Aluminum alloy sheet for magnetic disk, aluminum alloy blank for magnetic disk, and aluminum alloy substrate for magnetic disk

Abstract

The present invention relates to an aluminum alloy sheet for a magnetic disk, a blank, and a substrate, containing Mg: 1.0 mass% or more and 6.5 mass% or less, and Cr: 0.10 mass% or more and 0.30 mass% or less, and satisfying Si: 0.20 mass% or less, and Cu: 1.00 mass% or less, and containing one or more of Fe: 1.70 mass% or less, Mn: 1.5 mass% or less, and Ni: 2.7 mass% or less, with the balance including Al and impurities, and having a gradient of the number of compounds in a depth region of 3 to 11% of the sheet thickness from the surface in the direction from the surface to the center of the sheet thickness of -400 / μm or more.

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. Background Technology

[0002] In disk substrates, "flatness" is a very important indicator because it largely affects the performance of hard disk drives (HDDs) using the substrate.

[0003] Therefore, research and development on the "flatness" of disk substrates has been ongoing to this day.

[0004] For example, Patent Document 1 describes a method for manufacturing a disk blank material, characterized in that it is a method for manufacturing a disk blank material composed of an aluminum alloy containing 3.0 to 6.0% by mass of Mg, with the balance being Al and impurities, and includes a pressure annealing process in which the disk blank material is subjected to a load of 1.5 MPa or more and 4 MPa or less while being annealed at an annealing temperature of 210°C or more and 280°C or less.

[0005] Furthermore, according to Patent Document 1, a blank material for disks with excellent flatness can be manufactured.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2012-123884 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] The inventors have repeatedly studied the "flatness" (more specifically, the "flatness of the blank") of aluminum alloy substrates for disks, and have confirmed that "flatness" needs to be studied from a technical aspect that is completely different from that described in Patent Document 1.

[0011] During casting, near the surface of the slab, the cooling rate is rapid, causing the compounds to become finer and more numerous. On the other hand, in the center of the slab's thickness, the cooling rate is slower, causing the compounds to become coarser and fewer in number.

[0012] Therefore, the blank made from such a slab has a large number of compounds near the surface and a small number of compounds in the center of the slab. The gradient of the number of compounds (the degree of decrease in the number of compounds) increases from the surface toward the center of the slab.

[0013] As a result, slight errors in the cutting amount on the front and back surfaces of the slab lead to differences in the microstructure on the front and back sides, resulting in differences in residual stress after rolling. Moreover, with the release of residual stress during annealing, these differences persist on both sides, ultimately preventing the annealed billet from achieving the desired flatness.

[0014] The present invention is proposed in view of the aforementioned problems, and its purpose is to provide an aluminum alloy plate for disk drives, an aluminum alloy blank for disk drives, and an aluminum alloy substrate for disk drives with excellent flatness.

[0015] Problem-solving methods

[0016] The inventors discovered through repeated research on the flatness of aluminum alloy plates for hard disks that excellent flatness can be achieved through a specific alloy composition and a specific gradient of the number of compounds from the surface to a specified region, thus creating this invention.

[0017] The aluminum alloy plate for disks of the present invention contains Mg: 1.0% or more and 6.5% or less by mass, and Cr: 0.10% or more and 0.30% or less by mass, and satisfies Si: 0.20% or less by mass and Cu: 1.00% or less by mass, and contains one or more of Fe: 1.70% or less by mass, Mn: 1.5% or less by mass and Ni: 2.7% or less by mass, with the balance containing Al and impurities. In a depth region of 3 to 11% of the plate thickness from the surface, the compound number gradient from the surface to the center of the plate thickness is -400 compounds / μm or more.

[0018] Furthermore, in the aluminum alloy plate for disks of the present invention, Cu is preferably 0.05% by mass or more.

[0019] In addition, the aluminum alloy plate for disks of the present invention preferably contains Be: 3 ppm or more and 100 ppm or less.

[0020] In addition, the aluminum alloy plate for disks of the present invention preferably contains Zn: 0.5% by mass or less.

[0021] In addition, the aluminum alloy plate for disks of the present invention preferably contains Sr: 10 ppm or more and 250 ppm or less.

[0022] Furthermore, the aluminum alloy blank for disks of the present invention is formed from the aluminum alloy plate for disks.

[0023] Furthermore, the aluminum alloy substrate for disks of the present invention is formed from the aluminum alloy blank for disks.

[0024] The effects of the invention

[0025] The aluminum alloy plate for disks of the present invention, when used as the raw material, can be made into a disk (or blank and substrate) with excellent flatness.

[0026] The aluminum alloy blank and substrate for disks of the present invention can achieve excellent flatness. Detailed Implementation

[0027] Hereinafter, an aluminum alloy plate for disk, an aluminum alloy blank for disk, and an aluminum alloy substrate for disk according to one embodiment of the present invention will be described.

[0028] Furthermore, in the following description, the aluminum alloy plate for disks, the aluminum alloy blank for disks, and the aluminum alloy substrate for disks in this embodiment will sometimes be referred to simply as "aluminum alloy plate," "blank," and "substrate," respectively.

