Study on corrosion resistance of trivalent chromium passivation films on zinc coatings electroplated by different processes

The Zn coatings electroplated respectively from acid potassium chloride,alkaline non-cyanide and alkaline cyanide electrolytes were passivated with a trivalent chromium iridescent passivating agent.The corrosion resistance of the passivation films was studied by neutral salt spray(NSS) test and electrochemical impedance spectroscopy(EIS).The results showed that the corrosion resistance of the passivation films and their electrical resistance in a 1%(mass fraction) NaCl solution for different Zn electroplating processes are in the following descending order:acid potassium chloride alkaline non-cyanide alkaline cyanide.The better corrosion resistance of the acid potassium chloride Zn plating coating may be attributed to the less incorporation of organic impurities.