Study On The Behavior Of Hot Deformation And Microstructure Evolution Of Magnesium Alloy At Elevated Temperature

Magnesium alloys have a great potential for wide applications in the automotive industry because of their high strength-to-gravity ratios. At present, the vast majority of magnesium products for the automotive applications are in the form of die castings. Wrought magnesium alloys have so far found very limited usage, although they are expected to have higher strength and ductility than the cast counterparts. One of the barriers to the applications of wrought magnesium alloys is their low workability, as a result of hexagonal crystal structure. Therefore, it is necessary to explore the hot working potential of this kind of materials. The present study aims to investigate the flow stress behavior and microstructure evolution of AZ31 and AZ80 alloys.In the present study, hot compression tests of AZ31 and AZ80 magnesium alloy were performed on Gleeble 3500 at strain rates between 0.01-50 s-1and 0.03-90 s-1 and deformation temperatures between 300-500℃, respectively. The influence of the parameters on the stress-strain curves was analyzed to determine the constants in the constitutive equations. The microstructures of magnesium alloy during compression were observed by using MM-6 horizontal optical microscope (OM) of LeitZ Company Limited of West German and transition electron microscope (TEM) of H-800.The results showed that as the temperature was increased and the strain rate was decreased, the flow stress decreased. At high strain rates, due to the increasing temperature of the samples during the deformation process, the true flow stress should be corrected. Correction results showed that the corrected flow stresses were generally higher than the uncorrected values. In addition, the constants of constitutive equations were also obtained. The influence of temperature and stain rate on the microstructure during the deformation process was discussed. Generally, the deformed grain size increased with the increasing of deformation temperature and the decreasing of strain rate. But at low temperature and a high strain rate, the deformed grains were coarser than those at middle strain rates as a result of the significant temperature during the deformation. For AZ80 alloy, Twinning was the dominate deformation mechanic at mediated temperatures. The primary grains were divided by the intersection twinnings. The deformed grain boundaries were straight and the distribution of grain size was non-homogeneous. Dynamic recrystallization occurred during the deformation of the alloy at high temperature with equiaxzed grain structure.