Evaluation of alumina nanoparticles concentration and stirring rate on wear and corrosion behavior of nanocomposite PEO coating on AZ31 magnesium alloy

The effect of electrolyte stirring rate and concentration of nanoparticles on alumina nanoparticles absorption in the coating fabricated by plasma electrolytic oxidation on magnesium substrate was investigated. Microstructure, corrosion resistance and wear behavior of the nanocomposite coating were analyzed by scanning electron microscopy (SEM), potentiodynamic polarization and electrochemical impedance spectroscopy, and pin-on-disk tests, respectively. The results showed that the highest amount of nanoparticle absorption happened at the stirring rate of 100 rpm, and decreased at higher stirring rates because of the high turbulence of the electrolyte, which washes the nanoparticles away from the surface of the anode. The effect of alumina concentration in the electrolyte on the alumina nanoparticles' absorption was also analyzed, and the results indicated that by increasing the concentration of nanoparticles in the electrolyte, the absorption of nanoparticles increased up to 30 g/L, and then reached the saturated level. Also the best corrosion resistance the lowest wear rate was obtained in the stirring rate of 100 rpm at a concentration of 30 g/L of alumina nanoparticles.