Aluminum wafer for mechanical hard disk without pits on surface and control method of aluminum wafer

Abstract

The invention relates to an aluminum wafer for a mechanical hard disk without pits on the surface. The thickness of the aluminum wafer is 0.500-1.300 mm, the diameter of the aluminum wafer is 95.0-98.2 mm, the surface defect depth of the aluminum wafer is smaller than 10 micrometers, and the second phase size and the melt impurity size of the aluminum wafer are smaller than or equal to 5 micrometers. The aluminum wafer is prepared from, by mass, 0.001%-0.035% of Si, 0.010%-0.025% of Fe, 0.005%-0.200% of Cu, smaller than or equal to 0.005% of Mn, 3.500%-8.500% of Mg, 0.010%-0.500% of Cr, smaller than or equal to 0.030% of Ni, 0.050%-0.650% of Zn, smaller than or equal to 0.010% of Ti and the balance Al and inevitable impurities. Pits with the size larger than 5 microns do not exist on the surface of the aluminum wafer before nickel plating, it is guaranteed that a magnetic recording medium of a mechanical hard disk product is continuous on the wafer, the product quality is improved, and it is guaranteed that the mechanical hard disk performance is stable; and the control process is simple and reasonable, is universally applicable to deformed aluminum materials, and is easy to implement industrially.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum material processing, and in particular to an aluminum disc for a mechanical hard disk without pits on the surface and a control method thereof. Background Art

[0002] The disc in the mechanical hard disk is the core component for storing information in the HDD (hard disk drive). After the aluminum disc is produced, it is subjected to surface grinding and polishing, chemical treatment, and surface nickel plating. Based on this, a NiP non-magnetic film is formed by electrolytic plating. This layer of NiP non-magnetic film is used as the bottom layer, and then a layer of Co-p alloy magnetic film is evenly coated as a magnetic recording medium. If there are pits larger than 5μm on the surface of the aluminum disc before nickel plating, the nickel plating layer may not be able to fill the pits, resulting in a discontinuous functional defect of the magnetic recording medium of the product on the disc. Summary of the invention

[0003] In view of this, the purpose of the present invention is to provide an aluminum disc with no pits on the surface for a mechanical hard disk and a control method thereof. There are no pits larger than 5 μm on the surface of the aluminum disc before nickel plating, thereby improving product quality and ensuring stable performance of the mechanical hard disk.

[0004] The present invention is implemented by the following scheme: an aluminum disc for a mechanical hard disk with no pits on the surface, the aluminum disc has a thickness of 0.500-1.300 mm, a diameter of 95.0-98.2 mm, a surface defect depth of <10 μm, a second phase size and a melt impurity size of ≤5 μm; the mass percentage of each component of the aluminum disc is: Si 0.001-0.035%, Fe 0.010-0.025%, Cu 0.005-0.200%, Mn≤0.005%, Mg 3.500-8.500%, Cr 0.010-0.500%, Ni≤0.030%, Zn 0.050-0.650%, Ti≤0.010%, and the balance is Al and unavoidable impurities.

[0005] Further, the method comprises the following steps: (1) preparing an aluminum ingot with a thickness of 290-460 mm; (2) performing surface milling on the aluminum ingot with a milling thickness of ≥10 mm / face, performing homogenization annealing at a temperature of 480-520°C and a holding time of 8-24 h, hot rolling the aluminum ingot into a hot-rolled plate with a thickness of 3.0 mm, and then cold rolling the aluminum plate into an aluminum sheet with a thickness of 0.5 mm; (3) performing alkali washing on the aluminum plate to remove surface oil and aluminum powder, and then performing a bending straightening process on the aluminum plate. The aluminum sheet is leveled by a machine; (4) the aluminum sheet is coated on one side with a plastic film having a viscosity of 20-40 g / 25 mm, and then the sheet is slit; (5) the aluminum sheet after slit is cleaned by tearing off the film, and then aluminum discs are punched out by a mold; (6) the aluminum discs are stacked, flattened and annealed; (7) the surface roughness of the aluminum discs after rough grinding and fine grinding is 0.5-0.9 μm, and the grinding amount is 10-15 μm / surface.

[0006] Furthermore, in step (1), the prepared aluminum melt is double filtered using a deep bed filtration system plus a tubular filtration system, and the accuracy level of the tubular filter reaches RC level or above, and the slag of the aluminum melt after filtration is less than 0.013 mm. 2 / kg; the Fe content in the aluminum ingot is 0.010~0.025%.

