最新刊期
卷 54 ， 期 2 ， 2024
- 摘要：With the unique advantages, keyhole plasma arc welding (K-PAW) is widely used in the welding and manufacturing of medium-thick plates, and is gradually developing for larger thicknesses welding. However, the increase of thickness is also accompanied by the problem of keyhole instability, which restricts its application in practical production. In order to provide theoretical basis for the design of stable piercing process, the characteristic size variation of K-PAW weld pool of 14 mm thick 304 stainless steel under the control strategy of "controlled constant piercing" and the weld pool behavior were analyzed. Through visual detection and electrical signal synchronous acquisition system, the morphology characteristics of molten pool in the process of large-penetration K-PAW were quantitatively analyzed, and the changes of molten pool characteristic parameters under controlled pulse conditions were explored, as well as the synchronous dynamic behavior rules of molten pool characteristics and electrical signals. In the blind hole stage of the first 14 seconds of plasma arc initiation, the weld pool is unstable with the accumulation of arc heat, and the size oscillates, with the maximum oscillation amplitude exceeding 10 mm. At the same time, the aspect ratio of the weld pool also changes in the range of 1.0~1.6. With the perforation occurring at the 15th second, the molten pool reached equilibrium, and the aspect ratio reached its peak at 19 s. The molten pool remained stable and its shape did not change greatly in the sustaining stage. In summary, the welding stage can be distinguished by the changing trend of the shape of the molten pool. Then, the authors compared the blind hole stage of different welding currents (280 A, 275 A, 270 A), and found that the use of larger initial current is conducive to shortening the blind hole time, from 22.9 s at 270 A to 19.8 s at 280 A, and reduce the possibility of welding holes. Finally, the authors found that the distance between the arc center and the front edge of the molten pool can reflect the perforation state. This study verifies the feasibility of the "controlled constant piercing " control strategy, and verifies the feasibility of distinguishing the welding stage and piercing by visual features.关键词：keyhole plasma arc welding;deep penetration welidng;visual features of weld pool;visual and electrical signal synchronization
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发布时间：2024-03-14 - 摘要：The Ti/TiAl micro-laminated material system has excellent strength, toughness, and high-temperature properties. This system effectively overcomes sudden cracking during the preparation and processing of titanium-aluminum alloys. This paper summarizes the manufacturing methods, strengthening and toughening mechanisms, and typical failure modes of the Ti/TiAl laminated structure. Numerous studies have shown that compared with traditional single materials or non-continuously reinforced composites, the laminated composite structure significantly improves the strength and toughness through the introduction of the toughness difference of multiple materials and multilayer interfaces. The main strengthening mechanism is the toughness difference of multiple materials and the introduction of multilayer interfaces in the composite structure, which causes crack deflection and secondary cracking during crack growth. The deflection and bridging effect of cracks greatly consume the tip energy of the main crack and inhibit its continuous growth. This structure breaks through the traditional trade-off relationship between strength and toughness, bringing new development directions to the field of materials science and engineering.关键词：laminated structure;additive manufacturing;strengthing and toughening mechanism;crack deflection;break of the trade-off relationship between strength and plasticity;resilience differences;main crack tip energy
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发布时间：2024-03-14 - 摘要：Graphene tends to agglomerate when mixed with metal powders and cannot be dispersed effectively and evenly, which prevents its excellent properties from being fully utilized. In order to solve the agglomeration problem of graphene in composite materials, this paper uses self-developed electrodetonation equipment to prepare graphene aerosol, mixes it with copper powder to get graphene/copper composite powder, and prepares composite coating. The graphene aerosols and composites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM), and the hardness and wear resistance of the coatings were tested. The results show that the graphene prepared by the electrodeposition method is mainly small-sized graphene with the diameter of 5~40 nm and the number of layers of 3~7. In the graphene aerosol with a concentration of 0.875 mg/L, a single small diameter graphene sheet was adsorbed on the substrate before the substrate was placed for 10 min, but no gel was found after coagulation. After the substrate was placed for 10min, many small pieces of diameter graphene were stacked together to form graphene aerosol gel. Moreover, the longer the substrate was placed, the more severe the coagulation was, and the graphene aerosol gel clusters were growing. Small and medium size graphene of graphene/copper composite powder was uniformly adsorbed on the surface of copper powder. After further preparation of composite coating, it was found that the distribution of C element on the surface was uniform, indicating that the method of mixing graphene aerosol with copper powder can effectively solve the problem of graphene agglomeration in composite materials. The average hardness of 0.5 wt.