Effect of TiB2 Content on Microstructure and Mechanical Properties of TiB2/Al-Zn-Mg-Cu Composites with High Zn Content

The addition of reinforcement particles can considerably improve the mechanical properties of 7xxx series aluminum alloy. In this work, the effects of TiB₂ reinforcement particles on the microstructure, mechanical properties, strengthening mechanisms, and aging precipitation of TiB₂/Al-Zn-Mg-Cu composites were systematically investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and tensile testing machine. The results indicate that when the TiB₂ content is 1 wt.%, the composite achieves a tensile strength of 831 MPa while maintaining an elongation of 6.7%, meeting the research objectives of this experiment. When the aging heat treatment temperature is set at 120 °C, the peak aging time is shortened to 20 h. The interfacial phase composed of solute elements preferentially nucleates near the TiB₂ particles during the cooling process. With the increase in TiB₂ content, clustering in localized regions slows down the diffusion rate of interfacial phases into the matrix, thereby increasing the required duration of the solution treatment. Excellent interfacial relationships exist between TiB₂ particles and both the aluminum matrix and the MgZn₂ phase. It is also found that with the increase in TiB₂ content, the aging-hardness response of TiB₂/Al-Zn-Mg-Cu composites is accelerated and the work hardening rate is reduced. In addition, a multi-component strengthening model for the yield strength of the composite was established based on various strengthening mechanisms, including second-phase strengthening, dislocation strengthening, age-precipitation strengthening, and fine-grain strengthening. The results indicate that age-precipitation strengthening and dislocation strengthening are the most significant contributors to strength in the composite.