METHOD FOR PRODUCING A CHROMATE SOLUTION OF GALVANIZED STEEL SHEETS WITH AN EXCELLENT SURFACE APPEARANCE AND CORROSION RESISTANCE

摘要

The method comprises adding a reducing agent to the chromic acid anhydride solution having 5˜20 g/l Cr concentration to convert to hexavant Cr, wherein the wt. ratio of reduced trivalent Cr to total Cr is 0.15˜0.25, and preparing the solution including 50˜1000 ppm of zinc concentration by adding 4˜15 g/l phosphoric acid and 0.1˜1.0 g/l fluoric compound. The chromated layer on zinc galvanized steel sheet has good corrosion resistance and surface appearance.