An improvement of the wear and corrosion resistances of AZ31 magnesium alloy by plasma electrolytic oxidation in a silicate-hexametaphosphate electrolyte with the suspension of SiC nanoparticles

Plasma electrolytic oxidation (PEO) of AZ31 magnesium alloy under pulsed bipolar constant current regimes has been carried out in a silicate-hexametaphosphate electrolyte without and with the suspension of SiC nanoparticles. The coatings were characterized by eddy current method, X-ray diffraction (XRD), scanning electron microscopy (SEM), dry sliding wear and electrochemical tests. Higher growth rates were found for the coatings formed with the presence of nanoparticles. The incorporation of SiC nanoparticles into the coatings has been verified by XRD and SEM, and the incorporated particles were found to distribute relatively uniformly along the coating depth. Weak sites existed in the SiC free coatings, which significantly lowered the wear performance of the coatings. In contrast, weak sites are not found in the coatings with the incorporation of SiC nanoparticles, resulting in an excellent wear performance of the coatings. The applied current densities of the PEO processes also affect the performance of the coatings, with higher wear rates for the coating prepared under higher current densities. All the coatings show improved corrosion resistances. (C) 2015 Elsevier B.V. All rights reserved.