Aluminum alloy plate for magnetic disk, method for manufacturing same, aluminum alloy blank for magnetic disk, and aluminum alloy substrate for magnetic disk

Abstract

Provided is an aluminum alloy plate for a magnetic disk, which is capable of reducing fine waviness after plating even if the content of Mn is low. Provided is an aluminum alloy plate for a magnetic disk, the aluminum alloy plate satisfying 3.0-6.5 mass% of Mg, 0.1 mass% or less of Mn, 0.01-0.35 mass% of Cr, 0.1 mass% or less of Fe, and 0.1 mass% or less of Si, and satisfying at least one of 0.01-0.5 mass% of Cu and 0.01-0.5 mass% of Zn, the remainder comprising impurities and Al, the average crystal grain diameter of the surface being 45 [mu] m or less, and the area ratio of the Brass orientation ({011} < 211 >) in the crystal orientation distribution of the surface being 11% or less.

Description

Technical Field

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

[0002] With the digitization of information and the widespread use of the internet, the processing of massive amounts of digital data has led to a demand for larger capacity hard disk drives (HDDs) centered around data centers. Along with the increase in HDD capacity, it is necessary to improve the recording density of the disks. For improving recording density, it is crucial to reduce the waviness of the plated surface after plating.

[0003] The waviness of a coating surface can be categorized into short-wavelength waviness and micro-waviness. Short-wavelength waviness refers to waviness with wavelengths below tens of μm. Micro-waviness, on the other hand, refers to waviness with wavelengths ranging from tens to hundreds of μm, which are relatively long.

[0004] Short-wavelength waviness can be removed by post-plating grinding of the coating surface, but minute waviness cannot be fully removed by the same grinding process. This is because minute waviness is caused by unevenness resulting from differences in etchability due to grain orientation differences during pre-plating treatment.

[0005] Minor waviness, especially noticeable when the grain diameter is large and uneven, is a cause of reduced disk performance.

[0006] In response, Patent Document 1 discloses an aluminum alloy substrate for disks with a specific composition, wherein the number of intermetallic compounds with a maximum length greater than 5 μm is 1 per mm. 2 The average grain diameter is 20 μm or less. This reduces the minute waviness of the Ni-P coating surface. Furthermore, Patent Document 2 discloses an aluminum alloy blank for disks with a specific composition, wherein the average grain diameter on the surface is 27 μm or less, the aspect ratio of the average grain diameter on the surface is 1.2 or less, and the yield strength is 140 MPa or more. This allows for the production of an aluminum alloy blank with sufficient impact resistance, minimal minute waviness on the coated surface, and few surface defects.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2009-242843

[0010] Patent Document 2: Japanese Patent Application Publication No. 2017-014584 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] The aluminum alloy substrate or aluminum alloy blank in the aforementioned Patent Documents 1 and 2 contains Mn, which precipitates as a fine intermetallic compound and plays a role in inhibiting grain growth. That is, it is a component that refines the grains and reduces the degree of micro-ripples.

[0013] On the other hand, the addition of Mn is one reason for the reduced machinability in mirror finishing and other processes when the aluminum alloy blank is used as a blank.

[0014] The present invention is made in view of the following circumstances, and its object is to provide an aluminum alloy plate for disks that can reduce the minute waviness after plating even with a low Mn content, and a method for manufacturing the same.

[0015] In addition, its purpose is to provide an aluminum alloy blank for disks and an aluminum alloy substrate for disks obtained from the aforementioned aluminum alloy sheet for disks.

[0016] Problem-solving methods

[0017] To address the aforementioned issues, the inventors conducted intensive research, achieving grain refinement by reducing the average grain diameter on the aluminum alloy plate surface without adding large amounts of Mn. However, it was found that this alone had limited effect on reducing the minute waviness after plating. Therefore, further research was conducted focusing on the grain aggregation structure. The results showed that by selectively increasing specific crystal orientations on the aluminum alloy plate surface, the aforementioned issues could be resolved, thus completing this invention.

[0018] That is, the present invention relates to the following [1] to [5].

[0019] [1] An aluminum alloy plate for disks is an aluminum alloy plate that satisfies the following conditions: Mg: 3.0 to 6.5 wt%, Mn: 0.1 wt% or less, Cr: 0.01 to 0.35 wt%, Fe: 0.1 wt% or less, Si: 0.1 wt% or less, and satisfies at least one of Cu: 0.01 to 0.5 wt% and Zn: 0.01 to 0.5 wt%, with the balance including impurities and Al, wherein the average grain diameter on the surface is 45 μm or less, and the area fraction of Brass orientation ({011} <211>) in the crystal orientation distribution on the surface is 11% or less.

[0020] [2] The aluminum alloy plate for disks described in [1] above, wherein the average grain diameter is less than 25 μm.

