Aging behavior of ultrafine-grained Al-Mg-Si-X (X= Cu, Ag, Pt, Pd) alloys produced by high-pressure torsion

Abstract

Age-hardenable Al Mg Si alloys containing additional elements of Ag, Cu, Pt or Pd were processed by high-pressure torsion (HPT) and they were subsequently aged at a temperature of 373K for up to a total period of 5,400 ks. It was found that, in all alloys, the grain sizes after HPT were refined to 300430nm and there were significant increases in the hardness through the HPT processing. The hardness was further increased by the subsequent aging treatment, confirming the simultaneous strengthening by grain refinement and fine precipitation. However, the aging behavior was different depending on the alloying elements. In the Cu-added excess Mg alloy, the hardness increase was large and the igher hardness retained for longer aging time when compared with those of non-added alloys. It was suggested that the precipitation of a few particles within a single grain with the size of a few hundred nanometer contributes to appreciable age hardening. © 2014 The Japan Institute of Metals and Materials.