MAIN TOPICS，ABSTRACTS & KEY WORDS

Researchprogressonparallelgapresistanceweldingmicro-connectiontechnology

Li Xun, Wang Min, Hua Xueming, Shen Chen

(Shanghai Jiao Tong University, Shanghai Key Laboratory of Materials Laser Processing and Modification, Shanghai 200240, China).p1-5,18

AbstractIn this paper, the connection mechanism of parallel gap resistance welding was introduced, that is, good interface bonding was mainly achieved by solid phase diffusion, and the influence law of contact resistance was discussed.The distribution of temperature field and stress-strain field in the welding process of wire/sheet and sheet/sheet was emphatically introduced, and the influence of welding parameters such as welding voltage, welding time, electrode pressure and electrode spacing on the welding quality was described in combination with test and simulation results.Finally, the application prospect of parallel gap resistance welding was prospected, and the direction of simulation research was discussed.

Keywords:parallelgapresistancewelding,connectionmechanism,contactresistance,numericalsimulation,temperaturefield

Researchandapplicationprogressofmulti-strandsweldingwire

Xu Kai1, Wu Pengbo1, Huang Ruisheng1, Liang Xiaomei1, Liang Yu2

(1.Harbin Welding Institute Co., Ltd., Harbin 150028, China；2.Jiangsu Lianjie Welding Technology Co., Ltd., Jiangyin 214400, Jiangsu, China).p6-18

AbstractStructural characteristics of the multi-strands welding wire and its arc characteristics as a fusion electrode welding material were introduced in detail, and its research progress of various welding methods and the current status of welding applications were discussed comprehensively.Moreover, its future development was prospected.Judging from the current research results, the research on multi-strands welding wire mainly focused on large-diameter carbon steel and stainless steel.As a molten electrode welding material, the multi-strands welding wire had characteristics of arc coupling, rotating arc and stirring molten pool to help improve comprehensive performance of welded joints, which could effectively solve problems that were difficult to solve for traditional welding wire, such as large heat input of large-diameter welding wire, uneven weld microstructure, large weld porosity, poor sidewall fusion and low deposition speed.Due to the high production cost, lack of relevant standards and supporting welding power and welding auxiliary equipment, the promotion and application of the multi-strands welding wire was restricted.Therefore, some suggestions were made for the future development of the multi-stranded welding wire in the paper.

Keywords:multi-strandsweldingwire,energyefficient,rotatingarc,highqualitywelding

Researchstatusofaviationhigh-strengthsteelinelectronbeamwelding

Hong Min, Wang Shanlin, Sun Wenjun, Wu Ming, Xu Yong

(Nanchang Hangkong University, Jiangxi Provincial Key Laboratory of Aviation Component Forming and Connection, Nanchang 330063, China).p19-29

AbstractFor the electronic beam welded joint of aviation high strength steel, law of formation, law of microstructure transformation, evaluation of mechanical properties, microstructure and performance control were discussed in detail in this paper.It was pointed out that the gas and liquid movement trajectory in the spoon hole of the aviation high-strength steel electron beam welded joint was complicated, and the material was sensitive to cracks, which easily resulted in porosity and cracking.Due to the different welding thermal cycles in joints, there were great differences in the microstructure of joints, which resulted in uneven mechanical properties.The focus of the research was to prevent the occurrence of cracks, solve the softening of the heat-affected zone and improve the fatigue performance of the joint.Finally, the key research directions of the electron beam welding technology for aviation high-strength steel materials were prospected.

Keywords:aviationhigh-strengthsteel,formationofweld,lawofmicrostructuretransformation,evaluationofmechanicalproperties,performancecontrol

Effectofinductionbrazingprocessonmicrostructureandpropertiesofbrazingseam

Zhang Guanxing, Zhang Lei, Shen Yuanxun, Dong Hongwei

(Zhengzhou Research Institute of Mechanical Engineering Co., Ltd., State Key Laboratory of Advanced Brazing Filler Metals & Technology, Zhengzhou 450001, China).p30-34,41

AbstractEffects of brazing temperature, flux amount and holding time on quality of the brazing seam for hard alloy milling cutters were systematically researched through methods of scanning electron microscope and universal mechanical testing machine.The research results showed that the damage degree of high temperature to the strength of the brazing seam was significantly higher than that of low temperature.The main reason was that the flux began to fail at high temperature and did not effectively protect the brazed area.The internal oxidation phenomenon of the brazed seam was very obvious and the oxygen content was as high as more than 30%.The enrichment of oxygen occurred in the entire observation area, and the oxidation resistance of the copper-rich phase was significantly lower than that of the silver-rich phase.When extending the holding time to 5 ～ 6 s at the same brazing temperature, the wettability of brazing filler metal on the base metal was significantly improved and the tensile strength of the brazed joint reached above 410 MPa.However, if the holding time continued to increase, the flux would lose its protective ability and the strength of the joint would begin to decrease.When the amount of flux applied was larger, some flux slag appeared at the interface of the brazed joint, which would easily affect the performance of the joint.The amount of flux must be reasonably controlled.