[0029] [Aluminum Alloy Sheet]

[0030] The aluminum alloy plate of this embodiment contains aluminum alloys in which the contents of Mg, Cr, Si, and Cu are within a specified range, and the contents of Fe, Mn, and Ni are within a specified range. Additionally, the aluminum alloy plate of this embodiment may also contain Be, Zn, and Sr.

[0031] Furthermore, in this embodiment, the aluminum alloy plate has a compound number gradient from the surface to the center of the plate thickness in the surface layer that is above a predetermined value.

[0032] The following describes in detail the components of the aluminum alloy plate of this embodiment.

[0033] (Mg: ≥1.0% by mass and ≤6.5% by mass)

[0034] Mg not only contributes to increased yield strength but also alters annealing softening properties, thereby improving flatness. Specifically, if the Mg content is 1.0% by mass or more, the aluminum alloy sheet becomes an O-type tempered material within an annealing temperature range around 320°C, exhibiting excellent flatness during straightening annealing. Furthermore, if the Mg content is 1.0% by mass or more, the addition of Mg can improve yield strength. On the other hand, if the Mg content exceeds 6.5% by mass, rollability may decrease. Therefore, the Mg content is between 1.0% by mass and 6.5% by mass.

[0035] Furthermore, from the viewpoint of improving flatness, the Mg content is preferably 1.1% by mass or more, 1.3% by mass or more, 1.5% by mass or more, 1.6% by mass or more, 1.8% by mass or more, or 2.0% by mass or more. Additionally, from the viewpoint of ensuring rollability, it is preferably 6.3% by mass or less, 6.1% by mass or less, 5.5% by mass or less, 4.5% by mass or less, 4.0% by mass or less, or 3.5% by mass or less.

[0036] (Cr: ≥0.10% by mass and ≤0.30% by mass)

[0037] Cr has the effect of refining primary grains and promoting uniform distribution of intermetallic compounds, which contributes to improved strength and yield strength. If the Cr content is below 0.10% by mass, the primary grains are not sufficiently refined, and the improvement in strength and yield strength gained from the addition of Cr cannot be fully realized. On the other hand, if the Cr content is above 0.30% by mass, the intermetallic compounds become coarser, edge cracks occur, and there is a possibility of reduced rollability. Therefore, the Cr content is between 0.10% by mass and 0.30% by mass.

[0038] Furthermore, from the viewpoint of improving strength and yield strength, the Cr content is preferably 0.15% by mass or more, or 0.16% by mass or more. Additionally, from the viewpoint of ensuring rollability, the Cr content is preferably 0.27% by mass or less, or 0.25% by mass or less.

[0039] (Si: less than 0.20% by mass)

[0040] Si is typically an unavoidable impurity in aluminum alloys, forming elemental Si or Al-Fe-Si intermetallic compounds. If the Si content exceeds 0.20% by mass, the Young's modulus is low, or elemental Si and Al-Fe-Si intermetallic compounds become coarse, resulting in poor rollability. Therefore, the Si content should be 0.20% by mass or less (including 0.00% by mass).

[0041] Furthermore, from the viewpoint of suppressing the reduction of Young's modulus and rollability, the Si content is preferably 0.10% by mass or less, 0.07% by mass or less, or 0.04% by mass or less. The lower the Si content, the better. Even if it is 0% by mass, it will not impair the characteristics of the present invention. However, since high-purity raw materials (Al ingots and intermediate alloy ingots, etc.) are required, the cost is high. Therefore, the Si content is preferably 0.004% by mass or more in industrial applications.

[0042] (Cu: less than 1.00% by mass)

[0043] Cu exhibits a low equilibrium partition coefficient, significantly lowering the solidus temperature of aluminum alloys. Therefore, Cu effectively widens the solid-liquid coexistence region on the phase diagram, reducing the frequency of melt leakage during casting. Additionally, Cu promotes uniform zinc (Zn) precipitation during zincate treatment. However, if the Cu content exceeds 1.00% by mass, the solid-liquid coexistence region on the phase diagram is excessively expanded. This results in coarsening of intermetallic compounds, edge cracking, and a potential decrease in rollability. Furthermore, if the Cu content exceeds 1.00% by mass, the density increases, potentially hindering weight reduction. Therefore, the Cu content is typically 1.00% by mass or less (including 0.00% by mass).

[0044] Furthermore, from the viewpoint of ensuring the desired effect of Cu addition, the Cu content is preferably 0.05% by mass or more. Additionally, from the viewpoint of ensuring rollability, the Cu content is preferably 0.70% by mass or less, or 0.60% by mass or less.

[0045] (Fe: less than 1.70% by mass)

[0046] Fe contributes to improved strength and Young's modulus. However, if the Fe content exceeds 1.70% by mass, the Al-Fe-Ni intermetallic compounds or Al-Mn-Fe intermetallic compounds coarsen, edge cracks occur, and there is a possibility of reduced rollability. Therefore, the Fe content should be 1.70% by mass or less (including 0.00% by mass).

