Analysis of forming loads, microstructure development and mechanical property evolution during equal channel angular extrusion of a commercial grade aluminum alloy

The process of equal channel angular extrusion (ECAE) is being widely investigated because of its potential for producing ultrafine grained structures. In the present study, a commercial grade aluminum alloy (AA 6063) was subjected to ECAE for three passes using two different processing routes: Route A where the specimen orientation is kept constant between passes; Route B where the specimen is rotated by 180° about its longitudinal axis between passes. Each extrusion pass imparts an equivalent true strain of 0.67 to the specimen. Analysis of the force–stroke diagram was carried out and compared with theoretical predictions. The mechanical properties and microstructure were investigated. In order to facilitate comparison of these parameters with those of conventional forming techniques, conventional cold extrusion studies were also carried out using an extrusion die that imparts an equivalent true strain of 0.65 to the material. The calculated extrusion loads were in the same range as the values experimentally observed for the first pass. The extrusion pressures increased slightly for processing by Route A but decreased for Route B with increasing number of passes. By processing through Route A, the tensile strength increased and elongation to failure (%) decreased as expected, but the elongation to failure (%) increased from the second to third pass when processed through Route B. After conventional cold extrusion, the mechanical properties were observed to be more or less similar but much higher extrusion loads were required. This implies that the material can be subjected to the same amount of plastic deformation by ECAE but with lower press loads to refine grain size and improve strength.