Synergistic effect of in-situ TiB2 particle and Ti solute on the microstructure and mechanical properties of cast Al-Li-Cu-X matrix composite

This study systematically investigated the effects of in-situ TiB₂ particles and Ti solutes on the grain structure, nanosized precipitates, precipitate-free zone (PFZ) near the grain boundaries, and the overall performance of the Al-Li-Cu-X alloy. The TiB₂ particles are predominantly hexagonal or equiaxed in shape, with sizes primarily ranging from 30 to 250 nm and an average size of 126 nm. The addition of TiB₂ particles and Ti solutes effectively refines the grain size of the alloy. Incorporating in-situ TiB₂ particles significantly improves the Young's modulus and hardness of the composites. Furthermore, the presence of TiB₂ particles and Ti solutes accelerates the aging process, thereby reducing the time required to reach peak aging. During aging, δ′ precipitates gradually grow while decreasing in number density. TiB₂ particles have little effect on the size and number density of δ′ precipitates; however, TiB₂ particles promote the nucleation of T₁-Al₂CuLi precipitates, leading to more uniform and finer T₁ precipitates in the composites compared to the alloy without TiB₂ reinforcement. The half-width of δ′-PFZ in the Al-Li-Cu alloy and its composites follows the order: Ti-free composite > 1TiB₂ composite > 5M2S alloy. This indicates that adding TiB₂ particles facilitates the growth of the δ′-PFZ, while Ti solutes significantly inhibit its broadening. Moreover, lower aging temperatures enhance the inhibitory effect on the broadening of the δ′-PFZ. The addition of Ti solutes and in-situ TiB₂ particles leads to a significant improvement in mechanical properties. Critically, the underlying mechanisms driving the microstructural evolution and the resulting mechanical performance were thoroughly analyzed.