In vitro corrosion of as-extruded Mg–Ca alloys—The influence of Ca concentration

• The microstructure is characterised by the α-Mg matrix and the Mg2Ca phase.
• Fe and Si coexist with the Mg2Ca particles.
• Ca plays a dual role in the corrosion of the Mg–Ca alloys.
• The Mg–0.79Ca alloy has the highest hardness, strength and corrosion resistance.

Microstructure, composition and the corrosion resistance of Mg–Ca alloys were analysed using SEM, EDS, XPS, EPMA, XRD, electrochemical and immersion tests. The results revealed that Ca played a dual role, decreasing the corrosion rate due to the refinement of grain size and accelerating corrosion due to the formation of the Mg2Ca phase. The Mg2Ca particles coexisted with Fe and Si led to pitting corrosion. The Mg–0.79Ca alloy had the highest hardness, ultimate tensile/yielding strength and corrosion resistance in comparison with the Mg–0.54Ca and Mg–1.35Ca alloys, representing the promising candidate for degradable biomaterials.