Effect of Aging Treatment on Precipitation Strengthening Phase and Mechanical Properties of Al–Cu–Li Alloy

The microstructure and mechanical properties of Al–Cu–Li alloy with different aging processes have been investigated. The experimental results indicate that increasing aging temperature enhances the precipitation kinetics of the alloy, which is beneficial for T 1 phase precipitation. The average size of δ ′ phase is decreased from 18.2 to 11.6 nm when aging process changes from 200 °C single‐stage aging to 150 °C/200 °C two‐stage aging. The two‐stage aging can effectively suppress the coarsening of δ ′ phase because T 1 phase competes with δ ′ phase for Li atoms. The past researches have pointed out that T 1 phase thickens when aging temperature exceeds 190 °C. However, the results indicate that two‐stage aging can not only retard thickening but also increase number density of T 1 phase. The alloy reaches maximum strength in two‐stage aging, and the ultimate tensile strength, yield strength, and elongation are 415 MPa, 376 MPa, and 5.9%, respectively. When the diameter of T 1 phase reaches a critical value, the strengthening mechanism of T 1 phase has changed from shear mechanism to bypass mechanism. The diameter distribution range of T 1 phase is large in this paper, and the strengthening mechanism of T 1 phase is a mixed strengthening mechanism of shear mechanism and bypass mechanism.