Taming cyclic reliability in high-strength Al alloys via gradient subgrain-nanoprecipitate composite structures

Cyclic reliability, a key indicator of a material’s mechanical stability under cyclic loading, is inherently tied to fatigue performance. Precipitation-strengthened high-strength Al alloys typically undergo significant cyclic softening under asymmetric stress cycles with a positive mean stress, thereby inducing premature fatigue failure. Here, we report a high-strength Al alloy engineered with a dual-gradient architecture, featuring both subgrains and nanoprecipitates, which displays remarkable resistance to cyclic softening, resulting in a nearly two-order-of-magnitude enhancement in fatigue life. This superior cyclic stability stems from the rapid dynamic hardening response and high mechanical energy dissipation intrinsic to this gradient subgrain-nanoprecipitate structure. Specifically, the synergistic interaction between the subgrain network and graded precipitate distribution reconfigures dislocation behavior from cross-slip to planar slip, while fragmenting dislocations into fine slip units. These unique interactions facilitate stable cyclic hardening and high internal damping. Consequently, strain localization is effectively suppressed, and both crack initiation and propagation are significantly delayed. This composite gradient strategy provides a novel paradigm for designing fatigue-resistant Al alloys.