Thermal-Mechanical Coupling Numerical Simulation Of Reciprocating Extrusion Processes On AZ31 Mg Alloy

The dissertation studied the forming process of reciprocating extrusion on AZ31 Mg alloy by numerical simulation and physical simulation, and provided some scientific evidences with establishment and optimization of real technology and exploration on deformation mechanism of reciprocating extrusion. The key technical problems of coupled FEM deformation-heat transfer in reciprocating extrusion process of AZ31 Mg alloy were studied. The nonlinear finite element software was used to simulate and analyze the reciprocating extrusion based on the rigid visco-plastic finite element model. The information of anamorphic mesh, equivalent strain field, equivalent strain rate field, equivalent stress field, temperature field, velocity field and loading-increments curves were obtained and the forming principle of reciprocating extrusion was revealed. The influences of different initial temperature of workpiece, different extruding velocities and different friction factors on fields and loading-increments curves were analyzed. The main conclusions of this study are as follows:The large deformation zone mainly concentrated at the areaâ…¡which closed to the wall of the die and the area which closed to the conic shrinking wall of areaâ… . The larger strain rate and larger stress concentrated at the conjoint area of areaâ… and areaâ…¡, the equivalent stress in the workpiece tended to equality with the increasing of extrusion passes. The temperature field distributed around the center of areaâ…¡, diffused from low to high in form of roundness and formed temperature gradient in the workpiece. The high flow velocity mainly distributed in the center of areaâ…¡.As the initial temperature of workpiece increased, the peak value of equivalent stress was decreasing, the peak value of equivalent strain, the equivalent strain rate and the flow velocityof workpiece increased and then level off.As the extrusion speed increased, the peak value of the equivalent strain rate and temperature increased steeply while the change of peak value of equivalent strain was not obvious, the peak value of equivalent stress increased firstly and then decreased and leveled off finally.The change of temperature in workpiece resulted from the change of friction factors could be ignored. As the friction factor increased, the change of the peak value of equivalent strain was very small, the peak value of equivalent stress and equivalent strain rate increased, the extent of rise decreased, and the peak value of flow velocity increased.In order to validate the reliability of numerical simulation, the physical simulation was designed and processed. The results indicated that numerical simulation results were reliability and had definite reference value to the actual production and theoretical analysis.