MAIN TOPICS,ABSTRACTS &KEY WORDS

Investigation on microstructure characteristics of Ti-48Al alloy fabricated using twin-wire directed energy depositionplasma arcWANG Lin,HUA Xueming,SHEN Chen,ZHANG Yuelong,LI Fang,ZHOU Wenlu,DING Yuhan(Shanghai Key Laboratory of Materials Laser Processing and Modification,School of Materials Science and Engineering,Shanghai Jiao Tong University,Shanghai,200240,China).pp 1-6

Abstract:Ti-48Al alloy is fabricated successfully using plasma arc powred twin wire-directed energy deposition-arc,and its microstructure characteristic before and after heat treatment is systematically investigated.The results show that asdeposited Ti-48Al alloy consists of α2and γ phase.The microstructure is characterized by the alternatively distributed dendritic grain and fully lamellar colony along the building direction for as-deposited Ti-48Al alloy,and there is interdendritic Al element segregation in the dendritic grain region.After heat treatment in 1 340 ℃/10 h/furnace cooling,the duplex microstructure with fine grain size is obtained,and the microstructure heterogeneity is significantly improved,the α2phase content is obviously increased,the preferred orientation of microstructure is also weakened.

Highlights:(1) Ti-48Al alloys are successfully fabricated using plasma arc powered twin wire-directed energy deposition-arc system.

(2) Microstructure characteristics and its evolution mechanism of as-deposited Ti-48Al alloy are revealed systematically.

(3) Heat treatment method to eliminate microstructural heterogeneity of additively manufactured Ti-48Al alloy is proposed.

Key words:directed energy deposition-arc；TiAl alloy；microstructure；heat treatment

Local dry underwater TIG welding process of positioning pin in nuclear power plantSUN Qingjie1,2,ZHANG Qinghua1,ZHAO Yongqing2,GUO Jiawei2,LI Tianyou2,BAN Huakang2,HOU Shaojun2(1.Harbin Institute of Technology,State Key Laboratory of Advanced Welding and Joining,Harbin,150001,China；2.Harbin Institute of Technology,Provincial Key Laboratory of Special Welding Technology,Weihai,264209,China).pp 7-12

Abstract:Taking the underwater welding of positioning pin in nuclear power plant as the research object,an underwater TIG welding gun with double-layer gas protection is developed.The motion trajectory is realized by DC motor driving the tungsten pole to rotate around a fixed diameter.The nuclear grade material Z2CN19-10 nitrogen-controlled stainless steel was welded.The weld formation of local dry underwater TIG welding was studied.The process parameters were optimized.The microstructure and mechanical properties of the joint were analyzed by combining the thermal cycle curve and arc shape.The results show that when the inner and outer layers are filled with argon,the weld is well formed and the arc shape is stable.Increasing the welding current or reducing the welding speed increases the weld penetration and the weld width.By comparing the underwater and onshore welded joints,it is found that the rapid cooling of water will promote the ferrite near the fusion line to change from dendritic to lath,reduce the austenite content and refine the grain.The microhardness and mechanical properties of underwater joints are slightly higher than those of onshore joints.

Highlights:(1) The effects of different parameters on underwater TIG welding were studied by using a self-designed underwater TIG welding gun.

(2) The differences of microstructure and properties between onshore and underwater TIG welding were compared,and excellent welded joints were obtained.

Key words:underwater local dry welding；TIG welding；nitrogen controlled austenitic stainless steel；appearance of weld；microstructure and Properties

Quality prediction of aluminum alloy resistance spot welding based on correlation analysis and SSA-BP neural networkDONG Jianwei,HU Jianming,LUO Zhen(School of Materials Science and Engineering,Tianjin University,Tianjin,300350,China).pp 13-18,32

Abstract:Based on the characteristics of the process signals in the resistance spot welding process,three working conditions of different spacing,different gaps and different spacing and gaps are analyzed,and correlation analysis is introduced to extract the correlation between the process signals and the diameter of nugget.A resistance spot welding quality prediction model based on Sparrow Search Algorithm-Back Propagation Neural Network (SSA-BP) was established,and power,welding current,welding voltage and dynamic resistance are used as input features of the prediction model.The results show that the BP neural network optimized by the sparrow search algorithm outperforms the BP model on the test set with R2,MSE,RMSE and MAE of 0.95,1.55,1.24 and 0.90,respectively.It is also determined that there exists a mapping relationship between power,welding current,welding voltage and dynamic resistance and the diameter of the nugget,which provides a basis for the design of process parameters for welding.

