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Articles in press have been peer-reviewed and accepted, which are not yet assigned to volumes /issues, but are citable by Digital Object Identifier (DOI).
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Establishment of pipe FEA model and influence of structural symmetry on its residual stress
Guangwei YU, Qingcheng XIE, Junliu YANG, Ruiyun SHI, Xiangyu CAI, Wenhai LI
Accepted Manuscript  doi: 10.12073/j.hjxb.20210428001
[Abstract](4) [FullText HTML](0) [PDF 3787KB](3)
At present, there is barely any research on the residual stress of the pipe welded by dissimilar metals in the drive shaft of the controllable pitch propeller. As the core power elements of the controllable pitch propeller, reliability of the pipe is particularly important. Based on the finite element software ANSYS, the thermal-elastoplastic finite element model for the analysis of the welding temperature field and stress field of the outer tubing was established with a four-ellipsoid heat source model to simulate the welding heat input. The model was verified by experiments. On this basis, the influence of the simplification method of the long weld FE model and the symmetry of the welded structure on the residual stress of the pipe is studied. The research results show that, on the basis of ensuring the calculation accuracy, the calculation speed of the simplified pipe finite element model is 8 times that of the original model. The residual stress of the pipe with asymmetrical structure is obviously greater than that of the pipe with symmetrical structure in numerical value. To a certain extent, the pipe with asymmetrical structure can reflect the residual stress distribution at the weakest position of the pipe with symmetrical structure.
Design and modeling analysis of saddle seam welding robot
Xiaofei CHENG, Sheng GAO, Jun LI, Yunlong PAN, Haichao LI
Accepted Manuscript  doi: 10.12073/j.hjxb.20210831001
[Abstract](11) [FullText HTML](0) [PDF 1431KB](4)
In view of the problems of poor flexibility, low degree of automation, and insufficient stability of joint quality of the current saddle-shaped weld welding equipment, a new type of external anchored four-axis welding robot was developed. The D-H link coordinate system is established by rationally simplifying the robot mechanism, the forward and inverse kinematics expressions of the robot are deduced, and the uniqueness of the inverse kinematics solution is determined by combining the limit values of the robot joint variables. The kinematics of the robot is simulated by MATLAB software, and the simulation results show that the derived forward and inverse kinematic equations are completely correct. Welding experiment by making a prototype, the experimental results show that the welding seam is compact and beautiful, and the deviation of the robot welding torch trajectory in the x, y and z directions is within ±0.35 mm, which fully meets the needs of automatic welding in engineering. It provides the theoretical basis and algorithm support for the continuous trajectory control and offline programming of the saddle-shaped seam welding robot.
Discussion on fatigue evaluation models of steel welded joints treated by HFMI
Xin HU, Yanqing LI, Jinhao HUANG
Accepted Manuscript  doi: 10.12073/j.hjxb.20210703003
[Abstract](0) [FullText HTML](0) [PDF 1483KB](0)
High frequency mechanical impact (HFMI) is widely used in the field as a reliable and efficient repost-weld treatment. In order to evaluate the fatigue life of steel welded joints treated with HFMI under different stress ratio R and material yield strength fy, extensive fatigue test data were re-analyzed using the notch stress approach combined with SWT (Smith-Watson-Topper) and Walker models. The results reveal that the relationship between the fatigue grades FAT, R and fy of the joints under nominal stress system can be expressed by FAT = 0.1 fy + M(R). Under the notched stress system, for joints made of the same material loaded under different R values, both models can be used to predict fatigue life, but the Walker model has higher accuracy. For joints of various materials with different R values, SWT model has a fixed form and can comprehensively consider the influence of R and fy. Based on this, the survival rate PS = 97.7% of the S-N curve with FAT = 325 MPa and slope m = 6.5 is obtained. The research will directly support the fatigue assessment and anti-fatigue design of engineering structures.
Multi-sensor data collaborative sensing algorithm for aluminum alloy TIG welding pool state
Kun ZHANG, Zongxuan ZOU, Ye LIU, Zhengjun LIU
Accepted Manuscript  doi: 10.12073/j.hjxb.20211025001
[Abstract](10) [FullText HTML](1) [PDF 1228KB](5)
Aiming at the non-linear correspondence between the real-time state of welding process parameters and the three-dimensional size of the weld pool in the tungsten inert gas arc (TIG) welding process of aluminum alloy, a multi-sensor TIG welding process based on cyber-physical fusion is studied to establish a multi-sensor TIG welding process collaborative sensing calculation method. First, build a TIG welding process molten pool state information physical fusion system architecture consisting of infrared temperature sensors, arc shape sensors, arc energy sensors and welding position sensors. Then, considering the influence of the environment and measurement noise in the welding process, a three-dimensional parameter state sensing strategy of the length, width and depth of the molten pool based on the exchange of temperature, position, and energy sensor information is designed. Based on the asynchronous and heterogeneous characteristics of multi-sensor data, a new method based on Multi-sensor data collaborative sensing algorithm for the state of the molten pool in the welding process based on trace Kalman filtering. Finally, taking the TIG welding process of 7075 super-hard aluminum alloy as the test object, the test results show that the proposed algorithm can calculate the welding pool parameter results in real time according to the motion characteristics of the welding torch and the arc in the welding seam of the TIG welding process. The error of the calculation results of the weld width and weld height can be controlled within 10%, and the response time of the algorithm is within 0.3 s, which can accurately evaluate the real-time state of the weld pool.
Analysis and application of explosive welding window for dissimilar metals
Wenxuan LI, Meixiang DAI, Xiaoming WU, Zerui SUN, Zhonghang FANG
Accepted Manuscript  doi: 10.12073/j.hjxb.20211013002
[Abstract](10) [FullText HTML](3) [PDF 1795KB](1)
Explosive welding window is an important method to obtain good bonding quality. The theoretical model and parameter selection of calculation are very important to the results. Starting from the parameters of explosive welding, by analyzing the development process, theoretical assumptions and parameter selection of the window boundary formula of explosive welding, a convenient window calculation formula is obtained. The formula is applied to titanium/aluminum welding, the welding methods of titanium and different grades of aluminum alloy are analyzed, and the quality of welding interface under different charge ratio is predicted. With the increase of aluminum alloy hardness, the welding window decreases gradually. When the welding parameters are located in the middle of the window, the interface is wavelet and the bonding quality is good; When the welding parameters are close to the upper limit of the window, the interface is large wave and there are a lot of micro defects. The results show that welding window is an important research means and can better guide production practice.
Microstructure and property of flash welded joint of FeCrAl alloy tube
Henglin WANG, Rui CAO, Xiang LI, Hongyan CHE, Tiejun WANG, Wei QIN
Accepted Manuscript  doi: 10.12073/j.hjxb.20210712002
[Abstract](18) [FullText HTML](2) [PDF 8074KB](3)
The butt joints of FeCrAl alloy were welded by flash light welding. The microstructure, oxide distribution and mechanical properties of the welded joints were investigated by scanning electron microscope and energy dispersive spectrometer. The results show that: the microstructure of FeCrAl alloy welded by flash light welding is mainly equiaxed grain. No obvious oxides are aggregated and segregated in the grain boundary of weld metal and heat-affected zone. Most oxides are dispersed in the grain and grain boundary. The tensile strength of the welded joint reaches 594 MPa, which is 90.5% of the strength of the base metal. The joint is fractured in the weld zone and presents the brittle fracture mode as a whole. The grain coarsening of the weld metal makes the hardness decrease, which leads to the softening of the welded joint.
Mechanism of 304 stainless steel underwater flux-cored arc cutting
Rui YU, Wenhang LI, Jianxin WANG, Jiayou WANG, Mingfang WU, Yuri Maksimov Sergii
Accepted Manuscript  doi: 10.12073/j.hjxb.20210811002
[Abstract](2) [FullText HTML](0) [PDF 3886KB](1)
As a high-efficiency, low-cost, and safe underwater cutting method, flux-cored wire arc cutting (FCAC) has broad application prospects. Due to the interference of the underwater complex environment, the stainless steel arc cutting mechanism of this method is still unclear. This research uses a combination of process tests, high-speed camera observation, and numerical simulation. Firstly, the relevant characteristic parameters of underwater cutting are determined through the process test; secondly, the semi-ellipsoid heat source is used to simulate the cutting heat source, and the movement and switching mode of the heat source is set according to the experimental observation; finally, the workpiece is meshed and ascertained the underwater boundary condition, the "birth and death" element method is applied to simulate the removal of molten metal during cutting; by comparing the simulated and actual temperature of measurement point and the kerf after cutting. The results showd that the kerf of underwater flux-arc cutting stainless steel is mainly divided into three types of shapes: "/ \" type, "‖" type and "\ /" type. The underwater stainless steel cutting process consists of multiple periodic continuous perforation processes observed by high-speed camera. It is also validated by simulation to predict the kerf forming process effectively, which helps to further optimize the process and control it effectively.
Research progress of low temperature sintering technology for Cu particles
Junlong LI, Yang XU, Xuelong ZHAO, Yinghui WANG, Suga Tadatomo
Accepted Manuscript  doi: 10.12073/j.hjxb.20210225002
[Abstract](8) [FullText HTML](2) [PDF 1668KB](2)
Metallic nanomaterials are one of the key electronic packaging materials required for power devices in service under high temperature, high pressure and high frequency operating conditions due to their good electrical, thermal conductivity and the ability to be sintered at low temperatures. In this paper, the research on sintering of Cu particles used in power device packaging is reviewed. The current research and development background of low-temperature bonding through Cu particle sintering technology is expounded. The mechanical and electrical properties of low-temperature sintered Cu particle material joints based on different sintering mechanisms are discussed and summarized from the key influencing factors such as preparation of Cu particle paste, technological parameters of sintering process and reduction methods. The excellent characteristics of Cu particle sintering technology applied in the field of die attach and all-Cu interconnects are introduced. The comprehensive analyses of researches show that the current Cu particle materials are still challenged by the oxidation problem, and further in-depth research is needed to achieve precise regulation of the joint properties.
