Corrosion resistance of micro-arc oxidation coatings formed on aluminum alloy with addition of Al2O3

Micro-arc oxidation (MAO)coatings were formed on the aluminum alloy in silicate-based electrolyte without and with the addition of Al2O3. It is showed that the coating produced in 7 g l(-1) Al2O3-containing electrolyte was of the most superior corrosion resistance. Besides, the corrosion properties of the coatings were studied by means of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) test in both 0.5 M and 1 M NaCl solution. The results proved that the coating is capable to protect the substrate from the corrosion of aggressive Cl- in 0.5 M NaCl after 384 h immersion. However, it can not offer protection to the aluminum alloy substrate after 384 h immersion in 1 M NaCl solution. The schematic diagrams illustrate the corrosion process and matched well with the corrosion test results.