Highlights:(1) Extracting the mapping of process signals to nugget diameter using correlation analysis.

(2) Improved SSA-BP-based prediction model of resistance spot welding nugget diameter with 95% prediction accuracy.

Key words:resistance spot welding；nugget diameter；sparrow search algorithm；BP neural network；correlation analysis

The metal transfer behavior in CMT-based wire arc direct energy deposition of 2219 aluminum alloyNI Yunqiang1,YANG Jiannan2,FANG Xuewei2,3,ZHANG Changchun1,LI Chunxu1,WANG Jian1,LU Bingheng2,3(1.Weichai Holding Group Co.,Ltd.,Weifang,261061,China；2.The State Key Laboratory for Manufacturing Systems Engineering,Xi’an Jiaotong University,Xi’an,710054,China；3.National Innovation Institute of Additive Manufacturing,Xi’an,710117,China).pp 19-32

Abstract:In the process of cold metal transfer (CMT) arc additive manufacturing,the flow behavior of the molten pool is easily affected by arc and droplet,which seriously affects the stability of the deposited layers and the quality of the formed parts.Using high-speed photography results and waveform graphs of electrical signal parameters and introducing a formula for calculating heat input,this article quantitatively analyses the influence of wire feeding speed and pulse correction coefficient on droplet transition process and single-pass form under CMT+PA mode from the aspects of characteristic electrical signals,droplet transition characteristics,heat input,etc.,and also analyses the influence of wire feeding speed and EP/EN coefficient ? on droplet transition process and singlepass form under CMT+PA mode,providing reference and guidance for subsequent process optimization.

Highlights:(1) Quantitative analysis of the influence mechanism of process parameters on the droplet transition behaviour under different arc modes;

(2) Establishing the correlation between the process parameters of CMT additive manufacturing of 2219 aluminium alloy and the shape morphology.

Key words:aluminum alloy；wire-arc direct energy deposition；metal transfer；arc characteristics；forming morphology

Effect of holding time on temperature field and residual stress in the vacuum brazing process of titanium alloy plate-fin heat exchangersLI Yue1,WANG Jianfeng1,MA Longfei1,DU Chunhui2,HU Fengjiao2,ZHAN Xiaohong1,2(1.Nanjing University of Aeronautics and Astronautics,Nanjing,211106,China；2.Beijing Research Institute of Mechanical &Electrical Technology,Beijing,100083,China).pp 33-40

Abstract:The power and environmental control systems of high-end equipment,such as aerospace,submarine and aircraft carrier,were commonly in service under extreme environment of high pressure,heavy load,strong vibration and elevated temperature corrosion,which put forward an urgent demand for efficient and high-strength plate-fin heat exchanger.However,due to low production yield,large residual stress and deformation for titanium alloy plate-fin heat exchanger,the corresponding efficient and reliable brazing technology need further breakthrough at present.Therefore,a thermal-solid coupling model was carried out in this paper for the vacuum brazing process of titanium alloy plate-fin structure.The temperature uniformity and the distribution characteristics of residual stress were explained,the influence of holding time on the temperature field and residual stress of the vacuum brazing process of titanium alloy plate-fin heat exchanger was verified.The results showed that the temperature of the plate-fin structure was higher on both sides and lower in the middle.Extending the insulation time could effectively improve the temperature uniformity of the plate-fin structure.The residual stresses were mainly concentrated on the upper surface of the fins and the middle of the back side of the spacer,and there were obvious stress concentrations at the brazing seam and the clamping point.When increasing holding time,the residual stresses decreased.The simulated residual stress during vacuum brazing process agreed with the test results,and the relative errors were 5.3%,verifying the accuracy of the model.

