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 this study,a 1400 MPa-grade ultra-high-strength steel thin-plate butt-welded joint was selected as the research object,and the joint was fabricated using the metal inert gas(MIG)welding process with ER307Si filler ...In this study,a 1400 MPa-grade ultra-high-strength steel thin-plate butt-welded joint was selected as the research object,and the joint was fabricated using the metal inert gas(MIG)welding process with ER307Si filler wire.Residual stress distributions were measured via the hole-drilling method,while micro-hardness was assessed using a micro-hardness tester.Simultaneously,both transverse shrinkage and angular distortion of the welded joint were experimentally determined.According to the hardness distribution of the joint,a thermalmetallurgical-mechanical finite element model was developed based on SYSWELD software platform.This model incorporates solid-state phase transformations(SSPT)and softening effect in the HAZ,as well as strain hardening and annealing behaviors in the weld metal.The temperature field,residual stress distribution,and welding deformation of single-pass butt-welded joint were simulated by the developed computational method.The simulation results were validated against experimental measurements,confirming the accuracy and reliability of the proposed computational approach.Furthermore,based on the numerical results,the influence mechanisms of SSPT and material softening on residual stress and deformation were analyzed.The findings indicate that SSPT exhibits considerable influences on the magnitude and distribution of welding residual stress.It reduces the peak longitudinal residual stress from 1620 MPa to 1350 MPa and increases the peak transverse residual stress from 350 MPa to 402 MPa.The results also manifest that the softening effect further reduces the peak longitudinal residual stress by 300 MPa,while exhibits minor effect on transverse residual stress.However,the results show that neither the SSPT nor the softening effect presents obvious influence on welding deformation.展开更多
Driven by efforts toward carbon-neutral steelmaking,increased scrap usage elevates Sn content in steels.While the general effects of Sn on steel have been studied,its specific influence on resistance spot welding(RSW)...Driven by efforts toward carbon-neutral steelmaking,increased scrap usage elevates Sn content in steels.While the general effects of Sn on steel have been studied,its specific influence on resistance spot welding(RSW)remains unclear.This study investigates Sn’s impact on the mechanical properties of RSW joint of 460 MPa HSLA steel.Cross-tension tests reveal that both the RSW joint without Sn and the RSW joint·containing 0.09wt%Sn exhibit pull-out failure.The RSW joint containing 0.09wt%Sn showing higher peak load and energy absorption attributed to Sn’s solid–solution strengthening.Conversely,the RSW joint containing 0.52wt%Sn exhibited the partial interface failure mode,significantly reducing the peak load and energy absorption.The primary reason is the segregation of Sn in the interdendritic regions of the fusion zone,which weakens atomic cohesion and reduces fracture toughness.Such severe segregation arises from RSW’s high cooling rates,which shift the primary solidification phase from δ-ferrite to austenite.Fortunately,double-pulse RSW mitigates Sn segregation,restoring failure mode and mechanical performance.This study assesses the impact of Sn on RSW joint properties,and these findings highlight the broader significance of understanding scrap-related residual element effects in sustainable steel production.展开更多
Low heat input welding is widely used in the industry.The microstructure and toughness of the welded joints under low heat input conditions have received less attention than those under high heat input.The impact toug...Low heat input welding is widely used in the industry.The microstructure and toughness of the welded joints under low heat input conditions have received less attention than those under high heat input.The impact toughness,microstructure and failure mechanisms of the coarse-grain heat-affected zone(CGHAZ)in a micro-alloyed steel were investigated by welding thermal simulation with the heat input ranging from 15 to 65 kJ/cm.The impact toughness of CGHAZ is highly sensitive to variations in low heat input.The failure mechanisms were discussed from the viewpoints of micro-voids formation and micro-cracks propagation.The micro-voids are preferred to be formed and grow at soft phase of grain boundary ferrite(GBF).At the heat inputs no more than 22 kJ/cm,martensite was dominantly formed,and the micro-cracks initiated from the GBF were propagated into the grain interiors,leading to the brittle fracture and low toughness.When the heat input was increased to 31.2 kJ/cm,granular bainite became the dominant constitute,causing cracks to deflect away from GBF and propagate into prior austenite grains.The high density high-angle and low-angle grain boundaries and the presence of retained austenite,effectively restricted the crack propagation,resulting in ductile fracture behavior and enhanced toughness.High heat input(62.3 kJ/cm)promoted coarse GBF formation,providing continuous paths for microcrack propagation.This direct intergranular crack progression caused brittle fracture and low toughness.Industrial cold cracking in the CGHAZ can thus be controlled by heat input optimization to maximize toughness.展开更多
