Dissimilar AZ31B magnesium alloy and DC56D steel were welded via AA1060 aluminum alloy by magnetic pulse welding.The effects of primary and secondary welding processes on the welded interface were comparatively invest...Dissimilar AZ31B magnesium alloy and DC56D steel were welded via AA1060 aluminum alloy by magnetic pulse welding.The effects of primary and secondary welding processes on the welded interface were comparatively investigated.Macroscopic morphology,microstructure,and interfacial structure of the joints were analyzed using scanning electron microscope,energy dispersive spectrometer,and X-ray diffractometer(XRD).The results show that magnetic pulse welding of dissimilar Mg/Fe metals is achieved using an Al interlayer,which acts as a bridge for deformation and diffusion.Specifically,the AZ31B/AA1060 interface exhibits a typical wavy morphology,and a transition zone exists at the joint interface,which may result in an extremely complex microstructure.The microstructure of this transition zone differs from that of AZ31B magnesium and 1060 Al alloys,and it is identified as brittle intermetallic compounds(IMCs)Al_(3)Mg_(2) and Al_(12)Mg_(17).The transition zone is mainly distributed on the Al side,with the maximum thickness of Al-side transition layer reaching approximately 13.53μm.Incomplete melting layers with varying thicknesses are observed at the primary weld interface,while micron-sized hole defects appear in the transition zone of the secondary weld interface.The AA1060/DC56D interface is mainly straight,with only a small number of discontinuous transition zones distributed intermittently along the interface.These transition zones are characterized by the presence of the brittle IMC FeAl_(3),with a maximum thickness of about 4μm.展开更多
Joining dissimilar materials encounters significant engineering challenges due to the contrast in material properties that makes conventional welding not feasible.Magnetic Pulse Welding(MPW)offers a solidstate joining...Joining dissimilar materials encounters significant engineering challenges due to the contrast in material properties that makes conventional welding not feasible.Magnetic Pulse Welding(MPW)offers a solidstate joining technique that overcomes these issues by using impact to create strong bonds without melting the substrate materials.This study investigates the weldability of aluminum alloy Al-5754 with Al-7075 and MARS 380 steel,used in armouring solutions of defense systems,by the use of MPW.In this work,weldability windows are investigated by varying standoff distances between the coating material and its substrate(0.25-4.5 mm)and discharge energies(5-13 kJ)with both O-shape and U-shape inductors.Mechanical strength of the welded joints were assessed through single lap shear tests,identifying optimal welding parameters.Then,the velocity profiles of the flyer plates were measured using heterodyne velocimetry to understand the dynamics of the impact.Then,substructures assembled with the optimal welding conditions were subjected to ballistic testing using 7.62 mm×51 mm NATO and 9 mm×19 mm Parabellum munitions to evaluate the resilience of the welds under ballistic impact.The outcomes demonstrate that MPW effectively joins Al-5754 with both Al-7075 and MARS 380,producing robust welds capable of withstanding ballistic impacts under certain conditions.This research advances the application of MPW in lightweight ballistic protection of defense systems,contributing to the development of more resilient and lighter protective structures.展开更多
In recent years,the effect of pulsed magnetic fields on improving the solidification structure of alloys has attracted significant attention.A GH4738 nickel-based alloy smelted using a self-designed 20-kg electromagne...In recent years,the effect of pulsed magnetic fields on improving the solidification structure of alloys has attracted significant attention.A GH4738 nickel-based alloy smelted using a self-designed 20-kg electromagnetic casting system was taken as the research object.Finite element software was used to numerically simulate the magnetic field intensity,distribution,and temperature field of the casting device.The effect of the pulsed magnetic field on the solidification process of the GH4738 alloy was studied by means of low-magnification microstructural analysis.The measured magnetic field shows that when the duty cycle is 20%,the pulse frequency is 50 Hz,the output current is in the range of 150–250 A,and the peak magnetic field intensity of the crucible center is 68–116 mT.The crucible temperature is heated to 600℃and the melt center solidification time is 12.844 s.The microstructural analysis of the ingot shows that its shrinkage hole is reduced from 130 to 100 mm,and the equiaxed crystal area is increased from 2275 to 3150 mm^(2).The solidification angle of the dendrite is changed under the action of the pulsed magnetic field,and the tilt angle is 45°.The results show that the pulsed magnetic field promotes the primary crystal core of the GH4738 alloy,improves the nucleation rate of the melt,reduces the size difference of the solidification structure between the center and the edge of the ingot,and improves the uniformity of the solidification structure.展开更多
The corrosion resistance of cobalt-based alloy cladding layers is crucial for the long-term reliability of materials in the nuclear power industry,where they are exposed to highly aggressive environmental conditions.A...The corrosion resistance of cobalt-based alloy cladding layers is crucial for the long-term reliability of materials in the nuclear power industry,where they are exposed to highly aggressive environmental conditions.A major challenge to their performance is the corrosion occurring at phase boundaries under harsh operating conditions.This study investigates the effects of pulsed magnetic field treatment(PMT)on improving corrosion resistance at phase boundaries,specifically at the carbide/matrix Co interface,and seeks to clarify the underlying mechanisms.Advanced characterization techniques,including scanning electron microscopy(SEM),in situ transmission electron microscopy(TEM),in situ scanning kelvin probe force microscopy(SKPFM),and density functional theory(DFT)calculations,were employed.PMT samples exhibited no interface corrosion cracking or carbide spalling and showed a significant reduction in corrosion depth.TEM analysis revealed reduced lattice distortion at phase boundaries and a partial transformation of face-centered cubic(FCC)Co to hexagonal closepacked(HCP)Co.The enhanced corrosion resistance at phase boundaries is attributed to changes in the electronic work function(EWF),as determined by SKPFM measurements and DFT calculations.展开更多
