Aluminum alloy plate for magnetic disks and its manufacturing method, aluminum alloy blank for magnetic disks, and aluminum alloy substrate for magnetic disks

Abstract

The present invention provides an aluminum alloy plate for magnetic disks that can reduce minute waviness after plating, even with a low Mn content. [Solution] An aluminum alloy plate satisfying the following: Mg: 3.0-6.5 mass%, Mn: 0.1 mass% or less, Cr: 0.01-0.35 mass%, Fe: 0.1 mass% or less, Si: 0.1 mass% or less, and at least one of Cu: 0.01-0.5 mass% and Zn: 0.01-0.5 mass%, with the remainder being impurities and Al, wherein the average grain size on the surface is 45 μm or less, and the crystal orientation distribution on the surface is such that the Brass orientation ({011} <211> An aluminum alloy plate for magnetic disks, having an area ratio of 11% or less.

Description

[Technical Field]

[0001] This invention relates to aluminum alloy plates for magnetic disks, aluminum alloy blanks for magnetic disks, and aluminum alloy substrates for magnetic disks. It also relates to a method for manufacturing aluminum alloy plates for magnetic disks. [Background technology]

[0002] With the digitalization of information and the spread of the internet, large amounts of digital data are being handled, leading to a demand for larger capacity hard disk drives (HDDs), particularly in data centers. Along with the increased capacity of HDDs, an improvement in the recording density of magnetic disks is necessary. Reducing the waviness of the plated surface after plating is crucial for improving recording density.

[0003] The undulation on the plated surface consists of short-wavelength undulation and minute undulation. Short-wavelength undulation refers to undulation with wavelengths of tens of micrometers or less. On the other hand, minute undulation refers to undulation with relatively long wavelengths ranging from tens to hundreds of micrometers.

[0004] Short-wavelength undulations can be removed by polishing the plated surface after plating, but minute undulations cannot be sufficiently removed by the above polishing method. This is because minute undulations are caused by irregularities that occur during the pre-plating treatment due to differences in etching properties caused by differences in grain orientation. Microscopic undulations are particularly noticeable when the crystal grain size is large or non-uniform, and contribute to a decrease in the performance of the magnetic disk.

[0005] In contrast, Patent Document 1 describes an intermetallic compound with a maximum length of 5 μm, with 1 compound / mm². 2A specific composition aluminum alloy substrate for magnetic disks is disclosed, having the following characteristics and an average grain size of 20 μm or less. This reduces minute waviness on the Ni-P plated surface. Furthermore, Patent Document 2 discloses a specific composition aluminum alloy blank for magnetic disks having an average grain size of 27 μm or less on the surface, an aspect ratio of the average grain size on the surface of 1.2 or less, and a yield strength of 140 MPa or more. This makes it possible to produce an aluminum alloy blank with sufficient impact resistance, less prone to minute waviness on the plated surface after plating, and with fewer surface defects. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2009-242843 [Patent Document 2] Japanese Patent Publication No. 2017-014584 [Overview of the project] [Problems that the invention aims to solve]

[0007] The aluminum alloy substrates or aluminum alloy blanks described in Patent Documents 1 and 2 contain Mn as a component that precipitates as fine intermetallic compounds and has the effect of suppressing the growth of crystal grains, that is, refining the crystal grains and reducing minute waviness. On the other hand, the addition of Mn contributes to a decrease in grindability during processes such as mirror finishing when using aluminum alloy blanks.

[0008] This invention was made in view of the above circumstances, and aims to provide an aluminum alloy plate for magnetic disks and a method for manufacturing the same that can reduce minute waviness after plating even with a low Mn content. Furthermore, the objective is to provide aluminum alloy blanks and aluminum alloy substrates for magnetic disks obtained from the above-mentioned aluminum alloy plates for magnetic disks. [Means for solving the problem]

[0009] In response to the above problems, the inventors diligently conducted research and succeeded in reducing the average grain size on the surface of the aluminum alloy plate without adding a large amount of Mn, thereby achieving grain refinement. However, it was found that this alone had limitations in reducing minute waviness after plating. Therefore, further research focusing on the texture of the grains was conducted, and as a result, it was discovered that the above problems could be solved by selectively increasing specific crystal orientations on the surface of the aluminum alloy plate, thus completing the present invention.

[0010] In other words, the present invention relates to the following [1] to [5]. [1] An aluminum alloy plate satisfying the following: Mg: 3.0-6.5 mass%, Mn: 0.1 mass% or less, Cr: 0.01-0.35 mass%, Fe: 0.1 mass% or less, Si: 0.1 mass% or less, and at least one of Cu: 0.01-0.5 mass% and Zn: 0.01-0.5 mass%, with the remainder being impurities and Al, wherein the average grain size on the surface is 45 μm or less, and the crystal orientation distribution on the surface is such that the Brass orientation ({011} <211> An aluminum alloy plate for magnetic disks, having an area ratio of 11% or less. [2] The aluminum alloy plate for magnetic disks according to [1], wherein the average grain size is 25 μm or less. [3] An aluminum alloy blank for magnetic disks obtained from the aluminum alloy plate for magnetic disks described in [1] or [2] above. [4] An aluminum alloy substrate for magnetic disks obtained from the aluminum alloy blank for magnetic disks described in [3] above.

