MAIN TOPICS,ABSTRACTS &KEY WORDS

Microstructure and mechanical properties of welds at keyhole closures in variable-polarity plasma arc welding of Al alloyWANG Xiaowei1,ZHANG Bin2,ZENG Ruchuan2,YAN Zhaoyang1,CHEN Shujun1(1.Engineering Research Center of Advanced Manufacturing Technology for Automotive Components,Beijing University of Technology,Beijing,100124,China；2.Beijing Spacecrafts Co.,Ltd.,Beijing,100124,China).pp 1-6

Abstract:Al alloy is widely used in aerospace,military industries,and other fields due to its low density and high specific strength.Variable polarity plasma arc keyhole welding is a preferred method for processing large aluminum alloy structural components.However,keyhole closure is a challenge in plasma arc welding of light metal alloys.To address this issue,a gas-electric separation timed pulse plasma arc ring welding method named keyhole self-closing method is proposed.The microstructure and properties of the keyhole closure in the ring welds by the proposed method and the manual TIG welding filling method was compared.The results demonstrate that by adjusting the welding arc starting and ending strategies,the keyhole closure was achieved,with the formation of wellshaped weld joints exhibiting a uniform equiaxed crystal microstructure.The tensile strength was about 329.9 MPa,with an elongation of 16.3%,representing a 22.91% increase in tensile strength and a 55.24% increase in elongation compared to the keyhole filled by the TIG welding.The average hardness value was 78.9 HV0.2,with the heat-affected zone showing a decreasing trend in hardness,the fusion line exhibiting an increasing trend,and the weld zone hardness fluctuating in the range of 75 to 81 HV0.2

Highlights:(1) Gas-electric separation timing pulse plasma arc ring weld closure method has been proposed.

(2) The advantages of the keyhole self-closure method compared to manual keyhole filling has been analyzed.

Key words:aluminum alloy；variable polarity plasma arc perforation welding；microstructure；mechanical properties

Effect of surface tension on molten pool and keyhole during laser weldingPENG Jin1,XU Hongqiao1,YANG Xiaohong2,3,WANG Xingxing1,XIE Shihua1,LI Liqun4,ZHANG Dingyu1(1.North China University of Water Resources and Electric Power，Material College,Henan International Joint Laboratory of High-efficiency Special Green Welding,Zhengzhou,Henan,450045,China；2.Jinhua Polytechnic,Jinhua,Zhejiang,321017,China；3.Key Laboratory of Crop Harvesting Equipment Technology of Zhejiang Province,Jinhua,Zhejiang,321017,China；4.State Key Laboratory of Advanced Welding and Joining,Harbin Institute of Technology,Harbin,Heilongjiang,150001,China).pp 7-14

Abstract:Based on fluent 19.0 software,the heat flow coupling model of laser welding was established,and the effects of different surface tension temperature coefficients (negative values) on the flow field of molten pool were compared and analyzed.The results showed that with the decrease of surface tension temperature coefficient,the trend of clockwise flow vortex behind the molten pool gradually weakened or even disappeared,and the amount of welding spatter increased,the length of longitudinal section molten pool gradually increased,the maximum flow velocity of longitudinal section molten pool gradually increased,and the cross-sectional area of molten pool gradually decreased.When the temperature coefficient of surface tension was −2.5 × 10−4N/(m·K),the average length of molten pool was 3.28 mm,the average maximum flow velocity of molten pool fluid was 2.89 m/s,and the average crosssectional area of molten pool was 4.52 mm2.When the temperature coefficient of surface tension was −3.5×10−4N/(m·K),the average length of molten pool was 3.73 mm,the average maximum flow velocity of molten pool fluid was 3.53 m/s,and the average cross-sectional area of molten pool was 4.03 mm2.When the temperature coefficient of surface tension was−4.9×10−4N/(m·K),the average length of molten pool was 4.14 mm,the average maximum flow velocity of molten pool fluid was 4.09 m/s,and the average cross-sectional area of molten pool was 3.28 mm2.

Highlights:The influence of different surface tension temperature coefficients (negative values) on the flow field in the molten pool and welding spatter were clarified.

