Investigation On The Micro Structure Evolution Of AZ80 Magnesium Alloy During Annular Channel Multi-angular Extrusion Process

As a commercialized high-strength wrought magnesium alloy,AZ80 magnesium alloy has excellent mechanical properties such as low density,good damping performance,and high specific stiffness and specific strength.It has broad application prospects in lightweight components in cutting-edge industrial fields such as transportation and aerospace.However,the low strength and poor plasticity of magnesium alloys restrict its application in load-bearing parts and secondary load-bearing parts of high-end equipment.As an effective means of grain refinement,equal channel angular extrusion is widely used in the grain refinement and toughening of magnesium alloys.However,it is difficult to form parts directly by the equal channel angular extrusion process.The forming and manufacturing of high-performance magnesium alloy components has become an urgent problem to be solved.Therefore,this paper proposes the AZ80 magnesium alloy annular channel multi-angle extrusion forming process,adopts the method of combining physical simulation,numerical simulation and experiment to study the dynamic recrystallization mechanism and law of the AZ80 magnesium alloy channel angle extrusion process,and establishes the process of considering the second phase.The dynamic recrystallization phase field method model was applied to the annular channel multi-angle extrusion forming process of ribbed plate components,providing a theoretical basis for the forming of high-performance components of AZ80 magnesium alloy.The main research work of this paper is as follows:The microstructure evolution characteristics of AZ80 magnesium alloy during unidirectional hot compression and equal channel angular extrusion were analyzed.The results show that the dynamic recrystallization mechanism is dominated by discontinuous dynamic recrystallization,the nucleation mechanism of discontinuous dynamic recrystallization includes dynamic recovery to promote subgrain nucleation and strain-induced grain boundary migration nucleation,and the nucleation mechanism of continuous dynamic recrystallization In order to increase the local misorientation inside the deformed grains to promote nucleation,the average equivalent diameter of the Mg17Al12 phase in the process of equal channel angular extrusion is 1.29 μm,while that in the process of unidirectional thermal compression is 0.66 μm.The average equivalent diameter of Mg17Al12 phase in the process of equal channel angular extrusion is A diameter greater than 1 μm is more likely to cause an increase in the local dislocation density and induce particle nucleation.A dynamic recrystallization phase field method model coupled with the second phase was established.The model reflects the increase in local dislocation density caused by the pinning of the second phase by correcting the dislocation density evolution law,and defines the grain interface of the second phase as the effective nucleation site It reflects the particle-induced nucleation of the second phase,and verifies that the established phase field model can predict the particle-induced nucleation and the macroscopic Reliability during mechanical response.Based on the established model,the grain growth and dynamic recrystallization of different second phase appearance,size and size were simulated,and the results showed that the pinning effect of fine and dispersed rectangular particles on grain boundary migration was more intense,and the second phase particles were promoting The increase of dislocation density promotes nucleation and inhibits nucleation due to the pinning effect,and the inhibition is dominant.Combining physical experiments,phase field method and finite element method,the microstructure evolution and macroscopic physical field changes of AZ80 magnesium alloy during equichannel corner multi-pass extrusion were studied.The results show that the average grain size after two extrusion passes is 6.57 μm,and the grain size is mainly distributed in the range of 7-10 μm,which is 13.4%smaller than that of a single pass;the average grain size after three passes It is 5.12μm,and the grain size is mainly distributed in the range of 2.5-7.5 μm,which is 22.07%more refined than that of the second pass.In the range of deformation parameters of deformation temperature 300℃～400℃ and extrusion speed 0.5～3.0 mm/s,the extrusion forming window and grain size contour map are determined,and the two are integrated to determine the equal channel angular extrusion The two fine grain windows are:extrusion speed 0.5 mm/s,deformation temperature 360℃～400℃;and extrusion speed 1.5 mm/s,deformation temperature 345℃～380℃.A circular channel multi-rotation extrusion forming process for magnesium alloy ribbed plate members was proposed.This process combines equal channel extrusion with A path in the annular channel for three passes of different internal angles and cross-sections to realize the combination with traditional extrusion.The macroscopic physical field and grain size evolution law of the forming process of this process were analyzed.The results show that the continuous metal streamline during the forming process can effectively avoid metal tearing,and the equivalent strain distribution of the rib position is uniform,and the deformation is mainly concentrated in the corner deformation area.Hydrostatic pressure and shear stress state are favorable to promote tissue refinement.The reduction of billet temperature has little effect on the average grain size,but makes the size distribution more uniform.When the billet temperature and extrusion speed are constant,and the die temperature increases from 340℃ to 380℃,the average grain size increases from 5.1 μm to 5.8 μm,and the standard deviation increases from 0.41 μm to 0.89 μm.In addition,the isothermal temperature of both the billet and the mold is 380℃.When the extrusion speed increases from 1 mm/s to 3 mm/s,the average grain size is refined from 5.8 μm to 5.3 μn,and the standard deviation is reduced from 0.89μm to 0.26 μm.The typical ribbed plate components of AZ80 magnesium alloy were successfully trial-produced,and the grain size was significantly refined to about 10 μm,which verified the feasibility of the annular channel multi-angle extrusion forming process.The formation of ground fine grains provides theoretical guidance.