On the evolution of microstructure and fracture behavior of multilayered copper sheet fabricated by accumulative roll bonding

Abstract

In this investigation, multi-layer copper sheets are fabricated using accumulative roll bonding (ARB). Evolution of microstructure and dislocation density during ARB and after that during annealing treatment at 500 °C are investigated. In addition, the evolution of voids at the interfaces between stacking layers which may cause delamination and premature fracture are statistically analyzed. It is found that the grain structure, dislocation density, size and volume fraction of voids can affect tensile properties and electrical resistivity. The average grain size in annealed multilayered copper sheets depends on the imposed strain during deformation, but as well, the thickness of the stacking layers which can control grain growth. A fraction of the interface is left out with no solid metallurgical bonding and form voids. The average void size reduces with further deformation. However, the surface fraction and number density of the voids increase which is due to the greater number of interfaces in line with larger number of stacking layers. With 2 cycles of ARB, the ultimate tensile strength of the samples increases significantly and the ductility reduces. However, with further deformation, ductility improves due to the reduction in dislocation density. After annealing, the ductility exceeds its initial values which is attributed to swarm necking resistance of many stacking layers in the multi-layer product. The specific electrical resistivity (SER) of the annealed multi-layer sheets would not equal the initially annealed sample which is due to the finer grain structure and the interfaces between stacking layers.