JP2024059016A - Aluminum alloy plates for magnetic disks, aluminum alloy blanks for magnetic disks, and aluminum alloy substrates for magnetic disks - Google Patents

Abstract

[Problem] To provide an aluminum alloy sheet for magnetic disks that has excellent plating properties and can suppress deformation due to thermal strain during sputtering of a magnetic film. [Solution] The aluminum alloy sheet for magnetic disks contains Mg: 0.1% by mass to 7.0% by mass, Ni: 1.0% by mass to 5.0% by mass, Fe: 0.3% by mass or less, Mn: 0.3% by mass or less, Si: 0.10% by mass or less, with the balance being Al and impurities. In addition, the linear expansion coefficient is 26.0 x 10-6 (1/°C) or less, and the number density of intermetallic compounds having a maximum length of 0.33 μm or more on the surface of the aluminum alloy sheet is 5 x 104 (pieces/mm2) or less. [Selected Figure] None

Description

The present invention relates to an aluminum alloy plate for magnetic disks, an aluminum alloy blank for magnetic disks, and an aluminum alloy substrate for magnetic disks.

Magnetic disks used as recording media for computers and the like are manufactured by forming a magnetic film on a non-magnetic substrate. Specifically, the manufacturing method for magnetic disks is as follows: first, an aluminum alloy is cast, the rolled surface is milled as necessary, and then the aluminum alloy plate is formed by soaking and rolling, after which it is punched into an annular (donut-shaped) shape and then correctively annealed to produce a blank. Next, the inner and outer peripheral end faces of the blank are cut, and a grinding process is performed to grind the front and back surfaces of the blank to remove the oxide film and reduce the surface roughness of the substrate before plating, thereby obtaining a substrate. Then, electroless Ni-P plating is applied to the substrate. However, since plating defects occur in this Ni-P plating film, the surface of the Ni-P plating film is polished to remove the plating defects and to smooth the Ni-P plating film. Then, a magnetic film is formed on the Ni-P plating film by sputtering, and a magnetic disk is manufactured from the aluminum alloy substrate.

Recently, with the digitalization of information and the spread of the Internet, large amounts of digital data are being handled, and there is a demand for larger capacity hard disk drives (HDDs), especially in data centers. In order to achieve larger capacity HDDs, efforts are being made to make magnetic disks thinner, with the aim of increasing the number of magnetic disks that can be installed per HDD.

On the other hand, making the magnetic disk thinner creates the problem that the probability of minute vibrations occurring increases when the magnetic disk is rotated, especially as the rotation speed increases. One method for suppressing the occurrence of these vibrations is, for example, to improve the rigidity of the substrate.

For example, Patent Document 1 proposes an aluminum alloy blank for magnetic disks and an aluminum alloy substrate for magnetic disks that are excellent in rigidity and in the smoothness of the electroless Ni-P plating film formed on the surface. The aluminum alloy blank for magnetic disks described in Patent Document 1 contains 3.00 mass% or less of Mg and 1.00 mass% or less of Si, and contains at least one of Fe, Mn, and Ni, with the respective contents and total contents being specified, and contains at least one of Cr, Ti, and Zr, with the respective contents and total contents being specified. In addition, the area ratio of intermetallic compounds occupying the surface is 5 to 40%, and the total area ratio of simple Si and Mg-Si intermetallic compounds is 1% or less.

Patent Document 2 proposes an aluminum alloy plate for magnetic disks that has good rigidity while suppressing deterioration of grindability caused by improving rigidity. The aluminum alloy plate for magnetic disks described in Patent Document 2 is specified to have Mg: 0.1 to 7.0 mass%, at least one of Fe, Mn, and Ni in total: 0.3 to 2.5 mass%, and Ni: 1.3 mass% or less. In addition, the number density of intermetallic compounds having a maximum diameter of more than 10 μm on the surface is 60 pieces/ ^mm2 or less, and the number density of intermetallic compounds having a maximum diameter of 3 to 10 μm is 600 pieces/ ^mm2 or more.

Furthermore, Patent Document 3 discloses a magnetic disk substrate that can suppress the generation of particles caused by external impact even if the substrate thickness is thin. The diameter and thickness of the substrate are specified for the magnetic disk substrate described in Patent Document 3, and the substrate can be, for example, a glass substrate made of amorphous glass with a Young's modulus E of 90 GPa or more. It is also described that by specifying the linear expansion coefficient to a specific value or less, thermal expansion can be suppressed, and when the substrate is fixed and gripped, thermal distortion of the substrate around the gripped portion can be suppressed.

Patent No. 6684139 JP 2021-93234 A JP 2022-10156 A

However, the aluminum alloy blank for magnetic disks described in Patent Document 1 has Fe and Mn added to improve Young's modulus, but the addition of Fe and Mn causes the compounds to coarsen, which causes deterioration of plating properties. Patent Document 2 also describes an aluminum alloy sheet for magnetic disks that can achieve both grindability and Young's modulus by specifying the compound number density, but does not consider reducing distortion due to heat. Furthermore, Patent Document 3 specifies the linear expansion coefficient for a glass substrate to suppress thermal distortion, but does not establish the requirements for suppressing thermal distortion for aluminum alloy sheets, etc.

