Improved creep age formability of an Al–Cu–Li alloy by applying pre-aging before high-speed pre-straining

In the present work, the creep behavior, mechanical properties and microstructural evolution of Al-Cu-Li alloy with different initial tempers have been experimentally investigated under 180 MPa at 160 °C for 16 h. The alloy was subjected to varying pre-aging treatments (0 h, 3 h, 9 h, 12 h),then processed by high-speed pre-strain (HSPS), and finally subjected to creep aging(CA). It is found that increasing pre-aging time enhances creep strain of the HSPS Al-Cu-Li alloy, while the “multi-stage” creep characteristic of the alloy gradually diminishes. The yield strength, ultimate tensile strength, and elongation of the HSPS specimen after creep first increased, then decreased, and then increased again with the increase of pre-aging time. Microstructural observations demonstrate that HSPS treatment increases the movable dislocations of the pre-aged alloy, promotes the uniform dispersion distribution of T 1 (Al 2 CuLi) and θʹ (Al 2 Cu) phases, and reduces the size of precipitation free zone (PFZ) at grain boundaries. In addition, with the increase of the pre-aging time, the size of the minor grain boundary undulations (MGBUs) of the HSPS alloy first increases and then decreases, and the average grain size gradually decreases. The results demonstrate that the combined pre-aging and HSPS process enhances both the creep behavior and mechanical properties of Al-Cu-Li alloys.