The twinning behavior, dynamic recrystallization(DRX) mechanism and the resultant texture evolution of the extruded Mg-xBi(x=0.5 wt.%, 2.0 wt.%) alloys were systematically investigated during hot compression at the st...The twinning behavior, dynamic recrystallization(DRX) mechanism and the resultant texture evolution of the extruded Mg-xBi(x=0.5 wt.%, 2.0 wt.%) alloys were systematically investigated during hot compression at the strain rate of 10 s^(-1) and temperature of 200℃. The results indicate that the types and intensities of the texture are greatly dependent on the twining behavior and DRX mechanism. At the initial stage, the evolution of texture is mainly domination by the formation and variation of {1012} extension twins, which is benefcial to the compression direction(CD)-tilted basal texture. With an increase in the strain, the texture evolution is more greatly regulated by the DRX mechanism. Besides, the pyramidal<c + a> slip and basal slip are activated during the compression process, resulting in the Schmid factors(SF) of pyramidal slip remain at ~0.4 and the average SFs for basal slip increase from 0.2 to0.34 as the strain increase. These fndings provide a new insight into controlling the texture of wrought Mg-Bi-based alloys during hot deformation processing.展开更多
In the present work,a new Mg-Bi based alloy is developed by the addition of Zn and Ca in equiva-lent atom fraction with Bi.Mg-Bi and Mg-Bi-Zn-Ca alloys were prepared by extrusion at a ram speed of 20 mm/s.Room tempera...In the present work,a new Mg-Bi based alloy is developed by the addition of Zn and Ca in equiva-lent atom fraction with Bi.Mg-Bi and Mg-Bi-Zn-Ca alloys were prepared by extrusion at a ram speed of 20 mm/s.Room temperature mechanical properties and creep behaviors at 423 K were investigated.The results show that Zn and Ca co-addition shows little influence on average grain size and texture in-tensity but changes the dispersive Mg_(3)Bi_(2)into Mg_(2)Bi_(2)Ca particles in different sizes and a lower density.Twinning is largely activated during room-temperature deformation.Consequently,a slightly decreased proof strength but tripled elongation is shown at room temperature.Unexpectedly,large enhancement in creep resistance is detected after the co-alloying of Zn and Ca and the minimum creep rate is reduced by 10 to 20 times in the BZX621 alloy.Stress exponent n=4-5 indicates that the creep is a dislocation-climb controlled type.Post-mortem characterization on microstructure shows slip of dislocationc+aare also largely found in B6 as well as BZX621 alloy and cross-slip is detected more severe in B6 alloy.Dynamic segregation and precipitation are also seen in both alloys.Bi-clusters are seen dispersive across the grains in B6 and so did the PFZs that could undermine creep resistance at the grain boundaries.By contrast,Zn-rich needle-like precipitates are developed at most“ends”ofc+adislocations,which would hinder the further dislocation motions and thus improve the creep resistance.First-principles cal-culations were adopted and the results show that the thermal stability and thermomechanical properties of Mg_(2)Bi_(2)Ca are much better than that of Mg_(3)Bi_(2).Stacking faults energy is lowered down with the co-addition of Ca and Zn,which could inhibit the rate of dislocation climb and cross-slip.As a result,the im-proved creep resistance is obtained in the Mg-Bi-Zn-Ca alloys.Microstructural and controlling mechanism changes by thermal activation result in the unexpected enhancement in creep resistance with decreased room-temperature proof strength after co-addition.These findings could contribute to the development and optimization of creep-resistant Mg alloys in the future.展开更多
A Mg−3.2Bi−0.8Ca(BX31,wt.%)ternary alloy with a yield strength of~358.1 MPa was fabricated by hot extrusion,room-temperature(RT)rotary swaging and subsequent aging treatment.A fine grain structure(~2μm)and a few seco...A Mg−3.2Bi−0.8Ca(BX31,wt.%)ternary alloy with a yield strength of~358.1 MPa was fabricated by hot extrusion,room-temperature(RT)rotary swaging and subsequent aging treatment.A fine grain structure(~2μm)and a few secondary phases were observed in the as-extruded alloy,accompanied by a weak non-basal texture.After RT rotary swaging,the average grain size was reduced to~1μm via continuous dynamic recrystallization(CDRX).In addition,a large number of residual dislocations piled up within the grain interior,along with the dynamic precipitation of nano-phases.Peak aging occurred rapidly at 448 K for 35 min.After aging,the grain size hardly changed,the density of residual dislocations slightly decreased,and a large number of nano-precipitates were introduced at the dislocation pile-up sites.The grain boundary strengthening,dislocation strengthening and precipitation strengthening co-dominated the strength of the as-aged alloy.展开更多
