Microstructure, Mechanical, and In Vitro Biocorrosion Performance of Mg-0.5Ca-Zn-Sn Alloys with Varying Sn and Zn Content for Biodegradable Orthopedic Implants

Abstract

Magnesium-based alloys are promising for biodegradable implants due to their biocompatibility and mechanical properties, though their rapid degradation in physiological environments poses challenges. This study evaluated the effects of tin (Sn) and zinc (Zn) additions on the mechanical and corrosion properties of squeeze-cast Mg-0.5Ca-xZn-ySn alloys for biodegradable applications. X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) confirmed the presence of alpha-Mg, Mg2Zn11, and Mg2Sn phases in the as-cast alloys. The addition of Sn to the Mg-0.5Ca-1.0Zn alloy enhanced its hardness, compressive strength, and biocorrosion performance. Notably, the Mg-0.5Ca-2.0Zn-1.0Sn alloy exhibited the highest compressive yield stress of similar to 153 MPa and ultimate compressive stress of similar to 294 MPa due to increased strain hardening and work fracture mechanisms through shear band formation. The Mg-0.5Ca-2.0Zn-1.0Sn alloy also demonstrated superior corrosion resistance, with the lowest weight loss, hydrogen evolution rate, and a corrosion rate of similar to 0.92 mm y(-1) after 21 days of immersion in HBSS. This was attributed to its refined grain structure, higher Sn and Zn content, and a stable protective layer. Potentiodynamic polarization analysis further confirmed enhanced corrosion resistance through increased polarization resistance (Rp) and reduced corrosion current density (I-corr). The presence of finer grains and Mg2Sn phases further reinforced both the corrosion protection and mechanical properties of the alloy.