SURFACE-TREATED AL OR AL ALLOY MATERIAL HAVING SUPERIOR FILIFORM CORROSION RESISTANCE

摘要

PURPOSE:To obtain a surface-treated Al or Al alloy material having superior filiform corrosion resistance, improved adhesion of a coating film and improved corrosion resistance by forming a Zn-based plating layer contg. a hydrophilic polymer on the surface of an Al or Al alloy base material and a chromate film contg. a specified amt. or more of Cr6+ on the surface of the plating layer. CONSTITUTION:A Zn-based plating layer contg. a hydrophilic polymer such as polyacrylamide by 0.1-5wt.% (expressed in terms of C) is formed on the surface of an Al or Al alloy base material preferably in =0.1mum thickness. A chromate film is then formed on the surface of the plating layer by coating, reaction, electrolysis or other treatment. It is necessary that the amt. of hexavalent Cr in the chromate film is regulated to iota10 atomic%, preferably =30 atomic% of the amt. of total Cr in the film from the viewpoint of corrosion resistance. By this method, a surface-treated Al or Al alloy material having superior filiform corrosion resistance is obtd.