Pre-treatment-mediated dislocation-precipitate interactions for enhanced creep formability-property synergy in an Al-Cu alloy

This study investigates how pre-treatment regulates the age-hardening and creep-ageing responses of a highly deformed (HD) Al-Cu alloy produced by 80% cold rolling. Five pre-treatment conditions were applied before cold rolling: as-quenched, natural ageing for 24 h or 2 weeks, and artificial pre-ageing at 165 °C for 5 or 24 h. All HD alloys were subsequently creep-aged at 120 °C under 150 MPa for 12 h. Mechanical testing and XRD, DSC, TEM, and STEM analyses showed that natural ageing had almost no measurable influence after rolling because the extremely fine Cu clusters and incipient GP I zones were readily sheared or redistributed. In contrast, artificial pre-ageing introduced GP zones and θ″ precipitates that promoted dislocation storage, increasing the post-rolling dislocation density from approximately 1.9×10 15 m -2 in the naturally aged alloys to 2.22-2.34×10 15 m -2 . Rolling fragmented the pre-existing precipitates into Cu-rich remnants that subsequently promoted the heterogeneous nucleation of segmented θ′ assemblies during creep ageing. Moderate pre-ageing for 5 h was inferred to balance dislocation retention and mobility. Consequently, AA5h achieved a creep strain of 0.89% at 120 °C, a yield strength of 494 ± 8 MPa, an elongation of 10.0 ± 0.34%, and the highest strength–ductility product of approximately 49 MPa. Extending pre-ageing to 24 h produced stronger dislocation pinning and a coarser, more heterogeneous precipitation structure, accelerating creep-rate decay. These results demonstrate that moderate artificial pre-ageing enables a favorable combination of creep formability and post-ageing mechanical properties by regulating dislocation–precipitate interactions throughout processing.