[0021] [3] An aluminum alloy blank for disks obtained from the aluminum alloy sheet for disks described in [1] and [2] above.

[0022] [4] An aluminum alloy substrate for a disk obtained from the aluminum alloy blank for a disk described in [3] above.

[0023] [5] A method for manufacturing an aluminum alloy plate for a hard disk, wherein the aluminum alloy plate satisfies the following conditions: Mg: 3.0-6.5 wt%, Mn: less than 0.1 wt%, Cr: 0.01-0.35 wt%, Fe: less than 0.1 wt%, Si: less than 0.1 wt%, and satisfies at least one of Cu: 0.01-0.5 wt% and Zn: 0.01-0.5 wt%, with the balance including impurities and Al, wherein the method includes the following steps: hot rough rolling of a hot rough rolled plate obtained by hot rough rolling of a homogenized ingot; hot finish rolling of the hot rough rolled plate to obtain a hot finish rolled plate, wherein the number of stands for hot finish rolling is n, where n is a natural number greater than or equal to 2, and the logarithmic strain of the i-th stand is ε. i When, the following relation (1) is satisfied.

[0024] Formula 1

[0025]

[0026] The effects of the invention

[0027] According to the present invention, it is possible to obtain aluminum alloy plates for disks, aluminum alloy blanks for disks, and aluminum alloy substrates for disks that are Mn-free or have low Mn content, and which can reduce minute waviness after plating. As a result, the recording density of the disk can be increased. Detailed Implementation

[0028] The following describes in detail the methods used to implement this embodiment for the aluminum alloy plate for disks, the aluminum alloy blank for disks, and the aluminum alloy substrate for disks (hereinafter also referred to as "alloy plate", "blank", and "substrate", respectively).

[0029] <Aluminum Alloy Plate for Disks>

[0030] The aluminum alloy plate for disks in this embodiment satisfies the following conditions: Mg: 3.0 to 6.5% by mass, Mn: 0.1% or less by mass, Cr: 0.01 to 0.35% by mass, Fe: 0.1% or less by mass, Si: 0.1% or less by mass, and at least one of Cu: 0.01 to 0.5% by mass and Zn: 0.01 to 0.5% by mass, with the balance including impurities and Al.

[0031] Furthermore, the average grain diameter on the surface of the aluminum alloy plate for disks is less than 45 μm, and the area fraction of the Brass orientation ({011} < 211>) in the crystal orientation distribution on the surface is less than 11%.

[0032] The average grain diameter on the surface of the alloy plate is less than 45 μm, which can reduce micro-ripples. This is because, during the pre-plating processes, namely degreasing, etching, and zincate treatment, the unevenness of the grains caused by the difference in reactivity due to the crystal orientation difference of the aluminum alloy plate can be reduced.

[0033] The average grain diameter on the surface of the alloy plate is preferably 25 μm or less, more preferably 22 μm or less. There is no particular limitation on the lower limit of the average grain diameter, but it is generally 2 μm or more.

[0034] In this specification, the average grain diameter on the surface of the alloy plate is a value measured in the following manner.

[0035] That is, test pieces are cut from each test material (bulk) and ground to make the surface parallel to the thickness direction of the plate observable, serving as a mirror surface. Subsequently, ion etching is performed on the same surface using ESCA (Electron Spectroscopy for Chemical Analysis), and the grains on the surface parallel to the thickness direction are measured using EBSD (Electron Back Scattering Diffraction).

[0036] The measurements were performed using the EBSD method with a scanning electron microscope (manufactured by Nippon Electron Ltd., FE-SEM7000F) and an accelerating voltage of 20 kV.

[0037] The above-mentioned grinding for surface observation was performed 20 μm along the thickness direction from the surface of each test material. Based on this, a 1000 μm × 1000 μm area was measured at 2 μm intervals.

[0038] Here, on the observed surface, the boundary with an orientation difference of 15° or more from the surrounding grains is defined as the grain boundary, and the region with equal orientation enclosed by the grain boundary is defined as the grain. Then, the equivalent circle diameter based on the projected area of ​​the grain is defined as the grain diameter, and the average grain diameter calculated relative to the grain diameter of all particles by weighted averaging based on area is defined as the average grain diameter of the alloy plate surface.

[0039] Among the crystal orientation distributions on the surface of the alloy plate, the Brass orientation ({011}<211>) has an area fraction of less than 11%, which can reduce minute waviness. Although the crystal orientations on the surface of the alloy plate vary, the specific orientation of Brass orientation ({011}<211>) has been found to be effective for uniformity in the pre-plating processes, namely etching and zincate treatment, thereby reducing minute waviness.

[0040] The aforementioned area ratio is preferably 10% or less, more preferably 9% or less. There is no particular limitation on the lower limit of the area ratio, but it is generally 2% or more.

