2 requires a large amount of chlorine to reduce the P concentration, which causes a problem of a large environmental load. The applicability of the method of Patent Document 3 to P is unclear, and in addition, the Mg concentration in the molten metal after impurity removal is high, making it difficult to apply the method to aluminum substrates for magnetic disks. The method of Patent Document 4 is effective for molten metal that does not contain Mg, but requires a step of reducing the Na component after removing the P, and may not be efficient. The method of Patent Document 5 requires that the molten metal be maintained at high temperatures for a long period of time, which may result in a large amount of energy required for the process and low productivity.

[0010] Therefore, in order to reuse discarded Ni-P plated disk substrates as Al-Ni alloys, a technology is needed to effectively remove P, which has a high risk of degrading mechanical properties.

[0011] The present invention has been made in consideration of the above circumstances, and aims to provide an aluminum secondary alloy, an aluminum substrate for magnetic disks, and a method for producing an aluminum secondary alloy in which the concentration of P derived from aluminum waste materials such as waste disk substrates is reduced. [Means for solving the problem]

[0012] As a result of extensive research into this problem, the inventors discovered that P in aluminum scrap can be efficiently removed by adding a specific amount of magnesium to the molten raw material, which led to the completion of the present invention.

[0013] That is, the present invention relates to the following. [1] An aluminum secondary alloy containing aluminum scrap as at least a part of a raw material, Contains Mg, Fe, Zn, Ni and P, The Mg: 3.0% by mass to 15% by mass, The aluminum secondary alloy has P of 0.1 ppm by mass to 25 ppm by mass. [2] Further, it contains Si, The aluminum secondary alloy according to [1], wherein the Si content is 0.1 mass% or less. [3] The aluminum secondary alloy according to [1], further comprising Cr and Mn. [4] The aluminum secondary alloy according to [1], wherein the Ni content is 0.5% by mass to 10% by mass. [5] The aluminum secondary alloy according to [1], wherein the Fe content is 0.01% by mass to 3.0% by mass. [6] The aluminum secondary alloy according to [1], wherein the Zn content is more than 0 mass% and 1.5 mass%. [7] The secondary aluminum alloy according to [1], further comprising: 3 ppm by mass to 50 ppm by mass of Be. [8] The aluminum secondary alloy according to [1], wherein the aluminum scrap includes at least one selected from at least one selected from scraps generated during the manufacturing process of aluminum substrates for magnetic disks, scraps before Ni-P plating generated when manufacturing magnetic disks, and scrap disk substrates. [9] The aluminum secondary alloy according to any one of [1] to [8], which is a recycled ingot.

[10] The aluminum secondary alloy according to any one of [1] to [8], which is a molten metal.

[11] An aluminum substrate for a magnetic disk, comprising the aluminum secondary alloy according to any one of [1] to [8].

[12] The aluminum substrate for magnetic disks according to

[11] , wherein the content of the aluminum secondary alloy is 12 mass % or more.

[13] A method for producing an aluminum secondary alloy according to any one of [1] to [8], Melting the raw material of the aluminum secondary alloy to obtain a molten metal; adding magnesium to the molten metal; A step of removing P-containing compounds from the molten metal, in this order; A method for producing a secondary aluminum alloy, wherein in the step of adding magnesium to the molten metal, a Mg concentration in the molten metal is 3.0% by mass to 15% by mass.

[14] The method for producing a secondary aluminum alloy according to

[13] , wherein the treatment temperature in the step of adding magnesium to the molten metal is 700 to 850°C. Effect of the Invention

[0014] According to the present invention, it is possible to provide an aluminum secondary alloy from which a magnetic disk substrate with high recyclability can be obtained, an aluminum substrate for a magnetic disk obtained using the same, and a method for producing the aluminum secondary alloy. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a flow diagram showing a method for producing a secondary aluminum alloy according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The secondary aluminum alloy, the aluminum substrate for a magnetic disk, and the method for producing the secondary aluminum alloy according to the present invention will be described in detail below. In this specification, the aluminum secondary alloy and the aluminum substrate for magnetic disks may hereinafter be simply referred to as the "aluminum secondary alloy" and the "aluminum substrate", respectively. Furthermore, the method for producing the aluminum secondary alloy and the method for producing the aluminum substrate for magnetic disks may hereinafter be simply referred to as the "method for producing the aluminum secondary alloy" and the "method for producing the aluminum substrate", respectively. In this specification, Al-P based compounds and Mg-P based compounds are collectively referred to as P-containing compounds.

