Effect of Ca Micro-Alloying on the Microstructure and Anti-Corrosion Property of Mg0.5Zn0.2Ge Alloy

Magnesium and its alloys have attracting rising attention as one of biodegradable metallic materials. However, the rapid corrosion and severe localized corrosion still hinder their extensive applications in clinics. In this study, micro-alloying of Ca (<= 0.1 wt%) into Mg0.5Zn0.2Ge alloy developed in our previous work was explored to further enhance the corrosion resistance and alleviate the localized corrosion of the alloy. The results reveal that the addition of Ca leads to the transformation of the cathodic Mg2Ge phase in Mg0.5Zn0.2Ca alloy into anodic MgCaGe phase in Ca-containing alloys, thereby changing the galvanic couples in alloys during immersion. The preferential dissolution of MgCaGe phase promotes the participation of Ca and Ge into the formation of corrosion products, resulting in the enrichment of Ca and Ge in the outmost of corrosion product layer, which stabilizes and passivates the corrosion product layer on Mg alloy surface. Additionally, the enrichment of Zn at the corrosion interface seems to further hinder the corrosion of Mg matrix. All of these factors confer a slower and more uniform corrosion on Mg0.5Zn0.2GexCa (x < 0.1 wt%) alloy, which provides favorable candidates for the further processing to gain suitable biodegradable Mg alloys.