Key words:laser welding；surface tension；molten pool；keyhole

Residual stress analysis in multi-pass underwater wet welded X80 pipeline steelYAN Chunyan1,GU Zhengjia1,NIE Rongqi1,ZHANG Kezhao1,WU Chen1,WANG Baosen2(1.Hohai University,Changzhou,213022,China；2.Baosteel Central Research Institute,Shanghai,200431,China).pp 15-21

Abstract:Underwater wet welding of X80 pipeline steel was performed using different welding currents.Onshore dry welding with welding current of 175 A was also implemented for comparison of underwater wet welded specimens.Influence of welding current on distribution of microstructure,hardness,temperature and residual stress was obtained.The results show that microstructure in underwater welded joints is different from that in onshore welded joints with the same welding current,with weld metal exhibiting a structure of proeutectoid ferrite,granular bainite,lath bainite and acicular ferrite,and coarse grained heat affected zone exhibiting a structure of predominant lath bainite and small amount of granular bainite.Underwater wet welded joint exhibits higher hardness,cooling speed and residual stress level compared to terrestrial welded joint with the same welding current.The residual stress levels in underwater wet welded joints are high.In the current range from 175 to 205 A,the amount of ferrite side plate and acicular ferrite in weld metal increases with increasing welding current.However,the maximum hardness,peak equivalent residual stress and peak longitudinal stress decrease moderately.

Highlights:Underwater wet welding of X80 pipeline steel was conducted.The effects of welding current on microstructure and residual stress distribution in underwater wet welded joints were obtained.

Key words:underwater wet welding；multi-pass welding；temperature field；residual stress

Atomic diffusion behavior in the interface formation of copper-aluminum electromagnetic pulse weldingLI Chengxiang,XU Chennan,ZHOU Yan,CHEN Dan,MI Yan(State Key Laboratory of Power Transmission Equipment&System Security and New Technology,Chongqing University,Chongqing,400044,China).pp 22-31

Abstract:Electromagnetic Pulse Welding (EMPW) technology is widely concerned because of the reliable connection of dissimilar metals driven by high-voltage discharge.However,the interface bonding mechanism is still unclear.A comprehensive experimental platform for copper-aluminum EMPW is set up,the welding dynamic process is captured,and the collision velocity and angle are obtained.Based on these parameters,a molecular dynamics simulation model is constructed for the formation of typical interfaces (flat interface and vortex interface) in EMPW.The atomic diffusion behavior in the welding process is studied,and the thickness of the diffusion layer at the typical interface is calculated.The microstructure of the bonding interface is analyzed by the transmission electron microscopy.The research results show that the severe collision drives the plastic deformation of the interface material,which forms metallurgical bonding and mechanical engagement.This is the bonding mechanism of the copper aluminum EMPW interface.And the atomic diffusion thickness at the vortex interface is greater than that at the flat interface.This paper can provide a scientific basis for further understanding the mechanism of EMPW and regulating the welding effect.

Highlights:(1) A hybrid calculation method of diffusion layer thickness based on molecular dynamics simulation results is proposed.

(2) The atomic diffusion behavior and the cause of the difference in the formation of typical welding interface are investigated.

(3) Through simulation and experiment,it is revealed that the bonding mechanism of the welding interface under this condition is the combined effect of metallurgical bonding and mechanical engagement.

Key words:electromagnetic pulse welding；interface formation；atomic diffusion behavior；molecular dynamics

The effect of welding method on the fracture toughness of X90 pipeline girth weld jointsREN Wei,SHUAI Jian(China University of Petroleum-Beijing,Beijing,102249,China).pp 32-42

