Tailoring the heterophase interfacial structures to improve both strength and ductility of Al-Li alloys by fine tuning major solute Mg

Nanoprecipitate strengthened Al-Li alloys have extraordinary mechanical properties and are widely applied in lightweight and high-strength structural applications. However, further strengthening Al-Li alloys usually relies on a high number density of hard nanoprecipitates, which unavoidably sacrifice ductility of the Al-Li alloys. In this work, we propose a new strategy based on controlling the Mg concentration to optimize the microstructure and tailor the interface structure between the nanoprecipitates and the matrix to achieve both high strength and ductility. Firstly, it is found that 4.9 wt.% Mg is very effective for refining grains and has a significant impact on the size, content and morphology of intermetallic compounds using Electron Back Scatter Diffraction (EBSD) and Synchrotron X-Ray Computed Tomography (X-CT). Secondly, High-Angle Annular Dark Field-Scanning Transmission Electron Microscope (HAADF-STEM) combined with first-principles calculations reveals that 4.9 wt.% Mg promotes the phase transition from the weakly binding a−Al/δ^′/β^′ heterophase interface to the anti-brittle/shear α−Al/Al₃(Li,Zr) heterogeneous interface upon aging, resulting in excellent heterophase interfacial bonding between the nanoprecipitates and the matrix. As a result, an outstanding combination of ultimate tensile strength of 420 MPa and elongation of 14.0 % for the Al-Li alloy has been achieved. Therefore, this study provides a prospective strategy for designing high strength and ductility Al-Li alloys by tailoring the heterophase interfacial structures using major solute Mg.