In particular, with the recent demand for thinner films, there is an increased demand for technology to prevent deformation caused by thermal distortion that occurs during sputtering of the magnetic film.

The present invention was made in consideration of these problems, and aims to provide an aluminum alloy plate for magnetic disks, an aluminum alloy blank for magnetic disks, and an aluminum alloy substrate for magnetic disks that have excellent plating properties and can suppress deformation due to thermal distortion during sputtering of the magnetic film.

The above object is achieved by the aluminum alloy plate for magnetic disks according to the present invention (1) below.

(1) Mg: 0.1% by mass or more and 7.0% by mass or less, and Ni: 1.0% by mass or more and 5.0% by mass or less,
Fe: 0.3 mass% or less,
Mn: 0.3 mass% or less,
Si: 0.10 mass% or less;
An aluminum alloy plate for magnetic disks, the balance of which is Al and impurities,
A linear expansion coefficient is 26.0×10 ⁻⁶ (1/° C.) or less,
An aluminum alloy sheet for magnetic disks, characterized in that the number density of intermetallic compounds having a maximum length of 0.33 μm or more on the surface of the aluminum alloy sheet is 5×10 ⁴ (pieces/mm ² ) or less.

The aluminum alloy plate for magnetic disks of the present invention preferably meets the following (2) to (5).

(2) The aluminum alloy plate for magnetic disks described in (1) further contains Be: 3 ppm by mass or more and 100 ppm by mass or less.

(3) The aluminum alloy plate for magnetic disks according to (1) or (2), further comprising Cr: 0.01% by mass or more and 1.0% by mass or less.

(4) An aluminum alloy plate for magnetic disks according to any one of (1) to (3), further comprising at least one of Cu: 0.5% by mass or less and Zn: 0.5% by mass or less.

(5) An aluminum alloy plate for magnetic disks according to any one of (1) to (4), characterized in that the Young's modulus is 70 GPa or more.

The above object is also achieved by the aluminum alloy blank for magnetic disks according to the present invention (6) below.

(6) An aluminum alloy blank for magnetic disks, characterized in that it is made of an aluminum alloy plate for magnetic disks described in any one of (1) to (5).

The above object is also achieved by the aluminum alloy substrate for magnetic disks according to the present invention (7) below.

(7) An aluminum alloy substrate for magnetic disks, characterized by being made of the aluminum alloy blank for magnetic disks described in (6).

When the aluminum alloy plate for magnetic disks according to the present invention is used as a base plate, it is possible to obtain an aluminum alloy blank for magnetic disks that has excellent plating properties, and an aluminum alloy substrate for magnetic disks that is suppressed from deforming due to thermal distortion during sputtering of the magnetic film.

In addition, the aluminum alloy blank for magnetic disks according to the present invention can provide excellent plating properties, and when this blank is used as a material, an aluminum alloy substrate for magnetic disks can be obtained in which deformation due to thermal distortion during sputtering of the magnetic film is suppressed.

Furthermore, the aluminum alloy substrate for magnetic disks according to the present invention is formed from an aluminum alloy blank with excellent plating properties, which improves the characteristics of the magnetic disk and allows for the production of a magnetic disk with reduced deformation.

The chemical compositions of the aluminum alloy plate for magnetic disks, the aluminum alloy blank for magnetic disks, and the aluminum alloy substrate for magnetic disks according to the embodiments of the present invention, as well as the reasons for the numerical limitations of their specific physical properties, will be described in detail below.
In this specification, the aluminum alloy plate for magnetic disks, the aluminum alloy blank for magnetic disks, and the aluminum alloy substrate for magnetic disks may be simply referred to as the "aluminum alloy plate", the "blank", and the "substrate", respectively.

[Aluminum alloy plate for magnetic disks]
The aluminum alloy plate for magnetic disk according to the present embodiment is a material plate for manufacturing an aluminum alloy blank for magnetic disk. First, the composition of the aluminum alloy plate and the reasons for the numerical limitations will be described. The alloy compositions of the blank and substrate described later are the same as the composition of the alloy plate.

(Mg: 0.1% by mass or more and 7.0% by mass or less)
Mg is an essential element in the aluminum alloy plate for magnetic disk according to the present embodiment, and is contained in the aluminum alloy plate to obtain good impact resistance. If the Mg content in the aluminum alloy plate is less than 0.1% by mass, the above effect cannot be obtained. Therefore, the Mg content is set to 0.1% by mass or more, preferably 1.0% by mass or more, more preferably 1.3% by mass or more, even more preferably 1.7% by mass or more, and particularly preferably 2.0% by mass or more.
On the other hand, if the Mg content in the aluminum alloy plate exceeds 7.0 mass%, the rigidity decreases. Therefore, the Mg content is set to 7.0 mass% or less, preferably 6.5 mass% or less, more preferably 6.0 mass% or less, even more preferably 5.5 mass% or less, and particularly preferably 4.0 mass% or less.

