Bone fractures remain a serious health concern over years which impair the organs and cause trauma and economic losses to the patients. Conventionally used orthopedic implant materials such as stainless steels, Co-Cr alloys and Ti based alloys for treatment of fractures render stress shielding effect due to disparity in the elastic modulus of natural bones and these materials. Thus, in many cases, these implants need to be removed via another surgery [1]. Mg-based alloys have become promising candidates for these applications owing to their excellent biomechanical characteristics. These alloys have density and modulus close to that of the natural bones. Nevertheless, the depletion of mechanical properties of Mg-alloys due to their accelerated degradation in bodily fluids hinders their biomedical applications. Alloying with elements like Ca, Mn, Sn, Zr, etc. and thermomechanical processing of these alloys considerably enhance their biomechanical properties [2,3]. This study attempts to elucidate the variation in mechanical and degradation properties of Mg-Zn alloys upon alloying with Ca and Sn.

In this study, the effect of Ca addition on the microstructure and deformation properties of Mg-Zn alloys has been studied by varying the Ca content from 0 to 1 wt.%. The Mg-Zn-Ca alloys were prepared by gravity casting and were then investigated for the microstructural evolution using scanning electron microscopy (coupled with energy dispersive spectroscopy), X-ray diffraction and 3D X-ray tomography. It has been found that MgZn phase is formed in Mg-Zn alloy along with the α-Mg matrix and upon Ca addition, this MgZn phase converts to Ca₂Mg₆Zn₃, and its fraction increases with increase in Ca content due to limited Ca solubility in Mg. This Ca₂Mg₆Zn₃ also forms an interconnected 3D network along the grain boundaries as its fraction increases. Uniaxial compression test showed an increase in the compressive strength with Ca addition till 0.4 wt.% attributed to the precipitation strengthening, which subsequently decreased upon further increase in Ca till 1 wt.% because of the easy crack propagation through the interconnected network. A similar trend was observed for the ductility as well. The effects of Sn addition on the microstructure, mechanical and degradation properties of Mg-Zn-Ca alloys have also been studied. Addition of Sn resulted in the improvement in mechanical as well as degradation behavior. The effect of thermomechanical treatment on these alloys has been evaluated and will be discussed.

References

[1] V. Tsakiris, C. Tardei, F.M. Clicinschi, Journal of Magnesium and Alloys, 2021, 9, 1884–1905.

[2] D. Bairagi, S. Mandal, Journal of Magnesium and Alloys, 2022, 10, 627–669.

[3] J. Chen, L. Tan, X. Yu, I.P. Etim, M. Ibrahim, K. Yang, J Mech Behav Biomed Mater, 2018, 87, 68–79.