Study On High-temperature Deformation Behaviour And Thermal Spinning Of Extrued ME20M Alloy

Mg alloys have attracted a great deal attention as the lightest structural materials sofar, due to their low density, higher strength, better heat and creep resistance anddimensional stability and so on. However, due to Mg alloys are studied later than Al andTi alloys, which cause the serious unbalance between its application and great potential.ME20M alloys, as a kind of Mg-Mn alloys, have a low strength because of serious hotshrink and cracking tendency when solidification. And it mainly improve its strengththrough deformation. So it is necessary to study the alloys that has been deformed.Besides spinning is the preferred technology for making tube workpieces which have awidely application in aerospace areas. But the use of spinning technology for Mgalloys is limited by difficulties of Mg alloys deformation. Hence, it is meaningful toconduct related research.Thermal compression experiment was conducted to study the evolution ofmicrostructure and mechanism of deformation of the extruded ME20M alloy in thispresent study. Meanwhile we established the processing maps to conduct the subsequentprocessing. Then we analyzed the stress, strain and defects in the processing of spinningthrough elastic finite element numerical simulation. Finally we discussed the evolutionof microstructure, the change of mechanical and the defects in the process of spinningexperiment. Based on all the work, the reasonable spinning parameters weredetermined.The results of the thermal compression experiment shows that The sample crack atthe process of compression, when the temperature is low325℃, when the temperaturestay between350℃to400℃, the sample crack only when the strain rate over1s-1, andthe sample is intact when the temperature is higher than425℃. The flow stress of theME20M alloys rises as the strain rate increases or the temperature decreases. Thedeformation mechanism is based mainly on the dislocation slip and dynamicrecrystallization dominates in the soften mechanism. It can be seen from themicrostructure when the temperature is higher than400℃, the phenomenon ofrecrystallization occured in the sample mainly, and the higher of the temperature, the more obvious of the phenomenon. It can be seen from the processing maps thereasonable processing parameters of ME20M alloys are400℃～420℃,0.001s-1～0.1s-1and420℃～460℃,0.1s-1～1s-1. If the temperature is low,but the strain rate is high, thesample will be crack due to the hardening which cause the stress concentration. Whenboth the temperature and the strain rate is relative high, the sample become instablewhen deformation due to the local deformation caused by local melting.It can be seen from the result of the finite element numerical simulation that theamount of deformation is different in the direction of thickness and the amount ofdeformation decrease from outside to inside of the tube. The stress state ofmaterials in the contact area are pressure in three directions. The height of swellincrease during the process and the maximum height decrease with the increase ofspinning pass. The spinning force increase at first and then remain constant, and withthe pass increase,the spinning force decrease.Based on the spinning experiment, we know the reasonable processing temperatureis400℃～420℃. At the lower temperature, deformation resistance is large and prone tocracking. At higher temperature, materials is easy to swell. With the temperature risefurther, the defect of burn occur. After spinning, the texture is more obvious and themicrostructure is more fine.