The fabrication of 304L stainless welding wires with a diameter 1.6 mm by using electrochemical cold drawing(ECD)of bars with a diameter of 5.6 mm was investigated,as well as that via traditional cold drawing(TCD)for ...The fabrication of 304L stainless welding wires with a diameter 1.6 mm by using electrochemical cold drawing(ECD)of bars with a diameter of 5.6 mm was investigated,as well as that via traditional cold drawing(TCD)for comparison.The results indicated that the dilute H_(2)SO_(4)aqueous solution was an appropriate electrolyte for ECD,and increasing the H_(2)SO_(4)concentration and current density within a range improved the corrosion rate and uniformity,leading to an easier and more coordinated deformation through uniformly distributing geometrically necessary dislocations and curved large-angle grain boundaries,and decreasing their density,and thus,an enhanced electrochemical plasticization(EP).Under the optimized electrochemical parameters(0.5 mol L^(-1)H_(2)SO_(4)electrolyte and current density of 12.2 mA cm^(-2)),the average cumulative reduction rate required for annealing was up to~34%,obviously higher than~20%of TCD due to the decreased work-hardening from the EP,so that the number of annealing was significantly reduced from 10 of TCD to 5,when the drawing pass was 23.In addition,the surface of the ECD wire was distinctly smoother and brighter than that of the TCD one.These findings confirm the large potential in engineering applications of the ECD technology based on the EP effect.展开更多
High entropy alloys(HEAs)have recently attracted significant attention due to their exceptional mechanical properties and potential applications across various fields.Friction stir welding and processing(FSW/P),as not...High entropy alloys(HEAs)have recently attracted significant attention due to their exceptional mechanical properties and potential applications across various fields.Friction stir welding and processing(FSW/P),as notable solid-state welding and processing techniques,have been proved effectiveness in enhancing microstructures and mechanical properties of HEAs.This review article summarizes the current status of FSW/P of HEAs.The welding materials and conditions used for FSW/P in HEAs are reviewed and discussed.The effects of FSW/P on the evolutions of grain structure,texture,dislocation,and secondary phase for different HEAs are highlighted.Furthermore,the influences of FSW/P on the mechanical properties of various HEAs are analyzed.Finally,potential applications,challenges,and future directions of FSW/P in HEAs are forecasted.Overall,FSW/P enable to refine grains of HEAs through dynamic recrystallization and to activate diverse deformation mechanisms of HEAs through tailoring phase structures,thereby significantly improving the strength,hardness,and ductility of both single-and dual-phase HEAs.Future progress in this field will rely on comprehensive optimization of processing parameters and alloy composition,integration of multi-scale modeling with advanced characterization for in-depth exploration of microstructural mechanisms,systematic evaluation of functional properties,and effective bridging of the gap between laboratory research and industrial application.The review aims to provide an overview of recent advancements in the FSW/P of HEAs and encourage further research in this area.展开更多
The influence of oscillation amplitude on molten pool thermal history,weld morphology characteristics,microstructural evolution,and mechanical properties during laser oscillating welding of QP980 steel was systematica...The influence of oscillation amplitude on molten pool thermal history,weld morphology characteristics,microstructural evolution,and mechanical properties during laser oscillating welding of QP980 steel was systematically investigated.Results show that laser beam oscillation significantly regulates molten pool thermomechanical behavior through optimized spatial energy distribution,thereby enabling microstructural reconstruction and joint performance enhancement.As the oscillation amplitude increases from 0 to 0.8 mm,the molten pool duration extends to 1.7 times the original value,while peak temperature and average cooling rate decrease by 19%and 39%,respectively.This thermal regulation promotes weld surface width expansion from 0.72 to 1.07 mm.The welding mode undergoes a progressive transition from keyhole mode→transitional mode→conduction mode.This transformation effectively suppresses porosity defects,substantially reducing porosity from 1.8%to 0.15%.Microstructural analysis indicates that oscillation modifies the maximum temperature gradient direction within the molten pool,facilitating preferential growth of coarse columnar grains along the welding centerline to establish load-transfer-favorable crystallographic orientations.The synergistic effects of these factors substantially improve joint mechanical properties:lap joint shear load increases by 81.5%(7.6→13.8 kN),and fracture elongation is enhanced by 135%(0.98→2.3 mm).The operational principles of laser oscillation parameters on the welding quality of QP980 steel were elucidated,providing theoretical foundations for joining process optimization.展开更多