[0011] [5] Mg: 3.0 to 6.5 mass%, Mn: 0.1 mass% or less, Cr: 0.01 to 0.35 mass%, Fe: 0.1 mass% or less, Si: 0.1 mass% or less, and at least one of Cu: 0.01 to 0.5 mass% and Zn: 0.01 to 0.5 mass%, a method for manufacturing an aluminum alloy plate for a magnetic disk, comprising a hot rough rolling step of hot rough rolling a homogenized ingot to obtain a hot rough rolled plate, and a hot finish rolling step of hot finish rolling the hot rough rolled plate to obtain a hot finish rolled plate, wherein the number of stands for performing the hot finish rolling is n, where n is a natural number of 2 or more, and when the logarithmic strain of reduction of the i-th stand is ε i satisfies the following relational expression (1). A method for manufacturing an aluminum alloy plate for a magnetic disk.

[0012]

Number

Advantages of the Invention

[0013] According to the present invention, an aluminum alloy plate for a magnetic disk, an aluminum alloy blank for a magnetic disk, and an aluminum alloy substrate for a magnetic disk that can reduce minute undulations after plating can be obtained even if Mn is not contained or the content of Mn is small. As a result, the recording density of the magnetic disk can be improved.

Modes for Carrying Out the Invention

[0014] [[ID=​​​​​​The aluminum alloy plate for a magnetic disk according to this embodiment satisfies Mg: 3.0 to 6.5% by mass, Mn: 0.1% by mass or less, Cr: 0.01 to 0.35% by mass, Fe: 0.1% by mass or less, Si: 0.1% by mass or less, and at least one of Cu: 0.01 to 0.5% by mass and Zn: 0.01 to 0.5% by mass, and the balance consists of impurities and Al. Furthermore, the average crystal grain size on the surface of the aluminum alloy plate for a magnetic disk is 45 μm or less, and among the crystal orientation distributions on the surface, the area ratio of the Brass orientation ({011}<211>) is 11% or less.

[0016] When the average crystal grain size on the surface of the alloy plate is 45 μm or less, minute undulations can be reduced. This is because, when performing degreasing, etching, and zincate treatment, which are pre-steps of the plating process, unevenness corresponding to crystal grains caused by differences in reactivity due to the crystal orientation difference of the aluminum alloy plate can be reduced. The average crystal grain size of the alloy plate surface is preferably 25 μm or less, more preferably 22 μm or less. The lower limit of the average crystal grain size of the surface is not particularly limited, but is usually 2 μm or more.

[0017] In this specification, the value obtained by measuring the average crystal grain size of the alloy plate surface as follows is used. That is, test pieces are cut out from each test material (blank), and polishing is performed to make a mirror surface so that the surface parallel to the plate thickness direction can be observed. Then, ion etching is performed on the same surface using ESCA (Electron Spectroscopy for Chemical Analysis), and the crystal grains of the surface parallel to the plate thickness direction are measured using the EBSD (Electron Back Scattering Diffraction) method.

[0018] The measurement by the EBSD method is performed using a scanning electron microscope (manufactured by JEOL Ltd., FE-SEM7000F), and the acceleration voltage of the measurement device is set to 20 kV. The above polishing for surface observation is performed 20 μm in the plate thickness direction from the surface of each test material. Then, a 1000 μm × 1000 μm region is measured under the condition of a measurement interval of 2 μm.

[0019] Here, on the surface being observed, the boundary where the orientation difference with the surrounding crystal grains is 15° or more is defined as the crystal grain boundary, and the region enclosed by the crystal grain boundary with equal orientation is defined as the crystal grain. The equivalent circular diameter based on the projected area of ​​the crystal grain is defined as the crystal grain size, and the average crystal grain size calculated by a weighted average based on the area of ​​all crystal grain sizes is defined as the average crystal grain size on the alloy plate surface.

[0020] Among the crystal orientation distributions on the surface of the alloy plate, the Brass orientation ({011} <211> The area ratio of ) is 11% or less, which reduces minute waviness. The crystal orientation on the surface of the alloy plate is diverse, but among them, the Brass orientation ({011} <211> We found that certain orientations, such as ), are effective in ensuring uniformity during etching and zincate treatments, which are pre-processing steps for plating, and as a result, can reduce minute undulations. The above area ratio is preferably 10% or less, and more preferably 9% or less. There is no particular lower limit to the area ratio, but it is usually 2% or more.