(Ni: 1.0 mass% or more and 5.0 mass% or less)
Ni is an essential element in the aluminum alloy plate for magnetic disk according to this embodiment, and is contained in the aluminum alloy plate to obtain good rigidity and linear expansion coefficient. If the Ni content in the aluminum alloy plate is less than 1.0 mass%, the above effect cannot be obtained. Therefore, the Ni content is 1.0 mass% or more, preferably 1.4 mass% or more, more preferably 1.6 mass% or more, even more preferably 1.8 mass% or more, and particularly preferably 2.0 mass% or more.
On the other hand, if the Ni content in the aluminum alloy sheet exceeds 5.0 mass%, the number density of the intermetallic compounds increases due to coarsening of the intermetallic compounds, and plating properties may be deteriorated. Therefore, the Ni content is set to 5.0 mass% or less, preferably 4.7 mass% or less, more preferably 4.4 mass% or less, and even more preferably 4.1 mass% or less. Moreover, the Ni content is more preferably 3.8 mass% or less, and particularly preferably 3.5 mass% or less.

(Fe: 0.3 mass% or less)
Fe is an element that is mixed in as an impurity from the base metal in the aluminum alloy plate for magnetic disk according to this embodiment. If the Fe content in the aluminum alloy plate exceeds 0.3 mass%, the number density of the intermetallic compounds increases due to the coarsening of the intermetallic compounds, and plating properties may be deteriorated. Therefore, the Fe content is set to 0.3 mass% or less, preferably 0.25 mass% or less, more preferably 0.20 mass% or less, and even more preferably 0.15 mass% or less.

(Mn: 0.3 mass% or less)
Mn is an element that may be mixed as an impurity from the base metal in the aluminum alloy plate for magnetic disk according to this embodiment. If the Mn content in the aluminum alloy plate exceeds 0.3 mass%, the number density of the intermetallic compounds increases due to coarsening of the intermetallic compounds, and plating properties may be reduced. Therefore, the Mn content is set to 0.3 mass% or less, preferably 0.25 mass% or less, more preferably 0.20 mass% or less, and even more preferably 0.15 mass% or less. In addition, the Mn content is more preferably set to 0.10 mass% or less, even more preferably 0.05 mass% or less, and particularly preferably 0.01 mass% or less.

(Si: 0.10 mass% or less)
In the aluminum alloy plate for magnetic disk according to the present embodiment, Si is an element mixed as an impurity from the base metal, and may be present in the aluminum alloy plate in the form of simple Si or may form an Al-Fe-Si intermetallic compound. If the Si content in the aluminum alloy plate exceeds 0.10% by mass, the plating smoothness may be reduced due to simple Si. Therefore, from the viewpoint of suppressing the generation of simple Si, etc., it is preferable to reduce the Si content in the aluminum alloy plate, and it may be 0% by mass, that is, it may not be contained. Therefore, the Si content is 0.10% by mass or less, preferably 0.05% by mass or less, more preferably 0.03% by mass or less, even more preferably 0.02% by mass or less, and particularly preferably 0.01% by mass or less.
However, in order to reduce the Si content, it is necessary to use high-purity raw materials such as Al ingots and intermediate alloy ingots, which results in high raw material costs. Therefore, the Si content may be 0.004 mass% or more.

(Be: 3 ppm by mass or more and 100 ppm by mass or less)
Be is an element that has the effect of forming an oxide film during casting and suppressing the formation of Mg oxide. Be also has the effect of improving the hot rolling property and formability of the aluminum alloy sheet, and further has the effect of weakening the adhesion between blanks by suppressing oxidation during corrective annealing, and suppressing the deterioration of flatness due to external force during subsequent peeling. Therefore, when Be is contained in the aluminum alloy sheet, the flatness of the substrate or magnetic disk can be improved.

In the aluminum alloy plate for magnetic disks according to this embodiment, Be is not an essential component, but when the Be content in the aluminum alloy plate is 3 ppm by mass or more, the above-mentioned effects of Be can be sufficiently obtained. Therefore, when Be is contained in the aluminum alloy plate, the Be content is preferably 3 ppm by mass or more, and more preferably 4 ppm by mass or more. Furthermore, when the Be content is 100 ppm by mass or less, it is possible to prevent the compounds containing Be from becoming coarse, prevent the occurrence of edge cracks, and suppress the deterioration of rolling properties. Therefore, the Be content is preferably 100 ppm by mass or less, and from the viewpoint of suppressing the coarsening of the compounds containing Be, it is more preferable to set it to 20 ppm by mass or less, and even more preferable to set it to 10 ppm by mass or less.

(Cr: 0.01% by mass or more and 1.0% by mass or less)
Cr is an element that has the effect of refining crystal grains, has the effect of refining primary crystals and distributing intermetallic compounds uniformly, and is an element that contributes to improving strength and yield strength. In the aluminum alloy plate for magnetic disks according to this embodiment, Cr is not an essential component, but if the Cr content in the aluminum alloy plate is 0.01 mass% or more, the above-mentioned effect of Cr can be sufficiently obtained. Therefore, when Cr is contained in the aluminum alloy plate, the Cr content is preferably 0.01 mass% or more, more preferably 0.05 mass%, even more preferably 0.1 mass% or more, and particularly preferably 0.15 mass% or more.
Furthermore, if the Cr content is 1.0 mass% or less, the deterioration of plating smoothness can be prevented. Therefore, the Cr content is preferably 1.0 mass% or less, more preferably 0.8 mass% or less, and even more preferably 0.5 mass% or less.

