Quenching transfer time-dependent microstructural evolution in a novel 7xxx aluminum alloys: Balancing strength, ductility, and stress corrosion cracking resistance

Quenching transfer time, a critical and adjustable parameter in high-strength aluminum alloy production, was systematically investigated for its impact on mechanical properties and stress corrosion cracking resistance in a novel 7xxx aluminum alloy. By varying quenching transfer time from 5 to 300 s, microstructural analyses revealed that shorter quenching transfer times of 60 s or less produced finely dispersed, semi-coherent MgZn₂ intragranular precipitates with sizes around 6 nm and semi-continuous grain boundary precipitates. At the optimal 60 s condition, the absence of precipitate-free zones combined with elevated Cu content in grain boundary precipitates synergistically enhanced stress corrosion resistance. This yielded a superior ultimate tensile strength (UTS) of 581 MPa, elongation of 13.2 %, and a stress corrosion sensitivity index (I SSRT ) of 24.9 %. Prolonged quenching transfer time exceeding 180 s induced significant coarsening of MgZn₂ precipitates and fragmentation of grain boundary precipitates into discontinuous morphologies, degrading mechanical performance and elevating the stress corrosion sensitivity due to accelerated crack propagation and corrosive attack. Fracture surface analysis confirmed a transition from ductile dimple structures in shorter quenching transfer time to brittle cleavage facets under extended conditions. The 60 s protocol outperforms existing alloys by harmonizing strength, ductility, and corrosion resistance, demonstrating the pivotal role of quenching kinetics in optimizing precipitation hardening and grain boundary engineering for aerospace applications. • The 60 s quenching transfer time balances 581 MPa UTS, 13.2 % e , and 24.9 % I SSRT . • The protocol removes PFZs, enriches 12.7 wt% Cu in GBPs, and retains 6 nm MgZn₂ MPs. • The protocol outperforms existing alloys by harmonizing strength, ductility, and SCC. • This work highlights quenching kinetics as a key for tailoring MPs, PFZs and GBPs.