[0017] [Aluminum secondary alloy] The aluminum secondary alloy according to this embodiment is an aluminum secondary alloy containing aluminum scrap as at least a part of the raw material, and contains Mg, Fe, Zn, Ni and P, with the Mg being 3.0 mass% to 15 mass%, and the P being 0.1 mass ppm to 25 mass ppm.

[0018] The aluminum secondary alloy according to the present embodiment, by having the above-mentioned chemical composition, can be mixed at a high ratio as a raw material for a high-rigidity disk material. Therefore, it is possible to obtain a magnetic disk substrate with a high ratio of aluminum scrap, i.e., a high recyclability. This can reduce the CO2 emissions generated during the production of ingots, and can also reduce raw material costs by effectively utilizing Ni, which has been rising in price in recent years. Hereinafter, each component of the secondary aluminum alloy according to this embodiment will be described in detail.

[0019] The aluminum secondary alloy according to this embodiment contains aluminum scrap as at least a part of the raw material, that is, the aluminum secondary alloy refers to a recycled ingot containing aluminum scrap as at least a part of the raw material. Examples of aluminum waste include scraps generated during the manufacturing process of aluminum products and discarded, discarded aluminum products, scraps generated during the manufacturing process of aluminum substrates for magnetic disks, discarded disk substrates, and the like.

[0020] In this specification, the waste disk substrate refers to waste magnetic disk substrates that contain a high concentration of impurities derived from Ni-P plating, such as magnetic disk substrates that do not meet the required quality as a product due to plating defects or the like, or used magnetic disk substrates. Examples of aluminum alloys used for magnetic disk substrates include those based on JIS 5086 alloy and high-rigidity aluminum alloys containing transition metals such as Fe, Mn, Ni, etc. Waste disk substrates using these aluminum alloys can be used as the aluminum waste material.

[0021] The aluminum scrap may also include scraps generated during the manufacture of magnetic disks before being subjected to Ni-P plating (for example, scraps of slabs generated during the manufacture of slabs in the casting process, scraps generated by cutting the leading and trailing ends or both widthwise ends in the hot rolling and cold rolling processes, aluminum alloy sheets for magnetic disks that do not meet the required quality, scraps generated during the punching process of aluminum alloy sheets for magnetic disks, scraps generated during the cutting process of aluminum alloy blanks for magnetic disks, etc.).

[0022] In an embodiment of the present invention, the aluminum scrap is preferably aluminum scrap containing a large amount of Ni or P. Examples of aluminum scrap containing a large amount of Ni or P include waste disk substrates, piston materials, machine tool parts, etc. In an embodiment of the present invention, it is more preferable that the aluminum waste includes at least one selected from scraps generated during the manufacturing process of aluminum substrates for magnetic disks, scraps generated during the manufacturing of magnetic disks before being subjected to Ni-P plating, and waste disk substrates.

[0023] The raw material of the aluminum secondary alloy according to the present embodiment may contain raw materials other than the aluminum waste. For example, as described later in the section on the manufacturing method of the aluminum secondary alloy, a metal or intermediate alloy may be used for the aluminum used in the molten aluminum for immersing and dissolving the waste disk substrates, or for the magnesium added in the magnesium adding step. From the viewpoint of improving recyclability, the ratio of scrap aluminum in the raw material of the secondary aluminum alloy is preferably 70 mass % or more, and more preferably 80 mass % or more.

[0024] (P:0.1 mass ppm~25 mass ppm) In the aluminum secondary alloy according to the present embodiment, when a waste disk substrate is used as the aluminum waste material, P derived from the waste disk substrate is inevitably contained. If the P concentration exceeds 25 mass ppm, the compounding ratio when manufacturing an aluminum substrate for a magnetic disk is limited, and recyclability is poor. Therefore, the P content (P concentration) is set to 0.1 mass ppm to 25 mass ppm. From the viewpoint of improving the blending ratio, the P content is preferably 20 ppm by mass or less, and more preferably 15 ppm by mass or less, and from the viewpoint of reducing costs, the P content is preferably 0.5 ppm by mass or more.