Control of the microstructure and mechanical properties of GTA-based wire arc additive manufactured TiAl alloys using post heat treatment
Xiaoyu CAI, Bolun DONG, Junzhe WANG, Sanbao LIN
Accepted Manuscript  doi: 10.12073/j.hjxb.20210921002
[Abstract](13) [FullText HTML](2) [PDF 6598KB](8)
The control of the microstructure and mechanical properties of deposited TiAl alloys with Al content of 45 at.% using heat treatment was studied. Based on the Ti-Al binary phase diagram, four heating temperatures were used 1 080, 1 200, 1 270 and 1 350 ℃, respectively. Furnace cooling was applied after holding for one hour. It was found that with the increase of the heating temperature, the segregation is gradually eliminated, and the γ phase on the grain boundary decreases. The microstructure changes from two-state structure to full lamellar structure, and the lamellar colony size increases gradually. Preservate heat at 1 350 ℃ for 5 min, 30 min and 60 min, respectively. It was found that the lamellar colony coarsened with the extension of holding time. Based on the single-stage heat treatment, the cyclic heat treatment process was proposed. The deposited parts were heated repeatedly between 900 to 1 200 ℃ and cooled after short-term insulation. The components with fine lamellar structure were obtained, whose hardness reduces, and the compressive strength and compression ratio both increase.
Study on the wettability and the microstructure of SiO2-BN multiphase ceramics
Jinghong YANG, Jiakun LIU, Xi FU, Wenqing WEI, Xiaoguo SONG, Lixia ZHANG, Changchun WANG
Accepted Manuscript  doi: 10.12073/j.hjxb.20210908002
[Abstract](7) [FullText HTML](1) [PDF 5872KB](1)
The wetting and spreading behavior of SiO2-BN multiphase ceramics by Ag-21Cu-4.5Ti alloy filler was studied using the base drop method. The microstructure and the formation mechanism of wetting interface was analyzed by SEM and XRD. The relationship among BN content and wetting and spreading behavior was established. The results showed that the typical interface reaction products of Ag-21Cu-4.5Ti/SiO2-BN were TiN and TiB2, and the wettability gradually improved with the increasing of BN content in the system. The SiO2-BN multiphase ceramics were brazed to the Nb. The typical interface structure was SiO2-BN multiphase ceramics /TiN + TiB2/Ti2Cu + (Ag,Cu)/(Ti,Nb)/Nb. The shear strength of the joint first increases and then decreases with the increasing of brazing temperature. When the brazing temperature was 880oC and the holding time was 10min, the shear strength of the brazing joint was 39 MPa.
Fatigue crack growth analysis of weathering steel joints based on analytical algorithm and J-integral method
Ning Li, Zongzheng Wang, Zihao Zhao, Hui Wang, Viyanit Ekkarut
Accepted Manuscript  doi: 10.12073/j.hjxb.20220121003
[Abstract](5) [FullText HTML](0) [PDF 3497KB](1)
The surface crack propagation dynamics of 12mm thick weathering steel butt joints were monitored by using multi-element ultrasonic phased array to accurately describe the dynamic process of fatigue crack propagation in welded joints, and the geometric evolution between semi-elliptical crack depth, length relating with fatigue life was obtained. By using Abaqus 2018, the finite element analysis model was established, with the geometric dimension of the crack as the input, the energy release rate G in seven directions of the crack tip was calculated, and then the range of stress intensity factor of the crack tip was calculated. The K value of the crack tip (θ = 90 °) is compared with the analytical formula recommended in the BS7910, and the results were in good agreement with each other. Furthermore, the fatigue life of the specimen was calculated by using the simplified formula and the two-stage propagation formula, respectively. The results show that the two-stage crack growth model could accurately predict the fatigue life of butt joints and was in good agreement with the experimental results.
Study on the microstructure and property of the SiC joint brazed with Ti foam/AlSiMg filler metal
Juan LI, Lixin LI, Qingdong QIN, Quan TU, Peng HE
Accepted Manuscript  doi: 10.12073/j.hjxb.20211213001
[Abstract](10) [FullText HTML](0) [PDF 2500KB](3)
In order to enrich the design idea of ceramic filler metal, a new Ti foam/AlSiMg composite filler was proposed. The interfacial adhesion between filler metal and SiC ceramic was improved by the dissolution of Ti element, and the in-situ reinforced brazing seam was obtained by the reaction between Ti foam and AlSiMg metal which improved the mechanical property of the joint. The joints were brazed at 700 oC, 60 min and 10 MPa, and the microstructure, composition and properties were analyzed by optical microscope, SEM, EDS, XRD, EPMA and Shearing test. The results shows that the structure of the joint with Ti foam/AlSiMg filler was “SiC/Al/Ti(Al,Si)3/Composite layer/Ti(Al,Si)3/Al/SiC”. The fracture occurred between the Al alloy interfacial layer and SiC ceramic, and some SiC ceramics were pulled out from the surface of the base materials. The shearing strength of the joint with Ti foam/AlSiMg filler metal was 110.7 MPa.
Accepted Manuscript  doi: 10.12073/j.hjxb.20211126001
[Abstract](9) [FullText HTML](0) [PDF 4865KB](1)
Optimization of PCCP welding process parameters based on improved MULTIMOORA method
Lei GUO, Sihao LI, Lixia GUO, Jun WANG, Pingping CHEN, Jiantao ZHU
Accepted Manuscript  doi: 10.12073/j.hjxb.20211018001
[Abstract](16) [FullText HTML](2) [PDF 701KB](6)
As the main technology of PCCP cylinder processing, welding process control parameters directly affect the quality of weld seams, which in turn affects the performance of PCCP applications. It is particularly important to determine the optimal welding process parameters of PCCP steel cylinder, and the spiral welding process is comprehensively optimized based on the method based on field data acquisition and improved MULTIMOORA method, based on weld characteristic index. Firstly, the data of each index is obtained and sorted, the indicators are converted into multi-attribute decision-making problems, through the evaluation of the index data, the weight factor is defined to allocate the priority, the index is quantified, the scheme is sorted according to the optimization principle, the process adopts the OWA operator and entropy weight method to eliminate the extreme value influence of the subjective evaluation value, the index comprehensive weight is obtained, the decision ranking is optimized, and finally the technical parameters of the welding control process are finally evaluated by using the dominant theory. The results show that the optimal welding parameters of PCCP steel tube are welding current 340 A, arc voltage 24 V and welding speed 10.81 mm/s, which can provide technical reference for PCCP steel tube welding process.
Spatial thermal field distribution characteristics of hollow tungsten arc welding with coaxial filler wire
Yicheng YANG, Bing DU, Jihua HUANG, Kai XU, Jian CHEN, Ruisheng HUANG
Accepted Manuscript  doi: 10.12073/j.hjxb.20210908001
[Abstract](11) [FullText HTML](1) [PDF 1299KB](2)
The source of welding wire melting heat in the process of hollow tungsten arc welding with coaxial wire feeding is systematically studied by using the method of theoretical modeling and experiment. The results show that the analysis results of the theoretical model based on magnetohydrodynamics are highly consistent with the actual situation. Under the combined action of high temperature arc heat radiation and cathode heat conduction, the gradient temperature zone formed in the inner hole of cathode will preheat the welding wire to a certain extent. The temperature near the geometric center on the central axis of annular hollow tungsten arc is the highest, and the temperature is up to 13 700 K, when the welding current is 400 A. The potential is equal after the droplet contacts with the liquid molten pool. Under the action of the principle of minimum voltage, the anode action area of some high-temperature arc will change from the liquid molten pool to the surface of the welding wire. At the same time, some welding current will flow through the welding wire, and the resistance heat formed is one of the main reasons for the high-efficiency fuse. The results of droplet transfer characteristics analysis show that hollow tungsten arc welding with coaxial filler wire has high process stability and is a new welding method with great development prospect.
Microstructure and mechanical property of the thick-walled dissimilar steel joint of FSS/ASS with the combined “TIG cold welding + UNGW”
Shaoxian ZHENG, Junping WANG, Xilong ZHAO, Wei SHI
Accepted Manuscript  doi: 10.12073/j.hjxb.20210720001
[Abstract](14) [FullText HTML](2) [PDF 6294KB](3)
To effectively solve the problems of grain coarsening in the welding HAZ of ferritic stainless steel (FSS), and the formation of vermicular δ-ferrite (δ-F) in the partial melted zone (PMZ) and nearby HAZ of joint when the austenitic stainless steel (ASS) was welded, which could reduce the corrosion resistance in the PMZ and nearby HAZ, the technology of the combined “TIG cold welding + UNGW” was proposed, by which the thick-walled dissimilar stainless steel of 1Cr17/1Cr18Ni9Ti had been carried out. After testing and analysis of the microstructure, mechanical properties and corrosion resistance of the obtained joint, the results showed that the HAZ grain of 1Cr17 base metal could not coarsened, and the vermicular δ-F in the PMZ and nearby HAZ of 1Cr18Ni9Ti base metal did not form. The tensile strength of the combined welding joint was higher than that of 1Cr17 base metal, the impact absorbed energy of the HAZ of 1Cr17 base metal was almost same as that of 1Cr17 base metal. The corrosion resistance of the cladding layer of the combined welding joint, 1Cr18Ni9Ti base metal, 1Cr17 base metal, weld zone of UNGW, the whole joint in turn took on the degressive trend.
The effect of O2 content on soldering quality in Sn-Zn low-temperature wave soldering
Anshi REN, Songtao QU, Xinhua DONG, Qingyu SHI, Gong ZHANG,
Accepted Manuscript  doi: 10.12073/j.hjxb.20211027003
[Abstract](19) [FullText HTML](1) [PDF 3257KB](5)
A new Sn-9Zn-2.5Bi-1.5In solder is prepared, a wave soldering nitrogen protection system is developed, and the soldering quality of the solder under different oxygen content is investigated. The results show that the modified nitrogen protection system can reduce the dynamic oxygen content to less than 0.06% by increasing the nitrogen flow. Reducing O2 content in soldering zone can significantly decrease the number of bridging, poor filling and pore defects, and the failure rate is controlled within 0.20%. Under the critical value of 0.50% oxygen content, the joint can be soldered at low temperature under the condition of 225℃ setting temperature , and the soldering quality can meet the needs of large-scale production. EDS analysis shows that the content of Zn in the oxide dregs is increased by 84.9% compared with the original Sn-9Zn-2.5Bi-1.5In alloy, and the easy oxidation tendency of Zn leads to the formation of a large amount of oxide slags. Reducing the oxygen content in the soldering zone can restrain the formation of oxide slags on the surface of the wave. Nitrogen protection can solve the soldering defects of Sn-Zn alloy, so as to realize low-temperature wave soldering at 225℃.