Pulsed magnet technology is the only way to generate ultra-strong magnetic fields higher than 45 T so far.However,the inherently fast-changing field strength(typically on the order of 1000 T/s)poses significant challe...Pulsed magnet technology is the only way to generate ultra-strong magnetic fields higher than 45 T so far.However,the inherently fast-changing field strength(typically on the order of 1000 T/s)poses significant challenges for spectroscopic measurements which rely on time integration of signals to improve spectral qualities.In this work,we report high-sensitivity spectroscopic measurements under pulsed high magnetic fields employing the long flat-top pulsed magnetic field technique.By means of a multiple-capacitor power supply,we were able to generate pulsed high magnetic fields with controllable flat-top pulse width and field stabilities.By synchronizing spectroscopic measurements with the waveform of the flattop magnetic field,the integration time of each spectrum can be increased by up to 100 times compared with that of the conventional spectroscopic measurements under pulsed magnetic fields,thus enabling high-sensitivity spectroscopic measurements under ultra-strong pulsed magnetic fields.These findings promise an efficient way to significantly improve the performance and extend the application of optical measurements under pulsed high magnetic fields.展开更多
During direct chilling(DC)casting of ZK61 alloys,the primary and secondary cooling causes strong thermal gradients,which leads to the uneven crystallization rate and thermal contraction in different positions of the i...During direct chilling(DC)casting of ZK61 alloys,the primary and secondary cooling causes strong thermal gradients,which leads to the uneven crystallization rate and thermal contraction in different positions of the ingot.The consequences manifested appearance of heterogeneous grains,huge casting stresses,and even hot cracking flaws.In this paper,chemical and physical methods were integrated to produce large-scale magnesium(Mg)alloy ingots.A φ525 mm ZK61-RE alloy ingot that was refined,homogeneous,and free from hot cracking was obtained via the DC process coupled with a differential low frequency pulsed magnetic field(DLPM).The effects of rare earth(RE)and DLPM on the hot cracking tendency were investigated,and the mechanism of hot cracking formation and modification in largescale ingots was revealed.The findings indicate that the addition of moderate amounts of RE lessens the tendency of hot cracking in large-scale ZK61 alloy ingots.This is mainly attributed to the addition of RE increases the content of the second phase,thus enhancing the ability of the eutectic liquid phase to feed the cracking.With the introduction of DLPM,the grain sizes are significantly refined and homogenized,and there is no obvious hot cracking observed in the ingot.This is because the coupling of the DLPM provides a more homogeneous temperature field,leading to the synchronization of the solidification process,and the consequent reduction of the casting stress,thus reducing the driving force for the formation of hot cracking.In addition,the casting conditions are modified to enhance the ability of solidification feeding and the resistance to hot cracking.This work provides theoretical and practical references for the preparation of large-scale high-quality Mg alloy ingots.展开更多
The corrosion resistance of aluminum(Al)cable-copper(Cu)terminal joints fabricated by magnetic pulse crimping(MPC)and hydraulic clamp crimping(HCC)was compared.Performance degradation was evaluated by mechanical and e...The corrosion resistance of aluminum(Al)cable-copper(Cu)terminal joints fabricated by magnetic pulse crimping(MPC)and hydraulic clamp crimping(HCC)was compared.Performance degradation was evaluated by mechanical and electrical properties.Additionally,corrosion behavior was analyzed by electrochemical testing.Microscopic characterization was performed by scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS).Results show that the tensile strength of the corroded joints is reduced.However,due to the advantages of high-speed forming and contact tightness unique to MPC,the contact resistance of the corroded joints still maintains excellent.Electrochemical tests demonstrate that the MPC joints have higher corrosion potentials and smaller corrosion currents,providing better corrosion resistance.The formation of a primary battery between Al and Cu at the lap joint leads to the formation of severer corrosion pits.展开更多
The effects of a low-voltage pulsed magnetic field on the solidified structure and mechanical properties of DC casting AZ80 magnesium alloy were investigated.The results showed that the solidified structure of the DC ...The effects of a low-voltage pulsed magnetic field on the solidified structure and mechanical properties of DC casting AZ80 magnesium alloy were investigated.The results showed that the solidified structure of the DC casting AZ80 magnesium alloy was refined obviously by the low-voltage pulsed magnetic field and significant grain refinement in the DC casting ingot of AZ80 magnesium alloy was achieved.Meanwhile,the morphology of the dentritic in the DC casting ingot was transformed from coarse dentritic to fine rosette with the application of low-voltage pulsed magnetic field.The ability of deformation of the ingot was enhanced and especially the plasticity of the ingot center after upsetting was improved greatly by more than 80%after deformation.展开更多
The grain refinement of superalloy IN718 under the action of low voltage pulsed magnetic field was investigated. The experimental results show that fine equiaxed grains are acquired under the action of low voltage pul...The grain refinement of superalloy IN718 under the action of low voltage pulsed magnetic field was investigated. The experimental results show that fine equiaxed grains are acquired under the action of low voltage pulsed magnetic field. The refinement effect of the pulsed magnetic field is affected by the melt cooling rate and superheating. The decrease of cooling rate and superheating enhance the refinement effect of the low voltage pulsed magnetic field. The magnetic force and the melt flow during solidification are modeled and simulated to reveal the grain refinement mechanism. It is considered that the melt convection caused by the pulsed magnetic field, as well as cooling rate and superheating contributes to the refinement of solidified grains.展开更多
The combined effects of direct current pulsed magnetic field （DC-PMF） and inoculation on pure aluminum were investigated, the grain refinement behavior of DC-PMF and inoculation was discussed. The experimental resul...The combined effects of direct current pulsed magnetic field （DC-PMF） and inoculation on pure aluminum were investigated, the grain refinement behavior of DC-PMF and inoculation was discussed. The experimental results indicate that the solidification micro structure of pure aluminum can be greatly refined under DC-PMF. Refinement of pure aluminum is attributed to electromagnetic undercooling and forced convection caused by DC-PMF. With single DC-PMF, the grain size in the equiaxed zone is uneven. However, under DC-PMF, by adding 0.05% （mass fraction） Al5Ti-B, the grain size of the sample is smaller, and the size distribution is more uniform than that of single DC-PMF. Furthermore, under the combination of DC-PMF and inoculation, with the increase of output current, the grain size is further reduced. When the output current increases to 100 A, the average grain size can decrease to 113 μn.展开更多
