Research On Microstructure Evolution And Simulation Of AZ80 Magnesium Alloys By Thermoplastic Forming

As one of the lightest metallic structural materials, magnesium and magnesium alloy have many favorable physical and mechanical properties in practical application. It has attracted more and more attention from researchers all over the world, considered to be the ecological metallic structural materials of the 21st century. Nowadays, magnesium and its alloys are widely used in various fields, such as aerospace, automotive, mechanical engineering and electronics. However, the material forming is very difficult because of it has special atomic arrangement structures in space. The study of magnesium alloy forming properties at high temperatures is great significance.This paper studies the thermoplastic deformation and finite element simulation of forming of magnesium alloy AZ80. First of all, the true stress-strain curves were obtained with the temperature 250℃,300℃,350℃,400℃and strain rates 0.01s-1,0.1s-1,1s-1,10s-1 respectively after the compression tests of AZ80 magnesium alloy used by hot-physical simulation machine. By analyzing the curves:flow stress increases rapidly as the strain increased, then decreased gradually after the peak and finally stabilized; when the strain rate is constant, the peak stress decreased with the temperature rising, but the peak stress increased with the strain rate rising as the temperature is constant.The constitutive model was neatened and optimized of AZ80 magnesium alloy. The model was calculated which used of the Fields-Backofen equation firstly. We found that the curves are more consistent but varied widely after the peak. A new equation model was advanced which added a new softening factor based on the Fields-Backofen equation. The result shows that the optimized curve and the values of experiment can consistent well which are able to reflect the actual situation by the optimization of the model.The microstructures of AZ80 magnesium alloy were observed after compressing. Found that the dynamic recrystallization has more prone with the temperature rised and the more fine and homogeneous microstructures have obtainde at a certain strain rate. When the temperature is constant, the dynamic recrystallization was increased as the strain rate decreased. According to the microstructure images of magnesium alloy AZ80, the critical equation of dynamic recrystallization, dynamic recrystallization grain size model and dynamic recrystallization volume fraction model were established. The various grain models were loaded into the finite element simulation software Deform-3D to simulate the hot forming tests. The results show that the peak stress error of experimental values and simulated values are about between 0.5% and 21.5%. The stroke-load curves are agreement with the experimental curves at strain rate 0.01s-1, 0.1s-1,1s-1 and the sample was broken as 10s-1. The average grain size of microstructure error is the highest of 23.56% and 1.97% minimum.Finally, we researched on the wheel forming process of magnesium alloy. The best forming process for this wheel were obtained by combinied the property of microstructure is 360℃and rate 0.1mm/sec.