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, delta ' precipitates gradually grow while decreasing in number density. TiB2 particles have little effect on the size and number density of delta ' precipitates; however, TiB2 particles promote the nucleation of T-1-Al2CuLi precipitates, leading to more uniform and finer T-1 precipitates in the composites compared to the alloy without TiB2 reinforcement. The half-width of delta '-PFZ in the Al-Li-Cu alloy and its composites follows the order: Ti-free composite > 1TiB(2) composite > 5M2S alloy. This indicates that adding TiB2 particles facilitates the growth of the delta '-PFZ, while Ti solutes significantly inhibit its broadening. Moreover, lower aging temperatures enhance the inhibitory effect on the broadening of the delta '-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.