STUDY OF THE CORROSION PROCESS OF A PEO-TREATED ALUMINUM ALLOY IN DIFFERENT CONCENTRATIONS OF NaCl

Plasma electrolytic oxidation (PEO) treated ceramic coatings were formed in silicate-based electrolytes without and with the addition of Al2O3, on an aluminum alloy. It was found that the coating produced in an electrolyte containing 7 g/L of Al2O3 exhibited the most superior corrosion properties. The corrosion properties of the coatings in 0.5 M and 1 M NaCl solutions were studied by means of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results proved that the coating can protect the substrate from the corrosion due to aggressive Cl- in 0.5 M NaCl after 384-h immersion. However, it cannot protect the substrate after 384-h immersion in 1 M NaCl solution. The potentiodynamic polarization results matched well with the EIS test results.