Effect of heat treatment on the microstructure, mechanical properties and fracture behaviors of ultra-high-strength SiC/Al-Zn-Mg-Cu composites

A high-zinc composite, 12vol% SiC/Al-13.3 Zn-3.27 Mg-1.07Cu (wt%), with an ultra-high-strength of 781 MPa was successfully fabricated through a powder metallurgy method, followed by an extrusion process. The effects of solid-solution and aging heat treatments on the microstructure and mechanical properties of the composite were extensively investigated. Compared with a single-stage solid-solution treatment, a two-stage solid-solution treatment (470 degrees C/1 h + 480 degrees C/1 h) exhibited a more effective solid-solution strengthening owing to the higher degree of solid-solution and a more uniform microstructure. According to the aging hardness curves of the composite, the optimized aging parameter (100 degrees C/22 h) was determined. Reducing the aging temperature and time resulted in finer and more uniform nanoscale precipitates but only yielded a marginal increase in tensile strength. The fractography analysis revealed that intergranular cracking and interface debonding were the main fracture mechanisms in the ultra-high-strength SiC/Al-Zn-Mg-Cu composites. Weak regions, such as the SiC/Al interface containing numerous compounds and the precipitate-free zones at the high-angle grain boundaries, were identified as significant factors limiting the strength enhancement of the composite. Interfacial compounds, including MgO, MgZn2, and Cu5Zn8, reduced the interfacial bonding strength, leading to interfacial debonding.