The structures and macro-segregation of 2124 Al-alloy were studied when a pulsed magnetic field (PMF) was applied during solidification. It is found through experi-ments that a remarkable change occurs in the solidifi...The structures and macro-segregation of 2124 Al-alloy were studied when a pulsed magnetic field (PMF) was applied during solidification. It is found through experi-ments that a remarkable change occurs in the solidification structures of 2124 Al-alloy under pulsed magnetic field. The eutectic phase at grain boundaries change from thick continuous eutectic network to thin discontinuous one, and the distribution of solute elements was also homogenized. The typical negative segregation phenomenon of Cu in common solidification condition was restrained, and the segregation of Mg decreased.展开更多
The effects of a pulsed magnetic field on the solidified microstructure of an AZ31 magnesium alloy were investigated.The experimental results show that the remarkable microstructural refinement is achieved when the pu...The effects of a pulsed magnetic field on the solidified microstructure of an AZ31 magnesium alloy were investigated.The experimental results show that the remarkable microstructural refinement is achieved when the pulsed magnetic field is applied to the solidification of the AZ31 alloy.The average grain size of the as-cast microstructure of the AZ31 alloy is refined to 107 μm.By quenching the AZ31 alloy, the different primary α-Mg microstructures are preserved during the course of solidification.The microstructure evolution reveals that the primary α-Mg generates and grows in globular shape with pulsed magnetic field, contrast with the dendritic shape without pulsed magnetic field.The pulsed magnetic field causes melt convection during solidification, which makes the temperature of the whole melt homogenized, and produces an undercooling zone in front of the liquid/solid interface, which makes the nucleation rate increased and big dendrites prohibited.In addition, the Joule heat effect induced in the melt also strengthens the grain refinement effect and spheroidization of dendrite arms.展开更多
The low voltage pulsed magnetic field(LVPMF)disrupts the columnar dendrite growth,and the columnarto-equiaxed transition(CET)occurs during the directional solidification of superalloy K4169.Within the pulse voltage ra...The low voltage pulsed magnetic field(LVPMF)disrupts the columnar dendrite growth,and the columnarto-equiaxed transition(CET)occurs during the directional solidification of superalloy K4169.Within the pulse voltage ranging from 100Vto 200 V,a transition from columnar to equiaxed grain was observed,and the grain size decreased as the pulse voltage rised.As the pulse frequency increased,the CET occurred,and the grains were refined.However,the grains became coarse,and the solidification structure was columnar crystal again when frequency increased to 10 Hz.The LVPMF had an optimal frequency to promote CET.The LVPMF on the CET was affected by the withdrawal speed and increasing the withdrawal speed enhances the CET.The distribution of electromagnetic force and flow field in the melt under the LVPMF were modeled and simulated to reveal the CET mechanism.It is considered that the CET should be attributed to the coupling effects of magnetic vibration and melt convection induced by the LVPMF.展开更多
The effects of a pulsed magnetic field （PMF） on the microsegregation of solute elements during directional solidification of a Ni-based single crystal superalloy were experimentally investigated, and the results sho...The effects of a pulsed magnetic field （PMF） on the microsegregation of solute elements during directional solidification of a Ni-based single crystal superalloy were experimentally investigated, and the results show that the PMF significantly affects the microsegregation of Al, Ti, Co, Mo and W elements in the alloy. However, the distribution behavior differs for both positive and negative segregation elements. With the PMF, the microsegregation of negative segregation elements, Co and W, was restrained effectively, while that of positive segregation elements, A1, Ti and Mo, was aggravated. A segregation model was estab- lished to reveal the distribution mechanism of the elements with PME It is considered that, under the action of PME the jumping of solute atoms from the liquid phase to solid phase is hindered, but the jumping of solute atoms from the solid phase into liquid phase is promoted during solidification. As a result, the effective distribution coefficient of the solute atoms is reduced, which leads to the reduction of microsegregation of negative segregation elements and aggravation of microsegregation of positive segregation elements.展开更多
To understand the solidification behavior of austenitic stainless steel in pulsed magnetic field, the solidification process is investigated by means of the self-made high voltage pulse power source and the solidifica...To understand the solidification behavior of austenitic stainless steel in pulsed magnetic field, the solidification process is investigated by means of the self-made high voltage pulse power source and the solidification tester. The results show that the solidification structure of austenitic stainless steel can be remarkably refined in pulsed magnetic field, yet the grains become coarse again when the magnetic intensity is exceedingly large, indicating that an optimal intensity range existed for structure refinement. The solidification temperature can be enhanced with an increase in the magnetic intensity. The solidification time is shortened obviously, but the shortening degree is reduced with the increase of the magnetic intensity.展开更多
The inactivation of microorganisms by pulsed magnetic field was studied. It was improved that the application of electromagnetic pulses evidently causes a lethal effect on E. coli cells suspended in phosphate buffer s...The inactivation of microorganisms by pulsed magnetic field was studied. It was improved that the application of electromagnetic pulses evidently causes a lethal effect on E. coli cells suspended in phosphate buffer solution Na 2HPO 4/NaH 2PO 4(0 334/0 867 mmol/L). Experimental results indicated that the survivability(N/N 0; where N 0 and N are the number of cells survived per mill il iter before and after electromagnetic pulses application, respectively) of E. coli decreased with magnetic field intensity B and treatment time t. It was also found that the medium temperatures, the frequencies of pulse f, and the initial bacterial cell concentrations have determinate influences in destruction of E. coli cells by the application of magnetic pulses. The application of an magnetic intensity B=160 mT at pulses frequency f=62 kHz and treatment time t=16 h result in a considerable destruction levels of E. coli cells (N/N 0=10 -4 ). Possible mechanisms involved in sterilization of the magnetic field treatment were discussed. In order to shorten the treatment time, many groups of parallel inductive coil were used. The practicability test showed that the treatment time was shortened to 4 h with the application of three groups of parallel coil when the survivability of E.coli cells was less than 0 01%; and the power consumption was about 0 2 kWh /m 3.展开更多