[0041] In this specification, the area fraction of the Brass orientation ({011}<211>) on the surface of the alloy plate is the value obtained by analysis using the EBSD method. The specific steps are described below.

[0042] Similar to the measurement of the average grain diameter on the alloy plate surface, each test material was polished to a mirror finish by grinding 20 μm along the thickness direction. Based on this, EBSD measurements were performed on a 1000 μm × 1000 μm region at 2 μm intervals. Subsequently, crystal orientation analysis was performed; regions within 15° of the ideal orientation were analyzed as having the same orientation composition. The area of ​​the Brass orientation ({011} < 211>) was calculated based on the area obtained above, and the area fraction of the Brass orientation ({011} < 211>) was calculated relative to the total area of ​​the analyzed region.

[0043] In the alloy plate of this embodiment, Mn is less than 0.1% by mass, Mg, Cr, Fe, Si, Cu and Zn meet the specific ranges mentioned above, and the balance is impurities and Al.

[0044] Each component is described.

[0045] (Mg: 3.0–6.5% by mass)

[0046] Mg is an effective element for improving the yield strength of alloy sheets. From the viewpoint of obtaining sufficient yield strength as an alloy sheet and achieving good impact resistance, the Mg content is 3.0% by mass or more, preferably 3.3% by mass or more, and more preferably 3.7% by mass or more. On the other hand, from the viewpoint of preventing increased crack sensitivity at high temperatures and preventing cracks from occurring during hot rolling, which would make rolling difficult, the Mg content is 6.5% by mass or less, preferably 6.0% by mass or less, more preferably 5.8% by mass or less, and even more preferably 5.5% by mass or less.

[0047] (Mn: less than 0.1% by mass)

[0048] Mn has the property of reducing the average grain diameter on the surface of alloy plates, but on the other hand, it reduces machinability. Therefore, the content of Mn is 0.1% by mass or less, preferably less than 0.1% by mass, more preferably less than 0.06% by mass, and even more preferably less than 0.03% by mass, or it may be absent. Therefore, there is no particular limitation on the lower limit of the Mn content, but it can be, for example, 0.0001% by mass or more.

[0049] (Cr: 0.01~0.35% by mass)

[0050] Cr precipitates as a fine compound in aluminum alloys, serving as the starting point for the formation of 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 in the aggregate structure of crystals, resulting in minute waviness, 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.

[0051] (Ti and Zr)

[0052] Ti and Zr are not essential, but they are components that have the same properties as Cr.

[0053] When at least one of Ti and Zr is present, the total content of Cr, Ti, and Zr is preferably higher 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.

[0054] (Fe: less than 0.1% by mass)

[0055] Fe is typically incorporated into aluminum alloys as a base metal impurity, causing Al-Fe intermetallic compounds to crystallize and precipitate during the casting process. During mirror finishing processes such as cutting or grinding when manufacturing blanks and substrates from alloy sheets, these Al-Fe intermetallic compounds may detach from the surface, forming pits. Furthermore, Al-Fe intermetallic compounds may dissolve due to acid etching, also forming pits. These pits can reduce the smoothness of the coating surface formed by plating. Therefore, the Fe content is 0.1% by mass or less, preferably 0.08% by mass or less, and more preferably 0.05% by mass or less.

[0056] There is no particular lower limit to the Fe content. As mentioned above, since it is mixed into the aluminum alloy as a base metal impurity, achieving 0% by mass (i.e., no Fe) is very difficult. From the perspective of raw material supply costs, the Fe content can be 0.003% by mass or more, or 0.005% by mass or more. Furthermore, as long as it falls within the above range, the presence of Fe is acceptable.

[0057] (Si: less than 0.1% by mass)

[0058] Si is typically incorporated into aluminum alloys as a base metal impurity. During processes such as casting aluminum alloy ingots, Mg-Si intermetallic compounds are formed on the surface of the ingots and alloy sheets. During mirror finishing processes such as cutting or grinding when manufacturing blanks and substrates from alloy sheets, these Mg-Si intermetallic compounds can detach from the surface, forming pits. Furthermore, Mg-Si intermetallic compounds may dissolve due to acid etching, also forming pits. These pits can reduce the smoothness of the coating surface formed by plating. Therefore, the Si content is 0.1% by mass or less, preferably 0.08% by mass or less, and more preferably 0.05% by mass or less.

[0059] There is no particular lower limit to the Si content, but as mentioned above, since it is mixed into the aluminum alloy as a base metal impurity, achieving 0% by mass (i.e., zero Si content) is very difficult. From the perspective of raw material supply costs, the Si content can be 0.003% by mass or more, or 0.005% by mass or more. Furthermore, as long as it falls within the above range, the presence of Si is acceptable.

