Anisotropic high-temperature embrittlement of laser powder bed fused Al-Fe-Cr alloy containing Si element

This study focused on an Al-Fe-Cr alloy system with a certain amount of Si (a major impurity in Al alloys) as a model for high-temperature alloys with an industrially produced composition suitable for laser-beam powder bed fusion (PBF-LB) processing. The phase equilibria and solidification sequence in the experimental alloy composition of Al-2.5Fe-2Cr-0.5Si (mass%) were analyzed via thermodynamic calculations. The gas-atomized alloy powder exhibited excellent processability in the PBF-LB process, resulting in the manufacture of fully dense alloy specimens with relative densities exceeding 99%. The PBF-LB-fabricated Al-Fe-Cr-Si alloy exhibited a melt-pool structure formed through repeated local melting and rapid solidification during scanning laser irradiation. Several grains containing high-density low-angle boundaries (sub-boundaries) were elongated along the building direction (BD) in the α-Al matrix with a crystallographic texture of //BD. The relatively coarsened Al 11 Cr 2 phases were localized around the melt pool boundaries, whereas numerous nanosized particles of the Al 6 Fe metastable phase containing Si and Cr were dispersed within the melt pool interior. Consequently, the strength of the Al-Fe-Cr-Si alloy specimen was considerably higher than that of the Al-Fe binary alloys. However, the Al-Fe-Cr-Si alloy specimen exhibited significant ductility loss only in the direction perpendicular to the BD upon elevating the test temperature to 300 °C. The high-temperature embrittlement may be attributed to preferential fracture at many precipitates of the Si-rich intermetallic phase (presumably brittle) formed at the boundaries of the α-Al grains elongated along the BD. These results provide new insights into the design of alloy composition, including impurity elements, for controlling the high-temperature mechanical performance of Al-Fe multi-elemental alloys suitable for PBF-LB processing.