JP7794722B2 - Aluminum alloy plates for magnetic disks, aluminum alloy blanks for magnetic disks, and aluminum alloy substrates for magnetic disks - Google Patents

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 other devices are manufactured by forming a magnetic film on a non-magnetic substrate. Specifically, the magnetic disk manufacturing process involves first casting an aluminum alloy, chamfering the rolled surface as needed, then soaking and rolling the aluminum alloy plate. This is then punched into a circular (donut-shaped) shape and subjected to corrective annealing to produce a blank. Next, the inner and outer edges of the blank are cut, and the front and back surfaces of the blank are ground to remove the oxide film and reduce the surface roughness of the substrate before plating, resulting in a substrate. The substrate is then electrolessly plated with Ni-P. However, because this Ni-P plating film has plating defects, the surface of the Ni-P plating film is polished to remove the plating defects and smooth the Ni-P plating film. A magnetic film is then formed on the Ni-P plating film by sputtering, thereby producing a magnetic disk from the aluminum alloy substrate.

In recent years, with the digitization of information and the spread of the Internet, large amounts of digital data are being handled, and this has led to demand for larger capacity hard disk drives (HDDs), particularly in data centers. To achieve this, thinner magnetic disks are being considered, with the aim of increasing the number of magnetic disks 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 rotational speed increases. One way to suppress these vibrations is to increase 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 have excellent rigidity and 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% by mass or less of Mg and 1.00% by mass or less of Si, and contains at least one of Fe, Mn, and Ni, with the respective contents and total contents specified. It also contains at least one of Cr, Ti, and Zr, with the respective contents and total contents specified. Furthermore, the area ratio of intermetallic compounds on the surface is 5 to 40%, and the total area ratio of elemental Si and Mg-Si-based intermetallic compounds is 1% or less.

Patent Document 2 proposes an aluminum alloy sheet for magnetic disks that has good rigidity while suppressing deterioration in grindability that occurs due to improved rigidity. The aluminum alloy sheet for magnetic disks described in Patent Document 2 is specified to contain 0.1 to 7.0 mass% Mg, 0.3 to 2.5 mass% total of at least one of Fe, Mn, and Ni, and 1.3 mass% or less Ni. Furthermore, the number density of intermetallic compounds on the surface having a longest diameter of more than 10 μm is 60 particles/ ^mm2 or less, and the number density of intermetallic compounds having a longest diameter of 3 to 10 μm is 600 particles/ ^mm2 or more.

Furthermore, Patent Document 3 discloses a magnetic disk substrate that can suppress the generation of particles caused by external impacts even when the substrate 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 also describes 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 gripping portion can be suppressed.

Patent No. 6684139 Japanese Patent Application Laid-Open No. 2021-93234 Japanese Patent Application Laid-Open No. 2022-10156

However, while the aluminum alloy blank for magnetic disks described in Patent Document 1 contains added Fe and Mn to improve Young's modulus, the addition of Fe and Mn causes the compounds to coarsen, resulting in poor plating properties. Furthermore, Patent Document 2 describes an aluminum alloy sheet for magnetic disks that specifies the compound number density to achieve both grindability and Young's modulus, but does not consider reducing thermal distortion. 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 in aluminum alloy sheets, etc.

In particular, with the recent demand for thinner media, there is an ever-increasing demand for technology to prevent deformation due to thermal distortion that occurs during sputtering of magnetic films.

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 objective is achieved by the following aluminum alloy plate for magnetic disks (1) of the present invention.

(1) Mg: 0.1 mass% or more and 7.0 mass% or less, and Ni: 1.0 mass% or more and 5.0 mass% or less,
Fe: 0.3% by mass or less,
Mn: 0.3% by mass or less,
Si: 0.10% by mass or less;
An aluminum alloy plate for magnetic disks, the balance of which is Al and impurities,
The linear expansion coefficient is 26.0×10 ⁻⁶ (1/°C) or less,
An aluminum alloy plate 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 plate is 5×10 ⁴ (pieces/mm ² ) or less.

Furthermore, the aluminum alloy sheet 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 containing 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 a magnetic disk, characterized by comprising an aluminum alloy plate for a magnetic disk according to 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 a magnetic disk, characterized by comprising the aluminum alloy blank for a magnetic disk described in (6).

When the aluminum alloy plate for magnetic disks according to the present invention is used as a base material, 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 deformation due to thermal distortion during sputtering of the magnetic film.

Furthermore, the aluminum alloy blank for magnetic disks according to the present invention provides excellent plating properties, and when this blank is used as a material, it is possible to obtain an aluminum alloy substrate for magnetic disks that is suppressed from deformation due to thermal distortion during sputtering of the magnetic film.

