ALUMINUM ALLOY SHEET FOR MOTOR VEHICLE AND PROCESS FOR PRODUCING THE SAME

摘要

An aluminum alloy sheet for motor vehicles excellent in press formability, resistance to surface roughening and shape fixability is produced without subjecting the sheet to stabilization treatment by casting a melt, containing 3.0-3.5 mass% Mg, 0.05-0.3 mass% Fe, 0.05-0.15 mass% Si, and further a limited amount of less than 0.1 mass% Mn, a balance substantially being inevitable impurities and Al, into a thin slab having a thickness of to 15 mm in a twin-belt caster so that the cooling rate at 1/4 depth of the thickness of the thin slab is 20 to 200°C/sec; winding the cast thin slab into a coil; subjecting the coiled thin slab to cold rolling with a roll having a surface roughness of 0.2 to 0.7 µm Ra at a cold rolling reduction of 50 to 98%; subjecting the cold rolled thin sheet to final annealing either continuously in a CAL at a holding temperature of 400 to 520°C or in a batch annealing furnace at a holding temperature of 300 to 400°C; and then subjecting the resulting sheet to straightening with a leveler.