Corrosion behavior of Ce(III) conversion coating in 3.5%NaCl solution by electrochemical impedance spectroscope

The corrosion behavior of cerium(III) conversion coating on B95 aluminum alloy in 3.5%NaCl solution was investigated by electrochemical impedance spectroscope (EIS). The process of corrosion and mechanism of cerium(III) conversion coating on B95 aluminum alloy were investigated through the changes of EIS in the process. The tested EIS based on equivalent circuit was analyzed. The results show that the variation of EIS can clearly display the corrosion behavior change of cerium(III) conversion coating on B95 aluminum alloy in 3.5%NaCl solution. Through investigating the EIS features, the respective model of each stage and its corresponding equivalent circuit were built to show the corrosion and destruction of the Ce(III) conversion coating on B95 aluminum alloy. They are, respectively, the early stage, the middle stage and the terminal stage of immersion. The early stage refers to the time when the conversion coating on aluminum alloy is moisturized by electrolyte solution and water begins to permeate into the coating. The middle stage refers to the time when this permeation into the conversion coating is destructed while the conversion coating undergoes self-rehabilitation, thus giving rise to the competition between the destruction and self-rehabilitation of the conversion coating. The terminal stage refers to the time when the destruction of conversion coating outweighs its self-rehabilitation, the alloy begins to get corroded and resolved. This model can predict the corrosion degree of the conversion coating surface.