| 摘要 |
PROBLEM TO BE SOLVED: To improve the filiform corrosion resistance as corrosion resistance after coating by incorporating Si, Mg and Cu in specified ranges into an Al alloy sheet and depositing the surface of the alloy sheet with zinc phosphate by the value equal to or above the specified one. SOLUTION: Into an Al alloy sheet for coating, by mass, 0.2 to 1.8% Si, 0.2 to 1.6% Mg and 0.3 to 1.5% Cu are incorporated. The surface of this Al alloy sheet is coated with zinc phosphate of >=1.5 g/m2 coating weight. The compsn. of the Al alloy can be incorporated with other elements such as Fe, Ni, V, Mn, Cr, Zr, Sc, Ag or the like in accordance with the use and the characteristics to be required. As a method for controlling the coating weight of zinc phosphate in the Al alloy sheet to >=1.5 g/m2, the one in which the amt. of free fluorine ions to be added to a zinc phosphate treating bath is increased for improving the etching properties of Al is given. This Al alloy sheet is excellent in filiform corrosion resistance although being incorporated with Cu. |
