COMPOSITE COATINGS COMBINING PEO LAYER AND EPD LAYER ON MAGNESIUM ALLOY

摘要

Protective composite coatings were prepared combining plasma electrolytic oxidation (PEO) treatment and cathodic electrophoretic deposition on magnesium alloy AZ91D. The corrosion protection of composite coatings were evaluated using potentiodynamic polarization measurements in 3.5% NaCl solution, copper accelerated acetate salt spray (CASS) test and immersion test in acid solution. The adhesion of composite coatings was evaluated using cross-cut test and pull-off test. It is indicated that the corrosion resistance of magnesium alloy AZ91D with the composite coatings is improved obviously compared to it merely with PEO coating and it is also shown that pitting corrosion of PEO coating on magnesium alloy is decreased with EPD post-treatment. The adhesion of composite coatings could be up to 11.3 N/mm~2 in quantitative method due to the interlocking effect of organic layer in pores of PEO layer.