Achieving strength-ductility balance in a laser powder bed fusion fabricated TiB₂/Al–Cu-Mg-Ag alloy

A crack-free, strong and ductile Al-Cu-Mg-Ag alloy with TiB₂ particles was successfully fabricated with laser powder bed fusion (L-PBF). Subsequent solution and aging were designed to modify the microstructure and strengthen the alloy. The as-fabricated alloy achieved an isotropic microstructure consisting of random-orientated and equiaxed grains with an average grain size of about 1.15 µm. The role of TiB₂ particles in reducing metallurgical defects (such as hot cracking) and enhancing mechanical performance of the alloy was revealed by multi-scale advanced microstructural characterizations. This benefits from the formation of two-dimensional compounds of Al₃Ti on the terminated (0001)_TiB2 plane, which could reduce the lattice mismatch, alter the potency of TiB₂ particles, and refine the grains. The as-built alloy shows an excellent combination of strength and ductility with a yield strength (YS) of 289 ± 5.7 MPa, ultimate tensile strength (UTS) of 390 ± 6.5 MPa, and elongation to failure (El) of 14.8 ± 1.8%. After the heat treatment, high-density of θ', Ω', and Ω phases were precipitated, significantly improving the YS to 405 ± 3.2 MPa and UTS to 470 ± 3.5 MPa, while slightly decreasing the El to 11.6 ± 0.9%. The strengthening mechanisms are quantitatively evaluated and the plastic instability phenomenon (Lüders band and Portevin-Le-Chatelier effect) of the as-built alloy was also analyzed.