This study investigates the microstructure evolution and mechanical behavior of a laser-welded dissimilar joint between wrought AZ80 and cast AM60 magnesium alloys.Microstructure analysis revealed a distinct fusion zo...This study investigates the microstructure evolution and mechanical behavior of a laser-welded dissimilar joint between wrought AZ80 and cast AM60 magnesium alloys.Microstructure analysis revealed a distinct fusion zone(FZ)spanning 1.5 mm and a heat-affected zone(HAZ)measuring 550μm in width adjacent to the AZ80 alloy.Meanwhile,the AM60 side showed no fusion-related structural changes.The FZ microstructure had a characteristic dendritic solidification pattern,with an average grain size around 20μm.The welded joint exhibited mechanical performance comparable to that of the base materials,with a yield strength of 137 MPa,an ultimate tensile strength of 250 MPa,and an elongation of 5.9%.These properties resulted from precipitated phases within the FZ,strengthening the joint and the coarse-grained structure’s significant work-hardening ability.Digital image correlation(DIC)during tensile testing indicated that strain concentrated within the FZ due to its coarse microstructure.As deformation continued,the AM60 base material experienced plastic deformation,sharing the main strain burden with the FZ.In later stages,microcracks formed specifically at the FZ-AM60 interface.These microcracks coalesced,accelerating crack propagation and resulting in a main crack that caused the joint to fracture.These findings offer valuable insights into controlling failure mechanisms in dissimilar magnesium alloy welds.展开更多
The compact torus injector(CTI)for the central fueling of the EAST tokamak has undergone significant upgrades to enhance its injection capability.During the initial phase of the platform testing phase,EAST-CTI demonst...The compact torus injector(CTI)for the central fueling of the EAST tokamak has undergone significant upgrades to enhance its injection capability.During the initial phase of the platform testing phase,EAST-CTI demonstrated relatively low performance,with a maximum velocity of 150 km s^(−1) and a single compact torus(CT)plasma mass of 90μg[Kong D et al 2023 Plasma Sci.Technol.25065601].These parameters were insufficient for conducting central fueling experiments on the EAST tokamak.Consequently,extensive upgrades were carried out to improve the performance of the EAST-CTI system.The compression region was extended from 280 mm to 700 mm to prevent rapid compression and deceleration of the CT plasma,along with an extension of the acceleration region to further increase the plasma acceleration.The power supply system has also been upgraded.These improvements elevated the operating voltage from 8 kV to 15 kV,increased the discharge current from 120 kA to 300 kA and enabled repetitive operation at a maximum rate of 2 Hz.As a result,significant advances in EAST-CTI performance were achieved,with the maximum velocity increasing to 330 km s^(−1) and the CT plasma density reaching 1.5×10^(22) m^(−3),thereby enhancing the system capability for future fueling experiments on EAST.This study offers valuable insights into CTI modification and the improvement of central fueling systems for prospective fusion reactors.展开更多
The present work reports the creep behavior and microstructural evolution of the sand-cast Mg-14Gd-0.4Zr alloy(wt.%) prepared by the differential pressure casting machine. Their compressive creep tests at 250 ℃ were ...The present work reports the creep behavior and microstructural evolution of the sand-cast Mg-14Gd-0.4Zr alloy(wt.%) prepared by the differential pressure casting machine. Their compressive creep tests at 250 ℃ were performed under various applied stresses(i.e., 60, 80 and100 MPa). Among them, the sand-cast Mg-14Gd-0.4Zr samples examined under 250 ℃/80 MPa for 39 and 95 h, respectively, were chosen to systemically analyze their creep mechanisms using high-angle annular dark field-scanning transmission electron microscopy(HAADF-STEM).The obtained results showed that the enhancement of creep resistance can be mainly attributed to the coherent β' and β'_F phases with an alternate distribution, effectively impeding the basal dislocations movement. However, with the creep time increasing, the fine β'+β'_F precipitate chains coarsened and transformed to semi-coherent β_1 phase and even to large incoherent β phase(surrounded by precipitate-free areas) in grain interiors. The precipitate-free zones(PFZs) at grain boundaries(GBs) were formed, and they could expand during creep deformation. Apart from the main cross-slip of basal and prismatic dislocations, type dislocations were activated and tended to distribute near the GBs. The aforementioned phenomena induced the stress concentrations, consequently leading to the increment of the creep strain.展开更多
