Preparation And Corrosion Inhibition Properties Of Non-chromate Passivation Films Of Galvanized Sheet

The non-chromate passivation technology can improve the corrosion resistance and anti-white rust ability of zinc coating, which is one of the important research for the corrosion and protection of galvanized sheet.The molybdate and the cerium salt on the hot-dip galvanized (HDG) sheet passivation technology had been studied, and a mixture of molybdate and cerium salt passivation craft had been preliminary discussed, the optimum conditions of inorganic film formation were established. The Pb(Ac)2 titration test could achieve 40s. The optimum process conditions for preparation silane (KH-560) film on zinc coating were also gained. The CuSO4 titration test could achieve 52s. The two-step passivation had been preliminary discussed, carried on the KH-560 passivating firstly, and the molybdate passivating afterwards, the corrosion resistance was more superior. The CuSO4 titration test could achieve 68s.The results of the salt immersion tests showed that: The inorganic compound film could protect the zinc coating well, the corrosion rate was 38% of HDG; the anti-corrosion property of the two-step passivation film was improved, the corrosion rate was 36% of HDG, near to chromates passivation level.The chemical structure and surface of each kind of passivation films were characterized and analyzed by SEM, EDS and XPS methods. The results indicated that: The structure of inorganic film was complete, Ce3+, Ce4+, Mo6+and Mo4+ ions were simultaneously existed in the coating surface, which proved that the forming process of the inorganic film taking the membrane theory as a foundation. Mo4+ was existed in the two-step passivation coating surface, which proved that the forming process of the two-step passivation film was the result of the interactional of adsorption and the membrane theory.The mechanism of corrosion was discussed by the electrochemistry test. The results showed that: The electrochemical corrosion reaction were restrained and the corrosion current density was reduced by the inorganic compound film and the two-step passivation film, which improved the corrosion resistance of the zinc coating.