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 properties of the magnetic disk and allows for the production of magnetic disks 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 limiting the numerical values 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 sheet for magnetic disks according to this embodiment is a material sheet for manufacturing an aluminum alloy blank for magnetic disks. First, the composition of the aluminum alloy sheet and the reasons for limiting the numerical values will be described. The alloy compositions of the blank and substrate, which will be described later, are the same as the composition of the alloy sheet.

(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 disks according to this 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-mentioned effects 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% by mass or more and 5.0% by mass or less)
Ni is an essential element in the aluminum alloy plate for magnetic disks according to this embodiment, and is contained in the aluminum alloy plate to obtain good rigidity and a good linear expansion coefficient. If the Ni content in the aluminum alloy plate is less than 1.0 mass%, the above-mentioned effects cannot be obtained. Therefore, the Ni content is set to 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, which may result in a decrease in platability. 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. Furthermore, the Ni content is further preferably 3.8 mass% or less, and particularly preferably 3.5 mass% or less.

(Fe: 0.3% by mass or less)
In the aluminum alloy sheet for magnetic disks according to this embodiment, Fe is an element that is mixed in as an impurity from the base metal. If the Fe content in the aluminum alloy sheet exceeds 0.3% by mass, the intermetallic compounds may become coarse, increasing the number density of the intermetallic compounds and potentially reducing plating properties. Therefore, the Fe content is set to 0.3% by mass or less, preferably 0.25% by mass or less, more preferably 0.20% by mass or less, and even more preferably 0.15% by mass or less.

(Mn: 0.3% by mass or less)
Mn is an element that may be mixed in as an impurity from the base metal in the aluminum alloy sheet for magnetic disks according to this embodiment. If the Mn content in the aluminum alloy sheet exceeds 0.3% by mass, the intermetallic compounds may become coarse, increasing the number density of the intermetallic compounds and potentially reducing platability. Therefore, the Mn content is set to 0.3% by mass or less, preferably 0.25% by mass or less, more preferably 0.20% by mass or less, and even more preferably 0.15% by mass or less. Furthermore, the Mn content is more preferably 0.10% by mass or less, even more preferably 0.05% by mass or less, and particularly preferably 0.01% by mass or less.

(Si: 0.10% by mass or less)
In the aluminum alloy sheet for magnetic disks according to this embodiment, Si is an element that is mixed in as an impurity from the base metal. It may be present in the aluminum alloy sheet in the form of elemental Si or may form an Al-Fe-Si intermetallic compound. If the Si content in the aluminum alloy sheet exceeds 0.10% by mass, the elemental Si may cause a decrease in plating smoothness. Therefore, from the viewpoint of suppressing the formation of elemental Si, the Si content in the aluminum alloy sheet is preferably reduced, and may be 0% by mass, i.e., no Si is contained. Therefore, the Si content is set to 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 aluminum ingots and intermediate alloy ingots, which results in an increase in raw material costs. Therefore, the Si content may be 0.004 mass% or more.

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

In the aluminum alloy sheet for magnetic disks according to this embodiment, Be is not an essential component. However, when the Be content in the aluminum alloy sheet is 3 ppm by mass or more, the above-described effects of Be can be fully achieved. Therefore, when Be is contained in the aluminum alloy sheet, 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 Be-containing compounds from becoming coarse, prevent the occurrence of edge cracks, and suppress a decrease in rollability. Therefore, the Be content is preferably 100 ppm by mass or less, and from the viewpoint of suppressing the coarsening of Be-containing compounds, it is more preferably 20 ppm by mass or less, and even more preferably 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 uniformly distributing intermetallic compounds, and is an element that contributes to improving strength and yield strength. In the aluminum alloy sheet for magnetic disks according to this embodiment, Cr is not an essential component, but if the Cr content in the aluminum alloy sheet is 0.01 mass% or more, the above-mentioned effects of Cr can be sufficiently obtained. Therefore, when Cr is contained in the aluminum alloy sheet, the Cr content is preferably 0.01 mass% or more, more preferably 0.05 mass% or more, 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, a decrease in 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% by mass or less, Zn: 0.5% by mass or less)
Cu and Zn are elements that widen the solid-liquid coexistence region on the phase diagram and contribute to reducing the frequency of molten metal leakage during casting. Furthermore, 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 sheet for magnetic disks according to this embodiment, Cu and Zn are not essential components and may be 0% by mass, but it is preferable that at least one of Cu and Zn is contained in the aluminum alloy sheet within the following ranges.