In order to improve the ductility of commercial WE43 alloy and reduce its cost,a Mg-3Y-2Gd-1Nd-0.4Zr alloy with a low amount of rare earths was developed and prepared by sand casting with a differential pressure casti...In order to improve the ductility of commercial WE43 alloy and reduce its cost,a Mg-3Y-2Gd-1Nd-0.4Zr alloy with a low amount of rare earths was developed and prepared by sand casting with a differential pressure casting system.Its microstructure,mechanical properties and fracture behaviors in the as-cast,solution-treated and as-aged states were evaluated.It is found that the aged alloy exhibited excellent comprehensive mechanical properties owing to the fine dense plate-shapedβ'precipitates formed on prismatic habits during aging at 200℃for 192 hrs after solution-treated at 500℃for 24 hrs.Its ultimate tensile strength,yield strength,and elongation at ambient temperature reach to 319±10 MPa,202±2 MPa and 8.7±0.3%as well as 230±4 MPa,155±1 MPa and 16.0±0.5%at 250℃.The fracture mode of as-aged alloy was transferred from cleavage at room temperature to quasi-cleavage and ductile fracture at the test temperature 300℃.The properties of large-scale components fabricated using the developed Mg-3Y-2Gd-1Nd-0.4Zr alloy are better than those of commercial WE43 alloy,suggesting that the new developed alloy is a good candidate to fabricate the large complex thin-walled components.展开更多
Microstructural evolution and strengthening mechanisms of Mg-3Sn-1Ca based alloys with additions of different amounts of Al N nanoparticles were investigated.It was found that with increasing the amount of AlN nano-pa...Microstructural evolution and strengthening mechanisms of Mg-3Sn-1Ca based alloys with additions of different amounts of Al N nanoparticles were investigated.It was found that with increasing the amount of AlN nano-particles the grain size decreases obviously.The existence of AlN nano-particles could refine the primary crystal phases CaMgSn,which provided more heterogeneous nucleation sites for the formation of magnesium.Moreover,such nano-particles could also restrict the grain growth during solidification.After adding AlN nano-particles,both the tensile properties at room temperature and high temperature 250℃and the hardness are largely improved.The improvement of strength is attributed to grain refinement and second phase refinement.展开更多
The effects of 1Zn and/or 2Ag additions on the hot tearing susceptibility(HTS)of Mg-14Gd-0.4Zr(wt%)alloy were studied.The HTS was evaluated by both theoretical predictions using Kou's criterion and experimental ob...The effects of 1Zn and/or 2Ag additions on the hot tearing susceptibility(HTS)of Mg-14Gd-0.4Zr(wt%)alloy were studied.The HTS was evaluated by both theoretical predictions using Kou's criterion and experimental observations based on the in situ force-temperature recorded constrained rod casting(ISFTCRC)method.The results show that the order of HTS from high to low is Mg-14Gd-2Ag-1Zn-0.4Zr,Mg-14Gd-2Ag-0.4Zr,Mg-14Gd-1Zn-0.4Zr and Mg-14Gd-0.4Zr.Adding 1Zn and/or 2Ag changes the solidification path and the solidification interval,which affects the hot tearing susceptibility.Alloying elemental 1Zn slightly increases the solidification interval and the temperature range in the square root of the solid phase fraction(f_(s)^(1/2))range of 0.949-0.995,resulting in a slight increase in the hot tearing susceptibility.The addition of 2Ag drastically widens both the solidification interval and the temperature range in the f_(s)^(1/2)range of 0.949-0.995,thus significantly increasing the hot tearing susceptibility.Compared to the addition of 2Ag alone,the broadening degree of both the solidification interval and the temperature range in the f_(s)^(1/2)range of 0.949-0.995 is greater by adding the composite 2Ag/1Zn,which further promotes the occurrence of hot tearing.A narrower solidification interval and a temperature range in the f_(s)^(1/2)range of 0.949-0.995 result in a lower hot tearing susceptibility.展开更多
基金supported by the National Natural Science Foundation of China,No.52425101.
