Tensile behaviour of an Al-4 wt.%Cu alloy deformed by equal-channel angular pressing

An Al-4 wt.%Cu alloy in the as-cast, homogenized condition was subjected to equal-channel angular pressing, and tensile tests showed a very good combination of strength and ductility. In order to explain a sharp drop in ductility observed after the first pass only, the equal-channel angular pressing was repeated on the same alloy but in the conventionally extruded condition. Results were similar to those of the ascast and homogenized material, but the ductility drop was absent. Fractographic observation indicated that the conventional extrusion eliminated solidification pores and voids; hence, the total absence of the ductility drop, whilst equal-channel angular pressing caused the same effect on the as-cast and homogenized group of samples, but only after the second pass. This is an important finding since it shows that equal-channel angular pressing has the capacity of closing solidification defects. Further observation of the stress-strain curves revealed the presence of the Portevin-Le Chatelier effect, whose relationship with dislocation density was tentatively discussed. (C) 2008 Elsevier B.V. All rights reserved.