Electrochemical response of VxOy-Al2O3 composite layer with dark-green color achieved by plasma electrolytic oxidation

Abstract In an endeavour to study the influence of vanadium pentoxide (V2O5) on 6061 Al alloy, a silicate-based electrolyte with suspended V2O5 particles was employed during plasma electrolytic oxidation for 90 and 180 s, and the electrochemical stability of the resultant oxide layers was investigated. The addition of V2O5 particles reduced the number of microdefects found in the oxide layer after electrolysis. This was attributed mainly to the incorporation of V2O5 particles whose tendency was observed to be increase with time. Surface analysis revealed that the oxide layer comprised vanadium oxides (VxOy) in the oxidation state of +5 and + 4 referred to V2O5 and VO2, respectively. The formation of VO2, which was evident in longer processing time, would be associated to the decomposition of the V2O5 particles by high energy plasma. Accordingly, when a suitable combination of V2O5 and VO2 was achieved in 180 s, an attractive dark-green layer would be obtained. Finally, the electrochemical stability of the samples was improved with the increase of vanadium content, which was interpreted on the basis of Tafel extrapolation and equivalent circuit model.