(Cu: 0.5 mass% or less, Zn: 0.5 mass% or less)
Cu and Zn are elements that broaden the solid-liquid coexistence region on the phase diagram and contribute to reducing the frequency of molten metal leakage during casting. Cu and Zn are also components that have the effect of uniformly precipitating zinc in zincate treatment, and also contribute to improving plating smoothness. In the aluminum alloy plate for magnetic disks according to this embodiment, Cu and Zn are not essential components and may be 0 mass%, but it is preferable that at least one of Cu and Zn is contained in the aluminum alloy plate in the following range.

That is, when the Cu content is 0.005% by mass or more, the above-mentioned effects of Cu can be sufficiently obtained. Therefore, when Cu is contained in the aluminum alloy sheet, the Cu content is preferably 0.005% by mass or more, and more preferably 0.01% by mass or more. On the other hand, when the Cu content is 0.5% by mass or less, it is possible to suppress the decrease in plating smoothness and also to suppress the decrease in smoothness of the electroless Ni-P plating film formed on the surface. Therefore, the Cu content is preferably 0.5% by mass or less, more preferably 0.1% by mass or less, and even more preferably 0.05% by mass or less.

In addition, when the Zn content is 0.1 mass% or more, the above effects of Zn can be sufficiently obtained. Therefore, when Zn is contained in the aluminum alloy sheet, the Zn content is preferably 0.1 mass% or more, and more preferably 0.2 mass% or more. On the other hand, when the Zn content is 0.5 mass% or less, as in the case of Cu, it is possible to suppress the decrease in plating smoothness and also to suppress the decrease in smoothness of the electroless Ni-P plating film formed on the surface. Therefore, the Zn content is preferably 0.5 mass% or less, more preferably 0.4 mass% or less, and even more preferably 0.35 mass% or less.

(balance: Al and impurities)
The remainder of the aluminum alloy plate for magnetic disk according to this embodiment is composed of Al and impurities. That is, the aluminum alloy plate for magnetic disk according to this embodiment may contain elements other than the above as impurities depending on the selection of the melting raw material during the production of the ingot. Specific examples of impurity elements include Ti, Zr, V, B, Na, K, Ca, Pb, P, Sn, Sr, Ag, Bi, and In. Of these elements, it is preferable that Ti, Zr, and V are each 0.10 mass% or less, and B, Na, K, Ca, Pb, P, Sn, Sr, Ag, Bi, and In are each 0.05 mass% or less. As long as these elements are within this range, they do not interfere with the effect of this embodiment not only when they are contained as unavoidable impurities, but also when they are actively added, such as by intentionally increasing the blending rate of scrap containing these elements.

When the elements shown as impurity elements are inevitably contained (i.e., when they are unavoidable impurities), it is more preferable that the content of each element is 0.005 mass% or less, and the total of the above impurity elements is 0.015 mass% or less.

In addition, when the above-mentioned Fe, Mn, Si, Be, Cr, Cu, and Zn are not contained in the aluminum alloy plate for magnetic disks according to this embodiment, but are contained in the aluminum alloy plate as unavoidable impurities, the content of Fe, Mn, Si, Cr, and Cu as unavoidable impurities is preferably 0.005 mass% or less, Be is preferably less than 3 mass ppm, and Zn is preferably 0.01 mass% or less.

(Linear expansion coefficient: 26.0×10 ⁻⁶ (1/° C.) or less)
The present inventors have carried out various studies on conditions for preventing deformation due to thermal distortion when an aluminum alloy plate is used as a substrate for a magnetic disk. As a result, they have found that it is effective to appropriately define the linear expansion coefficient of the aluminum alloy plate. The linear expansion coefficient is a value that indicates how much a material expands when the temperature rises by 1°C, and is calculated by measuring the difference in thermal expansion when the temperature of a material is raised from 100°C to 300°C, for example, and dividing the difference by the temperature. It is presumed that by controlling the linear expansion coefficient to a value lower than a predetermined value, deformation due to thermal distortion during sputtering of a magnetic film can be suppressed.

If the linear expansion coefficient of the aluminum alloy plate exceeds 26.0×10 ⁻⁶ (1/° C.), deformation due to thermal distortion may occur. Therefore, the linear expansion coefficient of the aluminum alloy plate is set to 26.0×10 ⁻⁶ (1/° C.) or less, and preferably 25.7×10 ⁻⁶ (1/° C.) or less. On the other hand, although there is no particular lower limit for the linear expansion coefficient of the aluminum alloy plate, if the linear expansion coefficient of the aluminum alloy plate becomes too small, when a magnetic disk manufactured using this aluminum alloy plate is used and the temperature inside the HDD rises, the expansion of the magnetic disk cannot follow the expansion of the spindle, and the magnetic disk may be deformed.
The linear expansion coefficient of the aluminum alloy plate can be adjusted mainly by controlling the Ni content in the aluminum alloy plate within the range specified in this embodiment.

