Investigation of Corrosion Protection Performance of Multiphase PEO (Mg2SiO4, MgO, MgAl2O4) Coatings on Mg Alloy Formed in Aluminate-Silicate- based Mixture Electrolyte

Abstract

Plasma electrolytic oxidation (PEO) coatings in the aluminate-silicate-based mixture electrolyte solution with different duty cycles were successfully applied on Mg alloy. The corrosion behavior of the samples was evaluated by water contact angle test, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and immersion tests. Hydrophobic PEO coating could be obtained by adjusting the duty cycle of the applied electric signal. This coating considerably diminished the Mg dissolution and could enhance the impedance values of Mg alloy in 3.5 wt % NaCl solution. However, the surface of other PEO coated samples showed more hydrophilic properties compared to that of the uncoated sample. Dense structure of the modified PEO multiphase (including Mg₂SiO₄, MgO and MgAl₂O₄ phases) coating and also its appropriate thickness provided an effective barrier to remarkably delay corrosive solution penetration into the PEO coating. This phenomenon led to major decrease in anodic current density of alloy in chloride solution.