Abstract:With the continuous increase in energy demand in China,the research and development of new generation highgrade pipeline materials has become a hot topic.And X90 pipelines have gradually become the focus of research.However,they have not yet been officially put into use.In the actual construction of oil and gas pipelines,the girth welded joint of the pipeline is a weak link.The welding quality is crucial to ensure the safety of long-distance oil and gas pipelines,and the welding method plays a decisive role in the welding quality of the pipeline.Therefore,it is necessary to study the effect of welding method on the fracture toughness of X90 pipeline girth welded joints and clarify the fracture performance of X90 pipeline girth weld joints.This provides theoretical guidance for the formal use of the X90 pipeline in practical engineering,and also provides technical support for the welding assessment of the X90 pipeline.In order to accurately obtain the fracture toughness of X90 girth welded joints,an improved regularization method was used to test the SENT specimens of X90 girth weld joints for fracture toughness.To accurately obtain the fracture toughness of the X90 circumferential welded joint,an improved regularization method was used to test the SENT specimen of the X90 circumferential welded joint for fracture toughness.Test specimens were extracted from X90 pipeline circumferential welded joints welded by manual welding,self-shielded flux-cored semi-automatic welding,and gas-shielded flux-cored semi-automatic welding,respectively,and fracture toughness tests were conducted.The results showed that the resistance curve obtained from the specimens with shallow cracks is lower than that obtained from the specimens with deep cracks under the same welding method.The specimens with deep cracks in the heat-affected zone have the highest resistance curve,while the specimens with shallow cracks in the heat-affected zone have the lowest resistance curve.The weld zone specimens were prone to brittle fracture during the test and had relatively poor fracture performance.Furthermore,they were greatly influenced by the welding method,with all of the weld zone specimens welded with gasshielded flux-cored semi-automatic welding experiencing brittle fracture.Therefore,gas-shielded flux-cored wire semiautomatic welding needs to be optimized as a reference method in practical X90 pipeline engineering applications,which is crucial for maintaining the integrity of the X90 pipeline structure.

Highlights:(1) A novel method for measuring the fracture toughness of pipeline girth welded joints with low constraint SENT specimens is proposed.

(2) The effect of welding method on the fracture toughness of X90 pipeline girth weld joint was studied to reveal the fracture toughness principle under different welding methods.

Key words:welding method；the girth weld；low constraint specimens；R curve；fracture toughness

Analysis of surface roughness of fluorocarbon aluminum powder coating during laser cleaning and its influence on laser absorptionZHU Ming1,2,ZHANG Hao1,SHI Kun1,HOU Xiaofei1,SHI Yu1,2(1.State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metals,Lanzhou University of Technology,Lanzhou,730050,China；2.Key Laboratory of Non-ferrous Metal Alloys and Processing of State Education Ministry,Lanzhou University of Technology,Lanzhou,730050,China).pp 43-53

Abstract:In the process of laser cleaning the paint layer on the surface of 2024 aluminum alloy aircraft skin,the formation and evolution of rough surfaces can significantly affect the thermal interaction between the paint layer and the laser,as well as the removal mechanism.This study analyzed the changes in surface morphology and roughness of the paint layer during the layer-by-layer removal process using a 1 064 nm pulsed laser.It investigated the generation mechanism and evolution pattern of rough surfaces,and calculated the effect of the rough surface of the paint layer on the laser absorption rate during the layer-by-layer removal process by establishing an equivalent analysis model for the rough surface of the paint layer.The results show that，rough surfaces appear on the paint layer after different removal mechanisms during the laser paint removal process,and there is a certain pattern in the evolution of rough surfaces during the layer-by-layer laser paint removal process;during the laser layer-by-layer paint removal process,the rough surfaces significantly increase the laser absorption rate,with an increase of 32.8% in the laser absorption rate after 7 laser treatments.If a fixed initial laser cleaning process is used,the increased absorption rate will lead to damage to the aluminum alloy substrate.

Highlights:(1) The evolution of surface roughness in paint layers during laser paint removal process was studied.

(2) The impact of the variation in surface roughness of fluorocarbon aluminum powder coatings on laser absorption was investigated by establishing an equivalent model for rough surface.

