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
Titanium alloy has the advantages of high strength,strong corrosion resistance,excellent high and low temperature mechanical properties,etc.,and is widely used in aerospace,shipbuilding,weapons and equipment,and other...Titanium alloy has the advantages of high strength,strong corrosion resistance,excellent high and low temperature mechanical properties,etc.,and is widely used in aerospace,shipbuilding,weapons and equipment,and other fields.In recent years,with the continuous increase in demand for medium-thick plate titanium alloys,corresponding welding technologies have also continued to develop.Therefore,this article reviews the research progress of deep penetration welding technology for medium-thick plate titanium alloys,mainly covering traditional arc welding,high-energy beam welding,and other welding technologies.Among many methods,narrow gap welding,hybrid welding,and external energy field assistance welding all contribute to improving the welding efficiency and quality of medium-thick plate titanium alloys.Finally,the development trend of deep penetration welding technology for mediumthick plate titanium alloys is prospected.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
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
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
Underwater welding plays a crucial role in repairing surface defects in submerged structures and improving their surface properties,particularly their resistance to corrosive-wear.Underwater surfacing layers were depo...Underwater welding plays a crucial role in repairing surface defects in submerged structures and improving their surface properties,particularly their resistance to corrosive-wear.Underwater surfacing layers were deposited using welding currents of 120,135 and 150 A.The microstructural characteristics of underwater-deposited surfacing layers were analyzed.Due to the limited heat input at 120 A welding current,the underwater-deposited surfacing layer primarily consists of polygonal ferrite(PF)and pearlite.In contrast,the surfacing layer deposited in air exhibited a microstructure composed of acicular ferrite(AF),ferrite with a second-phase arrangement(FSP),PF,and pearlite.Additionally,the high heat transfer rate underwater induces the formation of columnar grains.As the welding current increased,the presence of AF,FSP,PF,and pearlite reappeared in the microstructure,and a fine-grain zone formed on the surface due to rapid water cooling.The columnar grain structure within the surfacing layer became increasingly distinct with rising welding current.Moreover,the increased welding current led to an elevated volume fraction of AF packets,subsequently raising the proportion of low-angle grain boundaries and dislocation density.Smaller grain size,equiaxed grain morphology,and higher dislocation density are identified as key factors influencing the properties,leading to a 36%increase in microhardness and an improvement in the corrosive-wear resistance of the surfacing layer.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
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
The dissimilar 2B06 and 7B04 Al alloy joints were prepared by refill friction stir spot welding(RFSSW),and the microstructural evolution and corrosion behavior of the joints were investigated.Based on microstructural ...The dissimilar 2B06 and 7B04 Al alloy joints were prepared by refill friction stir spot welding(RFSSW),and the microstructural evolution and corrosion behavior of the joints were investigated.Based on microstructural analysis,the welded joints exhibit distinct microstructural zones,including the stir zone(SZ),thermomechanically affected zone(TMAZ),and heat-affected zone(HAZ).The grain size of each zone is in the order of HAZ>TMAZ>SZ.Notably,the TMAZ and HAZ contain significantly larger secondary-phase particles compared to the SZ,with particle size in the HAZ increasing at higher rotational speeds.Electrochemical tests indicate that corrosion susceptibility follows the sequence of HAZ>TMAZ>SZ>BM,with greater sensitivity observed at increased rotational speeds.Post-corrosion mechanical performance degradation primarily arises from crevice corrosion at joint overlaps,but not from the changes in the microstructure.展开更多
Laser twin-arc GTAW(LTA-GTAW)process has been developed by using the synergic interaction effects of laser and a coupled arc in a weld pool to achieve higher energy efficiency.In this study,bead-on-plate welding was c...Laser twin-arc GTAW(LTA-GTAW)process has been developed by using the synergic interaction effects of laser and a coupled arc in a weld pool to achieve higher energy efficiency.In this study,bead-on-plate welding was conducted on 8-mm-thick Q235B work-pieces to investigate the variation of hybrid arc profile,the influence of hybrid arc profile on weld forming,microstructure and mech-anical properties of the joint during the LTA-GTAW process.The influence of Laser-GTAW and LTA-GTAW methods on weld surface appearance,heat input per unit length,and weld metal microstructure were also demonstrated systematically.The LTA-GTAW can make the distribution of arc energy more reasonable in welding depth and width.When defocus is 0,I_(f)is 330 A,I_(b)is 240 A,laser power is 2.4 kW,and spacing between heat sources of tungsten electrode is 10 mm,the weld shape is better.Compared with Laser-GTAW,LTA-GTAW can achieve lower heat input at the same penetration depth,and the microstructure of the weld is refined.The tensile strength of the welded joint is 121.8%of the base material,and the fracture mode of the welded joint is ductile fracture,the comprehensive mechanical properties are better.展开更多
