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

Abstract

The invention provides an aluminum secondary alloy, an aluminum substrate for a magnetic disk, and a method for manufacturing the aluminum secondary alloy. The aluminum secondary alloy can obtain a magnetic disk substrate with high recyclability, the aluminum substrate for the magnetic disk obtained by using the aluminum secondary alloy, and the method for manufacturing the aluminum secondary alloy. An aluminum secondary alloy containing aluminum scrap in at least a part of a starting material, the aluminum secondary alloy containing Mg, Fe, Zn, Ni, and P, in which the content of Mg is 3.0 to 15 mass% and the content of P is 0.1 to 25 mass ppm.

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 Art

[0002] Aluminum is a metal material with excellent recyclability. Most aluminum products, such as aluminum cans and die-cast products, are remelted and recycled into new products after being discarded. However, discarded aluminum products have impurities attached to them, and the concentration of impurity elements gradually increases due to repeated recycling. Therefore, they are generally recycled in stages using products with looser composition standards.

[0003] The same is true for hard disk substrates. The surfaces of used substrates are treated with zinc or Ni-P. It is usually difficult to remove them individually, so it is assumed that they are also recycled in stages as in the above example.

[0004] In addition, as the use of aluminum products expands, new alloys that are not specified by the JIS standard are currently being developed. In disc materials, materials that actively add transition metal elements (Fe, Mn, Ni, Cr, etc.) to impart rigidity are also being developed (Patent Document 1). Because of its high impurity concentration, although it is expected that scrap can be used, if undesigned elements are mixed in due to scrap, it will have an adverse effect on quality. For example, in the JIS AC3A alloy, if a high concentration of P is contained in the molten raw material, the eutectic Si phase will be coarse, the iron-based compounds will be coarsened, and the mechanical properties will also be reduced (Non-Patent Document 1). Therefore, in order to maintain high quality, it is important to strictly manage the composition of the molten raw materials.

[0005] The mainstream aluminum substrate for magnetic disks is based on JIS5086 alloy, but since the surface of the waste disk substrate is plated with Ni-P, it contains a high concentration of P. If it is directly blended as a recycled material, P will cause the coarsening of transition metal compounds containing Fe and the reduction of mechanical properties, or there is a risk that compounds containing P will be suspended as inclusions. Therefore, there is a problem that the recycled waste disk substrate cannot be used directly as a raw material.

[0006] As a method for removing impurities from molten aluminum, for example, Patent Document 2 describes a method of removing P and / or Sb by adding Mg and blowing chlorine gas into molten aluminum containing P and / or Sb at a molten metal temperature of 650 to 850°C.

[0007] Patent document 3 describes an impurity removal method, which comprises the following steps: a step of adding Mg or Mg alloy to aluminum or aluminum alloy molten metal containing impurities; a step of maintaining the molten metal after the above-mentioned addition step in a temperature range of not less than 470°C and not more than 650°C; and a step of separating intermetallic compounds generated in the above-mentioned maintaining step from the above-mentioned molten metal.

[0008] Patent Document 4 describes a method of removing phosphorus from a molten metal of an aluminum alloy for casting using a dephosphorization flux.

[0009] Patent Document 5 describes a method of removing phosphorus by keeping a molten metal at 700 to 850° C. for 3 hours or more.

[0010] Prior art literature

[0011] Patent Literature

[0012] Patent Document 1: Japanese Patent No. 7132289

[0013] Patent Document 2: Japanese Patent No. 3524519

[0014] Patent Document 3: Japanese Patent Application Publication No. 2019-183265

[0015] Patent Document 4: Japanese Patent Application Publication No. 2020-007630

[0016] Patent Document 5: Japanese Patent Application Publication No. 2023-032363

[0017] Non-patent literature

[0018] Non-patent document 1: Oshiro et al., Light Metals, 47 (1997), 341. Summary of the invention

[0019] Problems to be solved by the invention

[0020] However, the method of Patent Document 2 has a problem that a large amount of chlorine is required to reduce the P concentration, resulting in a large environmental burden.

[0021] The method of Patent Document 3 is unclear in its applicability to P, and the Mg concentration in the molten metal after impurities are removed is high, so it may be difficult to apply it to aluminum substrates for magnetic disks.

