The Simulation Of Flow And Grain Size Of AZ31 Magnesium Alloy Under Large Deformation Process

As the lightest metallic structural materials in engineering applications currently with high specific strength and specific stiffness,the grain of cast magnesium alloy can be refined significantly after severe plastic deformation.The strength and the ductility of magnesium can be improved significantly.In present work,based on the process of backward extrusion and Equal Channel Angular Pressing(ECAP),the metal flow during extrusion deformation is simulated by finite element method with AZ31 magnesium alloy using DEFORM-3D software.And the grain sizes of alloy during the deformation process are simulated using CA model The effects of extrusion temperature on metal flow and grain size have been investigated for AZ31 magnesium alloy tubes.The optimum technology parameters of backward extrusion of AZ31 magnesium alloy tubes have been decided by orthogonal experiment of numberial simulation.The back ward extrusion experiment of AZ31 magnesium alloy tube has been carried out on the condition of the optimum technology parameters,and the tube is observed microscopically.Finally,the effects of die structural parameters and extrusion process parameters on deformation uniformity and grain size of EC AP have been analyzed.The main conclusions are as follows.1.The effects of extrusion temperature,extrusion speed and die angle on deformation and grain size during backward extrusion of AZ31 magnesium alloy tubes(1)With the increasing of preheat temperature,the maximum temperature,the damage factor and the average grain size during backward extrusion increase,and the maximum load,the effective stress,the effective strain and the surface pressure of die during backward extrusion decrease.(2)With the increasing of extrusion speed,the temperature drop of billet,the load peak value,the average grain size and the surface pressure of die during backward extrusion decrease,and the flow rate,the strain rate,the damage factor of the metal and the wear depth of die during backward extrusion increase.(3)With the increasing of die angle,the flow rate of metal increase,and the maximum load decreases first and then increases.The load peak value is minimum when the die angle is 45°.(4)The results of orthogonal experiment of extrusion temperature and extrusion speed show that the effect of extrusion temperature on maximum load and grain size is more pronounced than that of extrusion speed.However,the tearing tendency of tube during extrusion process is susceptible to extrusion speed.(5)The optimal technology parameters are 370? and 1mm·s-1 that are determined by orthogonal experiment of numberial simulation.The surface quality of tube is excellent with uniform thickness.Grain can be refined to 3?m which is coinciding with the simulated results.2.The effects of die structural parameters and extrusion process parameters on metal flow and grain size during ECAP of AZ31 magnesium alloy(1)With the increasing of inner corner radius,the gap at the top of the lateral channel reduced until it disappears,and the load of stabilization stage of extrusion decreases.The homogeneity of effective strain of transverse and longitudinal cross-section is better when the inner corner radius is 2 to 4mm.The surface pressure and the wear depth of die can be reduced by setting a certain inner corner radius.However,the effect becomes deteriorated when inner corner radius is more than 6mm.(2)With the increasing of corner angle,the shear strain of billet,the peak and the growth rate of load decrease.When corner angle increases from 0° to 40°,the homogeneity of effective strain of transverse and longitudinal cross-section is reduced.The surface pressure and the wear depth of die can be reduced significantly when corner angle is 20° comparing with 0°,however the surface pressure and the wear depth of die change little when corner angle continues to increase.(3)When the billet enters into the die corner deformation zone,the temperature of metal increased significantly.After extrusion,the temperature increases gradually from the front to the end,and temperature of the bottom generally higher than the top.The effective strain of both axial ends of the workpiece is almost zero,but the effective strain of middle part is large after extrusion With the increasing of extrusion temperature,the effective strain of transverse and longitudinal cross-section increases gradually.After four passes of ECAP,the grain is refined obviously.With the increasing of extrusion temperature,the grain size of the workpiece increases after extrusion.(4)On the condition of the same preheat temperature,the greater the extrusion speed is,the faster the temperature of billet rises.When the extrusion speed is 1mm·s-1,the change of the workpiece temperature is minimum.The greater the extrusion speed is,the worse the homogeneity of effective strain of longitudinal cross-section is.When the extrusion speed is below 5mm·s-1,the greater the extrusion speed is,the smaller the grain size of alloy is after extrusion.However when the extrusion speed increases to 10mm·s-1,the grain size becomes larger.