The need for lightweight structures is becoming increasingly critical in our demanding world.Therefore,highquality joints in similar material combinations or hybrid metal structures are equally crucial for various wel...The need for lightweight structures is becoming increasingly critical in our demanding world.Therefore,highquality joints in similar material combinations or hybrid metal structures are equally crucial for various welding techniques.This implies that adding auxiliary assisting sources during the process can significantly mitigate the problems associated with inadequate softening,a known drawback of the friction stir welding(FSW)process.It has been discovered that laser beam preheating can soften the weld region of the workpieces when implemented in a pre-planned manner.Subsequently,it induces a temperature rise in the workpieces by enhancing their plasticization characteristics.A satisfactory laser beam induces changes in the materials'condition,facilitating a more straightforward joining process than the traditional FSW process.Moreover,it is even easier to join aluminum alloys to other harder metals,e.g.,steel or copper,let alone joining aluminum alloy,magnesium alloy,and nickel-based superalloy.This article presents the influence of incorporating a laser beam source as an auxiliary energy source during the FSW process.It discusses the most recent progress on changes in the behaviour of joints produced with and without laser beam sources,particularly in terms of temperature distribution,appearance,joint formation,microstructure,and mechanical properties.Furthermore,the benefits of laser-assisted FSW(LAFSW)joints compared to traditional FSW have been thoroughly highlighted.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
Friction stir lap welding of AA2195 Al-Li alloy and Ti alloy was conducted to investigate the formation,microstructure,and mechanical properties of the joints.Results show that under different welding parameters,with ...Friction stir lap welding of AA2195 Al-Li alloy and Ti alloy was conducted to investigate the formation,microstructure,and mechanical properties of the joints.Results show that under different welding parameters,with the decrease in welding heat input,the weld surface is smoother.The Ti/Al joint interface is flat without obvious Ti and Al mixed structure,and the hook structure is not formed under optimal parameters.Due to the enhanced breaking effect of the stirring head,the hook structural defects and intermetallic compounds are more likely to form at the Ti/Al interface at high rotational speed of 1000 r/min,thereby deteriorating the mechanical properties of joints.Decreasing the heat input is beneficial to hardness enhancement of the aluminum alloy in the weld nugget zone.Under the optimal parameters of rotation speed of 800 r/min and welding speed of 120 mm/min,the maximum tensile shear strength of joint is 289 N/mm.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financially supported by the Key Research and Development Program of Ningbo(Grant No.2023Z098)Natural Science Foundation of Inner Mongolia(Grant No.2023MS05040)+1 种基金Shenyang Collaborative Innovation Center Project for Multiple Energy Fields Composite Processing of Special Materials(Grant No.JG210027)Shenyang Key Technology Special Project of The Open Competition Mechanism to Select the Best Solution(Grant Nos.2022210101000827,2022-0-43-048).
文摘Titanium alloy has the advantages of high strength,strong corrosion resistance,excellent high and low temperature mechanical properties,etc.,and is widely used in aerospace,shipbuilding,weapons and equipment,and other fields.In recent years,with the continuous increase in demand for medium-thick plate titanium alloys,corresponding welding technologies have also continued to develop.Therefore,this article reviews the research progress of deep penetration welding technology for medium-thick plate titanium alloys,mainly covering traditional arc welding,high-energy beam welding,and other welding technologies.Among many methods,narrow gap welding,hybrid welding,and external energy field assistance welding all contribute to improving the welding efficiency and quality of medium-thick plate titanium alloys.Finally,the development trend of deep penetration welding technology for mediumthick plate titanium alloys is prospected.
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(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funded by the Open Research Fund of National Engineering Research Center of Water Resources Efficient Utilization and Engineering Safety(No.GJGCZX-JJ-202408).
文摘Underwater welding plays a crucial role in repairing surface defects in submerged structures and improving their surface properties,particularly their resistance to corrosive-wear.Underwater surfacing layers were deposited using welding currents of 120,135 and 150 A.The microstructural characteristics of underwater-deposited surfacing layers were analyzed.Due to the limited heat input at 120 A welding current,the underwater-deposited surfacing layer primarily consists of polygonal ferrite(PF)and pearlite.In contrast,the surfacing layer deposited in air exhibited a microstructure composed of acicular ferrite(AF),ferrite with a second-phase arrangement(FSP),PF,and pearlite.Additionally,the high heat transfer rate underwater induces the formation of columnar grains.As the welding current increased,the presence of AF,FSP,PF,and pearlite reappeared in the microstructure,and a fine-grain zone formed on the surface due to rapid water cooling.The columnar grain structure within the surfacing layer became increasingly distinct with rising welding current.Moreover,the increased welding current led to an elevated volume fraction of AF packets,subsequently raising the proportion of low-angle grain boundaries and dislocation density.Smaller grain size,equiaxed grain morphology,and higher dislocation density are identified as key factors influencing the properties,leading to a 36%increase in microhardness and an improvement in the corrosive-wear resistance of the surfacing layer.
