Microstructural evolution and mechanical properties of TiB2/2195 composites fabricated by ultrasonic-assisted in-situ casting.

The distribution and size of particles in particle-reinforced aluminum matrix composites are crucial to the mechanical properties of the composites. In this paper, 2 wt.% TiB2/2195 composites were prepared by ultrasonic-assisted in-situ casting technology, and the samples' phase composition, microstructure, and mechanical properties were tested. The results showed that: compared with the remelted matrix, the stomatal defects in the composites disappeared, and the grains were refined, but the second phase structure and TiB2 particles agglomerated significantly when no ultrasonic treatment (UT) was applied. The UT made the grains further refined, the area fraction of the coarse second phase network decreased, the concentrations of Ti and Cu elements in the grains increased, and more TiB2 particles entered the grains. At the same time, the formation of TiB2 particles and UT increased the dislocation density in the composites and promoted the precipitation of the T1 phase. With UT for 180 s, the TiB2 particles were evenly distributed, and the size was the smallest. The tensile strength, yield strength, and elongation were increased by 115.4 %, 49.8 %, and 342.9 %, respectively, compared to the remelted matrix, and by 30.9 %, 21.8 %, and 67.2 %, respectively, compared to the composite without UT. The mechanism of the synergistic effect of UT and TiB2 to enhance the mechanical properties of composites was also discussed.