For obtaining the finer grains of magnesium alloy,a novel combined pulsed magnetic field with different initial phases,also called out-ofphase pulsed magnetic field(OPPMF),was applied to study the solidification struc...For obtaining the finer grains of magnesium alloy,a novel combined pulsed magnetic field with different initial phases,also called out-ofphase pulsed magnetic field(OPPMF),was applied to study the solidification structure of AZ80 magnesium alloy.The numerical simulation was simultaneously conducted to investigate the refinement mechanisms.The experimental results showed that the macrostructure could be effectively refined by applying external magnetic field.Meanwhile,finer grains were obtained with the higher current intensity.However,the increase of current intensity could only refine the grains to about 0.5 mm.Furthermore,compared to a single pulsed magnetic field(PMF)and alternating series of OPPMF(Connection II),a finer structure was observed when the consecutive series of OPPMF(Connection I)was imposed.In contrast with a single PMF and Connection II,the numerical results showed that the greater axial Lorentz force was obtained under the Connection I,generating the stronger forced flow in the melt.It is believed that abundant nuclei could detach from the mold wall and move faster into the interior melt due to the stronger forced flow;besides,the lower superheat and greater temperature uniformity in bulk melt were realized,accounting for the finest structures under the Connection I.展开更多
The application of pulse magnetic field to metal solidification is an advanced technique which can remarkably refine solidification structure. In this paper, the effect of pulse magnetic field on solidification struct...The application of pulse magnetic field to metal solidification is an advanced technique which can remarkably refine solidification structure. In this paper, the effect of pulse magnetic field on solidification structure, mechanical properties and conductivity of pure copper was experimentally investigated. The results showed that the solidification structure transformed from coarse columnar crystal to fine globular crystal with increasing pulse voltage. Increasing pulse voltage also improved the tensile strength. However, with the increase of pulse voltage, the elongation and electrical resistivity firstly decreased, then increased when the pulse voltage beyond a critical value. Moreover, in some conditions, pulse magnetic field can simultaneously improve the conductivity and mechanical property of pure copper.展开更多
Pulsed magnetic field is generated when imposing pulse signal on high-frequency magnetic field. Distribution of the inner magnetic intensity in induction coils tends to be uniform. Furthermore oscillation and disturba...Pulsed magnetic field is generated when imposing pulse signal on high-frequency magnetic field. Distribution of the inner magnetic intensity in induction coils tends to be uniform. Furthermore oscillation and disturbance phenomena appear in the melt. In. situ Al2O3 and Al3Zr particulate reinforced aluminum matrix composites have been synthesized by direct melt reaction using AlZr（CO3）2 components under a foreign field. The size of reinforced particulates is 2-3 μm. They are well distributed in the matrix. Thermodynamic and kinetic analysis show that high-frequency pulsed magnetic field accelerates heat and mass transfer processes and improves the kinetic condition of in-situ fabrication.展开更多
The crystallization, microstructure, and soft magnetic properties of Fe52Co34Hf7B6Cul alloy are studied. Amorphous Fe52Co34Hf7B6Cul alloys are first treated by a pulsed magnetic field with a medium frequency, and then...The crystallization, microstructure, and soft magnetic properties of Fe52Co34Hf7B6Cul alloy are studied. Amorphous Fe52Co34Hf7B6Cul alloys are first treated by a pulsed magnetic field with a medium frequency, and then annealed at 100 ℃-400 ℃ for 30 min in a vacuum. The rise in temperature during the treatment by a pulsed magnetic field is measured by a non-contact infrared thermometer. The soft magnetic properties of specimens are measured by a vibrating sample magnetometer （VSM）. The microstructure changes of specimens are observed by a MSssbauer spectroscopy and transmission electron microscope （TEM）. The results show the medium-frequency pulsating magnetic field will pro- mote nanocrystallization of the amorphous alloy with a lower temperature rise. The nanocrystalline phase is （α-Fe（Co） with bcc crystal structure, and the grain size is about 10 nm. After vacuum annealing at 100 ℃ for 30 min, scattering nanocrystalline phases become more uniform, the coercive force and the saturation magnetization of the specimens are 41.98 A/m and 185.15 emu/g.展开更多
文摘Dissimilar AZ31B magnesium alloy and DC56D steel were welded via AA1060 aluminum alloy by magnetic pulse welding.The effects of primary and secondary welding processes on the welded interface were comparatively investigated.Macroscopic morphology,microstructure,and interfacial structure of the joints were analyzed using scanning electron microscope,energy dispersive spectrometer,and X-ray diffractometer(XRD).The results show that magnetic pulse welding of dissimilar Mg/Fe metals is achieved using an Al interlayer,which acts as a bridge for deformation and diffusion.Specifically,the AZ31B/AA1060 interface exhibits a typical wavy morphology,and a transition zone exists at the joint interface,which may result in an extremely complex microstructure.The microstructure of this transition zone differs from that of AZ31B magnesium and 1060 Al alloys,and it is identified as brittle intermetallic compounds(IMCs)Al_(3)Mg_(2) and Al_(12)Mg_(17).The transition zone is mainly distributed on the Al side,with the maximum thickness of Al-side transition layer reaching approximately 13.53μm.Incomplete melting layers with varying thicknesses are observed at the primary weld interface,while micron-sized hole defects appear in the transition zone of the secondary weld interface.The AA1060/DC56D interface is mainly straight,with only a small number of discontinuous transition zones distributed intermittently along the interface.These transition zones are characterized by the presence of the brittle IMC FeAl_(3),with a maximum thickness of about 4μm.