Key words:laser cleaning；aluminium alloy；paint layer；rough surface；absorptivity

Microstructure and properties of aluminum/copper bluered hybrid laser welded jointSHI Yingjie1,CUI Zeqin1,2,DING Zhengxiang3,HAO Xiaohu1,2,3,WANG Wenxian1,2,LI Weiguo4(1.College of Materials Science and Engineering,Taiyuan University of Technology,Taiyuan,030024,China；2.Shanxi-Zhejiang University New Materials and Chemical Research Institute,Taiyuan,030032,China；3.Technology for Ships,CSSC Huangpu Wenchong Shipbuilding Company Limited,Guangzhou,Guangzhou,510715,China；4.Engineering Training Center of Taiyuan University of Technology,Taiyuan,030024,China).pp 54-60

Abstract:In order to realize efficient and reliable welding of power battery,1050 aluminum/T2 copper lap welding was carried out by using blue-red laser heat source.The effects of laser power on the microstructure,phase distribution mechanical properties and electrical conductivity of the joint were investigated.The results show that the weld surface of Al/Cu lap joint is smooth and the section is “T” shape.When PB (Blue laser power) remains 300 W,PR(Infrared laser power) increases in 700 W～ 1 400 W,the copper side penetration depth increases from 60 μm to 1 000 μm,achieving a good metallurgical bonding withPR=800 W.The weld microstructure is composed of Al solid solution,Al-Cu eutectic alloy and Al2Cu intermetallic compound phases.With the increase of laser power,Al4Cu9phases appear locally in the weld,and AlCu,Al4Cu9and AlCu3phases appear at the edge.WhenPR=800 W,the weld strength reaches the maximum of 108.6 MPa,and the contact resistance reaches the minimum of 94 μΩ.The crack starts from the junction of two plates region (Al2Cu) and extends along the weld edge from the outer Al2Cu region to the junction of Al solid solution and Al-Cu eutectic alloy at the bottom.The fracture form is cleavage fracture.

Highlights:With the characteristics of high absorption of blue laser by non-ferrous metals and high energy density of infrared laser,the blue-infrared hybrid laser are used to realize the connection of dissimilar metals with high reflectivity and heat conductivity.

Key words:hybrid laser welding；Al/Cu dissimilar material；reaction at interface；micro-structure；mechanical properties；conductivity

Fatigue crack initiation simulation of weld toe based on the Roe-Siegmund cyclic cohesive zone modelZHAO Qiu1,TANG Kun1,LI Yinghao1,WU Weiqing2(1.School of Civil Engineering,Fuzhou University,Fuzhou,350116,China；2.Fujian College Association Instrumental Analysis Center,Fuzhou University,Fuzhou,350116,China).pp 61-67

Abstract:In order to establish a simulation method for the fatigue crack initiation behavior of the weld toe,ABAQUS was developed based on the Roe-Siegmund cyclic cohesive zone model to form the VUMAT subroutine for reflecting the fatigue cumulative damage.The cohesive parameters of Q345 weld zone materials were obtained by referring to the literature and experimental data.The Voronoi diagram method and cohesive element method were used to generate a microscopic model with fatigue cumulative damage characteristics and grain characteristics.This model was then merged with the macroscopic butt weld model to simulate multi-scale fatigue crack initiation.The results show that this method can spontaneously select the crack initiation location and the short crack extension path in accordance with the actual situation,and complete the simulation of the microfracture process of the material in the welded area,the critical cycle number obtained by different simulation groups exists in a certain distribution range,and the cumulative cohesive length needs to be fitted by experimental data.

Highlights:(1) Based on the Roe-Siegmund cyclic cohesive zone model,the VUMAT subroutine is written to realize the fatigue damage accumulation of cohesive elements.

(2) Based on Voronoi diagram method and cohesive element method,multi-scale fatigue crack initiation simulation is accomplished with Python script modeling and material assignment.

Key words:weld toe；crack initiation；cyclic cohesive zone model；cohesive element method；Voronoi diagram method

Numerical simulation of residual stress in YG8/GH4169 dissimilar material brazed jointsQIAO Ruilin1,LONG Weimin1,QIN Jian1,2,LIAO Zhiqian3,FAN Xigang4,WEI Yongqiang5(1.State Key Laboratory of Advanced Brazing Filler Metals &Technology,Zhengzhou Research Institute of Mechanical Engineering Co.,Ltd.,Zhengzhou,450001,China；2.University of Science and Technology Beijing,Beijing,100083,China；3.Luoyang Ship Material Research Institute,Luoyang,471039,China；4.Beijing Xinghang Electro-mechanical Equipment Co.,Ltd.,Beijing,100074,China；5.Zhengzhou University of Aeronautics,Zhengzhou,450046,China).pp 68-74

