The constant amplitude loading fatigue tests were carried out on the 6061/7075 aluminum alloy TIG fillet welded lap specimens in this study,and the weld seam cross-section hardness was measured.The experimental result...The constant amplitude loading fatigue tests were carried out on the 6061/7075 aluminum alloy TIG fillet welded lap specimens in this study,and the weld seam cross-section hardness was measured.The experimental results show that most specimens mainly failed at the 7075 side weld toes even though the base material tensile strength of 7075 is higher than that of 6061.The maximum stress-strain concentration in the two finite element models is located at the 7075 side weld toe,which is basically consistent with the actual fracture location.The weld zone on the 7075 side experiences severe material softening,with a large gradient.However,the Vickers hardness value on the 6061 side negligibly changes and fluctuates around 70 HV.No obvious defects are found on the fatigue fracture,but a large number of secondary cracks appear.Cracks germinate from the weld toe and propagate in the direction of the plate thickness.Weld reinforcement has a serious impact on fatigue life.Fatigue life will decrease exponentially as the weld reinforcement increases under low stress.It is found that the notch stress method can give a better fatigue life prediction for TIG weldments,and the errors of the predicted results are within the range of two factors,while the prediction accuracy decreases under low stress.The equivalent structural stress method can also be used for fatigue life prediction of TIG weldments,but the errors of prediction results are within the range of three factors,and the accuracy decreases under high stress.展开更多
The quality of rebar welds directly impacts the overall service performance of highway infrastructure.However,current assessments of weld appearance quality primarily rely on traditional inspection methods such as man...The quality of rebar welds directly impacts the overall service performance of highway infrastructure.However,current assessments of weld appearance quality primarily rely on traditional inspection methods such as manual visual inspection,which suffer from significant limitations in accuracy,reliability,and efficiency.Given the increasing demand for safety performance inspections of highway infrastructure in China,traditional methods struggle to meet modern rapid inspection requirements.Therefore,this study proposes the design of a portable,non-destructive inspection device for rebar weld appearance,utilizing visible light vision and line-structured light 3D scanning technology.The device is equipped with an STM32 master control chip to manage encoder reading,scanning laser control,ring fill light,industrial camera synchronization,image acquisition,and serial port command transmission.Additionally,a weld image processing and detection software system was developed to receive,store,and identify weld defects.A field inspection prototype was created and subjected to various defect weld detection experiments in a laboratory setting.Experimental results demonstrate that the device can accurately measure weld parameters by acquiring multimodal images,fulfilling defect detection requirements.The device features high detection accuracy,portability,and user-friendliness,making it significant for the objective inspection and evaluation of rebar weld appearance and welding quality.展开更多
The study aimed to address the issue of elevated residual stress levels in dissimilar girth welds of cast steel joints.To achieve this,the hybrid welding technology,which yields high welding speeds while simultaneousl...The study aimed to address the issue of elevated residual stress levels in dissimilar girth welds of cast steel joints.To achieve this,the hybrid welding technology,which yields high welding speeds while simultaneously reducing residual stresses,has been introduced.This study utilizes a numerical simulation method to investigate the temperature and residual stress field in the hybrid welding of G20Mn5 casting-Q355 low-alloy steel welded pipe.A com-parison of the findings of this study with those of other welding processes revealed the technological advantages of hybrid welding.The research outcomes show that due to geometric discontinuities and material differences,the temperature field of the joint exhibits uneven distribution characteristics,and the peak temperatures on the Q355 steel side exceeds those on the G20Mn5 steel side.An evident stress gra-dient is present in the residual stress field of the joint post-welding,with peak stress located at the weld root on the Q355 steel.Compared with arc welding,the hybrid welding leads to decreased residual stresses and deformation,with high stress outside the heat-affected zone diminishing rapidly.Furthermore,it significantly improves the welding efficiency.This study elucidates the distribution and underlying causes of thermal and residual stress fields in dissimilar girth welds.This serves as a foundation for the application of hybrid welding technology in welded cast steel joints.展开更多
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
In this work,microstructure and mechanical properties of Mg weld with addition of carbon nanotubes(CNTs)and Ti C particles were investigated.The results showed that the weld microstructure was mainly presented as equi...In this work,microstructure and mechanical properties of Mg weld with addition of carbon nanotubes(CNTs)and Ti C particles were investigated.The results showed that the weld microstructure was mainly presented as equiaxed grains with almost high angle grain boundaries.The introduction of reinforcements promoted the formation of precipitates and refined the grains effectively,the average grain size was refined by 51%and 23%with addition of CNTs and Ti C particles,respectively.The dislocation density and the fraction of CSL boundaries were increased with addition of CNTs,while those were decreased with addition of Ti C particles.Besides,the infrequent{10¯13}contraction twins formed within the weld due to the stress concentration caused by dislocation accumulation,which contributed to theΣ29 CSL boundary.The ultimate tensile strength and elongation rate were increased by 13.5%and 40%with addition of CNTs,while the ultimate tensile strength and micro-hardness were increased by 14.8%and 20.9%with addition of Ti C particles.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