[0047] Furthermore, from the viewpoint of improving rigidity, the Fe content is more preferably 0.1% by mass or more, 0.2% by mass or more, or 0.3% by mass or more.

[0048] (Mn: less than 1.5% by mass)

[0049] Mn contributes to improved strength and Young's modulus. However, if the Mn content exceeds 1.5% by mass, the Al-Mn-Fe intermetallic compounds coarsen, edge cracks occur, and there is a possibility of reduced rollability. Therefore, the Mn content should be 1.5% by mass or less (including 0.0% by mass).

[0050] Furthermore, from the viewpoint of improving rigidity, the Mn content is preferably 0.1% by mass or more. In addition, from the viewpoint of ensuring rollability, the Mn content is preferably 1.3% by mass or less, 1.2% by mass or less, 1.0% by mass or less, 0.9% by mass or less, 0.6% by mass or less, or 0.4% by mass or less.

[0051] (Ni: less than 2.7% by mass)

[0052] Ni contributes to improved strength and Young's modulus. However, if the Ni content exceeds 2.7% by mass, the Al-Fe-Ni intermetallic compounds coarsen, edge cracks occur, and there is a possibility of reduced rollability. Therefore, the Ni content should be 2.7% by mass or less (including 0.0% by mass).

[0053] Furthermore, from the viewpoint of improving rigidity, the Ni content is preferably 0.3% by mass or more, or 0.5% by mass or more. Additionally, from the viewpoint of ensuring rollability, the Ni content is preferably 2.5% by mass or less, 2.4% by mass or less, or 2.3% by mass or less.

[0054] (Be: 3 ppm or more and 100 ppm or less)

[0055] During casting, Be forms an oxide film, which inhibits the formation of Mg oxide. In addition, it improves the hot rollability and formability of aluminum alloys. Furthermore, it can weaken the adhesion between billets caused by oxidation inhibition during straightening annealing and suppress the deterioration of flatness caused by external forces during subsequent peeling, thereby achieving excellent flatness.

[0056] If the Be content is below 3 ppm by mass, the effect of Be addition cannot be fully obtained. On the other hand, if the Be content is above 100 ppm by mass, the Be-containing compound becomes coarse, edge cracks occur, and there is a possibility of reduced rollability. Therefore, when adding Be, the Be content is preferably 3 ppm by mass or more and 100 ppm by mass or less.

[0057] Furthermore, from the viewpoint of suppressing the coarsening of Be-containing compounds, the Be content is preferably 20 ppm by mass or less and 10 ppm by mass or less.

[0058] (Zn: less than 0.5% by mass)

[0059] Zn has the effect of improving the smoothness of the electroless Ni-P coating formed on the surface of the substrate. Zn is uniformly dissolved in the substrate, and during the zincate treatment before plating, Zn ions in the zincate bath are uniformly and finely precipitated onto the surface of the substrate. In other words, by including Zn, a zincate film can be formed uniformly, inhibiting the formation of nodules on the Ni-P coating surface, resulting in a smoother coating.

[0060] On the other hand, if the Zn content is higher than 1.0% by mass, the Zn precipitates become larger, and consequently, the pits formed during the acid etching process performed as a pre-plating treatment tend to be larger as well. Therefore, if the Zn content is higher than 1.0% by mass, the smoothness of the Ni-P coating surface may decrease. Furthermore, if the Zn content is higher than 1.0% by mass, Al-Mg-Zn intermetallic compounds precipitate at the grain boundaries, resulting in over-etching of the grain boundaries during the acid etching process performed as a pre-plating treatment, and a large number of nodules tend to form on the Ni-P coating surface. In addition, if the Zn content is higher than 1.0% by mass, Al-Mg-Zn intermetallic compounds also dissolve and form pits, which remain after plating. Therefore, the Zn content is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, further preferably 0.3% by mass or less, and even more preferably 0.1% by mass or less. In addition, Zn may not be necessary, but when it is included, it is preferably 0.01% by mass or more.

[0061] (Sr: ≥10 ppm by mass and ≤250 ppm by mass)

[0062] Sr promotes the branching of dendrites formed during casting, thus refining the crystal structure. The effect of Sr addition is fully realized when the Sr content is 10 ppm by mass or more. Conversely, when the Sr content is 250 ppm by mass or less, it prevents Sr-containing compounds such as Al-Sr from becoming coarse, causing edge cracks, and reducing rollability. Therefore, when adding Sr, the Sr content is preferably 10 ppm by mass or more and 250 ppm by mass or less.

[0063] Furthermore, from the viewpoint of ensuring the desired effect of adding Sr, the Sr content is preferably 20 ppm or more by mass and 40 ppm or more by mass. Additionally, from the viewpoint of suppressing the coarsening of Sr-containing compounds, the Sr content is preferably 200 ppm or less by mass and 120 ppm or less by mass.

