Microstructures, mechanical properties and degradation behavior of as-extruded Mg-1.8Zn-0.5Zr-xGd (0 ≤ x ≤ 2.5 wt%) biodegradable alloys

Abstract

As-extruded Mg-1.8Zn-0.5Zr-xGd alloys are thoroughly investigated for their microstructure, mechanical properties and degradation behavior in a wide range of minor Gd alloying (0 ≤ x ≤ 2.5 wt%). These alloys show complete dynamic recrystallization when the extrusion ratio and extrusion temperature are 7.7 and 350 °C, respectively. The resultant grain size decreases with the increase in Gd content until its stabilization. Of many observed second phases in these alloys, one type of second phase mainly consists of the granular (Mg, Zn)3Gd phase, the volume of which gradually increases with the increase in Gd content. The other precipitated nanoscale (Mg, Zn)3Gd second phase shows a coherent interfacial relationship with the alloy matrix. At Gd greater than 1.0wt%, a fraction of the insoluble second phase shows transformation into black paralleled strips, which are noted to be distributed along the extrusion direction. The mechanical characteristics of these alloys show optimal performances at x = 1.5 wt%, while decreasing (increasing) trend for 1.5 < x ≤ 2.5 (0 < x ≤ 1.5). Together with the best corrosion resistance at x = 1.0 wt%, these alloys show increment in the corrosion resistance first and then weakens with the increase in Gd content. This study reveals an optimized scale for minor Gd alloying toward the optimal mechanical properties and corrosion resistance of extruded Mg-Zn-Zr alloys, and hopefully beneficial in biomedical applications.