Tailored aluminium oxide layers by bipolar current adjustment in the Plasma Electrolytic Oxidation (PEO) process

The plasma electrolytic oxidation process of aluminium alloys is investigated for two different current waveforms. It is shown that particular conditions may be established which strongly reduce the arcing that usually cause detrimental defects in the oxide layer for treatment time greater than typically 40-50 min. This results in a "softer" process. As a consequence thick homogenous layers may be grown with no large discharge channels. Through the presented results, the importance of the negative charge density relative to the positive one is evidenced thus pointing out the need of using a pulse bipolar current supply. (c) 2006 Elsevier B.V. All rights reserved.