Highlights:(1) A thermal-solid coupling model was established for the simultaneous vacuum brazing of titanium alloy plate-fin heat exchangers.

(2)The temperature uniformity and the distribution characteristics of residual stress was discussed.

(3)The effect of holding time on temperature field and residual stress in the vacuum brazing process of titanium alloy plate-fin heat exchangers was investigated.

Key words:plate-fin heat exchangers；titanium alloy；vacuum brazing；thermal-solid coupling；simulation

Arc behavior and droplet transfer in self-adaptive shunt alternating arc WAAMHU Qingsong1,2,YAN Zhaoyang1,2,ZHANG Pengtian1,2,CHEN Shujun1,2(1.Engineering Research Center of Advanced Manufacturing Technology for Automotive Components Ministry of Education,Beijing University of Technology,Beijing,100124,China；2.China Spacesat Co,Ltd.Beijing Spacecrafts,Beijing,100124,China).pp 41-46

Abstract:The traditional arc welding heat source could't be directly applied to wire and arc additive manufacturing(WAAM) due to high heat input and low deposition rate.A technology for alternating-arc-based additive manufacturing was proposed through self-adaptive shunt.The technology form alternating arcs between the tungsten electrode,workpiece,and welding wire,and induce the alternating arc based on the EN/EP current transition.The heat source utilized the EN arc melting wire with wire anode-tungsten electrode cathode，and the workpiece was cleaned by the EP arc of the tungsten electrode anode-workpiece cathode,achieving decoupling of arc heat and force transfer through proper adjustment.The applicability of the innovative source had been verified,and the influence of welding speed and wire height on arc behavior and droplet transition had been compared and analyzed in this article.The results showed that when the welding speed was 5.7 mm/s and the wire height was 8 mm,the morphology of the deposited layer was better and the droplet transfer was better.Furthermore,compared to traditional VPPA-WAAM，the adaptive-shunt alternating arc significantly increased the deposition efficiency and reduces the heat input to the substrate,while maintaining a balance between additive manufacturing quality and efficiency.

Highlights:(1) The effects of welding speed and wire height on the formation of deposited layers were studied of self-adaptive shunt alternating arc WAAM;

(2) Compared with VPPA,the adaptive-shunt alternating arc had the advantage of lower heat input.

Key words:WAAM；alternating arc；droplet transfer；arc behavior；weld bead formation

The effect of trace elements on the microstructure and properties of coarse grain heat affected zone of EH36 ship steel with super large heat inputHAN Mei1,2,3,ZHANG Xi4,MA Qingjun2,3,WEI Yushun2,3,WEI Chen2,3,WANG Zejun2,3,JIA Yunhai1(1.Central Iron &Steel Research Institute,Beijing,100081,China；2.National Inspection Center for Special Equipment Welding Consumables Quality,Tianjin,300350,China；3.Tianjin Special Equipment Inspection Institute,Tianjin,300350,China；4.Tianjin Bridge Welding Materials Group Co.,Ltd.,Tianjin,300385,China).pp 47-53

Abstract:The influence of Al,Mg,and Ti element content on the microstructure and properties of the coarse grain zone in the heat affected zone of EH36 high-strength ship steel during large heat input welding was studied through welding thermal simulation.The relationship between Al,Mg,and Ti element content and oxide type,size,quantity,and coarse grain zone phase transformation in the base material was revealed using Thermo-Calc thermodynamic calculation combined with SEM and EDS testing.The results showed that Al2O3couldn`t induce the transformation of acicular ferrite.When the mass percent of Al element was below 0.005%,Ti,Mg or their composite oxides could be formed in the steel,which could promote the transformation of acicular ferrite in the coarse grain area.When Ti and Mg were added together,and the mass percent of Mg element decreased from 0.0 042% to 0.0 013%,the oxide type changed from MgO to Mg2TiO4,the number of oxides in 20 fields of view increased from 408 to 503,the average diameter of the oxide reduced from1.37 μm to 1.10 μm.The specific surface area of non-uniform nucleation was significantly increased,the formation of grain boundary ferrite was suppressed,and the impact energy of the thermal simulation sample at -20 ℃ in the coarse grain zone was increased from 43 J to 127 J att8/5=300 s.

