A phase-based approach to optimizing the mechanical and corrosion properties of biodegradable Mg-Zn-Ca alloys

Mg-Zn-Ca alloys are a most promising biodegradable alloy system for biomedical applications. However, it is challenging to design alloys in this system to meet both strength and corrosion requirements for various biomedical applications. In this paper, we report on a phase-based approach to investigate the effects of Mg2Ca and Ca2Mg6Zn3 phases on microstructure, mechanical properties, and the corrosion resistance of Mg-Zn-Ca alloys. More specifically, as-cast Mg-xZn-0.5Ca alloys (x = 0.96, 1.15, 1.47, 1,69, and 1.94) were studied to investigate the effects of Mg2Ca and Ca2Mg6Zn3 phases on the microstructure, mechanical properties, and corrosion properties of Mg-Zn-Ca alloys. These alloys were analyzed to examine phase distribution and its correlation with mechanical and corrosion properties. The grain size of the Mg-xZn-0.5Ca alloy decreased as the Zn/ Ca atomic ratio increased from 1.18 to 2.38, with a transition at a Zn/Ca atomic ratio of 2.07 where the Ca2Mg6Zn3 phase fraction surpassed the formation of Mg2Ca. Electrochemical analysis, immersion tests, and corroded surface observations all indicate that corrosion resistance is optimized at a Zn/Ca atomic ratio of about 1.80, where the micro-galvanic effect between Mg2Ca and Ca2Mg6Zn3 phases was balanced. Tensile testing showed that yield strength increased with the Zn/Ca atomic ratio, while ultimate tensile strength and elongation improved up to a Zn/Ca atomic ratio of 2.07 before declining due to excessive intermetallic phase formation. This study provides critical understanding in optimizing the mechanical and corrosion properties of this important alloy system for biomedical applications.