Applied Basic Researches On Extrusion-Shear Forming Technology For AZ31 Magnesium Alloy Thin-Walled Tube

Traditional extrusion is the most mature processing technology at present,but the grain refinement is limited;equal channel angular extrusion is a method of large plastic deformation,the alloy must be pretreated in the mold before deformation,and then multi-pass extrusion,Thus the superfine crystal is obtained,the method can not only refine the crystal grains while weakening the base texture,but the process complexity can not be continuously produced,and the forming size is limited;Hot extrudate will form fibrous structure and strong basal texture,forming uneven,so that the thin tube is less tough and forming accuracy.Based on this,it is conceivable to combine traditional extrusion and Equal Channel Angular Extrusion(ECAE).Therefore,the project proposed an extrusion extrusion(Shear)composite short flow forming new technology(referred to as TES)containing rare earth magnesium alloy thin-walled tube(Tube).In this paper,the TES deformation process was studied by experiments and finite element analysis,focusing on the evolution of the microstructure,texture,and mechanical properties of magnesium alloys during TES deformation.At the same time using the above process through the mold design,extrusion cylinder design,extrusion rod design and extrusion needle design,etc.,processing die out of the final successful extrusion of magnesium alloy thin-walled pipe.The flow stress-strain curves of az31 magnesium alloy were drawn from the data obtained by thermal compression test of AZ31 magnesium alloy with glee ble-1500 D thermal simulation tester,which provided material support for deform-3D finite element simulation software.By comparing the simulated values with the theoretical values at equivalent strain of 16.8,9.33 and 6.88,the results show that the values are basically the same and the changing trend is completely consistent,which can explain the validity of the simulation.Through the analysis of TES extrusion force and equivalent stress and the consideration of die service life,the reasonable internal structure(extrusion ratio G= 9.33,transition angle ? = 150,transition radius r = 0.5 mm)was selected and the whole die was machined.In addition,a combination mold is machined for ease of disassembly and easy observation of the extrusion in the TES extrusion process.At the extrusion process analysis of the equivalent stress,velocity field,equivalent strain and damage coefficient,found that the extrusion force curve shows special changes,appeared repeatedly extrusion platform;When the temperature rises,the velocity is reduced and the friction coefficient decreases,the extrusion pressure can be reduced.In addition,When the temperature rises,the equivalent stress decreases and the distribution is evenly distributed.The metal flow velocity increases at every corner of the mold,but each corner applies a back pressure on the previous corner,which reduces the metal flow velocity before the corner.Increasing extrusion temperature and decreasing friction factor increase the outflow velocity of metal,but have little effect on the uniformity of metal flow.The effective strain increases by 0.5 and up to 3.37 in each time the shear.In addition,the strain at the last two corners is bigger and bigger,the deformation is more and more serious,the residual stress increases,the failure coefficient increases.Analysis of ordinary extrusion and TES extrusion shows that the average grain size after TES extrusion is significantly refined,the hardness of value increases.At the same time,EBSD experimental analysis shows that a large number of compression twins { 10-11 } and tensile twins { 10-12 } are produced after TES extrusion.Schmidt factor increased significantly,and the initial texture of AZ31 magnesium alloy was improved.CA cellular automaton method was used to analyze the grain evolution process during TES extrusion process.It was found that the average grain size decreased with the extrusion-shearing,but the average grain size during the adjustment stage increased.The reason is that the grain grew up at elevated temperature under the action of friction,which was consistent with metallographic test and hardness test.At 400 ?,with the increase of deformation temperature,the atomic thermal activation effect increased,the recrystallization percentage increaseed,the grain size distribution was uniform,the average grain size increaseed,and the hardness change trend was consistent with 370 ?,but the value decreased.