On the complex intermetallics in an Al-Mn-Sc based alloy produced by laser powder bed fusion

Abstract

The recently-developed Al-Mn-Sc based alloys specific for laser powder bed fusion (LPBF) have shown excellent mechanical performance. However, the complicated intermetallic particles in the microstructure remain to be identified, hindering the deep understanding of their effects on mechanical properties and further property improvement. In this work, a range of phases in a LPBF-built Al-Mn-Sc based alloy have been systematically studied by atom probe tomography. The results clarify characteristic intermetallic phases in two different grain-size regions in the microstructure. In the fine grain (FG) region, three distinct phases have been identified. A Sc-rich phase having an average composition of Al3.3(Sc0.8Zr0.2) is observed at both the grain boundary (GB) and grain interior, but they have different morphologies. The Mn-rich phase with an average composition of Al4.3(Mn0.9Fe0.1) is only observed along GBs. In addition, Mg-rich oxide has been observed either with a separate distribution or attached to Sc-rich particles. In the coarse grain (CG) region, the GB particles exhibit different size and composition from FG region. The Sc-rich GB particles contain Mg enrichment rather than Zr and the composition is determined to be Al3.4(Sc0.75Mg0.25). The Mn-rich GB particles in the CG region, with higher Fe contents, are Al4.3(Mn0.8Fe0.2) along the GBs and Al4.5(Mn0.85Fe0.15) inside the grains. Many smaller Mg-rich oxides and Sc-rich particles are also observed in the internal grains of the CG region.