Size distribution and growth mechanism of interfacial intermetallic compounds in Sn3.0Ag0.5Cu/Cu reflow solder joints
Linmei YANG, Guowan MU
Accepted Manuscript  doi: 10.12073/j.hjxb.20210915001
[Abstract](14) [FullText HTML](1) [PDF 1911KB](6)
In the process of electronic packaging, an intermetallic compounds layer is formed at the interface between solder and Cu substrate. The intermetallic compounds layer is mainly composed of Cu6Sn5 compounds. The size and morphology of the Cu6Sn5 intermetallic compounds have a notable influence on the reliability of solder joints. A series of Sn3.0Ag0.5Cu/Cu solder joints were prepared by reflow welding method. Image-pro Plus software was used to statistically analyze the size distribution and the thickness of the Cu6Sn5 grains. The results show that the average diameter of Cu6Sn5 grains was proportional to t0.38, where t is the reflow time. The mean thickness of interfacial compounds layer was in proportion to t0.32. With the increase of reflux time, the growth rate of interfacial compound slows down, and Cu6Sn5 grain size distribution becomes more uniform. The particle size distribution of Cu6Sn5 in samples with longer reflux time is basically consistent with the theoretical curve of FRD model, while for samples with short reflux time, the grain size distribution deviates from the FRD theory. The statistical results show that the grain size with the highest frequency is less than the average value. It is attributed to the diffusion of Cu atoms in substrate by the interfacial spaces between Cu6Sn5 grains in reflowing process. The growth mechanism of Cu6Sn5 grains at interface was discussed. The effects of reflow time on the behaviors of Cu6Sn5 grains were analyzed. The growth mechanism of interfacial Cu6Sn5 grains was discussed, and the effect of reflow time on the growth way of Cu6Sn5 grains was analyzed.
Analysis of competitive failure mechanisms and mechanical properties of self-piercing riveted joints in corrosive environments
jin YANG, Baoying XING, xiaocong HE, Kai ZENG, Lu ZHOU
Accepted Manuscript  doi: 10.12073/j.hjxb.20211024002
[Abstract](54) [FullText HTML](1) [PDF 1282KB](18)
In order to study the transformation mechanism of the failure mode and Mechanical performance characteristics of self-piercing riveted joints under corrosive environment, a 0.06 mol/L NaCl solution was used to conduct circumferential immersion corrosion tests on several groups of self-piercing rivet joints, Static properties and failure modes of joints are analyzed by mechanical testing, competitive failure mechanisms and scanning electron microscopy. The results show that the failure mode of heterogeneous joints changes from Ⅰ to Ⅲ with the prolongation of corrosion cycle, and the transformation rate depends on the joint material, while the failure mode of homogeneous joints is not affected by the corrosion cycle. Under short-term corrosion, the inter-plate corrosion products of self-piercing riveted joints increase the static strength of both homogeneous and heterogeneous joints, the static strength of heterogeneous joints varies widely throughout the corrosion cycle. Heterogeneous joints are less stable, and homogeneous combination joints prepared by convex dies are more stable than flat dies. Heterogeneous joint electrochemical corrosion is intense, self-piercing riveted joints bottom material off by the stress concentration generated by the tear lines.
Research progress of welding and joining by using the high entropy alloys as filler metals
Chengcong ZHANG, Liling YU, Yuhua Wang, Baohua Chang, Shirzadi Amir, Kaiming Wu
Accepted Manuscript  doi: 10.12073/j.hjxb.20211013001
[Abstract](25) [FullText HTML](1) [PDF 1898KB](13)
High entropy alloys (HEAs) are new generation of alloys which have been developed rapidly in recent years. The composition design of HEAs is a breakthrough of the traditional alloy design idea, and it is a new developing direction of alloy theories. With the high entropy effect, severe lattice distortion effect, sluggish diffusion effect and cocktail effect, the HEAs have promising applications in welding fields. This paper summarized the research status and existing problems in developing the welding filler materials and welding processes utilizing the four effects of HEAs, and the trend of development is prospected as well.
Effects of β-Sn Grain Orientation and Temperature on the Interfacial Reaction in Cu/SAC305/Cu Micro Solder Joints during Aging
Yuanyuan QIAO, Minghui ZHANG, Lungao SUN, Haitao MA, Ning ZHAO
Accepted Manuscript  doi: 10.12073/j.hjxb.20210930003
[Abstract](33) [FullText HTML](6) [PDF 6831KB](13)
Quasi-in-situ method was carried out to study the effects of β-Sn grain orientation and grain boundary feature on the growth behavior of interfacial intermetallic compounds (IMCs) in Cu/Sn3.0Ag0.5Cu/Cu(Cu/SAC305/Cu) micro solder joints under different aging temperatures. The results showed that the IMCs containing Cu6Sn5 + Cu3Sn phases at both interfaces of the micro solder joints grew symmetrically under all the aging conditions, proving that β-Sn grain orientation and grain boundary played no obvious effect on the interfacial IMCs growth either between the two interfaces of a same joint or those from different joints. While with increasing aging temperature, the morphology and thickness of the interfacial IMCs were changing apparently. Scallop-type Cu6Sn5 and thin discontinuous Cu3Sn formed at the interfaces after aging at 100 ℃; scallop-type Cu6Sn5 and thin continuous Cu3Sn formed at the interfaces after aging at 125 ℃; while bilayer structured IMCs containing Cu6Sn5 and Cu3Sn formed at the interfaces after aging at 150 ℃. The increasing aging temperature accelerated the diffusion of Cu and Sn atoms, which could promote the transition of Cu6Sn5 from scallop to layer and the rapid growth of Cu3Sn. Finally, based on the variation of interfacial IMCs thickness with aging time, the growth curves of the interfacial IMCs layers under different aging conditions were obtained which may be helpful for reliability assessment of Sn-based micro solder joints.
A controllable self-triggered arc image acquisition system based on electric signal monitoring
Xiaoqing LV, Fuwang HAO, Zhuangzhuang WANG, Lianyong XU, Hongyang JING
Accepted Manuscript  doi: 10.12073/j.hjxb.20211108002
[Abstract](11) [FullText HTML](3) [PDF 1682KB](1)
According to the characteristics of high-speed camera trigger mode, a new method of controllable self-triggered arc image acquisition based on electrical signal monitoring was proposed. The hardware platform composition and software framework of the system were introduced, the shooting trigger algorithm based on the effective value of the electric signal as the monitoring condition was discussed, and the specific implementation method of synchronous collection of the electric signal and the arc image were described. The arc image acquisition system was verified by the welding experiment of the specimen with greasy surface. The experiment showed that the system can effectively and reliably trigger high speed camera shooting based on electrical signals and capture the transition process information of greasy surface. Finally, the characteristics of greasy surface transition process were compared and analyzed from transition period and arc image.
Effect of Welding Voltage on Resistance Thermocompression Microwelded Joint of Insulated Copper Wire
Yuanbo Li, Songjie Wen, Dingchen Du, Zhiyuan Cui, Zilin Peng
Accepted Manuscript  doi: 10.12073/j.hjxb.20210710002
[Abstract](33) [FullText HTML](3) [PDF 1487KB](7)
The resistance thermocompression microwelding process for welding high temperature resistant fine insulated copper wires was adopted. The appearance, cross-sectional microstructure, breaking force and formation process of the joints under various welding voltages were studied. When the welding time is 20 ms, the electrode pressure is 12 N, and the welding voltage is greater than 2.05 V, the process can be used to remove the insulating paint from the wire and obtain a bonding joint within one output pulse, without paint pre-removal. Corresponding to the increase in welding voltage, the length of the joint changes little, the width of the joint and the joint breaking force increase constantly; the order of joint fracture mode is joint interface separation, joint front section fracture and joint middle fracture. The joint evolution process includes pre-pressure plastic deformation, weak bonding joint, thermally assisted indentation, strong bonding joint and melt extrusion.
Impact performance optimization of supermartensitic stainless steel welding wire deposited metal by MAG welding
Shuaijie JIAO, Guofu WANG, Yuli JIA, Xiangyang LI, Yuting YANG, Ying HAN
Accepted Manuscript  doi: 10.12073/j.hjxb.20210920002
[Abstract](29) [FullText HTML](6) [PDF 3255KB](4)
Baihetan 1000 MW hydro unit is all welded with domestic HS13/5L welding wire, which has successfully achieved a major breakthrough in China's high-end equipment manufacturing. HS13/5L welding wire is the welding material identical with the hydraulic turbine runner, belonging to 13Cr supermartensitic stainless steel. However, the toughness of the deposited metal in MAG welding is lower than that of the base metal. In view of this problem, the welding process is adjusted from flat to vertical-up welding position, to improve the impact toughness of MAG welding deposited metal. And the microstructure and impact properties of the deposited metal are compared and analyzed.The composition of HS13/5L welding wire belongs to 13Cr supermartensitic stainless steel, and the room temperature impact value of MAG welding deposited metal is less than 100 J in the hydropower industry. In this paper, the impact toughness of deposited metal is improved by vertical-up MAG welding. The microstructure and impact properties of deposited metal in the flat and vertical-up welding position are analyzed. Results show that the room temperature impact absorption energy of the as-tempered deposited metal in the vertical welding position reaches more than 120 J, which is about 40% higher than the flat welding position. There is no obvious difference in the phase composition of the deposited metal microstructure between the two welding positions, the as-welded microstructure is composed of quenched martensite, retained austenite and delta ferrite and the as-tempered microstructure is tempered lath martensite, reversed austenite and delta ferrite. The density of oxide inclusions in the vertical-up welding deposited metal is about 22% lower than the flat welding position. The impact fracture of the deposited metal shows the characteristics of ductile fracture for both welding composition as a whole, and the toughness of the deposited metal in the vertical-up welding position is better than that in the flat welding position.
Effect of wire extension on stability and bead formation of Triple-Wire Gas Indirect Arc Welding
Guoning DIAO, Guomin XU, Tianyi ZHANG, Zeli WANG, Liming LIU
Accepted Manuscript  doi: 10.12073/j.hjxb.20210926001
[Abstract](17) [FullText HTML](2) [PDF 2787KB](7)
Triple-wire gas indirect arc welding is a new and efficient welding method. In order to study the effect of wire extension on TW-GIA welding, welding analyzer and high-speed imaging equipment were used to collect the arc, droplet, current and voltage in the welding process The results show that it is difficult to form a stable welding process when the extension of the main wire and the side wire is not equal. When the extension of main wire and side wire was equal, with the increase of wire extension, the concentration of arc became worse, the fluctuation of current and voltage increased, the droplet size increased, and the angle between main wire droplets and side wire droplets increased. When the extension of main wire and side wire was 10 mm, the welding process was the most stable and the bead formation was the best.
