Effect of ageing treatments on the precipitation behavior and mechanical properties of Al–Cu–Li alloys

A new ageing treatment method was developed in this work to improve the strength and ductility of Al–Cu–Li alloy. Al–Cu–Li alloy treated via pre-deformation followed by double ageing process (PDA) exhibited excellent yield strength and ultimate tensile strength of 609 and 629 MPa, respectively, while maintaining higher elongation (11.5%). The precipitates in matrix and sub-grains regions indicated that both the PCA (pre-deformation followed by creep ageing) and PDA treatments increased the precipitation number density and yielded refined precipitates (i.e., T1 and θ′ precipitates) in the matrix due to the dislocations produced by pre-strain. Uniform and fine strengthening precipitates in the matrix are beneficial to increase the strength of the alloy. In addition, eliminating precipitation free zones, reducing the δ′ precipitation and regulating the T1 precipitates at sub-grain boundaries further promote the plasticity of aged alloys. When this excellent structure is obtained simultaneously, the alloy can obtain high strength while maintaining high elongation.