PASSIVATION AND CORROSION RESISTANCE OF MECHANICALLY PLATED ZINC COATING

The mechanically plated zinc coating was passivated with chemicals containing trivalent chromium,rare earth metal and hexavalent chromium respectively.Then the corrosion resistance and electrochemical behavior of the passivated coatings were compared by salt spay test and electrochemical test.The result of salt spay test showed that the coatings passivated with trivalent chromium and rare earth metal are superior to that with hexavalent chromium by one fold in corrosion resistance.The coating passivated with rare earth metal was the best in corrosion resistance and that with trivalent chromium was the next.The electrochemical test showed that all the passivation treatments with trivalent chromium,rare earth metal and hexavalent chromium could suppress the cathode reactions to some extent.The effectiveness of passivation chemicals in suppression of the cathodic reaction might be ranking as follows: rare earth metal,trivalent chromium,and hexavalent chromium.Therefore,chemicals containing trivalent chromium and rare earth metal had good application foreground for their good corrosion resistance and environmental-friendly.