That is, when the Cu content is 0.005% by mass or more, the above-mentioned effects of Cu can be fully achieved. Therefore, when Cu is contained in an 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 a decrease in plating smoothness and also to suppress a decrease in the 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.

Furthermore, when the Zn content is 0.1% by mass or more, the above-mentioned effects of Zn can be fully achieved. Therefore, when Zn is contained in an aluminum alloy sheet, the Zn content is preferably 0.1% by mass or more, and more preferably 0.2% by mass or more. On the other hand, when the Zn content is 0.5% by mass or less, as in the case of Cu, deterioration in plating smoothness can be suppressed, and deterioration in the smoothness of the electroless Ni-P plating film formed on the surface can also be suppressed. Therefore, the Zn content is preferably 0.5% by mass or less, more preferably 0.4% by mass or less, and even more preferably 0.35% by mass or less.

(balance: Al and impurities)
The balance of the aluminum alloy plate for magnetic disks according to this embodiment is composed of Al and impurities. That is, the aluminum alloy plate for magnetic disks according to this embodiment may contain elements other than those mentioned above as impurities depending on the selection of melting raw materials during ingot production. 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. Within these ranges, these elements do not interfere with the effects of this embodiment, not only when they are contained as unavoidable impurities, but also when they are intentionally added, for example, by increasing the blending ratio of scrap containing these elements.

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

Furthermore, if 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% by mass or less, Be is preferably less than 3 ppm by mass, and Zn is preferably 0.01% by mass or less.

(Linear expansion coefficient: 26.0×10 ⁻⁶ (1/°C) or less)
The present inventors have conducted various studies to determine conditions for preventing deformation due to thermal strain when an aluminum alloy plate is used as a magnetic disk substrate. As a result, they have found that it is effective to appropriately specify the linear expansion coefficient of the aluminum alloy plate. The linear expansion coefficient is a value that represents the amount of expansion of a material when the temperature rises by 1°C. For example, it can be calculated by measuring the difference in thermal expansion when the temperature of a material is raised from 100°C to 300°C and dividing the result by the temperature difference. It is estimated that by controlling the linear expansion coefficient to a low value below a predetermined value, deformation due to thermal strain during sputtering of the 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 strain 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 is 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 may not be able to keep up with 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 larger 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 from the surface of the blank or dissolving during acid etching. The pits formed in this manner may reduce the surface smoothness of the plating film formed by the plating process. Therefore, the number density of intermetallic compounds having a maximum length of 0.33 μm or larger on the surface of the aluminum alloy plate is set to 5×10 ⁴ (particles/mm ² ) or less. The lower the number density of the intermetallic compounds, the more preferable it is, and for example, 4×10 ⁴ (particles/mm ² ) or less is preferred.

The maximum length of an intermetallic compound refers to the distance between the two furthest points on the intermetallic compound as recognized when observed, for example, using a backscattered electron composition image (COMPO image) of a scanning electron microscope (SEM). Even if intermetallic compounds with a maximum length of less than 0.33 μm are present on the surface of an aluminum alloy sheet, they are unlikely to form pits and there is no risk of reduced platability. In other words, the smaller the absolute maximum length of the intermetallic compound, the lower the risk of plating defects due to the shedding of coarse crystals. Therefore, in this embodiment, the number density of intermetallic compounds with a maximum length of 0.33 μm or more is specified.

Intermetallic compounds observed on the surface of the aluminum alloy sheet include, for example, 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. Furthermore, when the aluminum alloy sheet for magnetic disks according to this embodiment contains Cr, Al-Cr intermetallic compounds, Al-Fe-Cr intermetallic compounds in which a portion of the Al-Fe intermetallic compounds is substituted, and Al-Mn-Cr intermetallic compounds in which a portion of the Al-Mn intermetallic compounds is substituted, are also observed. Furthermore, when the aluminum alloy sheet for magnetic disks according to this embodiment contains at least one of Cu and Zn in the amount specified by this invention, Al-Cu intermetallic compounds, Al-Zn intermetallic compounds, and the like are also observed. Furthermore, in this embodiment, elemental Si is treated in the same way as an intermetallic compound.

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

(Young's modulus: 70 GPa or more)
In this embodiment, the Young's modulus can be used as an index for determining 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 a 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 in an air atmosphere at room temperature in accordance with the high temperature Young's modulus test method for metallic materials specified in JIS Z 2280:1993.

