A through-process model for predicting the precipitation evolution and mechanical property of stress-aged Al-Zn-Mg-Cu alloy

Abstract

As one of the most commonly used metals, Al-Zn-Mg-Cu alloys are now facing the increasing performance challenges caused by the more stringent service environment in modern industry. Through acting the external stress on material, the stress aging (SA) technique has been applied as an effective strategy to improve the comprehensive performances of precipitate-strengthened alloys. To further unveil the influence mechanisms of external stress, this work establishes a novel through-process model framework, including the classical Kampmann-Wagner numerical (KWN) model and viscoplastic self-consistent (VPSC) model. The former tracks the precipitation evolution and offers the precipitate information for the later VPSC calculation. The commonly-formed precipitate free zone (PFZ) is systematically investigated and modeled, achieving a more comprehensive description of the aging process. Furthermore, the stress-induced nucleation and growth acceleration of precipitation is described by the innovatively-proposed elastic energy caused by applied stress. The proposed model is validated by a wide range of stress (0 to 250 MPa) and gives an accurate prediction for both the precipitation evolution and the subsequent mechanical properties. It is demonstrated that the stress-induced precipitation acceleration effectively enhances the alloy strength for the early aging time, while this enhancing effect is gradually weakened with increasing aging time. Furthermore, the strength variation for different SA conditions mainly depends on the competition between precipitation strengthening and PFZ weakening.