Fabrication and Strengthening Mechanism of Dual-Phased and Bimodal-Sized (si3n4p + TiB2p)/6061Al Hybrid Composite

The dual-phased and bimodal-sized (Si3N4p + TiB2p)/6061Al hybrid composites were successfully fabricated. The effects of particle size on microstructure and strengthening mechanisms were clarified. It was found that both Si3N4p and TiB2p stimulated the nucleation of recrystallization and distorted the fibrous distribution of elongated grains. A strong grain refinement effect was realized by introducing fine Si3N4p and fine TiB2p, while the grain aspect ratio was the lowest in the composite reinforced by coarse particles. The texture intensity was weakened by the addition of particles, while the texture types were not changed. Si3N4p and TiB2p were tightly bonded with Al matrix, and MgAl2O4 was formed at the Si3N4p/6061Al and TiB2p/6061Al interfaces, causing a large consumption of Mg element. Hence, the number of precipitates in matrix was reduced, and the precipitation strengthening was weakened. The composite reinforced by fine Si3N4p and coarse TiB2p owned a highest room-temperature strength due to the strengthening of load transfer, thermal mismatch, and precipitates. The combination of fine Si3N4p and fine TiB2p achieved a highest high-temperature strength, and load transfer and pinning effect of particles on grain boundaries became the main strengthening mechanisms.