Given the limitations of traditional hot extrusion methods in improving the microstructure and mechanical properties of magnesium(Mg)alloys,this paper attempts to treat AZ31 Mg alloy billet by pre-upsetting continuous...Given the limitations of traditional hot extrusion methods in improving the microstructure and mechanical properties of magnesium(Mg)alloys,this paper attempts to treat AZ31 Mg alloy billet by pre-upsetting continuous variable cross-section direct extrusion(U-CVCDE).The effects of dynamic recrystallization behavior and slip system activity on texture evolution and mechanical properties of CVCDE Mg alloys with different pre-upsetting amounts were systematically analyzed.The results indicate that the introduction of the pre-upsetting process promotes dynamic recrystallization during the CVCDE process.The recrystallization proportion shows a trend of first rising and then decreasing with the increase of the pre-upsetting amount.Among them,the proportion of recrystallization grains in the U2-CVCDE-formed structural parts is as high as 88.3%.The average grain sizes of U1-CVCDE,U2-CVCDE,and U3-CVCDE were 6.01μm,4.90μm,and10.45μm,respectively.In addition,following U-CVCDE,the pyramidal slip of each forming component consistently maintains a high level of activation and opening and dominates,making more grains deflect in the axial extrusion direction of C to varying degrees,which is conducive to the uniform distribution of stress in more grains during plastic deformation.The synergistic effect of dynamic recrystallization behavior and the high activity of the pyramidal slip system significantly weakened the(0001)basal texture strength,and the maximum basal texture strength showed a gradually decreasing trend,among which the base surface texture strength of U3-CVCDE formed parts was only 9.9.The U-CVCDE process is employed to achieve deep modification of Mg alloy,and excellent comprehensive mechanical properties are obtained;among them,the yield and tensile strength of U2-CVCDE are as high as 243.4 MPa and 317.5 MPa,respectively,and the elongation after breaking is up to 21.3%.This study introduces a practical new idea for investigating the extrusion forming technology of high-performance Mg alloys.展开更多
Various characteristic structures in typical magnesium alloys,including dislocation cells,substructures and twins,have an important influence on the dynamic recrystallization behavior,and the DRX(dynamic recrystalliza...Various characteristic structures in typical magnesium alloys,including dislocation cells,substructures and twins,have an important influence on the dynamic recrystallization behavior,and the DRX(dynamic recrystallization)behavior is closely related to the grain refinement and texture weakening of the hot deformed structure.Therefore,this study reveals the influence of the above characteristic structures on the dynamic recrystallization behavior of magnesium alloys,which have great significance for regulating the high-performance hot deformed microstructure of magnesium alloys and optimizing the macro mechanical properties.In this study,continuous variable channel direct extrusion(CVCDE)magnesium alloy was prepared by CVCDE,and its macro mechanical properties including hardness and uniaxial tension were characterized.The thermoplastic deformation behavior and texture evolution of magnesium alloy with characteristic structure were analyzed by electron back-scattering diffraction technology.It is found that the dislocation recombination was realized by deformation mechanism(slip,climb and cross slip),the formation of grain substructure in coarse grains and the induction of recrystallization by twins promote the recrystallization behavior in hot deformed structures more adequate,which effectively improves the degree of microstructure refinement and deformation uniformity.展开更多
In order to study the influence of die combination on continuous variable cross-section direct extrusion （CVCDE） in the extrusion process, the accumulative strain formula is derived, and it can be known that the ext...In order to study the influence of die combination on continuous variable cross-section direct extrusion （CVCDE） in the extrusion process, the accumulative strain formula is derived, and it can be known that the extrusion ratio of various stages directly determines the size of corresponding stage strain by formula. In this paper, as an example of the two interim dies, three die combinations of different angles and extrusion ratio are designed. Aviation magnesium alloy ZM6 is studied, and the results show that dynamic recrystallization is even more complete when continuous shear deformation occurs, so that the refinement and homogenization of microstructure are obtained. By the use of different die combinations, the accumulative strain increases under the conditions of same total extrusion ratio. Thus, the refined crystalline strengthening effect of extrusion deformation can be further analyzed. Due to the dead-zone defects, the actual accumulative strain decreases significantly and the effect of microstructure and performance improvements also decreases with it. Therefore, the optimal design of die combination is the key to the process and product of CVCDE, which provides a scientific basis for the development of severe plastic deformation.展开更多
Magnesium（Mg） alloy AZ31 was produced by continuous variable cross-section direct extrusion（CVCDE）to study its deformation behavior. Metallographic microscopy（OM）, transmission electron microscopy（TEM）, and sc...Magnesium（Mg） alloy AZ31 was produced by continuous variable cross-section direct extrusion（CVCDE）to study its deformation behavior. Metallographic microscopy（OM）, transmission electron microscopy（TEM）, and scanning electron microscopy（SEM） were used to observe the variations in microstructure and fracture morphology of Mg alloy AZ31 as a function of processing methods. The results reveal that grains of Mg alloy AZ31 were refined and their microstructure was homogenized by CVCDE. The recrystallization in Mg alloy AZ31 produced by CVCDE with 2 interim dies was more complete than that produced by conventional extrusion（CE） and CVCDE with 1 interim die, and the grains were finer and more uniform.Plasticity of the AZ31 alloy was improved. Fracture mode was evolved from a combination of ductility and brittleness to a sole ductile form. In summary, a CVCDE mold structure with 2 interim dies can improve microstructure, plasticity, and toughness of Mg alloy AZ31.展开更多
