Influence of Ca and Zn on the microstructure and corrosion of biodegradable Mg–Ca–Zn alloys

• Cross-sections in SEM show that Mg2Ca dissolves before α-Mg within Mg–Ca alloys.
• Mg6Ca2Zn3 locally, temporarily blocks corrosion; is undermined by corrosion.
• More ternary phases by higher alloying contents of Zn and Ca increase corrosion rate.
• At Zn/Ca = 1.84, Zn-enrichment of α-Mg decreases potential differences between phases.
• Larger, more dendritic grains for higher alloying contents in Mg–Ca–Zn alloys.

This investigation aims at providing deeper understanding of the interactive influence of the alloying elements calcium and zinc on biodegradable magnesium. Through the low-concentration variation of both alloying elements, the formation and distribution of microstructural phases and the in-vitro degradation behavior were investigated to gain mechanistic insights. Mg2Ca dissolves preferentially to α-Mg within Mg–Ca alloys. Mg6Ca2Zn3 temporarily blocks local corrosion but is ultimately undermined due to its discontinuity. More ternary phases obtained by higher alloying contents of Zn and Ca increase the corrosion rate. At a Zn/Ca (atomic) of 1.84, a Zn-enrichment of α-Mg decreases potential differences between the phases.