Plasma electrolytic oxidation coatings on cp-Mg with cerium nitrate and benzotriazole immersion post-treatments

Cerium nitrate (Ce(NO₃)₃) and benzotriazole (BTA) were applied as immersion post-treatments for Plasma Electrolytic Oxidation (PEO) coatings on commercially pure magnesium. The surface morphology of the coated samples was characterised by Scanning Electron Microscopy (SEM), and it was found that the micro-pores on the coating surface can be effectively sealed by Ce(NO₃)₃ immersion post-treatment, whereas BTA did not show any significant effect on the coating microstructure. The corrosion resistance behaviour of the coated samples was examined by electrochemical tests in a 3.5 wt% NaCl solution. According to the results, the Ce(NO₃)₃ immersion post-treatment showed the better effect in enhancing the corrosion resistance of the PEO coating, compared with BTA immersion post-treatment. The insoluble Ce-containing compounds can provide both a sealing effect and continuous longer-term protection for the PEO-Ce(NO₃)₃ coating. At the same time, BTA provides only a short-term improvement in the corrosion resistance, due to adsorption on the coating surface.