Breaking the strength–ductility trade-off in additively manufactured aluminum alloys through grain structure control by duplex nucleation.

• The novel duplex nucleation mechanism was first proposed in AM of Al alloys. • The TiB 2 -Al 3 Ti inoculant system was designed by CALPHAD and phase-filed simulation. • Duplex nucleation induced the formation of uniform ultrafine grain structures. • The designed AlCuMgTi-TiB2 composites presented superior strength and ductility. 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 TiB 2 and in situ Al 3 Ti for controlling the grain structure of additively manufactured AlCuMgTi-TiB 2 composites. We conducted thermodynamic calculations and phase-field simulations to elucidate the duplex nucleation-based grain structure control. The Al 3 Ti-coated TiB 2 inoculant 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 TiB 2 -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. [ABSTRACT FROM AUTHOR]