Plasma electrolytic oxidation of aluminium using conventional anodizing precursors and electrolytic colouring with Cu, Sn and Ni

Previous studies have demonstrated that conventional anodizing precursors can reduce the energy consumption of plasma electrolytic oxidation (PEO) by facilitating the transition to the soft sparking regime, which produces denser coatings with improved wear performance. Here, we investigate the influence of anodizing precursors electrolytically coloured with Cu, Sn and Ni prior to PEO. Metal species accelerate the transition to soft sparking, with Cu exhibiting the greatest energy savings (~ 54 %) due to deposits in the inner precursor regions promoting dielectric breakdown. Wear resistance of the most energy-efficient system (A(Cu)-PEO) was comparable to Cu-free coatings (PEO, A-PEO), although A-PEO exhibited a lower friction coefficient (~ 0.69) after long sliding distances, linked to a more compact coating from extended soft sparking. Electrochemical impedance spectroscopy (EIS) revealed that Cu led to a weaker barrier layer in A(Cu)-PEO, yet the substrate showed negligible corrosion after 28 days in 3.5 wt% NaCl. Overall, A-PEO and A(Cu)-PEO are viable alternatives to conventional PEO, offering substantial energy savings without compromising performance. • PEO coatings are developed on electrolytic coloured (Sn, Cu and Ni) anodic films. • A(Cu)-PEO achieved the highest energy savings (56 % vs. PEO). • A-PEO showed reduced friction coefficient after long sliding distances. • Similar corrosion performance of PEO coatings with/without precursors in 3.5 % NaCl