[0022] The method of Patent Document 4 is effective for a molten metal that does not contain Mg, but requires a step of reducing the Na component after removing P, which may be inefficient.

[0023] The method of Patent Document 5 requires that the molten metal be kept at a high temperature for a long time, and there is a case where the energy required for the treatment is large and the productivity is low.

[0024] Therefore, in order to effectively utilize scrap disk substrates that have been plated with Ni—P as Al—Ni alloys, a technology for effectively removing P that has a high risk of causing a decrease in mechanical properties has been desired.

[0025] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an aluminum secondary alloy having a reduced P concentration in aluminum scraps derived from waste disk substrates and the like, an aluminum substrate for a magnetic disk, and a method for producing an aluminum secondary alloy.

[0026] Means of solving the problem

[0027] As a result of repeated and intensive research on this subject, the inventors found that P in aluminum scrap can be efficiently removed by adding a specific amount of magnesium to the molten raw material, thereby completing the present invention.

[0028] That is, the present invention relates to the following.

[0029] [1] An aluminum secondary alloy, wherein at least a portion of the raw materials contain aluminum scrap, wherein:

[0030] Contains Mg, Fe, Zn, Ni and P,

[0031] Mg: 3.0 mass % to 15 mass %,

[0032] The P is 0.1 mass ppm to 25 mass ppm.

[0033] [2] The aluminum secondary alloy according to [1], further comprising Si, wherein the Si content is 0.1 mass % or less.

[0034] [3] The aluminum secondary alloy according to [1], further comprising Cr and Mn.

[0035] [4] The aluminum secondary alloy according to [1], wherein the Ni content is 0.5 mass % to 10 mass %.

[0036] [5] The aluminum secondary alloy according to [1], wherein the Fe content is 0.01 mass % to 3.0 mass %.

[0037] [6] The aluminum secondary alloy according to [1], wherein the Zn content is higher than 0 mass % and not more than 1.5 mass %.

[0038] [7] The aluminum secondary alloy according to [1], further comprising 3 to 50 ppm by mass of Be.

[0039] [8] The aluminum secondary alloy according to [1], wherein the aluminum scrap includes at least one selected from scraps generated in the manufacturing process of aluminum substrates for magnetic disks, scraps generated in the manufacturing of magnetic disks before Ni—P plating, and waste disk substrates.

[0040] [9] The aluminum secondary alloy according to any one of [1] to [8], which is a recycled block.

[0041]

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

[0042]

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

[0043]

[12] The aluminum substrate for a magnetic disk according to

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

[0044]

[13] A method for producing an aluminum secondary alloy, which is the method for producing an aluminum secondary alloy described in any one of [1] to [8], comprising the following steps in order:

[0045] A step of melting the raw material of the aluminum secondary alloy to obtain molten metal;

[0046] A step of adding magnesium to the molten metal;

[0047] a step of removing P-containing compounds from the molten metal,

[0048] In the step of adding magnesium to the molten metal, the Mg concentration in the molten metal is 3.0 mass % to 15 mass %.

[0049]

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

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

[0050] Effects of the Invention

[0051] According to the present invention, it is possible to provide an aluminum secondary alloy capable of obtaining a magnetic disk substrate with high recyclability, an aluminum substrate for a magnetic disk obtained by using the aluminum secondary alloy, and a method for producing the aluminum secondary alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a flowchart showing a method for producing an aluminum secondary alloy according to one embodiment of the present invention. DETAILED DESCRIPTION

[0053] Hereinafter, the aluminum secondary alloy, the aluminum substrate for a magnetic disk, and the method for producing the aluminum secondary alloy according to the present invention will be described in detail.

[0054] In addition, in this specification, the aluminum secondary alloy and the aluminum substrate for magnetic disk are hereinafter referred to as "aluminum secondary alloy" and "aluminum substrate", respectively. In addition, the method for manufacturing the aluminum secondary alloy and the method for manufacturing the aluminum substrate for magnetic disk are hereinafter referred to as "the method for manufacturing the aluminum secondary alloy" and "the method for manufacturing the aluminum substrate", respectively.

[0055] In this specification, Al—P-based compounds and Mg—P-based compounds are collectively referred to as P-containing compounds.

[0056] [Aluminum secondary alloy]

[0057] The aluminum secondary alloy of the present embodiment contains aluminum scrap in at least a portion of the raw materials, 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.

