Microstructure evolution and ductility improvement of additively manufactured biodegradable zinc–magnesium alloys via annealing

Abstract

Zinc–magnesium (Zn–Mg) alloys, fabricated by laser powder bed fusion (LPBF) additive manufacturing techniques, have emerged as promising candidates for biomedical implants due to their biodegradation capability, superior mechanical strength, and excellent biocompatibility. However, LPBF-fabricated Zn–Mg alloys still face challenges related to extremely low ductility and limited exploration of degradation characteristics. In this study, the impact of Mg incorporation on the printability, degradation properties, microstructure, and mechanical properties of LPBF-fabricated Zn–Mg alloys was primarily investigated. Furthermore, we proposed a viable annealing post-processing route for the first time to tailor the microstructural characteristics of the fabricated Zn–Mg alloy and enhanced its limited ductility. The results demonstrated that by applying a laser power of 80 W and a scanning speed of 600 mm/s, the relative density of LPBF-fabricated Zn–Mg alloy reached 98.62%. Increasing the Mg amount from 1 to 5 wt% refined the grain size while promoting an increase in Mg2Zn11 and MgZn2 phases. Among these compositions, the Zn–1Mg alloy exhibited the greatest degradation rate at 0.126 mm/year. The annealing treatment facilitated the microstructure evolution of the Zn–1Mg alloy, resulting in equiaxed grains, increased average grain size, high-angle grain boundaries, and enrichment of Mg at grain boundaries. After annealing at 300°C for 0.5 h, the tensile strength of Zn– 1Mg alloy decreased from 254.92 to 170.93 MPa, while the elongation significantly increased by a factor of 14.3 from 0.55% to 8.43%. These findings provide valuable insights into an effective post-processing approach for tailoring the microstructure and resultant mechanical properties of LPBF-fabricated Zn and its alloys.