Microstructural control and mechanical properties of a high Li-containing Al-Mg-Li alloy

Al Li alloys, as promising ultra-light airframe structural materials, have attracted extensive attention with respect to improving their mechanical properties. However, due to the detrimental effect of Li, the strength and ductility of Al-Mg-Li alloys have been found to be relatively low. In this work, high strength and simultaneously improved ductility were achieved in an Al-Mg-Li alloy with a high Li content by accurately controlling the microstructure through equal channel angular pressing (ECAP) and post-heat treatment. During the ECAP procedure, ultrafine grains with precipitating S1 phases were obtained in the alloy. Then, relatively coarse S1 phases due to the high Li content were effectively refined, large amounts of fine metastable δ’ phase particles uniformly precipitated without precipitate-free zones (PFZs), and ultrafine grains remained during subsequent heat treatment, thus achieving a combination of high strength (>450 MPa) and good ductility (>13.5%). The heat treatment including short-term solution and ageing after severe plastic deformation (SPD) was verified to be applicable to other Al Li alloys to adjust the ultrafine microstructure and achieve an optimal combination of strength and ductility, which can increase the applications of Al Li alloys for lightweight key components in the aerospace field