[0058] The aluminum secondary alloy of this embodiment can be prepared at a high ratio as a raw material for a high-rigidity disk material by adopting the above-mentioned chemical composition. Therefore, a disk substrate with a high mixing ratio of aluminum scrap, i.e., high recyclability, can be obtained. This can reduce the CO generated during the manufacture of the ingot. 2 The emission volume can be reduced, and Ni, whose price has risen in recent years, can be effectively utilized, thereby reducing the raw material cost.

[0059] Hereinafter, each structure of the aluminum secondary alloy according to the present embodiment will be described in detail.

[0060] The aluminum secondary alloy of the present embodiment contains aluminum scrap in at least a portion of the raw material. That is, the aluminum secondary alloy refers to a regenerated mass containing aluminum scrap in at least a portion of the raw material.

[0061] Examples of the aluminum scraps include scraps discarded in the process of manufacturing aluminum products, discarded aluminum products, scraps generated in the process of manufacturing aluminum substrates for magnetic disks, and waste disk substrates.

[0062] In this specification, the waste disk substrate refers to waste disk substrates that do not meet the quality requirements as products due to plating defects and used disk substrates, which contain impurities derived from Ni—P plating at high concentrations.

[0063] Examples of aluminum alloys used for magnetic disk substrates include high-rigidity aluminum alloys based on JIS 5086 alloy and to which transition metals such as Fe, Mn, and Ni are added. As aluminum scraps, waste disk substrates using these aluminum alloys can be used.

[0064] Aluminum scraps include, in addition to this, scraps before Ni-P plating that are generated when manufacturing magnetic disks (for example, scraps of slabs generated when slabs are manufactured by a casting process, or scraps generated by cutting off the front and rear ends and both ends in the width direction during hot rolling and cold rolling processes, aluminum alloy plates for magnetic disks that do not meet the required quality, scraps generated when punching aluminum alloy plates for magnetic disks, scraps generated when cutting aluminum alloy blanks for magnetic disks, etc.).

[0065] In the embodiment of the present invention, the aluminum scrap is preferably aluminum scrap containing a large amount of Ni or P. Examples of the aluminum scrap containing a large amount of Ni or P include waste disk substrates, piston materials, and machine tool parts.

[0066] In the embodiment of the present invention, the aluminum scrap preferably includes at least one selected from the following: scraps generated in the manufacturing process of magnetic disk aluminum substrates; scraps generated in the manufacturing of magnetic disks before Ni—P plating; and waste disk substrates.

[0067] The raw materials of the aluminum secondary alloy of the present embodiment may include raw materials other than aluminum scrap. For example, in the item of the method for manufacturing the aluminum secondary alloy, as described later, ingots and intermediate alloys may be used among the aluminum used for impregnating the molten aluminum for melting the scrap disk substrate and the magnesium added in the magnesium adding step.

[0068] From the viewpoint of improving recyclability, the proportion of aluminum scrap in the raw material of the aluminum secondary alloy is preferably 70 mass % or more, more preferably 80 mass % or more.

[0069] (P: 0.1 mass ppm to 25 mass ppm)

[0070] In the aluminum secondary alloy of this embodiment, when waste disk substrates are used as aluminum scrap, P from the waste disk substrates is inevitably included. If the P concentration is higher than 25 mass ppm, the mixing ratio when manufacturing the aluminum substrate for magnetic disks is limited, and the recycling property is poor. Therefore, the P content (P concentration) is 0.1 mass ppm to 25 mass ppm.

[0071] From the viewpoint of improving the mixing ratio, the P content is preferably 20 mass ppm or less, more preferably 15 mass ppm or less. From the viewpoint of reducing costs, the P content is preferably 0.5 mass ppm or more.

[0072] (Mg: 3.0 mass% to 15 mass%)

[0073] Mg is an essential constituent element added in the manufacturing process of the aluminum secondary alloy of the present embodiment in order to reduce the P concentration. Mg reacts with P in the molten metal to generate Mg-P series P-containing compounds, thereby reducing the solubility of P in the molten metal. On the other hand, the higher the Mg concentration, the more it promotes the formation of Mg-P series P-containing compounds, but this effect has an upper limit. In addition, if the Mg concentration is too high, the mix ratio when manufacturing the aluminum substrate for the magnetic disk may be limited from the perspective of Mg concentration, which is inefficient. Therefore, the Mg content (Mg concentration) is 3.0 mass % to 15 mass %.