(Number density of intermetallic compounds having a maximum length of 0.33 μm or more: 5×10 ⁴ (pieces/mm ² ) or less)
If the number density of intermetallic compounds of a predetermined size or more is high on the surface of the aluminum alloy plate, pits may be formed during mirror finishing such as cutting and grinding in manufacturing a substrate due to the intermetallic compounds falling off the surface of the blank or dissolving the intermetallic compounds during acid etching. The pits formed in this way may reduce the smoothness of the surface of the plating film formed by plating. Therefore, the number density of intermetallic compounds having a maximum length of 0.33 μm or more on the surface of the aluminum alloy plate is set to 5×10 ⁴ (pieces/mm ² ) or less. The lower the number density of the intermetallic compounds, the more preferable, for example, 4×10 ⁴ (pieces/mm ² ) or less is preferable.

The maximum length of an intermetallic compound refers to the distance between the two most distant points of the intermetallic compound recognized when observed, for example, in a backscattered electron composition image (COMPO image) of a scanning electron microscope (SEM). Even if an intermetallic compound having a maximum length of less than 0.33 μm is present on the surface of an aluminum alloy sheet, there is a low possibility of forming pits and there is no risk of reduced plating properties. In other words, the smaller the absolute maximum length of the intermetallic compound, the lower the risk of plating defects caused by the detachment of coarse crystals. Therefore, in this embodiment, the number density of intermetallic compounds having a maximum length of 0.33 μm or more is specified.

Examples of intermetallic compounds observed on the surface of the aluminum alloy plate include Mg-Si intermetallic compounds, Al-Fe intermetallic compounds, Al-Mn intermetallic compounds, Al-Ni intermetallic compounds, Al-Fe-Mn intermetallic compounds, Al-Fe-Ni intermetallic compounds, Al-Mn-Ni intermetallic compounds, and Al-Fe-Mn-Ni intermetallic compounds. In addition, when the aluminum alloy plate for magnetic disks according to this embodiment contains Cr, Al-Cr intermetallic compounds, Al-Fe-Cr intermetallic compounds in which a part of the Al-Fe intermetallic compounds is substituted, and Al-Mn-Cr intermetallic compounds in which a part of the Al-Mn intermetallic compounds is substituted, are observed. Furthermore, when the aluminum alloy plate for magnetic disks according to this embodiment contains at least one of Cu and Zn in the content specified in the present invention, Al-Cu intermetallic compounds, Al-Zn intermetallic compounds, and the like are also observed. Furthermore, in this embodiment, elemental Si is treated the same as an intermetallic compound.

The maximum length of the above-mentioned predetermined intermetallic compound can be adjusted by changing the content of Mg, Ni, Fe, Mn, Si, Cr, Cu, and Zn. By setting the content of the above elements within the content range specified in this embodiment, the number density of intermetallic compounds having a maximum length of 0.33 μm or more can be controlled to a predetermined value or less.

(Young's modulus: 70 GPa or more)
In this embodiment, the Young's modulus can be used as an index for judging the rigidity of the aluminum alloy plate. If the Young's modulus of the aluminum alloy plate is 70 GPa or more, even if the magnetic disk is thinned, the generation of vibration can be suppressed when the magnetic disk is rotated in the HDD, which is of critical significance. Therefore, the Young's modulus of the aluminum alloy plate is preferably 70 GPa or more, more preferably 71.0 GPa or more, and even more preferably 72.0 GPa. On the other hand, the upper limit of the Young's modulus is not particularly specified, but is usually 80 GPa or less.
In this specification, Young's modulus refers to a value measured by a free resonance method at room temperature in an air atmosphere in accordance with the high temperature Young's modulus test method for metallic materials specified in JIS Z 2280:1993.

<Method of manufacturing aluminum alloy plate for magnetic disk>
Next, an example of a method for producing an aluminum alloy sheet for a magnetic disk according to this embodiment will be described.
The aluminum alloy plate according to the present embodiment can be manufactured by a manufacturing method and equipment under general conditions for manufacturing an aluminum alloy plate for a magnetic disk. For example, an aluminum alloy plate can be manufactured by a manufacturing method including, in this order, a casting process in which a raw material is melted and the molten aluminum alloy adjusted to a predetermined chemical composition is cast into an aluminum alloy ingot by a semi-continuous casting method or the like, a homogenization heat treatment process in which the cast aluminum alloy ingot is surface-cut and subjected to a homogenization heat treatment, a hot rolling process in which the homogenization heat-treated aluminum alloy ingot is hot-rolled to obtain a hot-rolled plate, and a cold rolling process in which the hot-rolled plate is cold-rolled. In addition, when a thin plate continuous casting method is adopted instead of the semi-continuous casting method, the surface-cutting process may be omitted. In addition, intermediate annealing may be performed before the cold rolling process or during the cold rolling process, as necessary.
Hereinafter, each step of producing an aluminum alloy sheet will be described in detail.

