Organization Uniformization Extrusion And Microstructure Evolution Simulation Of Casting AZ91D Magnesium Alloy

The purpose of this paper is to examine the uniaxial compression behavior, extruding in the reversed temperature field and the microstructure evolution in the deformation of casting AZ91D Mg alloy under different conditions, and to determine the optimum process conditions for the best deformation properties of this alloy, thus supplying a reliable basis for the development and application for the deformation technology of Mg alloy.Uniaxial compression tests were carried out at the temperature range 250~450℃and the strain rate of 0.0015s-1, 0.015s-1, 0.15s-1 to evaluate the uniaxial compression behavior of casting AZ91D Mg alloy. The influence of deformation temperature, strain rate and strain to the rheological stress under compression was analyzed. Considering the effect of recrystallize-emollience during thermal deformation, the rheological stress mathematic model including the emollience factor which is fit for AZ91D Mg alloy was put forward. The microstructure of specimens were observed by optical microscopy. It is demonstrated that the initial grain size of casting AZ91D Mg alloy is 40μm. The continuous dynamic recrystallization occurred when the deformation temperature is 300℃, 350℃and the strain rate is 1.5×10-3s-1. The dynamic recrystallization is mostly in the grain boundary. When the deformation temperature is 400℃and the strain rate is 1.5×10-3s-1 the dynamic recrystallization occurred altogether. The microstructure is homogeneous large angle boundary equiaxed grain and the grain size is 8~10μm. There is no crack in the surface of specimen so this is the best condition for the deformation. The recrystal grain size gradually reduced with the strain rate improved and the temperature reduced.With Yada model which is amended, a finite element soft ware called SuperForm was used to analyze microstructure evolution in the deformation of AZ91D Mg alloy. The results show that the simulation of microstructure evolution of the uniaxial compression and the experiment results are anastomotic.The extruding experiment of AZ91D Mg alloy was carried out at the temperature range 300~400℃under the reversed temperature. The extruding ratio are 4:1 and 9:1. The microstructure of extruding specimens was observed by optical microscopy. The experiment results indicated that the microstructure was more homogeneous when the temperature contrast between die and specimens was 100℃. The microstructure was homogeneous equiaxed grain which was 8μm when the die and the specimen was 400℃and 300℃and the extruding ratio was 9:1. This is the best condition for extruding.