[0074] In addition, from the viewpoint of reducing the solubility of P, the Mg content is preferably 3.5 mass% or more, more preferably 4.0 mass% or more, and further preferably 5.0 mass% or more. In addition, from the viewpoint of improving the mixing ratio, it is preferably 12 mass% or less, and more preferably 10 mass% or less.

[0075] (Ni: 0.5 mass% to 10 mass%)

[0076] The scrap disk substrate contains Ni derived from Ni-P plating. In addition, the scrap disk substrate with high rigidity also contains Ni to ensure rigidity. Therefore, when the scrap disk substrate is used as aluminum scrap, the aluminum secondary alloy of this embodiment contains Ni derived from the aluminum scrap.

[0077] The Ni concentration in the aluminum secondary alloy of the present embodiment may be 0.5 mass % to 10 mass %, or 1.0 mass % to 7.0 mass %.

[0078] (Fe: 0.01 mass% to 3.0 mass%)

[0079] Aluminum scrap contains Fe derived from the ingot. In addition, Fe is also contained in a scrap disk substrate having high rigidity in order to ensure rigidity. Therefore, when the scrap disk substrate is used as aluminum scrap, Fe derived from the aluminum scrap is contained in the aluminum secondary alloy of the present embodiment.

[0080] The Fe concentration in the aluminum secondary alloy of the present embodiment may be 0.01 mass % to 3.0 mass %, or 0.5 mass % to 1.5 mass %.

[0081] (Zn: more than 0 mass% to 1.5 mass%)

[0082] The scrap disk substrate contains Zn derived from zincate treatment. In addition, it is contained in the alloy as an essential element for ensuring performance. Therefore, when the scrap disk substrate is used as aluminum scrap, the aluminum secondary alloy of this embodiment contains Zn derived from the aluminum scrap.

[0083] The Zn concentration in the aluminum secondary alloy of the present embodiment may be higher than 0 mass % and 1.5 mass % or less, or may be 0.05 mass % to 0.5 mass %.

[0084] (Cr, Mn)

[0085] The aluminum secondary alloy of this embodiment may also 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 aluminum scrap, the aluminum secondary alloy of this embodiment contains Cr and Mn derived from the aluminum scrap.

[0086] The aluminum secondary alloy of the present embodiment may contain 0.01% by mass to 5.0% by mass of Cr, or 0.05% by mass to 1.0% by mass of Cr.

[0087] The Mn concentration may be 0.01% by mass to 5.0% by mass, or 0.1% by mass to 2.5% by mass.

[0088] (Cu)

[0089] The aluminum secondary alloy of the present embodiment may further contain Cu. In the scrap disc substrate of JIS5086 alloy, Cu is contained as an essential element for ensuring performance. Therefore, when the scrap disc substrate using JIS5086 alloy is used as aluminum scrap, the aluminum secondary alloy of the present embodiment contains Cu derived from the aluminum scrap.

[0090] The aluminum secondary alloy of the present embodiment may contain Cu at a concentration of 0.01% by mass to 2.5% by mass, or may contain Cu at a concentration of 0.05% by mass to 0.5% by mass.

[0091] (Si: 0.1 mass % or less)

[0092] If Si-based compounds (monomer Si, Al-Fe-Si-based compounds) are present on the surface of the aluminum substrate for magnetic disks, this portion will be poorly treated with zincate, resulting in plating defects. Therefore, in order to use the aluminum secondary alloy of this embodiment as a raw material for an aluminum substrate, from the viewpoint of suppressing the generation of Si-based compounds, the aluminum secondary alloy of this embodiment further contains Si, and the Si concentration is preferably 0.1% by mass or less. It is more preferably 0.04% by mass or less, and even more preferably 0.01% by mass or less.

[0093] In addition, since only the front and back surfaces of the aluminum substrate pose a problem, there is no particular restriction on the amount of Si when it is used as a core material of a cladding material.