Direct friction welding of Ti Al alloy to 40 Cr steel rods was conducted, and the microstructure and mechanical properties of the resultant joints in as-welded and post-weld heat treatment（PWHT） states were investig...Direct friction welding of Ti Al alloy to 40 Cr steel rods was conducted, and the microstructure and mechanical properties of the resultant joints in as-welded and post-weld heat treatment（PWHT） states were investigated. The martensitic transformation occurred and brittle Ti C phase formed near the interface due to C agglomeration, which degraded the joint strength and increased the microhardness at the interface in as-welded state. Feathery and Widmanstatten structure generated near the interface on Ti Al alloy side. After PWHT at 580 °C and 630 °C for 2 h, the sorbite formed and C dispersed at the interface, leading to the increase of the joint strength from 86 MPa in as-welded state to 395 MPa and 330 MPa, respectively. The heat-treated specimen fractured with quasi-cleavage features through the zone 1 mm away from the interface on TiA l alloy side, but the as-welded specimen failed through the interface.展开更多
The microstructure, microhardness and quasi-static failure behavior of resistance spot welds of AA6111-T4 aluminum alloy were experimentally investigated. Optical metallography and high-resolution hardness traverses w...The microstructure, microhardness and quasi-static failure behavior of resistance spot welds of AA6111-T4 aluminum alloy were experimentally investigated. Optical metallography and high-resolution hardness traverses were utilized to characterize the weld nugget, heat affected zone and base metal. The AA6111 spot welds displayed a softer nugget and hardened heat affected zone, compared with the base metal. The through-thickness hardness of the base metal sheet was not constant and had to be carefully considered to determine the effect of welding on material properties. Quasi-static lap-shear tensile tests were used to determine the failure load and failure mode. All tensile specimens failed through the interfacial fracture. This failure mode is consistent with the observed reduced hardness in the weld nugget.展开更多
Defect-free dissimilar Al/zinc coated steel and Al/AlSi coated steel welds were successfully fabricated by refill friction stir spot welding. However, Al alloy and uncoated steel could not be welded under the same wel...Defect-free dissimilar Al/zinc coated steel and Al/AlSi coated steel welds were successfully fabricated by refill friction stir spot welding. However, Al alloy and uncoated steel could not be welded under the same welding condition. Al-Zn eutectic layer formed at the Al/zinc coated steel interface showed nonuniformity in thickness and nanoscale intermetallic(IMC) produced was discontinuous. The bonding formation between the Al-Zn layer and the surrounding materials was attributed to a liquid/solid reaction mechanism. Bonding formation at Al alloy and AlSi coated steel interface was attributed to a solid/solid reaction mechanism, as the joining process did not involve with melting of base metals or AlSi coating materials. Kissing bond formed at the weld boundary acted as a crack initiation and propagation site,and the present study showed that weld strength of Al 5754/AlSi coated steel was greatly influenced by properties of original IMC layer.展开更多
With the development of the manufacturing technology, electron beam welding（EBW） is capable of producing titanium alloy large parts in aero fields. To increase the applications and improve the properties, EBW with b...With the development of the manufacturing technology, electron beam welding（EBW） is capable of producing titanium alloy large parts in aero fields. To increase the applications and improve the properties, EBW with beam oscillation was investigated on TC4-DT alloy with50 mm thickness. We detected the welding samples by X-ray NDT, observed the microstructures of the welds, and tested the fatigue properties of the joints. The results showed that EBW with beam oscillation improved the weld morphology as well as welding quality, and the microstructure homogeneity of the welds and HAZ along the weld penetration were also improved. The fatigue properties of the joints with beam oscillation were more excellent than those of conventional EBW, even equal to those of the base metal under high stresses. The influences of the processing and the microstructure on the properties with beam oscillation were discussed.展开更多
Brittle fracture occurs frequently in rails and thermite welded joints, which intimidates the security and reliability of railway ser- vice. Railways in cold regions, such as Qinghai-Tibet Railway, make the problem of...Brittle fracture occurs frequently in rails and thermite welded joints, which intimidates the security and reliability of railway ser- vice. Railways in cold regions, such as Qinghai-Tibet Railway, make the problem of brittle fi＇acture in rails even worse. A series of tests such as uniaxial tensile tests, Charpy impact tests, and three-point bending tests were carried out at low temperature to investigate the mechanical properties and fracture toughness of U71Mn and U75V rail steels and their thermite welds. Fracture micromechanisms were analyzed by scanning electron microscopy （SEM） on the fracture surfaces of the tested specimens. The ductility indices （percentage elongation aider frac- ture and percentage reduction of area） and the toughness indices （Charpy impact energy Ak and plane-strain fracture toughness Kic） of the two kinds of rail steels and the corresponding thermite welds all decrease as the temperature decreases. The thermite welds are more critical to fracture than the rail steel base metals, as indicated by a higher yield-to-ultimate ratio and a much lower Charpy impact energy. U71Mn rail steel is relatively higher in toughness than U75V, as demonstrated by larger Ak and Klc values. Therefore, U71Mn rail steel and the corresponding thermite weld are recommended in railway construction and maintenance in cold regions.展开更多
