Microalloying effects have been proved to be efficient in artificially manipulating the solid-state transformation in heat-treatable aluminum alloys. Varying grain size from coarse-grained to nanocrystalline, the microalloying effect displays a significant length-scale dependence. Here we report that the coupling of Sc microalloying and cryogenic rolling can produce a highly heterogeneous lamella structure in the ultrafine-grained Al-Cu alloys. Artificial aging leads to prominent grain size-dependent precipitation behaviors: large-sized θ′ precipitates form in micro-grained lamellae while finely distributed θ′′ precipitation exclusively occurs in hard ultrafine-grained lamella matrix. The largely promoted back stress, originating from the heterogeneously distributed lamellae and further enhanced by the grain size-dependent precipitations, yields to remarkable hetero-deformation-induced strengthening and work hardening, and thus achieves a superior strength/ductility synergy in the lamella structured Al-Cu-Sc alloys. The novelty of microstructural design lies in the coupled effects of heterogenous lamella structure and grain size-dependent precipitation, which are promising to be generalized to other precipitation hardening alloy systems or adapted to reduce the Sc content, thereby increasing the broader application.
Wang et al. (2026) studied this question.