[0060] (Cu: 0.01–0.5% by mass, Zn: 0.01–0.5% by mass)

[0061] Cu is an effective element for improving plating properties. When an aluminum alloy sheet is used as the blank, Cu is uniformly dissolved in the blank. During zincate treatment, Cu has the effect of uniformly and finely precipitating Zn ions from the zincate bath onto the blank, i.e., the surface of the substrate. Therefore, by containing Cu in the alloy sheet, a zincate film can be uniformly formed, inhibiting the formation of nodules on the coating surface. As a result, the smoothness of the coating surface is improved.

[0062] Like Cu, Zn inhibits the formation of nodules on the coating surface. Furthermore, with increasing Zn content, it readily becomes an etching initiation point during acid etching and a site for Zn ion deposition during zincate treatment. As a result, it effectively suppresses height differences caused by grain size.

[0063] Based on the above viewpoint, it satisfies at least one of the following: the Cu content is 0.01% by mass or more, and the Zn content is 0.01% by mass or more.

[0064] When Cu is present, the Cu content is 0.01% by mass or more, or 0.02% by mass or more.

[0065] When Zn is present, 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.

[0066] On the other hand, Cu precipitates at the grain boundaries, and the grain boundaries are over-etched during acid etching, resulting in pits. From the viewpoint of preventing the formation of nodules on the coating surface from becoming severe, the Cu content is 0.5% by mass or less, preferably 0.2% by mass or less, and more preferably 0.1% by mass or less.

[0067] In addition to the above-mentioned views related to Cu, since the pits increase with the development of Zn precipitation nuclei, which leads to a decrease in the smoothness of the coating surface, from the viewpoint of suppressing this, the Zn content is 0.5% by mass or less, preferably 0.4% by mass or less, and more preferably 0.35% by mass or less.

[0068] As long as the contents of Cu and Zn are within the above-mentioned ranges, the total content of Cu and Zn is not particularly limited, but is preferably 0.01% by mass or more, and more preferably 0.03% by mass or more. The upper limit of the total content is, for example, 1.0% by mass or less.

[0069] (margin)

[0070] The basic components that make up the aluminum alloy sheet are as described above, with the balance being Al and impurities.

[0071] Impurities are components other than those mentioned above, and are components that may be included depending on the choice of molten raw materials during the casting process, but are permitted to be present within a range that does not impair the properties of the aluminum alloy sheet. Examples of impurities include, for instance, V, B, Ni, Na, Pb, Be, Ca, Sn, In, Cd, Bi, and Ge.

[0072] Impurities include not only unavoidable impurities that are not intentionally included but are unavoidably present, but also impurities that are intentionally added to the extent that they do not impair the effects of the invention. Unavoidable impurities are generally impurities that are unavoidably mixed in during the melting of the raw materials.

[0073] As impurities, there are cases where V, B, Ni, Na, Pb, Be, Ca, Sn, In, Cd, Bi, Ge, etc. are unavoidably included, but there are also cases where they are actively added.

[0074] The content of each component as an impurity is preferably 0.005% by mass or less, and the total content of the impurity components is preferably 0.015% by mass or less.

[0075] As a margin for aluminum alloy sheets, Al purity is preferred, i.e., Al content is 85% by mass or more, and more preferably 92% by mass or more.

[0076] The aluminum alloy sheet of this embodiment reduces the minute waviness after plating. As an indicator of the degree of reduction, the root mean square waviness (Wq) of the substrate surface after pre-plating treatment, from the alloy sheet to the alloy blank, can be used.

[0077] The so-called pre-plating treatment is a process for mirror-finished substrates, which involves degreasing with alkaline cleaning agents, acid etching, cleaning, zincate treatment, Zn removal treatment, and a second zincate treatment.

[0078] The root mean square waviness (Wq) is the height of the reference length at the root mean square, representing the standard deviation of the surface roughness. In this specification, it means the value obtained by surface observation using a three-dimensional white light interferometer microscope, based on JIS B 0601-6:2014.

[0079] Furthermore, the substrate used for evaluating root mean square waviness (Wq) is prepared by pre-plating treatment of the aluminum alloy substrate under the following conditions.

[0080] First, the substrate is degreased by immersing it in a pre-plating treatment solution (manufactured by Uemura Industries, Ltd., AD-68F) at 50°C for 5 minutes. Next, it is acid-etched by immersing it in a pre-plating treatment solution (manufactured by Uemura Industries, Ltd., AD-101F) at 65°C for 2 minutes. Then, it is decontaminated by immersing it in 22% nitric acid at 20°C for 30 seconds, followed by zincate treatment in a zincate treatment solution (manufactured by Uemura Industries, Ltd., AD-301F-3X) at 20°C for 30 seconds. Next, it is first dissolved in 22% nitric acid, then zincate treatment is performed again under the same conditions, and finally, it is dissolved in 22% nitric acid again to obtain a substrate for evaluating minute waviness.

