Investigation of the mechanism of plasma electrolytic oxidation of aluminium using 18O tracer

18O is used as a tracer to investigate the mechanism of plasma electrolytic oxidation of aluminium under AC conditions, with distributions of 18O species in the coatings determined by imaging SIMS. The transport of the oxygen species to the inner part of the coating occur through short-circuit paths, leading to formation of fresh alumina within the coating material near to the substrate. With increased times of PEO treatment the coating growth rate declines substantially, and concentration of 18O tracer is much reduced in the coating, either due to dispersal of the tracer in the coating or loss of coating material.