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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