PURPOSE: To manufacture an Al alloy substrate with a superior surface state for magnetic discs by removing intermetallic cpds. and non-metallic inclusions of larger diameter in an Al alloy, followed by casting and specific heat treatment.
CONSTITUTION: An Al alloy is melted contg. Mg; 3W6%, Mn<0.4% and Cr< 0.03%, and Fe<0.1%, Si<0.2% and Ti<0.02% as impurities. The molten alloy is passed through a below 10 μ mesh filter to remove coarse intermetallic cpds. and non-metallic inclusions in the alloy, followed by casting. The resulting ingot is heated at 400W480°C for 3W10 hr and further heated at 500W560°C for 3W48 hr to dissolve or disperse the added elements and impurities. The ingot is then rolled to a 2 mm thick sheet and annealed at 360°C for 4 hr to obtain a substrate for magnetic discs. The surface of the substrate is planed or buffed to give a lightweight Al alloy substrate with superior corrosion resistance, mechanical properties and no protrusion and recess on the surface for magnetic discs.
NAKAGAWA HIDENORI
MATSUDA WAKATAKE
SATOU TAKEHIKO
FURUKAWA ALUMINIUM
FUJITSU LTD