On the Sc induced solidification-heterogeneous microstructure in selective laser melted Al-5Mn alloys

Al-Mn-Sc based alloys present potential in manufacturing high-performance aluminum alloy by selective laser melting (SLM) technology. However, the solidification and solid-state phase transformation behaviors induced by SLM layer-by-layer deposition and the interaction between the Al-Mn and Al-Sc systems result in complexity in the precipitation of Mn-bearing phases and Al3Sc. In this work, ternary Al-5Mn-xSc (x = 0, 0.7, 1.5 wt%) alloys were fabricated via SLM, and their microstructure and mechanical behavior were investigated. The results indicated that the Sc/Mn ratio and the precipitation sequence were critical in controlling the grain and precipitate characteristics of the Al-Mn-Sc alloy deposits. The precipitation of primary Al3Sc was inhibited by the pre-precipitated Mn-bearing particles in Al-5Mn-0.7Sc alloy, resulting in columnar grain structure similar to that of Al-5Mn. In the case of Al-5Mn-1.5Sc alloy, the preferentially precipitated Al3Sc induced a bimodal grain structure. However, with the mismatch in plastic deformation capacity between different grain regions, micron-sized Al6(Mn,Fe) particles formed around the equiaxed/columnar grain region interface tended to induce cracking.