Creep in ultrafine grained aluminium

Extremely coarse-grained high purity (99.99%) aluminium was subjected to equal-channel angular pressing (ECAP) to refine its grain size. The ECAP was conducted at room temperature with a die that had a 90° angle between the die channels and one or repetitive pressing followed either route A, B and C. Constant stress compression creep was conducted at 473 K on billets after different number of ECAP passes (up to eight passes) and, for comparison purposes, on unpressed material. The creep resistance of the ECAP processed material was markedly improved with respect to unpressed material. In addition the creep behaviour of pressed material depends on the number of ECAP passes, because the microstructure and microtexture is homogenized with increasing number of passes. Processing route had little apparent effect on the creep behaviour of pressed material.