[0021] In this specification, the Brass orientation ({011}) of the alloy plate surface is used. <211> The area ratio of ) will be the value obtained by analyzing using the EBSD method. The specific procedure is as follows. Similar to the measurement of the average grain size on the alloy plate surface, each test material is polished to a mirror finish by 20 μm in the thickness direction from the surface. Then, an EBSD measurement is performed on a 1000 μm × 1000 μm area with a measurement interval of 2 μm. Subsequently, crystal orientation analysis is performed, and components within 15° of the ideal orientation are analyzed as components of the same orientation. Based on the above, the Brass orientation ({011} <211> ) calculate the area and, from the ratio to the total area of ​​the analysis region, determine the Brass orientation ({011} <211> Calculate the area ratio of ).

[0022] The composition of the alloy plate according to this embodiment is such that Mn is 0.1% by mass or less, Mg, Cr, Fe, Si, Cu, and Zn satisfy the above-mentioned specific ranges, and the remainder is impurities and Al. Let's explain each component.

[0023] (Mg:3.0~6.5% by mass) Mg is an effective element for improving the yield strength of alloy sheets. From the viewpoint of obtaining sufficient yield strength and good impact resistance as an alloy sheet, the Mg content is 3.0 mass% or more, preferably 3.3 mass% or more, and more preferably 3.7 mass% or more. On the other hand, from the viewpoint of preventing increased crack susceptibility at high temperatures and the occurrence of cracks during hot rolling, which would make rolling difficult, the Mg content is 6.5 mass% or less, preferably 6.0 mass% or less, more preferably 5.8 mass% or less, and even more preferably 5.5 mass% or less.

[0024] (Mn: 0.1% by mass or less) Mn has the property of reducing the average grain size on the surface of the alloy plate, but it is also a component that reduces grindability. Therefore, the Mn content is 0.1% by mass or less, preferably less than 0.1% by mass, more preferably 0.06% by mass or less, even more preferably 0.03% by mass or less, and may not be included at all. Therefore, there is no particular limit to the lower limit of the Mn content, but for example, it may be 0.0001% by mass or more.

[0025] (Cr:0.01~0.35% by mass) Cr precipitates as fine compounds in aluminum alloys, acting as a nucleation site for recrystallized grains and refining the microstructure by inhibiting grain growth. It also contributes to improving the yield strength of the alloy sheet. Therefore, the Cr content is 0.01% by mass or more, preferably 0.02% by mass or more, and more preferably 0.04% by mass or more. On the other hand, from the viewpoint of preventing increased anisotropy of the crystalline texture and the resulting generation of minute undulations, the Cr content is 0.35% by mass or less, preferably 0.20% by mass or less, and more preferably 0.15% by mass or less.

[0026] (Ti and Zr) Ti and Zr are not essential, but they are components that have similar properties to Cr. When at least one of Ti and Zr is included, the total content of Cr, Ti, and Zr is preferably greater than 0.01% by mass, more preferably 0.02% by mass or more, and even more preferably 0.04% by mass or more. On the other hand, the total content is preferably 0.40% by mass or less, more preferably 0.20% by mass or less, and even more preferably 0.15% by mass or less.

[0027] (Fe: 0.1% by mass or less) Fe is typically present in aluminum alloys as a metal impurity, and Al-Fe intermetallic compounds crystallize during the casting process. During mirror finishing processes such as cutting and grinding when manufacturing blanks and substrates from alloy sheets, Al-Fe intermetallic compounds may detach from the surface, forming pits. Additionally, Al-Fe intermetallic compounds may dissolve during acid etching, also forming pits. These formed pits may reduce the surface smoothness of the plating film formed during the plating process. Therefore, the Fe content should be 0.1% by mass or less, preferably 0.08% by mass or less, and more preferably 0.05% by mass or less. There is no particular lower limit to the Fe content, but as mentioned above, since Fe is mixed into the aluminum alloy as a metal impurity, it is extremely difficult to achieve 0% by mass, i.e., no Fe content. From the standpoint of raw material procurement costs, the Fe content may be 0.003% by mass or more, or 0.005% by mass or more. Furthermore, within the above range, Fe may be actively included.

[0028] (Si: 0.1% by mass or less) Si is typically present in aluminum alloys as a metal impurity, and during processes such as casting aluminum alloy ingots, it generates Mg-Si intermetallic compounds on the surface of the aluminum alloy ingots and alloy sheets. During mirror finishing processes such as cutting and grinding when manufacturing blanks and substrates from alloy sheets, Mg-Si intermetallic compounds may detach from the surface, forming pits. In addition, Mg-Si intermetallic compounds may dissolve during acid etching, also forming pits. The formed pits may reduce the surface smoothness of the plating film formed by the plating process. Therefore, the Si content should be 0.1% by mass or less, preferably 0.08% by mass or less, and more preferably 0.05% by mass or less. While there is no particular lower limit to the Si content, as mentioned above, it is extremely difficult to achieve 0% by mass, i.e., no Si content, because Si is mixed into the aluminum alloy as a metal impurity. From the standpoint of raw material procurement costs, the Si content may be 0.003% by mass or more, or 0.005% by mass or more. Furthermore, within the above range, Si may be actively included.

