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 S-1 phases were obtained in the alloy. Then, relatively coarse S-1 phases due to the high Li content were effectively refined, large amounts of fine metastable delta' 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

Automated summary

By accurately controlling the microstructure through ECAP and post-heat treatment, high strength and improved ductility were achieved in an Al-Mg-Li alloy with a high Li content. Refining coarse S-1 phases, uniformly precipitating fine metastable delta' phase particles, and maintaining ultrafine grains resulted in a combination of high strength (>450 MPa) and good ductility (>13.5%). The heat treatment method was also found to be applicable to other Al-Li alloys for adjusting microstructure and achieving an optimal combination of strength and ductility, expanding applications in the aerospace field.