Effect of in-situ synthesized TiC particles on microstructure and mechanical properties of directed energy deposited AA2219 Al-Cu alloy

Directed energy deposition (DED) process can enable rapid and low-cost manufacturing of large-scale high-strength AA2219 Al-6.3 wt%Cu alloy components, displaying broad prospects for structural lightweighting in aerospace applications. However, a high tendency to prominent porosity defects and inhomogeneous layered microstructure are intrinsically present in DED-processed Al-Cu alloy, leading to significant performance degradation and anisotropy. Herein, we demonstrate a robust DED process to fabricate high-quality formed AA2219 alloy deposits, based on in-situ synthesized TiC-containing wires and an ultrasonic-frequency pulsed (UFP) arc. The effects of in-situ synthesized submicron-scale TiC particles (average diameter 0.7 ± 0.4 µm) in microstructural evolution and mechanical performance were comparatively investigated through multi-scale microstructural characterization and mechanical property measurement. The introduction of TiC particles into the as-deposited AA2219 component results in a homogeneous refined equiaxed microstructure with an average α-Al grain diameter of 23.4 ± 2.9 µm, and a dramatical elimination of porosity defects. After undergoing a T6 solution and aging treatment, the TiC-reinforced AA2219 deposit demonstrates excellent resistance against grain coarsening, porosity defects growth, and particle segregation. Moreover, the introduced TiC particles lead to a noticeably enhanced precipitation hardening behavior. A homogeneous precipitation microstructure of dispersed θ′-Al2Cu particles with an average diameter of 84.1 ± 34.5 nm and a high fraction of 9.8 ± 2.5 vol% was obtained in the heat-treated AA2219 deposit. Based on the as-built multiscale homogeneous microstructure, the heat-treated deposit embedded with TiC particles exhibits a synergy of unprecedented tensile strength of 501 ± 14 MPa and excellent ductility of 9.6 ± 3.3%.