| Compared with other metals,magnesium alloy has low density and better electromagnetic shielding property.However,due to the crystal structure of magnesium alloy,its plastic forming ability and mechanical properties are poor,which limits its application scope.In industry,magnesium alloy is deformed by extrusion method,and pipe bar profiles with good mechanical properties are prepared.However,the regulation of the mechanical properties of extruded materials often requires a large number of process experiments to clarify the influence law of the change of process parameters on the microstructure properties,so as to obtain a reasonable process window for extruded materials.However,there are some problems in this process,such as large workload,long cycle and high experimental cost.The relationship between process parameters and deformed tissue can be obtained by using the existing Arrhenius constitutive equation and Jmak recrystallization model through numerical simulation,which is the main research method for the control of material micro structure.In this paper,DEFORM-3D finite element software and cellular automata method were used to study the microstructure evolution of the extrusion process of bar and pipe under different technological parameters and AZ80 and AZ31 were selected as two typical deformed magnesium alloys.For AZ80 rod extrusion research show that the vertical backward extrusion pier coarse stage,close to the extrusion die part first occurs extrusion shear zone and in the near side is strong,and as a result of thermal deformation and temperature rise,and with the increase of extrusion deformation,the temperature rising of billet deformation area,near the sizing with peak.When the extrusion temperature is 250℃,the maximum temperature rise reaches about 100℃,and there are obvious temperature differences successively,and the deformation temperature of the latter extrusion is higher than that of the first extrusion.The extrusion temperature and velocity have a significant influence on the extrusion load and its variation rule during the extrusion process.Reducing the extrusion temperature will increase the extrusion load and deformation heat significantly,especially at low temperature.The numerical simulation results show that the temperature rise caused by deformation heat can significantly reduce the extrusion load in the low temperature section（250℃～350℃）,while in the high temperature section（350℃～400℃）,the temperature rise is small and the extrusion load is stable.Increasing the extrusion speed has little influence on the extrusion load,but it will significantly increase the deformation heat and the extrusion temperature of the deformable billet,so that the extrusion load gradually decreases and the reduction speed increases with the increase of the extrusion speed.At the speed of 1mm/s,AZ80 magnesium alloy bar was completely recrystallized at all extrusion temperatures（250℃～400℃）,and the recrystallization structure presented a linear thinning trend when the extrusion temperature was reduced,and the recrystallization structure was the smallest at 250℃.The numerical simulation results are consistent with the experimental results,which prove that the tissue simulation has good accuracy.At 250℃,when the extrusion speed was lmm/s～3mm/s,the recrystallization structure did not change much,but when it increased to 5mm/s,the extrusion structure was obviously coarsened.The effect of extrusion temperature and extrusion speed on the extrusion load of AZ80 pipe and bar extrusion is similar,but the change of extrusion parameters has little influence on the extrusion deformation heat and the change of recrystallization structure,but the high speed extrusion of pipe leads to the coarsening of recrystallization structure.The peak value of extrusion load of AZ31 pipe is slightly lower than AZ80 during extrusion,and its recrystallization temperature is slightly higher,and fine recrystallization grains can be seen at grain boundary during deformation. |
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