Highly efficient removal of impurity Bi element from scrap brass can facilitate the recycling process of brass.The effects of melting temperature,holding time and Mg-Ca alloy content on the removal effect of impurity ...Highly efficient removal of impurity Bi element from scrap brass can facilitate the recycling process of brass.The effects of melting temperature,holding time and Mg-Ca alloy content on the removal effect of impurity Bi element were investigated by compound-separation method.The mechanism of the compound-separation method was revealed for removing the Bi element from a thermodynamic point of view.The results showed that the Bi content was decreased from 1.95 wt.%to 0.178 wt.%at the optimum process parameters of melting temperature of 980°C,holding time of 20 min,and Mg-Ca alloy content of 6 wt.%,achieving a removal rate of 90.9%.A small amount of Ca-Bi compound remained in the brass matrix after refining.NaF flux can effectively wet and adsorb Ca-Bi compounds due to its low viscosity and the function of lowering the surface tension,which facilitate the agglomeration and flotation of Ca-Bi compounds to the melt surface,thereby ensuring the sufficient removal of Bi element.展开更多
The microstructures and mechanical properties of Mg-x Bi(x=2,5,and 8 wt%)were investigated compared with pure Mg.The ascast Mg-Bi billets consist of dendriticα-Mg grain matrix,divorced eutectic Mg_(3)Bi_(2)phase and ...The microstructures and mechanical properties of Mg-x Bi(x=2,5,and 8 wt%)were investigated compared with pure Mg.The ascast Mg-Bi billets consist of dendriticα-Mg grain matrix,divorced eutectic Mg_(3)Bi_(2)phase and secondary precipitated Mg_(3)Bi_(2)phase.After homogenization,secondary precipitated Mg_(3)Bi_(2)particles were all dissolved into the matrix,while most of the divorced eutectic Mg_(3)Bi_(2)intermetallic compounds retained.All the as-extruded samples exhibit fully dynamic recrystallization(DRX)and the average grain size decreases and the amount of nano-scale Mg_(3)Bi_(2)precipitates increases with increasing Bi content.Additionally,Bi alloying has little influence on the texture of the as-extruded pure Mg,with all the samples showing typical basal texture.As the results of grain refinement and precipitation hardening,the strengths of the as-extruded samples increase under both tensile and compressive tests.Besides,the yield asymmetry significantly decreases with Bi content.Moreover,all the as-extruded samples represent similar ductility under compression,while the tensile elongation first increases and then decreases with more Bi added.The as-extruded Mg-5Bi alloy demonstrates good combination of strength and ductility.However,Mg-8Bi alloy displays lower tensile ductility than that of Mg-5Bi alloy due to the presence of abundant undissolved coarse Mg_(3)Bi_(2)particles,which act as cracking sources during tensile test.Furthermore,the strain hardening rate,strain hardening exponent n,and hardening capacity Hc are greatly reduced by Bi addition,mainly owing to the enhanced synergy effects of grain refinement and numerous Mg_(3)Bi_(2)precipitates.展开更多
基金supported by the National Natural Science Foundation of China(Nos.51704209,51701060 and 51901153)the Natural Science Foundation of Shanxi province(Nos.201801D121088 and 201901D211096)the Science and Technology Major Project of Shanxi Province(Nos.20191102007 and 20191102008)。
文摘The twinning behavior, dynamic recrystallization(DRX) mechanism and the resultant texture evolution of the extruded Mg-xBi(x=0.5 wt.%, 2.0 wt.%) alloys were systematically investigated during hot compression at the strain rate of 10 s^(-1) and temperature of 200℃. The results indicate that the types and intensities of the texture are greatly dependent on the twining behavior and DRX mechanism. At the initial stage, the evolution of texture is mainly domination by the formation and variation of {1012} extension twins, which is benefcial to the compression direction(CD)-tilted basal texture. With an increase in the strain, the texture evolution is more greatly regulated by the DRX mechanism. Besides, the pyramidal<c + a> slip and basal slip are activated during the compression process, resulting in the Schmid factors(SF) of pyramidal slip remain at ~0.4 and the average SFs for basal slip increase from 0.2 to0.34 as the strain increase. These fndings provide a new insight into controlling the texture of wrought Mg-Bi-based alloys during hot deformation processing.