In this study,the microstructures and mechanical properties of 9%Cr reduced activation ferritic/martensitic（RAFM） steel friction stir welded joints were investigated.When a W-Re tool is used,the recommended welding ...In this study,the microstructures and mechanical properties of 9%Cr reduced activation ferritic/martensitic（RAFM） steel friction stir welded joints were investigated.When a W-Re tool is used,the recommended welding parameters are 300 rpm rotational speed,60 mm/min welding speed and10 kn axial force.In stir zone（SZ）,austenite dynamic recrystallization induced by plastic deformation and the high cooling rates lead to an obvious refinement of prior austenite grains and martensite laths.The microstructure in SZ contains lath martensite with high dislocation density,a lot of nano-sized MX and M3C phase particles,but almost no M23C6 precipitates.In thermal mechanically affect zone（TMAZ）and heat affect zone（HAZ）,refinement of prior austenite and martensitic laths and partial dissolution of M（23）C6 precipitates are obtained at relatively low rotational speed.However,with the increase of heat input,coarsening of martensitic laths,prior austenite grains,and complete dissolution of M23C6 precipitates are achieved.Impact toughness of SZ at-20℃ is slightly lower than that of base material（BM）,and exhibits a decreasing trend with the increase of rotational speed.展开更多
The activated TIG(ATIG) welding process mainly focuses on increasing the depth of penetration and the reduction in the width of weld bead has not been paid much attention.The shape of a weld in terms of its width-to-d...The activated TIG(ATIG) welding process mainly focuses on increasing the depth of penetration and the reduction in the width of weld bead has not been paid much attention.The shape of a weld in terms of its width-to-depth ratio known as aspect ratio has a marked influence on its solidification cracking tendency.The major influencing ATIG welding parameters,such as electrode gap,travel speed,current and voltage,that aid in controlling the aspect ratio of DSS joints,must be optimized to obtain desirable aspect ratio for DSS joints.Hence in this study,the above parameters of ATIG welding for aspect ratio of ASTM/UNS S32205 DSS welds are optimized by using Taguchi orthogonal array(OA)experimental design and other statistical tools such as Analysis of Variance(ANOVA) and Pooled ANOVA techniques.The optimum process parameters are found to be 1 mm electrode gap,130 mm/min travel speed,140 A current and 12 V voltage.The aspect ratio and the ferrite content for the DSS joints fabricated using the optimized ATIG parameters are found to be well within the acceptable range and there is no macroscopically evident solidification cracking.展开更多
The effects of pulsing current parameters on weld pool geometry namely front height, back height, front width and back width of pulse current gas tungsten arc welded （GTAW） titanium alloy was analysed. Four factors,...The effects of pulsing current parameters on weld pool geometry namely front height, back height, front width and back width of pulse current gas tungsten arc welded （GTAW） titanium alloy was analysed. Four factors, five levels, central composite design were used to develop empirical relationships, incorporating pulsed current parameters and weld pool geometry.展开更多
In marine application,marine grade steel is generally used for haul and superstructures.However,aluminum has also become a good choice due to its lightweight qualities,while rusting of aluminum is minimal compared to ...In marine application,marine grade steel is generally used for haul and superstructures.However,aluminum has also become a good choice due to its lightweight qualities,while rusting of aluminum is minimal compared to steel.In this paper a study on friction stir welding of aluminum alloys was presented.The present investigation deals with the effects of different friction stir welding tool geometries on mechanical strength and the microstructure properties of aluminum alloy welds.Three distinct tool geometries with different types of shoulder and tool probe profiles were used in the investigation according to the design matrix.The effects of each tool shoulder and probe geometry on the weld was evaluated.It was also observed that the friction stir weld tool geometry has a significant effect on the weldment reinforcement,microhardness,and weld strength.展开更多
Self-shielded flux-cored wire is a convenient and efficient consumable for pipeline field girth welding because of its self-protection characteristic and high deposition rate, especially for remote construction sites ...Self-shielded flux-cored wire is a convenient and efficient consumable for pipeline field girth welding because of its self-protection characteristic and high deposition rate, especially for remote construction sites in rugged terrain. From the perspective of pipeline safety, the impact toughness of the girth welds is an important factor in pipeline integrity ,which determines the crack arrest behavior in the girth welds. Therefore, improving the girth weld impact toughness is of primary importance in the field of pipeline girth welding. Three self-shielded flux-cored wires comprising different chemical composition systems have been applied to large diameter X80 UOE （U-ing-O- ing-Expanding） pipeline semi-automatic girth welding,and the impact toughness of the welds has been evaluated by girth weld chemical composition analysis and microstructural analysis using scanning electron microscopy （SEM） and energy dispersive spectrometry （EDS） to investigate pipeline girth weld impact toughness and find ways to improve it. This helps in determining the main factors that influence girth weld impact toughness. Pipeline girth weld impact toughness is mainly determined by the final microstructure produced in the solid-state phase transition. In the as-weld state,acicular ferrite （AF） and fine bainite （FB） are a benefit to the impact toughness. For multilayer semiautomatic self-shielded flux-cored wire welding, the normalizing and tempering function of the latter beads to the initial beads plays an important role in the transition of girth weld microstructure, which affects the impact toughness. The original AF and FB and the corresponding heat treatment microstructure of the fine and uniform block ferrite and pearlite result in very good impact toughness. The following two mechanisms are found to promote the production of AF and FB in the girth weld. First, elements promoting the broadening of the austenitic region, such as Ni, C, Cu, and Mn, induce low temperature phase transitions and restrain the opposing function of Al, which is a benefit to the production of AF and FB. Second, dispersed high-melting-point inclusions, especially Al2O3 ,induce the nucleated production of AF. The advantageous function of inclusions is determined by their shape, distribution, and dimension. Dispersed spherical inclusions of small dimension are a benefit to the production of AF, and result in good impact toughness.展开更多