Abstract:Drilling sampling is the preferred method to achieve lunar soil sample collection.To address the issue of high residual stress and poor connection quality in dissimilar material brazed joints within drilling sampling tools,this paper uses ANSYS finite element software as a platform and a numerical simulation method to study the distribution of residual stress in a YG8/GH4169 brazed joint,as well as the influence of adding Cu and Mo interlayers on the residual stress in the joint.The results indicate that there is a great deal of residual stress in the brazed joint of cemented carbide/superalloy.The dangerous area of stress concentration is the vertex of the cemented carbide near the welding seam,with a maximum axial residual stress of about 1 304 MPa.Adding Cu and Mo interlayers can effectively alleviate residual stress in the joint.When the thickness of the interlayers is less than 0.6 mm,Cu has a better relieving effect on residual stress in the joint.When the thickness of the interlayers is greater than 0.6 mm,Mo has a better relieving effect.When Cu and Mo are used as interlayers,the optimal thickness for relieving residual stress in the joint is around 1.0 mm.The experimental results of residual stress in dissimilar materials brazed joints are basically consistent with the numerical simulation results.

Highlights:(1) The distribution of residual stresses in the joints was analyzed by establishing a residual stress model for cemented carbide/superalloy brazed joints.

(2) The influence of various interlayer materials and thickness on the residual stresses of brazed joints was investigated.

Key words:numerical simulation；residual stress；cemented carbide；superalloy；brazing

Microstructure and toughness of heat-affected zone in girth welding of X80 steel pipe with different Nb contentHE Xiaodong1,2,YANG Yaobin1,2,CHEN Yuefeng1,2,David Han2,ZHANG Yongqing2,3(1.State Key Laboratory for Performance and Structure Safety of Petroleum Tubular Goods and Equipment Materials,CNPC Tubular Goods Research Institute,Xi’an,710077,China；2.International Welding Technology Center,Xi’an,710077,China；3.CITIC Metal Co.,Ltd.,Beijing,100004,China).pp 75-81

Abstract:In order to study the effect of Nb content on the microstructure and properties of heat affected zone (HAZ),the 0.055%Nb and 0.075%Nb content X80 steel pipes were girth welded by Gas metal arc welding (GMAW) and shielded metal arc welding (SMAW).Charpy impact test and metallographic analysis were used to study the impact toughness and microstructure differences in the HAZ.The effects of the microstructure of X80 pipe body with different Nb content on the properties of the heat-affected zone were analyzed by scanning electron microscope and confocal laser microscope with high temperature.The results show that at 0 ℃ and −20 ℃,0.075%Nb and 0.055%Nb X80 steel pipes have high impact toughness in the HAZ of GMAW girth welded joints,and their average impact absorbed energy are higher than 150J.However,the Charpy impact absorbed energy in the HAZ of GMAW girth welded joint of X80 steel pipe with 0.055% Nb is higher than that of X80 steel pipe with 0.075%Nb.When GMAW is used,the ductile-brittle transition temperature(DBTT) of X80 girth welded joint with 0.055%Nb is lower than that of X80 with 0.075%Nb because of the low welding heat input.When SMAW is used,due to higher heat input,the coarse grain heat affected zone (CGHAZ) of X80 girth welding joint with 0.075%Nb has higher impact absorbed energy on the upper-shelf and lower temperature of upper-shelf zone and DBTT,and its low temperature toughness is better.It is also discussed that the impact toughness of the HAZ of X80 girth welded joint is not only related to the heat input and the shape,size and distribution of M-A,but also genetically influenced by the content of Nb in the pipe body and the original strength,toughness and microstructure state.

Highlights:(1) The toughness distribution of HAZ in GMAW girth welded joint of X80 steel pipe with different Nb content was investigated.

(2) The ductile to brittle transition behavior of HAZ in the girth welded joint under different heat inputs for X80 steel pipes with different Nb content was compared and analyzed.

(3) The genetic effects of strength,toughness and microstructure of X80 steel pipe with different Nb content on toughness of HAZ were analyzed.