Multiview solder joint defect detection based on improved ResNet
Zhi-chao DENG, Run-ming YAN, Hui-tong YANG, Hao-lin CHEN, Jin-xiang LAI, Liang LEI
Accepted Manuscript  doi: 10.12073/j.hjxb.20210928004
[Abstract](13) [FullText HTML](4) [PDF 2218KB](5)
The single view detection based on convolutional neural network cannot effectively identify 3D shape defect targets. As a result, in practical applications, the low-precision detection requirements are often achieved by detecting only one of the most representative views or detecting each face in turn, which brings large time cost and use restrictions. To solve this problem, this paper proposes an improved residual network and applies it to 3D shape solder joint defect detection. The model can firstly obtain all view images of solder joints at one time, and then get detection results through feature aggregation and adaptive learning module. The multi-view solder joint data set was obtained from cooperative enterprises and photographed in a laboratory environment, and the identification accuracy of the proposed method reached 99.48%. The results show that the improved residual network can effectively improve the image identification accuracy under the same number of network layers. Compared with the single view detection, the multi-view detection structure can achieve greater accuracy with less time cost, and can effectively complete the detection task of 3D shape defect targets in actual industrial production.
Diffusion bonding V-4Cr-4Ti and RAFM-steel by hot isostatic pressing with interface characterization
Qihang Zhang, Jialin Li, Jiming Chen, Changhao Wang, Bo Yang, Chi Zhang
Accepted Manuscript  doi: 10.12073/j.hjxb.20211119002
[Abstract](30) [FullText HTML](2) [PDF 3387KB](8)
Reduced Activation Ferritic-Martensitic (RAFM) Steels and Vanadium alloys are considered candidate as structural materials for the first wall of fusion reactors in the future, each has its own advantages. In this study, hot isostatic pressing technology was used to connect V4Cr4Ti alloy and RAFM steel at 800 ℃/150 MPa/2 h, and the interface microstructure, element diffusion characteristics and shear mechanical properties were analyzed. The results show that a decarburized layer is present in the CLF-1 steel within a distance of 120 μm from the connection interface, while a high-hard brittle carbide layer with a width of about 1.5 μm exists on the V4Cr4Ti side. The V4Cr4Ti/CLF-1 steel connection interface has no defects, and the room temperature shear strength of the joint is up to 238 MPa. The fracture analysis results show that the fracture occurs in the high-hard brittle carbide layer near the vanadium alloy side, and the fracture shows the characteristics of overall toughness and local brittle fracture.
The effect of UV light on the corrosion behaviors of aluminum alloy welded joints
Lihua GONG, Weimin GUO
Accepted Manuscript  doi: 10.12073/j.hjxb.20210827002
[Abstract](7) [FullText HTML](0) [PDF 7558KB](2)
The results showed that the uniformity of the MIG joint microstructure was poor, and the content of Mg in weld zone was much higher than that in base metal. So the MIG joint showed the poor thermodynamic stability. UV light could accelerate the corrosion rate of the base metal and the welded joints, in particular, the MIG joint was significantly affected. The effect of 30 days UV light illumination on the FSW joint was similar to that of the base metal. These effects are closely related to the corrosion resistance of the material and the corrosion products of semiconductor properties formed on the surface of the aluminum alloy.
Research on reliability of CCGA reinforcement process for aerospace electronic products
Haichao WANG, Xiaowei PENG, Fan GUO, Yingjie DING, Qiang CHEN
Accepted Manuscript  doi: 10.12073/j.hjxb.20210907001
[Abstract](12) [FullText HTML](1) [PDF 5814KB](3)
Abract: Ceramic column array packages (CCGA) are widely used in aerospace electronic products. The assembly and welding quality of CCGA is closely related to the device size and reinforcement process. This paper studied the effects of PCB constraints and CCGA reinforcement process on solder joint reliability by experiment and numerical simulation. The results show that optimized PCB restraint and using EC-2216 epoxy adhesive to strengthen CCGA can significantly reduce solder joint stress during random vibration. After reliability tests, using a small amount of EC-2216 to strengthen CCGA meets the reliability requirements of QJ3086A, the vibration resistance of solder joint is improved, and it has little influence on the thermal fatigue resistance. With the increase of epoxy adhesive amount, the thermal fatigue resistance of solder joints decreased significantly, and the high failure risk of solder joints exists in the service environment with large temperature difference. Under the condition of fully optimizing PCB board level constraints, using GD414 to reinforce the CCGA meets the high reliability assembly requirements of aerospace electronics. The above results provide reference for the reinforcement process of CCGA.
Effect of low-frequency phase on metal transfer and weld formation in double-wire double-pulse GMAW
Kaiyuan WU, Ziwei CHEN, Hao HUANG, Peimin XIE
Accepted Manuscript  doi: 10.12073/j.hjxb.20211102001
[Abstract](12) [FullText HTML](0) [PDF 4696KB](5)
In order to improve the weld formation quality in gas metal arc welding (GMAW) and investigate the effect of low-frequency phase on metal transfer and weld formation, experiments were carried out on low-frequency synchronous and alternating modes respectively under the premise of high-frequency synchronous mode. The metal transfer processes of low-frequency synchronous and alternating modes were photographed using a high-speed camera, and the influence mechanism of metal transfer on the weld pool was analyzed combined with the current change during welding. Combine the analysis results of metal transfer process and weld formation, the result shows that the droplet collision and fusion is reduced, thus the impact of large volume droplet on the weld pool is reduced in the alternating mode, and the splash is reduced. Compared with the synchronous mode, the weld formation is more flat and weld reinforcement variance is smaller in the alternating mode. The fish-scale pattern in the alternating mode is more regular than that of synchronous mode and the weld formation is optimized.
Numerical simulation of Explosive Welding of metal tube and rod based on different algorithms
Guang-hong Miao, Yu Hu, Jiu-ying Ai, Jun-xiang Qi, Qiu-yue Ma, Zhi-hao Sun, Hong-hao Ma, Zhao-wu Shen
Accepted Manuscript  doi: 10.12073/j.hjxb.20211219002
[Abstract](12) [FullText HTML](3) [PDF 6140KB](5)
The 1060 aluminum tube / T2 copper rod are selected as the explosive composite rod preparation materials, and the T2 copper tube / Q235 steel tube are selected as the explosive composite pipe preparation materials. Using ANSYS/LS-DYNA19.0 software and combining the three algorithms of Lagrangian method, ALE method and SPH-FEM coupling method, the numerical simulation of the explosive welding experiment of preparing two groups of explosive composite pipe and rod at one time was carried out. The simulation results show that the early modeling of Lagrange method is the most concise, followed by the ALE method; In the simulation process, SPH-FEM coupling method takes the most time, and ALE method takes the shortest time. The error between the collision velocity measured by the three algorithms and the theoretical calculation value is 0.9 ~ 5.3 %. The error of SPH-EFM coupling method is the smallest, and the error of Lagrange method is the largest. The principle of energy accumulation inside the tubes is used to explain the diameter expansion of the external composite pipe during the welding process, and the pressure distribution at the composite interface of T2 copper tube / Q235 steel tube was used to verify this phenomenon.
Reconstructed quality evaluation of asymmetric arc emission coefficient by PSO-OSSART algorithm
Haitao Hong, Lu Wang, Yongquan Han, Le Chang
Accepted Manuscript  doi: 10.12073/j.hjxb.20210823001
[Abstract](10) [FullText HTML](5) [PDF 1387KB](4)
Due to the shortcomings of strong subjectivity for selecting the parameters of ordered subsets - simultaneous algebraic reconstruction technique(OSSART), in this paper, a random particle swarm optimization algorithm with reconstruction area minimal error as fitness function is proposed to obtain the best reconstruction parameters. The quality of reconstruction from sparse angle of the asymmetric arc emission coefficient is evaluated. The results show that, compared with the maximum likelihood expectation maximum (MLEM) algorithm, the OSSART algorithm based on particle swarm optimization can not only reduce the reconstruction error significantly under the condition of large projection angle interval, but also have a stronger edge retention ability, which can effectively improve the reconstruction quality of the central area of the arc. In order to ensure the reconstructed quality of VPPA-MIG hybrid welding arc emission coefficient using OSSART algorithm, six feature line projections with equal spacing should be collected at least in the range of 180 degrees. The results provide a theoretical basis for the reliable study of asymmetric arc spectroscopic diagnostics.
Analysis of weld forming in magnetically controlled Plasma-FCAW underwater hybrid welding process
Bo WANG, Fan YANG, Lianbo LI, Hongtao ZHANG, Qingwen DENG
Accepted Manuscript  doi: 10.12073/j.hjxb.20211104005
[Abstract](18) [FullText HTML](2) [PDF 8007KB](7)
Magnetically controlled Plasma-FCAW hybrid welding technology is proposed as a new efficient underwater welding method. The advantages of the two independent welding processes are complementary through the special welding torch structure design. Aiming at the problem of arc repulsion caused by different polarity of power supply in hybrid welding process, an external magnetic field was designed to regulate the coupling degree between two arcs, and the influence of main process parameters on the weld forming and section geometry characteristics of Q355B steel was studied. The results show that the external magnetic field can effectively improve the stability of hybrid welding process and weld forming. FCAW voltage has great influence on the stability of underwater hybrid welding process. Plasma welding current and FCAW voltage have great influence on weld penetration and the plasma current has an approximate linear relationship with weld penetration. Compared with the underwater FCAW process, the welding depth of the hybrid welding process is increased by more than 40%, with higher welding efficiency and welding stability.
Fatigue properties of AZ31 magnesium alloy welded joint by double-sided friction stir welding
Zhifeng YAN, Zhuoran WANG, Shubang WANG, Hongxia ZHANG, Xiuli HE, Peng DONG
Accepted Manuscript  doi: 10.12073/j.hjxb.20211119001
[Abstract](12) [FullText HTML](2) [PDF 4837KB](6)
In order to solve the problem of the low fatigue strength of single-sided welding(SSFSW) caused by the uneven heat input on both sides of the stir head, double-sided friction stir welding(DSFSW) was used to weld AZ31 magnesium alloy with a thickness of 10 mm. The results show that the yield strength of DSFSW joint is 130 MPa, which is 5% higher than that of SSFSW joint; The fatigue limit of DSFSW joint is 85 MPa, which is 76% higher than SSFSW joint; The fatigue crack of DSFSW joint starts at the advancing side(AS) of the upper/lower side, crossing the interface of the upper/lower weld seam and breaking in the retreating side(RS) the one weld seam finally. The fatigue fracture surface of DSFSW is brittle fracture mainly composed of cleavage. The strain range of one side of DSFSW joint is close to the RS strain of SSFSW. The fatigue strength and life of magnesium alloy joint welded by DSFSW has been greatly improved.