[0064] (Balance: Al and impurities)

[0065] The aluminum alloy plate of this embodiment may contain elements other than those mentioned above as impurities, depending on the selection of the molten raw materials during ingot manufacturing. Specifically, impurity elements include Ti, Zr, V, B, Na, K, Ca, Pb, P, Sn, Ag, Bi, and In. Among these, Ti, Zr, and V are each limited to 0.10% by mass or less, and B, Na, K, Ca, Pb, P, Sn, Ag, Bi, and In are limited to 0.05% by mass or less. If these elements are within these ranges, their presence is not only unavoidable as impurities, but even if they are actively added, such as by intentionally increasing the proportion of scrap containing these elements, the effect of this embodiment will not be hindered.

[0066] When each of the elements shown as impurity elements is unavoidably contained (in other words, when it is an unavoidable impurity), it is preferable that the content of each element is 0.005% by mass or less, and the total content of each element is preferably 0.015% by mass or less.

[0067] Furthermore, if the chemical composition of Si, Cu, Fe, Mn, Ni, Be, Sr, and Zn is not added, the content of these unavoidable impurities is preferably Si, Cu, Fe, Mn, and Ni at 0.005% by mass or less, Be at 3 ppm by mass or less, Sr at 10 ppm by mass or less, and Zn at 0.01% by mass or less.

[0068] (Compound number gradient)

[0069] In this embodiment, the aluminum alloy plate has a compound number gradient of -400 compounds / μm or more in a depth region of 3 to 11% of the plate thickness from the surface to the center of the plate thickness.

[0070] If the compound number gradient is below -400 compounds / μm, the surface layer (a depth region of 3–11% of the plate thickness from the surface) exhibits a significant variation in the number of compounds. Therefore, even with small errors in the cutting amount on the front and back surfaces of the slab, differences in the microstructure can easily occur. As a result, residual stress after rolling differs on the front and back surfaces of the plate, leading to differences in the release of residual stress during annealing. Ultimately, the annealed billet does not achieve the desired flatness.

[0071] Furthermore, from the viewpoint of achieving better flatness, the compound number gradient is preferably -300 compounds / μm or more, and more preferably -250 compounds / μm or more.

[0072] The compound number gradient in the surface layer (a depth region of 3–11% of the plate thickness from the surface) can be controlled by the casting speed during the casting process. Specifically, by slowing down the casting speed, the compound number gradient can be increased (in other words, large changes in the compound number are suppressed from the surface towards the center of the plate thickness).

[0073] Furthermore, the compound number gradient in the surface layer can also be controlled by whether or not the slab shape abnormality removal process (removal step) described later exists. In detail, by performing the removal of the slab shape abnormality, the compound number gradient can be increased.

[0074] Regarding the method for measuring the compound number gradient in the surface portion (depth region of 3 to 11% of the plate thickness from the surface) of the aluminum alloy plate in this embodiment, the following methods can be listed as an example.

[0075] On the surface portion of a single side (side A) of an aluminum alloy plate (depth area of ​​3–11% of the plate thickness from the surface), mirror cutting was performed to two depths. The number of compounds on these surfaces was counted using FE-SEM (field emission scanning electron microscope) images. Then, the number of compounds per unit area at each depth was plotted in a table (X-axis: depth (μm), Y-axis: number of compounds (cells / mm)). 2 Then, a straight line is created using these two plots, and the coefficient (slope) of the X-axis of the resulting straight line is the "compound number gradient of surface A (single surface)".

[0076] Next, the same measurements and calculations are performed on the surface of the other single-sided surface (surface B) opposite to surface A to obtain the "compound number gradient of surface B (the other single-sided surface)".

[0077] Then, by calculating the average of the "compound number gradient of side A" and the "compound number gradient of side B", the value of the "compound number gradient" of the surface part of the aluminum alloy plate can be obtained.

[0078] Furthermore, regarding the two depths of the surface layer, although it is only necessary to be located in the depth range of 3 to 11% of the plate thickness from the surface, specifically, it is located at two depths: 3 to 5% of the plate thickness from the surface and 9 to 11% of the plate thickness from the surface.

[0079] Thus, the so-called compound number gradient can be described as the increase in unit area (1 mm²) when deepening a unit distance (1 μm) along the center direction of the aluminum alloy plate in the surface layer (a depth region of 3–11% of the plate thickness from the surface). 2 The increase or decrease in the number of compounds is expressed in units of "({components / mm²)". 2} / μm)”.

[0080] [Manufacturing method of aluminum alloy sheet]

[0081] The aluminum alloy sheet of this embodiment can be manufactured using manufacturing methods and equipment under normal conditions for manufacturing disk substrates. For example, an aluminum alloy sheet can be manufactured by a manufacturing method that sequentially includes the following steps: a casting step, in which raw materials are melted and molten metal with a specified chemical composition is cast into an ingot; a homogenization heat treatment step, in which the cast ingot is subjected to homogenization heat treatment; a hot rolling step, in which the ingot subjected to homogenization heat treatment is hot rolled to obtain a hot-rolled sheet; and a cold rolling step, in which the hot-rolled sheet is cold-rolled to obtain a cold-rolled sheet. Furthermore, intermediate annealing can be performed before or during the cold rolling step, as needed.

[0082] However, the casting process in the manufacturing method of the aluminum alloy plate of this embodiment has characteristics.