A phase-field model including magnetic field induced dendrite fragmentation was established and applied to the cases with different initial crystal nuclear positions for AA5754 aluminum alloy electromagnetic laser bea...A phase-field model including magnetic field induced dendrite fragmentation was established and applied to the cases with different initial crystal nuclear positions for AA5754 aluminum alloy electromagnetic laser beam welding.Compare the calculated results that include dendrite fragmentation caused by the thermal electromagnetic Lorentz force with the results that consider only the thermal electromagnetic Lorentz force,without fragmentation,at the characteristic time instants.Both in the early and late stages,the small fragmentation at the dendrite tip promotes the number of higher-order branches and their growth,especially in the direction perpendicular to the solidification.The later stage fragmentation has the possibility of breaking one grain into several,which verifies the possibility of grain refinement caused by dendrite fragmentation.The fracture surface caused by fragmentation also makes more solid-liquid interfaces and their growth.In addition,the cases with different initial nuclear positions were compared.The grain growth in the low-temperature zone can be inhibited by the equiaxed grains'fragmentation at the high-temperature area(179.8μm^(2) and 14.7% start at the center,115.4μm^(2) and 9.4% start at the high-temperature corner,134.3μm^(2) and 10.9%start at the low-temperature corner),which is another kind of grain refinement by the dendrite fragmentation.This kind of inhibition effect on grain growth in the low-temperature region will be enhanced with the increasing time interval between the two crystal nuclei’appearance(179.8μm^(2) and 14.7%when virtual grains appear at t=4.3803 s and t=4.3803 s,134.3μm^(2) and 10.9%at t=4.0977 s and t=3.9564 s,and 115.4μm^(2) and 9.4%at t=3.8151 s and t=3.5325 s).展开更多
Marine thin plates are susceptible to welding deformation owing to their low structural stiffness.Therefore,the efficient and accurate prediction of welding deformation is essential for improving welding quality.The t...Marine thin plates are susceptible to welding deformation owing to their low structural stiffness.Therefore,the efficient and accurate prediction of welding deformation is essential for improving welding quality.The traditional thermal elastic-plastic finite element method(TEP-FEM)can accurately predict welding deformation.However,its efficiency is low because of the complex nonlinear transient computation,making it difficult to meet the needs of rapid engineering evaluation.To address this challenge,this study proposes an efficient prediction method for welding deformation in marine thin plate butt welds.This method is based on the coupled temperature gradient-thermal strain method(TG-TSM)that integrates inherent strain theory with a shell element finite element model.The proposed method first extracts the distribution pattern and characteristic value of welding-induced inherent strain through TEP-FEM analysis.This strain is then converted into the equivalent thermal load applied to the shell element model for rapid computation.The proposed method-particularly,the gradual temperature gradient-thermal strain method(GTG-TSM)-achieved improved computational efficiency and consistent precision.Furthermore,the proposed method required much less computation time than the traditional TEP-FEM.Thus,this study lays the foundation for future prediction of welding deformation in more complex marine thin plates.展开更多
Twinning-induced plasticity(TWIP)steel was processed using electrically assisted friction stir welding(EFSW).The microstructure,mechanical properties,and deformation behavior of the welded joints were systematically i...Twinning-induced plasticity(TWIP)steel was processed using electrically assisted friction stir welding(EFSW).The microstructure,mechanical properties,and deformation behavior of the welded joints were systematically investigated.The results show that the average grain size was refined from 3.67μm in the base material(BM)to 1.39μm in the stir zone(SZ),while it increased to 4.19μm in the heat-affected zone(HAZ).The fraction of twin boundaries(TBs)decreased from 20.7%in the BM to 6.9%in the SZ and increased to24.5%in the HAZ.The ultimate tensile strength,yield strength,and elongation of the BM were 1021 MPa,505 MPa,and 65.8%,respectively.In comparison,the EFSW joint exhibited values of 1055 MPa,561 MPa,and 60.8%,corresponding to 103.3%,111.1%,and 92.4%of those of the BM,respectively.During tensile testing,plastic deformation was primarily concentrated in the BM,although both the SZ and HAZ also exhibited notable plastic deformation.Fracture ultimately occurred in the BM.展开更多
