Effect of microstructural inhomogeneity on mechanical anisotropy of Al–Cu–Li alloy plate

In order to reveal the relationship between microstructure inhomogeneity and mechanical anisotropy, the Al–Cu–Li alloy 100 mm thick plate for aerospace was evaluated. The grain structure, crystallographic texture, phase structure and fractography of different thickness positions and directions were observed by optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The in-plane and through-thickness anisotropy were characterized by tensile properties, fracture toughness and hardness tests. The results demonstrate a greater in-plane anisotropy in yield strength at the same thickness position of the plate. The Brass texture component increases successively at T, T/4, and T/2 positions, while the Cu texture component exhibits minimal variation. The in-plane anisotropy mainly arises from the Brass texture. Through-thickness anisotropy in the same direction is primarily influenced by the diameter, number density, and volume fraction of the T1 strengthening phase. The average diameter and number density of the primary strengthening phase T1 within grains are highest at the T/2 position and lowest at the T position. The plate contains unrecrystallized, elongated pancake-like grains along the rolling direction. Fracture toughness tests conducted in the L-T and T-L directions predominantly reveal dimple-type transgranular shear fractures, while the S-L direction exhibits intergranular fracture as the primary characteristic. The crack divider delamination toughening mechanism is the main contributor to higher fracture toughness values in the L-T and T-L directions compared to those in the S-L direction. The results reveal the corresponding relationship between the microstructure inhomogeneity and the mechanical anisotropy of Al–Li alloy ultra-thick plates, and provide ideas for the adjustment of process parameters during processing deformation and the regulation of microstructure during heat treatment of large-scale Al–Li alloy thick plates, which has engineering application reference value.