Abstract: A magnetic hard disc substrate made of an aluminum alloy for memory devices such as a computer must correspond to an improved structure in which the interval between a head and a medium is made narrower to attain high density recording. In order to prevent head crash, it is required that the magnetic hard disc substrate have a smooth surface and decreased defects. The present invention provides a process for manufacturing a magnetic hard disc substrate made of an aluminum alloy which satisfies the above requirements and also provides a disc substrate which has a surface roughness Ra≦0.5 nm and is free from abrasive flaws with a depth of 5 nm or more and from micro-waviness or provides a disc substrate which has a surface roughness Ra≦5 angstroms and a surface roughness Rmax≦80 angstroms and in which the number of scratches with a depth of 50 angstroms or more is 5 or less and the number of pits with a depth of 50 angstroms or less is 5 or less in the surface.

Abstract: Magnetic disk substrates are produced by subjecting glass substrates to at least steps of degreasing, etching, sensitization with tin chloride, activation and sensitivity-enhancing treatment in that order, then plating the pretreated substrates with a nickel/phosphorus film, and thereafter polishing the plated substrates. In the process, the substrates being processed are washed with hot pure water at a temperature of not lower than 50° C. for a period of from 20 to 90 seconds, after the sensitization step but before the activation step, and heated at a temperature of not lower than 70° C. for a period of from 5 to 100 minutes, after the sensitization step but before the nickel/phosphorus-plating step.

Abstract: A provision of a magnetic disk substrate using, as a plated substrate, glass with high hardness in place of aluminum. The magnetic disk substrate is small-sized, can stand against an impact when it is carried, and avoids leaving struck damages (head snap) even if it is used for recent note- or mobile-type computers having a head which is located as closely as possible to the substrate. The magnetic disk substrate comprises forming a nickel/phosphorus coating with a film thickness of 8 &mgr;m-20 &mgr;m or less on crystallized glass with a roughness Ra of 0.05 to 0.5 &mgr;m, the roughness being measured by a tracer and contact type roughness meter after the glass is ground (lapped) and polishing the nickel/phosphorus coating to a depth of 3 &mgr;m or more in a polishing process with the thickness of the plating film left unremoved being 5 &mgr;m or more.

Abstract: A magnetic hard disc substrate made of an aluminum alloy for memory devices such as a computer must correspond to an improved structure in which the interval between a head and a medium is made narrower to attain high density recording. In order to prevent head crash, it is required that the magnetic hard disc substrate have a smooth surface and decreased defects. The present invention provides a process for manufacturing a magnetic hard disc substrate made of an aluminum alloy which satisfies the above requirements and also provides a disc substrate which has a surface roughness Ra.ltoreq.0.5 nm and is free from abrasive flaws with a depth of 5 nm or more and from micro-waviness or provides a disc substrate which has a surface roughness Ra.ltoreq.5 angstroms and a surface roughness Rmax.ltoreq.80 angstroms and in which the number of scratches with a depth of 50 angstroms or more is 5 or less and the number of pits with a depth of 50 angstroms or less is 5 or less in the surface.