Corrosion, erosion and erosion-corrosion performance of plasma electrolytic oxidation (PEO) deposited Al2O3 coatings

Electrolytic plasma techniques have been used to surface modify 6082 aluminium alloy to a depth of 100 μm. Potentiodynamic polarisations and electrochemical impedance spectroscopy (EIS) have been made under static conditions in order to evaluate the corrosion performance of both unsealed and sealed PEO coatings. The erosion and erosion-corrosion performance of the unsealed PEO Al2O3 coating has also been assessed for a range erodent kinetic energies which varied between 0.016 and 7.1 μJ. The erosion and erosion-corrosion tests were carried out using subangular sand particles ranging in size from 135 to 235 μm. Scanning electron microscopy (SEM) was used to investigate the coating microstructure and the coating/substrate interface. The analyses show that the PEO Al2O3 coatings studied in this investigation had a pore/crack network to the Al alloy substrate, which compromised the corrosion performance and ultimately the erosion-corrosion performance.