Development of high strength and ductile Zn-Al-Li alloys for potential use in bioresorbable medical devices

Abstract

A series of Zn-Al-Li alloys with potential application in bioresorbable implants were cast, thermomechanically processed and tested. The formation of secondary phases, such as LiZn4, LiZn3Al and Al3Li, contributed to both dynamic recrystallization and grain refinement of the matrix (η-phase) during the hot-extrusion process, leading to grain sizes as small as 1.75 μm for Zn-4Al-0.6Li alloy (wt%). This alloy exhibited an ultimate tensile strength (UTS) of 451 MPa, a total elongation of 46% and a corrosion rate of 60 μm/year in simulated body fluid. The grain refinement played a major role in increasing the strength, but it also weakened the basal texture and promoted non-basal slip and grain boundary sliding, thus contributing to the increased plastic deformation of the alloy. The corrosion rate was affected by a layer of zinc oxide and phosphate formed in the early stages of the immersion tests. The corrosion products protected the substrate and tended to reduce the corrosion rate over time. The developed Zn-4Al-0.6Li and Zn-6Al-0.4Li alloys which showed promising mechanical and corrosion properties appeared to be cytocompatible in the mouse fibroblast cell line and human umbilical mesenchymal stem cells making them promising candidates for bioresorbable stent and implant applications.