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 degrees C and 400 degrees 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 (rho(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.