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The hardenability of the 2050 Al–Li alloy ultra-thick plate was evaluated by end quenching and interrupted quench methods. Microstructural investigation at different thickness positions after quenching and aging were conducted using optical microscopy, scanning electron microscope, and transmission electron microscope. The factors affecting the hardenability were discussed in combination with cooling rate and composition examination using energy dispersive spectroscopy. The results indicated that the tensile strength of different thickness positions decreased as the distance from the quenching end increases. Coarse Cu-rich phase particles, formed at the grain and grain boundaries during the end quenching process, lead to solute depletion around the grain boundaries, causing a precipitate-free zone. This zone obstructs the formation of the T1 phase, thereby reducing strength. At identical distances from the quenching end, the tensile strength at the mid-thickness (T/2) location consistently exceeds that at the quarter-thickness (T/4) location. This is due to the original microstructural differences, where the T/2 position experiences a slower cooling rate, has a lower copper content, and shows an increase in the number but a decrease in the size of precipitated coarse Cu-rich phase particles from the supersaturated solution, with the solute consumption remaining relatively constant. Consequently, the tensile strength variation at equal distances from the quenching end is minimal.

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.