[0025] (Mg: 3.0% by mass to 15% by mass) Mg is an essential element that is added in the manufacturing process of the aluminum secondary alloy according to this embodiment in order to reduce the P concentration. Mg reacts with P in the molten metal to generate Mg-P-based P-containing compounds, and therefore can reduce the P solubility in the molten metal. On the other hand, the higher the Mg concentration, the more the generation of Mg-P-based P-containing compounds is promoted, but there is an upper limit to this effect. In addition, if the Mg concentration becomes too high, the compounding ratio when manufacturing an aluminum substrate for a magnetic disk may be limited from the viewpoint of the Mg concentration, which is not efficient. Therefore, the Mg content (Mg concentration) is set to 3.0 mass% to 15 mass%. The Mg content is preferably 3.5% by mass or more, more preferably 4.0% by mass or more, and even more preferably 5.0% by mass or more from the viewpoint of reducing the solubility of P. Also, from the viewpoint of increasing the compounding ratio, the Mg content is preferably 12% by mass or less, and more preferably 10% by mass or less.

[0026] (Ni: 0.5% by mass to 10% by mass) The scrapped disk substrate contains Ni derived from Ni-P plating. In addition, the scrapped disk substrate with high rigidity contains Ni to ensure rigidity. Therefore, when the scrapped disk substrate is used as the scrapped aluminum material, the secondary aluminum alloy according to the present embodiment contains Ni derived from the scrapped aluminum material. The Ni concentration in the secondary aluminum alloy according to this embodiment may be 0.5 mass % to 10 mass %, or 1.0 mass % to 7.0 mass %.

[0027] (Fe:0.01 mass%~3.0 mass%) The aluminum scrap contains Fe derived from the base metal. In addition, in the high-rigidity scrap disk substrate, Fe is also contained to ensure the rigidity. Therefore, when the scrap disk substrate is used as the aluminum scrap, the aluminum secondary alloy according to the present embodiment contains Fe derived from the aluminum scrap. The Fe concentration in the secondary aluminum alloy according to this embodiment may be 0.01 mass % to 3.0 mass %, or 0.5 mass % to 1.5 mass %.

[0028] (Zn: more than 0 mass% to 1.5 mass%) The scrapped disk substrate contains Zn derived from the zincate treatment. It is also contained in the alloy as an essential element for ensuring performance. Therefore, when the scrapped disk substrate is used as the scrapped aluminum material, the secondary aluminum alloy according to this embodiment contains Zn derived from the scrapped aluminum material. The Zn concentration in the secondary aluminum alloy according to this embodiment may be greater than 0 mass % and up to 1.5 mass %, or may be 0.05 mass % to 0.5 mass %.

[0029] (Cr, Mn) The aluminum secondary alloy according to the present embodiment may further contain Cr and Mn. These elements are contained in the high-rigidity scrap disk substrate to ensure strength and rigidity. Therefore, when the high-rigidity scrap disk substrate is used as the scrap aluminum, the aluminum secondary alloy according to the present embodiment contains Cr and Mn derived from the scrap aluminum. The Cr concentration in the secondary aluminum alloy according to this embodiment may be 0.01 mass % to 5.0 mass %, or 0.05 mass % to 1.0 mass %. The Mn concentration may be 0.01% by mass to 5.0% by mass, or 0.1% by mass to 2.5% by mass.

[0030] (Cu) The aluminum secondary alloy according to the present embodiment may further contain Cu. The waste disk substrate of JIS 5086 alloy contains Cu as an essential element for ensuring performance. Therefore, when the waste disk substrate using JIS 5086 alloy is used as the aluminum waste, the aluminum secondary alloy according to the present embodiment contains Cu derived from the aluminum waste. The Cu concentration in the secondary aluminum alloy according to this embodiment may be 0.01 mass % to 2.5 mass %, or 0.05 mass % to 0.5 mass %.

[0031] (Si: 0.1% by mass or less) If Si-based compounds (simple Si, Al-Fe-Si-based compounds) are present on the surface of an aluminum substrate for magnetic disks, the zincate treatment will be poor at that portion, resulting in plating defects. Therefore, in order to use the aluminum secondary alloy according to this embodiment as a raw material for an aluminum substrate, the aluminum secondary alloy according to this embodiment further contains Si, and the Si concentration is preferably 0.1 mass% or less, more preferably 0.04 mass% or less, and even more preferably 0.01 mass% or less, in order to suppress the generation of Si-based compounds. Since only the front and back layers of the aluminum substrate are of concern, there are no particular restrictions on the amount of Si when used as the core material of the clad material.

