Heat Treatment Behavior, Microstructure and Mechanical Properties of TiO2@CNTs/7075 Al Composites Fabricated by Ultrasonic-Assisted Casting

The carbon nanotubes coated with TiO2 reinforced 7075 Al composites were fabricated by ultrasonic-assisted casting in this study. The heat treatment behavior, microstructure and mechanical properties of TiO2@CNTs/7075 Al composites were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), transmission electron microscope (TEM), tensile and hardness tests. The experimental results reveal that CNTs accelerate the precipitation process of the TiO2@CNTs/7075 Al composites owing to the formation of dislocations caused by TiO2@CNTs. 7075 Al alloy reaches the peak aging time at 24 h with the hardness of 152.3 HV, while TiO2@CNTs/7075 Al composites reach the peak aging time at 18 h with the hardness of 171.1 HV. Meanwhile, the aging strengthening effect of the TiO2@CNTs/7075 Al composites is less significant than that of matrix alloy, due to the introduction of TiO2@CNTs leading to a significant reduction and an uneven distribution of the precipitations.