[0007] Furthermore, in step (2), the surface roughness of the rollers used in the cold rolling process is required to be Ra ≤ 0.5 μm, and the rolling oil needs to be filtered using a Boll filter ≤ 10 μm.

[0008] Furthermore, in step (3), the conductivity of the alkali solution used for alkali washing is 14-20 ms / cm, and the alkali washing time is 2-3 seconds.

[0009] Compared with the prior art, the present invention has the following beneficial effects: there are no pits larger than 5 μm on the surface of the aluminum disc before nickel plating, which ensures that the magnetic recording medium of the mechanical hard disk product is continuous on the disc, improves product quality, and ensures stable performance of the mechanical hard disk; and the control process is simple and reasonable, generally applicable to deformed aluminum materials, and easy to implement in industry.

[0010] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below through specific embodiments and related drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a surface inspection image of an aluminum wafer with pit defects in the prior art; Figure 2 This is a surface detection image of the aluminum disc processed by the present invention. DETAILED DESCRIPTION

[0012] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0013] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0014] An aluminum disc for a mechanical hard disk with no pits on the surface, the aluminum disc has a thickness of 0.500-1.300 mm, a diameter of 95.0-98.2 mm, a surface defect depth of less than 10 μm, a second phase size and a melt impurity size of ≤5 μm; the mass percentage content of each component of the aluminum disc is: Si 0.001-0.035%, Fe 0.010-0.025%, Cu 0.005-0.200%, Mn≤0.005%, Mg3.500-8.500%, Cr 0.010-0.500%, Ni≤0.030%, Zn 0.050-0.650%, Ti≤0.010%, and the remainder is Al and unavoidable impurities; the second phase of the aluminum disc is mainly Al3Fe, and the second phase and the melt impurity size are required to be ≤5 μm, so that the surface of the aluminum disc for the mechanical hard disk can be controlled to have no pit defects with a size of ≥5 μm.

[0015] In this embodiment, the following steps are included: (1) preparing an aluminum ingot with a thickness of 290-460 mm, using a conventional industrial smelting and casting method, such as a direct cooling casting method; (2) performing surface milling on the aluminum ingot with a milling thickness of ≥10 mm / face, performing homogenization annealing at a temperature of 480-520°C and a holding time of 8-24 h, and hot rolling it into a hot-rolled plate with a thickness of 3.0 mm, and then cold rolling it into an aluminum plate with a thickness of 0.5 mm; (3) performing alkali washing on the aluminum plate to remove surface oil and dirt Aluminum powder, and then use a stretch bending and straightening machine to straighten the aluminum plate to improve the shape of the coil; (4) The surface of the aluminum plate is coated on one side, using a plastic film with a viscosity of 20~40g / 25mm, and then it is cut into strips; (5) The aluminum material after cutting is torn off the film and cleaned, and then it is punched into aluminum discs by mold; (6) The aluminum discs are stacked, flattened and annealed; (7) The surface roughness of the aluminum discs after rough grinding and fine grinding is 0.5~0.9μm, and the grinding amount is 10~15μm / surface.

[0016] In this embodiment, in step (1), the prepared aluminum melt is double filtered using a deep bed filtration system plus a tubular filtration system, and the accuracy level of the tubular filter reaches RC level or above, and the slag measurement of the aluminum melt after filtration is less than 0.013 mm. 2 / kg; the Fe content in the aluminum ingot is 0.010-0.025%. The second phase of the aluminum disc is analyzed by scanning electron microscope energy spectrum. The analysis result shows that the second phase is mainly Al3Fe. In order to control the amount and size of the second phase, the Fe content needs to be controlled. However, the lower the Fe content, the lower the subsequent grinding efficiency. In order to control the balance between the size of the second phase and the grinding efficiency, Fe needs to be kept in a certain range, that is, 0.010-0.025%.

[0017] The mass percentage of each component of the aluminum ingot is: Si 0.001~0.035%, Fe 0.010~0.025%, Cu 0.005~0.200%, Mn≤0.005%, Mg 3.500~8.500%, Cr 0.010~0.500%, Ni≤0.030%, Zn 0.050~0.650%, Ti≤0.010%, and the balance is Al and unavoidable impurities.

