Synergistic improvement of strength and plasticity under novel heat treatment approach for laser powder bed fusion processed Ti modified Al-Li-Cu alloy

A Ti-modified 2196 Al-Li-Cu alloy was fabricated via laser powder bed fusion (L-PBF), and a novel multi-stage heat treatment (MST) strategy was developed to achieve the synergistic improvement of strength and plasticity. Compared with the conventional T6-treated specimens, fine-grained microstructures are preserved while the precipitation of secondary Al3Ti, S′-Al2CuMg and T1-Al2CuLi phases is effectively promoted with the new heat treatment strategy. A superior combination of yield strength (442.9 ± 1.4 MPa) and elongation (12.5 ± 0.46%) is achieved by the under-aged (MST_UA) treatment, with elongation rate ∼85% higher than the T6 peak-aged specimens with comparable strength. A yield strength of 499.2 MPa is obtained with the peak-aged (MST_PA) treatment, which is ∼50 MPa higher than the T6 peak-aged specimens and comparable to extruded T8 alloys. Microstructural analysis reveals that enhancement of the strength should be attributed to a synergistic strengthening effect from the fine grain boundaries and the precipitations of secondary Al3Ti and T1 phase, while improved ductility is associated with increased geometrically necessary dislocation density and suppressed dislocation annihilation. The tailored heat treatment integrating multi-stage solution and artificial aging significantly improve the mechanical performance of L-PBF Al-Li-Cu alloys, offering new insights into high-performance alloy design for additive manufacturing.