基金supported by the National Key R&D Program of China(No.2021YFB3701100)the Joint Funds of the National Natural Science Foundation of China(No.U22A20187)+4 种基金the Science and Technology Innovation Program of Hunan Province(Nos.2023RC3268,2021JC0005 and 2020RC4013)the Science Fund of State Key Laboratory of Advanced Design and Manu-facturing Technology for Vehicle(No.32117009)the Projects“Development of lightweight high-performance Mg alloys profiles manufacturing technologies”and“Research and development of room-temperature bendable Mg alloy thin sheets manufactur-ing technology”from QingHai Salt Lake Industry Co.,Ltd.(Nos.2022-Z-0810000000-21-ZC0609-0001 and 2022-Z-08)the“Technology Innovation 2025”Major Special Project of Ningbo CityThe first-principles calculations work was carried out using software provided by the High Performance Computing Center of Central South University.
文摘In the present work,a new Mg-Bi based alloy is developed by the addition of Zn and Ca in equiva-lent atom fraction with Bi.Mg-Bi and Mg-Bi-Zn-Ca alloys were prepared by extrusion at a ram speed of 20 mm/s.Room temperature mechanical properties and creep behaviors at 423 K were investigated.The results show that Zn and Ca co-addition shows little influence on average grain size and texture in-tensity but changes the dispersive Mg_(3)Bi_(2)into Mg_(2)Bi_(2)Ca particles in different sizes and a lower density.Twinning is largely activated during room-temperature deformation.Consequently,a slightly decreased proof strength but tripled elongation is shown at room temperature.Unexpectedly,large enhancement in creep resistance is detected after the co-alloying of Zn and Ca and the minimum creep rate is reduced by 10 to 20 times in the BZX621 alloy.Stress exponent n=4-5 indicates that the creep is a dislocation-climb controlled type.Post-mortem characterization on microstructure shows slip of dislocationc+aare also largely found in B6 as well as BZX621 alloy and cross-slip is detected more severe in B6 alloy.Dynamic segregation and precipitation are also seen in both alloys.Bi-clusters are seen dispersive across the grains in B6 and so did the PFZs that could undermine creep resistance at the grain boundaries.By contrast,Zn-rich needle-like precipitates are developed at most“ends”ofc+adislocations,which would hinder the further dislocation motions and thus improve the creep resistance.First-principles cal-culations were adopted and the results show that the thermal stability and thermomechanical properties of Mg_(2)Bi_(2)Ca are much better than that of Mg_(3)Bi_(2).Stacking faults energy is lowered down with the co-addition of Ca and Zn,which could inhibit the rate of dislocation climb and cross-slip.As a result,the im-proved creep resistance is obtained in the Mg-Bi-Zn-Ca alloys.Microstructural and controlling mechanism changes by thermal activation result in the unexpected enhancement in creep resistance with decreased room-temperature proof strength after co-addition.These findings could contribute to the development and optimization of creep-resistant Mg alloys in the future.
基金supported by the financial supports from the National Key Research and Development Program of China(No.2021YFB3701100)the National Natural Science Foundation of China(Nos.51901204,52161023,52204407)+3 种基金Key Research and Development Plan of Shanxi Province,China(No.202102050201005)Science and Technology Project of Yunnan Precious Metal Laboratory,China(No.YPML-2023050208)Yunnan Science and Technology Planning Project,China(Nos.202201AU070010,202301AT070276,202302AB080008,202303AA080001)the Second Professional Practice Innovation Project of Yunnan University,China(No.ZC-22221620).