[0018] In this embodiment, in step (2), the industrial preferred temperature for the homogenization annealing process is 500-510°C and the holding time is 10-20 hours; the surface roughness of the rollers used in the cold rolling process is required to be Ra≤0.5μm, and the rolling oil needs to be filtered using a Boll filter of ≤10μm.

[0019] In this embodiment, in step (3), the conductivity of the alkaline solution used for alkaline washing is 14-20 ms / cm, and the alkaline washing time is 2-3 seconds.

[0020] In this embodiment, in step (5), the aluminum material needs to be cleaned with high-pressure water and a roller brush before and after the stamping process to remove surface debris.

[0021] Through a detailed investigation and analysis of the causes of pits on the surface of aluminum wafers, the main causes are: First, after the aluminum wafers are polished for 10-15μm, the second phase and impurity particles of the aluminum substrate are exposed, and fall off during chemical pretreatment before electroplating, forming surface pits. Pits with a size of >5μm cannot be completely filled during nickel electroplating; Reason 2: Aluminum is generated during the production process. Aluminum powder or aluminum chips on the surface of the aluminum are pressed into the surface of the aluminum by tension rollers, resulting in mechanical damage pits with a depth of ≥10μm.

[0022] During the ingot casting process, the melt purity is controlled, the ingot size thickness is controlled below 460mm, the homogenization annealing is optimized, and the Fe content is controlled within 0.010~0.025%, so as to refine the second phase and the melt impurity size, and avoid the second phase or melt impurities exposed after the aluminum disc is ground to fall off and form pits larger than 5μm; secondly, the aluminum powder and aluminum chips generated during the finishing and stripping process and the stamping process are controlled to be removed, so as to avoid the aluminum powder or aluminum chips being crushed by external forces to cause pit defects with a depth of ≥10μm on the surface of the aluminum disc, and the surface defect depth of less than 10μm can be eliminated after grinding the surface of the aluminum disc. After the above aluminum disc second phase size, melt purity, and surface mechanical damage are controlled according to the requirements of the present invention, no pits are generated on the surface of the aluminum disc for mechanical hard disk after nickel plating, and the surface quality is evaluated as qualified.

[0023] The following sample experiments are used to compare and illustrate the effects of aluminum ingot thickness and homogenization annealing process on pit defects.

[0024] The morphology and distribution of the second phase in the sample were observed using the backscattering mode of a JSM7800F field emission electron microscope. Four BSD images (total area of ​​about 1 mm²) were taken at a magnification of 200 times, and the distribution of the second phase on the aluminum surface was statistically analyzed using Olycia m3 metallographic analysis software.

[0025] Examples 1-2 and Comparative Example 1: According to the content of each component of the above-mentioned aluminum ingot, the aluminum ingot was prepared by the conventional industrial smelting and casting method, and aluminum ingots of different thicknesses were cast. The same soaking process was adopted, and then hot-rolled and cold-rolled into aluminum alloy plates. The distribution of the second phase on the surface of the plate was observed by scanning electron microscopy, and the statistical results are shown in Table 1. The ingot sizes of Examples 1-2 were 300*1400*6000mm and 420*1400*6000mm, respectively. The soaking process was 510°C×10h. The physical size of the obtained aluminum alloy plate was <5μm, and the quality was evaluated as qualified. The ingot size of Comparative Example 1 was 560*1400*6000mm, the soaking process was 510×10h, and the physical size of the obtained aluminum alloy plate was >5μm, which was evaluated as unqualified.

[0026] Examples 3 to 6 and Comparative Examples 2 to 3: According to the content of each component of the above-mentioned aluminum ingot, the aluminum ingot is prepared by the conventional industrial smelting and casting method. The size of the aluminum ingot is 420*1400*6000mm, and then it is subjected to homogenization annealing treatment at different temperatures and holding times, and then hot-rolled and cold-rolled into aluminum alloy plates. The distribution of the second phase on the surface of the plate is observed by scanning electron microscopy, and the statistical results are shown in Table 1. The heat-saturation processes of Examples 3 to 5 are 510°C×20h, 480°C×10h and 480°C×20h, respectively. The physical size of the obtained aluminum alloy plate is <5μm, and it is evaluated as qualified. The heat-saturation processes of Comparative Examples 2 and 3 are 460°C×10h and 460°C×20h, and the physical size of the obtained aluminum alloy plate is >5μm, which is evaluated as unqualified.

