Enhanced isotropic ductility by controlling microstructures of Al–Fe alloy manufactured by laser powder bed fusion: Distinct roles of added Ti

• Ti addition enables highly isotropic tensile ductility (∼15%) in L-PBF Al–Fe alloys, unlike conventional anisotropic L-PBF Al alloys. • Velocity-dependent partitioning of Ti and Fe, described by the Aziz model, leads to solute-enriched α-Al matrix and refined Al 6 Fe metastable phases. • Nanoscale Ti-rich phases (presumably Al 3 Ti) promote heterogeneous nucleation, resulting in grain refinement and mechanically homogeneous melt-pool structures. • Suppressed strain localization at melt-pool boundaries, confirmed by in-situ SEM–DIC analyses, is responsible for enhanced ductility and strain hardening. An attempt was made to control the microstructural factors of the melt-pool structure in Al-Fe alloys manufactured by laser powder bed fusion (L-PBF) by adding Ti to improve mechanical performance. The L-PBF fabricated Al–2.5Fe–1.5Ti (mass%) alloy exhibited a representative melt-pool structure with numerous refined particles of the Al 6 Fe metastable phase in the α-Al matrix containing highly concentrated solute Ti and Fe. Variations in solute content across the melt-pool structure (inside melt pools and around melt-pool boundaries) were qualitatively assessed using a velocity-dependent partition coefficient model that simulates the non-equilibrium solid–liquid interface. The solute elements would enhance strain hardening, resulting in high strength (approximately 350 MPa) and high tensile ductility (approximately 15%). Furthermore, the high ductility was independent of the loading direction relative to the building direction, unlike the conventional L-PBF Al alloys. The isotropic tensile ductility would be responsible for the mechanically homogeneous microstructures in the melt-pool structure, developed via heterogeneous nucleation enhanced by the formation of nanoscale Ti-rich phases during solidification. The digital image correlation analysis experimentally confirmed the suppressed strain localization at melt-pool boundaries. These results provide new insights into controlling tensile ductility and its anisotropy, originating from the melt-pool structure of Al alloys manufactured via L-PBF.