Effect of magnetic field on precipitation kinetics of an ultrafine grained Al–Zn–Mg–Cu alloy

Abstract

To explore the effect of a stable magnetic field on precipitation kinetics in Al–Zn–Mg–Cu alloys (AA7075) with ultrafine-grained (UFG) structure, the precipitation kinetics of UFG Al alloys after ageing at 110–170 °C for 10 min without and with magnetic field of 1T were investigated in detail by small angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and X-ray diffraction (XRD). It was found that the dislocation and solute atoms can move more easily under the magnetic field due to the fact that the magnetic field decreases critical shear stress of dislocation and increases the solute diffusivity. The magnetic field can enhance the nucleation rate of η′ phases at low temperature (110–140 °C) and facilitate the coarsening at high temperature (150–170 °C), which is mainly attributed to the synergistic effect of dislocation motion and solute atom diffusion. These results imply unambiguously that the precipitation kinetics of UFG Al alloys with the magnetic field is significantly accelerated compared to those alloys without the magnetic field. A novel insight and systematic study put forward on the precipitation kinetics of UFG Al alloys under magnetic field and an exciting possibility to optimize precipitation kinetics, which could improve mechanical performances of alloys.