ALUMINUM AND ALUMINUM ALLOY SHEET FOR STRETCH-FLANGING

PURPOSE:To obtain substantial stretch-flanging property even in a high-strength and thin-walled stock by applying a method for roughening the surface of an Al material sheet to improve the press formability thereof in the stage of rolling to the titled sheet stock and specifying the range of the surface roughness thereof. CONSTITUTION:The surface roughness of the Al or Al alloy sheet is so adjusted by rolling rolls in such a manner that the length l measured in the direction at least parallel with the rolling direction and perpendicular thereto is 25.4mm, the max. peak-to-valley height Rmax (height of the highest peak M0) ranges 1.5-3.5mu and the number of the peaks M having >=1.27mu (50mu inch) height H is >=25 pieces at the length l. The stretch-flanging property of the Al or Al alloy sheet stock can be thereby improved. The assurance of the substantial stretch-flanging property is thus made possible even with the high-strength and thin-walled stock.