(Casting process)
In the casting process, the raw materials are melted at 700 to 800° C. to produce a molten aluminum alloy, which is then cast into an aluminum alloy ingot by a known semi-continuous casting method (DC casting method: Direct Chill Casting).

(Homogenization heat treatment process)
In the homogenization heat treatment step, the cast aluminum alloy ingot is subjected to surface grinding and homogenization heat treatment. The surface grinding amount can be, for example, 2 to 40 mm per side. The homogenization heat treatment can be performed, for example, by holding the ingot at a temperature of 400 to 600° C. for 4 to 48 hours.

(Hot rolling process)
In the hot rolling step, the homogenized aluminum alloy ingot is hot rolled to obtain a hot rolled plate. The starting temperature of the hot rolling can be, for example, 490° C. or higher. The ending temperature of the hot rolling can be 300 to 350° C. The thickness of the hot rolled plate obtained by hot rolling can be, for example, 3 mm or less.

(Cold rolling process)
In the cold rolling step, the obtained hot rolled sheet is cold rolled to obtain a cold rolled sheet. The thickness of the cold rolled sheet is preferably, for example, 0.35 to 0.75 mm.
By undergoing these steps in order, the aluminum alloy plate according to this embodiment can be obtained.

[Aluminum alloy blanks for magnetic disks]
The aluminum alloy blank for a magnetic disk according to this embodiment is manufactured from the above-mentioned alloy plate, and the chemical composition of the blank does not change from that of the above-mentioned aluminum alloy plate, and has the same composition.
In addition, the linear expansion coefficient of the blank, the number density and Young's modulus of intermetallic compounds of a certain size or more on the surface of the blank, grindability, and other characteristic values are equivalent to the characteristic values of the aluminum alloy sheet. Therefore, the characteristic values measured on the aluminum alloy sheet can be regarded as being similar to the characteristic values of the blank. Conversely, the characteristic values measured on the blank can also be regarded as being similar to the characteristic values of the aluminum alloy sheet.

<Method of manufacturing an aluminum alloy blank for magnetic disk>
Next, an example of a method for manufacturing an aluminum alloy blank for a magnetic disk according to this embodiment will be described.
The aluminum alloy blank according to the present embodiment can be manufactured by a manufacturing method and equipment under general conditions for manufacturing an aluminum alloy blank for a magnetic disk. For example, the blank can be manufactured by further undergoing, in this order, a punching process in which the aluminum alloy plate obtained after the cold rolling process is punched into an annular shape, and a correction annealing process in which the annular substrate obtained in the punching process is subjected to correction annealing, for example, while applying a load, to flatten the substrate.
Each step of manufacturing an aluminum alloy blank will be described in detail below.

(Punching process)
In the punching process, the aluminum alloy plate is tempered as necessary, and then punched into a circular shape so that it can be used as a substrate for a 3.5-inch HDD having an inner diameter of 24 mm and an outer diameter of 96 mm, or a substrate for a 2.5-inch HDD having an inner diameter of 19 mm and an outer diameter of 66 mm.

(Straightening annealing process)
In the correction annealing step, it is preferable to stack the annular substrates by sandwiching them between spacers having a high degree of flatness, and anneal the substrates while applying a load to them to flatten them. The annealing temperature is 250 to 500° C., and the holding time can be, for example, about 3 to 10 hours.
The temperature increase rate in the corrective annealing can be, for example, about 80° C./hour on average, and is preferably 150° C./hour or less at the fastest. The temperature can be decreased (cooled) by, for example, opening the door of the annealing furnace.

Regarding the temperature rise in the corrective annealing, even if the temperature is raised stepwise, the effect of the present embodiment is not impaired. For example, as described in paragraphs 0068 and 0069 of Japanese Patent No. 5815153, the temperature may be raised at a plurality of heating rates, i.e., stepwise heating, such that the heating rate in a specific temperature range is a predetermined rate or a predetermined rate or more and the heating rate outside the specific temperature range is a different heating rate.
In this embodiment, the annealing temperature for the corrective annealing is assumed to be in the practical temperature range of 250 to 400° C. within the above-mentioned general annealing temperature range.
By going through these steps in order, the blank according to this embodiment can be obtained.

[Aluminum alloy substrate for magnetic disks]
The aluminum alloy substrate for a magnetic disk according to this embodiment is manufactured from the blank, and the chemical composition of the substrate does not change from that of the blank, and is the same composition.
Furthermore, the linear expansion coefficient of the substrate, the number density and Young's modulus of intermetallic compounds of a certain size or larger on the surface of the substrate, grindability, and other characteristic values are equivalent to the characteristic values of the aluminum alloy sheet and blank. Therefore, the characteristic values measured on the aluminum alloy sheet and blank can be regarded as being similar to the characteristic values of the substrate. Conversely, the characteristic values measured on the substrate can also be regarded as being similar to the characteristic values of the aluminum alloy sheet and blank.

