Microstructural heterogeneity of AlSi10Mg alloy lattice structures fabricated by selective laser melting: Phenomena and mechanism

The mechanical properties of metallic lattice structures fabricated by additive manufacturing depended on the microstructure heterogeneities, geometric defects and spatial location of struts significantly. This work studies the microstructural heterogeneity for inclined struts of body-centered cubic alloy lattice structures systematically. On the one hand, multiple experimental characterization methods for observing the microstructural features are carried out for searching the different phenomena in inclined strut for lattice structure with that in bulk material or vertical strut. On the other hand, a powder-scale Finite Volume Discrete Method (FVM)-Discrete Element Method (DEM) coupled model was built considering the thermal-fluid coupled behavior in inclined strut different with that in previous researches. The experimental results demonstrated that the dendritic structure size and porosity of the angle zone in the inclined struts are larger (about 5 times and 25 times, respectively) compared to those of the horizontal zone. Moreover, the surface roughness of the angle zone is larger than that of the horizontal zone in inclined struts. The powder-scale simulation results revealed the underlying physical mechanisms for the observed phenomena: The difference of the cooling rates in the horizontal and angle zones of the inclined strut leads the difference of grain size. The unstable molten flow by the competitive effects of dynamic forces induces the porosity formation in the angle zone. As a result, the value of roughness in the lower surface of inclined strut is larger than that in the upper surface. This work will facilitate the enhancement of the stability of the SLM manufacturing technique for metallic lattice structures in a robust and practical manner.