Design of Al–Fe–Mn alloy for both high-temperature strength and sufficient processability of laser powder bed fusion

This paper presents a novel design concept for Al alloys with both sufficient laser powder bed fusion (L-PBF) processability and high-temperature mechanical performance using an Al–Fe–Mn ternary alloy with a refined α-Al/Al6M (M = Fe, Mn) two-phase microstructure. The near-eutectic (liquid → α-Al(fcc) + Al6M) composition of Al–2.5Fe–2Mn (mass%) was designed to avoid the formation of coarse primary intermetallics (having a detrimental effect on the PBF processability for densification) based on non-equilibrium liquidus projection thermodynamic calculations. The designed Al–2.5Fe–2Mn alloy powder exhibited sufficient L-PBF processability, and fully dense centimeter-sized samples (relative densities of above 99%) were successfully prepared. The L-PBF Al–2.5Fe–2Mn alloy samples exhibited a significantly refined solidification microstructure consisting of Al6M and α-Al phases in the melt-pool regions. Fe and Mn alloying elements contributed to the formation of nanoscale Al6M-phase particles and a high solid solution concentration in the α-Al matrix. The strength of the L-PBF Al–2.5Fe–2Mn alloy was slightly reduced at higher temperatures, but remained above 240 MPa at an elevated temperature of 300 °C. This superior high-temperature mechanical performance was attributed to the high thermal stability of the refined α-Al/Al6M two-phase microstructure and the formation of nanosized Al6M-phase precipitates.