Pretreatment method of aluminum moldings or aluminum alloy moldings painted

摘要

PURPOSE: To provide a pretreatment method to form a pretreatment film on an aluminum molded body and aluminum alloy molded body which maintains the appearance of the raw material and has excellent corrosion resistance as a pretreatment film, excellent corrosion resistance (especially corrosion resistance against filiform errosion) after coating, and adhesivity. ;CONSTITUTION: The surface of an aluminum molded body or aluminum alloy molded body is subjected to coating pretreatment by cathode electrolytic treatment in an acid soln. of pH0.5-2.0 containing ≥2g/l hexavalent chromium ion, 0.02-2.0g/l sulfuric acid ion with 0.5-205A/dm² current density for ≥30sec. Thus, a colorless chromating film having 30-250mg/m² chromium deposition is formed. Further, a rather thick and colorless chromating film is formed by adding colloidal silica, etc., to the acid soln. above described. Or with addition of titanium, corrosion resistance against filiform errosion can be further improved.;COPYRIGHT: (C)1993,JPO&Japio