[0083] (Casting process)

[0084] In the casting process, the raw materials are melted at 700-800℃ and cast using well-known semi-continuous casting methods such as DC casting.

[0085] The casting speed in the casting process is preferably 50 mm / min or less. By casting at a low casting speed, the compound number gradient in the surface layer of the aluminum alloy sheet (the depth region of 3 to 11% of the sheet thickness from the surface) can reach a specified value or higher.

[0086] However, by implementing the removal process for abnormal slab shapes described later, and by making the compound number gradient of the surface portion of the aluminum alloy sheet reach a specified value or higher, the casting speed of the casting process can also be higher than 50 mm / min (e.g., less than 60 mm / min).

[0087] Furthermore, there is no specific lower limit for the casting speed in the casting process, but it can be, for example, above 30 mm / minute or above 35 mm / minute.

[0088] In addition, regarding the slab thickness in the casting process, for example, it is above 400mm and below 650mm.

[0089] (Removal process for abnormally shaped parts of the slab)

[0090] In the casting process, slabs manufactured by semi-continuous casting are generally rectangular in shape, but abnormal shapes such as warping or protrusion of the bottom of the slab may occur, especially at the bottom of the pouring (the front end that is first sent out from the mold) and the gate (the rear end that is last sent out from the mold).

[0091] Here, in the surface cutting process described later, the surface is cut by placing the opposite side of the surface being cut against a platform (a planar platform that serves as the reference for the surface cutting operation). If the slab has an abnormal shape, even if the slab is placed against the platform, the surface being cut will not be parallel to the contact surface of the platform (the surface against which the slab is contacted). As a result, the possibility of not being able to perform surface cutting properly (not achieving the desired amount of surface cutting, and not being able to cut the entire surface evenly) increases.

[0092] Therefore, in the process of removing the abnormal shape parts of the slab, it is preferable to remove the abnormal shape parts. Specifically, this involves cutting off the pouring bottom and gate areas, which are prone to shape abnormalities, to make the surfaces (both sides) to be cut as flat as possible. By performing such a process of removing the abnormal shape parts, when the slab abuts against the platform, the abutting surface of the platform is substantially parallel to the surface cutting surface of the slab, allowing for appropriate surface cutting. As a result, the compound number gradient of the surface layer of the aluminum alloy sheet of this embodiment can reach a predetermined value or higher.

[0093] Furthermore, the aforementioned cutting process, in detail, refers to the process of cutting off a specified length of the pouring bottom and the gate portion from both ends of the slab in the longitudinal direction (from the direction of delivery from the mold). The cutting length of the pouring bottom is preferably 500 mm or more from the end of the pouring bottom side of the slab in the longitudinal direction, and the cutting length of the gate portion is preferably 200 mm or more from the end of the gate side of the slab in the longitudinal direction.

[0094] (Surface cutting process)

[0095] The cast slab is preferably surface-cut, and the amount of surface cutting, for example, can be 10 to 40 mm per side (preferably 10 to 30 mm per side).

[0096] Then, in the surface cutting process, surface cutting of surface A is performed with the side opposite to the surface being cut (surface A) abutting the contact surface of the platform (the side that the slab abuts). After that, surface cutting of surface B is performed with surface A abutting the contact surface of the platform.

[0097] Furthermore, in the surface cutting process, surface cutting can be performed simultaneously on both sides (side A and side B). In this case, if the abnormal shape of the blank is removed, both sides can be cut evenly, and the compound number gradient of the surface layer of the aluminum alloy sheet can reach a specified value or higher.

[0098] The surface cutting process in the surface cutting process is not particularly limited as long as it is a machining process that cuts surface A and surface B into planes. It can be surface grinding (grinding the surface of the slab by a grinding machine on a disc) or slicing (sawing the surface of the slab parallel to the casting direction).

[0099] The homogenization heat treatment process, for example, can be carried out at a homogenization heat treatment temperature of 400 to 600°C for a holding time of 4 to 48 hours.

[0100] In the hot rolling process, for example, the starting temperature can be 490°C or higher. Additionally, the ending temperature can be 300–350°C. Hot rolling at 520°C to 400°C is preferably completed within 30 minutes, more preferably within 15 minutes. Furthermore, the thickness of the hot-rolled sheet obtained can be, for example, 3 mm or less.

[0101] In the cold rolling process, the thickness of the cold-rolled sheet obtained by cold rolling is preferred, for example, preferably 0.3 to 1.3 mm, more preferably 0.7 mm or less.

[0102] [Blank]

[0103] The blank of this embodiment is formed from the aluminum alloy sheet of this embodiment. Moreover, the blank of this embodiment is formed by stamping the aluminum alloy sheet of this embodiment into a perforated disc shape (ring shape) and performing straightening annealing. Its chemical composition is unchanged compared to the aluminum alloy sheet, in other words, it is the same as the aluminum alloy sheet.

[0104] Furthermore, the compound number gradient of the blank in this embodiment is unchanged compared to that of the aluminum alloy plate; in other words, it is the same as that of the aluminum alloy plate.