[0027] Table 1 Second phase distribution on aluminum sheet surface Maximum size of the second phase Note: The maximum size of the second phase is less than 5μm, which is qualified; the maximum size of the second phase is ≥5μm, which is unqualified.

[0028] Unless otherwise stated, any technical solution disclosed in the present invention disclosed above, if it discloses a numerical range, then the disclosed numerical range is a preferred numerical range, and any technician in the field should understand that the preferred numerical range is only a numerical value with a more obvious technical effect or representative value among many implementable numerical values. Since there are too many numerical values ​​to be exhaustive, the present invention discloses some numerical values ​​to illustrate the technical solution of the present invention, and the numerical values ​​listed above should not constitute a limitation on the scope of protection of the present invention.

[0029] If the present invention discloses or involves components or structures that are fixedly connected to each other, then, unless otherwise stated, the fixed connection can be understood as: a detachable fixed connection (for example, connection using bolts or screws), and can also be understood as: a non-detachable fixed connection (for example, riveting, welding). Of course, the mutual fixed connection can also be replaced by an integrated structure (for example, manufactured by integrated molding using a casting process) (except when it is obviously impossible to use an integrated molding process).

[0030] In addition, unless otherwise stated, the terms used to indicate positional relationships or shapes in any of the technical solutions disclosed in the present invention include states or shapes that are approximate, similar, or close to them.

[0031] Any component provided by the present invention may be assembled from a plurality of separate components, or may be a separate component manufactured by an integral forming process.

[0032] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. An aluminum disc for a mechanical hard disk having no pits on the surface, characterized in that: The aluminum disc has a thickness of 0.500-1.300 mm, a diameter of 95.0-98.2 mm, a surface defect depth of <10 μm, a second phase size and a melt impurity size of ≤5 μm; the mass percentage of each component of the aluminum disc is: Si 0.001-0.035%, Fe 0.010-0.025%, Cu 0.005-0.200%, Mn≤0.005%, Mg 3.500-8.500%, Cr 0.010-0.500%, Ni≤0.030%, Zn 0.050-0.650%, Ti≤0.010%, and the balance is Al and unavoidable impurities.

2. A control method for an aluminum disc with no pits on the surface for a mechanical hard disk, characterized in that: The steps include: (1) preparing aluminum ingots with a thickness of 290-460 mm; (2) performing surface milling on the aluminum ingots with a milling thickness of ≥10 mm / face, performing homogenization annealing at a temperature of 480-520°C and a holding time of 8-24 h, and hot rolling them into hot-rolled plates with a thickness of 3.0 mm, and then cold rolling them into aluminum plates with a thickness of 0.5 mm; (3) performing alkali washing on the aluminum plates to remove surface oil and aluminum powder, and then performing bending and straightening on the aluminum plates using a tension and bending machine. (4) The aluminum sheet is coated on one side with a plastic film having a viscosity of 20-40 g / 25 mm, and then the sheet is cut into strips; (5) The aluminum sheet after cutting is cleaned by tearing off the film, and then aluminum discs are punched out by a die; (6) The aluminum discs are stacked, flattened and annealed; (7) The surface roughness of the aluminum discs after rough grinding and fine grinding is 0.5-0.9 μm, and the grinding amount is 10-15 μm / surface.

3. The method for controlling the surface of the aluminum disc for a mechanical hard disk to be free of pits according to claim 1, characterized in that: In step (1), the prepared aluminum melt is double filtered using a deep bed filtration system plus a tubular filtration system, and the accuracy level of the tubular filter reaches RC level or above, and the slag of the aluminum melt after filtration is less than 0.013mm 2 / kg; the Fe content in the aluminum ingot is 0.010~0.025%.

4. The method for controlling the surface of the aluminum disc for a mechanical hard disk to be free of pits according to claim 1, characterized in that: In step (2), the surface roughness of the rollers used in the cold rolling process is required to be Ra ≤ 0.5 μm, and the rolling oil needs to be filtered using a Boll filter ≤ 10 μm.

5. The method for controlling the surface of the aluminum disc for a mechanical hard disk to be free of pits according to claim 1, characterized in that: In step (3), the conductivity of the alkali solution used for alkali washing is 14-20 ms / cm, and the alkali washing time is 2-3 seconds.

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