[0094] (Be: 3 mass ppm to 50 mass ppm)

[0095] Be forms an oxide film on the surface of the molten aluminum alloy during the manufacture of the aluminum alloy, which has the effect of inhibiting the formation of Mg oxides. On the other hand, even if the concentration is higher than 50 mass ppm, the oxidation inhibition effect will not be improved. Therefore, the Be concentration in the aluminum secondary alloy of this embodiment is preferably 3 mass ppm to 50 mass ppm.

[0096] In order to fully obtain the effect of Be addition, the Be concentration is more preferably 5 mass ppm or more, and more preferably 30 mass ppm or less as a range to fully obtain the oxidation inhibition effect.

[0097] (margin)

[0098] The aluminum secondary alloy of the present embodiment may contain Al and elements other than the above as impurities derived from aluminum scrap. Specifically, Ti, Na, Pb, Ca, Zr, V, B, Sn, In, Cd, Bi, Ge, etc. may be contained as impurities. The concentration of these impurities in the aluminum secondary alloy of the present embodiment is preferably 0.005 mass % or less for each element, and preferably 0.015 mass % or less in total.

[0099] In addition, as impurities derived from aluminum scrap contained in the aluminum secondary alloy of the present embodiment, the total amount of Fe, Mn, Ni, Ti, Zr, and V is preferably 6.0 mass % or less.

[0100] The aluminum secondary alloy of the present embodiment may be liquid or solid. That is, the aluminum secondary alloy of the present embodiment may be a regenerated mass having the above-mentioned composition or a molten metal.

[0101] [Aluminum substrate for magnetic disk]

[0102] The present invention also relates to an aluminum substrate for a magnetic disk using the above-mentioned aluminum secondary alloy.

[0103] The aluminum substrate for magnetic disks of this embodiment has a higher content of the above-mentioned aluminum secondary alloy, and its recyclability is more excellent. The above-mentioned aluminum secondary alloy can be combined to improve its mixing ratio. The aluminum substrate of this embodiment is preferably a high-rigidity aluminum substrate for magnetic disks to which transition metal elements such as Fe, Mn, and Ni are actively added.

[0104] As an alloy composition of the aluminum substrate for magnetic disks with high rigidity, the composition shown in Japanese Patent No. 7132289 can be mentioned, for example.

[0105] In the aluminum substrate for magnetic disk of the present embodiment, the content of the aluminum secondary alloy can be at least about 12 mass % when the P concentration in the aluminum substrate is 3 mass ppm or less from the viewpoint of suppressing the reduction of mechanical properties, for example. That is, the content of the aluminum secondary alloy is preferably 12 mass % or more, more preferably 15 mass % or more, and further preferably 20 mass % or more. In addition, the upper limit of the content of the aluminum secondary alloy is not limited within the range of the alloy composition of the desired aluminum substrate for magnetic disk, for example, 30 mass % or less.

[0106] [Method for producing secondary aluminum alloy]

[0107] The manufacturing method of the aluminum secondary alloy of the embodiment of the present invention comprises the following steps in order: a step of melting the raw materials of the aluminum secondary alloy of the embodiment of the present invention to obtain a molten metal; a step of adding magnesium to the molten metal; a step of removing P-containing compounds in the molten metal, wherein the Mg concentration in the molten metal in the step of adding magnesium to the molten metal is 3.0 mass % to 15 mass %. Figure 1 1 is a flowchart showing a method for producing an aluminum secondary alloy according to an embodiment of the present invention. Each step will be described below.

[0108] <Raw material melting process>

[0109] In the method for producing an aluminum secondary alloy according to an embodiment of the present invention, first, a raw material of the aluminum secondary alloy is melted to obtain a molten metal. The raw material of the aluminum secondary alloy contains aluminum scrap. The temperature (melting temperature) when the raw material is melted is usually 700 to 850°C, preferably 720 to 800°C.

[0110] As aluminum waste, as mentioned above, there can be listed scraps generated in the manufacturing process of aluminum substrates for magnetic disks (for example, scraps generated after Ni-P plating is implemented when manufacturing magnetic disks); discarded aluminum products, waste disk substrates, scraps generated before Ni-P plating is implemented when manufacturing magnetic disks (for example, scraps of slabs generated when slabs are manufactured by a casting process, and scraps generated by cutting off the front and rear ends and both ends in the width direction in the hot rolling and cold rolling processes, aluminum alloy plates for magnetic disks that do not meet the required quality, scraps generated when punching aluminum alloy plates for magnetic disks, scraps generated when cutting aluminum alloy blanks for magnetic disks, etc.), etc.

