Effects of Current Density on the Microstructure and the Corrosion Resistance of Alumina Coatings Embedded with SiC Nano-particles Produced by Micro-arc Oxidation

To improve the surface corrosion resistance of the alumina films fabricated by micro-arc oxidation (MAO), Al2O3 coatings at different current densities (5, 7 and 10 A/dm2) were produced on aluminum alloys by adding SiC nano-particles into electrolyte during MAO process. The morphology and phase composition of the coatings were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Furthermore, the corrosion performance of the coatings was evaluated via a three-electrode system in a 3.5 wt pct NaCl solution. From the obtained morphology of alumina coatings, it was believed that the Al2O3 coatings embedded with SiC nano-particles were formed. The electrochemical impedance spectroscopy (EIS) plots and potentiodynamic polarization plots of the Al2O3 coatings with and without SiC nano-particles at different current densities reveal that the Al2O3 coatings with SiC nano-particles formed at 10 A/dm2 showed the better corrosion resistance than the other coatings produced at 5 and 7 A/dm2.