<Method of manufacturing an aluminum alloy plate for magnetic disks>
Next, an example of a method for manufacturing an aluminum alloy plate for a magnetic disk according to this embodiment will be described.
The aluminum alloy sheet according to this embodiment can be manufactured using a manufacturing method and equipment generally used for manufacturing aluminum alloy sheets for magnetic disks. For example, the aluminum alloy sheet can be manufactured using a manufacturing method including, in this order: a casting step in which raw materials are melted and the resulting 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 step in which the cast aluminum alloy ingot is chamfered and subjected to a homogenization heat treatment; a hot rolling step in which the homogenized heat-treated aluminum alloy ingot is hot-rolled to obtain a hot-rolled sheet; and a cold rolling step in which the hot-rolled sheet is cold-rolled. Note that if a continuous thin-plate casting method is used instead of the semi-continuous casting method, the chamfering step may be omitted. Furthermore, if necessary, intermediate annealing may be performed before the cold rolling step or during the cold rolling step.
Hereinafter, each step of manufacturing an aluminum alloy plate will be described in detail.

(Casting process)
In the casting process, 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: 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 carried out by holding the ingot at a temperature of 400 to 600°C for 4 to 48 hours, for example.

(Hot rolling process)
In the hot rolling step, the aluminum alloy ingot that has been subjected to the homogenization heat treatment is hot rolled to obtain a hot rolled sheet. 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 sheet 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 set to, 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 blank for magnetic disks]
The aluminum alloy blank for a magnetic disk according to this embodiment is manufactured from the above alloy plate, and the chemical composition of the blank does not change from that of the above aluminum alloy plate, and is the same composition.
Furthermore, the linear expansion coefficient of the blank, the number density and Young's modulus of intermetallic compounds of a predetermined size or larger on the surface of the blank, grindability, and other characteristic values are equivalent to those of the aluminum alloy sheet. Therefore, the characteristic values measured on the aluminum alloy sheet can be considered to be the same as those of the blank. Conversely, the characteristic values measured on the blank can also be considered to be the same as those of the aluminum alloy sheet.

<Method of manufacturing an aluminum alloy blank for a 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 this embodiment can be manufactured by a manufacturing method and equipment under general conditions for manufacturing aluminum alloy blanks for magnetic disks. For example, the blank can be manufactured by further undergoing, in this order, a punching step in which the aluminum alloy plate obtained after the cold rolling step is punched into a circular shape, and a correction annealing step in which the circular substrate obtained in the punching step is subjected to correction annealing, for example, by annealing while applying a load to flatten it.
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 ring shape so that it can be used for, for example, a substrate for a 3.5-inch HDD with an inner diameter of 24 mm and an outer diameter of 96 mm, or a substrate for a 2.5-inch HDD with an inner diameter of 19 mm and an outer diameter of 66 mm.

(Straightening annealing process)
In the correction annealing step, the annular substrates are preferably stacked, sandwiched between spacers having high flatness, and annealed while applying a load to the substrates to flatten them. The annealing temperature can be 250 to 500°C, and the holding time can be, for example, about 3 to 10 hours.
The temperature rising 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 lowered (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 this 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 temperature rise rates, i.e., stepwise, so that the temperature rise rate in a specific temperature range is a predetermined rate or a predetermined rate or more, and the temperature rise rate outside the specific temperature range is a different 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 range of general annealing temperatures.
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 predetermined size or larger on the surface of the substrate, grindability, and other characteristic values are equivalent to those of the aluminum alloy sheet or blank. Therefore, the characteristic values measured on the aluminum alloy sheet or blank can be considered to be the same as those of the substrate. Conversely, the characteristic values measured on the substrate can also be considered to be the same as those of the aluminum alloy sheet or blank.

<Method of manufacturing an aluminum alloy substrate for magnetic disks>
The substrate according to this embodiment can be manufactured using manufacturing methods and equipment generally used for manufacturing aluminum alloy substrates for magnetic disks. Specifically, the substrate can be manufactured by carrying out a cutting process (end surface processing) to cut the end faces of a blank, and a grinding process (mirror finish) to grind the surface (main surface) of the blank.

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

<Magnetic Disk Manufacturing Method>
A magnetic disk can be manufactured using the above substrate. The magnetic disk is manufactured using a manufacturing method and equipment under typical conditions for manufacturing magnetic disks. For example, the surface of the substrate is subjected to acid etching and zincate treatment to form an electroless Ni-P plating film, 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 explained in more detail below using 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 produced 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 resulting blanks were measured. Additionally, the linear expansion coefficients of the blanks and the hot-rolled sheets obtained during the manufacturing process were measured. Below, we will provide a detailed explanation of the blank manufacturing conditions and the methods for measuring the physical properties of each test material.