[0111] In the embodiment of the present invention, the aluminum scrap preferably includes at least one selected from the following: scraps generated in the manufacturing process of magnetic disk aluminum substrates; scraps generated in the manufacturing of magnetic disks before Ni—P plating; and waste disk substrates.

[0112] In addition, the raw materials of the aluminum secondary alloy can be used in any proportion within the range of obtaining the aluminum secondary alloy composition of the present embodiment after the magnesium addition step and the P-containing compound removal step described later. From the viewpoint of improving recyclability, the proportion of aluminum scrap in the raw materials of the aluminum secondary alloy is preferably 70% by mass or more, and more preferably 80% by mass or more, as described above.

[0113] The method of melting the scrap tray substrate is not particularly limited, but from the viewpoint of suppressing oxidation of the substrate, it is effective to melt the scrap tray substrate by immersing it in molten aluminum prepared separately.

[0114] In the molten metal of the aluminum secondary alloy raw material including the scrap disk substrate, most of P exists as Al—P compounds and is in a state of being dissolved in the molten metal at a concentration of several tens of mass ppm.

[0115] <Magnesium Addition Process>

[0116] In the step of adding magnesium, magnesium is added to the molten metal so as to achieve a predetermined concentration. Magnesium may be in the form of an ingot, an intermediate alloy containing Mg, scrap, or the like.

[0117] Magnesium reacts with P in the molten metal to generate P-containing compounds of the Mg-P system, so the solubility of P in the molten metal decreases. If the Mg concentration in the molten metal is less than 3.0 mass%, it is difficult to generate P-containing compounds of the Mg-P system, and the effect of reducing the solubility of P cannot be obtained. Therefore, the lower limit is 3.0 mass% or more, preferably 3.5 mass% or more, more preferably 4.0 mass% or more, and further preferably 5.0 mass% or more. The higher the Mg concentration, the more it promotes the generation of P-containing compounds of the Mg-P system, but there is an upper limit to its effect. In addition, if the Mg concentration is too high, the proportion of aluminum scrap in the aluminum substrate may be limited based on the viewpoint of Mg concentration, thereby losing efficiency. Therefore, the upper limit of the Mg concentration is 15 mass% or less, preferably 12 mass% or less, and more preferably 10 mass% or less.

[0118] In addition, the higher the Mg concentration in the molten metal, the easier it is to generate oxides. In order to inhibit oxidation, it is preferred that all processes after magnesium addition be carried out under N 2 , Ar or other inert atmosphere.

[0119] In addition, Be is also preferably added to the molten metal. Be forms an oxide film on the surface of the molten aluminum secondary alloy, which has the effect of inhibiting the formation of Mg oxides. Therefore, it is preferred to add Be in a manner such that the concentration of Be in the molten metal is 5 to 50 mass ppm, and more preferably 10 to 30 mass ppm.

[0120] In order to suppress oxidation, it is also preferable to take measures such as sprinkling flux.

[0121] The treatment temperature can be implemented in the range of 700 to 850°C in the usual melting process. That is, in the method for manufacturing aluminum secondary alloys, the treatment temperature of the process of adding magnesium to the molten metal is preferably 700 to 850°C. By being above 700°C, the treatment of the next process such as the removal process of P-containing compounds (for example, flux refining, etc.) can be easily performed. In addition, by being below 850°C, the reduction in refining efficiency caused by the increase in the solubility of P in the molten metal can be suppressed. In addition, the melting cost can be suppressed, and the evaporation of Mg can also be suppressed.

[0122] The holding time of the molten metal after magnesium addition can be the time for the Mg concentration to be uniform and the reaction to reach equilibrium, for example, preferably more than 5 minutes, more preferably more than 10 minutes. Long-term holding will increase the melting cost, so the upper limit can be less than 60 minutes, preferably less than 40 minutes.

