Comparative Corrosion Resistance of Molybdate Conversion Coatings Containing SiO2 or TiO2 Nanoparticles

In this paper, corrosion resistance was compared between molybdate conversion coatings containing SiO2 or TiO2 nanoparticles, on five magnesium alloys exposed to a 3.5 wt.% NaCl solution. The surface morphology of the molybdate conversion coatings containing SiO2 or TiO2 nanoparticles was examined by scanning electron microscopy (SEM). The corrosion resistance of the nanocoatings was investigated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and potentiodynamic cyclic anodic polarization measurements. The electrochemical methods showed that the addition of SiO2 or TiO2 nanoparticles to the conversion treatment has significantly improved the corrosion resistance property of molybdate conversion coatings for all tested Mg alloys, but revealed that TiO2 was more effective.