[0029] (Cu:0.01~0.5% by mass, Zn:0.01~0.5% by mass) Cu is an effective element for improving plating properties. When an aluminum alloy sheet is used as a blank, Cu uniformly dissolves in the blank and, during zincate treatment, has the effect of uniformly depositing Zn ions from the zincate bath onto the surface of the blank, i.e., the substrate. Therefore, the inclusion of Cu in the alloy sheet allows for the uniform formation of a zincate film, suppressing the generation of nodules on the surface of the plated film, and as a result, improving the smoothness of the plated surface. Like copper, zinc suppresses the formation of nodules on the surface of the plated film. Furthermore, as the zinc content increases, it becomes easier for zinc to act as an etching initiation point and a site for Zn ion deposition during acid etching and zincate treatment. As a result, it can effectively suppress steps caused by crystal grains.

[0030] From the above perspective, the Cu content is 0.01% by mass or more, and the Zn content is 0.01% by mass or more, satisfying at least one of these conditions. If Cu is included, the Cu content is 0.01% by mass or more, and may be 0.02% by mass or more. If Zn is included, the Zn content is 0.01% by mass or more, preferably 0.02% by mass or more, more preferably 0.08% by mass or more, and even more preferably 0.1% by mass or more.

[0031] On the other hand, in order to prevent Cu from precipitation at grain boundaries, which would lead to over-etching of the grain boundaries during acid etching, the formation of pits, and the generation of a large amount of nodules on the surface of the plating film, the Cu content is preferably 0.5% by mass or less, more preferably 0.2% by mass or less, and more preferably 0.1% by mass or less. Furthermore, in addition to the above-mentioned viewpoints regarding Cu, from the viewpoint of suppressing the decrease in the smoothness of the plating film surface due to the increase in pits associated with the development of Zn deposition nuclei, the Zn content is preferably 0.5% by mass or less, more preferably 0.4% by mass or less, and more preferably 0.35% by mass or less. The total content of Cu and Zn is not particularly limited as long as the individual content of Cu and Zn is within the above range, but for example, it is preferably 0.01% by mass or more, and more preferably 0.03% by mass or more. The upper limit of the above total content is, for example, 1.0% by mass or less.

[0032] (Remainder) The basic components of the composition of the aluminum alloy sheet are as described above, with the remainder being Al and impurities. Impurities are components other than those mentioned above that may be present depending on the selection of raw materials used in the ingot manufacturing process, but their presence is permissible as long as it does not impair the properties of the aluminum alloy sheet. Examples of impurities include V, B, Ni, Na, Pb, Be, Ca, Sn, In, Cd, Bi, Ge, etc.

[0033] Impurities include not only unavoidable impurities that are unintentionally and inevitably present, but also impurities that are intentionally added to the extent that they do not hinder the effects of the present invention. Unavoidable impurities are generally those that are inevitably mixed in when the raw materials are dissolved. Impurities such as V, B, Ni, Na, Pb, Be, Ca, Sn, In, Cd, Bi, and Ge may be present as unavoidable impurities, but they may also be added intentionally. The content of each impurity component is preferably 0.005% by mass or less, and the total content of the impurity components is preferably 0.015% by mass or less.

[0034] As for the remainder of the aluminum alloy sheet, the Al purity, i.e., the Al content, is preferably 85% by mass or more, and more preferably 92% by mass or more.

[0035] The aluminum alloy sheet according to this embodiment exhibits reduced minute waviness after plating. As an indicator of the degree of reduction, the root mean square waviness (Wq) on the surface of the substrate after pre-plating treatment can be used, which is obtained by converting the alloy sheet into an alloy blank and then into an alloy substrate. Pre-plating treatment involves sequentially performing degreasing using an alkaline cleaning agent, acid etching, desmatting, zincate treatment, zinc removal treatment, and a second zincate treatment on a mirror-finished substrate. Root mean square waviness (Wq) is the height represented by the root mean square of the reference length, and represents the standard deviation of surface roughness. In this specification, it refers to the value obtained by surface observation using a three-dimensional white light interference microscope in accordance with JIS B 0601-6:2014.

[0036] For evaluating the root mean square waviness (Wq), the substrate used will be an aluminum alloy substrate that has undergone the following pre-plating treatment. First, the substrate is degreased by immersing it in a 50°C pre-plating solution (AD-68F, manufactured by Uemura Kogyo Co., Ltd.) for 5 minutes. Next, it is acid-etched by immersing it in a 65°C pre-plating solution (AD-101F, manufactured by Uemura Kogyo Co., Ltd.) for 2 minutes. Then, it is de-matted by immersing it in 22% nitric acid at 20°C for 30 seconds, followed by zincate treatment using a 20°C zincate treatment solution (AD-301F-3X, manufactured by Uemura Kogyo Co., Ltd.) for 30 seconds. Next, it is immersed in 22% nitric acid to dissolve Zn, then zincate treatment is performed again under the same conditions as above, and finally, it is immersed in 22% nitric acid again to dissolve Zn, thereby obtaining a substrate for evaluating minute waviness.