[0081] If the root mean square waviness (Wq) measured using a substrate for evaluating micro-waviness obtained in the manner described above is 14 nm or less, it can be said that the reduction effect of micro-waviness after plating is good; if it is 13 nm or less, it is even better, and the smaller the better. On the other hand, the root mean square waviness (Wq) is usually 5 nm or more.

[0082] <Aluminum alloy blank for disk>

[0083] The aluminum alloy blank for disks in this embodiment is obtained from the alloy plate described in the above-mentioned <Aluminum Alloy Plate for Disks>.

[0084] The blank can be obtained using existing known methods, for example, by punching an aluminum alloy sheet into a disc shape using a process such as pressure forming; followed by a stacking annealing process. Afterwards, the inner and outer periphery ends of the disc-shaped sheet can be face-machined as needed.

[0085] The chemical composition of the obtained billet is unchanged from that of the alloy plate, being the same. Furthermore, the characteristic values, primarily the average grain diameter and crystal orientation distribution on the billet surface, are also identical to those of the alloy plate. Therefore, the characteristic values ​​obtained for the alloy plate can be considered as characteristic values ​​for the billet. Conversely, the characteristic values ​​obtained for the billet can also be considered as characteristic values ​​for the alloy plate.

[0086] <Aluminum alloy substrate for hard disks>

[0087] The aluminum alloy substrate for disks in this embodiment is obtained from the blank described in the above-mentioned <Aluminum Alloy Blank for Disks>.

[0088] The substrate can be obtained using existing known methods, such as mirror finishing the surface of the blank or grinding it to the desired thickness. Alternatively, end-face machining by cutting the end face of the blank can also be performed.

[0089] The chemical composition of the obtained substrate remains unchanged compared to the billet, exhibiting the same composition. Furthermore, the characteristic values, primarily the average grain diameter and crystal orientation distribution on the substrate surface, are identical to those of the billet. Therefore, the characteristic values ​​obtained for the alloy plate and the billet can be considered as characteristic values ​​relating to the substrate. Conversely, the characteristic values ​​obtained for the substrate can also be considered as characteristic values ​​relating to the alloy plate and the billet.

[0090] The obtained substrate is subjected to pre-plating treatment as needed. Subsequently, it is subjected to plating treatment with Ni-P, etc. to form a coating, surface grinding, and the formation of a base film, magnetic film and protective film, etc., to obtain a disk.

[0091] <Manufacturing Method of Aluminum Alloy Plates for Disks>

[0092] The method for manufacturing an aluminum alloy plate for disk drives according to this embodiment is a method for manufacturing an aluminum alloy plate for disk drives that satisfies the following conditions: Mg: 3.0-6.5 wt%, Mn: 0.1 wt% or less, Cr: 0.01-0.35 wt%, Fe: 0.1 wt% or less, Si: 0.1 wt% or less, and satisfies at least one of Cu: 0.01-0.5 wt% and Zn: 0.01-0.5 wt%, with the balance including impurities and Al. The aluminum alloy plate obtained by the above manufacturing method has an average grain diameter of 45 μm or less on its surface, and preferably, the area fraction of the Brass orientation ({011} <211>) is 11% or less among the crystal orientation distributions on the surface. Other preferred embodiments of the aluminum alloy plate are the same as those described in the above-described <Aluminum Alloy Plate for Disks>.

[0093] The method for manufacturing aluminum alloy plates for hard disks according to this embodiment includes steps 3 and 4 below. The number of stands for hot precision rolling is n, where n is a natural number greater than or equal to 2. Let ε be the logarithmic strain of the i-th stand. i When, the following relation (1) is satisfied.

[0094] Step 3: Hot roughing rolling. The hot roughing process involves obtaining hot-rolled plates from homogenized ingots.

[0095] Process 4: Hot finishing rolling process to obtain hot finished plate from hot rough rolled plate.

[0096] Formula 2

[0097]

[0098] There are no particular limitations on the processes other than process 3 and process 4 mentioned above, and they can be manufactured using manufacturing methods and equipment under general conditions for manufacturing aluminum alloy plates for disks.

[0099] As an example, the manufacturing method of the alloy plate preferably includes the following steps 1 to 5 in sequence.

[0100] Process 1: The casting process of melting raw materials and casting the molten metal with the specified chemical composition into ingots;

[0101] Step 2: A homogenization heat treatment process for the cast ingots;

[0102] Step 3: Hot roughing process to obtain hot roughed plates from homogenized castings;

[0103] Process 4: Hot finishing rolling process to obtain hot finishing plate from hot rough rolled plate;

[0104] Process 5: Cold rolling process of cold rolling hot-rolled plate to obtain cold-rolled plate;

[0105] Furthermore, step 3 above, after step 2 above, can be understood as a hot rough rolling process of hot rough rolling a casting that has undergone homogenization heat treatment to obtain a hot rough rolled plate.

