Development of microstructure and texture during high temperature equal channel angular extrusion of aluminium

The feasibility of using the equal channel angular extrusion (ECAE) process for the breakdown of cast structures in commercial purity aluminium has been investigated. Billets of an as-cast coarse grained Al (99.7% pure) were subjected to ECAE at 500°C using a die that imparts an equivalent plastic strain of 0.67 per pass. Multiple extrusion passes were performed using two different processing routes: Route I in which the billet orientation was kept constant from pass to pass, and Route II in which the billet was rotated by 180° about its longitudinal axis from one pass to the next resulting alternately in shear in planes oriented at 120° to each other. Processing by Route I through five passes produced elongated grains showing evidence of dynamic recovery. Processing by Route II through five passes however produced largely equiaxed grains with a dynamically recovered substructure due to the intervention of static recrystallization during the reheating to extrusion temperature between passes. Both processing routes produced a dynamically recovered structure with equiaxed subgrains approximately 6 μm in size. Sharp deformation textures were not obtained. The relevance of this technique to industrial processing is discussed.