A modified two state variable unified constitutive model is presented to model the high temperature stress-strain behavior of a 319 cast aluminum alloy with a T7 heat treatment. A systematic method is outlined with which to determine the material parameters used in the experimentally based model. The microstructural processes affecting the material behavior were identified using TEM microscopy and consequently correlated with the model parameters. The stress-strain behavior was found to be dominated by the decomposition of the metastable θ′ precipitates within the dendrites and subsequent coarsening of the θ phase which is manifested through remarkable softening with cycling and time. Pronounced dimensional instabilities were observed to occur rapidly if the material was exposed to 300°C. The model was found to accurately simulate experimental stress-strain behavior such as strain rate sensitivity, cyclic softening, aging effects, transient material behavior, and stress relaxation in addition to capturing the main deformation mechanisms and microstructural changes as a function of temperature and inelastic strain rate.
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