[0032] (Be: 3 mass ppm~50 mass ppm) Be forms an oxide film on the surface of the molten aluminum alloy during production of the aluminum alloy, and has the effect of suppressing the formation of Mg oxide. However, even if the Be content exceeds 50 ppm by mass, the oxidation suppression effect is not improved. Therefore, the Be concentration in the secondary aluminum alloy according to this embodiment is preferably 3 ppm by mass to 50 ppm by mass. In order to fully obtain the above-mentioned effect of the addition of Be, the Be concentration is more preferably 5 ppm by mass or more, and more preferably 30 ppm by mass or less in order to fully obtain the oxidation suppression effect.

[0033] (Remainder) The aluminum secondary alloy according to the present embodiment may contain Al and other elements as impurities derived from the aluminum waste material. Specifically, the aluminum secondary alloy according to the present embodiment may contain Ti, Na, Pb, Ca, Zr, V, B, Sn, In, Cd, Bi, Ge, etc. as impurities. The concentration of these impurities in the aluminum secondary alloy according to the present embodiment is preferably 0.005 mass% or less for each element, and the total of these is preferably 0.015 mass% or less. Moreover, as impurities derived from the aluminum scrap contained in the secondary aluminum alloy according to this embodiment, the total content of Fe, Mn, Ni, Ti, Zr and V is preferably 6.0 mass % or less.

[0034] The aluminum secondary alloy according to the present embodiment may be liquid or solid. That is, the aluminum secondary alloy according to the present embodiment may be a regenerated lump having the above composition or may be a molten metal.

[0035] [Aluminum substrates for magnetic disks] The present invention also relates to an aluminum substrate for a magnetic disk, which uses the above-mentioned aluminum secondary alloy. The higher the content of the above-mentioned aluminum secondary alloy, the more excellent the recyclability of the aluminum substrate for magnetic disk according to this embodiment. From the viewpoint of enabling the blending of the above-mentioned aluminum secondary alloy and increasing the blending ratio, the aluminum substrate for magnetic disk according to this embodiment is preferably an aluminum substrate for magnetic disk with high rigidity to which transition metal elements such as Fe, Mn, Ni, etc. are actively added.

[0036] An example of an alloy composition for a high-rigidity aluminum substrate for a magnetic disk is the composition disclosed in Japanese Patent No. 7132289.

[0037] In the magnetic disk aluminum substrate according to this embodiment, the content of the above-mentioned aluminum secondary alloy can be at least about 12 mass% when the P concentration in the aluminum substrate is set to 3 mass ppm or less from the viewpoint of suppressing deterioration of mechanical properties, etc. That is, the content of the aluminum secondary alloy is preferably 12 mass% or more, more preferably 15 mass% or more, and even more preferably 20 mass% or more. The upper limit of the content of the above-mentioned aluminum secondary alloy is not limited as long as it does not deviate from the alloy composition in the desired magnetic disk aluminum substrate, and is, for example, 30 mass% or less.

[0038] [Method of manufacturing secondary aluminum alloys] The method for producing an aluminum secondary alloy according to an embodiment of the present invention includes the steps of melting raw materials of the aluminum secondary alloy according to an embodiment of the present invention to obtain a molten metal, adding magnesium to the molten metal, and removing a P-containing compound from the molten metal, in this order, and the Mg concentration in the molten metal in the step of adding magnesium to the molten metal is 3.0 mass% to 15 mass%. Fig. 1 is a flow diagram showing the method for producing an aluminum secondary alloy according to an embodiment of the present invention. Each step will be described below.

[0039] <Raw material melting process> In the method for producing a secondary aluminum alloy according to the embodiment of the present invention, the raw material of the secondary aluminum alloy is first melted to obtain a molten metal. The raw material of the secondary aluminum alloy includes aluminum scrap. The temperature at which the raw material is melted (melting temperature) is usually 700 to 850°C, preferably 720 to 800°C.

[0040] As described above, examples of aluminum waste include scraps generated during the manufacturing process of aluminum substrates for magnetic disks (for example, scraps after Ni-P plating generated when manufacturing magnetic disks), discarded aluminum products, waste disk substrates, scraps generated during the manufacturing of magnetic disks before Ni-P plating (for example, scraps of slabs generated when manufacturing slabs in the casting process, scraps generated by cutting the leading and trailing ends or both widthwise ends in the hot rolling and cold rolling processes, aluminum alloy plates for magnetic disks that do not meet the required quality, scraps generated during punching of aluminum alloy plates for magnetic disks, scraps generated during cutting of aluminum alloy blanks for magnetic disks, etc.).

