| Rare earth magnesium alloy materials have become the focus of current research,and the plastic strength of magnesium alloy directly affects its development.However,the traditional plastic deformation technology can not meet the application of aerospace and national defense industry,and its strength and toughness still need to be improved.Therefore,researchers at home and abroad have introduced large strain shear deformation into molds or devices,the most typical of which is equal channel angular pressing(ECAP)process,which changes its structural characteristics and refines grains through large strain shear deformation at the corner.However,with the existing equal channel extrusion process technology,the extrusion path does not change,resulting in uneven microstructure and different mechanical properties of bars.Under multi-pass extrusion,it is necessary to keep the blank warm,which is not conducive to grain refinement.In view of the existing shortcomings of equal channel extrusion,a continuous equal channel extrusion die is designed.Its characteristic is that by rotating the extrusion channel around its axis at different angles,the extrusion path changes continuously every two adjacent passes,so that the shear plane and shear direction of the bar can be changed to strengthen the shear strain.Mg-10Gd-6Y-1.5Zn-0.5Zr alloy was used to complete the process exploration.The alloy was solution aged to improve its microstructure and explore its thermal deformation behavior.Finally,the continuous equal channel extrusion test was carried out at different temperatures,the relevant data were obtained,processed and analyzed,and the microstructure evolution law in the forming process was studied.The conclusions of this paper are as follows:(1)Heat treatment can effectively improve the microstructure of the initial extruded alloy.The average grain size after solution treatment is 35.7?m.It has a good solid solution effect.The aging treatment of solid solution samples proves that it has a good age hardening effect.The thermal deformation experiment was carried out.In the process of deformation,affected by dislocation slip,twinning and lpso phase,grain boundary and lpso phase at grain boundary are conducive to the accumulation of dislocations,so as to promote dynamic recrystallization.(2)The continuous equal channel angle extrusion die is designed.The shear bending angle of each channel angle is 120°,and the fillet radius inside the corner is 20mm.The extrusion path changes continuously every two adjacent passes,so that the shear plane and shear direction of the bar can be changed.With the increase of forming temperature,it shows better microstructure uniformity,and its 400?peak load is 1.2×10~5N,while the peak load at 500?is only 2.0×10~4N?Continuous equal channel angular extrusion is the key to affect the blank of magnesium alloy.(3)The addition of continuous equal channel extrusion has an obvious effect on the microstructure of the formed bar and plays a good role in refining the grain.It can perform well at 450?or 500?,and the size changes from the initial 35.7?m is refined to 3?4?m.Secondly,after two equal channel angular pressing,the overall grain size distribution is more uniform,the original coarse parent crystal is significantly reduced,and the degree of grain orientation dispersion is increased.And in the forming process,the Lpso phase at the grain boundary hinders the slip and causes the accumulation of dislocations,which provides more energy for recrystallization.The material is more prone to microstructure evolution,the nucleation of dynamic recrystallization is easier,and its recrystallization degree is very high.Therefore,its plastic deformation mechanism is dislocation slip and the coordinated deformation of the second phase. |
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