文摘This study investigates the microstructure evolution and mechanical behavior of a laser-welded dissimilar joint between wrought AZ80 and cast AM60 magnesium alloys.Microstructure analysis revealed a distinct fusion zone(FZ)spanning 1.5 mm and a heat-affected zone(HAZ)measuring 550μm in width adjacent to the AZ80 alloy.Meanwhile,the AM60 side showed no fusion-related structural changes.The FZ microstructure had a characteristic dendritic solidification pattern,with an average grain size around 20μm.The welded joint exhibited mechanical performance comparable to that of the base materials,with a yield strength of 137 MPa,an ultimate tensile strength of 250 MPa,and an elongation of 5.9%.These properties resulted from precipitated phases within the FZ,strengthening the joint and the coarse-grained structure’s significant work-hardening ability.Digital image correlation(DIC)during tensile testing indicated that strain concentrated within the FZ due to its coarse microstructure.As deformation continued,the AM60 base material experienced plastic deformation,sharing the main strain burden with the FZ.In later stages,microcracks formed specifically at the FZ-AM60 interface.These microcracks coalesced,accelerating crack propagation and resulting in a main crack that caused the joint to fracture.These findings offer valuable insights into controlling failure mechanisms in dissimilar magnesium alloy welds.
基金supported by the National MCF Energy R&D Program of China(Nos.2024YFE03130001 and 2024YFE03130002)the Institute of Energy,Hefei Comprehensive National Science Center(Anhui Energy Laboratory)(Nos.21KZS202 and 23KHH140)+3 种基金the University Synergy Innovation Program of Anhui Province(Nos.GXXT-2021-014 and GXXT-2021-029)National Natural Science Foundation of China(Nos.12105088 and 12305247)the Fundamental Research Funds for the Central Universities of China(No.PA2024GDSK0097)the Anhui Province Key Research and Development Plan Program(Nos.202304a05020006 and 2021006).
文摘The compact torus injector(CTI)for the central fueling of the EAST tokamak has undergone significant upgrades to enhance its injection capability.During the initial phase of the platform testing phase,EAST-CTI demonstrated relatively low performance,with a maximum velocity of 150 km s^(−1) and a single compact torus(CT)plasma mass of 90μg[Kong D et al 2023 Plasma Sci.Technol.25065601].These parameters were insufficient for conducting central fueling experiments on the EAST tokamak.Consequently,extensive upgrades were carried out to improve the performance of the EAST-CTI system.The compression region was extended from 280 mm to 700 mm to prevent rapid compression and deceleration of the CT plasma,along with an extension of the acceleration region to further increase the plasma acceleration.The power supply system has also been upgraded.These improvements elevated the operating voltage from 8 kV to 15 kV,increased the discharge current from 120 kA to 300 kA and enabled repetitive operation at a maximum rate of 2 Hz.As a result,significant advances in EAST-CTI performance were achieved,with the maximum velocity increasing to 330 km s^(−1) and the CT plasma density reaching 1.5×10^(22) m^(−3),thereby enhancing the system capability for future fueling experiments on EAST.This study offers valuable insights into CTI modification and the improvement of central fueling systems for prospective fusion reactors.
基金the Shanghai Sailing Program (23YF1417100)National Natural Science Foundation of China (U2037601)China Scholarship Council (Grant No: 202006890008) for the financial support。
文摘The present work reports the creep behavior and microstructural evolution of the sand-cast Mg-14Gd-0.4Zr alloy(wt.%) prepared by the differential pressure casting machine. Their compressive creep tests at 250 ℃ were performed under various applied stresses(i.e., 60, 80 and100 MPa). Among them, the sand-cast Mg-14Gd-0.4Zr samples examined under 250 ℃/80 MPa for 39 and 95 h, respectively, were chosen to systemically analyze their creep mechanisms using high-angle annular dark field-scanning transmission electron microscopy(HAADF-STEM).The obtained results showed that the enhancement of creep resistance can be mainly attributed to the coherent β' and β'_F phases with an alternate distribution, effectively impeding the basal dislocations movement. However, with the creep time increasing, the fine β'+β'_F precipitate chains coarsened and transformed to semi-coherent β_1 phase and even to large incoherent β phase(surrounded by precipitate-free areas) in grain interiors. The precipitate-free zones(PFZs) at grain boundaries(GBs) were formed, and they could expand during creep deformation. Apart from the main cross-slip of basal and prismatic dislocations, type dislocations were activated and tended to distribute near the GBs. The aforementioned phenomena induced the stress concentrations, consequently leading to the increment of the creep strain.
