Effects of Ag and Mg microalloying on mechanical and degradation performance of Zn-Li alloys for biodegradable implant applications

Zinc (Zn) alloys have received extensive attention in recent years owing to their good biocompatibility, suitable biodegradation rate, and favorable mechanical properties, which make them promising candidates for biodegradable metallic implants. However, the effects of minor Mg or Ag addition on the microstructure, mechanical properties, and degradation behavior of Zn-Li alloys have not been fully clarified. In this study, a series of novel Zn-based alloys were prepared by hot-rolling, namely Zn-0.5 wt.%Li (ZL), Zn-0.5 wt.%Li-0.1 wt.%Mg (ZLM), and Zn-0.5 wt.%Li-0.1 wt.%Ag (ZLA) alloys. The effects of Mg or Ag addition on the microstructure evolution, corrosion properties, and biodegradation behavior of these alloys in Dulbecco's Modified Eagle's Medium (with fetal bovine serum) were systematically evaluated. The results show that all alloys exhibit second-phase strengthening due to the presence of nano-sized LiZn4 precipitates. Despite the low addition level of 0.1 wt.%, Mg and Ag exert markedly different effects, and Mg alters the type and size of the second phase, whereas Ag refines the grain structure and optimizes the distribution of LiZn4 precipitates. However, the addition of Mg or Ag leads to distinctly different effects on the mechanical properties. The addition of Mg significantly reduced the elongation from 77.8% to 27.9%. In contrast, the addition of Ag had minimal influence on hardness, elastic modulus, and ultimate tensile strength (1.02 GPa, 83.17 GPa, and 251.6 MPa, respectively), but markedly improved the elongation from 77.8% to 92.7%. In terms of degradation behavior, the Jcorr of the ZL, ZLM, and ZLA alloys were 9.278, 9.886, and 8.484 μA·cm-2, respectively, indicating that Mg addition slightly increased the corrosion rate by 6.6%, whereas Ag addition reduced it by 8.6%. Among all compositions, the ZLA alloy achieved the best combination of mechanical properties and the lowest corrosion rate.