Effect of Current Density on Microstructure and Corrosion Behavior of Plasma Electrolytic Oxidation Coated 6063 Aluminum Alloy

Plasma electrolytic oxidation(PEO) coatings were fabricated on 6063 aluminum alloy in a cheap and convenient electrolyte. The effect of different current densities, i e, 5, 10, 15, and 20 A/dm2on the microstructure and corrosion behavior of coatings was comprehensively studied by scanning electron microscopy(SEM), stereoscopic microscopy, potentiodynamic polarization and electrochemical impedance spectroscopy(EIS), respectively. It is found that the pore density decreases and the pore size increases with increasing current density. The XRD results show that the coatings are only composed of α-Al2O3and γ-Al2O3. Potentiodynamic polarization test proves that the coating formed under 10 A/dm2possesses the best anticorrosion property. The long time EIS test shows that the coating under 10 A/dm2is able to protect the aluminum alloy substrate after long time of immersion in 0.59 M NaCl solution, which confirms the salt solution immersion test results in 2 M NaCl solution.