Corrosion Resistance of Organic Chromate-Free Passivation Coating for Galvanized Steel

A new passivation bath(ACM) using a non\|toxic water solubility acrylic resin(AC) with some molybdate and phosphate(M) was developed for galvanized steel to instead of toxic chromate. Corrosion resistance and mechanism were studied by salt spaying test, SEM and electrochemistry tests etc. Results showed that ACM coating retarded the formation of white rust on the galvanized steel and the corrosion resistance of coating was closed to that of the chromate conversion coating. The corrosion mechanism of ACM coating might be concluded that cross linking reaction between inorganic groups such as MoO\+\{2-\}\-4, PO\+\{3-\}\-4 and certain organic groups of acrylic resin in passivation could prohibit the development of cracks in the coating and increase the corrosion resistance because of the inhibition of Mo and P in coating.