Microstructure and bio-corrosion behavior of Mg-Zn and Mg-Zn-Ca alloys for biomedical applications

The microstructure and bio-corrosion behavior of binary Mg-xZn (x = 1.25, 2.5, 4) and ternary Mg-Ca-xZn (x = 1.25, 2.5, 4) alloys have been studied using scanning electron microscopy (SEM), electrochemical, and immersion tests. Microstructure analysis indicated that the binary Mg-Zn alloys are composed of primary alpha-Mg matrix and Mg12Zn13 phases, while, ternary Mg-Ca-Zn alloys are composed of alpha-Mg, Mg2Ca, and IM1 (Ca3MgxZn15-x) (4.6 <= x <= 12) phases or alpha-Mg, IM1 and IM3 (Ca2Mg5Zn13) phases. Electrochemical results showed that Mg-4Zn alloy has lowest corrosion rate among binary alloys. At constant Ca content of 0.8 wt.%, the addition of Zn up to 1.25 wt.% decreased the corrosion rate, while further addition of Zn increased the corrosion rate of ternary alloys. Immersion tests results demonstrated that the formation of Zn oxide layer in binary Mg-Zn alloy and evolution of eutectic phase (alpha-Mg+IM1+Mg2Ca) significantly retard the bio-degradation rate of the ternary alloys.