Combining multi-scale simulations and experiments, this work elucidates how Cu (0–4 wt.%) affects the precipitation behavior and mechanical properties of an Al-Si-Mg alloy. Increasing Cu contents drives a sequential evolution of dominant precipitates: β′′ → β′′ + QP → QP → QP + θ′, raising yield strength from 285 MPa to 364 MPa but reduces ductility from 10.1% to 6.8%. Critically, atomistic simulations elucidate the kinetic pathway through which Cu addition suppresses β′′ precipitation and confirm that the dominant interaction between dislocations and the θ′ shifts to Orowan looping. This mechanistic change is identified as the fundamental origin of the observed strength-ductility trade-off. These findings offer a theoretical foundation for the future design of high-performance Al alloys.
Xue et al. (Sun,) studied this question.