[0106] The following will describe the process in sequence, starting with step 1.

[0107] (Process 1: The casting process of melting raw materials and casting the molten metal with the specified chemical composition into an ingot)

[0108] The melting of aluminum alloys as raw materials can be carried out, for example, at 700–800°C. In addition, when melting aluminum alloys, it is preferable to blow inert gases such as argon (Ar) into the molten metal to perform dehydrogenation treatment.

[0109] After melting, the ingot is cast using a known semi-continuous casting method such as DC casting. Depending on the requirements, face cutting or other methods can be applied to the cast ingot. The face cutting amount can be appropriately varied depending on the degree of segregation, but for example, 3–20 mm per face is preferred.

[0110] (Step 2: Homogenization heat treatment process for the cast ingot)

[0111] Homogenization heat treatment can homogenize the ingot obtained in step 1 above by holding it at a temperature of 400–600°C for 0.5–48 hours, for example. This allows for the complete solid solution formation of Mg-Si intermetallic compounds such as Mg₂Si.

[0112] The heat treatment temperature is more preferably 500°C or higher, more preferably 530°C or higher, and 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 higher, more preferably 4 hours or higher, and even more preferably 12 hours or lower, and even more preferably 10 hours or lower.

[0113] (Process 3: Hot roughing process to obtain hot roughed plates from homogenized castings)

[0114] In hot roughing, the starting temperature is above 490°C, and a reversible hot roughing mill is used to make the ingot reach a thickness of, for example, 20 to 50 mm.

[0115] (Process 4: Hot finishing rolling process to obtain hot finishing plate from hot roughing plate)

[0116] The hot finishing rolling, which follows the hot roughing rolling, is performed over n stands, where n is a natural number of 2 or more. Throughout the entire hot finishing rolling process, from the first stand to the nth stand (the last stand), the starting temperature is, for example, above 400°C, and the ending temperature is 300–350°C. Furthermore, it is preferable to complete the temperature range of 490–400°C within 30 minutes, and more preferably within 10 minutes.

[0117] From the viewpoint of preventing the formation of Lüders bands in the subsequent cold rolling process 5, the finishing temperature is preferably 300°C or higher. Lüders bands will not remain on the ground surface, thus not affecting the function as a substrate for disk drives, but they will detract from the aesthetics of the alloy sheet and blank before grinding.

[0118] By completing the temperature range of 490–400 °C within 30 minutes, the coarsening and precipitation of Mg-Si intermetallic compounds such as Mg2Si can be suppressed.

[0119] For n frames, the logarithmic strain ε1 to ε2 of the first to (n-1)th frames is... n－1 The logarithmic strain ε of the compression of the nth frame, which is the last frame. n , set in a manner that satisfies the following relation (1).

[0120]

Formula 3

[0121]

[0122] The logarithmic reduction strain ε is the natural logarithm of the ratio of the plate thickness before hot finishing rolling to the plate thickness after hot finishing rolling on a given stand. For example, if the thickness of the hot rough-rolled plate after process 3 is t1, and the thickness after hot finishing rolling on the first stand is t2, then the logarithmic reduction strain ε1 on the first stand is calculated from log... e (t1 / t2) represents the compression logarithmic strain ε of the i-th frame. i From log e (t) i / t i＋1 ) represents. Here, the so-called t i It is the thickness of the plate after hot finishing rolling on the (i-1)th stand, that is, the thickness of the plate before hot finishing rolling on the i-th stand. Additionally, t... i＋1 It is the thickness of the plate after hot finishing rolling on the i-th stand.

[0123] That is, when there are 3 racks, the value represented by {ε3-(ε1+ε2) / 2} is set to be greater than or equal to -0.15; when there are 4 racks, the value represented by {ε4-(ε1+ε2+ε3) / 3} is set to be greater than or equal to -0.15.

[0124] Adjust ε1~ε in a manner that satisfies the above relation (1). n The value of is uncertain, but the average grain diameter of the resulting alloy plate surface is small, and the area ratio of the Brass orientation in the crystal orientation distribution on the surface is reduced.

[0125] As a way to satisfy relation (1), one can list ways to make ε n The value is larger than the previous method, making ε1~ε n－1 The two methods are those where the value is smaller than before.

[0126] In order to make ε n The value is larger than before. For example, methods that make the reduction amount and reduction rate of the nth rack larger than before can be listed.

[0127] In order to make ε1~ε n－1 The value is smaller than before. For example, methods can be listed in at least one rack of the first to (n-1) racks to make the reduction amount and reduction rate smaller than before.

