Effect of pre-straining on the aging behavior and mechanical properties of an Al-Cu-Mg-Ag alloy

The effects of cold deformation prior to aging on the precipitation behavior, microstructure and mechanical properties of an Al-5.6Cu-0.72 Mg-0.5Ag-0.32Mn-0.17Sc-0.12Zr (in wt%) alloy were investigated. Pre-straining disrupts the formation of Mg-Ag co-clusters, modifying the normal precipitation sequence. A strong increase in the dislocation density by a factor of 100 leads to a ~40% decrease in the number density, NV, of the Ω-phase at pre-strains of ε≥1% (ε≥0.01). The aspect ratios of the platelets in this phase increased from ~21 to ~42 after a negligible pre-strain of ≤1% (ε≤0.01) and further decreased to ~25 in the pre-strain interval of 1-80% (ε~0.01-1.61). In addition, the nucleation of the Cu-rich θ′-phase occurs on dislocations. The heterogeneous nucleation of the thick Ω-phase particles with low aspect ratios (~12) and equiaxed particles of S-phase with dimensions ≤5 nm on the deformation-induced boundaries was found. After peak aging, the yield stress (YS) and ultimate tensile strength (UTS) increased from 478±4 MPa and 522±8 MPa for the as-quenched alloy to 516±4 MPa and 568±6 MPa in the longitudinal and 554±5 MPa and 601±3 MPa in the transversal directions, respectively, for the alloy subjected to pre-straining with a rolling reduction of 80% (ε~1.61). Cold rolling prior to aging induces the anisotropy in mechanical behavior through the formation of deformation bands.