Tailoring a high-strength Al–4Cu alloy through processing of powders by up to 100 turns of high-pressure torsion

Abstract

Processing by high-pressure torsion (HPT) was applied to a cold-pressed mixture of Al and Cu (4%wt) powders to successfully synthesise a high-strength nanocomposite. The powder consolidation and redistribution of second phases involved the stretching and fragmentation of the Cu domains into shorter strips and submicrometre particles. After 1 turn, the Al+4 wt%Cu alloy was not fully consolidated and exhibited numerous microvoids at the disc centre. For this reason, the material displayed comparatively low microhardness at this location which triggered early metal cracking during testing through plane strain compression. An adequate consolidation was achieved after 30 HPT revolutions as the composite exhibited a homogenous distribution of Cu fragments without any visible microcavities. This is consistent with the high flow stresses achieved during plane strain compression without incipient metal cracking. At this processing stage, there is evidence of partial dissolution of Cu into the Al–Cu solid solution followed by dynamic precipitation of Al2Cu nanoprecipitates. Additional straining up to 100 turns promoted further hardening up to 270 Hv and grain refinement down to ∼48 nm. However, this occurs concurrently with the coalescence and loss of coherency of the Al2Cu precipitates with the Al matrix.