Hot deformation behavior and constitutive equation of Mg-9Al-3Si-0.375Sr-0.78Y alloy

Abstract

The Mg-9Al-3Si-0.375Sr-0.78Y alloy specimens were compressed at constant isothermal strain rate by Gleeble 3500 thermal-simulation machine. The hot deformation behavior in the range of 250-400℃ and strain rate 0.001-10 s-1were studied. The results show that the peak stress decreases with the decreasing of strain rate and the increasing of temperature, meanwhile, the sensitivity of peak stress to strain rate increases with the decreasing of deformation temperature. In addition, the Arrhenius constitutive equation of hot deformation considering strain is established. The calculated flow stresses are compared with the experimental results, in the range of 300, 350℃ and 0.001-10 s-1, the mean absolute errors of the model are 1.57% and 1.76%, respectively. The average deformation activation energy is about 183.58 kJ/mol, and the average strain rate sensitivity index is 0.1616. The α-Mg phases exhibit dynamic recrystallization characteristics obviously. The size of β-Mg17Al12 phases decreases and its distribution becomes uniform, and the morphology of primary Mg2Si phase changes little. At low temperature (250-300℃), dynamic recrystallization occurs only at the grain boundary. Under high temperature (350-400℃) deformation, the primary α-Mg grains show significant dynamic recrystallization. With the increasing temperature and decreasing strain rate, recrystallization degree increases and recrystallization grain grows gradually.

Keywords

• magnesium alloy
• hot deformation
• constitutive equation
• dynamic crystallization