The transformation of the dissimilar metals in the welding area into a single metal is an important method for achieving high-quality welded connection in the dissimilar metal laminated composite plate.In this study,a...The transformation of the dissimilar metals in the welding area into a single metal is an important method for achieving high-quality welded connection in the dissimilar metal laminated composite plate.In this study,a high-performance titanium/steel composite plate(TSCP)with pure titaniumization in the welding area was prepared by cold spraying,hot rolling and heat treatment processes.The results indicate that cold spraying achieves effective pre-composite deposition of titanium particles while inhibiting interfacial oxidation and Fe-Ti alloying reactions,producing a relatively dense pure titanium coating with a low porosity of only 1.2%.Hot rolling eliminates internal defects and promotes strong metallurgical bonding of the composite interface.The heat treatment promotes the recrystallization and reduces the dislocation density within the coating.The interfacial bonding strength of the welding area with pure titaniumization of TSCP is 257 MPa,and the tensile strength of that is 414 MPa,reaching 95.6%of the TSCP’s base material.展开更多
The microstructural evolution and mechanical properties of a vacuum electron beam welded aerospace 5B70 aluminum alloy joint were studied.Quantitative analyses of the phase composition,microstructural evolution,grain ...The microstructural evolution and mechanical properties of a vacuum electron beam welded aerospace 5B70 aluminum alloy joint were studied.Quantitative analyses of the phase composition,microstructural evolution,grain size,grain boundary density,and texture changes were performed by X-ray diffraction,scanning electron microscopy,and electron backscatter diffraction.The fusion zone(FZ)comprises equiaxed cellular crystals,and a fine~20μm-thick crystal layer forms in the transition zone(TZ)between the FZ and heat affected zone(HAZ).The HAZ closely resembles the base material(BM),retaining the original rolling microstructure.Mechanical property testing shows that the fine-grained layer in the TZ exhibits the highest nanohardness,with the FZ corresponding to the lowest microhardness.The welded-joint sample has lower yield strength,ultimate tensile strength,and elongation after fracture than the BM.These reductions of mechanical properties are primarily influenced by the grain size and distribution of the precipitated phases.展开更多
To improve the weld formation of underwater-welded Q355B steel and enhance its corrosion resistance,this study introduced pulsed laser welding technology into local dry underwater welding process,building upon continu...To improve the weld formation of underwater-welded Q355B steel and enhance its corrosion resistance,this study introduced pulsed laser welding technology into local dry underwater welding process,building upon continuous laser welding process.A systematic investigation was carried out covering process exploration,weld morphology,microstructure,and comprehensive properties.The results indicate that the pulsed laser weld seam exhibited a distinct ripple pattern on the surface,along with significantly less spatter compared to continuous laser weld seam.Both the weld penetration depth and weld bead width showed a decreasing trend with increasing pulse frequency.The weld metal was primarily composed of ferrite and martensite phases.As the pulse frequency increased,the ferrite content first rose and then declined,reaching a maximum of 39%at 80 Hz.The microhardness and tensile strength of the weld metal were both higher than those of the base material,and all tensile specimens fractured within the base metal during testing.Furthermore,the elongation initially increased and then decreased with rising pulse frequency.The weld produced at 80 Hz achieved the highest elongation of 23.1%,which was 8.9% higher than that of the continuous laser weld seam and reached 93.9% of the base material.Electrochemical corrosion tests revealed that the weld produced at 80 Hz exhibited the best corrosion resistance,reaching 67.0% of that of the base material,while the continuous laser weld seam attained only 47.3% of the base material.This study provides critical theoretical and data support for the process optimization and application of local dry underwater laser welding in the fabrication of marine engineering structures.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funded by the National Natural Science Foundation of China(Grant No.52471032).
