Formation of defects during equal channel angular extrusion

By theoretical definition, damage imparted to a material by its processing method is proportional to plastic deformation and unites several types of defects; such as that of gram-boundary voids and micro-cavities formed by decochesion of hard particles from the softer surrounding matrix. Since Equal Channel Angular Extrusion is a process of severe plastic deformation, the damage accumulated during processing of a material is significant. The intensity of damage accumulation depends on the route of extrusion taken and back-pressure applied during extrusion. In this paper, the damage accumulation-recovery model introduced in our previous works is proven experimentally. The damage distribution before, during and after ECAE was studied for by high resolution Field Emission Gun Scanning Electron Microscopy and Charpy impact testing. Samples of wrought aluminium alloy AA 6061 in T6 temper were extruded without rotation between passes (route A) without and with back-pressure. Application of back-pressure was found to change the character of fracture in samples produced, because the decohesion of particles within the matrix and brittle fracture of hard particles was suppressed. The source for the formation of voids during ECAE was therefore reduced.