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 T₁ phase precipitation. The average size of δ' phase is decreased from 18.2 to 11.6 nm when aging process changes from 200 °C singlestage aging to 150 °C/200 °C two-stage aging. The two-stage aging can effectively suppress the coarsening of δ' phase because T₁ phase competes with δ' phase for Li atoms. The past researches have pointed out that T₁ 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 T₁ 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 T₁ phase reaches a critical value, the strengthening mechanism of T₁ phase has changed from shear mechanism to bypass mechanism. The diameter distribution range of T₁ phase is large in this paper, and the strengthening mechanism of T₁ phase is a mixed strengthening mechanism of shear mechanism and bypass mechanism. [ABSTRACT FROM AUTHOR]