Tensile deformation and fracture behaviours of cold rolled Cu-3wt.%Ag-0.5wt.%Zr thin sheets with different annealed microstructures

Analyses of the microstructures, plastic deformation behaviours and fracture behaviours with respect to annealing conditions are presented for Cu-3wt.%Ag-0.5wt.%Zr sheets rolled to achieve a 90% overall thickness reduction at room temperature. The results show that the starting temperatures of recovery and recrystallization are approximately 200 °C and 400 °C, respectively. The microstructural evolution manifests as the lamellar boundaries disappearing and sub-grains (SGs) coarsening during recovery. The average size of the dislocation cell (d_DC) is clearly elevated during recrystallization. By constructing relationships among mobile dislocation density (ρ_m), dislocation mean free path (L) and d_DC, a constitutive equation is built for describing plastic deformation behaviour. The parameters of the simplified Kubin-Estrin (KE) and new model describing mobile dislocation multiplication, mutual annihilation, dynamic recovery, L and d_DC are related to the annealing conditions. A microstructure with a larger d_DC value possesses a higher strain-hardening capacity, which leads to a large unstable plastic deformation stage and a large shear dimple region on the fracture surface.