Abstract:Solution-aging treatment is a critical approach for optimizing the microstructure and enhancing the mechanical properties of laser directed energy deposition (LDED)-fabricated Ti6Al4V alloys. The results show that as-deposited Ti6Al4V alloys consist of primary β columnar grains with width ranging from 200 μm to 500 μm. The intragranular features include grain-boundary α phase, Widmanst?tten structure at grain boundaries, and basket-weave microstructure. The ultimate tensile strengths in the directions perpendicular and parallel to the printing direction are 1010 and 996 MPa, with corresponding elongations of 8.1% and 11.2%, respectively. After sub-β-transus solution treatment followed by intermediate-temperature aging, the microstructure consists of discontinuous grain-boundary α phase, short rod-like α phase, and transformed β phase (composed of retained β phase and secondary α phase). Solution treatment above the β-transus causes pronounced grain coarsening and coarse Widmanst?tten structure. The treatment of 850 °C/2 h+500 °C/4 h with air cooling (AC) yields the excellent strength-ductility balance at room temperature. The ultimate tensile strengths perpendicular and parallel to the printing directions reach 1033 and 1007 MPa, respectively, with corresponding elongations of 12.1% and 15.8%. The strength-plasticity synergy originates from the multiscale α/β structure formed by sub-β-transus solution combined with intermediate-temperature aging. Specifically, the grain-boundary α phase transforms from a continuous to a discontinuous/spheroidized morphology, thereby weakening the cracking propagation channels along boundaries. The intragranular α phase is moderately coarsened and evolves from acicular to short-rod morphology, which improves deformation compatibility. Meanwhile, the secondary α phase dispersed within the transformed β phase and the residual β phase jointly promote slip transfer and work hardening.