The improvement of corrosion resistance of Ce conversion films on aluminum alloy by phosphate post-treatment

A phosphate post-treatment process for Ce conversion film on aluminum was studied. SEM (scanning electronic microscope), XPS (X-ray photoelectron spectroscopy) and electrochemical measurements were used to characterize the properties of the films. After the post-treatment the micro-cracks on the film surface obviously diminished, and corrosion resistance of the conversion film in NaCl solution increased. The conversion film, without post-treatment, was mainly composed of hydrated cerium oxides, and the dehydration of the film may cause cracking of the films. After phosphate treatment, stable cerium phosphate CePO4 was formed on the surface, and the content of crystal water decreased greatly, leading to improvement of the film performance with less micro-cracks.