Effect of 2nd step voltage on the microstructure and corrosion resistance of plasma electrolytic oxidation coating layer on 6061 aluminium alloy

In this study, a two-step hybrid Plasma Electrolytic Oxidation (PEO) process was used to produce a continuous alumina (Al2O3) coating layer on the 6061 aluminium alloy. The main objective of this study is to analyze the effect of varying the 2nd step voltage on the defect content, including micro-cracks and micro-pores, and the Amorphous Alumina Layer (AAL) thickness on the corrosion resistance of PEO coatings. In addition, the influence of the microstructural soundness of the coating layer on the corrosion properties is investigated. In the first step, a Pulsed Unipolar Mode (PUM) was used at an anode voltage of 500 V to produce a thin continuous alumina layer. Then, in the 2nd step, a Pulsed Bipolar Mode (PBM) was used with the anode voltage increased in 50 V increments from 400 V to 600 V to facilitate the formation of a thicker alumina layer. These results showed that the formation of a sound PEO coating layer with minimal microcrack and micropore content and a higher AAL thickness can significantly improve the corrosion resistance of 6061 aluminium alloy.