Effect of plastic deformation on the ageing behaviour of an Al-Cu-Mg alloy with a high Cu/Mg ratio

The effect of tensile strain ranging from 1% to 7% on the decomposition sequence and mechanical properties of an AA2519 alloy with low Si content is studied. Pre-straining promotes the precipitation of θ′- and Ω-phases at dislocations and suppresses the precipitation of GP-zones and θ″-phase. The aspect ratio (AR) of the homogeneously nucleated ΩΙ-phase is higher than that of the ΩΙΙ-phase nucleated on the θ′-phase/Al interfaces by a factor of ~ 4. Replacement of θ″-phase by a dispersion of θ′- and Ω-phases took place under peak-ageing condition and thus imparted only a minor hardening effect, despite a seven-fold increase in the volume fraction of the strengthening precipitates. An increase in the yield stress by 30% with increasing pre-strain from 1% to 7% is attributed to an increase in the lattice dislocation density. Over-ageing leads to replacement of the ΩΙΙ-phase by the θ′-phase.