Microstructure and formation mechanism of cerium conversion coating on alumina borate whisker-reinforced AA6061 composite

Cerium conversion coatings, formed on alumina borate whisker-reinforced aluminum composite with pre-treatment for different time, were characterized by SEM/EDX, TEM and electrochemical method. The structure and formation mechanism of the coatings were investigated in detail. It was found that the pre-treatment prior to coatings has strong influence on formation, growth and morphology as well as granular size of coatings. Two typical coating morphologies existed at the pre-treated substrate surfaces. Cracks only presented on thick coatings because of the higher deposition rate and the greater inner stress. Cracks preferably produced at the whisker/matrix interface and the grain boundary of matrix.