Keywords:brazingprocess,silverbasedbrazingfillermetal,microstructure,brazingstrength,defect

Effectofdefocusingamountonkeyholebehaviorin30kWfiberlaserweldingofaluminumalloy

Nie Xin, Yang Yicheng, Huang Ruisheng, Zhou Jun, Jiang Bao

(Harbin Welding Institute Limited Company, Harbin 150028, China).p35-41

AbstractAiming at the problem of poor formation of weld in 30 kW fiber laser welding of aluminum alloy, the images of weld pool and keyhole in the welding process were taken by high-speed camera, and effect of different defocusing amount on keyhole behavior was studied comparatively.The results showed that defocusing amount had a great influence on keyhole and molten pool behavior.In the case of positive defocusing amount, the fluctuation degree of keyhole opening area was more violent, and the back wall of keyhole was easy to form upward flowing liquid column, accompanied by a large number of splashes.The large-scale mutation of keyhole opening area and the falling process of liquid column would greatly disturb the stable flow of liquid molten pool, resulting in defects such as depression and undercut on the weld surface.In the case of negative defocusing amount, the area of keyhole opening was relatively small in both fluctuation amplitude and duration of abrupt change.In the case of-20 mm defocusing amount, the duration of sudden expansion contraction of keyhole was only 1/3 of that of positive defocusing amount, the tendency of liquid column formed by liquid metal upwelling was also small, the welding process was more stable, and the quality of weld surface forming was significantly improved.The penetration of single laser weld reached 29 mm.

Keywords: 30kWfiberlaser,aluminumalloy,keyhole,moltenpool,formationofweld

Onlinedetectionofdefectsinarcadditivemanufacturingbasedoninfraredtemperaturefield

Xiao Yu, Chen Xi, Hu Jiannan, Zhang Haiou

(Huazhong University of Science and Technology, Wuhan 430074, China).p42-46,54

AbstractAccording to the particularity of layer by layer accumulation in additive manufacturing, the idea of online layer detection could avoid irreparable wastes after finishing processing.A nondestructive detection method was adopted based on real-time acquisition and analysis of the infrared temperature field of the fusion layer.The infrared contour of the fusion layer by stacking multiple frames of temperature field data was obtained, and the forming quality of the current fusion layer was judged according to the extracted infrared contour characteristics.Finally, the infrared contour image was classified and identified through the residual network ResNet18.Through online verification, the accuracy of detection classification could reach 97.16%, and the detection and classification time of the single infrared contour image was only 1.35 ms.This method could be used to detect the forming quality in the process of additive manufacturing, which was convenient for subsequent milling, repair welding and optimization of process parameters.It had practical engineering significance.

Keywords:arcadditivemanufacturing,onlinedetection,stackingtemperaturefield,contourofthefusionlayer

Transientbehaviorandinfluencefactorsofkeyholeinlaserdeeppenetrationspotwelding

Liu Tong, Han Xiaohui, Zhang Tiehao, Li Gangqing

(CRRC Qingdao Sifang Rolling Stock Co., Ltd., Qingdao 266111,Shandong, China).p47-54

AbstractThe transient behavior of keyhole in laser deep penetration spot welding was studied by method of numerical simulation.A numerical model of two-dimensional transient keyhole in laser spot welding was established.The evolution and transient behavior of keyhole in the process of both continuous and pulse laser spot welding were analyzed respectively.The various factors that affected the growth of keyhole were studied by applying different calculation conditions.The results showed that depth of the keyhole increased with the accumulation of heat input and the keyhole oscillated constantly in the continuous laser spot welding.However, the evolution of the keyhole was periodic and consistent with the pulse period in the pulse laser spot welding.When the laser was turned off, the depth of the keyhole decreased or even closed.When the laser was turned on, the keyhole increased quickly to the depth before the laser was turned off.The recoil pressure was the necessary factor to form the keyhole, while the surface tension was the force to hinder the formation of the keyhole.With the increase of viscosity, the width of weld pool decreased and the depth of keyhole and weld pool increased.

Keywords:laserwelding,keyhole,transientbehavior,numericalsimulation

EffectofheattreatmentonmicrostructureandpropertiesofTP304H/R102dissimilarsteelweldedjoints

Bai Fengchen1, Ma Wenshu2, Yu Yandong3, Song Haijiang1

(1.Heilongjiang Vocational College, Harbin 150080, China; 2.Guangzhou Urban Construction Vocational College, Guangzhou 510925, China; 3.Harbin University of Science and Technology, Harbin 150080, China).p55-60

AbstractIn order to improve the high-temperature performance of ferrite-austenite dissimilar steel welded joints in the high-temperature section of the heating surface pipe system of power plant boilers, and improve the service life of the joint, a special heat treatment system and aging treatment conditions were formulated.Through mechanical properties test, high temperature creep rupture strength test, optical metallographic microstructure observation and other methods, the mechanical properties at room temperature, microstructures under different aging conditions, hardness distribution and carbon migration of TP304H/R102 dissimilar steel joints in welded state and different heat treatment regimes were analyzed.The results showed that under the selected filler material and welding process, proper heat treatment process played a positive role in eliminating the hardening tendency of TP304H/R102 dissimilar steel joints, improving the microstructure stability of low alloy heat-resistant steel and reducing carbon migration and diffusion(from low alloy steel side to weld metal)and carbides accumulation, so as to ensure the high temperature creep rupture strength and improve service condition of joints.

Keywords:dissimilarsteeljoint,impacttoughness,hightemperaturecreeprupturestrength,carbonmigration,post-weldheattreatment