The mechanism of evolution of microdischarges at the beginning of the PEO process on aluminum

In this study, we present the results of investigation of plasma electrolytic anodization of aluminum by means of different experimental techniques, in few first minutes of the process. Scanning electron microscopy equipped with X-ray energy dispersive spectroscopy was used to study the aluminum oxide coating morphology, microstructure and composition as well as cross-sections of the obtained coating. The mechanism of evolution of microdischarges at the beginning of the plasma electrolytic anodization process is proposed. Our results indicate that during a single discharge event, new inner oxide layer is formed at the bottom of discharge channel, between the metal substrate and the Al2O3 layer. That new oxide layer and the gas that remains in the channel seem to present a higher barrier for dielectric breakdown then the original coating layer. (C) 2016 Elsevier B.V. All rights reserved.