Effect of micro-nano hybrid SiCp on microstructure and mechanical properties of 7075Al alloy

In this study, micro-nano hybrid SiCp/7075Al composites were successfully prepared for the first time by ultrasonic-assisted semi-solid stirring casting method. The effects of micro-nano hybrid SiCp on the microstructure and mechanical properties of 7075 Al were studied. The results show that the distribution of SiCnp and micron SiCp in the microstructure was uniform. During the extrusion process, most of the micron SiCp were subjected to significant load and broken, which increased the contact area with the matrix and promoted the interface bonding. In addition, the enhanced interfacial interaction promoted the formation of MgAl2O4 phase, which significantly improved the mechanical properties. SiCnp not only had a significant effect on grain refinement, but also promoted the enrichment of Cu, accelerated the formation of GP zone, and promoted the formation of more nano-MgZn2 precipitates. The yield strength and the elastic modulus of micro-nano hybrid SiCp/7075 Al composites reached 450 MPa and 94 GPa, respectively. The synergistic effect of SiCnp and micron SiCp could produce composite strengthening effects such as load transfer strengthening, thermal mismatch strengthening and Orowan strengthening. Moreover, a large number of dislocation pile-ups were observed near the interface between micron and nano SiCp and Al matrix. This leaded to a higher work hardening rate of the composites as the particle content increases. The higher work hardening rate enhanced the strain hardening ability of the material during plastic deformation, thereby significantly improving the tensile strength and elongation of the material.