The evidence of cathodic micro-discharges during plasma electrolytic oxidation process

Plasma electrolytic oxidation (PEO) processing of EV31 magnesium alloy has been carried out in fluoride containing electrolyte under bipolar pulse current regime. Unusual PEO cathodic micro-discharges have been observed and investigated. It is shown that the cathodic micro-discharges exhibit a collective intermittent behavior, which is discussed in terms of charge accumulations at the layer/electrolyte and layer/metal interfaces. Optical emission spectroscopy is used to determine the electron density (typ. 1015 cm−3) and the electron temperature (typ. 7500 K) while the role of F− anions on the appearance of cathodic micro-discharges is pointed out.