Biodegradable Zn–0.5Li alloys with supersaturated solid solution—aging treatment for implant applications

Abstract

To solve the problems of poor mechanical properties and local corrosion caused by the coarse dendrites grain and the second phase of as-cast (AC) Zn–Li alloy, AC Zn-0.5Li alloys were treated by ultra-high pressure (3 GPa) solid solution-aging treatment (UHPS-AT) at 375 °C. The microstructure, mechanical, corrosion behavior, cell compatibility, and antibacterial properties of UHPS-AT Zn-0.5Li alloys were characterized and evaluated. After the UHPS-AT treatment, the TEM images showed the presence of large Zn/β-LiZn4 layered grain inside UHPS-AT alloy, and the dendritic grain and coarse second phase disappeared. The mechanical properties and wear resistance of Zn-0.5Li alloys were improved compared with AC alloys after UHPS-AT treatment. However, the compressive yield strength of UHPS Zn-0.5Li alloy decreased after aging, indicating that the strengthening effect of solid solution is better than that of the second phase precipitation, which was also proved by theoretical calculation. A dense passivation film was formed on the surface of the UHPS-AT sample, hindering further corrosion of the alloy, resulting in the change of the corrosion mechanism from local corrosion in the as-cast state to uniform corrosion in the UHPS-AT state. Cytotoxicity assays with Zn-0.5Li alloys showed that extracts at concentrations below 12.5% were not cytotoxic. Moreover, the Zn-0.5Li alloy exhibited good antibacterial properties against E. coli bacteria.