Base metals of domestic pipeline steels were used to study the effect of Mn on corrosion properties of SSCC(Sulfide Stress Corrosion Cracking), and welds were carried out to study the effect of MnS on corrosion proper...Base metals of domestic pipeline steels were used to study the effect of Mn on corrosion properties of SSCC(Sulfide Stress Corrosion Cracking), and welds were carried out to study the effect of MnS on corrosion properties of HIC (Hydrogen Induced Cracking) both in solutions with wet hydrogen sulfide(H_2S). They were respectively conducted by referring to the standards of SSCC and HIC. Testing results revealed that with the increase of content Mn, the resistance of SSCC will be decreased, from the point of metallurgic view, and it is Mn element not C element to lead to the testing results of SSCC. Meanwhile, even under the condition without inclusions MnS, HIC in welds still occurred. That is to say, MnS is not necessary for HIC, the presence of local banded structures in which Mn and P are inclined to aggregate cause to the phenomena of HIC.展开更多
As a vehicle passing through a track with different weld irregularities, the dynamic performance of track com- ponents is investigated in detail by using a coupled vehi- cle-track model. In the model, the vehicle is m...As a vehicle passing through a track with different weld irregularities, the dynamic performance of track com- ponents is investigated in detail by using a coupled vehi- cle-track model. In the model, the vehicle is modeled as a multi-body system with 35 degrees of freedom, and a Timoshenko beam is used to model the rails which are dis- cretely supported by sleepers. In the track model, the sleepers are modeled as rigid bodies accounting for their vertical, lat- eral and rolling motions and assumed to move backward at a constant speed to simulate the vehicle running along the track at the same speed. In the study of the coupled vehicle and track dynamics, the Hertizian contact theory and the theory proposed by Shen-Hedrick-Elkins are, respectively, used to calculate normal and creep forces between the wheel and the rails. In the calculation of the normal forces, the coefficient of the normal contact stiffness is determined by transient contact condition of the wheel and rail surface. In the calcu- lation of the creepages, the lateral, roll-over motions of the rail and the fact that the relative velocity between the wheel and rail in their common normal direction is equal to zero are simultaneously taken into account. The motion equations of the vehicle and track are solved by means of an explicit integration method, in which the rail weld irregularities are modeled as local track vertical deviations described by some ideal cosine functions. The effects of the train speed, the axle load, the wavelength and depth of the irregularities, and the weld center position in a sleeper span on the wheel-rail impact loading are analyzed. The numerical results obtained are greatly useful in the tolerance design of welded rail pro- file irregularity caused by hand-grinding after rail welding and track maintenances.展开更多
It is difficult to achieve Al/Cu dissimilar welds with good mechanical properties for medium-thick plates due to the inherent high heat generation rate at the shoulder-workpiece contact interface in conventional frict...It is difficult to achieve Al/Cu dissimilar welds with good mechanical properties for medium-thick plates due to the inherent high heat generation rate at the shoulder-workpiece contact interface in conventional friction stir welding.Thus,doubleside friction stir welding is innovatively applied to join 12-mm medium-thick 6061-T6 aluminum alloy and pure copper dissimilar plates,and the effect of welding speeds on the joint microstructure and mechanical properties of Al/Cu welds is systematically analyzed.It reveals that a sound Al/Cu joint without macroscopic defects can be achieved when the welding speed is lower than 180 mm/min,while a nonuniform relatively thick intermetallic compound(IMC)layer is formed at the Al/Cu interface,resulting in lots of local microcracks within the first-pass weld under the plunging force of the tool during friction stir welding of the second-pass,and seriously deteriorates the mechanical properties of the joint.With the increase of welding speed to more than 300 mm/min void defects appear in the joint,but the joint properties are still better than the welds performed at low welding speed conditions since a continuous uniform thin IMCs layer is formed at the Al/Cu interface.The maximum tensile strength and elongation of Al/Cu weld are,respectively,135.11 MPa and 6.06%,which is achieved at the welding speed of 400 mm/min.In addition,due to the influence of welding distortion of the first-pass weld,the secondpass weld is more prone to form void defects than the first-pass weld when the same plunge depth is applied on both sides.The double-side friction stir welding is proved to be a good method for dissimilar welding of medium-thick Al/Cu plates.展开更多
The influence of different welding processes on the mechanical properties and the corresponding variation in the microstructural features have been investigated for the dissimilar weldments of 18% Ni maraging steel 25...The influence of different welding processes on the mechanical properties and the corresponding variation in the microstructural features have been investigated for the dissimilar weldments of 18% Ni maraging steel 250 and AISI 4130 steel. The weld joints are realized through two different fusion welding processes, tungsten inert arc welding(TIG) and laser beam welding(LBW), in this study. The dissimilar steel welds were characterized through optical microstructures, microhardness survey across the weldment and evaluation of tensile properties. The fiber laser beam welds have demonstrated superior mechanical properties and reduced heat affected zone as compared to the TIG weldments.展开更多
