• The fine-grained matrix specimens exhibit superior precipitate thermal stability and high-temperature performance. • The blocky σ phases within coarse-grain welding areas inhibit the aging response of T 1 phases. • The pre-stretching and low-temperature pre-aging promoted homogeneous precipitation of T 1 and suppressed its coarsening. This study investigated high-temperature mechanical performance of 2196 Al‒Cu‒Li extrusions with different heat treatments. At 100°C, extrusions’ performance is close to that at room temperature. At 200°C, the strength decreases by 10%, and at 300°C, it decreases by more than 30%, which is attributed primarily to the coarsening of T 1 , widening of no precipitation zone (PFZ) at grain boundaries and reduction of dislocation density caused by dynamic recovery (DRV). The prestretching with low-temperature preaging thermomechanical treatment (CPT-5%-IA) promoted the uniform precipitation of T 1 and suppressed its coarsening; therefore, the CPT-5%-IA fine-grained matrix specimen exhibited favorable high-temperature performance, and possessed a yield strength of over 350 MPa at 300°C. However, CPT-5%-IA has limited effectiveness in improving the high-temperature performance of coarse-grained welding areas after abnormal grain growth (AGG). The precipitates in the AGG area exhibit low thermal stability, and the substantial precipitation of σ phases in the AGG area depleted strengthening elements and weakened aging response, thereby resulting in coarsening and low density of T 1 phases, and the precipitation of T 2 and η phases at the grain boundaries. Finally, welding area exhibits brittle intergranular fracture even at high temperatures.
Shi et al. (Wed,) studied this question.