[0128] The left side of equation (1) can be -0.15 or higher, but is more preferably -0.13 or higher. In addition, there is no particular upper limit, but from the viewpoint of good strain of the hot-rolled plate, it is preferred to be 0.60 or lower.

[0129] The thickness of the hot-rolled plate finally obtained after step 4 can be, for example, 8 mm or less, more preferably 7 mm or less, and even more preferably 6 mm or less. In addition, 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.

[0130] (Process 5: Cold rolling process to obtain cold-rolled sheet from hot-rolled sheet)

[0131] When the alloy sheet is used to form the billet, from the viewpoint of accumulating the strain energy required for grain refinement after stacked annealing, the reduction rate of cold rolling is preferably 50% or more, and more preferably 70% or more. This allows for a more suitable reduction in post-plating waviness, and also provides good yield strength as both the billet and the substrate.

[0132] Intermediate annealing can be performed before or during cold rolling. In this case, it is preferable to perform cold rolling with a cold rolling rate of 70% or more after intermediate annealing.

[0133] The thickness of the cold-rolled sheet is determined by the desired thickness of the alloy sheet, billet, or substrate. Repeated cold rolling can also be used to achieve the target thickness.

[0134] The thickness of cold-rolled steel sheets can be, for example, 1.3mm, 1mm, 0.9mm, 0.8mm, 0.7mm, etc.

[0135] Furthermore, the alloy plate, blank, and substrate of this embodiment are obtained by the above method, but other processes may be performed between or before each process without adversely affecting each process.

[0136] Example

[0137] The present invention will be described in more detail below with examples and comparative examples, but the present invention is not limited to these examples. Modifications may be made to the invention within the scope of its spirit, and these modifications are all included within the technical scope of the present invention.

[0138] (Examples and Comparative Examples)

[0139] The raw material is melted at 700℃, and the composition is adjusted according to the composition shown in Table 1 (No. 1 to No. 3), and then cast into an ingot. The ingot is then face-cut to remove the segregation layer on the surface. (Step 1)

[0140] Next, the ingot is subjected to homogenization heat treatment at 530–560°C for 4–12 hours. (Step 2)

[0141] After homogenization heat treatment, hot roughing is started immediately, followed by hot finishing rolling. Hot finishing rolling is carried out using 4 stands, and the left side of the relationship between the logarithmic strain ε1 and ε4 used for each stand is shown in Table 2. Furthermore, the entire hot rolling is completed within 10 minutes at a temperature between 490°C and 410°C. (Step 3, Step 4)

[0142] The hot-rolled sheet obtained by cold rolling. Furthermore, in cold rolling, the material is passed through multiple times at a temperature not exceeding 100°C, ultimately achieving a sheet thickness of 1.3 mm to obtain an aluminum alloy sheet for hard disks. (Process 5)

[0143] Furthermore, No.1 and No.2 are examples, and No.3 is a comparative example.

[0144] Table 1

[0145]

[0146] (Evaluation: Average grain diameter on the surface)

[0147] The obtained aluminum alloy plate was ground to make the surface parallel to the plate thickness direction observable, serving as a mirror surface. Subsequently, for the same surface, ion etching was performed using ESCA (Electron Spectroscopy for Chemical Analysis), and the grains on the surface parallel to the plate thickness direction were measured using EBSD (Electron Back Scattering Diffraction).

[0148] The EBSD method was measured using a scanning electron microscope (manufactured by Nippon Electron Ltd., FE-SEM7000F), with an accelerating voltage of 20kV.

[0149] The above-mentioned grinding for surface observation was performed 20 μm along the thickness direction from the surface of each test material. Based on this, a 1000 μm × 1000 μm area was measured at 2 μm intervals.

[0150] Here, on the observed surface, boundaries with an orientation difference of 15° or more from surrounding grains are defined as grain boundaries, and regions with equal orientations enclosed by these grain boundaries are defined as grains. Then, the diameter of the equivalent circle of the grain's projected area is taken as the grain diameter. For all grain diameters, the average grain diameter is calculated using a weighted average based on area and is taken as the average grain diameter of the alloy plate surface. The results are shown in Table 2, "Average Grain Diameter".

[0151] In Table 2, the evaluation is as follows: if the average grain diameter is below 25 μm, it is very good (marked with ◎); if it is above 25 μm but below 45 μm, it is good (marked with ○); and if it is above 45 μm, it is poor (marked with ×).

[0152] (Evaluation: Area ratio of the Brass orientation ({011}<211>) on the surface)

[0153] For the obtained aluminum alloy plates, similar to the measurement of the average grain diameter on the surface, a mirror finish was formed by grinding 20 μm along the thickness direction of each test material. Based on this, EBSD measurements were performed on a 1000 μm × 1000 μm region at 2 μm intervals. Subsequently, crystal orientation analysis was performed; those within 15° of the ideal orientation were analyzed as having the same orientation composition. The area fraction of the Brass orientation ({011} <211>) was determined. The results are shown in Table 2, "Brass Orientation Area Fraction".