[0037] If the root mean square waviness (Wq) measured using the micro-waviness evaluation substrate obtained above is 14 nm or less, it can be said that the reduction effect of micro-waviness after plating is good, and if it is 13 nm or less, it is even better; the smaller the value, the better. On the other hand, the root mean square waviness (Wq) is usually 5 nm or more.

[0038] <Aluminum alloy blank for magnetic disks> The aluminum alloy blank for magnetic disks according to this embodiment is obtained from the alloy plate described above as <Aluminum alloy plate for magnetic disks>. A conventionally known method can be used to obtain the blank, for example, by punching an aluminum alloy sheet into a disc shape using press forming, followed by a stacking and annealing process. After that, the inner and outer edges of the disc-shaped sheet material may be processed as desired.

[0039] The chemical composition of the resulting blank will be the same as that of the alloy sheet, without any change. Furthermore, the characteristic values ​​on the blank surface, including the average grain size and crystal orientation distribution, will be equivalent to those of the alloy sheet. Therefore, characteristic values ​​obtained for the alloy sheet can be considered as characteristic values ​​for the blank. Conversely, characteristic values ​​obtained for the blank can also be considered as characteristic values ​​for the alloy sheet.

[0040] <Aluminum alloy substrate for magnetic disks> The aluminum alloy substrate for magnetic disks according to this embodiment is obtained from the blank described in the above-mentioned <Aluminum alloy blank for magnetic disks>. A substrate can be obtained using conventionally known methods, for example, by performing a mirror finish by grinding the surface of the blank until the desired thickness is achieved. Alternatively, the end faces of the blank may also be machined by cutting.

[0041] The chemical composition of the resulting substrate remains unchanged from that of the blank, exhibiting the same composition. Furthermore, various characteristic values ​​on the substrate surface, including average grain size and crystal orientation distribution, are equivalent to those of the blank. Therefore, characteristic values ​​obtained for alloy plates or blanks can be considered as characteristic values ​​for the substrate. Conversely, characteristic values ​​obtained for the substrate can also be considered as characteristic values ​​for alloy plates or blanks.

[0042] A magnetic disk is obtained by first performing a pre-plating treatment on the obtained substrate as desired, followed by the formation of a plating film by plating with Ni-P or the like, surface polishing, and the formation of an undercoat, magnetic film, and protective film in that order.

[0043] <Manufacturing method for aluminum alloy plates for magnetic disks> The present embodiment provides a method for manufacturing an aluminum alloy plate for magnetic disks that satisfies the following conditions: Mg: 3.0 to 6.5 mass%, Mn: 0.1 mass% or less, Cr: 0.01 to 0.35 mass%, Fe: 0.1 mass% or less, Si: 0.1 mass% or less, and at least one of Cu: 0.01 to 0.5 mass% and Zn: 0.01 to 0.5 mass%, with the remainder being impurities and Al. The aluminum alloy sheet obtained by the above manufacturing method has an average grain size of 45 μm or less on its surface, and of the crystal orientation distribution on the surface, the Brass orientation ({011} <211> It is preferable that the area ratio of ) is 11% or less. Other preferred embodiments of the aluminum alloy plate are the same as those described above for <Aluminum alloy for magnetic disks>.

[0044] The method for manufacturing an aluminum alloy plate for a magnetic disk according to this embodiment includes steps 3 and 4 below, wherein the number of stands for hot finishing rolling is n, where n is a natural number of 2 or more, and the logarithmic reduction strain of the i-th stand is ε i In this case, the following relation (1) is satisfied. Step 3: Hot rough rolling process to obtain a hot rough rolled plate by hot rough rolling the homogenized ingot. Process 4: Hot finishing rolling process to obtain a hot-finished rolled sheet by hot finishing rolling the hot-roughed sheet.

[0045]

number

[0046] The processes other than steps 3 and 4 described above are not particularly limited and can be manufactured using general manufacturing methods and equipment for producing aluminum alloy plates for magnetic disks.

[0047] As an example, the method for manufacturing an alloy sheet preferably includes the following steps 1 to 5 in order. Process 1: A casting process in which raw materials are melted and the molten metal, adjusted to a predetermined chemical composition, is cast into an ingot. Step 2: Homogenization heat treatment process in which the cast ingot is subjected to homogenization heat treatment. Step 3: Hot rough rolling process to obtain a hot rough rolled plate by hot rough rolling the homogenized ingot. Process 4: Hot finishing rolling process to obtain a hot-finished rolled sheet by hot finishing rolling the hot-roughed sheet. Process 5: Cold rolling process to obtain a cold-rolled sheet by cold-rolling a hot-rolled sheet. Furthermore, if the above step 2 has been completed, step 3 can be reinterpreted as a hot rough rolling step in which the homogenized heat-treated ingot is hot rough-rolled to obtain a hot rough-rolled plate. The following explains the process step by step, starting from Step 1.

