Unconventional structure evolution stabilizes the ultrahigh specific strength in a nanostructured Al–Mg–Li alloy

A nanostructured (NS) Al–Mg–Li alloy with an average grain size of ∼ 26 nm was prepared via laser inert-gas condensation (laser-IGC) method. By integrating in-situ synchrotron-based high-energy X-ray diffraction, atom probe tomography and transmission electron microscopy, unconventional structure evolution (grain boundary segregation and ordered precipitates → Guinier–Preston (GP) zones) during annealing process was captured in this NS Al–Mg–Li alloy, which is contradictory to that of bulk counterparts (GP zones → ordered phases). The segregation and room temperature relaxation give rise to an ultrahigh specific strength by enhancing the stress level required for dislocation emission from interfaces in the alloy. Intriguingly, the highest specific strength can be maintained even thermally exposed at 200 °C, which benefits from GP zones, sub-structures and retained intragranular nanoprecipitation. Hitherto the unconventional structure evolution was unrecognized in any experimental observations in NS Al alloys, and is proved to be a reliable way to improve mechanical properties of NS Al alloys. This work provides insights into the relationship between modulated microstructure and superior mechanical properties, paving the road to the development of high-performance lightweight Al–Mg–Li alloys for diverse applications.