Changes induced by process parameters in oxide layers grown by the PEO process on Al alloys

The present work focuses on the influence of the distance between the substrate and the counter electrodes on the plasma electrolytic oxidation process. Depending on the waveform parameters of the applied current, two working regimes may be achieved referred to as "soft PEO regime" and "conventional (arcing) PEO regime." At constant process duration, it is shown that the layer thickness increases with the electrode gap distance in the soft regime, whereas it is almost constant in the conventional regime whatever the distance between the electrodes. By using a fast video camera with a time resolution of 8 mu s, it was possible to count the micro-discharges and to determine their position on the surface as a function of the process time. Non-homogeneity in the layer thickness is correlated with the spark and micro-discharge distribution over the surface. (C) 2011 Elsevier B.V. All rights reserved.