Mechanisms of processing map difference between laser powder bed fusion of Mg solid cubes and lattice structures

Laser powder bed fusion (LPBF) enables the fabrication of geometrically customized lattice structures and opens new opportunities for the biomedical and mechanical engineering fields. However, due to the locally delicate architectures, the LPBF metallic lattices exhibit more complex processing characteristics compared to the regular manufacturing of solid cubes. In this study, LPBF printability maps of solid cubes and lattices for self-developed MgNdZn-Zr alloy (JDBM) are built by analyzing the surface morphologies and internal densification. The top surface morphology of the LPBF JDBM lattices exhibits a similar trend to that of the solid cubes under the varied processing parameters. However, the side surface morphology of the lattices is dominated by the staircase effect, demonstrating uneven transitions of struts with substantial powder particle adherence. Additionally, the inclined struts of JDBM lattices exhibit rougher down-facing surfaces with dross defects, which are induced by the gravity and capillary forces in the molten pool flow. In contrast, the LPBF JDBM lattices present a keyhole-shifted printability map with narrowed forming regime and enlarged keyholing regime as compared to the solid cubes. To clarify the mechanisms involved, multi-physics thermal-fluid flow simulations are conducted and reveal that a higher recoil pressure with the unconsolidated powder bed than that with the solid substrate causes a larger molten pool depth under identical processing parameters. This phenomenon further results in the keyholing dominance and subsequent deviation in the processing map of the LPBF lattice structures as compared to the solid cubes. This work demonstrates the need for tailored process parameters for lattice structures and shows how simulations can guide the design of process parameters for this endeavor.