Effect of aging treatment on the microstructure and mechanical properties of TiO2@CNTs/2024 composite.

Novel TiO2 nanoparticles-coated CNTs (TiO2@CNTs) fabricated by the alcohol-thermal method were used as the reinforcement to prepare aluminum matrix composites through high-intensity ultrasonic-assisted casting, followed by heat treatment. The results of optical microscope showed that the optimum heat treatment process was solution treatment (495 °C, 2 h) + aging treatment (180 °C, 12 h). Under this condition, the Al2Cu and Al2CuMg phases were uniformly precipitated in the composites, and most of them were in a discrete state. TEM results revealed that TiO2 nanoparticles dispersed on the surface of CNTs played the role of an interlayer structure between CNTs and matrix, locking the CNTs and improving the CNTs–Al interfacial bonding. The ultimate tensile strength (UTS) and yield strength (YS) of 1.0 wt%TiO2@CNTs/2024 composite after T6 heat treatment reach 324 MPa and 219 MPa, respectively, which exhibited enhanced UTS and YS than the monolithic 2024 alloy. This was attributed to the synergistic strengthening of multi-mechanisms, such as grain refinement strengthening, load transfer strengthening, dislocation strengthening and, especially, Orowan strengthening. [ABSTRACT FROM AUTHOR]