<Method of manufacturing aluminum alloy substrate for magnetic disk>
The substrate according to this embodiment can be manufactured by a manufacturing method and equipment under general conditions for manufacturing aluminum alloy substrates for magnetic disks. Specifically, the substrate can be manufactured by carrying out a cutting process (end surface processing) for cutting the end surfaces of a blank, and a grinding process (mirror finish) for grinding the surface (main surface) of the blank.

The aluminum alloy plate, blank, and substrate according to this embodiment can be obtained by the above-mentioned methods, but other processes may be performed between or before or after each process, as long as they do not adversely affect each process.

<Magnetic Disk Manufacturing Method>
A magnetic disk can be manufactured using the above substrate. The magnetic disk is manufactured by a manufacturing method and equipment under general conditions for manufacturing magnetic disks. For example, the surface of the substrate is subjected to an acid etching treatment and a zincate treatment, an electroless Ni-P plating film is formed, and then the surface of the electroless Ni-P plating film is polished. Next, an underlayer, a magnetic film, a protective film, etc. are formed on the surface of the substrate, thereby manufacturing the magnetic disk.

The present embodiment will be described in more detail below with reference to examples, but the present invention is not limited to these examples, and modifications can be made within the scope of the invention, and all such modifications are within the technical scope of the invention.

Alloy blanks for magnetic disks were made using molten aluminum alloys with various chemical compositions, and the number density and Young's modulus of the intermetallic compounds on the surface of the obtained blanks were measured. In addition, the linear expansion coefficients of the blanks or the hot-rolled plates obtained during the manufacturing process were measured. The manufacturing conditions of the blanks and the methods for measuring the physical properties of each test material are described in detail below.

<Preparation of Aluminum Alloy Blanks for Magnetic Disks>
The raw materials were melted, and the components of the aluminum alloys were adjusted to have various chemical compositions, and the molten aluminum alloys were used to produce slabs, which were aluminum alloy ingots. The slabs thus obtained were then chamfered on both sides perpendicular to the thickness direction, and subjected to homogenization heat treatment at a temperature range of 500 to 550°C for a holding time of 2 to 18 hours.

Next, hot rolling was performed to obtain hot rolled plates. Test materials No. 1 to 3 had a hot rolled plate thickness of 3.0 mm, and test material No. 4 had a thickness of 2.3 mm. Then, cold rolling was performed to obtain aluminum alloy plates. Test materials No. 1 to 3 had an aluminum alloy plate thickness of 0.6 mm, and test material No. 4 had a thickness of 0.7 mm.

The resulting aluminum alloy plate was then punched into a circular shape to produce a 3.5-inch substrate (outer diameter approximately 95 mm, inner diameter approximately 25 mm). The circular substrate was then subjected to correction annealing to flatten it while applying a load, producing an aluminum alloy blank for magnetic disks. Correction annealing was performed by holding the substrate at a temperature range of 260 to 350°C for 3 to 6 hours.

In addition, among test materials No. 1 to 4, the homogenization heat treatment and corrective annealing conditions and rolling ratios differ, but within the above ranges, the linear expansion coefficient, number density of intermetallic compounds of a specific size, and Young's modulus are not affected by the conditions.

<Measurement of physical properties>
(Linear expansion coefficient)
The linear expansion coefficient was measured by thermomechanical analysis (TMA: Thermomechanical Analysis) using a thermomechanical analyzer (TMA402F1 (total expansion method) manufactured by NETZSCH). The measurement conditions were a load of 5 gf, a heating rate of 5 ° C./min, and a measurement temperature range of room temperature to 300 ° C. Considering measurement stability, the linear expansion coefficient was obtained as an average linear expansion coefficient of 25 ° C. or more and 300 ° C. or less. For test materials No. 1 to 3, measurement test pieces of 5 mm × 19 mm × 0.55 mm were taken from the obtained blanks and measured by the tensile method. For test material No. 4, measurement test pieces of 4 mm × 18 mm × 2.3 mm were taken from the hot-rolled plate and measured by the compression method. The measurement results were the same in both measurement methods.

If the linear expansion coefficient is 26.0×10 ⁻⁶ (1/° C.) or less, it can be determined that the effect of suppressing deformation due to thermal distortion is present, and if the linear expansion coefficient is 25.7×10 ⁻⁶ (1/° C.) or less, it can be determined that the effect of suppressing deformation is even more excellent.

(Number density of intermetallic compounds having a maximum length of 0.33 μm or more)
The surface of the blank was cut with a diamond bit to make it a mirror surface, and this surface was photographed at a magnification of 2000 times, 108 fields of view, and an observation area of 0.29 mm 2 using an FE-SEM (JSM-7001F manufactured by JEOL Ltd., built-in particle analysis software EX-35110, particle analysis software Ver. 3.84: Ver. information described in the release notes, acceleration voltage ¹⁵ kV), to obtain a composition image called a COMPO image. The threshold was set to the gray matrix part, and the matrix part, that is, the part that appears whiter than the parent phase, was regarded as an intermetallic compound, and their maximum length was measured. The maximum length of the intermetallic compound means the maximum value of the distance between any two points on the contour line of the intermetallic compound particle. Then, the number of intermetallic compounds having a maximum length of 0.33 μm or more was counted using the above particle analysis software, and the number density per unit area was calculated.