文摘In this study,a 1400 MPa-grade ultra-high-strength steel thin-plate butt-welded joint was selected as the research object,and the joint was fabricated using the metal inert gas(MIG)welding process with ER307Si filler wire.Residual stress distributions were measured via the hole-drilling method,while micro-hardness was assessed using a micro-hardness tester.Simultaneously,both transverse shrinkage and angular distortion of the welded joint were experimentally determined.According to the hardness distribution of the joint,a thermalmetallurgical-mechanical finite element model was developed based on SYSWELD software platform.This model incorporates solid-state phase transformations(SSPT)and softening effect in the HAZ,as well as strain hardening and annealing behaviors in the weld metal.The temperature field,residual stress distribution,and welding deformation of single-pass butt-welded joint were simulated by the developed computational method.The simulation results were validated against experimental measurements,confirming the accuracy and reliability of the proposed computational approach.Furthermore,based on the numerical results,the influence mechanisms of SSPT and material softening on residual stress and deformation were analyzed.The findings indicate that SSPT exhibits considerable influences on the magnitude and distribution of welding residual stress.It reduces the peak longitudinal residual stress from 1620 MPa to 1350 MPa and increases the peak transverse residual stress from 350 MPa to 402 MPa.The results also manifest that the softening effect further reduces the peak longitudinal residual stress by 300 MPa,while exhibits minor effect on transverse residual stress.However,the results show that neither the SSPT nor the softening effect presents obvious influence on welding deformation.
基金financially supported by the National Nat-ural Science Foundation of China(Nos.52293390 and 52293393)Liaoning Academy of Materials,China.
文摘Driven by efforts toward carbon-neutral steelmaking,increased scrap usage elevates Sn content in steels.While the general effects of Sn on steel have been studied,its specific influence on resistance spot welding(RSW)remains unclear.This study investigates Sn’s impact on the mechanical properties of RSW joint of 460 MPa HSLA steel.Cross-tension tests reveal that both the RSW joint without Sn and the RSW joint·containing 0.09wt%Sn exhibit pull-out failure.The RSW joint containing 0.09wt%Sn showing higher peak load and energy absorption attributed to Sn’s solid–solution strengthening.Conversely,the RSW joint containing 0.52wt%Sn exhibited the partial interface failure mode,significantly reducing the peak load and energy absorption.The primary reason is the segregation of Sn in the interdendritic regions of the fusion zone,which weakens atomic cohesion and reduces fracture toughness.Such severe segregation arises from RSW’s high cooling rates,which shift the primary solidification phase from δ-ferrite to austenite.Fortunately,double-pulse RSW mitigates Sn segregation,restoring failure mode and mechanical performance.This study assesses the impact of Sn on RSW joint properties,and these findings highlight the broader significance of understanding scrap-related residual element effects in sustainable steel production.
基金supported by the National Natural Science Foundation of China(No.51804232)Beijing Municipal Natural Science Foundation(No.2212041)+1 种基金supported by the Interdisciplinary Research Project for Young Teachers of USTB(Fundamental Research Funds for the Central Universities)(FRF-IDRY-20-020)GIMRT Program of the Institute for Materials Research,Tohoku University(202303-RDKGE-0518).
文摘Low heat input welding is widely used in the industry.The microstructure and toughness of the welded joints under low heat input conditions have received less attention than those under high heat input.The impact toughness,microstructure and failure mechanisms of the coarse-grain heat-affected zone(CGHAZ)in a micro-alloyed steel were investigated by welding thermal simulation with the heat input ranging from 15 to 65 kJ/cm.The impact toughness of CGHAZ is highly sensitive to variations in low heat input.The failure mechanisms were discussed from the viewpoints of micro-voids formation and micro-cracks propagation.The micro-voids are preferred to be formed and grow at soft phase of grain boundary ferrite(GBF).At the heat inputs no more than 22 kJ/cm,martensite was dominantly formed,and the micro-cracks initiated from the GBF were propagated into the grain interiors,leading to the brittle fracture and low toughness.When the heat input was increased to 31.2 kJ/cm,granular bainite became the dominant constitute,causing cracks to deflect away from GBF and propagate into prior austenite grains.The high density high-angle and low-angle grain boundaries and the presence of retained austenite,effectively restricted the crack propagation,resulting in ductile fracture behavior and enhanced toughness.High heat input(62.3 kJ/cm)promoted coarse GBF formation,providing continuous paths for microcrack propagation.This direct intergranular crack progression caused brittle fracture and low toughness.Industrial cold cracking in the CGHAZ can thus be controlled by heat input optimization to maximize toughness.
