Effects of trace amounts of lithium on the microstructure, mechanical properties, corrosion behavior, antibacterial activity and biocompatibility of Zn-Cu alloy

To investigate the effects of adding trace amounts of Li on the microstructure, mechanical properties, corrosion behavior, antibacterial activity and biocompatibility of the Zn-Cu alloy, Zn-1.2Cu, Zn-1.2Cu-0.02Li as well as Zn-0.02Li (as a reference) alloys were prepared in this work. The results showed that the grain size of the as-cast Zn-1.2Cu-0.02Li alloy is significantly smaller than that of the Zn-1.2Cu alloy, suggesting a notable effect of the trace amounts of Li on the grain refinement. Moreover, a bimodal structure was formed in both the hot-extruded Zn-1.2Cu and Zn-1.2Cu-0.02Li alloys due to the precipitation of submicron-sized epsilon-CuZn4 particles. However, the latter has a much higher volume fraction of submicron-sized epsilon-CuZn4 particles than the former. Furthermore, nano-sized epsilon-CuZn4 particles precipitate from the matrix of the fine-grained region in the latter alloy. The hot-extruded Zn-1.2Cu-0.02Li alloy exhibits a yield strength (YS) of 278 +/- 3 MPa and ultimate tensile strength (UTS) of 320 +/- 1 MPa, which are 76% and 25% higher than the hot-extruded Zn-1.2Cu alloy (YS = 158 +/- 3 MPa and UTS = 225 +/- 1 MPa), indicating a strong strengthening effect of trace amounts of Li. Furthermore, the hot-extruded Zn-1.2Cu-0.02Li alloy has a lower corrosion rate than the Zn-1.2Cu alloy, indicating a positive effect of trace amounts of Li on the corrosion resistance. In addition, the hot-extruded Zn-1.2Cu and Zn-1.2Cu-0.02Li alloys both demonstrate hemolysis rates of less than 5% and antibacterial rates of more than 97%, indicating good hemocompatibility and antibacterial property. Also, the MC3T3-E1 cells show over 110% viability in the 50% extracts of both alloys, exhibiting excellent cytocompatibility.