基金funded on the one hand by Agence de l'Innovation de Défense(AID)grant reference number 2021650044on the other hand by Ecole Centrale de Nantes。
文摘Joining dissimilar materials encounters significant engineering challenges due to the contrast in material properties that makes conventional welding not feasible.Magnetic Pulse Welding(MPW)offers a solidstate joining technique that overcomes these issues by using impact to create strong bonds without melting the substrate materials.This study investigates the weldability of aluminum alloy Al-5754 with Al-7075 and MARS 380 steel,used in armouring solutions of defense systems,by the use of MPW.In this work,weldability windows are investigated by varying standoff distances between the coating material and its substrate(0.25-4.5 mm)and discharge energies(5-13 kJ)with both O-shape and U-shape inductors.Mechanical strength of the welded joints were assessed through single lap shear tests,identifying optimal welding parameters.Then,the velocity profiles of the flyer plates were measured using heterodyne velocimetry to understand the dynamics of the impact.Then,substructures assembled with the optimal welding conditions were subjected to ballistic testing using 7.62 mm×51 mm NATO and 9 mm×19 mm Parabellum munitions to evaluate the resilience of the welds under ballistic impact.The outcomes demonstrate that MPW effectively joins Al-5754 with both Al-7075 and MARS 380,producing robust welds capable of withstanding ballistic impacts under certain conditions.This research advances the application of MPW in lightweight ballistic protection of defense systems,contributing to the development of more resilient and lighter protective structures.
基金supported by National Natural Science Foundation of China(No.52074092)the Fundamental Research Funds for Inner Mongolia University of Science&Technology(No.2023QNJS007)+1 种基金Program for Young Talents of Science and Technology in Universities of Inner Mongolia Autonomous Region(No.NJYT23115)the Inner Mongolia Natural Science Foundation(No.2022MS05039).
文摘In recent years,the effect of pulsed magnetic fields on improving the solidification structure of alloys has attracted significant attention.A GH4738 nickel-based alloy smelted using a self-designed 20-kg electromagnetic casting system was taken as the research object.Finite element software was used to numerically simulate the magnetic field intensity,distribution,and temperature field of the casting device.The effect of the pulsed magnetic field on the solidification process of the GH4738 alloy was studied by means of low-magnification microstructural analysis.The measured magnetic field shows that when the duty cycle is 20%,the pulse frequency is 50 Hz,the output current is in the range of 150–250 A,and the peak magnetic field intensity of the crucible center is 68–116 mT.The crucible temperature is heated to 600℃and the melt center solidification time is 12.844 s.The microstructural analysis of the ingot shows that its shrinkage hole is reduced from 130 to 100 mm,and the equiaxed crystal area is increased from 2275 to 3150 mm^(2).The solidification angle of the dendrite is changed under the action of the pulsed magnetic field,and the tilt angle is 45°.The results show that the pulsed magnetic field promotes the primary crystal core of the GH4738 alloy,improves the nucleation rate of the melt,reduces the size difference of the solidification structure between the center and the edge of the ingot,and improves the uniformity of the solidification structure.
基金financially supported by the National Key Research and Development Program of China(No.2020YFA0714900)the Joint Fund of the Ministry of Education(No.8091B012201)
文摘The corrosion resistance of cobalt-based alloy cladding layers is crucial for the long-term reliability of materials in the nuclear power industry,where they are exposed to highly aggressive environmental conditions.A major challenge to their performance is the corrosion occurring at phase boundaries under harsh operating conditions.This study investigates the effects of pulsed magnetic field treatment(PMT)on improving corrosion resistance at phase boundaries,specifically at the carbide/matrix Co interface,and seeks to clarify the underlying mechanisms.Advanced characterization techniques,including scanning electron microscopy(SEM),in situ transmission electron microscopy(TEM),in situ scanning kelvin probe force microscopy(SKPFM),and density functional theory(DFT)calculations,were employed.PMT samples exhibited no interface corrosion cracking or carbide spalling and showed a significant reduction in corrosion depth.TEM analysis revealed reduced lattice distortion at phase boundaries and a partial transformation of face-centered cubic(FCC)Co to hexagonal closepacked(HCP)Co.The enhanced corrosion resistance at phase boundaries is attributed to changes in the electronic work function(EWF),as determined by SKPFM measurements and DFT calculations.
