Abstract: The present invention provides a substrate for a magnetic recording medium in which bulges are not easily formed on a surface thereof by a physical impact in a size for a 2.5-inch type hard disk drive, and a width of displacement caused by fluttering is small. The substrate for a magnetic recording medium includes an Al alloy substrate and a Ni alloy plating film formed on a surface of the Al alloy substrate, has a diameter of 54 to 70 mm, and a disk shape having a hole whose inner diameter ranges from 19 to 26 mm in the center thereof. The Al alloy substrate has a Young's modulus (E) of 74 GPa or more, a density (?) of 2.75 g/cm3 or less, and a ratio (E/?) of 27 or more between the Young's modulus (E) and the density (?). The Ni alloy plating film has a thickness of 4 to 7 ?m, and when an indentation is formed by pressing a diamond indentor whose tip has a square pyramid shape against a surface of the Ni alloy plating film with a test force of 0.

Abstract: What is provided is an aluminum alloy substrate for a magnetic recording medium which has high rigidity and an excellent plating properties. The aluminum alloy substrate for a magnetic recording medium has a constitution in which coarse grains whose average grain size is within a range that exceeds 2 ?m and is less than or equal to 20 ?m are dispersed, the average number of coarse grains per area of 0.042 mm2 is 100 or more, and a surface roughness Ra is less than or equal to 0.2 ?m.

Abstract: The present invention provides a substrate for a magnetic recording medium in which bulges are hardly formed on a surface thereof by a physical impact in a size for a 3.5-inch type HDD, and a width of displacement caused by fluttering is small. The substrate for a magnetic recording medium includes an Al alloy substrate and a Ni alloy plating film formed on a surface of the Al alloy substrate, and has a diameter of 95 to 98 mm, a disk shape having a hole whose inner diameter ranges from 19 to 26 mm in the center thereof, a thickness of 0.48 to 0.64 mm, and a mass of 9.0 to 15.0 g. The Al alloy substrate has a Young's modulus (E) of 74 GPa or more, a density (?) of 2.75 g/cm3 or less, and a ratio (E/?) of 27 or more between the Young's modulus (E) and the density (?). The Ni alloy plating film has a thickness of 4 to 7 ?m, and when an indentation is formed by pressing a diamond indentor whose tip has a square pyramid shape against a surfaces of the Ni alloy plating film with a test force of 0.

Abstract: A base for a magnetic recording medium, includes a substrate made of an Al alloy and having a surface, and a film made of a NiWP-based alloy and plated on the surface of the substrate. The film includes W in a range of 15 mass % to 22 mass %, P in a range of 3 mass % to 10 mass %, and Pb in a range of 0.03 mass % to 0.08 mass %. The film has a thickness of 5 ?m or greater.

Abstract: A method of producing an aluminum alloy substrate for a magnetic recording medium, which uses a grinding apparatus (10) for grinding both principal planes of the aluminum alloy substrate by a grinding pad (14) by arranging the aluminum alloy substrate in an opening (13a) provided in a carrier plate (13), and relatively moving the carrier plate (13) in a plane with respect to an upper platen (11) and a lower platen (12), while supplying a grinding fluid onto a surface of the aluminum alloy substrate, wherein the grinding pad (14) has a structure in which a plurality of tile-shaped convex portions having a flat top portion are provided side by side and diamond abrasive grains are included in the convex portion and fixed in the convex portion by a binder, an average particle diameter of the diamond abrasive grains is from 2 to 15 ?m, and a content of diamond abrasive grains in the convex portions is from 5 to 50% by volume.

Abstract: A base for a magnetic recording medium, includes a substrate made of an Al alloy and having a surface, and a film made of a NiWP-based alloy and plated on the surface of the substrate. The film includes W in a range of 15 mass % to 22 mass %, P in a range of 3 mass % to 10 mass %, and Pb in a range of 0.03 mass % to 0.08 mass %. The film has a thickness of 5 ?m or greater.

Abstract: A base for a magnetic recording medium includes, a substrate made of an Al alloy, and a film made of a NiP-based alloy and provided on the substrate. The Al alloy of the substrate includes Mg in a range of 0.2 mass % to 6 mass %, Si in a range of 3 mass % to 17 mass %, Zn in a range of 0.05 mass % to 2 mass %, and Sr in a range of 0.001 mass % to 1 mass %. An average grain diameter of Si grains in an alloy structure of the substrate is 2 ?m or less. The film has a thickness of 10 ?m or greater. The substrate has an outer diameter of 53 mm or greater, a thickness of 0.9 mm or less, and a Young's modulus of 79 GPa or higher.

Abstract: A base for a magnetic recording medium includes, a substrate made of an Al alloy, and a film made of a NiP-based alloy and provided on the substrate. The Al alloy of the substrate includes Mg in a range of 0.2 mass % to 6 mass %, Si in a range of 3 mass % to 17 mass %, Zn in a range of 0.05 mass % to 2 mass %, and Sr in a range of 0.001 mass % to 1 mass %. An average grain diameter of Si grains in an alloy structure of the substrate is 2 ?m or less. The film has a thickness of 10 ?m or greater. The substrate has an outer diameter of 53 mm or greater, a thickness of 0.9 mm or less, and a Young's modulus of 79 GPa or higher.

Abstract: A substrate for a magnetic recording medium having a disc shape with a central hole is provided in which the surface roughness of the principal surface of the substrate is 1 angstrom or less in terms of root mean square roughness (Rq) when a space period (L) of an undulation in the circumferential direction is in the range 10 to 1,000 ?m, and in which when a component in the vertical axis direction of a line segment Z connecting a point A with the space period (L) of 10 ?m and a point B with the space period (L) of 1,000 ?m in a curve S marked on a double logarithmic graph which is obtained by analyzing the surface roughness using a spectrum and in which the horizontal axis is set to the space period (L) (?m) and the vertical axis is set to the power spectrum density (PSD) (k·angstrom2·?m) (where k is a constant) is defined as H and a displacement at which the component in the vertical axis direction of the curve S is the maximum with respect to the line segment Z is defined as ?H, a value (P) expressed by (?