Deformation Mechanism And Microstructure And Property Evolution Of Pure Mg During Canned Ecap At Room Temperature

In recent years,as an effective mean of grain refinement and superfine or even nanocrystallization in metal materials,the equal channel angular pressing(ECAP)is widely used in the tissue refinement and performance enhancement of magnesium and magnesium alloys.However,the temperature used in the ECAP processing of magnesium and magnesium alloys usually exceeds 200?,the grain refinement is limited.Therefore,The paper successfully used the method of package extrusion to solve the problem of sample cracking in the ECAP of pure magnesium at room temperature.And The paper deeply studied the deformation mechanism and microstructure and property evolution of pure magnesium during canned ECAP processing at room temperature.In this paper,the annealed pure magnesium was used for 1 pass and multi-pass canned ECAP extrusion along the BC path at room temperature,and the extruded sample was successfully obtained.And the 1 pass extruded samples were annealed under different conditions.The microstructures of the extruded and annealed samples were observed by SEM and TEM.And the pure magnesium and each pass extruded pure magnesium were used to conduct tensile test at room temperature.The deformation mechanism of pure magnesium in the process of ECAP extrusion at room temperature and the microstructural stability of extruded pure magnesium were studied.And the effects of extrusion passes on the microstructure and mechanical properties of pure magnesium were studied.The results show that:(1)After one pass ECAP extrusion at room temperature,the microstructure of the extruded magnesium has coarse grains with no refinement and small dynamic recrystallization grains(DRX),showing a significant nonuniformity.In addition,pure magnesium occurred twin deformation in the canned ECAP extrusion process at room temperature,forming a large number of {1012} tensile twin and a small number of secondary twin in the primary twin.In the process of canned ECAP extrusion of pure magnesium at room temperature,the pure magnesium suffered a strong shear deformation at the corner of the mold,a strong base texture produced which formed an angle with the extrusion direction(ED),and non-basal sliding also had some degree of movement.The coordinate of slip and twins successfully achieved room temperature canned ECAP extrusion of pure magnesium.(2)After annealing of extruded pure magnesium,due to the static recrystallization and the grain growth,the proportion of low-angle grain boundary(LAGB)rapidly decreased and the number of high-angle grain boundary(HAGB)continually increased.so that the distribution of grain became uniform.In addition,the increase in annealing time will continue to eliminate the {1012} tensile twins produced during the deformation process.Although the grains after annealing grew normally,the grains with the base texture were more likely to grow.With the increase of annealing time and temperature,the(0002)base texture strength of grains continually increased.(3)Canned ECAP extrusion at room temperature can significantly refine the matrix structure of pure magnesium.After one pass ECAPed extrusion,the organization was very nonuniform,and there were a large number of tensile twin.With the increase of ECAP extrusion passes,the grains gradually refined,the number of dynamic recrystallization grains increased,and the number of tensile twin rapidly decreased.After four pass ECAPed extrusion,a more uniform equiaxed crystal structure formed and the average grain size refined to 4 ?m or so.The multi-pass canned ECAP extrusion at room temperature reduced the base texture strength of the pure magnesium and the weakening effect became more and more obvious with the increase of the ECAP passes.In addition,with the increase of ECAP passes,the low-angle grain boundary gradually decreased and the high-angle grain boundary continually increased,the average schmid factor of base slip system exhibited a tendency to decrease first and then increase.After canned ECAP extrusion at room temperature,the room-temperature mechanical properties of pure magnesium significantly improved.The tensile strength(UTS)increased from 35 MPa to 121 MPa,and the elongation(EL)decreased slightly.