Non-isothermal creep ageing in a largely pre-deformed Al–Cu alloy

Creep age forming (CAF) utilizes both the heating and isothermal holding stages to govern final deformation and properties. This work investigates the non-isothermal creep ageing behavior of an AA2219 aluminum alloy subjected to 80% cold rolling, tested at 140 °C under applied stresses of 100-200 MPa. The pre-deformed alloy achieves considerable creep strains (0.89-6.08%) while maintaining high yield strength (>450 MPa) and good ductility. Critically, the heating stage alone generates a significant absolute creep strain (>0.4% at 150 MPa), comparable to the total creep strain of a T3 temper alloy aged at 165 °C under the same stress for 12 h, and accounting for ∼25% of the total strain at this stress. Although most deformation accumulates during the subsequent isothermal hold, the relative contribution from heating decreases with increasing stress. Microstructural analysis reveals a stable, highly tangled dislocation substructure. The dislocation density decreases gradually but remains high after ageing, with localized creep-recovery zones near dislocation cell walls indicating recovery and the release of mobile dislocations that facilitate creep. Precipitation evolves from sparse θ' and fine early-stage phases after heating to a dense distribution of coarsened θ' plates following full ageing. A dislocation-based constitutive model, integrating a modified Kocks-Mecking-Estrin (KME) evolution law with an Arrhenius-type hyperbolic-sine creep equation, successfully captures the multi-stage non-isothermal creep response. These findings demonstrate that the heating stage contributes a non-negligible fraction of the total creep strain in high-dislocation-density Al-Cu alloys-an essential consideration for designing precise non-isothermal CAF processes for high-performance components.