Microstructural characterization of interrupted aging on an AA7050 aluminum alloy

Abstract

Interrupted aging heat treatments are used to maximize the gain in mechanical properties in 7xxx aluminum alloys through the production of a microstructure with a high density of fine precipitates, which are homogeneously dispersed in the aluminum matrix. In an interrupted aging heat treatment, the first stage, at higher temperature, aims at creating sites for subsequent nucleation of precipitate particles, while the second stage, at lower temperature, aims at the nucleation and growth of precipitate particles. The Interrupted aging heat treatment has been increasingly studied because it confers resistance levels similar to, or even higher than conventional heat treatments (e.g. T6), in addition to producing a more stable microstructure. In this study, a microstructural characterization was carried out using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) in an AA7050 aluminum alloys that was submitted to aging heat treatments T7451, T6 and T6I4-65, seeking a better understanding of the microstructure produced in each heat treatment and the reasons of the gain in mechanical properties. The results indicated that the T6I4-65 interrupted aging heat treatment was the most efficient in creating sites for nucleation of phases in the aluminum matrix, when compared with other conditions, due to the higher density of particles of the phases η′, η and T, in addition to being the only condition to have GPII zones and S phase in its microstructure.