Synergistic strengthening-toughening effect of SiCp(CNT) hybrid reinforcements on Mg-compensated SiCp(CNT)/Al-Zn-Mg-Cu composites

In this study, SiCp(CNT) hybrid reinforcements were prepared by in-situ growth of CNTs on the SiCp surface by chemical vapor deposition (CVD) process. The yield strength (YS) and ultimate tensile strength (UTS) of SiCp (CNT)/7075Al were significantly improved by compensating Mg into the SiCp(CNT)/7075Al composites. The results showed that the SiCp(0.5CNT)/7075Al-Mg composites exhibited the best balance of strength and ductility at a Mg compensation of 1.0 wt %, not only the UTS (-651 MPa) was higher than that of SiCp/7075Al1.0 Mg, but also the elongation (3.5 %) was improved by more than 20 %. This is attributed to the fact that the Mg compensation can effectively improve the aging precipitation behavior of the interfacial micro-zones of SiCp (CNT)/7075Al-Mg, allowing it to be effectively strengthened and thus to transfer the load adequately and give full play to the strengthening effect of the SiCp(CNT) hybrid reinforcement. In addition, the toughness of the SiCp (CNT)/7075Al composites was significantly higher than that of SiCp/7075Al with or without the compensation of Mg. Further studies showed that the toughening mechanism of CNTs is divided into the following three main points: (1) the introduction of CNTs can effectively strengthens the interfacial micro-zones, thus retarding the crack initiation. And CNTs can redirect the motion of cracks through the initiation of daughter cracks; (2) the bridging, pull-out and fracture of CNTs can cause the composites to consume more energy during deformation; (3) the introduction of CNTs can effectively prolong the crack propagation path and make the deformation around SiCp more uniform.