[0048] (Step 1: A casting process in which raw materials are melted and the molten metal, adjusted to a predetermined chemical composition, is cast into an ingot.) The raw material, aluminum alloy, can be melted at, for example, 700-800°C. Furthermore, it is preferable to perform dehydrogenation by blowing an inert gas such as argon (Ar) into the molten metal during the melting process. After melting, the ingot is cast using a known semi-continuous casting method such as DC casting. The cast ingot may be subjected to surface grinding or other treatments as desired. The amount of surface grinding can be appropriately adjusted considering the degree of segregation, but for example, 3 to 20 mm per side is preferred.

[0049] (Step 2: Homogenization heat treatment process in which the cast ingot is subjected to homogenization heat treatment) Homogenization heat treatment can be performed by holding the ingot obtained in step 1 at a temperature of, for example, 400 to 600°C for 0.5 to 48 hours. This allows for sufficient solid solution of Mg-Si intermetallic compounds such as Mg2Si. The heat treatment temperature is more preferably 500°C or higher, even more preferably 530°C or higher, even more preferably 570°C or lower, and even more preferably 560°C or lower. The heat treatment time is more preferably 2 hours or more, even more preferably 4 hours or more, even more preferably 12 hours or less, and even more preferably 10 hours or less.

[0050] (Step 3: Hot rough rolling process to obtain a hot rough rolled plate by hot rough rolling the homogenized ingot) Hot rough rolling starts at a temperature of 490°C or higher, and the ingot is rolled to a thickness of, for example, 20 to 50 mm using a reverse-type hot rough rolling mill.

[0051] (Process 4: Hot finishing rolling process to obtain a hot-finished rolled sheet by hot finishing rolling of a hot-roughed sheet) The hot finish rolling performed immediately after hot rough rolling is carried out on n stands, where n is a natural number of 2 or more. For the entire hot finish rolling from the first stand to the nth stand, that is, the last stand, for example, the starting temperature is set to 400 °C or higher and the finishing temperature is set to 300 - 350 °C. Also, it is preferable to finish the temperature range from 490 °C to 400 °C within 30 minutes, and more preferably within 10 minutes. From the viewpoint of preventing the occurrence of Lüder's bands in the subsequent cold rolling in step 5, the finishing temperature is preferably 300 °C or higher. Since Lüder's bands do not remain on the surface after grinding, although it does not affect the function as a substrate for magnetic disks, it impairs the aesthetics of the alloy plate and blank before grinding. By finishing the temperature range from 490 °C to 400 °C within 30 minutes, coarsening and precipitation of Mg - Si based intermetallic compounds such as Mg2Si can be suppressed.

[0052] For the n stands, the logarithmic strain ε1 to ε n-1 in the 1st to (n - 1)th stands and the logarithmic strain ε n in the nth stand, which is the last stand, are set to satisfy the following relational expression (1).

[0053]

Equation

[0054] The logarithmic strain ε is the value obtained by taking the natural logarithm of the ratio of the thickness of the plate before hot finish rolling by a certain stand to the thickness of the plate after hot finish rolling by the same stand. For example, when the thickness of the hot rough rolled plate after passing through step 3 is t1 and the thickness after hot finish rolling by the first stand is t2, the logarithmic strain ε1 in the first stand is log e (t1 / t2). Similarly, the logarithmic strain ε i in the ith stand is loge(t i / t i+1 ). Here, t iThis is the thickness of the plate after hot finishing rolling by the (i-1)th stand, i.e., the thickness of the plate before hot finishing rolling by the i-th stand. Also, t i+1 This refers to the thickness of the plate after hot finishing rolling by the i-th stand.

[0055] In other words, if there are 3 stands, the value represented by {ε3-(ε1+ε2) / 2} should be set to be -0.15 or greater, and if there are 4 stands, the value represented by {ε4-(ε1+ε2+ε3) / 3} should be set to be -0.15 or greater.

[0056] ε1~ε such that the above relation (1) is satisfied n By adjusting the value of , for reasons that are not entirely clear, the average grain size of the resulting alloy plate surface becomes smaller, and the area ratio of the Brass orientation in the crystal orientation distribution on the surface also becomes smaller.

[0057] As a way to satisfy relation (1), ε n A method to make the value of larger than before, ε1~ε n-1 Methods include reducing the value of the variable compared to conventional methods, or both. ε n To increase the value of compared to conventional methods, for example, one method is to increase the reduction amount or reduction ratio by the nth stand compared to conventional methods. ε1~ε n-1 To reduce the value of the first stand to the (n-1)th stand, for example, one method is to reduce the reduction amount or reduction ratio compared to the conventional method.

[0058] The left-hand side of relation (1) should be -0.15 or greater, but -0.13 or greater is more preferable. Furthermore, there is no particular upper limit, but from the viewpoint of improving the distortion of the sheet after hot finishing rolling, 0.60 or less is preferable.

