Numerical Simulation Of AZ31 Magnesium Alloy During Continuous Variable Cross-section Twist Extrusion Process

Magnesium alloys have some unique excellent properties,so they are widely used in aerospace,transportation,electronic communications,medical materials and other fields.At present,the preparation of ultra-fine grained magnesium alloys by severe plastic deformation and the development of new severe plastic deformation process have become the research hotspots in the field of material processing.As a new method of severe plastic deformation,the twist extrusion process has the advantages of two shear planes,no change in the cross section of billet,high utilization rate of materials and processing of special cross section materials.However,there are also some problems such as low deformation efficiency,inhomogeneous deformation and difficult manufacturing of dies.In order to solve the problems existing in the twist extrusion process,a continuous variable cross-section twist extrusion method is proposed in this paper.By connecting multi-segment forward extrusion die and twist extrusion die,a modular die cavity with variable cross-section is formed.A series of continuous composite plastic deformation will occur in the process of billet deformation,which will accumulate larger plastic strain continuously,in order to achieve uniform refinement of microstructures and improve the mechanical properties of materials.In this paper,the continuous variable cross-section twist extrusion process of AZ31 magnesium alloy was simulated by software Deform 3D.The influence of die cavity structure,process parameters and deformation routes on the deformation process is systematically studied.The design of die cavity structure is the primary problem in the study of continuous variable cross-section twist extrusion method.Optimizing the die cavity structure will effectively improve the uniform deformation.In this paper,six groups of die cavity structures are designed by different β and γ.At the same time,the simulation results are systematically compared from the aspects of extrusion load,metal flow,effective stress,effective strain and point tracking.The results show that the die cavity is optimized when β is 42 degrees.Deformation process parameters are one of the main factors affecting deformation behavior.In this paper,hybrid orthogonal table is used for statistical analysis to obtain the range of process parameters.The effects of extrusion temperature,extrusion speed and friction factor on the continuous variable crosssection twist extrusion process of AZ31 magnesium alloy were systematically studied by numerical simulation method,and the simulation data were analyzed.The results show that the optimum process parameters are temperature 300 °C,speed 1 mm/s and friction factor 0.1.The effect of deformation routes on the continuous variable cross-section twist extrusion process of AZ31 magnesium alloy needs further verification.In this paper,two groups of die structures were designed according to the torsion direction of the twist channel,namely,the same direction(N+N)and Opposite direction(N+S)continuous variable cross-section twist extrusion die.By comparing the temperature field,extrusion load,strain field and microstructure refinement,it is clear that different deformation routes have little influence on the continuous variable cross-section twist extrusion process of AZ31 magnesium alloy.