Study on resistance spot weldability of nuclear ODS steel
Shitong WEI, Chen LIU, Xin JIA, Shanping LU, Yiyi Li
Accepted Manuscript  doi: 10.12073/j.hjxb.20210928001
[Abstract](11) [FullText HTML](1) [PDF 2379KB](3)
For evaluating the resistance spot weldability of ODS steel, the microstructure of different regions of 9CrYWT-ODS steel spot weld was observed by optical microscope and scanning electron microscope, and the tensile and shear properties of spot welds were tested Finally the appropriate welding current range was confirmed. Results show that the size of the oxides in different areas of the spot weld exhibits obvious differences. The tempered zone in the heat affected zone contains tiny, dispersed oxides due to the low temperature during welding process. The phase transformation zone in the heat affected zone contains less small oxides and more large oxides owing to the higher temperature. The very high temperature in the weld nugget zone results in obvious coarsening of the oxides. As the welding current increases, the increase of the nugget size leads to the increase of tensile hear strength, and the tensile shear failure mode gradually changes from the interfacial mode to the partial interfacial - partial pullout mode, and then further transformed into the fully pullout mode. Continuing to increase the current to the occurrence of splash, the decrease of the nugget size results in the decrease of tensile shear strength. The failure mode again changes to the partial interfacial - partial pullout mode and interfacial mode. According to the tensile and shear test results, the appropriate welding current range is 6.6-7.0 kA.
Study on Controlled Stability of Variable Polarity Welding Current in VPPAW Process
Yang Zhou, Bojin Qi
Accepted Manuscript
[Abstract](16) [FullText HTML](1) [PDF 2194KB](2)
In the Variable Polarity Plasma Arc Welding (VPPAW) process of aluminum alloy, the controlled stability of variable polarity welding current is the premise to ensure the welding forming quality. However, the shape of plasma arc will change with the shear of welding current polarity, which makes the plasma arc as the output load of VPPAW power supply have significant nonlinear characteristics, the conventional PID control strategy can not ensure the distortion of the output current waveform of VPPAW power supply, and the distortion of the output welding current waveform will further aggravate the nonlinear characteristics of the arc load and reduce the controlled stability of variable polarity welding current. In order to improve the controlled stability of variable polarity welding current of the VPPAW process, the controlled stability of welding current and the dynamic stability of plasma arc of aluminum alloy through hole vertical upward welding process under the conventional PID control strategy are studied, the fuzzy control theory is introduced, and then, a fuzzy PID controller with parallel computing ability is designed based on the parallel logic timing design method of FPGA. The verification test results show that the fuzzy PID controller can effectively improve the stability of the variable polarity welding current in the VPPAW process.
Mechanism of wire and arc interaction in hollow tungsten arc welding with coaxial filler wire
Yicheng YANG, Bing DU, Jihua HUANG, Ruisheng HUANG, Jian CHEN, Fujia XU
Accepted Manuscript  doi: 10.12073/j.hjxb.20210913001
[Abstract](16) [FullText HTML](2) [PDF 3788KB](4)
The interaction between welding wire and arc (wire-arc) is the key factor to determine the welding quality. Firstly, the shape of hollow tungsten electrode arc and solid tungsten electrode arc, and their influence on the weld forming characteristics are observed and analyzed by high-speed camera, then the stress model of fuse process is constructed. Then, the dynamic characteristics of droplet formation and transition process in coaxial wire filling welding are systematically analyzed. The research results show that the surface irradiation area of hollow tungsten electrode is larger than that of solid tungsten electrode, and the weld formation is stable under the condition of high welding current process. At the stage of droplet formation, the droplet at the end of the welding wire is in static equilibrium, and it cannot spontaneously transition from the end of the welding wire to the molten pool under the action of large surface tension. In the droplet transition stage, part of the welding current flows through the welding wire, producing electromagnetic shrinkage force, causing the droplet swing between the welding wire and the molten pool.
Investigation on forming mechanism and processing of stationary upper shoulder BT-FSW
Quan WEN, Wenya LI, Xuemeng WU, Shouwei REN, Jing ZHAO
Accepted Manuscript  doi: 10.12073/j.hjxb.20211128002
[Abstract](9) [FullText HTML](3) [PDF 1911KB](0)
Taking the stationary upper shoulder bobbin tool friction stir welded joint of AA6056 aluminum alloy as the research object, the distributions of temperature and strain fields have been clarified based on combining with experimental and numerical simulation methods. Results show that the upper shoulder of SSUBT-FSW is in a static state, which effectively increases the welding stability and decreases the maximum torque to 55N·m (the maximum torque of conventional BT-FSW is 65 N·m). The pressure of the upper stationary shoulder on the weld surface reduces the height difference between the peak and trough of the arc corrugations from 60μm to 10μm, which significantly improves the surface finish of the joint. The diameter of plastic strain zone driven by the lower rotating shoulder is larger than that developed by the probe, promoting the plastic strain field shows a trapezoidal shape on the cross section of the joint, which is good agreement with the shape of the temperature field. In the SSUBT-FSW process, the material flow of the lower shoulder is significantly better than that of the upper stationary shoulder, and the material asymmetry flow characteristics are formed along the thickness direction of the joint.
Microstructure and properties of 5A06 aluminum alloy T-joints welded by stationary shoulder friction stir welding
Accepted Manuscript  doi: 10.12073/j.hjxb.20220201001
[Abstract](9) [FullText HTML](6) [PDF 1169KB](0)
The 5A06 aluminum alloy T-joints with 10 mm thick have been welded by stationary shoulder friction stir welding. Through different welding parameter selection of low rotation speed matching high transverse speed and high rotation speed matching low transverse speed, combined with tensile testing, macroscopic and microscopic metallographic analysis, electron backscatter diffraction (EBSD) analysis and scanning electron microscopy (SEM) fracture analysis, the effect of heat input on mechanical properties and microstructure of T-joints was studied. The results show that the two sets of welding parameters can both be obtained full penetration T-joints without any hole defects, the weld surfaces are smooth and flat and almost no thinning occurs; The different heat input will change the friction form between the stirring needle and the surrounding material which may cause weak bonding defects in the welding joint, consequently affect the tensile strength of the joint; Under the parameter of high rotation speed matching low transverse speed, the center of the weld overlap zone is prone to weak bonding defects at the top, resulting in a lower tensile strength of 198 MPa, tensile specimen fracture in the middle plate. Under the parameter of low rotation speed matching high transverse speed, the weld is free of defects and the tensile strength of the joint is 287MPa, with the tensile specimen fractured in the bottom plate.
Analysis of Mechanical Properties and Application Effect of Over-matching Lap Angle Weld Joint
Yan Xu, Yinglai Liu, Xianghui Nie, Zhenjun Feng, Liang Li, Fengping Yang
Accepted Manuscript  doi: 10.12073/j.hjxb.20211021001
[Abstract](9) [FullText HTML](0) [PDF 4857KB](0)
The experimental analysis of repairing high-grade steel pipeline with high-grade B-type sleeves is completed by using matching and over-matching welding materials. The results show that the fillet weld joints of matching welding and over-matching welding have good tensile strength and impact toughness. The impact toughness of cladding metal of over-matching welded joint is slightly lower than that of matching, and the ductility of welded joint is slightly poor. No welding defects were found in the matching lap fillet weld after welding. The maximum Vickers hardness of the welded joint was 293hv10, which appeared at the lap weld between the outer surface of the fillet weld and the sleeve. The transverse crack originated from the outer surface layer of the fillet weld appeared in the high match lap fillet weld, and the hardness of the welded joint is generally high. The maximum value appears at the weld at the center of the outer surface, with a value of 403hv10, which corresponds to the crack initiation position. The reason is related to the cooling rate of molten pool metal in different parts during the welding process, especially the cooling rate at the welding place of the outer surface cover is fast, the hardness value of the outer wall layer is abnormally high, and cracks are initiated. Therefore, it is suggested that when selecting welding materials for lap fillet weld, try to reduce the matching strength grade of the weld without affecting the sealing and bearing.
Effect of heat treatment on microstructure evolution and mechanical properties of 2219 aluminum alloy joint as fabricated by double-pulsed TIG welding
Yuhuan Yin, Caiyou Zeng, Han Gao, Tiemin Zhang, Bojin Qi, Baoqiang Cong
Accepted Manuscript  doi: 10.12073/j.hjxb.20211102003
[Abstract](11) [FullText HTML](1) [PDF 6724KB](3)
In the present study, the effects of typical post-welding heat treatments, including direct aging treatment (AT) and solution treatment + aging treatment (STAT), on the strengthening effect of 2219-T6 joint fabricated by double-pulsed variable polarity tungsten inert gas welding were investigated comparatively. The evolution of α-Al grain, eutectic structure and precipitations during different post-welding heat treatments were analysis. Moreover, the influence mechanism of microstructure heterogeneity on the plastic deformation behavior of the joint was discussed. Obtained results show that AT affected slightly α-Al grain and eutectic structure, and introduced low-density coarse θ'-Al2Cu precipitation into the welding seam. AT has limited strengthening effect on 2219-T6 aluminum alloy joint and a damage to plasticity. While, STAT lead to coarsening of α-Al grain and decrease in the content and size of eutectic structure. Meanwhile, a high-density fine θ''-Al3Cu particles with a mean diameter of 22 nm was introduced by STAT into the welding seam. STAT can significantly improve the strength and plasticity of the joint, make the strength coefficient of the joint reach 0.84 and the elongation increase to 7.0%. The strengthening and plasticizing effect of the joint caused by STAT result from a more homogeneous strength matching among each region of the joint, due to the significant precipitation strengthening of nano θ'' particles in welding seam. That promoted a more uniform overall plastic deformation and lead to the increase in ultimate tensile strength.
Interfacial bonding properties of titanium foil/steel explosive welding
Zhixiong BI, Xuejiao LI, Yong WU, Su XIONG, Quan WANG, Kai RONG
Accepted Manuscript  doi: 10.12073/j.hjxb.20211105002
[Abstract](35) [FullText HTML](5) [PDF 5396KB](6)
In order to reduce the titanium layer thickness of titanium/steel explosive welding, the explosive welding between 200μm thick TA1 titanium foil and Q235 steel was realized by using salt as pressure transfer layer and low detonation velocity as welding explosive. The microstructures at the interface were analyzed by Metallographic Microscope, Scanning Electron Microscope and Energy Dispersive Spectroscopy. Tensile and bending tests were carried out by universal testing machine to test the bonding properties of the clad plate. The results show that the titanium foil/steel interface shows a regular waveform and is mainly bonded by melting layer, which has good bonding quality. The metal near the interface produces strong plastic deformation, and the steel grains are linear. The vortex of wave peak contains melting block, and no holes, cracks are observed. According to the atomic ratio of Ti and Fe elements, the main components of melting block are FeTi and Fe2Ti intermetallic compounds. The bonding interface did not separate when the three-point bending and tensile specimens were destroyed, which indicates that the clad plate has good plastic deformation ability and bonding performance. There are dimples with different sizes in the titanium and steel layers of tensile failure specimens, which are mainly plastic fracture.