基金financially supported by the National Key Research and Development Program of China(Grant No.2022YFA1602700)the National Natural Science Foundation of China(Grant No.12274159)。
文摘Pulsed magnet technology is the only way to generate ultra-strong magnetic fields higher than 45 T so far.However,the inherently fast-changing field strength(typically on the order of 1000 T/s)poses significant challenges for spectroscopic measurements which rely on time integration of signals to improve spectral qualities.In this work,we report high-sensitivity spectroscopic measurements under pulsed high magnetic fields employing the long flat-top pulsed magnetic field technique.By means of a multiple-capacitor power supply,we were able to generate pulsed high magnetic fields with controllable flat-top pulse width and field stabilities.By synchronizing spectroscopic measurements with the waveform of the flattop magnetic field,the integration time of each spectrum can be increased by up to 100 times compared with that of the conventional spectroscopic measurements under pulsed magnetic fields,thus enabling high-sensitivity spectroscopic measurements under ultra-strong pulsed magnetic fields.These findings promise an efficient way to significantly improve the performance and extend the application of optical measurements under pulsed high magnetic fields.
基金Project supported by the Jiangxi Province Key Laboratory of Light Alloy(2024SSY05031)the National Natural Science Foundation of China(52061028)+1 种基金the National Key Research and Development Program of China(2021YFB3501001)the Major Research and Development Projects of Jiangxi Province(20223BBE51021,20213AAE02014)。
文摘During direct chilling(DC)casting of ZK61 alloys,the primary and secondary cooling causes strong thermal gradients,which leads to the uneven crystallization rate and thermal contraction in different positions of the ingot.The consequences manifested appearance of heterogeneous grains,huge casting stresses,and even hot cracking flaws.In this paper,chemical and physical methods were integrated to produce large-scale magnesium(Mg)alloy ingots.A φ525 mm ZK61-RE alloy ingot that was refined,homogeneous,and free from hot cracking was obtained via the DC process coupled with a differential low frequency pulsed magnetic field(DLPM).The effects of rare earth(RE)and DLPM on the hot cracking tendency were investigated,and the mechanism of hot cracking formation and modification in largescale ingots was revealed.The findings indicate that the addition of moderate amounts of RE lessens the tendency of hot cracking in large-scale ZK61 alloy ingots.This is mainly attributed to the addition of RE increases the content of the second phase,thus enhancing the ability of the eutectic liquid phase to feed the cracking.With the introduction of DLPM,the grain sizes are significantly refined and homogenized,and there is no obvious hot cracking observed in the ingot.This is because the coupling of the DLPM provides a more homogeneous temperature field,leading to the synchronization of the solidification process,and the consequent reduction of the casting stress,thus reducing the driving force for the formation of hot cracking.In addition,the casting conditions are modified to enhance the ability of solidification feeding and the resistance to hot cracking.This work provides theoretical and practical references for the preparation of large-scale high-quality Mg alloy ingots.
基金supported by the National Natural Science Foundation of China (No.52175315)the Shenzhen Science and Technology Program,China (No.KQTD20200820113110016)the Hunan Provincial Postgraduate Research Innovation Program,China (No.CX20220404)。
文摘The corrosion resistance of aluminum(Al)cable-copper(Cu)terminal joints fabricated by magnetic pulse crimping(MPC)and hydraulic clamp crimping(HCC)was compared.Performance degradation was evaluated by mechanical and electrical properties.Additionally,corrosion behavior was analyzed by electrochemical testing.Microscopic characterization was performed by scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS).Results show that the tensile strength of the corroded joints is reduced.However,due to the advantages of high-speed forming and contact tightness unique to MPC,the contact resistance of the corroded joints still maintains excellent.Electrochemical tests demonstrate that the MPC joints have higher corrosion potentials and smaller corrosion currents,providing better corrosion resistance.The formation of a primary battery between Al and Cu at the lap joint leads to the formation of severer corrosion pits.
基金Project(51034012)supported by the the National Natural Science Foundation of ChinaProject(2013CB632205)supported by the National Basic Research Program of China
文摘The effects of a low-voltage pulsed magnetic field on the solidified structure and mechanical properties of DC casting AZ80 magnesium alloy were investigated.The results showed that the solidified structure of the DC casting AZ80 magnesium alloy was refined obviously by the low-voltage pulsed magnetic field and significant grain refinement in the DC casting ingot of AZ80 magnesium alloy was achieved.Meanwhile,the morphology of the dentritic in the DC casting ingot was transformed from coarse dentritic to fine rosette with the application of low-voltage pulsed magnetic field.The ability of deformation of the ingot was enhanced and especially the plasticity of the ingot center after upsetting was improved greatly by more than 80%after deformation.
基金Project(2010CB631205)supported by the National Basic Research Program of ChinaProject(51034012)supported by the National Natural Science Foundation of China
文摘The grain refinement of superalloy IN718 under the action of low voltage pulsed magnetic field was investigated. The experimental results show that fine equiaxed grains are acquired under the action of low voltage pulsed magnetic field. The refinement effect of the pulsed magnetic field is affected by the melt cooling rate and superheating. The decrease of cooling rate and superheating enhance the refinement effect of the low voltage pulsed magnetic field. The magnetic force and the melt flow during solidification are modeled and simulated to reveal the grain refinement mechanism. It is considered that the melt convection caused by the pulsed magnetic field, as well as cooling rate and superheating contributes to the refinement of solidified grains.