[0105] [Method for manufacturing the billet]

[0106] The blank of this embodiment can be manufactured using a manufacturing method and equipment under normal conditions for manufacturing substrates for disks. For example, the blank can be manufactured by a manufacturing method that sequentially includes the following steps: a punching step of stamping a cold-rolled aluminum alloy sheet into a ring shape, and a straightening annealing step of performing a straightening annealing on the punched substrate.

[0107] The punching process is the process of stamping aluminum alloy sheets into a desired shape. For example, punching can be performed to make them suitable for 3.5-inch HDD substrates with an inner diameter of 24mm and an outer diameter of 96mm, or 2.5-inch HDD substrates with an inner diameter of 19mm and an outer diameter of 66mm.

[0108] In the straightening annealing process, it is preferable to stack the substrates by clamping them with partitions having high flatness, and anneal while applying a load to the substrates. The annealing temperature can be, for example, 250 to 500°C, and the holding time can be, for example, about 2 to 5 hours. The heating rate of the straightening annealing can be, for example, an average of 80°C / hour (Max. 150°C / hour), and the cooling can be achieved, for example, by opening the door of the annealing furnace. Furthermore, regarding the heating of the straightening annealing, even if the heating is performed in stages, the effect of the present invention will not be impaired. For example, as described in paragraphs 0068 to 0069 of Japanese Patent No. 5815153, the heating rate within a specific temperature range can be a predetermined rate (or higher), and different heating rates can be applied outside that specific temperature range, thus performing heating at multiple heating rates (staged heating).

[0109] [Base film]

[0110] The substrate of this embodiment is formed from the blank of this embodiment. Moreover, the substrate of this embodiment is formed by cutting the end face of the blank of this embodiment and grinding the main face, and its chemical composition is unchanged compared to the blank and the aluminum alloy plate. In other words, it is the same as the blank and the aluminum alloy plate.

[0111] Furthermore, the compound number gradient of the billet in this embodiment is not different from that of the billet and the aluminum alloy plate; in other words, it is the same as that of the billet and the aluminum alloy plate.

[0112] [Substrate manufacturing method]

[0113] The substrate of this embodiment can be manufactured using manufacturing methods and equipment typically used for manufacturing disk substrates. For example, the substrate can be manufactured using a manufacturing method that sequentially includes the following steps: an end-face machining step of cutting the end face of a blank; and a grinding step of grinding the main face of the blank.

[0114] [Disk manufacturing methods]

[0115] Disks can be manufactured using methods and equipment typically employed in disk manufacturing. For example, after acid etching is performed on the surface of a substrate to form an electroless Ni-P coating, the surface of the electroless Ni-P coating is ground. Then, an underlayer, a magnetic layer, a protective film, etc., are formed on the surface of the substrate, thereby enabling the manufacture of a disk.

[0116] Furthermore, details regarding the manufacturing conditions of the blank, substrate, etc., are recorded, for example, in Japanese Patent No. 3471557 and Japanese Patent No. 5199714. The manufacturing of the blank, substrate, etc., can be referenced in these documents.

[0117] Example

[0118] The following describes embodiments of the present invention in detail. However, the scope of the present invention is not limited thereto.

[0119] (Preparation of test materials)

[0120] Test materials No. 1 to 4 were manufactured using aluminum alloys with the chemical composition shown in Table 1, under the following conditions.

[0121] First, slabs were produced using DC casting with a 500 mm thick ingot for molten metal, at the casting speeds shown in Table 1. Then, the resulting slabs were surface-cut 16 mm on both sides (thickness direction). Subsequently, a homogenization heat treatment was performed at 540 °C for 8 hours.

[0122] Then, the test materials No. 1 to 3 were hot-rolled (finishing temperature: approximately 330°C) until a thickness of 2.3 mm was achieved, and then cold-rolled until a thickness of 0.69 mm was achieved. Afterwards, they were stamped using a press at 96°C and... The blank was punched using the same method as the blank used for the No. 1 test material, and then subjected to straightening annealing (heating rate: approximately 70–140°C / h (average approximately 110°C / h), annealing temperature: approximately 320°C, holding time: approximately 3 hours) to produce a blank with a thickness of 0.69 mm (O-type quenched and tempered material). For the No. 4 test material, it was hot-rolled to a thickness of 2.0 mm and then cold-rolled to a thickness of 0.44 mm. Subsequently, a blank with a thickness of 0.44 mm (O-type quenched and tempered material) was produced by the same operation as the No. 1 test material.

[0123] Furthermore, for test materials No. 1 to 4, before surface cutting, in the longitudinal direction of the slab (the direction from which it is delivered from the mold), cut off the pouring bottom of the length shown in Table 1 from the end of the pouring bottom side, and cut off the gate portion of the length shown in Table 1 from the end of the gate side.

[0124] For each manufactured test material, the compound number gradient and flatness are evaluated in the following manner.

[0125] (Compound number gradient)

[0126] The compound number gradient of test materials No. 1 to 3 is calculated as follows.

