Achieving near-isotropic strength and ductility in laser additively manufactured zinc via columnar-to-equiaxed grain transition under thermoelectric magnetic effect

Abstract

This work explored the modulation of grain characteristics in Zn during the laser powder bed fusion (LPBF) process by leveraging the thermoelectric magnetic effect induced by an static magnetic field (SMF) for the first time, aiming to reduce the mechanical anisotropy of the printed Zn material while retaining its excellent ductility at specified strength levels. The solidification behavior in the Zn molten pool during the LPBF process under the influence of thermoelectric magnetic effects was simulated using a physical model that integrated SMF. The results indicated that the thermal electromagnetic force induced by SMF reached up to 10⁶ N/m³, effectively fragmenting regular Zn columnar dendrites and enhancing heterogeneous nucleation efficiency, thus promoting the columnar-to-equiaxed transition and grain refinement. Consequently, compared to samples printed without SMF assistance, the mechanical anisotropy index of yield strength and elongation in the SMF-assisted LPBF-printed Zn sample was significantly reduced from 18.63% and 16.49% to 2.46% and 2.58%, respectively, while maintaining superior strength-ductility synergy. This nearly isotropic mechanical behavior primarily resulted from well-modulated grain characteristics that served as a sustainable source of strength-ductility by coordinating grain boundary strengthening and dislocation strengthening mechanisms, as well as utilizing balanced basal <a> slip and pyramidal <c+a> slip deformation modes. These findings can provide a microstructure manipulation strategy to effectively mitigate the mechanical anisotropy of laser powder bed fusion additively manufactured Zn-based materials for biomedical applications.