Substitutes of Chromate (Cr₆₊) in Passivating Solution for Hot-dip Galvanizing of Steel

Cerium salts,cobalt salts and silicon dioxide were used as chromate (Cr6+) replacers for continuous galvanizing steel sheets.The structure of passive films were observed by scanning electronic microscopy (SEM).The corrosion behavior of the films was evaluated with neutral salt spray test (NSS) and studied with electrochemical technique.The result of SEM showed that a perfect composite film was obtained on the steel sheet and SiO2 blocked the extension of microcracks and decreased the deformation range.The results of NSS and linear polarization showed that the corrosion resistance of the composite film was better than that of chromate (Cr6+) passivated film,cerium and cobalt salts could retard the anodic polarization of corrosion.