Defecting monitored of friction stir welding based on acoustic emission multi-feature fusion
Yibo Sun, Haiwei Long, Li Zou, Xinhua Yang
Accepted Manuscript  doi: 10.12073/j.hjxb.20211126004
[Abstract](10) [FullText HTML](5) [PDF 1687KB](0)
Friction stir welding (FSW) is a multi-physical field coupling process. The acoustic emission signal in the welding process is directly related to the welding defects. Based on acoustic emission detection and multi-feature fusion, the defecting monitored of FSW method is studied. Experiments of prefabricated defect FSW are carried out. The acoustic emission signal in the solid medium is detected in real time, and analyzed by short-time fourier transform, wavelet transform and Mel spectrum which explore the correlation between welding defects and acoustic emission signal. Finally, multi-feature vectors are constructed by the concat fusion method. It is indicated that FSW has different acoustic emission signal characteristics at the prefabricated defects. Short-time fourier and wavelet time-frequency analysis shows that the frequency of acoustic emission signal is concentrated in 20kHz and the power at prefabricated defects is more than -40dB and 0.8dB respectively. Mel time-frequency analysis shows that the frequency of acoustic emission signal is mainly concentrated in 3.5kHz and the power is more than - 40dB at prefabricated defects. The multi-layer neural network is applied to establish the welding defect recognition model based on single feature and multi-feature vector respectively. The average recognition accuracy of the multi-feature welding defect recognition model is 97% in the dataset, which is 18% higher than the single-feature defect recognition model. The average accuracy of the multi-feature defect recognition model is 86% in the new test set, which is 34% higher than the single-feature recognition model. The multi-feature welding defect recognition model can recognize and monitor the welding state more accurately. The multi-feature welding defect recognition model can more accurately recognize and monitor the welding state.
Microstructures and mechanical properties of friction stir welded joint of 2A14-T4 aluminum alloy thick plate
Huijie LIU, Yisong GAO, Quansheng ZHANG, Huihui ZHAO
Accepted Manuscript  doi: 10.12073/j.hjxb.20210615001
[Abstract](16) [FullText HTML](2) [PDF 2996KB](3)
With the progress of industrial technology, aerospace, transportation and other fields put forward higher and higher demand for the bearing capacity of components. In this paper, friction stir welding method was used to connect 9 mm thick 2A14-T4 aluminum alloy, and the microstructure and mechanical properties of high strength thick aluminum alloy plate joints along the thickness direction were studied. The results indicate that the butt joint has good appearance at 400 r/min and 100 min / min, and the tensile strength of the joint is 360 MPa, which is 83.9 % of the base metal. There are significant differences in the microstructure of the joint along the thickness direction. The average grain diameters of the top, middle and bottom of the weld are 7.9 μm, 5.0 and 2.8 μm, respectively. The dimples at the bottom of the joint are equiaxed, with small diameter and shallow depth. The fracture position and the minimum microhardness of the joint appear in the retreating side TMAZ. The microhardness of the top, middle and bottom of the weld are 99.9 HV, 97.9 HV and 94.7 HV, respectively.
Carbon steel bypass-current wire-heating PAW additive manufacturing forming and tissue performance modulation
Yugang MIAO, Chunwang LI, dandna SHAO, Yuyang ZHAO, Chao WEI, Benshun ZHANG
Accepted Manuscript  doi: 10.12073/j.hjxb.20220109001
[Abstract](20) [FullText HTML](5) [PDF 3653KB](7)
In order to solve the problems of poor forming and coarse grain size caused by excessive arc heat input in the wire-arc additive manufacturing process, this paper conducted a study on forming and tissue optimization of bypass-current wire-heating plasma arc welding (PAW) additive manufacturing with H08Mn2Si carbon steel as the additive material. The effect of main/bypass current ratio on the fusion forming and heat input was first investigated in a single-layer single-pass deposition test; then a multi-layer single-pass deposition test was conducted to analyze the forming, microstructure and hardness of carbon steel at different interlayer temperatures; finally, the tensile properties of the well formed additive samples were tested. The results show that when the main/bypass current is small, a uniform and smooth surface can be obtained, and the dilution rate of the base material can be reduced to 10%; when the interlayer temperature is controlled at a lower temperature of 100 °C, the surface quality of the formed additive is good, and the microstructure in the middle stable area of the specimen has a small grain size and an increased percentage of pearlite, and the average hardness can reach 294 HV. The tensile test shows that the strength and plastic properties are uniform in all directions, and the fracture form is ductile fracture..
Microstructure and Mechanical Properties of Electron Beam Welded Joints in Different State of TC4
Taiqi Yan, Yu Wu, Xu Cheng, An Li, Shuquan Zhang
Accepted Manuscript
[Abstract](418) [FullText HTML](211) [PDF 1235KB](38)
This paper studied the influence of a specification of electron beam welding on the structure of ‘rolled+ laser deposited’ TC4 welded joints, and analyzed the mechanical properties of the joints. Results show that on the rolled side, the microstructure of heat affected zone changes obviously, the shorter the distance away from welding center, the more amount of transformed β generates, and the columnar grain gradually transforms into equiaxed grain, with the appearance of clustered martensite α'. However, on the laser-deposited side, few changes are observed in the heat affected zone, β grain stays the shape of columnar, in which martensite α' generates, no equiaxed grain generates. The change trend of microhardness on both sides is similar, the closer the distance from the center, the higher the microhardness gets, the maximum hardness is around 400HV found in the fusion zone. The mechanical properties of welding joints are similar to that of forged TC4, all the fractures locate in the laser-deposited base metal region.
Accepted Manuscript  doi: 10.12073/j.hjxb.20180320001
[Abstract](223) [FullText HTML](51) [PDF 1199KB](30)
Development of a narrow gap welding experiment system for oscillating arc sensing
Wenji Liu, Zhenyu Guan, Liangyu Li, Jianfeng Yue
Accepted Manuscript
[Abstract](266) [FullText HTML](142) [PDF 945KB](9)
In order to improve the precision and reliability of welding arc sensor in narrow gap, as well as to research the principle of arc sensor characteristic parameters influenced by the distance between welding torch and the side wall, by measuring the torch position using high precision laser displacement sensor, an experiment system for swing arc sensor which can simultaneously acquire welding voltage, welding current, welding torch swing position and arc image four signals was developed based on TMS320F2812 and Labview. Experiment was carried out by the welding method of P-GMAW. It was proved by the experiment that the established system is reliable and effective. The system has laid the necessary foundation for the further study of the characteristics of the narrow gap oscillating arc sensing.
Laser Welding of T91 Martensite Heat-resistant Steel with Feeding Wire
Xiaoyong Qi, Bing Ye, Shiwen Yu, Liang Yu
Accepted Manuscript  doi: 10.12073/j.hjxb.201940
[Abstract](346) [FullText HTML](83) [PDF 1011KB](32)
The research on laser welding 5-mm thick T91 martensite heat-resistant steel with filler wires is conducted, and the effects on weld appearance, microstructures, and porosity are studied, also the weld mechanical properties of the optimal parameter are tested. The results show that when welding heat input increased by using same material wire to weld T91 steel, weld seam width, porosity decreased, and grain size changed a little, microstructure of weld zone and HAZ are tempered martensite. The weld seam can be pore-free with the parameter of power 5 600 w, speed 1.2 m/min, feeding speed 1.2 m/min, its microhardness is 300 HV, tensile strength is 697 Mpa, no cracks appear by 180° bending and back bending, and the impact properties are better than base metal at 20/0/–20 °C.
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Microstructure and properties of brazed W-Cu composites and Beryllium bronze joint
Yuanxun SHEN, Luyi WANG, Xiupeng LI, Yunyue LI, Xiaoguo SONG, Weimin LONG
 doi: 10.12073/j.hjxb.20210818002
[Abstract](37) [FullText HTML](7) [PDF 2225KB](9)
W-Cu composites and Beryllium bronze dissimilar joints were prepared by induction brazing method using BAg56CuZnSn、BAg50ZnCdCuNi and BAg49ZnCuNiMn, respectively. Interfacial microstructure and mechanical properties of the brazed joints were studied. The results show that all the brazed joints displayed perfectly bonded interface. Obvious diffusion zone was formed between braze and Beryllium bronze interface. Meanwhile, clear boundary between braze and W-Cu interface was also observed. In addition, the braze had obviously infiltrated into the W-Cu matrix near braze/W-Cu interface, which lead to increasing of the interface bonding strength. The addition of nickel in braze further improved the metallurgical bonding of the interface due to the diffusion and mutual dissolution of nickel and tungsten. Furthermore, the addition of manganese can refine the grain size of brazed joint and improve the joint strength.
Microstructure characteristics of duplex stainless steel CMT-P composite welding
Lianyong XU, Yujie BAI, Yongdian HAN, Hongyang JING, Zhiqiang ZHANG
 doi: 10.12073/j.hjxb.20210821002
[Abstract](27) [FullText HTML](0) [PDF 3643KB](11)
By introducing the CMT-P welding method, the welded joints of UNS S32750 super duplex stainless steel with excellent forming quality were successfully prepared. Metallographic microscope, X-ray diffractometer, scanning electron microscope, energy dispersive spectrometer and transmission electron microscope were used to study the microstructure of different regions of the joint. The results showed that the weld, heat-affected zone and base metal structure showed significant differences. Compared with the base metal and the weld, the austenite content in the heat-affected zone is the lowest (32.3%), but the austenite content in each micro-zone of the welded joint meets the standard requirement of not less than 30%. Due to the effect of reheating during the welding thermal cycle, intra-grain γ2 and grain boundary γ2 with different scales and morphologies are precipitated in the weld root and heat-affected zone, but there is no γ2 precipitation in the weld filling zone. In addition, short rod-shaped Cr2N precipitated in the weld root and heat-affected zone, mainly distributed in the ferrite grains and grain boundaries. The precipitation of Cr2N caused the adjacent ferrite matrix to form an obvious Cr-poor zone.