<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. The molten aluminum alloys were used to produce slabs, which were aluminum alloy ingots. The resulting slabs were then chamfered on both sides perpendicular to the thickness direction, and subjected to a 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. Subsequently, 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 form a 3.5-inch substrate (outer diameter approximately 95 mm, inner diameter approximately 25 mm). The circular substrate was then subjected to correction annealing, in which it was annealed while under load to flatten it, to produce an aluminum alloy blank for a magnetic disk. Correction annealing was performed by holding the substrate at a temperature range of 260 to 350°C for 3 to 6 hours.

Note that among test materials No. 1 to 4, the homogenization heat treatment and corrective annealing conditions and rolling reduction ratios differed, but as long as they remained within the above ranges, the linear expansion coefficient, number density of intermetallic compounds of specific sizes, and Young's modulus were not affected by these conditions.

<Measurement of physical properties>
(Coefficient of linear expansion)
The linear expansion coefficient was measured by thermomechanical analysis (TMA) 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. Taking into consideration measurement stability, the linear expansion coefficient was determined as the average linear expansion coefficient from 25°C to 300°C. For test materials Nos. 1 to 3, measurement specimens measuring 5 mm x 19 mm x 0.55 mm were taken from the obtained blanks and measured by the tensile method. For test material No. 4, measurement specimens measuring 4 mm x 18 mm x 2.3 mm were taken from the hot-rolled plate and measured by the compression method. The measurement results were the same regardless of the measurement method.

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 strain 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 better.

(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 create a mirror finish, and this surface was photographed using an FE-SEM (JSM-7001F manufactured by JEOL Ltd., equipped with built-in particle analysis software EX-35110, particle analysis software Ver. 3.84: version information described in the release notes, accelerating voltage 15 kV) at 2000x magnification, 108 fields of view, and an observation area of 0.29 ^mm2 to obtain a composition image called a COMPO image. A threshold was set for the gray matrix portion, and the matrix portion, i.e., the portion appearing whiter than the parent phase, was considered to be an intermetallic compound, and their maximum length was measured. The maximum length of the intermetallic compound refers to the maximum value of the distance between any two points on the outline of an intermetallic compound particle. The number of intermetallic compounds with a maximum length of 0.33 μm or more was then counted using the particle analysis software, and the number density per unit area was calculated.

If the number 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 property is excellent and that the surface smoothness of the plating film can be reduced. If the number density is 4×10 ⁴ (pieces/mm ² ) or less, it can be determined that the plating property is even better.

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

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

The chemical composition of the aluminum alloy used and the measurement results for 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 raw materials alone; the result is rounded to one decimal place. In the Be column, "-" indicates that Be was not actively added, and therefore no measurement was performed; however, taking contamination from the raw materials into account, it is estimated to be less than 1 ppm by mass. 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 raw materials alone. Note that the chemical composition shown in Table 1 is the content of each element rounded to the nearest decimal place, so the total content of all elements may exceed 100% by mass.

As shown in Table 1 above, in 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, and therefore 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 strain can be suppressed and excellent plating properties can be obtained. Furthermore, because the Young's modulus was 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 was below the lower limit of the range specified in the present invention, and the Fe content exceeded the upper limit of the range specified in the present invention. As a result, the linear expansion coefficient and the number density of intermetallic compounds could not be kept within the range specified in the present invention. Therefore, deformation due to thermal strain could not be suppressed, and it can be determined that the platability was also poor.

Furthermore, in the comparative example, Test Material No. 4, the Fe content and Mn content in the aluminum alloy exceeded the upper limits of the ranges specified in the present invention. As a result, the number density of intermetallic compounds could not be kept within the ranges specified in the present invention. Therefore, it can be determined that the platability was poor.

Claims (4)

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% by mass or less,
Mn: 0.3% by mass or less,
Si: 0.10% by mass or less;
Be: 3 mass ppm or more and 100 mass ppm or less, and
Contains Cr: 0.01% by mass or more and 1.0% by mass or less,
Contains at least one of Cu: 0.5 mass% or less and Zn: 0.5 mass% or less,
An aluminum alloy plate for magnetic disks, the balance of which is Al and impurities,
The linear expansion coefficient is 26.0×10 ⁻⁶ (1/°C) or less,
An aluminum alloy plate 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 plate is 5×10 ⁴ (pieces/mm ² ) or less. 2. The aluminum alloy plate for magnetic disks according to claim 1 , wherein the Young's modulus is 70 GPa or more. An aluminum alloy blank for a magnetic disk, comprising the aluminum alloy plate for a magnetic disk according to claim 2 . An aluminum alloy substrate for a magnetic disk, comprising the aluminum alloy blank for a magnetic disk according to claim 3 .