Research On Thermoplastic Deformation Behavior And Numerical Simulation Of AZ31 Magnesium Alloy

Magnesium alloy is regarded as one of the most prospective metallic materials in 21th century due to its low density, high specific strength, high specific stiffness, good damping capacity, excellent electromagnetic shielding properties, and good machinability. Unfortunately, its hexagonal structure, the lower tensile yield strength and the poor room-temperature formability confine the further application of magnesium alloy. In this dissertation, in order to solve this different problem numerical simulation and experiment research were conducted on thermoplastic deformation behavior of AZ31 magnesium alloy. It will provide guidance to reasonably establish the technological parameter of Magnesium alloys extrusion and provide the basic data for further system research on the alloy.This paper studied the stress, strain and temperature fields of AZ31 magnesium alloy under different conditions by using the forming simulation software Deform 2D,3D. Metallic phase analysis was used to analyze the microstructure mechanical properties of the AZ31 magnesium alloy after hot deformation. In addition, Vickers microhardness tester, electronic almighty material experiment machine and scanning electron microscope (SEM) were exploited to characterize the mechanical properties of AZ31 magnesium alloy after extrusion. The main results are as follows:1. During the compression process of AZ31 magnesium alloy, both the stress and strain gradually increase. The stress among different samples becomes bigger with the strain rate increases and the temperature decreases. The temperature rise effect is found during the compression process of alloy, and it becomes more obvious with the increasing of the strain rate and decreasing of grain size.2. During the compression process of AZ31 magnesium alloy, the deformation extent in the core part of the samples was higher than that in the edge part and then the grain in the center is elongated which exhibits the apparent direction. When the compression temperature is too high, it is easy to form twin on the edge.3. Plastic deformation mainly occurs in the extrusion exit during the extrusion process of AZ31 magnesium alloy. The stress increases with the increasing of the strain rate and decreasing of the temperature. Temperature rise effect is discovered during the extrusion process of AZ31 magnesium alloy and temperature rise becomes more obvious when the strain rate gets bigger. As the proceeding of the extrusion, stress, strain and temperature distribution are gradually reduced from the center to both of sides.4. The dynamic recrystallization turned up in the alloy during the extrusion process of AZ31 magnesium alloy. After extruding, the grains received a remarkable refinement. When the extrusion rate was low, the extrusion microstructure was a mixed crystal structure which composed of big elongate grain and dynamic recrystallization grains. As the extrusion rate increased, the mix microstructure significantly reduced. Besides, the organization became uniform and the crystalline grain was tiny. During the process of high-speed extrusion, it was easy to form a coarse grain structure when the edge size of the grain was less than 20μm.5. After extruding, the mechanical property of AZ31 magnesium alloy was improved. Hardness, tensile strength and elongation increased to different degrees. There were a lot of dimples throughout the fracture and it was the ductile rupture.6. The results showed that there were more homogeneous extrusion texturization in AZ31 magnesium alloy which was treated by grain refining than that was not pre-treated. The crystal grains were finer. Meanwhile, hardness and tensile strength were higher along with the elongation decreasing slightly.