Selective laser melting Al-3.4Mg-0.5Mn-0.8Sc-0.4Zr alloys: From melting pool to the microstructure and mechanical properties

The addition of Sc and Zr into an Al–Mg–Mn alloy produced by selective laser melting exhibited exceptional properties. Multiple factors eventually lead to the improvement of properties, such as densification behaviors, grain characteristics, texture and the precipitated phases. We firstly investigate evolution of the melt pool characteristics which are varied under different processing parameters and lead to different solidified microstructures, densification behaviors and corresponding mechanical properties. Meanwhile, the characteristics of melt pool can be predicted through the normalized enthalpy of input energy, which presents more credible relationship with the melt pool dimensions. To this end, the relative density is up to 99.88% when the volume energy density and normalized enthalpy are combined used. Recrystallisation inhabitations induced by the added Sc and Zr is supposed after comparing the grain sizes under different conditions. Regrettably, the relationship between melt pool characteristics and the equiaxed/columnar ratio can not be described accurately, which due to the pseudo-equiaxed regions in XZ/YZ sections through regulating the melt track orientations via 67° scanning rotation. There are dispersed Al6Mn and Al3(Sc, Zr) particles exist in as-fabricated samples result in better mechanical properties and the subsequent aging treatment can further improve the comprehensive mechanical properties. Finally, the ultimate tensile strength and ductility is separately about 494.32 ± 4.16 MPa and 15 ± 1.27% after aging for 4 h at 325 °C. In contrast, the processing parameters have little impact on mechanical properties, especially for the yield strength, mainly owing to the homologous precipitate phase and grain sizes when the relative density is similar. The connection involving the whole periods from solidification to the final mechanical properties is discussed that may offer feasible ideas for alloy design and corresponding parameter optimization.