[0059] The thickness of the hot-finished rolled sheet finally obtained in step 4 can be, for example, 8 mm or less, more preferably 7 mm or less, and even more preferably 6 mm or less. The lower limit can be, for example, 1.5 mm or more, more preferably 1.8 mm or more, and even more preferably 2.0 mm or more.

[0060] (Step 5: Cold rolling process to obtain a cold-rolled sheet by cold-rolling a hot-finished rolled sheet) From the viewpoint of accumulating the strain energy necessary to refine the crystal grains after stacking annealing when forming blanks from alloy sheets, a reduction ratio of 50% or more is preferable in cold rolling, and more preferably 70% or more. This allows for a more favorable reduction in waviness after plating, and also results in good yield strength when used as blanks or substrates.

[0061] Intermediate annealing may be performed before or during cold rolling. In this case, it is preferable to perform cold rolling with a cold rolling ratio of 70% or more after intermediate annealing. The thickness of the cold-rolled sheet after cold rolling is determined according to the desired thickness for the alloy sheet, blank, or substrate. Cold rolling may be repeated multiple times to achieve the desired thickness. Examples of cold-rolled sheet thicknesses include 1.3 mm, 1 mm, 0.9 mm, 0.8 mm, and 0.7 mm.

[0062] Although the alloy plate, blank, and substrate according to this embodiment are obtained by the above method, other processes may be carried out between or before / after each process, as long as they do not adversely affect each process. [Examples]

[0063] 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 can be implemented with modifications to the extent that is consistent with its spirit, and all such modifications are included within the technical scope of the present invention.

[0064] (Examples and Comparative Examples) The raw materials were melted at 700°C, and the composition was adjusted to match the component compositions shown in Table 1, No. 1 to No. 3, and an ingot was cast. The ingot was then surface-machined to remove the segregation layer on its surface. (Step 1) Next, the ingot underwent a homogenization heat treatment, holding it at 530-560°C for 4-12 hours. (Step 2) Immediately after homogenization heat treatment, hot rough rolling was started, followed by hot finish rolling. Hot finish rolling was performed using four stands, and the values ​​of the left-hand side of equation (1), using the logarithmic reduction strains ε1 to ε4 at each stand, are shown in Table 2. The entire hot rolling process was completed within 10 minutes, reaching a temperature of 490°C to 410°C. (Steps 3 and 4) The obtained hot-rolled sheet was cold-rolled. The cold-rolling process involved multiple passes to ensure the material temperature did not exceed 100°C, resulting in a final sheet thickness of 1.3 mm, thus obtaining an aluminum alloy sheet for magnetic disks. (Step 5) Note that No. 1 and No. 2 are examples, and No. 3 is a comparative example.

[0065] [Table 1]

[0066] (Evaluation: average surface grain size) The obtained aluminum alloy plate was polished to a mirror finish so that a surface parallel to the thickness direction could be observed. Subsequently, ion etching was performed on this surface using ESCA (Electron Spectroscopy for Chemical Analysis), and the crystal grains on the surface parallel to the thickness direction were measured using the EBSD (Electron Back Scattering Diffraction) method. Measurements using the EBSD method were performed using a scanning electron microscope (FE-SEM7000F, manufactured by JEOL Ltd.), with the acceleration voltage of the measurement device set to 20kV. The polishing described above for surface observation was performed on a 20 μm area in the thickness direction from the surface of each test material. Then, a 1000 μm × 1000 μm area was measured with a measurement interval of 2 μm. Here, on the observed surface, the boundary where the orientation difference with the surrounding crystal grains is 15° or more was defined as the grain boundary, and the region enclosed by the grain boundary with equal orientation was defined as the crystal grain. The equivalent diameter of the projected area circle of the crystal grain was defined as the crystal grain size, and the average crystal grain size calculated by a weighted average based on area relative to the crystal grain size of all particles was defined as the average crystal grain size on the alloy plate surface. The results are shown in "Average Crystal Grain Size" in Table 2. In Table 2, the evaluation is as follows: ◎ indicates excellent if the average crystal grain size is 25 μm or less, ○ indicates good if it is between 25 μm and 45 μm, and × indicates poor if it is greater than 45 μm.

[0067] (Evaluation: Brass orientation on the surface ({011} <211> (area ratio) The obtained aluminum alloy plates were polished to a mirror finish by 20 μm in the thickness direction from the surface, similar to the measurement of the average grain size on the surface. Then, EBSD measurements were performed on a 1000 μm × 1000 μm area with a measurement interval of 2 μm. Afterward, crystal orientation analysis was performed, and components within 15° of the ideal orientation were analyzed as components of the same orientation. Among these, the Brass orientation ({011}) was analyzed. <211> The area ratio of ) was calculated. The results are shown in Table 2, "Brass Azimuth Area Ratio". In Table 2, the evaluation is as follows: if the area ratio of the Brass orientation is 9% or less, it is marked as excellent (◎); if it is between 9% and 11%, it is marked as good (○); and if it is above 11%, it is marked as poor (×).