基金This work was funded by the National Natural Science Foundation of China(No.U2037601 and No.52074183)The authors appreciate Ge Chen,Wenbin Zou as well as Shiwei Wang for preparing the alloys,Wenyu Liu as well as Xuehao Zheng from ZKKF(Beijing)Science&Technology Co.,Ltd for the TEM measurement,Gert Wiese as well as Petra Fischer for SEM and hardness measurement and Yunting Li from the Instrument Analysis Center of Shanghai Jiao Tong University(China)for SEM measurement.Lixiang Yang also gratefully thanks the China Scholarship Council(201906230111)for awarding a fellowship to support his study stay at Helmholtz-Zentrum Geesthacht.
文摘In order to improve the ductility of commercial WE43 alloy and reduce its cost,a Mg-3Y-2Gd-1Nd-0.4Zr alloy with a low amount of rare earths was developed and prepared by sand casting with a differential pressure casting system.Its microstructure,mechanical properties and fracture behaviors in the as-cast,solution-treated and as-aged states were evaluated.It is found that the aged alloy exhibited excellent comprehensive mechanical properties owing to the fine dense plate-shapedβ'precipitates formed on prismatic habits during aging at 200℃for 192 hrs after solution-treated at 500℃for 24 hrs.Its ultimate tensile strength,yield strength,and elongation at ambient temperature reach to 319±10 MPa,202±2 MPa and 8.7±0.3%as well as 230±4 MPa,155±1 MPa and 16.0±0.5%at 250℃.The fracture mode of as-aged alloy was transferred from cleavage at room temperature to quasi-cleavage and ductile fracture at the test temperature 300℃.The properties of large-scale components fabricated using the developed Mg-3Y-2Gd-1Nd-0.4Zr alloy are better than those of commercial WE43 alloy,suggesting that the new developed alloy is a good candidate to fabricate the large complex thin-walled components.
基金financially supported by the Study Abroad Program by the Government of Shandong Province(201802005)Linyi Industrial Technology Research Institute and Shandong Yinguang Yuyuan Light Metal Precise Forming Co.,Ltd。
文摘Microstructural evolution and strengthening mechanisms of Mg-3Sn-1Ca based alloys with additions of different amounts of Al N nanoparticles were investigated.It was found that with increasing the amount of AlN nano-particles the grain size decreases obviously.The existence of AlN nano-particles could refine the primary crystal phases CaMgSn,which provided more heterogeneous nucleation sites for the formation of magnesium.Moreover,such nano-particles could also restrict the grain growth during solidification.After adding AlN nano-particles,both the tensile properties at room temperature and high temperature 250℃and the hardness are largely improved.The improvement of strength is attributed to grain refinement and second phase refinement.
基金Project supported by the National Natural Science Foundation of China(U2037601,52074183)Shanghai Sailing Program(23YF1417100)。
文摘The effects of 1Zn and/or 2Ag additions on the hot tearing susceptibility(HTS)of Mg-14Gd-0.4Zr(wt%)alloy were studied.The HTS was evaluated by both theoretical predictions using Kou's criterion and experimental observations based on the in situ force-temperature recorded constrained rod casting(ISFTCRC)method.The results show that the order of HTS from high to low is Mg-14Gd-2Ag-1Zn-0.4Zr,Mg-14Gd-2Ag-0.4Zr,Mg-14Gd-1Zn-0.4Zr and Mg-14Gd-0.4Zr.Adding 1Zn and/or 2Ag changes the solidification path and the solidification interval,which affects the hot tearing susceptibility.Alloying elemental 1Zn slightly increases the solidification interval and the temperature range in the square root of the solid phase fraction(f_(s)^(1/2))range of 0.949-0.995,resulting in a slight increase in the hot tearing susceptibility.The addition of 2Ag drastically widens both the solidification interval and the temperature range in the f_(s)^(1/2)range of 0.949-0.995,thus significantly increasing the hot tearing susceptibility.Compared to the addition of 2Ag alone,the broadening degree of both the solidification interval and the temperature range in the f_(s)^(1/2)range of 0.949-0.995 is greater by adding the composite 2Ag/1Zn,which further promotes the occurrence of hot tearing.A narrower solidification interval and a temperature range in the f_(s)^(1/2)range of 0.949-0.995 result in a lower hot tearing susceptibility.
