Study of deformation homogeneity in the multi-pass equal channel angular extrusion process

Ultra-fine grained and nanostructured materials have been widely investigated in the past decade due to the enhanced material properties such as improved tensile strength, hardness, toughness, fatigue life, and the optical and electrical related properties. The property improvement of the ultra-fine grained and nanostructured materials is usually achieved through severe plastic deformation (SPD). The SPD is currently an efficient technique for the production of bulk ultra-fine or nanostructured materials and it is realized via equal channel angular extrusion (ECAE) process. In this paper, the experimental research on ECAE process of conventionally used aluminum 6061 alloy is conducted and the deformation homogeneity in ECAE process is investigated. The aluminum samples are first treated with a pre-ECAE ageing heat treatment and then they are extruded in the ECAE die for up to 16 passes at room temperature without any rotation of the workpiece in each extrusion. To investigate the deformation homogeneity of the ECAE process, finite element simulation is conducted. The simulation results show that the materials on the outer side of the extrusion channel undergo severe plastic deformation compared to those on the inner side of the extrusion channel. To verify the simulation results, a series of Vickers microhardness measurement conducted on the polished cross-sections of the ECAE processed billets to map out the distribution of the hardness over the cross-section. The hardness distribution due to strain hardening is found to be inhomogeneous and its value increases significantly with the extrusion passes of ECAE process.