Determination of a constitutive relationship for AZ31B magnesium alloy and validation through comparison between simulated and real extrusion

In the present study, cylindrical hot compression tests were performed to determine the dependence of the flow stress of a wrought magnesium alloy, AZ31B, on temperature, strain and strain rate. The tests covered wide ranges of temperature (300-500 degrees C) and strain rate (0.03-90 s(-1)), as possibly encountered in real-fife metal-forming processes. It was found that at a low strain rate, the flow curve reached a steady state at a large strain after the flow stress peak. At a high strain rate, however, the flow curve exhibited continuous flow softening after the peak. In addition, it was noticed that with increasing strain rate, deformation heating became more pronounced. Thus, a correction of flow stress for deformation heating at a high strain rate was a necessity. The constants in the constitutive equation of the hyperbolic sine form were determined with the measured flow stresses corrected for deformation heating. Validation tests were then performed through 3D computer simulation of hot extrusion based on the corrected and uncorrected flow stress data, followed by real extrusion experiments under the identical conditions. Good agreements between the predicted and measured values in extrudate temperature and extrusion pressure were achieved. (c) 2005 Elsevier B.V. All rights reserved.