Key words:X80 steel pipe containing niobium；girth welded joint；HAZ；impact toughness；M-A

Image processing technology for ship plate melt pool based on MS-FCM algorithmXU Yuanzhao1,2,LUO Jiutian1,2,FANG Naiwen3,FENG Zhiqiang1,2,WU Pengbo3,LI Quan1,2(1.Guangxi Ship Digital Design and Advanced Manufacturing Engineering Technology Research Center,Beibu Gulf University,Qinzhou,535011,China；2.Guangxi Key Laboratory of Marine Engineering Equipment and Technology,Qinzhou,535011,China；3.China National Machinery Engineering Corporation Harbin Welding Research Institute Co.,Ltd.,Harbin,150028,China).pp 82-90

Abstract:The image processing and feature extraction technology of molten pool is an important part of intelligent welding quality monitoring for gas metal arc welding (GMAW) on ships.To address the unstable characteristics of large smoke and spatter during GMAW welding of ship hull plates,such as blurred image acquisition and difficult edge extraction,a fuzzy c-means clustering (FCM) based on mean shift (MS) optimization is proposed The image processing algorithm for In the optimization design of the welding dynamic visual sensing system,on the basis of maximizing the clarity of image information acquisition,the MS algorithm is used to obtain superpixel images to solve the sensitivity of the FCM algorithm to noise.At the same time,a weighted neighborhood window is introduced on the FCM algorithm to enhance the robustness of the MS-FCM algorithm,overcome the effects of smoke,spatter,arc light,noise,etc.,and complete image segmentation and edge extraction Finally,four different image processing methods were designed for FCM,fuzzy c-means with spatial constraints (FCM-S),enhanced fuzzy c-means (ENFCM),and fuzzy local information c-means clustering (FLICM) algorithms.The edge segmentation effects were compared with the MS-FCM optimization model to obtain the extracted fusion widths from these methods,Verify the accuracy of extracting geometric features of the molten pool The results show that the MS-FCM algorithm can effectively suppress noise interference,smooth information,and achieve high extraction accuracy in ship welding pool image processing.

Highlights:(1) Using the MS algorithm to optimize the FCM algorithm,it overcomes the sensitivity of traditional FCM algorithms to noise and extracts the complete contour of the molten pool from images containing a large amount of noise interference.

(2) Based on the FCM algorithm,a weighted neighborhood window is added to enhance the robustness of the algorithm.

Key words:Fuzzy C-means clustering；mean drift；image segmentation；hull plate；melting gas shielded welding

Study on factors affecting high temperature anisotropic stress rupture properties of SLM-IN718 alloyHE Siyi1,2,LIU Xiangyu1,2,GUO Shuangquan3,WANG Ning4,XIAO Lei5,XU Yi1,2(1.School of Materials Science and Engineering,Southwest Jiaotong University,Chengdu,610031,China；2.Key Laboratory of Advanced Technologies of Materials,Ministry of Education,Southwest Jiaotong University,Chengdu,61003,China；3.Chengdu Tianxiang Power Technology Research Institute Co.,Ltd.,Chengdu,610095,China；4.Sichuan Hitaipu Technology Co.,Ltd.,Chengdu,610095,Chin；5.Sichuan Liuhe Special Metallic Materials Co.,Ltd.,Jiangyou,621700,China).pp 91-98

Abstract:IN718 components often need to be used in high temperature complex stress environment for a long time.High temperature stress rupture and anisotropy are important performance indexes.In order to study the influence factors on the lasting anisotropy of Selective Laser Melting (SLM) forming IN718,the printing state was treated by solution aging (SA)and direct aging (DA) respectively.X-ray diffraction (XRD),scanning electron microscopy (SEM) and electron backscattering diffraction (EBSD) were used to characterize the phase,microstructure and texture of XY and YZ plane of the samples in two states.The stress rupture of the horizontal/vertical samples in two states was tested at 690 MPa and 650 ℃.After the test,the fracture and section crack were characterized and quantified.The results show that the printed microstructure of DA samples is maintained to a large extent,and there are obvious molten pool traces.The grain size hardly changes.The microstructure shows a large amount of segregation,and XRD shows a slight peak of MC phase.The grain size and distribution of SA samples are similar to that of DA samples,and there is a large range of δ phase precipitation.The difference of high temperature stress rupture between horizontal/vertical specimens decreases with the decrease of the number of crack initiation points.The difference of molten pool structure and grain boundary structure perpendicular to the stress loading axis is the key factor affecting its stress rupture anisotropy at high temperature.

