Microstructural evolution and mechanical properties of an Al-10Zn-3Mg-2.5Cu alloy processed by stress-aging coupled artificial aging

• An innovative coupled high-stress aging and artificial aging process was developed for Al–10Zn–3Mg–2.5Cu alloys. • Following coupled stress and artificial aging, specimens maintained a tensile strength of 700 MPa while achieving an elongation of 9.1 %, a 116.6 % improvement over the baseline (T6) 4.2 %. • The rare ε-CuZn 4 formation was confirmed in this alloy, effectively suppressing η-phase coarsening and providing further beneficial contributions to ductility. • ε-CuZn 4 combined with the well-established η-phase, points to a new direction for tailoring mechanical properties in highly alloyed Al-Zn-Mg-Cu alloys. Herein, we investigate the effect of stress-aging on the precipitate characteristics, grain structure, dislocation evolution, and mechanical properties of an Al–10Zn–3Mg–2.5Cu (wt.%) alloy. Stress aging was performed at 120 °C for 24 h under applied stresses of 135–450 MPa, which considerably enhanced the tensile strength to 700 MPa and resulted in dislocation multiplication as the dominant strengthening mechanism. However, the alloy ductility was constrained to 3.7 %–5.4 %. The stress-aged specimens with 270 MPa and 450 MPa were subjected to artificial aging (140 °C–160 °C). This considerably enhanced the strength–ductility synergy, endowing a tensile strength of 700 MPa along with elongations of 9.1 % and 6.5 %. ε-CuZn 4 precipitation was facilitated by synergistic high-alloying and dislocation effects. This rare phase effectively suppressed the coarsening of η-phase, thereby preserving the intrinsic strength, while its superior capability to trap and accumulate dislocations significantly enhanced the ductility. Thus, high-stress aging and thermal treatment offered transformative phase-transformation pathways, distinct from conventional η-phase evolution, making it ideal for fabricating high-strength Al–Zn–Mg–Cu alloys.