基金Partially funded by the National Natural Science Foundation of China(No.51065012)。
文摘The constant amplitude loading fatigue tests were carried out on the 6061/7075 aluminum alloy TIG fillet welded lap specimens in this study,and the weld seam cross-section hardness was measured.The experimental results show that most specimens mainly failed at the 7075 side weld toes even though the base material tensile strength of 7075 is higher than that of 6061.The maximum stress-strain concentration in the two finite element models is located at the 7075 side weld toe,which is basically consistent with the actual fracture location.The weld zone on the 7075 side experiences severe material softening,with a large gradient.However,the Vickers hardness value on the 6061 side negligibly changes and fluctuates around 70 HV.No obvious defects are found on the fatigue fracture,but a large number of secondary cracks appear.Cracks germinate from the weld toe and propagate in the direction of the plate thickness.Weld reinforcement has a serious impact on fatigue life.Fatigue life will decrease exponentially as the weld reinforcement increases under low stress.It is found that the notch stress method can give a better fatigue life prediction for TIG weldments,and the errors of the predicted results are within the range of two factors,while the prediction accuracy decreases under low stress.The equivalent structural stress method can also be used for fatigue life prediction of TIG weldments,but the errors of prediction results are within the range of three factors,and the accuracy decreases under high stress.
基金Supported by the Central Public-Interest Scientific Institution Basal Research Fund(2023-9062)the Transport Power Pilot Project(2021-C334)。
文摘The quality of rebar welds directly impacts the overall service performance of highway infrastructure.However,current assessments of weld appearance quality primarily rely on traditional inspection methods such as manual visual inspection,which suffer from significant limitations in accuracy,reliability,and efficiency.Given the increasing demand for safety performance inspections of highway infrastructure in China,traditional methods struggle to meet modern rapid inspection requirements.Therefore,this study proposes the design of a portable,non-destructive inspection device for rebar weld appearance,utilizing visible light vision and line-structured light 3D scanning technology.The device is equipped with an STM32 master control chip to manage encoder reading,scanning laser control,ring fill light,industrial camera synchronization,image acquisition,and serial port command transmission.Additionally,a weld image processing and detection software system was developed to receive,store,and identify weld defects.A field inspection prototype was created and subjected to various defect weld detection experiments in a laboratory setting.Experimental results demonstrate that the device can accurately measure weld parameters by acquiring multimodal images,fulfilling defect detection requirements.The device features high detection accuracy,portability,and user-friendliness,making it significant for the objective inspection and evaluation of rebar weld appearance and welding quality.
基金The SEU Innovation Capability Enhancement Plan for Doctoral Students(No.CXJH_SEU 24115)Marine Economic Development Project of Guangdong Province(No.GDNRC[2022]25).
文摘The study aimed to address the issue of elevated residual stress levels in dissimilar girth welds of cast steel joints.To achieve this,the hybrid welding technology,which yields high welding speeds while simultaneously reducing residual stresses,has been introduced.This study utilizes a numerical simulation method to investigate the temperature and residual stress field in the hybrid welding of G20Mn5 casting-Q355 low-alloy steel welded pipe.A com-parison of the findings of this study with those of other welding processes revealed the technological advantages of hybrid welding.The research outcomes show that due to geometric discontinuities and material differences,the temperature field of the joint exhibits uneven distribution characteristics,and the peak temperatures on the Q355 steel side exceeds those on the G20Mn5 steel side.An evident stress gra-dient is present in the residual stress field of the joint post-welding,with peak stress located at the weld root on the Q355 steel.Compared with arc welding,the hybrid welding leads to decreased residual stresses and deformation,with high stress outside the heat-affected zone diminishing rapidly.Furthermore,it significantly improves the welding efficiency.This study elucidates the distribution and underlying causes of thermal and residual stress fields in dissimilar girth welds.This serves as a foundation for the application of hybrid welding technology in welded cast steel joints.
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financially supported by the National Natural Science Foundation of China(grant nos.52275364 and 52025052)。
文摘In this work,microstructure and mechanical properties of Mg weld with addition of carbon nanotubes(CNTs)and Ti C particles were investigated.The results showed that the weld microstructure was mainly presented as equiaxed grains with almost high angle grain boundaries.The introduction of reinforcements promoted the formation of precipitates and refined the grains effectively,the average grain size was refined by 51%and 23%with addition of CNTs and Ti C particles,respectively.The dislocation density and the fraction of CSL boundaries were increased with addition of CNTs,while those were decreased with addition of Ti C particles.Besides,the infrequent{10¯13}contraction twins formed within the weld due to the stress concentration caused by dislocation accumulation,which contributed to theΣ29 CSL boundary.The ultimate tensile strength and elongation rate were increased by 13.5%and 40%with addition of CNTs,while the ultimate tensile strength and micro-hardness were increased by 14.8%and 20.9%with addition of Ti C particles.
