Hot Deformation Stability of Extruded AZ61 Magnesium Alloy Using Different Instability Criteria

The hot deformation stability of extruded AZ61 magnesium alloy was investigated by means of hot com- pression tests at the temperature range of 250-400 ℃ and strain rate range of 0.001-1 s^-1. The 3D instability maps considering the effect of strain were developed to delineate the regions of unstable flow on the basis of Jonas＇s, Semiatin＇s, Prasad＇s, Murty＇ s, Gegel＇s and Alexander＇s criteria. Since non-uniform deformation occurs due to the initial microstructure inhomogeneity, the friction, etc., finite element simulations were performed to determine the position of the specimens which can mostly represent the preset deformation parameter. Detailed microstructural investigation on such position was carried out to examine the validity of the instability maps, and the results indicate that for extruded AZ61 magnesium alloy： （1） Jonas＇s and Semiatin＇s criteria conservatively predict the instability regions; （2） Gegel＇s and Alexander＇s criteria inadequately predict the instability regions; （3） Prasad＇s and Murty＇s criteria provide more effective predictions of the instability regions than Jonas＇s, Semiatin＇s, Gegel＇s and Alexander＇s criteria,

3D processing map for hot working of extruded AZ80 magnesium alloy

The hot deformation behavior of extruded AZ80 magnesium alloy was investigated using compression tests in the temperature range of 250–400 °C and strain rate range of 0.001–1.000 s–1. The 3D power dissipation map was developed to evaluate the hot deformation mechanisms and determine the optimal processing parameters. Two domains of dynamic recrystallization were identified from the 3D power dissipation map, with one occurring in the temperature and strain rate range of 250–320 °C and 0.001–0.010 s–1and the other one occurring in the temperature and strain rate range of 380–400 °C and 0.001–0.003 s–1. In order to delineate the regions of flow instability, Prasad’s instability criterion, Murty’s instability criterion and Gegel’s stability criteria were employed to develop the 3D instability maps. Through microstructural examination, it is found that Prasad’s and Murty’s instability criteria are more effective than Gegel’s stability criteria in predicting the flow instability regions for extruded AZ80 alloy. Further, the 3D processing maps were integrated into finite element simulation and the predictions of the simulation are in good agreement with the experimental results.