基金Projects(51074031,51271042,50874022)supported by the National Natural Science Foundation of ChinaProject(2013M530913)supported by the China Postdoctoral Science FoundationProject(DUT12RC(3)35)supported by the Fundamental Research Funds for the Central Universities of China
文摘The combined effects of direct current pulsed magnetic field （DC-PMF） and inoculation on pure aluminum were investigated, the grain refinement behavior of DC-PMF and inoculation was discussed. The experimental results indicate that the solidification micro structure of pure aluminum can be greatly refined under DC-PMF. Refinement of pure aluminum is attributed to electromagnetic undercooling and forced convection caused by DC-PMF. With single DC-PMF, the grain size in the equiaxed zone is uneven. However, under DC-PMF, by adding 0.05% （mass fraction） Al5Ti-B, the grain size of the sample is smaller, and the size distribution is more uniform than that of single DC-PMF. Furthermore, under the combination of DC-PMF and inoculation, with the increase of output current, the grain size is further reduced. When the output current increases to 100 A, the average grain size can decrease to 113 μn.
基金This research was supported by National Key Basic Research and Development Programme of China "973" (No. G19990649051).
文摘The structures and macro-segregation of 2124 Al-alloy were studied when a pulsed magnetic field (PMF) was applied during solidification. It is found through experi-ments that a remarkable change occurs in the solidification structures of 2124 Al-alloy under pulsed magnetic field. The eutectic phase at grain boundaries change from thick continuous eutectic network to thin discontinuous one, and the distribution of solute elements was also homogenized. The typical negative segregation phenomenon of Cu in common solidification condition was restrained, and the segregation of Mg decreased.
基金Project(ZC304009103) supported by the Doctoral Fund of Zhejiang Normal University,ChinaProject(KYJ06Y09157) supported by School-level Project of Zhejiang Normal University,China
文摘The effects of a pulsed magnetic field on the solidified microstructure of an AZ31 magnesium alloy were investigated.The experimental results show that the remarkable microstructural refinement is achieved when the pulsed magnetic field is applied to the solidification of the AZ31 alloy.The average grain size of the as-cast microstructure of the AZ31 alloy is refined to 107 μm.By quenching the AZ31 alloy, the different primary α-Mg microstructures are preserved during the course of solidification.The microstructure evolution reveals that the primary α-Mg generates and grows in globular shape with pulsed magnetic field, contrast with the dendritic shape without pulsed magnetic field.The pulsed magnetic field causes melt convection during solidification, which makes the temperature of the whole melt homogenized, and produces an undercooling zone in front of the liquid/solid interface, which makes the nucleation rate increased and big dendrites prohibited.In addition, the Joule heat effect induced in the melt also strengthens the grain refinement effect and spheroidization of dendrite arms.
基金supported by the National Natural Science Foundation of China(No.51674236)the Key Research and Development Program of Liaoning Province(2019JH2/10100009)+1 种基金the National Science and Technology Major Project(No.2017-VI-00-0073)the National Key Research and Development Program(No.2018YFA0702900).
文摘The low voltage pulsed magnetic field(LVPMF)disrupts the columnar dendrite growth,and the columnarto-equiaxed transition(CET)occurs during the directional solidification of superalloy K4169.Within the pulse voltage ranging from 100Vto 200 V,a transition from columnar to equiaxed grain was observed,and the grain size decreased as the pulse voltage rised.As the pulse frequency increased,the CET occurred,and the grains were refined.However,the grains became coarse,and the solidification structure was columnar crystal again when frequency increased to 10 Hz.The LVPMF had an optimal frequency to promote CET.The LVPMF on the CET was affected by the withdrawal speed and increasing the withdrawal speed enhances the CET.The distribution of electromagnetic force and flow field in the melt under the LVPMF were modeled and simulated to reveal the CET mechanism.It is considered that the CET should be attributed to the coupling effects of magnetic vibration and melt convection induced by the LVPMF.
基金the financial support from the National Natural Science Foundation of China(No.51034012)the National Basic Research Program of China(No.2010CB631205)
文摘The effects of a pulsed magnetic field （PMF） on the microsegregation of solute elements during directional solidification of a Ni-based single crystal superalloy were experimentally investigated, and the results show that the PMF significantly affects the microsegregation of Al, Ti, Co, Mo and W elements in the alloy. However, the distribution behavior differs for both positive and negative segregation elements. With the PMF, the microsegregation of negative segregation elements, Co and W, was restrained effectively, while that of positive segregation elements, A1, Ti and Mo, was aggravated. A segregation model was estab- lished to reveal the distribution mechanism of the elements with PME It is considered that, under the action of PME the jumping of solute atoms from the liquid phase to solid phase is hindered, but the jumping of solute atoms from the solid phase into liquid phase is promoted during solidification. As a result, the effective distribution coefficient of the solute atoms is reduced, which leads to the reduction of microsegregation of negative segregation elements and aggravation of microsegregation of positive segregation elements.
基金Item Sponsored by National Natural Science Foundation of China (50274050) and Shanghai Baoshan Iron and Steel Group
文摘To understand the solidification behavior of austenitic stainless steel in pulsed magnetic field, the solidification process is investigated by means of the self-made high voltage pulse power source and the solidification tester. The results show that the solidification structure of austenitic stainless steel can be remarkably refined in pulsed magnetic field, yet the grains become coarse again when the magnetic intensity is exceedingly large, indicating that an optimal intensity range existed for structure refinement. The solidification temperature can be enhanced with an increase in the magnetic intensity. The solidification time is shortened obviously, but the shortening degree is reduced with the increase of the magnetic intensity.
