Aluminum substrate for magnetic recording media
AssigneeNippon Light Metal Company, Ltd.
InventorsKoichi Yoshida, Yoshio Hirayama, Yasuo Oka, Takashi Kajiyama, Kunihiko Hotta
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Abstract
An aluminum substrate for magnetic recording media such as magnetic disks, etc., is composed of an aluminum alloy plate containing 2 to 6% by weight magnesium and impurities in only limited amounts and having on the surface an anodic oxidation film with thickness more than 3 .mu.m formed by a chromic acid process. In the thus-anodized aluminum substrate, the occurrence of black spot defects is greatly reduced and the formation of cracks upon heating the substrate to high temperatures is prevented in spite of the thicker anodic oxidation film.
Claims3
An aluminum substrate for magnetic recording media comprising an aluminum alloy plate composed of 2 to 6% by weight magnesium, the remainder being aluminum and impurities, the limits of the allowable contents of said impurities being 0.003% iron, 0.005% silicon, 0.25% copper, 0.5% zinc, 0.0005% manganese, 0.0005% chromium, 0.0005% nickel, and 0.0005% titanium and for the total amount of other impurities 0.001%, said aluminum base plate having on the surface thereof an anodic oxidation film having a thickness more than 3 .mu.m formed by a chromic acid anodization process.
Dependencies are inferred from the claim text.