[0068] (Evaluation: Minor waviness after plating) The obtained aluminum alloy plate was used as an aluminum alloy blank, and then as an aluminum alloy substrate. The minute waviness on the substrate surface after plating was then evaluated. As an indirect indicator for evaluating minute waviness after plating, the root mean square waviness (Wq) on the surface of the substrate after pre-plating treatment was determined using the following method.

[0069] The obtained aluminum alloy sheet was punched out into a disc shape with an outer diameter of 95 mm and an inner diameter of 25 mm, subjected to pressure annealing called stack annealing, and then the end faces were processed to obtain an aluminum alloy blank for a 3.5-inch HDD. Stack annealing was performed by heating to 200-280°C at a heating rate of 50°C / h or more, followed by holding at 300-400°C for no more than 7 hours. Next, the surface of the blank was ground to a mirror finish using a diamond cutting tool to obtain an aluminum alloy substrate.

[0070] The obtained aluminum alloy substrate was subjected to the following pre-plating treatment. First, the substrate was degreased by immersing it in a 50°C pre-plating solution (AD-68F, manufactured by Uemura Kogyo Co., Ltd.) for 5 minutes. Next, it underwent acid etching by immersing it in a 65°C pre-plating solution (AD-101F, manufactured by Uemura Kogyo Co., Ltd.) for 2 minutes. Then, it underwent de-matting by immersing it in 22% nitric acid at 20°C for 30 seconds, followed by zincate treatment using a 20°C zincate treatment solution (AD-301F-3X, manufactured by Uemura Kogyo Co., Ltd.) for 30 seconds. Next, it was immersed in 22% nitric acid to dissolve Zn, and then zincate treatment was performed again under the same conditions as above. Finally, it was immersed in 22% nitric acid again to dissolve Zn, and the substrate after pre-plating treatment was obtained. This was used as a substrate for evaluating minute waviness.

[0071] The substrate used for evaluating micro-undulations, obtained as described above, was observed using a 3D white light interference microscope (Contour GTX3, Bruker Nano Inc.). The results were then analyzed using the included analysis software (Vision64, Version 5.4) for the microscope. Six fields of view, each measuring 1088 μm × 816 μm, were captured, and undulations with wavelengths between 10 and 500 μm were measured. The results are shown in Table 2 under "Micro-undulations". In Table 2, the evaluation is as follows: if the root mean square waviness (Wq) value is 12 nm or less, it is marked with ◎, indicating very good; if it is between 12 nm and 14 nm, it is marked with ○, indicating good; and if it is above 14 nm, it is marked with ×, indicating poor.

[0072] [Table 2]

[0073] From the above results, it was found that by using a reduction logarithmic strain that satisfies relation (1) in the hot finishing rolling process, the average grain size of the surface can be reduced, and the area ratio of the Brass orientation in the crystal orientation distribution can be reduced. As a result, it was found that aluminum alloy sheets, blanks, and substrates that can reduce minute waviness after plating can be obtained even without actively including Mn.

Claims

1. Mg: 3.0 to 6.5% by mass, Mn: 0.1% by mass or less, Cr: 0.01 to 0.35% by mass, Fe: 0.1% by mass or less, Si: 0.1% by mass or less, At least one of Cu: 0.01 to 0.5 mass% and Zn: 0.01 to 0.5 mass% An aluminum alloy plate that satisfies the following conditions, with the remainder being impurities and Al, The average grain size on the surface is 45 μm or less. An aluminum alloy plate for magnetic disks, wherein the area ratio of the Brass orientation ({011}<211>) in the crystal orientation distribution on the surface is 11% or less.

2. The aluminum alloy plate for magnetic disks according to claim 1, wherein the average crystal grain size is 25 μm or less.

3. An aluminum alloy blank for magnetic disks obtained from an aluminum alloy plate for magnetic disks according to claim 1 or 2.

4. An aluminum alloy substrate for magnetic disks obtained from an aluminum alloy blank for magnetic disks as described in claim 3.

5. Mg: 3.0 to 6.5% by mass, Mn: 0.1% by mass or less, Cr: 0.01 to 0.35% by mass, Fe: 0.1% by mass or less, Si: 0.1% by mass or less, At least one of Cu: 0.01 to 0.5 mass% and Zn: 0.01 to 0.5 mass% A method for manufacturing an aluminum alloy plate for magnetic disks that satisfies the following conditions, with the remainder being impurities and Al, A hot rough rolling process is performed to obtain a hot rough rolled plate by hot rough rolling a homogenized ingot, The process includes a hot finishing rolling step, in which the hot rough-rolled sheet is hot-finished-rolled to obtain a hot-finished-rolled sheet, The number of stands for performing the hot finishing rolling is n, where n is a natural number of 2 or more. The logarithmic distortion of the i-th stand is ε ｉ A method for manufacturing an aluminum alloy plate for magnetic disks that satisfies the following relation (1). [Math 1]

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