Formation of the barrier layer during the initial stage of plasma electrolytic oxidation of aluminium-simulation and experimental validation

During plasma electrolytic oxidation (PEO), an electrochemical oxide layer formation is essential for the substrate passivation, both during the initial stage of the PEO process, prior to the onset of discharges, and at the bottom of discharge channels during ongoing PEO treatment. Therefore, the final properties of the PEO coating are linked to the electrochemical formation of the oxide layer. This study presents a two-dimensional simulation of the barrier layer formation during the initial stage of PEO on aluminium. The high-field model was used to calculate the oxide layer growth as a function of the transferred electric charge. The model was validated by comparing the simulated results with experimentally measured current–potential curves obtained from polarisation experiments and with oxide-layer thicknesses determined by electron microscopy. Good agreement between the simulation and the experimental results was achieved when the electron current contribution was taken into account. The maximum current density was found to be 2.35 A dm -2 in the experiment and 2.51 A dm -2 in the simulation. The resulting barrier layer thickness is (127 ± 4) nm according to the experiments and 128.6 nm according to the simulation.