Phytic acid conversion coatings on magnesium surface treatment with cerium chloride solution.

A chromium-free composite conversion treatment for magnesium by phytic acid and CeCl solutions was studied. The composite coatings on the surface of magnesium presented network-like cracks, which was consisted of Mg, O, C, P and Ce elements. The distribution of Ce on the surface layer was non-uniform. The crack sizes of the composite coating were smaller than that of the phytic acid conversion coating. The corrosion process of the coatings was evaluated through electrochemical impedance spectroscopy in 3.5% NaCl solution, and the equivalent circuit of RL(Q(R(QR))) model was obtained through the characteristics of EIS. The average corrosion rate of the composite coating was reduced at least 50% compared with that of pure phytic acid conversion coating. [ABSTRACT FROM AUTHOR]