Stress-level-dependent microstructure evolution and deformation behaviors during creep age forming of AA2219 alloy

Abstract

Creep age forming (CAF) can shape and strengthen the sheet metals loaded externally at elevated temperature by corresponding creep/stress-relaxation and age hardening. Understanding the deformation and strengthening behavior at different stress levels plays a pivotal role in accurate prediction of CAF. This work experimentally investigates the effect of stress level on the evolution of both properties and microstructures, including precipitates and dislocations, during CAF. The microstructural evolution is characterized in detail by scanning/transmission electron microscopy (S/TEM) and X-ray diffraction (XRD). Stress orienting effect of θ» occurs at low-stress loaded samples and results in a decline in the hardening potential of creep-aging. A bimodal distribution of precipitates consisted of θ» homogeneously formed in the matrix and θ' heterogeneously formed on dislocations is found in the high-stress loaded samples, giving rise to a significant enhancement of hardening response. In addition, the creep strain increases drastically when the loading stress is higher than the initial yield strength. The relevant mechanisms for the transition of the obtained strength and creep behaviors with the applied stress are discussed based on microstructure observations.