Improving the tribocorrosion performance of plasma electrolytic oxidized coatings on AZ31B magnesium alloy using pullulan as an electrolyte additive

Abstract

This study aimed to investigate the enhancement of the corrosion and tribocorrosion performance of AZ31B magnesium (Mg) alloys after plasma electrolytic oxidization (PEO) treatment using pullulan as an electrolyte additive. The effects of different concentrations of pullulan in the electrolyte solutions on the mechanical and corrosion-resistance properties of the PEO coatings were investigated. The microstructures and chemical compositions of the coatings were investigated via scanning electron microscopy, energy dispersive spectrum, and X-ray diffraction. The corrosion resistance of the samples in simulated body fluid was evaluated via potentiodynamic polarization and electrochemical impedance spectroscopy. The tribocorrosion performance was determined by simultaneously recording the change in the friction coefficient and the open circuit potential over time during sliding experiments. The results indicated that the addition of pullulan to the silicate-based electrolyte solutions resulted in an increase in the unit-area adsorptive capacity of the negative ions at the anode/electrolyte interface, which enhanced the compactness of the PEO coating. The PEO coating produced in electrolyte solution containing 1.0 g/L pullulan exhibited the greatest thickness (50 μm), the lowest surface roughness (1.25 μm), the highest corrosion resistance, and the best anti-tribocorrosion performance, all of which corroborated the potential application of PEO-coated Mg alloys as biological implants.