Highlights:(1) The influence of Al,Mg,Ti ratio on the type,quantity and size distribution of second phase was established through experiment and thermodynamic calculations.

(2) It was found that the combined addition of Mg and Ti can increase the number of oxides,refine the size of oxides,and ensure the toughness of CGHAZ under super large heat input.

Key words:trace element；ship plate；super large heat input；coarse grain heat affected zone

"Γ" shaped arc and its promotion method in Tri-Arc dual wire weldingZHONG Pu,LI Liangyu,REN Guochun,WANG Tianqi,GUO Dongbo(Tianjin Key Laboratory of Advanced Mechatronics Equipment Technology,Tiangong University,Tianjin,300387,China).pp 54-60

Abstract:The Tri-Arc dual wire welding achieves a high deposition rate and low heat input by redistributing the heat input through an intermediate third arc called M-Arc.The M-arc is coupled to the main arc and exhibits "Γ" and "μ" shapes and their mirror images throughout the dynamic cycle.In this paper,the formation mechanism of the "Γ"-shaped arc and the heat input regulation mechanism are investigated first.The results indicate that the "Γ" shape evolves from the "μ" shape,the oscillation of adhered molten droplets induces a variation in the distance between two wire ends,thereby facilitating the formation of "Γ" shape in the coupled arc.In this case,the M-arc does not touch the workpiece,rendering a lower heat input during welding than the "μ"-shaped arc.In order to enhance the low heat input effectiveness of the Tri-Arc dual wire welding,the alteration of the distance at two wire ends is achieved by elevating the welding torch.Simultaneously,the length of the conductive nozzle should be increased to maintaining a constant distance between the tip of the conductive nozzle and the workpiece.When the length of the conductive nozzle is increased from 30 mm to 35 mm,as the welding torch is elevated,the duration of the "Γ" shaped arc phase gradually extends.This extended duration effectively facilitates arc thermal distribution,consequently reducing the heat input during Tri-Arc dual wire welding.As a result,peak value of the highest temperature within the molten pool diminishes,thereby reduced the weld bead width-to-height ratios and weld penetration.

Highlights:(1) The heat input distribution mechanism of Tri-Arc dual wire welding is investigated,revealing that the coupled arc heat input is lower in "Γ"-shape.

(2) The process of arc coupling is elucidated,confirming that the formation of the "Γ"-shaped arc is affected by the distance between the ends of the welding wires.

(3) It is proposed and verified that reducing the distance between 2 wire ends can effectively promote the generation of the "Γ"-shaped arc.

Key words:tri-arc dual wire welding；coupled arc；arc shape；arc thermal distribution；weld thermal input

Three-dimensional reconstruction of GMAW weld pool appearance based on variational stereo matching algorithmLIANG Zhimin1,2,GAO Xu1,REN Zheng1,WU Ziqin1,WANG Liwei1,2,WANG Dianlong1,2(1.School of Material Science and Engineering,University of Science and Technology,Shijiazhuang,050000,China；2.Hebei Key Laboratory of Material Near-net Forming Technology,Shijiazhuang,050000,China).pp 61-66

Abstract:In order to realize the complete three-dimensional sensing of weld pool surface morphology,a stereo vision sensing system with biprism and single camera was constructed.Aiming at the difficulty of stereo matching caused by the lack of texture in weld pool map,a globally optimized variational stereo matching algorithm was introduced.By establishing the feasibility function of energy function containing gray difference data item and spatial continuity constraint item,the dense disparity figure of weld pool surface with rich details was obtained through iterative.The results of stereo matching and three-dimensional reconstruction of the self-made non-standard concave shape show that the width error is less than 3.16%and the depth error is less than 4.82%.Based on this algorithm,the dense disparity map of weld pool surface is calculated and reconstructed under the conditions of bead on plate and V-groove butt welding with different penetration states.