基金financially supported by the National Natural Science Foundation of China(No.52475341)the Natural Science Foundation of Heilongjiang Province(No.JQ2022E004)。
文摘Given the limitations of traditional hot extrusion methods in improving the microstructure and mechanical properties of magnesium(Mg)alloys,this paper attempts to treat AZ31 Mg alloy billet by pre-upsetting continuous variable cross-section direct extrusion(U-CVCDE).The effects of dynamic recrystallization behavior and slip system activity on texture evolution and mechanical properties of CVCDE Mg alloys with different pre-upsetting amounts were systematically analyzed.The results indicate that the introduction of the pre-upsetting process promotes dynamic recrystallization during the CVCDE process.The recrystallization proportion shows a trend of first rising and then decreasing with the increase of the pre-upsetting amount.Among them,the proportion of recrystallization grains in the U2-CVCDE-formed structural parts is as high as 88.3%.The average grain sizes of U1-CVCDE,U2-CVCDE,and U3-CVCDE were 6.01μm,4.90μm,and10.45μm,respectively.In addition,following U-CVCDE,the pyramidal slip of each forming component consistently maintains a high level of activation and opening and dominates,making more grains deflect in the axial extrusion direction of C to varying degrees,which is conducive to the uniform distribution of stress in more grains during plastic deformation.The synergistic effect of dynamic recrystallization behavior and the high activity of the pyramidal slip system significantly weakened the(0001)basal texture strength,and the maximum basal texture strength showed a gradually decreasing trend,among which the base surface texture strength of U3-CVCDE formed parts was only 9.9.The U-CVCDE process is employed to achieve deep modification of Mg alloy,and excellent comprehensive mechanical properties are obtained;among them,the yield and tensile strength of U2-CVCDE are as high as 243.4 MPa and 317.5 MPa,respectively,and the elongation after breaking is up to 21.3%.This study introduces a practical new idea for investigating the extrusion forming technology of high-performance Mg alloys.
基金the Natural Science Foundation of Heilongjiang Province(JQ2022E004).
文摘Various characteristic structures in typical magnesium alloys,including dislocation cells,substructures and twins,have an important influence on the dynamic recrystallization behavior,and the DRX(dynamic recrystallization)behavior is closely related to the grain refinement and texture weakening of the hot deformed structure.Therefore,this study reveals the influence of the above characteristic structures on the dynamic recrystallization behavior of magnesium alloys,which have great significance for regulating the high-performance hot deformed microstructure of magnesium alloys and optimizing the macro mechanical properties.In this study,continuous variable channel direct extrusion(CVCDE)magnesium alloy was prepared by CVCDE,and its macro mechanical properties including hardness and uniaxial tension were characterized.The thermoplastic deformation behavior and texture evolution of magnesium alloy with characteristic structure were analyzed by electron back-scattering diffraction technology.It is found that the dislocation recombination was realized by deformation mechanism(slip,climb and cross slip),the formation of grain substructure in coarse grains and the induction of recrystallization by twins promote the recrystallization behavior in hot deformed structures more adequate,which effectively improves the degree of microstructure refinement and deformation uniformity.
基金financially supported by the National Natural Science Foundation of China(No.51205094)
文摘In order to study the influence of die combination on continuous variable cross-section direct extrusion （CVCDE） in the extrusion process, the accumulative strain formula is derived, and it can be known that the extrusion ratio of various stages directly determines the size of corresponding stage strain by formula. In this paper, as an example of the two interim dies, three die combinations of different angles and extrusion ratio are designed. Aviation magnesium alloy ZM6 is studied, and the results show that dynamic recrystallization is even more complete when continuous shear deformation occurs, so that the refinement and homogenization of microstructure are obtained. By the use of different die combinations, the accumulative strain increases under the conditions of same total extrusion ratio. Thus, the refined crystalline strengthening effect of extrusion deformation can be further analyzed. Due to the dead-zone defects, the actual accumulative strain decreases significantly and the effect of microstructure and performance improvements also decreases with it. Therefore, the optimal design of die combination is the key to the process and product of CVCDE, which provides a scientific basis for the development of severe plastic deformation.
基金financial support from the National Natural Science Foundation of China (No. 51675143)
文摘Magnesium（Mg） alloy AZ31 was produced by continuous variable cross-section direct extrusion（CVCDE）to study its deformation behavior. Metallographic microscopy（OM）, transmission electron microscopy（TEM）, and scanning electron microscopy（SEM） were used to observe the variations in microstructure and fracture morphology of Mg alloy AZ31 as a function of processing methods. The results reveal that grains of Mg alloy AZ31 were refined and their microstructure was homogenized by CVCDE. The recrystallization in Mg alloy AZ31 produced by CVCDE with 2 interim dies was more complete than that produced by conventional extrusion（CE） and CVCDE with 1 interim die, and the grains were finer and more uniform.Plasticity of the AZ31 alloy was improved. Fracture mode was evolved from a combination of ductility and brittleness to a sole ductile form. In summary, a CVCDE mold structure with 2 interim dies can improve microstructure, plasticity, and toughness of Mg alloy AZ31.
