The Thermal Deformation Behavior And Structure Properties Of AZ31 Magnesium Alloy

Magnesium and magnesium alloy are the lightest metallic structural material at present. They have been used widely in the aviation, automotive, computer, and electronics industries, due to their unique properties such as low density, high specific strength and rigidity, good damping capacity and heat conductivity, excellent electromagnetic shield effectiveness and machinability, good dimensional stability and recycle character, and so on.Because of the close grain, low composition segregation and high strength and plasticity, wrought Mg alloy has better properties than cast Mg alloy. But Mg alloy is the HCP crystal structure, therefore its plastic deformation is worse at room temperature, and processed yield is also lower, which could be limit its application. The plasticity of wrought Mg alloy will be greatly improved with higher temperature. The behavior of pyroplastic deformation of AZ31 alloy was systematically studied with optical microscope and SEM. Physics and numerical simulation technique such as Gleeble-1500 thermal analog computer and ANSYS software were also employed.With excellent properties, AZ31 alloy are widely applicable for plastic forming technology such as extrusion, foundry and roll at present. The influence of hot extrusion technology on bar property of AZ31 alloy was studied in this paper. Real stress-strain curve was gained by thermal analog test. The influence rule of deformation temperature, strain rate and deformation quantity on rheological stress of the material was studied. Constitutive equations of rheological stress were built. It can be seen that peak rheological stress decreases with higher deformation temperature, and rises with the reduction of strain rate. Based on this, mathematic model of rheological stress was gained by linear regression method, and the introduction of parameter Z provided the basis for computer simulation.By using numerical simulation method of rigid-plastic finite element, the extrusion process of Mg alloy bars was stimulated, and the distribution curve of equivalent stress, equivalent strain and extrusion pressure were obtained. The stimulation results show that the adjustable zone was the focus ares for the maximum equivalent stress during the extruding. Both the stress and strain were maximum here.Room temperature tensile property, elongation percentage, room temperature tensile fracture and metallurgical structure were studied before and after the extrusion when the extrusion temperature, extrusion rate and extrusion ratio were 350℃, 10mm/s and 9 respectively. It is concluded that grain size and comprehensive mechanical property of Mg alloy are coherent, small grain can not only enhance strength, but also improve plastic.