基金supported by Major Science and Technology Project of Gansu Province(Grant No.23ZDGA010)National Natural Science Foundation of China(Grant No.51971105).
文摘The fabrication of 304L stainless welding wires with a diameter 1.6 mm by using electrochemical cold drawing(ECD)of bars with a diameter of 5.6 mm was investigated,as well as that via traditional cold drawing(TCD)for comparison.The results indicated that the dilute H_(2)SO_(4)aqueous solution was an appropriate electrolyte for ECD,and increasing the H_(2)SO_(4)concentration and current density within a range improved the corrosion rate and uniformity,leading to an easier and more coordinated deformation through uniformly distributing geometrically necessary dislocations and curved large-angle grain boundaries,and decreasing their density,and thus,an enhanced electrochemical plasticization(EP).Under the optimized electrochemical parameters(0.5 mol L^(-1)H_(2)SO_(4)electrolyte and current density of 12.2 mA cm^(-2)),the average cumulative reduction rate required for annealing was up to~34%,obviously higher than~20%of TCD due to the decreased work-hardening from the EP,so that the number of annealing was significantly reduced from 10 of TCD to 5,when the drawing pass was 23.In addition,the surface of the ECD wire was distinctly smoother and brighter than that of the TCD one.These findings confirm the large potential in engineering applications of the ECD technology based on the EP effect.
基金supported by National Natural Science Foundation of China(Grant No.52171032)Hebei Natural Science Foundation(Grant No.E2023501002)Fundamental Research Funds for the Central Universities(Grant No.2024GFYD003)。
文摘High entropy alloys(HEAs)have recently attracted significant attention due to their exceptional mechanical properties and potential applications across various fields.Friction stir welding and processing(FSW/P),as notable solid-state welding and processing techniques,have been proved effectiveness in enhancing microstructures and mechanical properties of HEAs.This review article summarizes the current status of FSW/P of HEAs.The welding materials and conditions used for FSW/P in HEAs are reviewed and discussed.The effects of FSW/P on the evolutions of grain structure,texture,dislocation,and secondary phase for different HEAs are highlighted.Furthermore,the influences of FSW/P on the mechanical properties of various HEAs are analyzed.Finally,potential applications,challenges,and future directions of FSW/P in HEAs are forecasted.Overall,FSW/P enable to refine grains of HEAs through dynamic recrystallization and to activate diverse deformation mechanisms of HEAs through tailoring phase structures,thereby significantly improving the strength,hardness,and ductility of both single-and dual-phase HEAs.Future progress in this field will rely on comprehensive optimization of processing parameters and alloy composition,integration of multi-scale modeling with advanced characterization for in-depth exploration of microstructural mechanisms,systematic evaluation of functional properties,and effective bridging of the gap between laboratory research and industrial application.The review aims to provide an overview of recent advancements in the FSW/P of HEAs and encourage further research in this area.
基金supported by the National Natural Science Foundation of China(Grant Nos.51805084 and 52474401)Guangdong Basic and Applied Basic Research Foundation(Grant Nos.2023B1515120086 and 2025A1515012873).
文摘The influence of oscillation amplitude on molten pool thermal history,weld morphology characteristics,microstructural evolution,and mechanical properties during laser oscillating welding of QP980 steel was systematically investigated.Results show that laser beam oscillation significantly regulates molten pool thermomechanical behavior through optimized spatial energy distribution,thereby enabling microstructural reconstruction and joint performance enhancement.As the oscillation amplitude increases from 0 to 0.8 mm,the molten pool duration extends to 1.7 times the original value,while peak temperature and average cooling rate decrease by 19%and 39%,respectively.This thermal regulation promotes weld surface width expansion from 0.72 to 1.07 mm.The welding mode undergoes a progressive transition from keyhole mode→transitional mode→conduction mode.This transformation effectively suppresses porosity defects,substantially reducing porosity from 1.8%to 0.15%.Microstructural analysis indicates that oscillation modifies the maximum temperature gradient direction within the molten pool,facilitating preferential growth of coarse columnar grains along the welding centerline to establish load-transfer-favorable crystallographic orientations.The synergistic effects of these factors substantially improve joint mechanical properties:lap joint shear load increases by 81.5%(7.6→13.8 kN),and fracture elongation is enhanced by 135%(0.98→2.3 mm).The operational principles of laser oscillation parameters on the welding quality of QP980 steel were elucidated,providing theoretical foundations for joining process optimization.
