Increasing the in-vitro corrosion resistance of AZ31B-Mg alloy via coating with hydroxyapatite using plasma electrolytic oxidation

Abstract

This study investigates the effect of hydroxyapatite (HA) coating by plasma electrolytic oxidation (PEO) on the corrosion resistance of AZ31B Mg alloy. The effect of the HA concentration (5, 10 and 15 g.L−1) on the microstructure and corrosion behavior of coatings in the electrolyte was studied. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques were used to study the microstructure and composition. Polarization and electrochemical impedance spectroscopy (EIS) tests were applied to the bare and coated samples in simulated body fluid (SBF) to determine the resistance behavior and the kinetics of corrosion coatings. The results showed that HA could be distributed inside the coating along with MgO and Mg3 (PO4)2. Moreover, it was found that the porosity declined and the thickness of coatings increased with increases in the HA concentration. The results also indicated that the corrosion resistance of AZ31B Mg alloy was enhanced by coating with any amount of HA. The highest corrosion resistance was obtained with an electrolyte comprising 15 g.L−1 HA. The lowest corrosion current density (1.99 × 10−6 A.cm−2) was monitored in respect to the highest corrosion resistance.