[0154] In the evaluation in Table 2, if the area percentage of the Brass orientation is below 9%, it is considered very good and is marked with ◎; if it is above 9% but below 11%, it is considered good and is marked with ○; and if it is above 11%, it is considered poor and is marked with ×.

[0155] (Evaluation: Minor waviness after plating)

[0156] The obtained aluminum alloy plate was used as an aluminum alloy blank, and then as an aluminum alloy substrate. The micro-ripples on the substrate surface after plating were evaluated.

[0157] As an indirect indicator for evaluating the minute waviness after plating, the root mean square waviness (Wq) of the substrate surface after pre-plating treatment is obtained by the following method.

[0158] The obtained aluminum alloy sheet is punched into a disc shape with an outer diameter of 95 mm and an inner diameter of 25 mm, and then subjected to pressure annealing, known as stack annealing. After end face machining, an aluminum alloy billet for 3.5-inch HDDs is obtained. Stack annealing is carried out by heating at a rate of 50 °C / h or higher between 200 and 280 °C, and then holding at 300 to 400 °C for no more than 7 hours.

[0159] Next, the surface of the blank is ground with a diamond tool to become a mirror finish, thus obtaining an aluminum alloy substrate.

[0160] The obtained aluminum alloy substrate is subjected to pre-plating treatment according to the following procedure.

[0161] First, the substrate was degreased by immersing it in a pre-plating treatment solution (manufactured by Uemura Industries, Ltd., AD-68F) at 50°C for 5 minutes. Next, it was acid-etched by immersing it in a pre-plating treatment solution (manufactured by Uemura Industries, Ltd., AD-101F) at 65°C for 2 minutes. Then, it was decontaminated by immersion in 22% nitric acid at 20°C for 30 seconds, followed by zincate treatment in a zincate treatment solution (manufactured by Uemura Industries, Ltd., AD-301F-3X) at 20°C for 30 seconds. Next, it was first dissolved in 22% nitric acid, and then zincate treatment was performed again under the same conditions. Finally, it was dissolved again in 22% nitric acid to obtain the pre-plating treated substrate. This substrate was used as a substrate for evaluating minute waviness.

[0162] The substrates used for evaluating minute waviness obtained above were observed on the surface using a three-dimensional white light interferometer microscope (Bruker Nano Inc., Contour GTX3). The results were analyzed using the accompanying analysis software (Vision64, Version 5.4) to capture six fields of view, each measuring a 1088 μm × 816 μm area, and waviness was measured at wavelengths ranging from 10 to 500 μm. The results are shown in Table 2, "Minor Waviness".

[0163] In the evaluation in Table 2, if the root mean square ripple (Wq) value is below 12nm, it is very good and is marked with ◎; if it is above 12nm but below 14nm, it is good and is marked with ○; if it is above 14nm, it is poor and is marked with ×.

[0164] Table 2

[0165]

[0166] The results above show that in the hot finishing process, due to the adoption of logarithmic strain that satisfies the relationship (1), the average grain diameter on the surface is small, and the area ratio of Brass orientation in the crystal orientation distribution can be reduced. As a result, even without actively containing Mn, aluminum alloy plates, billets, and substrates that can reduce the micro-wrinkle after plating can still be obtained.

Claims

1. An aluminum alloy sheet for a magnetic disk, which satisfies: 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%, the balance consisting of impurities and Al, wherein in the aluminum alloy sheet for a magnetic disk, an average grain diameter in a surface is 45 μm or less, and a Brass orientation {011} <211> in a crystal orientation distribution in the surface is 11% or less. The average grain diameter is 25 μm or less.

3. An aluminum alloy blank for a magnetic disk, which is obtained from the aluminum alloy sheet for a magnetic disk according to claim 1 or 2.

4. An aluminum alloy substrate for a magnetic disk, which is obtained from the aluminum alloy blank for a magnetic disk according to claim 3.

5. A method of manufacturing an aluminum alloy sheet for a magnetic disk, which satisfies: 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%, the balance consisting of impurities and Al, the method comprising: a hot rough rolling step of hot-rough-rolling a cast block subjected to homogenization to obtain a hot-rough-rolled sheet; and a hot finish rolling step of hot-finish-rolling the hot-rough-rolled sheet to obtain a hot-finish-rolled sheet, wherein the number of stands in which the hot finish rolling is performed is n, and the n is a natural number of 2 or more. ​ ​ ​ ​ ​ 2. The aluminum alloy sheet for magnetic disks according to claim 1, wherein ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ When the logarithmic strain of the reduction of the i-th said stand is ε i , the following relation (1) is satisfied, 。

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