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.
基金supported by the National Natural Science Foundation of China (Nos. 52075449, 51975480)。
文摘The dissimilar 2B06 and 7B04 Al alloy joints were prepared by refill friction stir spot welding(RFSSW),and the microstructural evolution and corrosion behavior of the joints were investigated.Based on microstructural analysis,the welded joints exhibit distinct microstructural zones,including the stir zone(SZ),thermomechanically affected zone(TMAZ),and heat-affected zone(HAZ).The grain size of each zone is in the order of HAZ>TMAZ>SZ.Notably,the TMAZ and HAZ contain significantly larger secondary-phase particles compared to the SZ,with particle size in the HAZ increasing at higher rotational speeds.Electrochemical tests indicate that corrosion susceptibility follows the sequence of HAZ>TMAZ>SZ>BM,with greater sensitivity observed at increased rotational speeds.Post-corrosion mechanical performance degradation primarily arises from crevice corrosion at joint overlaps,but not from the changes in the microstructure.
基金supported by the Industrial Innovation Major Technology Global Unveiling Project of Jining City(2022JBZP004)Taishan Scholars Project.
文摘Laser twin-arc GTAW(LTA-GTAW)process has been developed by using the synergic interaction effects of laser and a coupled arc in a weld pool to achieve higher energy efficiency.In this study,bead-on-plate welding was conducted on 8-mm-thick Q235B work-pieces to investigate the variation of hybrid arc profile,the influence of hybrid arc profile on weld forming,microstructure and mech-anical properties of the joint during the LTA-GTAW process.The influence of Laser-GTAW and LTA-GTAW methods on weld surface appearance,heat input per unit length,and weld metal microstructure were also demonstrated systematically.The LTA-GTAW can make the distribution of arc energy more reasonable in welding depth and width.When defocus is 0,I_(f)is 330 A,I_(b)is 240 A,laser power is 2.4 kW,and spacing between heat sources of tungsten electrode is 10 mm,the weld shape is better.Compared with Laser-GTAW,LTA-GTAW can achieve lower heat input at the same penetration depth,and the microstructure of the weld is refined.The tensile strength of the welded joint is 121.8%of the base material,and the fracture mode of the welded joint is ductile fracture,the comprehensive mechanical properties are better.
基金supported by the National Natural Science Foundation of China(Grant No.52035005)。
文摘The need for lightweight structures is becoming increasingly critical in our demanding world.Therefore,highquality joints in similar material combinations or hybrid metal structures are equally crucial for various welding techniques.This implies that adding auxiliary assisting sources during the process can significantly mitigate the problems associated with inadequate softening,a known drawback of the friction stir welding(FSW)process.It has been discovered that laser beam preheating can soften the weld region of the workpieces when implemented in a pre-planned manner.Subsequently,it induces a temperature rise in the workpieces by enhancing their plasticization characteristics.A satisfactory laser beam induces changes in the materials'condition,facilitating a more straightforward joining process than the traditional FSW process.Moreover,it is even easier to join aluminum alloys to other harder metals,e.g.,steel or copper,let alone joining aluminum alloy,magnesium alloy,and nickel-based superalloy.This article presents the influence of incorporating a laser beam source as an auxiliary energy source during the FSW process.It discusses the most recent progress on changes in the behaviour of joints produced with and without laser beam sources,particularly in terms of temperature distribution,appearance,joint formation,microstructure,and mechanical properties.Furthermore,the benefits of laser-assisted FSW(LAFSW)joints compared to traditional FSW have been thoroughly highlighted.
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National Natural Science Foundation of China(52275349)Key Research and Development Program of Shandong Province(2021ZLGX01)。
文摘Friction stir lap welding of AA2195 Al-Li alloy and Ti alloy was conducted to investigate the formation,microstructure,and mechanical properties of the joints.Results show that under different welding parameters,with the decrease in welding heat input,the weld surface is smoother.The Ti/Al joint interface is flat without obvious Ti and Al mixed structure,and the hook structure is not formed under optimal parameters.Due to the enhanced breaking effect of the stirring head,the hook structural defects and intermetallic compounds are more likely to form at the Ti/Al interface at high rotational speed of 1000 r/min,thereby deteriorating the mechanical properties of joints.Decreasing the heat input is beneficial to hardness enhancement of the aluminum alloy in the weld nugget zone.Under the optimal parameters of rotation speed of 800 r/min and welding speed of 120 mm/min,the maximum tensile shear strength of joint is 289 N/mm.
