Investigation of anisotropy evolution of an aluminium‑lithium alloy with increasing pre-deformation in creep age forming

The 3rd generation aluminium‑lithium (Al-Li) alloy demonstrates promising potential in various applications due to its advanced synergy of strength, toughness, corrosion resistance and weight reduction. However, like its predecessors, this alloy also suffers from the anisotropy issue which can exert significant impact on the manufacturing processes. This study seeks to investigate the anisotropy evolution of a T8 temper 3rd generation Al-Li alloy when subjecting to increased tensile pre-deformation at 0°, 45°, and 90° to the rolling direction. Uniaxial creep-ageing and tensile tests were conducted to reveal the anisotropic behaviours of the material during creep and tensile deformation. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) methods were used to investigate the microstructural evolutions and their influence on the material anisotropy evolvement with treatments of tensile pre-deformation and creep-ageing. It was found that with the increase of tensile pre-deformation level, the creep deformation increased at 0° while decreased at 45° and 90°, due to different configurations of the dislocation substructures at 0°, 45° and 90°. Furthermore, the in-plane anisotropy (IPA) was reduced in both the creep deformation and material strength with increasing tensile pre-deformation and subsequent creep-ageing. The enhanced creep deformation at 0° and decreased deformation at 45° and 90°, as well as the reduction of anisotropy, can be attributed to the reconfiguration of dislocation structures and different extents of precipitation promotion at different directions when subjected to tensile pre-deformation and creep-ageing.