[0041] In an embodiment of the present invention, it is more preferable that the aluminum waste includes at least one selected from scraps generated during the manufacturing process of aluminum substrates for magnetic disks, scraps generated during the manufacturing of magnetic disks before being subjected to Ni-P plating, and waste disk substrates. The raw materials of the secondary aluminum alloy may be used in any proportion within the range in which the secondary aluminum alloy composition according to the present embodiment described above can be obtained after the magnesium addition step and the P-containing compound removal step described below. From the viewpoint of improving recyclability, the proportion of the scrap aluminum in the raw materials of the secondary aluminum alloy is preferably 70 mass% or more, and more preferably 80 mass% or more, as described above.

[0042] The method for melting the waste disk substrates is not particularly limited, but from the viewpoint of suppressing oxidation of the substrates, it is effective to melt the waste disk substrates by immersing them in a separately prepared molten aluminum.

[0043] In the molten aluminum secondary alloy raw material containing the waste disk substrate, most of the P exists as Al-P based compounds, and several tens of ppm by mass are dissolved in the molten metal.

[0044] <Magnesium addition process> In the magnesium addition step, magnesium is added to the molten metal to a predetermined concentration. The magnesium may be in any form, such as ingot, intermediate alloy containing Mg, or scrap. Magnesium reacts with P in the molten metal to generate Mg-P-based P-containing compounds, which reduces the P solubility in the molten metal. If the Mg concentration in the molten metal is less than 3.0% by mass, Mg-P-based P-containing compounds are difficult to generate, and the P solubility reduction effect cannot be obtained, so the lower limit is 3.0% by mass or more, preferably 3.5% by mass or more, more preferably 4.0% by mass or more, and even more preferably 5.0% by mass or more. The higher the Mg concentration, the more the generation of Mg-P-based P-containing compounds is promoted, but there is an upper limit to this effect. In addition, if the Mg concentration becomes too high, the blending ratio of aluminum waste material in the aluminum substrate may be limited from the viewpoint of Mg concentration, which is not efficient. Therefore, the upper limit of the Mg concentration is 15% by mass or less, preferably 12% by mass or less, and more preferably 10% by mass or less.

[0045] In addition, the higher the Mg concentration in the molten metal, the more easily oxides are generated. In order to prevent oxidation, it is preferable to carry out all steps after the addition of magnesium in an inert atmosphere such as N2 or Ar. It is also preferable to add Be to the molten metal. Be has the effect of forming an oxide film on the surface of the secondary aluminum alloy melt and suppressing the formation of Mg oxide. Therefore, it is preferable to add Be so that the Be concentration in the molten metal becomes 5 ppm by mass to 50 ppm by mass, and more preferably 10 ppm by mass to 30 ppm by mass. In addition, it is also preferable to take measures such as scattering flux to suppress oxidation.

[0046] The treatment temperature is preferably carried out in the range of 700 to 850 °C which is a normal melting process. That is, in the method for producing an aluminum secondary alloy, the treatment temperature in the step of adding magnesium to the molten metal is preferably 700 to 850 °C. By setting it to 700 °C or higher, the treatment in the subsequent steps such as the removal step of P-containing compounds (for example, flux refining, etc.) becomes easier. Also, by setting it to 850 °C or lower, the decrease in refining efficiency due to the increase in the solubility of P in the molten metal can be suppressed. Furthermore, the melting cost can be reduced and the evaporation of Mg can also be suppressed.

[0047] The holding time of the molten metal after adding magnesium is preferably the time when the Mg concentration is homogenized and the reaction reaches equilibrium. For example, it is preferably 5 minutes or more, and more preferably 10 minutes or more. Since holding for a long time leads to an increase in melting cost, the upper limit is preferably set to 60 minutes or less, and more preferably 40 minutes or less.