Highlights:(1) The phase composition,grain morphology and preferred orientation of IN718 alloy formed by SLM under different heat treatments were determined.

(2) The relationship between the microstructure of IN718 alloy formed by SLM and the anisotropic stress rupture properties at high temperature was revealed.

Key words:selective laser melting；high temperature stress rupture；anisotropy；microstructure

Microstructure evolution and property analysis of Mg1/Al1060 vacuum diffusion welded jointsZHUANG ZhiGuo,DING Yunlong,ZHANG Encheng,ZHOU Zheng(University of Science and Technology Liaoning,Anshan,114051,China).pp 99-106

Abstract:The reaction of industrial pure magnesium Mg1 and industrial pure aluminum Al1060 was realized by using vacuum diffusion welding technology.Scanning electron microscope,energy spectrometer,universal mechanical testing machine,microhardness tester and electrochemical workstation were used to study the microstructure,physical composition and properties of diffusion bonding layer.The results show that Mg/Al vacuum diffusion welding generated a diffusion reaction layer composed of magnesium-aluminum intermetallic compounds at the joint,and with the prolongation of the holding time,the thickness of the reaction layer gradually increases,and the microstructure morphology undergoes obvious changes.At the initial stage of diffusion,the reaction layer shows a monolayer structure,and the Mg2Al3phase precipitates preferentially at the joint interface;when the holding time reaches 60 min,the interface generates a new phase layer of Mg17Al12;when the holding time is extended to 90 min,the reaction layer evolves into a three-layer structure consisting of a Mg2Al3layer,a Mg17Al12layer,and a (Mg17Al12+Mg-based solid solution) layer.With the prolongation of the holding time,the shear strength of the joint showed a tendency of increasing and then decreasing,and the shear force that could be withstood during the holding time of 60 min reached 1 245.7 N,and the fracture occurred at the Mg2Al3reaction layer near the aluminum side.The microhardness of each welded layer was significantly higher than that of the magnesium and aluminum base material,and the Mg2Al3layer exhibited the highest microhardness of 320.6 HV.The corrosion current density of the Mg1 layer was the smallest,2.199 × 10−3A/cm2,while the corrosion current density of the Al1060 layer,the Mg2Al3layer,the Mg17Al12layer,and the (Mg17Al12+Mg based solid solution) layer increased by one order of magnitude.The order of corrosion rate is Mg1 >(Mg17Al12+Mg based solid solution)>Mg2Al3>Mg17Al12>Al1060.

Highlights:(1) The evolution of the microstructure of vacuum diffusion welded layers of Mg1 and Al1060 was investigated.

(2) The mechanical properties and corrosion resistance of magnesium-aluminum intermetallic compounds were analyzed.

Key words:diffusion welding；microstructure；diffusion reaction layer；intermetallic compound

Effect of Nb components on the microstructure and mechanical properties of high-entropy alloy coatingsWANG Yongdong,GONG Shulin,CHANG Mengyang,WANG Jinyu,REN yuanda,JING zonghao(Heilongjiang University of Science and Technology,Harbin,150022,China).pp 107-113

Abstract:CoCrFeNiTi0.8Nby(y=0.25,0.5,0.75,1.0)coatings were prepared on the surface of Q235 steel using laser cladding.The phase structure and microstructure of the coatings were analyzed by optical microscope (OM),X-ray diffractometer (XRD),scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS).The hardness and wear resistance of the coatings were tested by micro-Vickers hardness tester and friction wear tester.The results show that the microstructure shows a typical dendritic crystal structure,and the addition of Nb elements decreases the size of the grains;by increasing the content of Nb elements,the crystal structure of the high-entropy alloy coatings consists of BCC phases,a small amount of FCC phases,and Fe2(Ti,Nb)-type Laves phases;the microhardness of the coatings is improved by the combined effect of fine-grained reinforcement,solid solution strengthening,and the strengthening of the second phase;The presence of the intermediate phase can hinder the plough cutting process to a certain extent,which improves the wear resistance of the coating;CoCrFeNiTi0.8Nb0.75coating has the best hardness and wear resistance,the hardness of 710 HV,about 4 times that of the substrate,and the coating has the smallest amount of abrasion,and the abrasion marks are relatively flat.

