Effects of confining pressure on flaw formation during the consolidation of ductile powders by angular extrusion

We describe an experimental investigation into the effects of confining pressure (back-pressure) on consolidation of both aluminum 6061 and unalloyed copper powders by equal-channel angular extrusion below 250 °C, using a single pass through a 90° die with channels of circular cross-section. Empirical relationships for punch pressure requirements as a function of back-pressure and billet length are determined experimentally and compared with published theory. Powder particle boundaries are examined in extruded billets, revealing pores and regions of localized shear formed under low back-pressure conditions. The back-pressures required to obtain homogeneous, pore-free microstructures are determined, and related to the response of the powders during the initial compaction stage of extrusion.