[0048] <Removal step of P-containing compounds> The P component in the molten metal is considered to exist in three forms: Al-P-based compounds, Mg-P-based compounds, and dissolved P. Among these, since the P-containing compounds, that is, Al-P-based compounds and Mg-P-based compounds, exist in granular form, for the removal of P-containing compounds, for example, a general refining flux for aluminum molten metal can be used. Specifically, JDR1170 (manufactured by Pyrotech Co., Ltd.), A700 (manufactured by Foundtech Co., Ltd.), etc. can be mentioned. Also, a method of blowing chlorine gas and attaching it to liquid MgCl2 to make it float is also possible. Furthermore, it is also possible to filter with a refractory filter. These methods can be carried out alone or in combination. Here, the usage amount of the refining flux may be about 0.2% to 1% with respect to the amount of molten metal which is a general usage amount.

[0049] Furthermore, although the refining cost and treatment time increase, a dephosphorization flux may be used. By using a dephosphorization flux, the P concentration in the molten metal after adding magnesium can be further reduced. As the dephosphorization flux, for example, the dephosphorization flux described in JP-A-2020-7630 can be used.

[0050] <Regenerated agglomeration process or process of holding the molten metal> The molten metal after the removal of the P-containing compounds can be cast into a mold of an appropriate shape and used as a regenerated ingot. That is, when the aluminum secondary alloy according to the present embodiment is a regenerated ingot, a regenerated ingot forming step of casting the molten metal is included after the P-containing compound removing step. In addition, in order to eliminate the need to remelt the regenerated block when manufacturing an aluminum substrate for a magnetic disk, the molten metal after removal of the P-containing compounds may be transferred to a furnace capable of maintaining the molten metal temperature and used as is. That is, when the aluminum secondary alloy according to the present embodiment is a molten metal, a step of maintaining the molten metal as it is is included after the step of removing the P-containing compounds. In this case, the temperature at which the molten metal is maintained can be lowered depending on the Mg concentration, and for example, when the Mg concentration in the molten metal is 10 mass%, it can be 620°C.

[0051] [Method of manufacturing aluminum substrates for magnetic disks] The aluminum secondary alloy containing aluminum scrap as at least a part of the raw material obtained through the above-mentioned process is an aluminum secondary alloy with a reduced P concentration, and after being mixed with other raw materials, can be produced by a production method and equipment under general conditions for aluminum substrates for magnetic disks. For example, a highly recyclable aluminum alloy plate for magnetic disks can be manufactured by a manufacturing method including, in this order, a casting step of melting a raw material containing the above-mentioned aluminum secondary alloy, and casting the molten aluminum alloy adjusted to a predetermined chemical composition into an aluminum alloy ingot by a semi-continuous casting method or the like, a homogenization heat treatment step of surface-cutting the cast aluminum alloy ingot and subjecting it to homogenization heat treatment, a hot rolling step of hot-rolling the homogenization heat-treated aluminum alloy ingot to obtain a hot-rolled plate, and a cold rolling step of cold-rolling the hot-rolled plate. The obtained aluminum alloy plate for magnetic disks can be further subjected to a punching step of punching into an annular shape, and a correction annealing step of annealing the annular substrate obtained in the punching step while applying a load to flatten it, in this order, to manufacture a magnetic disk blank. Then, a magnetic disk substrate (aluminum substrate for magnetic disk) can be manufactured by carrying out a cutting process (end surface processing) for cutting the end surfaces of the magnetic disk blank and a grinding process (mirror finish) for grinding the surface (main surface) of the magnetic disk blank.

[0052] As described above, the amount of the aluminum secondary alloy with reduced P concentration in the aluminum substrate for magnetic disk is preferably 12% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more. There is no upper limit as long as it does not deviate from the desired alloy composition in the aluminum substrate for magnetic disk, and it is, for example, 30% by mass or less. EXAMPLES

[0053] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to these examples, and can be practiced with modifications within the scope of the invention, all of which are included in the technical scope of the present invention.

[0054] (Examples 1 to 4, Comparative Example 1) In order to carry out the test with an alloy composition simulating a waste disk substrate, aluminum ingot, Al-Ni intermediate alloy, and Cu-P alloy were mixed to Ni: 3.4 mass%, Mg: 0 mass%, P: 0.125 mass%, Cu: 0.71 mass%, Al: balance, and a total of about 5 kg of sample was used. Note that, although Fe and Zn are essential elements in the aluminum secondary alloy of the present invention, the composition does not contain Fe and Zn in this embodiment and comparative example because they do not affect the formation of Mg-P compounds.