文摘The inactivation of microorganisms by pulsed magnetic field was studied. It was improved that the application of electromagnetic pulses evidently causes a lethal effect on E. coli cells suspended in phosphate buffer solution Na 2HPO 4/NaH 2PO 4(0 334/0 867 mmol/L). Experimental results indicated that the survivability(N/N 0; where N 0 and N are the number of cells survived per mill il iter before and after electromagnetic pulses application, respectively) of E. coli decreased with magnetic field intensity B and treatment time t. It was also found that the medium temperatures, the frequencies of pulse f, and the initial bacterial cell concentrations have determinate influences in destruction of E. coli cells by the application of magnetic pulses. The application of an magnetic intensity B=160 mT at pulses frequency f=62 kHz and treatment time t=16 h result in a considerable destruction levels of E. coli cells (N/N 0=10 -4 ). Possible mechanisms involved in sterilization of the magnetic field treatment were discussed. In order to shorten the treatment time, many groups of parallel inductive coil were used. The practicability test showed that the treatment time was shortened to 4 h with the application of three groups of parallel coil when the survivability of E.coli cells was less than 0 01%; and the power consumption was about 0 2 kWh /m 3.
基金This work was supported by the National Key Re-search and Development Program of China(Grant No.2016YFB0301101)the National Natural Science Foundation of China(Grant No.51971054)the Fundamental Research Funds for the Central Universities(Grant No.N180904006 and N2009006).
文摘For obtaining the finer grains of magnesium alloy,a novel combined pulsed magnetic field with different initial phases,also called out-ofphase pulsed magnetic field(OPPMF),was applied to study the solidification structure of AZ80 magnesium alloy.The numerical simulation was simultaneously conducted to investigate the refinement mechanisms.The experimental results showed that the macrostructure could be effectively refined by applying external magnetic field.Meanwhile,finer grains were obtained with the higher current intensity.However,the increase of current intensity could only refine the grains to about 0.5 mm.Furthermore,compared to a single pulsed magnetic field(PMF)and alternating series of OPPMF(Connection II),a finer structure was observed when the consecutive series of OPPMF(Connection I)was imposed.In contrast with a single PMF and Connection II,the numerical results showed that the greater axial Lorentz force was obtained under the Connection I,generating the stronger forced flow in the melt.It is believed that abundant nuclei could detach from the mold wall and move faster into the interior melt due to the stronger forced flow;besides,the lower superheat and greater temperature uniformity in bulk melt were realized,accounting for the finest structures under the Connection I.
基金The projects was supported by the Pre-research Foundation of the National Basic Research Program (973 Program, grant No. 2004CCA07000)the Science and Technology Committee of Shanghai Municipality (Grant No. 04XD14008).
文摘The application of pulse magnetic field to metal solidification is an advanced technique which can remarkably refine solidification structure. In this paper, the effect of pulse magnetic field on solidification structure, mechanical properties and conductivity of pure copper was experimentally investigated. The results showed that the solidification structure transformed from coarse columnar crystal to fine globular crystal with increasing pulse voltage. Increasing pulse voltage also improved the tensile strength. However, with the increase of pulse voltage, the elongation and electrical resistivity firstly decreased, then increased when the pulse voltage beyond a critical value. Moreover, in some conditions, pulse magnetic field can simultaneously improve the conductivity and mechanical property of pure copper.
基金This work was financially supported by the Foundation for Key Program of the Ministry of Education of China (No.207038)the Technological Achievement Conversion Program of Jiangsu Province in China (No.BA2005054)+1 种基金the High Technology Research Program of Jiangsu Province (No.BG2005026)the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province, China (No. 05KJD450043).
文摘Pulsed magnetic field is generated when imposing pulse signal on high-frequency magnetic field. Distribution of the inner magnetic intensity in induction coils tends to be uniform. Furthermore oscillation and disturbance phenomena appear in the melt. In. situ Al2O3 and Al3Zr particulate reinforced aluminum matrix composites have been synthesized by direct melt reaction using AlZr（CO3）2 components under a foreign field. The size of reinforced particulates is 2-3 μm. They are well distributed in the matrix. Thermodynamic and kinetic analysis show that high-frequency pulsed magnetic field accelerates heat and mass transfer processes and improves the kinetic condition of in-situ fabrication.
基金Project supported by the National Natural Science Foundation of China(Grant No.50771025)
文摘The crystallization, microstructure, and soft magnetic properties of Fe52Co34Hf7B6Cul alloy are studied. Amorphous Fe52Co34Hf7B6Cul alloys are first treated by a pulsed magnetic field with a medium frequency, and then annealed at 100 ℃-400 ℃ for 30 min in a vacuum. The rise in temperature during the treatment by a pulsed magnetic field is measured by a non-contact infrared thermometer. The soft magnetic properties of specimens are measured by a vibrating sample magnetometer （VSM）. The microstructure changes of specimens are observed by a MSssbauer spectroscopy and transmission electron microscope （TEM）. The results show the medium-frequency pulsating magnetic field will pro- mote nanocrystallization of the amorphous alloy with a lower temperature rise. The nanocrystalline phase is （α-Fe（Co） with bcc crystal structure, and the grain size is about 10 nm. After vacuum annealing at 100 ℃ for 30 min, scattering nanocrystalline phases become more uniform, the coercive force and the saturation magnetization of the specimens are 41.98 A/m and 185.15 emu/g.