基金supported by the Alexander von Humboldt Foundation,and Deutsche Forschungsgemeinschaft(DFG,German Research Foundation,Project No.506270597 and No.466939224).
文摘A phase-field model including magnetic field induced dendrite fragmentation was established and applied to the cases with different initial crystal nuclear positions for AA5754 aluminum alloy electromagnetic laser beam welding.Compare the calculated results that include dendrite fragmentation caused by the thermal electromagnetic Lorentz force with the results that consider only the thermal electromagnetic Lorentz force,without fragmentation,at the characteristic time instants.Both in the early and late stages,the small fragmentation at the dendrite tip promotes the number of higher-order branches and their growth,especially in the direction perpendicular to the solidification.The later stage fragmentation has the possibility of breaking one grain into several,which verifies the possibility of grain refinement caused by dendrite fragmentation.The fracture surface caused by fragmentation also makes more solid-liquid interfaces and their growth.In addition,the cases with different initial nuclear positions were compared.The grain growth in the low-temperature zone can be inhibited by the equiaxed grains'fragmentation at the high-temperature area(179.8μm^(2) and 14.7% start at the center,115.4μm^(2) and 9.4% start at the high-temperature corner,134.3μm^(2) and 10.9%start at the low-temperature corner),which is another kind of grain refinement by the dendrite fragmentation.This kind of inhibition effect on grain growth in the low-temperature region will be enhanced with the increasing time interval between the two crystal nuclei’appearance(179.8μm^(2) and 14.7%when virtual grains appear at t=4.3803 s and t=4.3803 s,134.3μm^(2) and 10.9%at t=4.0977 s and t=3.9564 s,and 115.4μm^(2) and 9.4%at t=3.8151 s and t=3.5325 s).
基金Supported by the National Natural Science Foundation of China under Grant No.51975138the High-Tech Ship Scientific Research Project from the Ministry of Industry and Information Technology under Grant No.CJ05N20the National Defense Basic Research Project under Grant No.JCKY2023604C006.
文摘Marine thin plates are susceptible to welding deformation owing to their low structural stiffness.Therefore,the efficient and accurate prediction of welding deformation is essential for improving welding quality.The traditional thermal elastic-plastic finite element method(TEP-FEM)can accurately predict welding deformation.However,its efficiency is low because of the complex nonlinear transient computation,making it difficult to meet the needs of rapid engineering evaluation.To address this challenge,this study proposes an efficient prediction method for welding deformation in marine thin plate butt welds.This method is based on the coupled temperature gradient-thermal strain method(TG-TSM)that integrates inherent strain theory with a shell element finite element model.The proposed method first extracts the distribution pattern and characteristic value of welding-induced inherent strain through TEP-FEM analysis.This strain is then converted into the equivalent thermal load applied to the shell element model for rapid computation.The proposed method-particularly,the gradual temperature gradient-thermal strain method(GTG-TSM)-achieved improved computational efficiency and consistent precision.Furthermore,the proposed method required much less computation time than the traditional TEP-FEM.Thus,this study lays the foundation for future prediction of welding deformation in more complex marine thin plates.
基金financially supported by the National Natural Science Foundation of China(Nos.52034005,52227807,52104383,and 52222410)the Shaanxi Province National Science Fund for Distinguished Young Scholars,China(No.2022JC-24)+1 种基金the Key Research and Development Program of Shaanxi Province,China(No.2022JBGS2-01)the Central Guidance on Local Science and TechnologyDevelopment Fund of Shaanxi Province,China(No.2024ZY-JCYJ-04-09).
