Synergistic effects of SiC and pre-stretching on the precipitate evolution and mechanical performance of an ultra-high strength Al-Zn-Mg-Cu-Sc-Zr alloy

The development of ultra-high-strength Al-Zn-Mg-Cu alloys is often constrained by the trade-off between strength and ductility and by low incipient melting temperatures. This study overcomes these limitations by using a modified AA7097 alloy and an AA7097-0.22 wt% micro-sized SiC composite alloyed with Sc and Zr. A multi-step homogenization strategy, designed using differential scanning calorimetry, safely raised the solidus temperature from 467.8°C to 478°C, thereby eliminating incipient melting during solution treatment. Following an 85% hot rolling reduction, a non-recrystallized “pancake” grain structure was thermally stabilized by nanoscale Al₃(Sc,Zr) dispersoids, which effectively suppressed static recrystallization. Crucially, the introduction of a 1% pre-stretch accelerated the multi-step aging response through dislocation-assisted heterogeneous nucleation. Under optimized processing conditions, the micro-SiC reinforced composite achieved an outstanding Ultimate Tensile Strength (UTS) of 705 MPa with 9% elongation, outperforming the monolithic base alloy (680 MPa UTS, 6.5% elongation). These findings demonstrate that coupling micro-sized reinforcement pinning with strain-induced precipitation kinetics provides a robust pathway for synthesizing advanced, high-ductility aluminum matrix composites.