Development of vanadium impregnated flat absorber composite PEO coating on AA6061 alloy

The formation of black plasma electrolytic oxidation (PEO) coating on aluminium alloy using vanadyl sulphate as additive in a silicate-based electrolyte is investigated. A brief discussion on the mechanism of incorporation of vanadium in PEO coating starting with a cationic species of vanadium (i.e., VO2+) in solution is attempted. The coating formation with respect to morphology and composition is systematically studied as a function of process time. With increase in process time, incorporation of vanadium ions in the coating increases and the formation of black colour is attributed to the presence of V3+ and V4+ species in the coating. A 55 ± 5 μm thick flat absorber black coating with high solar absorptance (0.92) and high infrared emittance (0.88) is obtained with a process time of 10 min. •Vanadyl sulphate is used as an additive to develop black PEO coating.•Novelty in using a cationic source of vanadium (VO2+) in solution.•Mechanism of incorporation of vanadium starting from VO2+ cation is discussed.•A flat absorber coating with absorptance (0.92) and emittance (0.88) is obtained.•SEM reveals interesting morphological variations with respect to process time.