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Project(51374048)supported by the National Natural Science Foundation of ChinaProject(2011CB013402)supported by the National Basic Research Program of ChinaProject(AWPT-Z01)supported by the State Key Laboratory of Advanced Welding and Joining,China
文摘Direct friction welding of Ti Al alloy to 40 Cr steel rods was conducted, and the microstructure and mechanical properties of the resultant joints in as-welded and post-weld heat treatment（PWHT） states were investigated. The martensitic transformation occurred and brittle Ti C phase formed near the interface due to C agglomeration, which degraded the joint strength and increased the microhardness at the interface in as-welded state. Feathery and Widmanstatten structure generated near the interface on Ti Al alloy side. After PWHT at 580 °C and 630 °C for 2 h, the sorbite formed and C dispersed at the interface, leading to the increase of the joint strength from 86 MPa in as-welded state to 395 MPa and 330 MPa, respectively. The heat-treated specimen fractured with quasi-cleavage features through the zone 1 mm away from the interface on TiA l alloy side, but the as-welded specimen failed through the interface.
基金Project(0211005303101)supported by the Fundamental Research Funds for the Central Universities,ChinaInternational Cooperation Project(2014DFA51270)supported by Ministry of Science and Technology of ChinaProject(2009-5043R)supported by the Ford Motor Company University Research Program,USA
文摘The microstructure, microhardness and quasi-static failure behavior of resistance spot welds of AA6111-T4 aluminum alloy were experimentally investigated. Optical metallography and high-resolution hardness traverses were utilized to characterize the weld nugget, heat affected zone and base metal. The AA6111 spot welds displayed a softer nugget and hardened heat affected zone, compared with the base metal. The through-thickness hardness of the base metal sheet was not constant and had to be carefully considered to determine the effect of welding on material properties. Quasi-static lap-shear tensile tests were used to determine the failure load and failure mode. All tensile specimens failed through the interfacial fracture. This failure mode is consistent with the observed reduced hardness in the weld nugget.
基金supported by the Natural Science and Engineering Council(NSERC)of Canada,the Canadian Foundation for Innovation
文摘Defect-free dissimilar Al/zinc coated steel and Al/AlSi coated steel welds were successfully fabricated by refill friction stir spot welding. However, Al alloy and uncoated steel could not be welded under the same welding condition. Al-Zn eutectic layer formed at the Al/zinc coated steel interface showed nonuniformity in thickness and nanoscale intermetallic(IMC) produced was discontinuous. The bonding formation between the Al-Zn layer and the surrounding materials was attributed to a liquid/solid reaction mechanism. Bonding formation at Al alloy and AlSi coated steel interface was attributed to a solid/solid reaction mechanism, as the joining process did not involve with melting of base metals or AlSi coating materials. Kissing bond formed at the weld boundary acted as a crack initiation and propagation site,and the present study showed that weld strength of Al 5754/AlSi coated steel was greatly influenced by properties of original IMC layer.
基金financially supported by the National Natural Science Foundation of China(No.50935008)Special Major Science and Technology of China(No.2010ZX04007041)the National Key Laboratory of High Energy Density Beam Processing Technology of China
文摘With the development of the manufacturing technology, electron beam welding（EBW） is capable of producing titanium alloy large parts in aero fields. To increase the applications and improve the properties, EBW with beam oscillation was investigated on TC4-DT alloy with50 mm thickness. We detected the welding samples by X-ray NDT, observed the microstructures of the welds, and tested the fatigue properties of the joints. The results showed that EBW with beam oscillation improved the weld morphology as well as welding quality, and the microstructure homogeneity of the welds and HAZ along the weld penetration were also improved. The fatigue properties of the joints with beam oscillation were more excellent than those of conventional EBW, even equal to those of the base metal under high stresses. The influences of the processing and the microstructure on the properties with beam oscillation were discussed.
基金supported by the Research Foundation of the Ministry of Railways and Tsinghua University (No.T200410)the National Natural Science Foundation of China (Nos.50778102 and 51178244)
文摘Brittle fracture occurs frequently in rails and thermite welded joints, which intimidates the security and reliability of railway ser- vice. Railways in cold regions, such as Qinghai-Tibet Railway, make the problem of brittle fi＇acture in rails even worse. A series of tests such as uniaxial tensile tests, Charpy impact tests, and three-point bending tests were carried out at low temperature to investigate the mechanical properties and fracture toughness of U71Mn and U75V rail steels and their thermite welds. Fracture micromechanisms were analyzed by scanning electron microscopy （SEM） on the fracture surfaces of the tested specimens. The ductility indices （percentage elongation aider frac- ture and percentage reduction of area） and the toughness indices （Charpy impact energy Ak and plane-strain fracture toughness Kic） of the two kinds of rail steels and the corresponding thermite welds all decrease as the temperature decreases. The thermite welds are more critical to fracture than the rail steel base metals, as indicated by a higher yield-to-ultimate ratio and a much lower Charpy impact energy. U71Mn rail steel is relatively higher in toughness than U75V, as demonstrated by larger Ak and Klc values. Therefore, U71Mn rail steel and the corresponding thermite weld are recommended in railway construction and maintenance in cold regions.
