Investigation of electrode distance impact on PEO coating formation assisted by simulation

The influence of electrode distance between anode and cathode during plasma electrolytic oxidation (PEO) process on the coating formation was investigated by combining experiments and simulation. Firstly a model was built to simulate the effect of electrode distance on the anodic current distribution using finite element analyses. Complementary, PEO coatings were fabricated on AM50 magnesium alloy in an alkaline electrolyte with different electrode distances applying constant voltage. Phase composition, coating morphology and thickness were studied for both the front and back sides of the PEO coating depending on the electrode distance. For paralleled plate-like electrodes, based on coating uniformity, an optimum electrode distance of 60-80 mm was identified under the chosen experimental conditions. Via correlation of simulation and experimental results, the influence of electrode distance on coating formation is explored. It is demonstrated that under constant voltage mode, PEO coating formation is affected by electrode distance on both front and back sides of magnesium substrates. This effect is ascribed to the influence of electrode distance on the current distribution in the bath and to the related average current density on the surfaces.