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., T-1 and theta' 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 delta' precipitation and regulating the T-1 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.