If the density of the intermetallic compounds of the specific size is 5×10 ⁴ (pieces/mm ² ) or less, it can be determined that the plating has excellent plating properties and can reduce the surface smoothness of the plating film. If the density of the intermetallic compounds of the specific size is 4×10 ⁴ (pieces/mm ² ) or less, it can be determined that the plating properties are even better.

(Young's modulus)
The Young's modulus was measured in accordance with JIS Z 2280:1993 (Method of testing Young's modulus at high temperatures for metallic materials) by preparing a test material of 60 mm x 10 mm with the rolling direction as the longitudinal direction, and using this test material. The measurement was performed by a free resonance method in an air atmosphere at room temperature using a test device JE-RT manufactured by Nippon Technoplus Co., Ltd.

If the Young's modulus is 70 GPa or more, it can be determined that the rigidity is excellent. If the Young's modulus is 71.0 GPa or more, it can be determined that the rigidity is even more excellent.

The chemical composition of the aluminum alloy used and the measurement results of each physical property are shown in Table 1 below. In the Mn column, "0.0" indicates that Mn was not actively added, and the Mn content was less than 0.05 due to contamination from the material alone, and is rounded to the first decimal place. In the Be column, "-" indicates that Be was not actively added, and therefore no measurement was performed, but considering contamination from the material, it is estimated to be less than 1 mass ppm. In the Zn column, "0.00" indicates that Zn was not actively added, and the Zn content was less than 0.005 due to contamination from the material alone. Note that the chemical composition shown in Table 1 is the content of each element rounded to the specified place, so the total content of all elements may exceed 100 mass%.

As shown in Table 1 above, in the test materials No. 1 and 2, which are examples of the invention, the composition of the aluminum alloy used is within the range specified by the present invention, so the linear expansion coefficient and the number density of intermetallic compounds with a maximum length of 0.33 μm or more are also within the range specified by the present invention. Therefore, it can be determined that deformation due to thermal distortion can be suppressed and excellent plating properties can be obtained. In addition, since the Young's modulus is also within the range specified by the present invention, it can be determined that the materials have excellent rigidity.

In contrast, in the comparative example, test material No. 3, the Ni content in the aluminum alloy is less than the lower limit of the range specified in the present invention, and the Fe content exceeds the upper limit of the range specified in the present invention. Therefore, the linear expansion coefficient and the number density of the intermetallic compounds could not be made within the range specified in the present invention. Therefore, it is not possible to suppress deformation due to thermal distortion, and it can be determined that the plating property is also poor.

In addition, in the comparative example, test material No. 4, the Fe content and Mn content in the aluminum alloy exceed the upper limit of the range specified in the present invention. Therefore, the number density of intermetallic compounds could not be set within the range specified in the present invention. Therefore, it can be determined that the plating property is poor.

Claims (11)

Mg: 0.1% by mass or more and 7.0% by mass or less, and Ni: 1.0% by mass or more and 5.0% by mass or less,
Fe: 0.3 mass% or less,
Mn: 0.3 mass% or less,
Si: 0.10 mass% or less;
An aluminum alloy plate for magnetic disks, the balance of which is Al and impurities,
A linear expansion coefficient is 26.0×10 ⁻⁶ (1/° C.) or less,
An aluminum alloy sheet for magnetic disks, characterized in that the number density of intermetallic compounds having a maximum length of 0.33 μm or more on the surface of the aluminum alloy sheet is 5×10 ⁴ (pieces/mm ² ) or less. The aluminum alloy plate for magnetic disks according to claim 1, further comprising Be: 3 ppm by mass or more and 100 ppm by mass or less. The aluminum alloy plate for magnetic disks according to claim 1, further comprising Cr: 0.01% by mass or more and 1.0% by mass or less. 2. The aluminum alloy plate for magnetic disks according to claim 1, further comprising: Be: 3 ppm by mass or more and 100 ppm by mass or less; and Cr: 0.01% by mass or more and 1.0% by mass or less. The aluminum alloy plate for magnetic disks according to claim 1 further contains at least one of Cu: 0.5 mass% or less and Zn: 0.5 mass% or less. The aluminum alloy plate for magnetic disks according to claim 2, further comprising at least one of Cu: 0.5% by mass or less and Zn: 0.5% by mass or less. The aluminum alloy plate for magnetic disks according to claim 3 further contains at least one of Cu: 0.5 mass% or less and Zn: 0.5 mass% or less. The aluminum alloy plate for magnetic disks according to claim 4, further comprising at least one of Cu: 0.5% by mass or less and Zn: 0.5% by mass or less. The aluminum alloy plate for magnetic disks according to any one of claims 1 to 8, characterized in that the Young's modulus is 70 GPa or more. An aluminum alloy blank for magnetic disks, comprising the aluminum alloy plate for magnetic disks according to claim 9. An aluminum alloy substrate for magnetic disks, comprising the aluminum alloy blank for magnetic disks according to claim 10.