| 摘要 |
PURPOSE:To reduce the size an weight of a magnetic disk and to improve the magnetic recording density by specifying the percentages of Al, Cu, Mn, Mg and inevitable impurities contained in an Al alloy so as to increase the strength. CONSTITUTION:This Al alloy consists of, by weight, 0.3-2.0% Cu, 0.1-0.5% Mn, 3.0-5.0% Mg and the balance Al with inevitable impurities including <=0.20% Si, <=0.50% Fe, <=0.05% Cr, <=0.04% Ni, <=0.50% Zn and <=0.01% Ti. Cu, Mn and Mg can remarkably increase the hardness and strength of the alloy, and Si, Fe, Cr, Ni, Zn and Ti as inevitable impurities each form an intermetallic compound. Since the Al alloy having said composition has high hardness, when it is used as the material of the substrate of a magnetic disk, the surface can be converted into a much superior mirror finished surface by buffing in a relatively short time. Intermetallic compounds present in the matrix are fine and uniform, and nonmetallic inclusions have been removed by filtering molten metal or by other means, so the thickness of a magnetic recording medium can be reduced. |
