Probing local corrosion performance of sol-gel/MAO composite coating on Mg alloy

In this study, sol-gel technique was used to prepare Ca10(PO4)6(OH)2 (HA) coating on Micro arc oxidation (MAO) coated degradable Mg matrix composites to reduce their primary degradation and enhance biocompatibility in simulated body fluid (SBF). The microstructure and phase composition were analyzed using Scanning electron microscopy (SEM) and X-ray diffraction (XRD). Potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) were used to examine their global corrosion behavior. Scanning vibrating electrode technique (SVET) and local electrochemical impedance spectroscopy (LEIS) were used to evaluate the potential distribution and impedance differences among the different zones. The global measurements show that the sol-gel/MAO coating has much better corrosion resistance than MAO coating, since the sol-gel coating sealed the pores produced in the MAO process. The post-corrosion microstructures of sol-gel/MAO composite coating on magnesium alloy are in agreement with the results of local corrosion performances. The corrosion mechanism is explained by proposing an empirical model.