Structural, tribological and electrochemical behavior of SiC nanocomposite oxide coatings fabricated by plasma electrolytic oxidation (PEO) on AZ31 magnesium alloy

This study investigated the microstructural, tribological and electrochemical properties of oxide layers containing silica (SiC) nanoparticles produced by plasma electrolytic oxidation (PEO) process on AZ31 magnesium alloy. For this purpose, PEO process was carried out in different current densities in aluminate-silicate and phosphate based electrolytes with and without SiC nanoparticles. Microstructure and composition of the coatings was studied by scanning electron microscope (SEM) equipped with energy dispersive spectroscope (EDS) and X-ray diffraction (XRD). Tribological properties of the uncoated AZ31 Mg alloy and PEO-synthesized oxide coatings were evaluated using a reciprocating ball-on-disk tribometer. The electrochemical behavior of the coated specimens was investigated by potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) measurements in 3.5 wt% NaCl solution. The coatings produced from aluminate-silicate electrolyte possess high hardness and provide a low wear rate and friction coefficient than those obtained from phosphate electrolyte. Furthermore, the SiC-containing coatings registered much lower friction coefficient and wear rate than the un-coated AZ31 Mg alloy and the SiC-free oxide coatings, exhibiting excellent self lubricating property. The coatings obtained from the aluminate-silicate electrolyte showed better corrosion resistance due to their compacter microstructure and higher chemical stability.