Influence of Heat Treatments on the Microstructure and Mechanical Properties of Two Fine Mg–Li–Y Alloy Wires for Bioresorbable Applications

Abstract

Two Mg–4Li–xY (x = 0.5 and 2.0 wt%) alloy wires are investigated for application in bioresorbable medical devices that experience high levels of plastic deformation. The two wires are supplied cold drawn to a diameter of 125 μm, and a series of thermal treatments are applied to maximize ductility. The ductility of the alloys is maximized soon after complete recrystallization. Prolonged annealing causes grain coarsening in the Mg–4Li–0.5Y alloy and precipitation of a Mg24Y5 phase in both alloys. Both wires are shown to achieve ≈20% elongation to failure in tension and survive high idealized bending strains (>40%). When heat treated for optimum mechanical properties for the intended application, the Mg–4Li–0.5Y alloy develops an intense transverse basal texture; however, this is shown to weaken with increased Y content in the Mg–4Li–2Y alloy wire. The increased Y content also prevents grain coarsening, indicating that the increased Y content restricts grain boundary mobility during annealing. Both alloys have relatively high ductility, meaning both are identified as promising new materials for application in bioresorbable medical devices that require to achieve and support high levels of plastic deformation during their life cycle.

Enhanced Strength–Ductility Synergy of Mg–6Zn Alloy Wire by Inducing Guinier–Preston Zone Precipitation

“…Comparison of ultimate tensile strength versus elongation for present Mg–6Zn alloy wires and recent developed thin Mg alloy wires. [ 4–22 ] …”

“…The sample C had an elongation of 28% and the ultimate tensile strength of 290 MPa, which are the best mechanical properties among the current thin Mg alloy wires, which could be attributed to the combination of high solid solution strengthening of Zn and the precipitation of the grain boundary phase and GP zone. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]…”

“…In recent years, a variety of magnesium alloy wires have been prepared by many combined forming processes consisting mainly of extrusion and multipass drawing. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Among these Mg wires, binary Mg-6Zn alloy wire is considered as the potential biomedical material because the 6 wt% Zn content reaches the maximum solid solubility of Zn in Mg at the eutectic temperature (325 °C) which means the high potential mechanical properties apart from its safe chemical composition. [23][24][25] Also, the cold workability of Mg-6Zn alloy is so good that it can stand the huge accumulative strain through continuous cold drawing.…”

“…Figure 4. Comparison of ultimate tensile strength versus elongation for present Mg-6Zn alloy wires and recent developed thin Mg alloy wires [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. …”