The correlation between the coating structure and the corrosion behavior of the plasma electrolytic oxidation coating on aluminum

Two kinds of plasma electrolytic oxidation (PEO) coatings with different microstructures were fabricated on AA1060 pure aluminum in two kinds of electrolytes, respectively. The electrochemical behavior of the coatings was evaluated by electrochemical impedance spectroscopy (EIS) in a long term immersion in 3.5 wt.% NaCl solution. Some coatings were detached from the substrate by an electrochemical method and the microstructure of the coatings before and after the immersion was observed by SEM. A compact thin layer of ~ 1 μm in thickness was observed at the coating/substrate interface region. Based on the EIS results and the SEM observation, the effect of the coating structure on the corrosion process changing with immersion time is discussed, especially the effect of the coating/substrate interface layer.