文摘A Mg−3.2Bi−0.8Ca(BX31,wt.%)ternary alloy with a yield strength of~358.1 MPa was fabricated by hot extrusion,room-temperature(RT)rotary swaging and subsequent aging treatment.A fine grain structure(~2μm)and a few secondary phases were observed in the as-extruded alloy,accompanied by a weak non-basal texture.After RT rotary swaging,the average grain size was reduced to~1μm via continuous dynamic recrystallization(CDRX).In addition,a large number of residual dislocations piled up within the grain interior,along with the dynamic precipitation of nano-phases.Peak aging occurred rapidly at 448 K for 35 min.After aging,the grain size hardly changed,the density of residual dislocations slightly decreased,and a large number of nano-precipitates were introduced at the dislocation pile-up sites.The grain boundary strengthening,dislocation strengthening and precipitation strengthening co-dominated the strength of the as-aged alloy.
基金the financial supplies supported by the National Natural Science Foundation of China(Nos.U2202255,52371038)the Science and Technology Innovation Program of Hunan Province,China(No.2023RC1019)。
文摘Highly efficient removal of impurity Bi element from scrap brass can facilitate the recycling process of brass.The effects of melting temperature,holding time and Mg-Ca alloy content on the removal effect of impurity Bi element were investigated by compound-separation method.The mechanism of the compound-separation method was revealed for removing the Bi element from a thermodynamic point of view.The results showed that the Bi content was decreased from 1.95 wt.%to 0.178 wt.%at the optimum process parameters of melting temperature of 980°C,holding time of 20 min,and Mg-Ca alloy content of 6 wt.%,achieving a removal rate of 90.9%.A small amount of Ca-Bi compound remained in the brass matrix after refining.NaF flux can effectively wet and adsorb Ca-Bi compounds due to its low viscosity and the function of lowering the surface tension,which facilitate the agglomeration and flotation of Ca-Bi compounds to the melt surface,thereby ensuring the sufficient removal of Bi element.
基金the financial supports from the National Natural Science Foundation of China (Nos. 51704209, 51701060, 51901153)the Natural Science Foundation of Shanxi Province, China (Nos. 201801D121088, 201901D211096)the Science and Technology Major Project of Shanxi Province, China (Nos. 20191102007, 20191102008)。
基金supported by the National Natural Science Foundation of China(grant number 51701060)the Natural Science Foundation of Hebei Province(grant number E2016202130)+4 种基金Tianjin city(grant number 18JCQNJC03900)the Scientific Research Foundation for the Returned Overseas Chinese Scholars of Hebei Province(grant number C20190505)100 Foreign Experts Plan of Hebei Provincethe National Research Council of Science&Technology(NST)grant by the Korea government(MSIP)(grant number CRC–15–06–KIGAM)the Joint Doctoral Training Foundation of HEBUT(grant number 2018HW0008)。
文摘The microstructures and mechanical properties of Mg-x Bi(x=2,5,and 8 wt%)were investigated compared with pure Mg.The ascast Mg-Bi billets consist of dendriticα-Mg grain matrix,divorced eutectic Mg_(3)Bi_(2)phase and secondary precipitated Mg_(3)Bi_(2)phase.After homogenization,secondary precipitated Mg_(3)Bi_(2)particles were all dissolved into the matrix,while most of the divorced eutectic Mg_(3)Bi_(2)intermetallic compounds retained.All the as-extruded samples exhibit fully dynamic recrystallization(DRX)and the average grain size decreases and the amount of nano-scale Mg_(3)Bi_(2)precipitates increases with increasing Bi content.Additionally,Bi alloying has little influence on the texture of the as-extruded pure Mg,with all the samples showing typical basal texture.As the results of grain refinement and precipitation hardening,the strengths of the as-extruded samples increase under both tensile and compressive tests.Besides,the yield asymmetry significantly decreases with Bi content.Moreover,all the as-extruded samples represent similar ductility under compression,while the tensile elongation first increases and then decreases with more Bi added.The as-extruded Mg-5Bi alloy demonstrates good combination of strength and ductility.However,Mg-8Bi alloy displays lower tensile ductility than that of Mg-5Bi alloy due to the presence of abundant undissolved coarse Mg_(3)Bi_(2)particles,which act as cracking sources during tensile test.Furthermore,the strain hardening rate,strain hardening exponent n,and hardening capacity Hc are greatly reduced by Bi addition,mainly owing to the enhanced synergy effects of grain refinement and numerous Mg_(3)Bi_(2)precipitates.