Highlights:(1) CoCrFeNiTi0.8Nbyhigh entropy alloy composite coating was successfully prepared.

(2) The appropriate Nb component was obtained by analyzing the microstructure and wear resistance of the coatings.

Key words:laser cladding；High-entropy alloy；microstructure；wear resistance；mechanical properties

Online monitoring of GMAW welding defect based on deep learningXU Donghui1,MENG Fanpeng1,SUN Peng1,ZHENG Xuchen1,CHENG Yongchao2,MA Zhi2,CHEN Shujun3(1.CRRC Qingdao Sifang Rolling Stock Research Institute Co.Ltd.,Qingdao,266114,China；2.CRRC Industrial Academy Co.Ltd.,Beijing,100160,China；3.Beijing University of Technology,Beijing,100124,China).pp 114-119

Abstract:Utilizing the aluminum alloy exterior plate of the driver's cab of high-speed railway in rail transit as the substrate,the research is conducted on key intelligent welding technologies,focusing on the issue of online monitoring of welding defects.With the help of process test platform and welding procedure specification,welding defect experiment design,batch data collection,expert experience calibration and database construction are implemented.The convolutional neural network algorithm is used to construct multi-dimensional information fusion models for different types of data,and parameters of the fusion models are optimized.Finally,training,verification and testing of fusion models are completed.The results show that the fusion model after training has better recognition results for welding defects than the single information model.The monitoring accuracy of welding defects in the training set and the testing set is 99.0% and 88.3%,respectively.The data acquisition and model response total time for this monitoring system is less than 100 ms,which meets the requirements for engineering applications,enhances the level of intelligence in robotic welding,and drives the digital transformation and upgrading of enterprises.

Highlights:(1) A welding quality online monitoring system has been developed,capable of real-time monitoring of welding state and the tracing of multi-dimensional information throughout the welding process.

(2) A multi-dimensional information fusion model based on deep learning has been constructed,enabling high-precision online recognition of welding state.

Key words:GMAW；deep learning；multi-dimensional information fusion；welding defects；online monitoring

Study on microstructure and low-temperature impact toughness of deposited metal form covered electrodes for 440 MPa grade high-strength steelZENG Daoping1,2,ZHENG Shaoxian1,AN Tongbang2,DAI Haiyang2,MA Chengyong2(1.Lanzhou Jiaotong University,Lanzhou,730070,China；2.Welding Research Institute,Central Iron and Steel Research Institute,Beijing,100081,China).pp 120-128

Abstract:To meet the welding material requirements of 440 MPa grade high-strength steel,three types of covered electrodes have been developed,and the welding test of deposited metal was carried out.The microstructure and low-temperature impact toughness of deposited metal were analyzed by means of the optical microscope,scanning electron microscope,and transmission electron microscope.The results show that with the increase of Mn,Ni,Cr,and Cu contents,the average impact absorption energy of the deposited metal at −40 ℃gradually increases from 35.7 J to 96.3 J,and the low-temperature impact toughness gradually increases;With the increase of Mn,Ni,Cr and Cu contents,although the content of M23C6type carbide in the deposited metals gradually increases,the CCT curve of the deposited metals gradually moves to the right,and the transformation temperature gradually decreases,which makes the content of acicular ferrite gradually increase,the size of ferrite lath gradually decreases,and the interlaced distribution trend between ferrite lath gradually increases,and the content and size of M-A constituent gradually decrease,which is the main reason for the gradual improvement of lowtemperature impact toughness;The outer layer of inclusions in the deposited metal containing Cu can form CuS,making it easier for acicular ferrite to form nuclei,which is conducive to improving low-temperature impact toughness.

Highlights:Three types of covered electrodes have been successfully developed for 440 MPa grade high-strength steel,and the influence of microstructure of deposited metal on low-temperature impact toughness has been described.

Key words:440 MPa grade high-strength steel；deposited metal；acicular ferrite；M-A constituent；low-temperature impact toughness