Highlights:(1) A biprism stereo visual sensing system based on a single camera is constructed.

(2) Disparity calculation and 3D reconstruction of the complete weld pool surface are implemented based on a variational stereo matching algorithm.

Key words:weld pool appearance；three-dimensional reconstruction；variational stereo matching algorithm；gas metal arc welding

Investigationof pulse VP-TIGweldingprocess of 2219/5A06 dissimilar aluminum alloyXU Guangpei1,WEI Yaoguang1,RAN Guangqi1,CHEN Yao1,LI Huan2(1.AVIC Chengdu Aircraft Industrial (Group) Co.,Ltd.,Chengdu,610073,China；2.Tianjin Key Laboratory of Advanced Joining Technology,Tianjin University,Tianjin,300072,China).pp 67-74

Abstract:In order to obtain the best performance of welded joints,dissimilar aluminum alloys of 2219-T87 and 5A06-H112 with a thickness of 5.5 mm was joined by pulsed VPTIG butt welding.The L27(39) type orthogonal table with five process parameters and three levels were designed,and the interaction between three factors was considered at the same time.The influence of each factor on the tensile strength of the joints was analyzed,and the results show that the influence of the process parameters on the joint performance is in the order:welding speed ＞ groove angle ＞ peak current ＞ pulse frequency ＞ wire feeding speed.Through orthogonal optimization,an ideal defect-free welded joint was obtained.The mechanical properties,microstructure and corrosion properties of the optimized welded joint were tested.The results show that the fracture edge of the joint was near the fusion line on the 2219 side,where the strain was the largest and the hardness was the lowest.The corrosion resistance of the 2219 side fusion line and the weld area is the worst,and it is the location where pitting corrosion occurs preferentially.

Highlights:Using L27(39) type orthogonal text,the ideal a defect-free dissimilar aluminum alloy pulse VP-TIG welded joints is obtained.Near the fusion line of 2219 side in the whole welded joint is the location of fracture,the area with the lowest hardness value,and the position where pitting corrosion occurs preferentially.

Key words:orthogonal experimental；plused VP-TIG welding；dissimilar aluminum alloy；mechanical property；corrosive property

Effect of microtexturing characteristics on the performance of laser welded aluminum alloy-CFRTP jointsXU Liang1,LI Kangning1,YANG Haifeng1,SONG Kunlin2,GU Shiwei1(1.HWI-NICHST Welding and Engineering Innovation Center(Qingdao)Co.,LTD.,Qingdao,266000,China；2.National Invitation Center of High Speed Train at Qingdao,Qingdao,266108,China).pp 75-81

Abstract:The effect of laser texturing on the performance of aluminium alloy-CFRTP laser welded joints was studied and the strengthening mechanism of laser texturing was analyzed.The results showed that the laser surfi-sculpt could be used to build texturing on the surface of aluminium alloys to obtain well-formed and high performance aluminium alloy-CFRTP laser welded lap joints,and the joint achieved tightly embedding.With the increasing of the depth-width ratio of the laser texturing,the molten CFRTP in the texturing was changed from fully filled to partially filled,and the joint shear properties showed a trend of first increasing and then decreased,and the joint failure mechanism was changed from hybrid fracture(adhesive failure+cohesive failure),CFRTP base material fracture to hybrid fracture.The joint performance reached its maximum when the depth-width ratio reached 1.2 to 1.6,at which point the fracture location was located in the CFRTP base material.The strengthening mechanisms of the aluminium alloy-CFRTP joint by laser texturing were enhancing mechanical embedding and the "nailing" effect of splashing.

Highlights:(1) The characteristics of laser texture and its effect on the filling effect of CFRTP were investigated.

(2) Effect of laser texture characteristics on the properties and fracture mechanism of welded joints was expounded.

