Study by DSC and HRTEM of the aging strengthening of Cu-Ni-Zn-Al alloys

Abstract The structural changes of a Cu–12 wt.% Ni–17 wt.% Zn–1.7 wt.% Al alloy as a function of the aging temperature have been studied by means of Differential Scanning Calorimetry (DSC), high resolution transmission electron microscopy (HRTEM) and hardness measurements. It has been proposed a hardening mechanism that implies the crystallization of a Ll 0 Cu 2 NiZn phase coherent with the matrix α phase followed, firstly, by its transformation into a Ll 2 coherent phase and, secondly, by the precipitation of this phase. It has been shown that aluminum play an important role in the precipitation hardening process because Cu 2 NiZn precipitates are not formed by aging a ternary Cu–Ni–Zn alloy of similar composition. It has been shown by the first time that DSC could be a powerful tool for discriminating the whole set of phase transformations undergone by alloys as a function of the annealing temperature from a single heating run.