Characterizations of micro-nano structure and tensile properties of a Sc modified Al[sbnd]Mn alloy fabricated by selective laser melting

In this work, bulk deposits of a Sc modified Al-Mn-Fe-Si alloy were prepared by selective laser melting (SLM), and the microstructural characteristics and tensile properties of the deposits were analyzed. The as-deposited sample presented a multiscale microstructure consisting of epitaxial columnar grains with width of 30–140 μm, in which there exist α-Al dendrite arrays with average primary dendrite arm spacing of 0.34 μm, and interdendritic nanoscale α-Al + Al₆(Mn,Fe) divorced eutectic. After an aging treatment, Al₆(Mn,Fe) transformed into Al₁₂(Mn,Fe)₃Si, and its morphology gradually evolved from skeleton into particle. Meanwhile, needle-like AlMnSi precipitated and grew up in the α-Al dendrite trunk. The ultimate tensile strength increased from 349 ± 9 MPa in the as-deposited state to 430 ± 3 MPa after aging at 300 °C. However, it dropped to 358 ± 1 MPa when the aging temperature increased to 350 °C. The addition of Sc caused precipitation strengthening of secondary Al₃Sc after aging treatment, but the grain refinement effect of primary Al₃Sc was inhibited since Sc tended to segregate at the frontier of the Mn-containing pre-precipitates.