Heterostructured Al-Cu alloy unifying high strength and enhanced ductility

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.