Synergistic effects of Li addition and extrusion on the microstructure, mechanical properties and bio-corrosion behavior of the new biodegradable Mg-3Zn-3Sn alloys for orthopedic applications

Magnesium (Mg) alloys are good candidates for biodegradable orthopedic implants, but they still have problems with their fast breakdown and poor mechanical performance. A new quaternary alloy system Mg-3Zn-3Sn-xLi (x = 0–5 wt.%) was created for this study. The effects of adding lithium (Li) and the extrusion process on the microstructure, mechanical properties, and in vitro corrosion behavior were carefully studied. Adding Li helped refine the grains and make the microstructure more uniform. Extrusion strengthened the material and increased its corrosion resistance by eliminating casting flaws. X-ray diffraction showed that all the alloys had α-Mg, Mg 7 Zn 3 , and Mg 2 Sn phases. However, Li 2 Sn 5 only formed when the Li content exceeded 4 wt.%. Adding too much Li accelerated corrosion due to micro galvanic effects, even though it strengthened the matrix. Among the investigated compositions, the extruded Mg–3Zn–3Sn–3Li alloy exhibited the most balanced performance, showing a low corrosion current density of 56.45 Μa/cm 2 in Dulbecco's Modified Eagle Medium (DMEM), a high compressive strength of 415.26 MPa, a wear rate of 2.72×10 -7 g/N.m, and a hardness of 68.52 HV. These results indicate that the mechanical properties and corrosion behavior of the alloy are greatly improved by adding 3 wt.% Li during extrusion. Therefore, the extruded biodegradable Mg-3Zn-3Sn-3Li alloy is a very promising candidate for next-generation orthopedic implants. • Lithium addition and extrusion synergistically refined the microstructure and enhanced alloy homogeneity. • At higher lithium concentrations, a new phase Li 2 Sn 5 was identified, and changes in lattice parameters and phase equilibrium were observed. • The Mg - 3Zn - 3Sn - 3Li alloy provided the best combination of strength and ductility with a compressive strength of 415 MPa. • Corrosion resistance decreased with increasing lithium content compared to other alloys, but the extruded ZTL333 alloy still maintained sufficient degradation in DMEM medium. • The extruded Mg–3Zn–3Sn–3Li alloy demonstrates strong potential as a next-generation biodegradable implant.