Abstract:

     Zinc and its alloys have been recently considered promising candidates for biodegradable implants due to their excellent biocompatibility and stable degradation rates, despite their low mechanical strength. Among advanced fabrication technologies for medical components, laser powder bed fusion (LPBF) provides significant advantages for manufacturing complex, patient-specific implants. However, the extremely high cooling rates associated with LPBF result in unique microstructural features that differ significantly from those produced via conventional processing methods. The correlation between these LPBF-induced microstructures and the mechanical behavior of Zn alloys is not yet fully understood. In this study, the plastic deformation micro-mechanisms of a Zn–1 wt.% Mg alloy fabricated by LPBF were systematically investigated for the first time using advanced characterization techniques including in situ scanning electron microscopy (SEM) integrated with electron backscatter diffraction (EBSD). Fully dense samples with a relative density of 99.95% were produced using optimized processing parameters. The resulting microstructure consisted of fine equiaxed α-Zn grains (average size ~3.7 µm) with no strong crystallographic texture, along with continuous lamellar eutectic Mg₂Zn₁₁ phases located primarily at grain boundaries. The results revealed that plastic deformation was dominated by <a> basal slip, with an increasing contribution of <c+a> pyramidal II slip at higher strain levels—particularly in grains that had already activated basal slip. Twinning played a negligible role, and grain boundary sliding was suppressed due to the presence of the continuous eutectic phase. Schmid factor analysis confirmed that both <a> and <c+a> slip systems followed the Schmid law, indicating that the local stress state closely corresponds to the global applied load. Additionally, dynamic recrystallization, driven by progressive lattice rotation and grain fragmentation, was identified as the primary softening mechanism. Fractographic analysis revealed that stress concentrations around oxide particles acted as crack initiation sites, leading to a semi-brittle fracture morphology. These findings provide insights into the deformation behavior of additively manufactured Zn-based alloys and can be valuable guidance for the development of next-generation biodegradable implants with enhanced mechanical performance.