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°C/1 h + 480°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°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.