Key words:laser texturing；carbon fiber；composite material；laser welding

Recognition algorithm of small-diameter tube X-ray welding defect imageXIAO Yang1,GAO Weixin1,2,DENG Guohao2(1.School of Electronic Engineering,Xi’an Shiyou University,Xi’an,710065,China；2.Key Laboratory of Gas-Oil Logging Technology,Xi’an Shiyou University,Xi’an,710065,China).pp 82-88

Abstract:To address the current situation of low accuracy rate of small-diameter tube welding image defect detection,by combining image feature analysis and sparse dictionary learning,a small-diameter tube welding defect detection algorithm based on image segmentation is proposed.Firstly,using twostep image segmentation way acquires the region of interest which is in small-diameter tube welding image.Secondly,the suspected defect region is obtained by extracting welding defect.Finally,we propose a mathematical model of the dictionary matrix of small-diameter tube welding defects with the objective of minimizing correlations between different types of atoms and solve it by using K-SVD algorithm.After that,the dictionary matrix is used to classify circular defects,strip defects and noise.To improve the real-time performance of the system,we use parallel programming to accelerate the image segmentation algorithm.The results show that the recognition rate of the proposed method is 0.974 for circular defects and 0.967 for strip defects,and the recognition speed is fast,which enables the effective recognition of defects in small-diameter tube welding image.

Highlights:(1) Propose a two-step image segmentation method to extract the weld seam area of small-diameter tubes,achieving adaptive segmentation of the weld seam region in small-diameter pipes.

(2) Propose a mathematical model for the dictionary matrix suitable for defect recognition in small-diameter tube X-ray weld seam images,reducing the number of dictionary matrix atoms.

(3) The weld seam defect recognition method based on parallel processing for image segmentation and sparse dictionary learning satisfies the accuracy requirements of on-site inspection.

Key words:small-diameter tube；welding defect；image segmentation；sparse dictionary learning

Effect of Sn on the microstructure and properties of Cu-Sn-Ti brazing filler metalDU Quanbin1,ZHANG Liyan1,LI Ang1,CUI Bing2,HUANG Junlan3(1.Henan Key Laboratory of Intelligent Manufacturing Equipment Integration for Superhard Materials,Henan Mechanical and Electrical Vocational College,Zhengzhou,451191,China；2.Key Laboratory of Green Fabrication and Surface Technology of Advanced Metal Materials,Ministry of Education,Anhui University of Technology,Ma'anshan,243002,China；3.State Key Laboratory of New Brazing Materials and Technology,Zhengzhou Reserch Institute of Mechanical Engineering Co.,Ltd.Zhengzhou,450001,China).pp 89-97

Abstract:In order to reveal the regulation of Sn on the microstructure and mechanical properties of Cu-Sn-Ti brazing filler metal,Cu-xSnxTi10 brazing filler metals were prepared by vacuum non-self-consumption melting method,and the effects of Sn on the microstructure,microhardness,shear strength and fracture morphology of Cu-Sn-Ti brazing filler metals were investigated by using scanning electron microscopy (SEM),Xray diffractometer (XRD),energy spectrometer (EDS),and universal material testing machine,etc.the results showed that:the microstructure evolution of the solder with the increase of Sn content was as follows : dendritic primary α-Cu matrix phase +eutectic tissue+intergranular tissue → primary α-Cu matrix phase+eutectic tissue → eutectic tissue → primary CuSn3Ti5phase+coarsened eutectic tissue+α-Cu matrix phase (Snrich)+Cu41Sn11phase+SnTi3phase,in which the intergranular tissue was a mixed structure of α-Cu phase and CuSn3Ti5phase+a small amount of SnTi3+CuTi phase+Cu3Ti phase.With the increase of Sn content,the microhardness of filler metal increases first and then decreased,the shear strength of filler metal decreasing gradually,and the fracture morphology changed from the quasi-cleavage fracture to the mixture of cleavage fracture and quasi-cleavage fracture.The increase of Sn content promoted the formation of coarsened CuSn3Ti5phase and eutectic tissue in the filler metal,which was the main reason for the decrease of shear strength of brazing metal.

