The Role of Potassium Permanganate Additive on Microstructure and Corrosion Behavior of Pulsed Plasma Electrolytic Oxidation Coatings on 7075 Al alloy

Plasma electrolytic oxidation (PEO) process using a pulsed current regime was performed on 7075 Al alloy in silicate based electrolytic bath with and without potassium permanganate as an additive. The results showed that with adding potassium permanganate to the electrolyte, an oxide coating containing Mn as the major element, Si and Al with a higher thickness was formed, which showed different microstructure and surface morphology than that produced in bath containing no additive. According to the observations, oxygen reduction became intense, the sparking quality on the surface was improved and the occurrence of destructive discharges were prevented and thus, a uniform and compact coating with lower defects was achieved. The corrosion behavior of the PEO coatings was evaluated using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization technique in 3.5 % NaCl solution at pH 4. The results showed that the coating produced in the presence of potassium permanganate had the higher corrosion resistance due to its higher thickness and compactness of the inner layer.