Research On Mechanical Behavior Of Extruded AZ31 Magnesium Alloys In The Process Of Plastic Deformation At Room Temperature

Magnesium alloys have high specific strength and high specific stiffness, low density, good shock absorption and excellent electromagnetic shielding performance. Because of these advantages, they have broad application prospects in the fields of transportation, communications and aerospace. However, the magnesium alloy is easy to form the deformation texture after the thermal deformation, which leads to significantly mechanical anisotropy. In terms of theoretical research, the research on the wrought magnesium alloys about texture and microstructure evolution during plastic deformation is relatively insufficient.In this thesis, the mechanical behavior of extruded AZ31 magnesium alloys was studied based on the three-directional tensile and compression tests at room temperature. The crystal plasticity constitutive model which includes slip and twinning mechanism was established by modifying the viscoplastic self-consistent(VPSC) model. Using this model, Axial tensile and three-directional compression tests of extruded AZ31 magnesium alloy at room temperature are simulated, activation and evolution of basal slip, prismatic slip, pyramidal slip, {1012}〈1011〉 tensile twinning and {1011}〈1012 〉 compression twinning are studied in the process of plastic deformation. Tensile-compression asymmetry and mechanical behavior of three-directional tensile and compression of extruded Mg alloy which has initial extruded fiber texture is studied from the microscopic plastic deformation mechanism through experiment and simulation.Main conclusions found are as following:(1) Basal slip and {1012}〈1011〉 tensile twinning respectively correspond to the dominated deformation mechanism in the early stage of axial tension and compression deformation which is the main reason for the formation of tensile and compressive yield strength asymmetry in extruded AZ31 magnesium alloy. Basal slip is the dominated deformation mechanism in the early stage of 45° and 90°compression to the extrusion direction which leads to that the yield strength of this two kinds of deformation process is similar and less than the axial compression yield strength;(2) The increase or decrease of strain hardening rate is the competing results of basal slip and {1012}〈1011〉 tensile twinning at the early stage of three-directional compression plastic deformation. Tensile twinning experiences a process of nucleation, growth and gradually swallow the base in the process of deformation. At the end of the compression deformation, the increased activity level of compression can release the cumulative stress which contributes to the reduction of strain hardening rate;(3) Although all the dominant deformation mechanism in the early stage of three-directional tensile plastic deformation is basal slip, different basal slip corresponds to different schmid factor which resulting in the anisotropy of tensile yield strength in three directions;(4) The interaction of deformation mechanism and texture evolution impacts on the mechanical behavior of magnesium alloys and determine the mechanical properties finally.