Highlights:(1) The influence of Sn on the microstructure and mechanical properties of Cu-Sn-Ti brazing filler metal was dissected.

(2) The shear fracture behavior of Cu-Sn-Ti brazing filler metal and its relationship with microstructure were revealed.

Key words:Cu-Sn-Ti brazing filler metal；microstructure；shear strength；microhardness

The difference of CTOD of X80M pipeline steel fully automatic welded jointsWEN Xue1,WANG Honghui1,LI Xiyan1,QIAN Jiankang1,BI Siyuan2,LEI Zhenglong2(1.Sinopec Jiangsu Oil Construction Engineering Co.,Ltd.,Yangzhou,225009,China；2.National Key Laboratory of Precision Welding &Joining of Materials and Structures,Harbin,150001,China).pp 98-104

Abstract:Aiming at the fully automatic welded joints of X80M steel pipe under different preheating conditions,the difference of crack tip opening displacement is studied.The CTOD test is carried out on single notch three-point bending specimen,and CTOD value is calculated according to the formula recommended in GB/T21143-2014 and ISO15653-2018.The results show that: Compared with GB/T21143-2014,the results of CTOD calculated by formula recommended by ISO 15653-2018 are 35% higher on average.This difference is mainly due to the difference in the emphasis of the correction methods of the two standards,that is,the GB standard corrects the change of crack length,while the ISO standard adjusts for temperature effects.The CTOD value of the joint sample under the preheating condition of 80 ℃ is low on the whole.According to GB/T21143-2014,three samples are lower than the standard,the lowest is 0.16 mm,and according to ISO 15653-2018,one sample is lower than the standard,the lowest is 0.20 mm.Under the preheating condition of 120 ℃,the calculated CTOD values of all samples under the two standards meet the standard requirements,and the fracture toughness of welded joints is better.Under the same preheating conditions,the CTOD values of the fusion zone are higher than that of the weld zone,and the maximum value of CTOD values appearing in the fusion zone,which has good fracture toughness.However,the CTOD value of the fusion zone is affected by the inhomogeneity of the structure,resulting in great differences between different positions and uneven performance distribution.

Highlights:(1) Compared with the GB/T21143-2014 standard，the CTOD values calculated according to the ISO 15653-2018 standard are 35% higher on average,and the difference mainly stems from the different correction methods of the two standards.

(2) Compared with preheating at 80 ℃,the CTOD values calculated for the specimens preheated at 120 ℃ satisfy the standard requirements under both criteria,and the CTOD values of the fusion zone are overall higher than those of the weld zone.

Key words:X80M pipeline steel；fully automatic welding；preheating temperature；CTOD

Liquid bridge blasting evolution behavior of rail AC flash weldingYANG Bo,DENG Jiarong,LIU Xin,LV Qibing(School of Materials Science and Engineering,Southwest Jiaotong University,Chengdu,610031,China).pp 105-112

Abstract:The heating of the weldment,the protection of the end face,the removal of oxides and dirt during the rail flash welding process are all caused by the formation and blasting process of the liquid bridge.This paper analyzing the evolution behavior of the liquid bridge during the welding process plays an important role in understanding the rail flash welding process and further studying the welding heating and protection mechanism.Through the flash welding test of specially designed rail joints and conventional rail joints,the liquid bridge formation and blasting process images of rail AC flash welding process were collected by high-speed photography,and the obtained graphics were calculated and analyzed.The research results show that the formation and blasting time of the liquid bridge is millisecond,which will generate a large amount of high-pressure metal vapor beneficial to the end face protection and liquid bridge blasting,and the high temperature metal jet velocity after blasting can reach more than 90 m/s;During the formation and growth of the liquid bridge,there will be dynamic movement on the rail end face that will affect the uniform heating of the rail end face.The liquid bridge blasting is not at the initial formation position of the liquid bridge;During the welding process,the melt can appear the phenomenon of "secondary explosion";Not only can the rail at the moving end form a liquid bridge,but also the vibration of the molten metal layer at the end is conducive to the formation of a liquid bridge.

