AC PEO of aluminium with porous alumina precursor films

The effect of the composition, morphology and thickness of pre-formed porous anodic films on the subsequent formation of coatings on aluminium by plasma electrolytic oxidation is investigated. The pre-formed films, of a wide range of thickness, are shown to be incorporated into the coatings. Further, an increased thickness of the film is revealed as beneficial to the establishment of a microarc regime that is favourable for the formation of the coatings. The anodic alumina undergoes melting under the microdischarges, which changes the cellular film morphology and reduces the concentration of anion contaminants.