基金financially supported by the National Natural Science Foundation of China (Grant Nos.51325401 and U1660201)the National Magnetic Confinement Fusion Energy Research Project (Grant No.2015GB119001)
文摘In this study,the microstructures and mechanical properties of 9%Cr reduced activation ferritic/martensitic（RAFM） steel friction stir welded joints were investigated.When a W-Re tool is used,the recommended welding parameters are 300 rpm rotational speed,60 mm/min welding speed and10 kn axial force.In stir zone（SZ）,austenite dynamic recrystallization induced by plastic deformation and the high cooling rates lead to an obvious refinement of prior austenite grains and martensite laths.The microstructure in SZ contains lath martensite with high dislocation density,a lot of nano-sized MX and M3C phase particles,but almost no M23C6 precipitates.In thermal mechanically affect zone（TMAZ）and heat affect zone（HAZ）,refinement of prior austenite and martensitic laths and partial dissolution of M（23）C6 precipitates are obtained at relatively low rotational speed.However,with the increase of heat input,coarsening of martensitic laths,prior austenite grains,and complete dissolution of M23C6 precipitates are achieved.Impact toughness of SZ at-20℃ is slightly lower than that of base material（BM）,and exhibits a decreasing trend with the increase of rotational speed.
文摘The activated TIG(ATIG) welding process mainly focuses on increasing the depth of penetration and the reduction in the width of weld bead has not been paid much attention.The shape of a weld in terms of its width-to-depth ratio known as aspect ratio has a marked influence on its solidification cracking tendency.The major influencing ATIG welding parameters,such as electrode gap,travel speed,current and voltage,that aid in controlling the aspect ratio of DSS joints,must be optimized to obtain desirable aspect ratio for DSS joints.Hence in this study,the above parameters of ATIG welding for aspect ratio of ASTM/UNS S32205 DSS welds are optimized by using Taguchi orthogonal array(OA)experimental design and other statistical tools such as Analysis of Variance(ANOVA) and Pooled ANOVA techniques.The optimum process parameters are found to be 1 mm electrode gap,130 mm/min travel speed,140 A current and 12 V voltage.The aspect ratio and the ferrite content for the DSS joints fabricated using the optimized ATIG parameters are found to be well within the acceptable range and there is no macroscopically evident solidification cracking.
文摘The effects of pulsing current parameters on weld pool geometry namely front height, back height, front width and back width of pulse current gas tungsten arc welded （GTAW） titanium alloy was analysed. Four factors, five levels, central composite design were used to develop empirical relationships, incorporating pulsed current parameters and weld pool geometry.
文摘In marine application,marine grade steel is generally used for haul and superstructures.However,aluminum has also become a good choice due to its lightweight qualities,while rusting of aluminum is minimal compared to steel.In this paper a study on friction stir welding of aluminum alloys was presented.The present investigation deals with the effects of different friction stir welding tool geometries on mechanical strength and the microstructure properties of aluminum alloy welds.Three distinct tool geometries with different types of shoulder and tool probe profiles were used in the investigation according to the design matrix.The effects of each tool shoulder and probe geometry on the weld was evaluated.It was also observed that the friction stir weld tool geometry has a significant effect on the weldment reinforcement,microhardness,and weld strength.
文摘Self-shielded flux-cored wire is a convenient and efficient consumable for pipeline field girth welding because of its self-protection characteristic and high deposition rate, especially for remote construction sites in rugged terrain. From the perspective of pipeline safety, the impact toughness of the girth welds is an important factor in pipeline integrity ,which determines the crack arrest behavior in the girth welds. Therefore, improving the girth weld impact toughness is of primary importance in the field of pipeline girth welding. Three self-shielded flux-cored wires comprising different chemical composition systems have been applied to large diameter X80 UOE （U-ing-O- ing-Expanding） pipeline semi-automatic girth welding,and the impact toughness of the welds has been evaluated by girth weld chemical composition analysis and microstructural analysis using scanning electron microscopy （SEM） and energy dispersive spectrometry （EDS） to investigate pipeline girth weld impact toughness and find ways to improve it. This helps in determining the main factors that influence girth weld impact toughness. Pipeline girth weld impact toughness is mainly determined by the final microstructure produced in the solid-state phase transition. In the as-weld state,acicular ferrite （AF） and fine bainite （FB） are a benefit to the impact toughness. For multilayer semiautomatic self-shielded flux-cored wire welding, the normalizing and tempering function of the latter beads to the initial beads plays an important role in the transition of girth weld microstructure, which affects the impact toughness. The original AF and FB and the corresponding heat treatment microstructure of the fine and uniform block ferrite and pearlite result in very good impact toughness. The following two mechanisms are found to promote the production of AF and FB in the girth weld. First, elements promoting the broadening of the austenitic region, such as Ni, C, Cu, and Mn, induce low temperature phase transitions and restrain the opposing function of Al, which is a benefit to the production of AF and FB. Second, dispersed high-melting-point inclusions, especially Al2O3 ,induce the nucleated production of AF. The advantageous function of inclusions is determined by their shape, distribution, and dimension. Dispersed spherical inclusions of small dimension are a benefit to the production of AF, and result in good impact toughness.