[0055] The above sample was charged into a graphite crucible, and after melting at 750° C. was confirmed, the molten metal was sampled and used as the molten metal of Comparative Example 1. Next, magnesium bullion was added to the molten metal so that the content was 3.5 mass%, and the molten metal temperature was returned to 750°C and held for 10 minutes, after which 10 g of refining flux (JDR1170, manufactured by Pyrotech Japan) was added and thoroughly stirred. Ar gas was bubbled at 3 NL / h for 5 minutes to remove floating dross, and the molten metal was sampled and used as the molten metal of Example 1. Next, magnesium ingot was added to the molten metal so that the amount was 5.0 mass %, and treatment was carried out in the same manner as in Example 1. After that, sampling was carried out and the molten metal of Example 2 was obtained. Thereafter, the same operation was repeated except that magnesium ingot was added to the molten metal so as to be 10 mass % and 15 mass %, and sampling was carried out to obtain molten metals of Example 3 and Example 4, respectively.

[0056] The molten metal was cast after collection, and the resulting ingot was appropriately cut and milled, and the Ni concentration was analyzed using ICP optical emission spectroscopy (instrument name: ICP-OES 5110, manufactured by Agilent), the P concentration was analyzed using absorptiometry (instrument name: UV-2600, manufactured by Shimadzu Corporation), and the Mg, Cu, and Si concentrations were analyzed using a solid-state optical emission analyzer (global calibration curve, instrument name ARL4460, manufactured by Thermo Fisher Scientific). Regarding the effect of reducing the P concentration, those with P concentration analysis results of 25 ppm or less were evaluated as passing (◯), and those with P concentration over 25 ppm were evaluated as failing (×), and these are shown in Table 1. The results are shown in Table 1.

[0057] [Table 1]

[0058] From the above results, it was confirmed that when 3.5 mass% or more of Mg was added, the P concentration in the molten metal was 25 ppm or less, the effect of reducing the P concentration was obtained, and it can be incorporated at a high concentration as a recycled material for magnetic disk substrates. In the molten metal of Comparative Example 1, the added P was unevenly distributed as an Al-P compound, which is thought to have resulted in the analysis result being a significantly lower concentration compared to the amount added.

Claims

1. An aluminum secondary alloy containing aluminum scrap as at least a part of a raw material, Contains Mg, Fe, Zn, Ni and P; The Mg: 3.0% by mass to 15% by mass, The aluminum secondary alloy, wherein the P is 0.1 ppm by mass to 25 ppm by mass.

2. Further, the compound contains Si, The aluminum secondary alloy according to claim 1, wherein the Si content is 0.1 mass% or less.

3. 2. The aluminum secondary alloy of claim 1, further comprising Cr and Mn.

4. The aluminum secondary alloy according to claim 1, wherein the Ni content is 0.5% by mass to 10% by mass.

5. The aluminum secondary alloy according to claim 1, wherein the Fe content is 0.01% by mass to 3.0% by mass.

6. The aluminum secondary alloy according to claim 1, wherein the Zn content is more than 0 mass% to 1.5 mass%.

7. The aluminum secondary alloy according to claim 1, further comprising Be: 3 ppm by mass to 50 ppm by mass.

8. The aluminum waste material includes at least one selected from at least one selected from scraps generated during the manufacturing process of an aluminum substrate for a magnetic disk, scraps generated during the manufacture of a magnetic disk before being subjected to Ni-P plating, and scrap disk substrates. The aluminum secondary alloy according to claim 1.

9. The aluminum secondary alloy according to any one of claims 1 to 8, which is a reclaimed ingot.

10. The aluminum secondary alloy according to any one of claims 1 to 8, which is a molten metal.

11. An aluminum substrate for magnetic disks, which uses the aluminum secondary alloy according to any one of claims 1 to 8.

12. 12. The aluminum substrate for a magnetic disk according to claim 11, wherein the content of the aluminum secondary alloy is 12 mass % or more.

13. A method for producing an aluminum secondary alloy according to any one of claims 1 to 8, Melting the raw material of the aluminum secondary alloy to obtain a molten metal; adding magnesium to the molten metal; a step of removing P-containing compounds from the molten metal, The method for producing an aluminum secondary alloy, wherein in the step of adding magnesium to the molten metal, a Mg concentration in the molten metal is 3.0% by mass to 15% by mass.

14. The method for producing an aluminum secondary alloy according to claim 13, wherein the treatment temperature in the step of adding magnesium to the molten metal is 700 to 850°C.

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