Effects of Ag addition on age-hardening and nano-scale precipitate microstructures of an Al-3%Mg-1%Cu alloy

Abstract

In this work, the bake-hardening (BH) response of Al-3.0%Mg-1.0%Cu alloys with and without Ag has been investigated by a hardness test, and related to the nano-scale precipitate microstructures observed by high resolution transmission electron microscopy (HRTEM) and a three-dimensional atom probe (3DAP). The small addition of Ag increased hardness under a BH condition (e.g. 443 K for 1.2ks) due to the rapidly formed nanoclusters containing Mg, Ag and/or Cu. The formation of the equiaxed Z phase was also accelerated by the Mg/Cu/Ag clusters, resulting in the more increased second-stage hardening. This strongly suggests that Mg/Cu/Ag clusters provide effective nucleation sites for the Z phase, whereas Mg/Cu clusters formed in the ternary alloy do less.