[0127] First, for a single side (side A) of the test material (green body) with a plate thickness of 0.69 mm, the observation image was obtained using FE-SEM (field emission scanning electron microscope) (magnification 1000x, 50 fields of view, observation area 0.54 mm²). 2The number of compounds (the number of compounds with a maximum length greater than 0.330 μm) on the surface was statistically analyzed at depths of 3.6% of the plate thickness (25 μm) and 10.9% of the plate thickness (75 μm). Then, the compound counts at each depth were converted to per unit area (1 mm²). 2 The number of compounds in the sample was then plotted in a table (X-axis: depth from the surface (μm), Y-axis: number of compounds / mm). 2 Then, create a straight line using the two plots of the table, and calculate the compound number gradient (coefficient of X: slope) of surface A.

[0128] Secondly, for the B side (the opposite side of the A side) of the test material (green body) with a plate thickness of 0.69 mm, the observation image obtained by FE-SEM (field emission scanning electron microscope) (magnification 1000x, 50 fields of view, observation area 0.54 mm²) 2 The number of compounds (the number of compounds with a maximum length greater than 0.330 μm) on the surface was statistically analyzed at depths of 3.6% of the plate thickness (25 μm) and 10.9% of the plate thickness (75 μm). Then, the number of compounds at each depth was converted to the value per unit area (1 mm²). 2 The number of compounds in the sample was then plotted in a table (X-axis: depth from the surface (μm), Y-axis: number of compounds / mm). 2 Then, create a straight line using the two plots of the table, and calculate the compound number gradient (coefficient of X: slope) on surface B.

[0129] Then, calculate the average value of the compound number gradient on surface A and the compound number gradient on surface B, and derive the "compound number gradient" of test materials No.1 to No.3.

[0130] The compound number gradient of test material No.4 is calculated as follows.

[0131] First, for the test material (bulk) with a plate thickness of 0.44 mm, one side (A side) was mirror-cut to a depth of 3.6% of the plate thickness, i.e., 16 μm from the surface, and 10.7% of the plate thickness, i.e., 47 μm from the surface. Otherwise, the number of compounds on the surface was counted in the same way as for the test material No.1, and the gradient of the number of compounds on A side (the coefficient of X: slope) was calculated.

[0132] Next, the B side (opposite side of the A side) of the 0.44 mm thick test material (bulk) was mirror-cut to a depth of 3.6% of the plate thickness, i.e., 16 μm from the surface, and to a depth of 10.7% of the plate thickness, i.e., 47 μm from the surface. Similar to the No.1 test material, the number of compounds on the surface was counted, and the gradient of the number of compounds on the B side (the coefficient of X: slope) was calculated.

[0133] Then, calculate the average of the compound number gradients on surface A and surface B to derive the "compound number gradient" of test material No.4.

[0134] Furthermore, the surface of the mirror-cut compound counting plate is roughly parallel to the surface of the blank.

[0135] As described above, the results of creating the straight lines and the gradient of the number of compounds for each test material are as follows:

[0136] [Test Material 1]

[0137] The straight line on plane A: Y = -408.78X + 89071

[0138] Compound number gradient on side A: -409

[0139] The straight line on side B: Y = -448.41X + 98427

[0140] The compound number gradient on side B: -448

[0141] Compound number gradient (average): -429

[0142] [Test Material 2]

[0143] The straight line on plane A: Y = -33.852X + 75193

[0144] The compound number gradient on side A: -34

[0145] The straight line on side B: Y = -144.59X + 84124

[0146] The compound number gradient on side B: -145

[0147] Compound number gradient (average): -89

[0148] [Test Material 3]

[0149] The straight line on plane A: Y = -383.89X + 111721

[0150] The compound number gradient on side A: -384

[0151] The straight line on side B: Y = -324.3X + 109089

[0152] The compound number gradient on side B: -324

[0153] Compound number gradient (average): -354

[0154] [Test Material 4]

[0155] The straight line on plane A: Y = -143.49X + 88072

[0156] The compound number gradient on side A: -143

[0157] The straight line on side B: Y = -198.56X + 88913

[0158] The compound number gradient on side B: -199

[0159] Compound number gradient (average): -171

[0160] Here, the term "compound" refers to compounds with a maximum length of 0.330 μm or more, such as Al-Fe-Ni compounds, Al-Fe compounds, Al-Ni compounds, Al-Mn-Ni compounds, Al-Fe-Mn-Ni-Mn-Si-Cr compounds, Al-Fe-Ni-Si compounds, Al-Ni-Si compounds, Al-Fe-Mn compounds, Al-Mn-Ni compounds, Al-Mn-Ni-Cr compounds, Al-Mn compounds, Al-Cr compounds, Al-Si compounds, Al-Cu compounds, Al-Cu-Mn-Ni-Cr compounds, Al-Cu-Fe-Mn-Ni-Mn-Si-Cr compounds, etc.

[0161] (flatness)

[0162] Flatness was measured using a Nidec flatness tester (FT-17) for each test material. For N-numbers of 75 or higher, the flatness was calculated as "average flatness + 3σ" (average flatness plus 3 × standard deviation).

