Investigation of corrosion resistance of ceramic coating on the surface of 6061 Al alloy created by plasma electrolytic oxidation technique

In this paper, the effect of sodium aluminate concentration on the corrosion behavior of coatings formed on the surface of 6061 Al alloy by plasma electrolytic oxidation is studied. This process applied by DC current mode with current density of 15 A/cm2 in two different concentration of sodium aluminate (6 and 8 g L-1). The corrosion behavior of coatings evaluated by potentiodynamic polarization test in 3.5 wt. % NaCl solution. The microstructure of coatings are investigated by scanning electron microscopy (SEM) images. X-ray diffraction (XRD) pattern confirmed the formation of ceramic compounds in coating. According to the results, increasing of sodium aluminate concentration caused to improvement of surface quality, decreasing of pores size and increasing of corrosion resistance of coatings. According to the potentiodynamic polarization test, the coating formed by 8 g L-1 sodium aluminate concentration presented 31 times lower corrosion current density compared to the aluminum substrate that shows improvement in corrosion resistance of substrate.