文摘Base metals of domestic pipeline steels were used to study the effect of Mn on corrosion properties of SSCC(Sulfide Stress Corrosion Cracking), and welds were carried out to study the effect of MnS on corrosion properties of HIC (Hydrogen Induced Cracking) both in solutions with wet hydrogen sulfide(H_2S). They were respectively conducted by referring to the standards of SSCC and HIC. Testing results revealed that with the increase of content Mn, the resistance of SSCC will be decreased, from the point of metallurgic view, and it is Mn element not C element to lead to the testing results of SSCC. Meanwhile, even under the condition without inclusions MnS, HIC in welds still occurred. That is to say, MnS is not necessary for HIC, the presence of local banded structures in which Mn and P are inclined to aggregate cause to the phenomena of HIC.
基金supported by the National Basic Research Program of China(2007CB714702)the National Natural Science Foundation of China(50821063,50675183 and 50875221)
文摘As a vehicle passing through a track with different weld irregularities, the dynamic performance of track com- ponents is investigated in detail by using a coupled vehi- cle-track model. In the model, the vehicle is modeled as a multi-body system with 35 degrees of freedom, and a Timoshenko beam is used to model the rails which are dis- cretely supported by sleepers. In the track model, the sleepers are modeled as rigid bodies accounting for their vertical, lat- eral and rolling motions and assumed to move backward at a constant speed to simulate the vehicle running along the track at the same speed. In the study of the coupled vehicle and track dynamics, the Hertizian contact theory and the theory proposed by Shen-Hedrick-Elkins are, respectively, used to calculate normal and creep forces between the wheel and the rails. In the calculation of the normal forces, the coefficient of the normal contact stiffness is determined by transient contact condition of the wheel and rail surface. In the calcu- lation of the creepages, the lateral, roll-over motions of the rail and the fact that the relative velocity between the wheel and rail in their common normal direction is equal to zero are simultaneously taken into account. The motion equations of the vehicle and track are solved by means of an explicit integration method, in which the rail weld irregularities are modeled as local track vertical deviations described by some ideal cosine functions. The effects of the train speed, the axle load, the wavelength and depth of the irregularities, and the weld center position in a sleeper span on the wheel-rail impact loading are analyzed. The numerical results obtained are greatly useful in the tolerance design of welded rail pro- file irregularity caused by hand-grinding after rail welding and track maintenances.
基金financially supported by the National Natural Science Foundation of China(No.51905309)the Science and Technology Planning Project of State Grid Henan Electric Power Company(No.52170220009Y)。
文摘It is difficult to achieve Al/Cu dissimilar welds with good mechanical properties for medium-thick plates due to the inherent high heat generation rate at the shoulder-workpiece contact interface in conventional friction stir welding.Thus,doubleside friction stir welding is innovatively applied to join 12-mm medium-thick 6061-T6 aluminum alloy and pure copper dissimilar plates,and the effect of welding speeds on the joint microstructure and mechanical properties of Al/Cu welds is systematically analyzed.It reveals that a sound Al/Cu joint without macroscopic defects can be achieved when the welding speed is lower than 180 mm/min,while a nonuniform relatively thick intermetallic compound(IMC)layer is formed at the Al/Cu interface,resulting in lots of local microcracks within the first-pass weld under the plunging force of the tool during friction stir welding of the second-pass,and seriously deteriorates the mechanical properties of the joint.With the increase of welding speed to more than 300 mm/min void defects appear in the joint,but the joint properties are still better than the welds performed at low welding speed conditions since a continuous uniform thin IMCs layer is formed at the Al/Cu interface.The maximum tensile strength and elongation of Al/Cu weld are,respectively,135.11 MPa and 6.06%,which is achieved at the welding speed of 400 mm/min.In addition,due to the influence of welding distortion of the first-pass weld,the secondpass weld is more prone to form void defects than the first-pass weld when the same plunge depth is applied on both sides.The double-side friction stir welding is proved to be a good method for dissimilar welding of medium-thick Al/Cu plates.
文摘The influence of different welding processes on the mechanical properties and the corresponding variation in the microstructural features have been investigated for the dissimilar weldments of 18% Ni maraging steel 250 and AISI 4130 steel. The weld joints are realized through two different fusion welding processes, tungsten inert arc welding(TIG) and laser beam welding(LBW), in this study. The dissimilar steel welds were characterized through optical microstructures, microhardness survey across the weldment and evaluation of tensile properties. The fiber laser beam welds have demonstrated superior mechanical properties and reduced heat affected zone as compared to the TIG weldments.