[0163] Flatness with an average value +3σ of less than 12.5 μm is rated as "0" (qualified), and flatness with an average value greater than 12.5 μm is rated as "×" (unqualified).

[0164] Table 1 shows the evaluation results for the alloy composition (chemical composition), compound number gradient, casting speed, amount of slab removed before surface cutting, and flatness of each test material.

[0165] Table 1

[0166]

[0167] The results in Table 1 show that, due to the slow casting speed, the compound number gradient of test material 2 is confirmed to be above the specified value. The results also confirm that test material 2 exhibits excellent flatness (flatness of the billet).

[0168] Furthermore, in test material 2, although the amount of slab removed was the same as before (pouring bottom side: less than 500 mm), the casting speed was slower than before (less than 50 mm / minute), so it can be inferred that the compound number gradient was above the specified value.

[0169] Because the amount of slab removed before surface cutting of test material 3 was greater than before, abnormal parts of the slab shape could be removed, thus confirming that the compound number gradient was above the specified value. As a result, it can be confirmed that the flatness (flatness of the billet) of test material 3 is excellent.

[0170] Furthermore, although the casting speed of test material 3 was the same as before (above 50 mm / min), the amount of slab removed was greater than before (pouring bottom side: more than 500 mm, gate side: more than 200 mm), which properly removed the abnormal parts of the slab shape. From this, it can be inferred that the compound number gradient is above the specified value.

[0171] The results from these test materials 2 and 3 confirm that, in order to make the compound number gradient above the specified value, it is sufficient to satisfy at least one of the following: "slowing down the casting speed" and "removing the abnormal part of the slab shape before surface cutting".

[0172] On the other hand, since test material 1 was manufactured at the existing casting speed (above 50 mm / min) and the amount of slab removed before surface cutting was also at the existing level (bottom side of the gating: less than 500 mm, gate side: less than 200 mm), it can be confirmed that the compound number gradient is lower than the specified value and the flatness is not good enough.

[0173] Furthermore, since the amount of slab removed before surface cutting in test material 4 was greater than before, abnormal parts of the slab shape could be removed, thus confirming that the compound number gradient was above the specified value. In addition, by containing Be, the flatness was found to be superior compared to test material 3. Moreover, the reason for this superior flatness is speculated to be that by correcting oxidation inhibition during annealing, the adhesion between the blanks can be weakened, thereby suppressing the deterioration of flatness caused by external forces during subsequent peeling operations.

[0174] The present invention has been described in detail with reference to specific embodiments, but it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2021-111036, filed July 2, 2021, and Japanese Patent Application No. 2022-073664, filed April 27, 2022, the contents of which are incorporated herein by reference.

Claims

1. An aluminum alloy plate for hard disks, comprising Mg: 1.0% by mass or more and 6.5% by mass or less, and Cr: 0.10% by mass or more and 0.30% by mass or less. And it must satisfy the following conditions: Si: less than 0.20% by mass, and Cu: less than 1.00% by mass. It contains one or more of the following: Fe: less than 1.70% by mass, Mn: less than 1.5% by mass, and Ni: less than 2.7% by mass. The balance includes Al and impurities. In the depth region of 3–11% of the plate thickness from the surface, the compound number gradient from the surface to the center of the plate thickness is greater than -400 compounds / μm. The plate thickness is 0.3 to 0.69 mm.

2. The aluminum alloy plate for disks according to claim 1, wherein, Cu: 0.05% by mass or more.

3. The aluminum alloy plate for disks according to claim 1, wherein, It also contains Be: 3 ppm or more but less than 100 ppm by mass.

4. The aluminum alloy plate for disks according to claim 2, wherein, It also contains Be: 3 ppm or more but less than 100 ppm by mass.

5. The aluminum alloy plate for disks according to claim 3, wherein, It also contains less than 0.5% by mass of Zn.

6. The aluminum alloy plate for disks according to claim 4, wherein, It also contains less than 0.5% by mass of Zn.

7. The aluminum alloy plate for disks according to claim 1, wherein, It also contains Sr: more than 10 ppm by mass and less than 250 ppm by mass.

8. The aluminum alloy plate for disks according to claim 2, wherein, It also contains Sr: more than 10 ppm by mass and less than 250 ppm by mass.

9. An aluminum alloy blank for a hard disk, formed from an aluminum alloy sheet for a hard disk according to any one of claims 1 to 8.

10. An aluminum alloy substrate for a hard disk, formed from the aluminum alloy blank for a hard disk as described in claim 9.

11. A method for manufacturing an aluminum alloy plate for a hard disk, as described in claim 1, wherein, The processes, in sequence, include casting, homogenization heat treatment, hot rolling, and cold rolling. The casting process is a semi-continuous casting method. The casting speed in the casting process is less than 50 mm / minute.

12. A method for manufacturing an aluminum alloy plate for a hard disk, as described in claim 1, wherein, The processes, in sequence, include casting, homogenization heat treatment, hot rolling, and cold rolling. The casting process is a semi-continuous casting method. It includes a process for removing shape defects from slabs produced by the semi-continuous casting method.

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