| 摘要 |
PURPOSE: To provide superior strength and bendability, even in the case of low temp. baking treatment by using water paint, by specifying a composition and controlling the state of distribution of second-phase compounds. CONSTITUTION: A composition, which contains, by weight ratio, 2.8-4.0% Mg, 0.5-1.0% Mn, 0.2-0.5% Fe, 0.005-0.2% Cu, and 0.01-0.1% Ti and satisfies Mn+Fe<=1.3% and has the balance Al with inevitable impurities and in which Si content is limited to <=0.4%, is provided. Further, in an alloy sheet of this composition, the second-phase compounds distributed in the surface are regulated so that those of <=2μm grain size are 100pieces/m<2> and those of 6-15μm grain size are 250pieces/m<2> , and also proof stress after baking finish is regulated to >=300MPa. This alloy sheet can be produced by subjecting an ingot to homogenizing treatment at 450-550 deg.C for 1-20hr, to hot rolling, and then to cold rolling at >=60% draft, and further, baking finish treatment is done by performing baking at 200-250 deg.C for <=2min after surface preparation of alkali etching and chemical conversion treatment. |