[0123] <P-containing compound removal process>

[0124] The P component in the molten metal is considered to exist in three forms: Al-P compounds, Mg-P compounds, and dissolved P. Among them, the P-containing compounds, namely the Al-P compounds and the Mg-P compounds, exist in granular form. Therefore, in the removal of the P-containing compounds, for example, a refining flux for molten aluminum can be used. Specifically, JDR1170 (manufactured by Pyrotech) and A700 (manufactured by Fountec) can be mentioned. In addition, chlorine gas can be blown in to make it adhere to and float on the liquid MgCl 2 The above method. In addition, filtering can also be performed using a filter made of refractory materials. These methods can be implemented alone or in combination. Here, the amount of refining flux used relative to the amount of molten metal as the usual amount can be about 0.2% to 1%.

[0125] In addition, although the refining cost and processing time increase, a dephosphorization flux may be used. By using a dephosphorization flux, the P concentration in the molten metal after magnesium addition can be further reduced. As a dephosphorization flux, for example, a dephosphorization flux described in Japanese Patent Application Laid-Open No. 2020-7630 can be used.

[0126] <Regeneration agglomeration process or process of maintaining the molten metal state>

[0127] The molten metal after the removal of the P-containing compounds can be cast in a mold of an appropriate shape and used as a regenerated mass. That is, when the aluminum secondary alloy of the present embodiment is a regenerated mass, it includes a regenerated massing step of casting the molten metal after the P-containing compound removal step.

[0128] In addition, when manufacturing an aluminum substrate for a magnetic disk, as a method that does not require a process of remelting the regenerated block, the molten metal after the removal of the P-containing compound can be moved to a furnace that can maintain the temperature of the molten metal and used in this state. That is, when the aluminum secondary alloy of this embodiment is a molten metal, after the process of removing the P-containing compound, a process of maintaining it in the state of molten metal is included. At this time, the holding temperature of the molten metal can be lowered according to the Mg concentration, for example, when the Mg concentration in the molten metal is 10 mass%, it can be 620°C.

[0129] [Method for manufacturing aluminum substrate for magnetic disk]

[0130] The aluminum secondary alloy containing aluminum scrap in at least a portion of the raw materials obtained through the above steps is an aluminum secondary alloy with a reduced P concentration. After the aluminum secondary alloy is mixed with other raw materials, an aluminum substrate for a magnetic disk can be manufactured using a manufacturing method and equipment under normal conditions.

[0131] For example, an aluminum alloy plate for magnetic disks with high recyclability can be manufactured by a manufacturing method that includes the following steps in sequence: a casting step, in which a raw material containing the aluminum secondary alloy is melted, and the molten metal of the aluminum alloy adjusted to a specified chemical composition is cast into an aluminum alloy ingot by a semi-continuous casting method or the like; a homogenization heat treatment step, in which the surface of the cast aluminum alloy ingot is cut and homogenized; a hot rolling step, in which the aluminum alloy ingot subjected to the homogenization heat treatment is hot-rolled to obtain a hot-rolled plate; and a cold rolling step, in which the hot-rolled plate is cold-rolled. The obtained aluminum alloy plate for magnetic disks can be further subjected to the following steps in sequence to manufacture a blank for magnetic disks: a punching step for punching into a circular ring shape; and a leveling annealing step, in which the circular ring-shaped substrate obtained in the punching step is subjected to leveling annealing, for example, by annealing while applying a load to flatten it. Then, by performing a cutting process (end surface processing) of cutting the end surface of the disk blank and a grinding process (mirror surface processing) of grinding the surface (main surface) of the disk blank, a disk substrate (aluminum substrate for disk) can be manufactured.

[0132] As mentioned above, the amount of aluminum secondary alloy in which the above-mentioned P concentration in the aluminum substrate for magnetic disk is reduced is preferably more than 12 mass %, more preferably more than 15 mass %, and further preferably more than 20 mass %. As the upper limit, there is no restriction within the range of the alloy composition of the aluminum substrate for magnetic disk that does not deviate from the desired, for example, less than 30 mass %.

[0133] Example

[0134] The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples and may be modified and implemented within the scope consistent with the gist thereof, and all of these are included in the technical scope of the present invention.

[0135] (Examples 1 to 4, Comparative Example 1)

[0136] In order to test the alloy composition simulating the waste disk substrate, aluminum ingot, Al-Ni intermediate alloy, Cu-P alloy were mixed in such a way that 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 the sample was used. In addition, although Fe and Zn are essential in the aluminum secondary alloy of the present invention, since they do not affect the formation of Mg-P compounds, the composition without Fe and Zn was adopted in the present embodiment and the comparative example.

