Modified Fields–Backofen model for constitutive behavior of as-cast AZ31B magnesium alloy during hot deformation

•Relationship between the strain related to the demarcation point on compression curves and the strain rate was modeled.•The dependency of flow stress of AZ31B magnesium alloy on temperature and its specific form were proposed.•Modified Fields-Backofen for characterizing the constitutive behavior of AZ31B accurately was established and optimized.

Uniaxial hot compression tests were carried out over a wide range of strain rates (0.005–5 s− 1) and temperatures (200–450 °C) to study the constitutive behavior of as-cast AZ31B magnesium alloy. Considering the macro results of compressions, deformation characteristics were analyzed to explain the abnormal extension of compressive curves at 200 °C and then the mathematical model was established approximately to predict the moment at which an occurrence of demarcation point took place. Constitutive behavior at (250–450 °C) was modeled using the Fields-Backofen (F-B) equation, which was modified in view of the dependency of flow stress on temperatures and its specific form. However, strain-rate sensitivity and temperature softening coefficient, characterizing the hardening and softening effect respectively, are constants in the F-B equation, resulting in the F-B equation cannot accurately characterize the complex deformation mechanism under different conditions. Later, another modified F-B equation with a higher prediction accuracy was proposed, including the effect of strain by considering the strain rate sensitivity and temperature softening coefficient as different functions of strain.

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