Tailoring hierarchical microstructures and nanoprecipitates in additive-manufactured Al-Zn-Mg-Cu-Nb alloys for simultaneously enhancing strength and ductility

Additive manufacturing provides an efficient way of producing metallic components with complex geometries. Their microstructure is substantially different to those from conventional processing, creating opportunities for manipulating the final microstructure and properties via heat treatment. Here, we demonstrate that as-built heterostructures in an Al-Zn-Mg-Cu-Nb alloy produced during the solidification of molten pools provide a driving force and additional Zener pinning sources for recrystallization. This creates a bimodal grain structure after solution treatment, causing additional hetero-deformation-induced strengthening and hardening. Coarse grains are found to promote work hardening and blunt the propagate of cracks during deformation, increasing ductility. Together with precipitation strengthening from a high number density nanoprecipitates, the simultaneous improvement of strength and ductility in a highly alloyed Al-Zn-Mg-Cu-Nb alloy is achieved. These results provide a simple strategy for the development of additively manufactured age-hardening alloys with improved strength and ductility for high performance structural applications. Additive manufacturing is known to create microstructures that cannot be achieved by conventional alloy processing. Here, heat treatment of an additively-manufactured aluminum alloy creates a hierarchical microstructure with a large number of precipitates, achieving high strength and ductility.