Comprehensive Comparative Study and Prospect of Inorganic - Based Chromium - Free Composite Passivation

Based on the chromium - free passivation technology on the surface of the galvanized layer, the advantages and disadvantages of four composite passivation systems with silicate, molybdate, titanium salt and rare earth metal salt as the main film - forming substances were summarized from the 3 aspects including the properties of the passivation film, the stability of the passivation solution and the corrosion resistance mechanism of the film, which showed that the system with the best corrosion resistance was the silicate system. The differences in the stability of the passivation solution of each system and the different influencing factors were compared, and the corresponding improvement methods of different systems were summarized, which indicated that the silicate system had the best stability. Besides, it was described that silicate, molybdate and titanium salt systems could obtain plenty of colors through different compounding methods. The corrosion resistance mechanisms of molybdate, titanium salt and rare earth metal salt systems were similar. The passivation solution environment caused Zn2+ reaction to produce precipitates that adhered to the surface of the substrate, while the complexation of silicate was obviously easy to form a network of macromolecular substances to achieve uniform adhesion. The best compatibility principles of each system were listed. Finally, through the above comprehensive comparison, it was found that the silicate system had a good application prospect as the main film - forming substance. Its film had excellent corrosion resistance, diverse film colors and minimal surface defects. Molybdenum ions and rare earth metal ions could be used as additives to improve self - repairing performance of film.