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High performance welding and evaluation
Creep-fatigue properties and life prediction method of new martensitic heat resistant steel
Lei ZHAO, Guocai FENG, Lianyong XU, Yongdian HAN, Hongyang JING
2022, 43(5): 1-7.   doi: 10.12073/j.hjxb.20220101003
[Abstract](16) [FullText HTML](2) [PDF 1513KB](8)
In this paper, the creep-fatigue properties of P92 and G115 new martensitic heat-resistant steels under load control are studied. Influence of dwell time and peak stress on the creep-fatigue properties under load control is analyzed. The results show that the creep-fatigue life decrease with the increase of peak stress and dwell time, and the creep-fatigue life of G115 steel is about 8-10 times that of P92 steel under the same peak stress, but G115 steel is more sensitive to the interaction between peak stress and dwell time. Changes in high temperature strength of materials lead to better creep-fatigue properties of G115 steel than P92 steel. Creep deformation and damage dominate creep-fatigue life during creep-fatigue under load control. For the creep-fatigue life prediction method under load control, the energy method, toughness exhaustion method, frequency separation method and frequency modified tensile hysteresis energy model are studied. Furthermore, based on the mechanism of load controlled creep-fatigue inelastic strain damage, the minimum cyclic creep rate method and the minimum creep rate method based on pure creep are proposed. The results show that the minimum cyclic creep rate model exhibited the highest prediction accuracy, and the method based on the minimum creep rate under pure creep predicts the high-life zone well, but the error in the low-life zone is relatively large.
Mechanism and elimination of hot cracks in laser additive manufacturing of NiFe based superalloy
Shuai WANG, Liming FU, Yong YUAN, Hongfei YIN, Jijin XU, Yuefeng GU
2022, 43(5): 8-13.   doi: 10.12073/j.hjxb.20220101001
[Abstract](33) [FullText HTML](5) [PDF 6135KB](8)
To solve the problem of hot cracking in laser additive manufacturing process of NiFe based superalloy, the formation mechanism of hot crack was investigated, and the method of interlayer temperature control and powder nitriding to reduce the sensitivity of hot crack was proposed in the laser additive process of NiFe based superalloy. The results show that the occurrence of hot crack is mainly caused by element segregation and thermal stress. Most of the hot cracks are located at the high angle grain boundary, which own higher grain boundary energy to extend existing time of liquid film in grain boundaries during the cooling process, so the obvious segregation phenomenon occurs. When the interlayer temperature is lower, the cooling rate is faster, which can reduce the growth of harmful carbides in the superalloy. The proportion of high angle grain boundary is reduced, and the probability of hot crack is reduced further. Another method is to form stable nitrides by pre-nitriding Ti, Nb elements in the powder, which inhibits element segregation, increases the nucleation points and promotes grain refinement, therefore, the hot crack sensitivity of the superalloy is decreased.
Effects of surface layer microstructure on liquation crack and fatigue properties of 6005A aluminum alloy MIG joints
Xiaohui HAN, Shuaizhen LI, Laijun WU, Caiwang TAN, Gangqing LI, Xiaoguo SONG
2022, 43(5): 14-20.   doi: 10.12073/j.hjxb.20210825004
[Abstract](17) [FullText HTML](0) [PDF 5133KB](6)
The effects of surface microstructure on liquation cracks and fatigue properties of 6005A aluminum alloy MIG joints used in high-speed train bodies were comparatively studied. The results showed that the second phase near the grain boundary of the coarse-grained microstructure was coarse, resulting in larger thickness of the grain boundary liquid film in the heat-affected zone reaching 8~10 μm, which made the liquefied grain boundary less resistant to tensile stress and more sensitive to liquation cracks. The liquation cracks formed by the surface coarse-grained microstructure become possible crack sources during the fatigue process, which adversely affect the fatigue properties of the joints. Improving the surface microstructure of the base metal could suppress the formation of liquation cracks and improve the fatigue performance of the joint. The fatigue strength of the surface coarse-grained joint was 93 MPa under 1 ×107 cycles, while that of the surface fine-grained joint was 107 MPa.
Comparative study on determination methods of resistance curves of circular joints based on single edge notched tensile specimens
Baoming GONG, Runming TIAN, Xiuguo LIU, Caiyan DENG, Dongpo WANG
2022, 43(5): 21-28.   doi: 10.12073/j.hjxb.20210610001
[Abstract](26) [FullText HTML](1) [PDF 1145KB](4)
In recent years, single edge notched tension (SENT) specimens have been used for strain-based design and evaluation of pipelines, and several fracture toughness testing standards have been developed, including DNVGL-RP-F108, CANMET, BMT, USP and BS 8571. However, there are still great differences between relevant test standards in test principles, test methods and calculation methods of fracture toughness. It is necessary to further study the differences between them. Therefore, different determination methods of crack tip opening displacement (δ) and J-integral resistance curves for clamped SENT specimens of API X80 pipeline girth weld joints were compared. By fitting the J-R curves, δ-R curves and initial fracture toughness values J0.2 and δ0.2, the recommended equations for the fracture toughness resistance curve of SENT specimens were given.
Strength and life assessment of TC4 titanium alloy welded frame for high-speed railway vehicles
Wenshun XI, Xinyan REN, Jinyuan ZHANG, Feng GUO, Shengchuan WU, Zhongwen LI, Xiaohui HAN
2022, 43(5): 29-35.   doi: 10.12073/j.hjxb.20210930001
[Abstract](29) [FullText HTML](5) [PDF 1452KB](9)
The hardness distribution, basic mechanics and high cycle fatigue properties of TC4 titanium alloy base metal and welded joint were obtained by TIG arc welding test. The finite element simulation model of titanium alloy welded bogie frame with pseudo-axis was established, and the static and fatigue strength of the new TC4 titanium alloy and the existing S355 weathering steel frame was checked respectively. Based on the experimental fatigue load spectrum and Miner linear fatigue cumulative damage theory, the fatigue life of TC4 titanium alloy and S355 weathering steel bogie frames was evaluated respectively. The results show that the safety factor of the minimum static strength of titanium alloy and weathering steel bogie frame is 2.8 and 1.5 respectively, which are both greater than the safety factor threshold and meet the design requirements. Both the critical safety location of titanium alloy and weathering steel bogie frame were within the envelope range of modified Goodman fatigue limit diagram, which meets the design requirements. In addition, the envelope space of TC4 titanium alloy Goodman fatigue limit diagram was much larger than S355 weathering steel. Under typical level 8 load spectrum, if the annual operation is estimated to be 30 × 107 km, all critical location of the bogie frame could meet the design requirements of 35 years of service life, and the estimated life of TC4 titanium alloy bogie frame is about 2 times than that of S355 weathering steel bogie frame. The research can provide scientific basis for the strength and structure design of bogie frame with higher speed and safety level.
Microstructure and properties of MAG and oscillating laser arc hybrid welded X80 steel
Zeyu LI, Lianyong XU, Kangda HAO, Lei ZHAO, Hongyang JING
2022, 43(5): 36-42.   doi: 10.12073/j.hjxb.20220101002
[Abstract](58) [FullText HTML](11) [PDF 2595KB](14)
Metal active gas welding (MAG) and oscillating laser arc hybrid welding (OLAHW) of X80 pipeline steel were carried out with backing weld by laser, the joint formation, microstructure and mechanical properties (microhardness, tensile properties and impact toughness) were studied. The results showed that sound joints without defects of pores, slag inclusion and crack were obtained by both the two processes. The joint microstructure was mainly composed of acicular ferrite (AF) and M-A components. Because of lower heat input, faster cooling rate and more nucleation sites promoted by the oscillated laser, more acicular ferrite and finer M-A components were formed within the OLAHW filled joints than those within MAG filled joints. The average microhardness and tensile strength of the joints obtained by the two filling processes were almost the same, but the hardness variation of OLAHW joints is gentler with less fluctuation. The impact energy of heat affected zone and weld zone of OLAHW filled joints were 277 and 217 J respectively, which is 64% and 42% higher than those of MAG filled joints.
Corrosion resistance of AlCoCrFeNi2.1 high entropy alloy welded joint by electron beam welding
Daochen FENG, Wenjian ZHENG, Guoben GAO, Zhou ZHOU, Yanming HE, Jianguo YANG
2022, 43(5): 43-48.   doi: 10.12073/j.hjxb.20220101006
[Abstract](17) [FullText HTML](4) [PDF 1963KB](9)
To clarify the corrosion resistance of high entropy alloy welded joint, the eutectic dual-phase high entropy alloy AlCoCrFeNi2.1 was welded by electron beam welding (EBW), and the corrosion resistance of the joint was studied by electrochemical corrosion method. The results show that the self-corrosion potential of weld zone (FZ) is about 0.16 V higher than the one of base metal (BM), the corrosion resistance is enhanced, and the self-corrosion current is reduced by one order of magnitude, and the corrosion rate is greatly reduced. The corrosion pits in the base metal area of the welded joint are expanding in depth, while the corrosion pits in the weld area are expanding horizontally, showing obvious phase selective corrosion. The grains in the weld area are obviously refined, the hardness is stable and slightly increased, and the two-phase distribution presents a dense "network" trend, which is more uniform than the macro distribution of elements in the base metal. These contributes for enhancing the corrosion resistance and penetration of welded joints.
Effect of beam oscillating and nitrogen alloying upon microstructure and mechanical properties in laser welding of molybdenum alloy
Han YU, Longzheng PAN, Linjie ZHANG, Wensheng LIANG, Li′an BAI
2022, 43(5): 49-55.   doi: 10.12073/j.hjxb.20220101005
[Abstract](15) [FullText HTML](1) [PDF 2628KB](5)
The problems of coarse grains and intergranular segregation in molybdenum alloy welding lead to poor mechanical properties of the joints. The experimental study was carried out by using laser beam oscillation and nitrogen alloying. The results show that when using beam oscillating only, the average grain size in the weld zone was reduced by about 28 %, the microhardness of the weld center was increased from 190 HV to 200 HV, and the tensile strength of molybdenum alloy joint was increased from 29.83 MPa to 130.03 MPa. When using nitrogen alloying only (shielding gas 10 % N2 + 90 % Ar), the microhardness of weld center was increased from 190 HV to 240 HV, and the tensile strength of molybdenum alloy joint was increased from 29.83 MPa to 350.94 MPa. Furthermore, the tensile strength of the joint reached 439.43 MPa which was 67.8% of the tensile strength of the base metal when laser oscillating and nitrogen alloying were used simultaneously, and the fracture mode changes from intergranular fracture to intergranular fracture and transgranular cleavage fracture. The analysis shows that the strengthening effect of nitrogen alloying on the properties of the joint benefits from the formation of Mo2N phase in the grain and at the grain boundary.
