Optimization of plasma electrolyte oxidation process parameters for corrosion resistance of Mg alloy

Plasma electrolyte oxidation (PEO) is a surface treatment method with high dependency on the process parameters. This paper focuses on maximizing the corrosion resistance of PEO coatings applied on Mg–5Zn–0.4Ca (ZX504) alloy by optimizing the process parameters. For this purpose, the Taguchi method based on L18 orthogonal array with mixed level design was used for optimization and determining effective parameters. Main process factors including electrolyte concentration, current density, frequency and duty cycle were considered at different levels. The corrosion resistance, as the performance indicator, was obtained using electrochemical impedance spectroscopy technique. Surface characteristics were also evaluated using SEM (scanning electron microscopy), EDS (energy dispersive spectroscopy), profilometer and contact angle goniometer. The statistical analysis showed that the optimum condition could be obtained at a current density of 200 mA/cm2, frequency of 500 Hz and at a duty cycle of 30%, in an electrolyte containing 15 g/L Na3PO4•12H2O and 10 g/L KF.