文摘Twinning-induced plasticity(TWIP)steel was processed using electrically assisted friction stir welding(EFSW).The microstructure,mechanical properties,and deformation behavior of the welded joints were systematically investigated.The results show that the average grain size was refined from 3.67μm in the base material(BM)to 1.39μm in the stir zone(SZ),while it increased to 4.19μm in the heat-affected zone(HAZ).The fraction of twin boundaries(TBs)decreased from 20.7%in the BM to 6.9%in the SZ and increased to24.5%in the HAZ.The ultimate tensile strength,yield strength,and elongation of the BM were 1021 MPa,505 MPa,and 65.8%,respectively.In comparison,the EFSW joint exhibited values of 1055 MPa,561 MPa,and 60.8%,corresponding to 103.3%,111.1%,and 92.4%of those of the BM,respectively.During tensile testing,plastic deformation was primarily concentrated in the BM,although both the SZ and HAZ also exhibited notable plastic deformation.Fracture ultimately occurred in the BM.
基金financially supported by the National Key R&D Program of China(No.2018YFA0707300)the National Natural Science Foundation of China(No.52374376)。
文摘The transformation of the dissimilar metals in the welding area into a single metal is an important method for achieving high-quality welded connection in the dissimilar metal laminated composite plate.In this study,a high-performance titanium/steel composite plate(TSCP)with pure titaniumization in the welding area was prepared by cold spraying,hot rolling and heat treatment processes.The results indicate that cold spraying achieves effective pre-composite deposition of titanium particles while inhibiting interfacial oxidation and Fe-Ti alloying reactions,producing a relatively dense pure titanium coating with a low porosity of only 1.2%.Hot rolling eliminates internal defects and promotes strong metallurgical bonding of the composite interface.The heat treatment promotes the recrystallization and reduces the dislocation density within the coating.The interfacial bonding strength of the welding area with pure titaniumization of TSCP is 257 MPa,and the tensile strength of that is 414 MPa,reaching 95.6%of the TSCP’s base material.
基金supported by the National Natural Science Foundation of China(Nos.52175206,52205187,52130509)the Science and Technology Planning Project of Guizhou Province,China(No.ZK[2022]013)。
文摘The microstructural evolution and mechanical properties of a vacuum electron beam welded aerospace 5B70 aluminum alloy joint were studied.Quantitative analyses of the phase composition,microstructural evolution,grain size,grain boundary density,and texture changes were performed by X-ray diffraction,scanning electron microscopy,and electron backscatter diffraction.The fusion zone(FZ)comprises equiaxed cellular crystals,and a fine~20μm-thick crystal layer forms in the transition zone(TZ)between the FZ and heat affected zone(HAZ).The HAZ closely resembles the base material(BM),retaining the original rolling microstructure.Mechanical property testing shows that the fine-grained layer in the TZ exhibits the highest nanohardness,with the FZ corresponding to the lowest microhardness.The welded-joint sample has lower yield strength,ultimate tensile strength,and elongation after fracture than the BM.These reductions of mechanical properties are primarily influenced by the grain size and distribution of the precipitated phases.
基金supported by the National Natural Science Foundation of China(Grant number U23A20625,U2141216,52375334)the Science and Technology Planning Project of Nansha District(Grant number 2025ZD003)the Science and Technology Program of Guangdong Province(Grant number 2023B1515250003).
文摘To improve the weld formation of underwater-welded Q355B steel and enhance its corrosion resistance,this study introduced pulsed laser welding technology into local dry underwater welding process,building upon continuous laser welding process.A systematic investigation was carried out covering process exploration,weld morphology,microstructure,and comprehensive properties.The results indicate that the pulsed laser weld seam exhibited a distinct ripple pattern on the surface,along with significantly less spatter compared to continuous laser weld seam.Both the weld penetration depth and weld bead width showed a decreasing trend with increasing pulse frequency.The weld metal was primarily composed of ferrite and martensite phases.As the pulse frequency increased,the ferrite content first rose and then declined,reaching a maximum of 39%at 80 Hz.The microhardness and tensile strength of the weld metal were both higher than those of the base material,and all tensile specimens fractured within the base metal during testing.Furthermore,the elongation initially increased and then decreased with rising pulse frequency.The weld produced at 80 Hz achieved the highest elongation of 23.1%,which was 8.9% higher than that of the continuous laser weld seam and reached 93.9% of the base material.Electrochemical corrosion tests revealed that the weld produced at 80 Hz exhibited the best corrosion resistance,reaching 67.0% of that of the base material,while the continuous laser weld seam attained only 47.3% of the base material.This study provides critical theoretical and data support for the process optimization and application of local dry underwater laser welding in the fabrication of marine engineering structures.