Analysis of reheat embrittlement and softening of coarse-grained zone of Q960E welding joint
Xianchun DONG, Nan ZHANG, Xiazhou ZHANG, Zhiling TIAN
2022, 43(5): 56-62.   doi: 10.12073/j.hjxb.20210702002
[Abstract](22) [FullText HTML](1) [PDF 2450KB](5)
In order to accurately obtain the microstructure and properties of the welding heat affected zone under different temperature gradient conditions, two simulated thermal cycle tests were carried out on a low carbon equivalent Q960E and its comparative steel by using the welding thermal simulation method. And the microstructures of CGHAZ after the first thermal simulation, and UA CGHAZ, SCR CGHAZ, ICR CGHAZ and SR CGHAZ after the second thermal simulation were obtained. Microstructures were analyzed, impact toughness test and hardness characterization were carried out in this paper. Results showed that both ICR CGHAZ and SR CGHAZ of Q960E and comparative steel had reheat embrittlement sensitivity. The impact toughness of SR CGHAZ of comparative steel was as low as 9 J at −40 ℃. And the distribution of point-type and strip-type carbides formed at the grain boundary was the main reason for reheating embrittlement. The softening of SR CGHAZ with low carbon equivalent Q960E is the most serious, which is caused by the combined loss of fine-grain strengthening, dislocation strengthening and precipitation strengthening.
Comparison of fatigue life predicting methods used in cracked welded component
Bingzhi CHEN, Zhengping HE, Xiangwei LI, Wenzhong ZHAO
2022, 43(5): 63-68.   doi: 10.12073/j.hjxb.20210824001
[Abstract](16) [FullText HTML](1) [PDF 2132KB](4)
Fatigue cracks appeared in a weld on a transverse shock absorber seat of a railway vehicle during service. By using the fatigue load spectrum, the numerical simulation calculation of fatigue life of cracked welds is carried out by using the nominal stress, hot spot stress and structural stress method respectively. The numerical simulation results show that, the calculation results of the structural stress method are the most consistent with the engineering practice compared with the nominal stress method and the hot spot stress method, and the structural stress method is also obviously better than the other two methods in the identification ability of the stress concentration. Combined with this specific engineering example, this paper further discusses the essential differences of these three methods, and puts forwards a concluding opinion, that is, the structural stress method is most worthy of being popularized in application in the process of anti-fatigue design of welded structures.
Process optimization on friction stir lap welding of 6061-T6 aluminum alloy/Q235 steel with ultrasonic vibration
Tao LIU, Song GAO, Guangchun XIAO, Chenghao WU, Lei SHI, Zhiping SUN
2022, 43(5): 69-75.   doi: 10.12073/j.hjxb.20220101007
[Abstract](35) [FullText HTML](5) [PDF 3966KB](16)
The effective connection between 6061-T6 aluminum alloy and Q235 steel was realized by ultrasonic vibration enhanced friction stir welding (UVeFSW) process. The effects of ultrasonic energy on weld formation, joint microstructure, mechanical properties and welding load were investigated. The results show that the application of ultrasonic energy can significantly improve the weld surface forming and expand the width of aluminum / steel interface zone and weld nugget zone. Ultrasonic energy refines the grain structure of weld nugget zone and thermal mechanically affected zone, changes the fracture mechanism and cracking location of lap joint, improves the mechanical properties of joint. The variation of welding loading during welding was analyzed. It is found that the tool torque, the welding axial force and the spindle power decrease after applying ultrasonic energy.
Master S-N curve fitting and life prediction method for very high cycle fatigue of welded structures
Shaoze ZHOU, Shuo GUO, Bingzhi CHEN, Jun ZHANG, Wenzhong ZHAO
2022, 43(5): 76-82.   doi: 10.12073/j.hjxb.20211116002
[Abstract](24) [FullText HTML](0) [PDF 2422KB](9)
Ultrasonic fatigue testing is a practical method for obtaining very high cycle fatigue (VHCF) strength of welded joints. However, there is no effective method to predict and evaluate the ultrasonic VHCF life of arbitrary welded joint forms. A transient structural stress method for assessing the fatigue life of welded joints under ultrasonic harmonic resonance conditions as well as a method for fitting the master S-N curve for VHCF are proposed. Based on the published test data of 300 welded joints, a 20 kHz VHCF master S-N curve of aluminum alloy welded joints was fitted. The response equivalent structural stress spectrum was obtained by resonance model transient simulation analysis and post rain flow counting. With the spectrum and the VHCF master S-N curve, the fatigue life of welded structures is predicted. The results show that the structural stress concentration factor does not change due to vibration or external load magnitude changes in welded joints. The fitted ultrasonic VHCF master S-N curve is a new narrow band with m = 16.5, which extends the applicability of the master S-N curve method theory to the very high cycle region and can be used for ultrasonic vibration VHCF life prediction of welded structural parts with any joint forms.
Effects of introductions of oxygen and nitrogen elements on impact toughness of gas pool coupled activating TIG weld metal
Yong HUANG, Wei GUO, Yanlei WANG
2022, 43(5): 83-89.   doi: 10.12073/j.hjxb.20210919001
[Abstract](6) [FullText HTML](1) [PDF 1011KB](4)
Through introducing oxygen and nitrogen elements from the outer gas of gas pool coupled activating TIG(GPCA-TIG) welding, deep penetration, high quantity and continuous welding are accessible. In order to obtain the dependence and mechanism of weld metal impact toughness on the introduced oxygen and nitrogen elements, GPCA-TIG welding for stainless steel SUS304 with the outer gases oxygen, nitrogen and nitrogen-oxygen gas mixture respectively were performed to gauge low temperature impact toughness of the weld metal. Then, a series of testing experiments including weld microstructure and chemical composition, nonmetallic inclusion and grain orientation were conducted. The results reveal that, the introduction of oxygen makes the low temperature impact toughness of weld metal decease obviously, nitrogen decease a little, while the low temperature impact toughness of weld metal can be increased a little conversely when oxygen and nitrogen are synchronously introduced. The main mechanism is proven that the synchronous introduction of oxygen and nitrogen elements leads to fine grain of weld microstructure, less increases of the contents of oxygen and nitrogen elements and the nonmetallic inclusions, much decrease of ferrite number in weld metal. Meanwhile, the high angle grain boundary number in austenite crystal and the matching property of grain orientations between ferrite and austenite are improved. All of these result in difficult cracking propagation and higher toughness.
Microstructure and impact toughness of laser-arc hybrid welding simulated heat affected zone of high strength low alloy steel
Liangliang BAO, Chunyu PAN, Fujian LIU, Xinming ZHANG, Tao HAN
2022, 43(5): 90-97.   doi: 10.12073/j.hjxb.20210817001
[Abstract](8) [FullText HTML](0) [PDF 2197KB](3)
Homogeneous specimens of the laser-arc hybrid welding heated affected zone (HAZ) of low alloy high strength steel were prepared by welding thermal simulation technology. The instrumented impact test and microstructure characterization technologies were used to analysis the relationship between the microstructure and toughness of the simulated specimens. The results showed that the simulated coarse grained HAZ (CGHAZ) and fine grained HAZ (FGHAZ) composed of lath martensite (LM) and the inter-critical HAZ (ICHAZ) compose of LM and grain boundary carbide, the sub-critical HAZ (SCHAZ) is comprised of tempered martensite. The peak temperature has little effect on the crack initiation energy, but large effect on the crack propagation energy. The simulated ICHAZ and CGHAZ specimens have poor resistance to crack propagation. When the peak temperature is the same, the impact energy of the simulated CGHAZ specimens have little change with various the cooling rates. The peak temperature mainly affects the crack stable propagation energy and the crack stable propagation energy decrease as the peak temperature increase. The fracture process of the simulated CGHAZ specimen was controlled by the crack propagation, and the block was the microstructure unit controlling the crack stable propagation.
Welding characteristics of Al/steel dissimilar metals based on magnetically controlled metallurgy
Fei YAN, Yifan ZHOU, Benkan TANG, Yonggang XU, Chunming WANG
2022, 43(5): 98-103.   doi: 10.12073/j.hjxb.20220101004
[Abstract](14) [FullText HTML](2) [PDF 1239KB](9)
Laser lap deep penetration welding was conducted on Al/steel dissimilar metals with longitudinal alternating magnetic field. Effects of alternating magnetic field on the macro-morphology, microstructure, element distribution, mechanical properties and fracture mode of the joints were carefully investigated using metallographic microscope, scanning electron microscope and other methodologies. The results showed that the weld width decreased and the weld depth increased under applied alternating magnetic field. The electromagnetic force induced by an alternating magnetic field promoted the transformation of resultant IMCs at interface from continuous distribution to discrete distribution. During this process, composition segregation and crack defects were also successfully suppressed. IMCs in interfacial layer may be composed of ζ-FeAl2, θ-FeAl3 and β2-FeAl. Laser welding with applied external magnetic field can improve the loading capacity of the joint. It can attribute to the increase of combined areas and refinement of IMCs structure.
Microstructure and corrosion resistance of 7075 aluminum alloy welded by TIG
Lixiang GUO, Xiaoping LI, Xiao LIU, Bin WANG, Zhaungzhuang WANG
2022, 43(5): 104-112.   doi: 10.12073/j.hjxb.20210811001
[Abstract](35) [FullText HTML](4) [PDF 6845KB](10)
In this paper, the self-developed 7075 aluminum alloy welding wire was used to conduct welding experiments on the 7075 aluminum alloy plate, and the effect of welding current (160-180 A) on the microstructure and corrosion resistance of the weld was studied, and the changes in performance after T6 heat treatment (480 ℃+1 h, 120 ℃+24 h) were observed. The microstructure at the weld is uniform isoaxial crystals, and with the increase of the current, the grain size continues to increase, and the grain boundary narrows after heat treatment, which is obviously seen to be less precipitation; XRD and SEM detection found that the weld is mainly composed of β phase (β-AlCu3), η phase (MgZn2) and a small amount of AlCuMg phase, and at the same time, Al13Fe4 intermetallic compounds and a small amount of Mg2Si were detected; after heat treatment, the solid solution of alloying elements dissolved into the matrix, and no common reinforced phase was precipitated after aging. Only Al13Fe4, Mg2Si and a small amount of Al5Fe3 and SiO2 impurity phases were found. Through heat treatment, the elements are severely segregated before heat treatment to uniform distribution after heat treatment, reducing the self-corrosion potential at the weld; at the same time, the impedance and phase angle are improved, and the best corrosion resistance is the weld under the current 165 A after heat treatment.

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