Abstract: Achieving a homogeneous equiaxed grain structure and breaking the strength-ductility trade-off in additively manufactured aluminum alloys is a great challenge. In this paper, we propose a novel duplex nucleation mechanism that combines ex situ TiB₂ and in situAl₃Ti for controlling the grain structure of additively manufactured AlCuMgTi-TiB₂composites. We conducted thermodynamic calculations and phase-field simulations to elucidate the duplex nucleation-based grain structure control. The Al₃Ti-coated TiB₂inoculant system formed via duplex nucleation during solidification enabled the formation of a homogeneous ultrafine equiaxed microstructure in both the as-fabricated and heat-treated states. Different from the AlCuMgTi alloy, the TiB₂-reinforced AlCuMgTi composites produced via laser powder bed fusion were amenable to the simultaneous enhancement of strength and ductility. The proposed alloy design approach and duplex nucleation mechanism can guide the tailoring of the microstructure and mechanical properties of additively manufactured aluminum parts.

Key words: Laser powder bed fusion, TiB₂-reinforced AlCuMgTi composite, Duplex effect, CALPHAD, Phase-field simulation, Mechanical properties