[0137] The above sample was filled in a graphite crucible, and after confirming melting at 750° C., the molten metal was collected and used as the molten metal of Comparative Example 1.

[0138] Next, magnesium ingots were added to the molten metal in an amount of 3.5 mass %, and after the molten metal temperature was lowered back to 750°C and kept for 10 minutes, 10 g of refining flux (JDR1170, manufactured by Pyrotech Japan) was added and stirred thoroughly. After Ar gas was bubbled at 3 NL / h for 5 minutes to remove the floating dross, the molten metal was sampled as the molten metal of Example 1.

[0139] Next, the magnesium ingot was added to the molten metal so as to account for 5.0 mass %, and the molten metal was sampled as the molten metal of Example 2 after treatment was performed in the same manner as in Example 1.

[0140] Thereafter, the same operation was repeated except that the magnesium ingot was added to the molten metal so as to account for 10 mass % and 15 mass %, and sampling was performed to obtain molten metals of Example 3 and Example 4, respectively.

[0141] The molten metal collected after casting was cut and cut into ingots as appropriate, and the following analyses were performed: Ni concentration was analyzed by ICP emission spectrometry (device name: ICP-OES 5110, manufactured by Agilent), P concentration was analyzed by absorptiometry (device name: UV-2600, manufactured by Shimadzu Corporation), and Mg, Cu, and Si concentrations were analyzed by solid luminescence analysis device (global calibration curve, device name ARL4460, manufactured by Thermo Fisher Scientific). Regarding the effect of reducing P concentration, the analysis results of P concentration below 25 ppm were evaluated as qualified (0), and those above 25 ppm were evaluated as unqualified (×), and are described in Table 1.

[0142] The results are shown in Table 1.

[0143]

Table 1

[0144] Table 1

[0145]

[0146] The above results confirm that when 3.5 mass % or more of Mg is added, the P concentration in the molten metal is below 25 ppm, and the P concentration can be reduced, and a high proportion of recycled materials for magnetic disk substrates can be mixed. In the molten metal of Comparative Example 1, since the added P is unevenly distributed as an Al-P compound, it is considered to be a significantly lower concentration than the added amount.

Claims

1. An aluminum secondary alloy, comprising aluminum scrap in at least a portion of the raw materials, wherein: Contains Mg, Fe, Zn, Ni and P, Mg: 3.0 mass % to 15 mass %, The P is 0.1 mass ppm to 25 mass ppm.

2. The aluminum secondary alloy according to claim 1, wherein: It also contains Si, The Si content is 0.1 mass % or less.

3. The aluminum secondary alloy according to claim 1, wherein: It also contains Cr and Mn.

4. The aluminum secondary alloy according to claim 1, wherein: The Ni: 0.5 mass % to 10 mass %.

5. The aluminum secondary alloy according to claim 1, wherein: The Fe: 0.01 mass % to 3.0 mass %.

6. The aluminum secondary alloy according to claim 1, wherein: The Zn content is higher than 0 mass % and less than 1.5 mass %.

7. The aluminum secondary alloy according to claim 1, wherein: It also contains Be: 3 to 50 mass ppm.

8. The aluminum secondary alloy according to claim 1, wherein: The aluminum scrap includes at least one selected from the following: scraps generated in the manufacturing process of aluminum substrates for magnetic disks; scraps generated in the manufacturing of magnetic disks before Ni—P plating; and waste disk substrates.

9. The aluminum secondary alloy according to any one of claims 1 to 8, wherein The aluminum secondary alloy is a recycled block.

10. The aluminum secondary alloy according to any one of claims 1 to 8, wherein The aluminum secondary alloy is a molten metal. 11 . An aluminum substrate for a magnetic disk, obtained by using the aluminum secondary alloy according to claim 1 .

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, the method for producing an aluminum secondary alloy according to any one of claims 1 to 8, wherein: The following steps are included in order: A step of melting the raw material of the aluminum secondary alloy to obtain molten metal; A step of adding magnesium to the molten metal; The process of removing P-containing compounds from the molten metal, In the step of adding magnesium to the molten metal, the Mg concentration in the molten metal is 3.0 mass % to 15 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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