Corrosion Behavior and Structure of Plasma Electrolytic Oxidation Coated Aluminum Alloy

In this study, the plasma electrolytic oxidation (PEO) coatings were formed on aluminum alloy in a cheap and convenient electrolyte. The effect of different current densities, i.e., 5 A/dm(2), 10 A/dm(2), 15 A/dm(2) and 20 A/dm(2) on microstructure and corrosion behavior of coatings was comprehensively studied by scanning electron microscopy (SEM), stereoscopic microscopy, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests, respectively. It was found that the pore density decreased and the pore size increased with the increment of the applied current density. The X-ray diffraction (XRD) results showed that the coatings were only composed of alpha-Al2O3 and gamma-Al2O3. Potentiodynamic polarization test proved that the coating formed under the current density of 10 A/dm(2) showed the best anti-corrosion property. The long time EIS test showed that the coating formed under the current density of 10 A/dm(2) was capable to protect the aluminum alloy substrate after long time of immersion in 0.59 M NaCl solution, which confirmed well with the salt solution immersion test results in 2 M NaCl solution.