Highlights:(1) The study is conducted on the evolutionary behavior and interaction during the blasting process of rail flash welding liquid bridge.

(2) It is found that the oscillation of molten metal layer contributes to the formation of liquid bridge.

Key words:rail flash welding；liquid bridge blasting；evolutionary behavior；high speed photography

Engineering application of structural strain method of low cycle fatigue in railway freight carbodySHAO Wendong1,2,ZHAO Shangchao2,LI Qiang1,PEI Xianjun3,MA Qiaoyan2,LI Xiangwei2(1.Beijing Jiaotong University,School of Mechanical,Electronic and Control Engineering,Beijing 100044,China；2.CRRC Qiqihar Rolling Stock Co.,Ltd.,Qiqihar,161000,China；3.Southeast University,Nanjing,211189,China).pp 113-120

Abstract:In order to solve the problem of low cycle fatigue life prediction of welded structure of railway freight car body,firstly,the structural strain calculation theory of low cycle fatigue under different yield states is derived,and the program is designed based on the calculation theory.and the theoretical verification is completed through the welded joint test.Secondly,in order to further illustrate the applicability of structural strain method calculation theory of low cycle fatigue,the plane strain finite element model and structural strain theory are compared;finally,the engineering application of low cycle fatigue life analysis of express freight car is carried out by combining virtual bench with structural stress strain.The results show that the structural strain method and program based on low cycle fatigue can solve the problem of low cycle fatigue of railway freight cars when the stress of welded structure is higher than the yield strength 150 MPa,and the result of plane strain model is consistent with that of structural strain theory,but after exceeding the yield strength 150 MPa,the error increases with the increase of structural stress.The research in this paper provides a good technical support for the popularization and application of structural strain method in low cycle fatigue.

Highlights:(1) The program design of structural strain calculation method based on plane strain state is completed for the first time.

(2) the applicability of structural strain method based on plane strain model is analyzed for the first time.

(3) the truck body engineering application of the combination of virtual bench and structural strain method is carried out systematically for the first time.

Key words:railway freight car；low cycle fatigue；structural strain method；virtual test rig

Growth behavior of inter metallic compounds at N06200 nickel alloy and S32168 stainless steelWU Jingwei,WANG Youyin,HOU Xirong,WANG Zhigang,CHE Wenbin,ZHANG Jianxiao,DUO Yuancai(Lanzhou LS heavy equipment co.,LTD.,Lanzhou,730314,China).pp 121-128

Abstract:The evolution process of IMCs at the interface between N06200 nickel-base alloy and S32168 stainless steel TIG welded joint after post-weld heat treatment was analyzed.The formation type,sequence and growth kinetics model of IMCs at the interface were analyzed through the perspective of thermodynamics and kinetics.The results showed that with the increase of heat treatment temperature,the tensile strength of the welding joint increases firstly and then decreases.With the increasing of holding time,the tensile strength of the joint increased.The IMCs at the interface between nickel base alloy and stainless steel after welding heat treatment were mainly composed of NiFe phase,Ni2Cr phase,FeCr phase and Ni3Fe phase.The thickness of IMCs layer at the interface increase with the increasing of heat treatment temperature and holding time.The formation sequence of IMCs was NiFe→FeCr→Ni2Cr→Ni3Fe.The growth of IMCs was in line with parabolic law.The kinetic model of IMCs wasW=1.725 × 10-13·exp[-45.98/(RT)]·t1/2by linear regression method.

Highlights:(1) The influence of heat treatment on the IMCs layer thickness and phase composition Element transport mechanism for TIG welding of N06200-S32168 dissimilar alloys were systematically studied.

(2) The thermodynamics and dynamics model for TIG welding of N06200-S32168 dissimilar alloys was established to analyze the types and sequence of generation of interface IMCs.

Key words:nickel-base alloy；stainless steel；IMCs；thermodynamics；kinetics