Impact of shot peening on corrosion performance of AZ31 magnesium alloy coated by PEO: Comparison with conventional surface pre-treatments

This paper deals with the evaluation of the influence of selected pre-treatments, namely shot peening, polishing and grinding, used prior to plasma electrolytic oxidation (PEO) on the corrosion characteristics of AZ31 magnesium alloy in solution of 0.1 M NaCl. Additionally, selected combinations of pre-treatment and PEO coating were optimized in terms of the PEO preparation time. Corrosion characteristics of prepared surfaces were determined by the electrochemical impedance spectroscopy (EIS) during 168 h of exposure at the laboratory temperature followed by the equivalent circuit analysis of measured Nyquist diagrams. Localised corrosion events of selected combinations of pre-treatment and PEO coating were observed by local electrochemical impedance spectroscopy (LEIM) in 1 mM NaCl supplied by the potentiodynamic polarization tests. The obtained results showed that despite the negative impact of shot peening on the electrochemical reactivity of AZ31 alloy, this technique significantly enhanced corrosion stability of the subsequently formed PEO coating.