The evidence of cathodic micro-discharges during plasma electrolytic oxidation of light metallic alloys and micro-discharge intensity depending on pH of the electrolyte

Plasma electrolytic oxidation processing of aluminum and magnesium alloys has been carried out in alkaline electrolyte. High probability of cathodic plasma micro-discharge realization in this electrolyte is pointed out It is determined that it is possible to control the energy which is released in anodic and cathodic micro-discharges during PEO processing by changing the pH. Realization of effective local anode, which mostly consists of hydrogen cations, by cathodic polarization of the work electrode in acid electrolyte at the gas-vapor phase/electrolyte is pointed out. Protons, at a relatively low intensity of electric field, may acquire high kinetic energy; because of their smallest radius, protons have a greater mean free path than other cations. They may therefore acquire high kinetic energy, even at relatively low intensity electric field, and hence implement an intensive bombardment of the vapor phase molecules and the metal substrate at the bottom of the coating pores. Electrons injected from molecules and metal substrate during the bombardment are likely to be the founders of electron avalanche. (C) 2015 Elsevier B.V. All rights reserved.