Study on process of black passivation for Zn-Fe alloy coatings II -Optimal process conditions and corrosion resistance of passivating film

Based on investigation of components in passivating solution, effects of process conditions on corrosion resistance of Zn-Fe alloy coatings after passivation were studied in detail, thereby optimal process conditions were identified. Properties of Zn-Fe alloy coatings after passivation were tested. Corrosion resistance of passivating films of Zn coatings, Zn-Fe alloy coatings and Zn-Fe-TiO2 composite coatings were studied and compared by dipping experiments in neutral solution of 5% NaCl. Results show that after black passivation, both Zn-Fe alloy coalings and Zn-Fe-TiO2 composite coatings were greatly improved in corrosion resistance. In addition, the corrosion resistance of Zn-Fe alloy coatings was more than 3 times of that of Zn coatings, while the corrosion resistance of Zn-Fe-TiO2 composite coatings was about 2 times of that of Zn-Fe alloy coatings and about 5 times of that of Zn coatings.