% graphene/copper coating is 74.8 HV0.05, and the friction coefficient is 0.18, which have different degrees of improvement compared with pure copper coating. The results indicate that graphene aerosols prepared by the electric explosion method can be used to prepare graphene/copper composite coatings, improving the hardness and wear resistance of the coatings. This method is expected to provide a new approach for the preparation of high-performance graphene/metal composites. The results indicate that graphene aerosols prepared by the electric explosion method can be used to prepare graphene/copper composite coatings, improving the hardness and wear resistance of the coatings. This method is expected to provide a new approach for the preparation of high-performance graphene/metal composites.关键词：electrical explosion method;graphene aerosol;graphene/copper composite powder;graphene/copper composite coating;wear resistance
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发布时间：2024-03-14 - 摘要：Using ABAQUS finite element software, a new numerical model of thermal mechanical coupling process of continuously driven friction welded joints was established. The following conclusion is drawn: the cooling and low-temperature insulation processes during the thermal cycle are the stages with the highest thermal stress; The appearance and location of joint necking are in good agreement with the experimental results, and the relative error between the necking location and the actual experiment is 6%. The essence of the necking phenomenon is the plastic deformation caused by the stress exceeding the strength limit when the aluminum is Free expansion and shrinkage; The cleavage fracture ring was observed on the tensile fracture surface, and its position and width are highly consistent with the strain concentration area of the simulation results.The numerical model accurately simulates the thermo-force coupling process of continuously driven friction welded joints, which provides strong support for actual production and process optimaztion.关键词：continuous drive friction welding;thermal cycling;thermal stress;finite element simulation;stress and strain field
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发布时间：2024-03-14 - 摘要：In order to investigate the microstructure characteristics of arc additive manufacturing GH4169 alloy during heat treatment, the study was conducted on the effects of different heat treatment processes on the microstructure and phases of GH4169 alloy, in order to determine the optimal homogenization heat treatment process. The effect of different homogenization heat treatment temperature on the microstructure and mechanical properties of the specimen was studied by using arc fuse additive manufacturing technology. The results show that with the increase of homogenization temperature, the Laves phase gradually dissolves to complete dissolution and the sample structure gradually became uniform. When the homogenization temperature is 1 100 ℃, the Laves phase is completely dissolved, the sample organization of the horizontal and vertical directions are equiaxed crystals, and eliminating organizational anisotropy. After homogenization treated at 1 100 ℃ and solid solution +double aging heat treatment, the strength of the material was significantly improved, increased by 50% compared to the deposited state, and creep performance of the material is much higher than the forging standard. Studies have shown that the mechanical properties and creep properties of GH4169 alloy can be effectively improved by controlling the homogenization heat treatment temperature and subsequent heat treatment process. It is of great significance to optimize the process parameters of arc additive manufacturing GH4169 alloy and improve its comprehensive performance.关键词：arc wire additive manufacturing;GH4169 superalloy;homogenization heat treatment;microstructure;mechanical properties
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发布时间：2024-03-14 - 摘要：In the fields of large-scale construction, bridges, shipbuilding, and heavy machinery, welding of thick steel plates is often required, and problems such as low welding efficiency and unstable welding quality may be encountered using conventional welding methods. An EH36 steel plate (80 mm thick) for large wire energy welding was developed, and a large wire energy welding test was carried out by using dual-wire gas-electric riser welding with 532 kJ/cm heat-input. The results show that after the large wire energy welding thermal cycle, the coarse grain heat-affected zone is inevitably coarsened, the average grain size of the original austenite is 312 μm, and through the uniform distribution of the composite oxide inclusions induced, the intracrystalline can be formed into the organization type of acicular ferrite dominated + a small amount of lateral lath ferrite, so that the coarse grain zone can obtain a more desirable level of toughness. Among them, under the condition of -20 ℃, the fusion line impact work of steel plate thickness center is 70~269 J, with an average value of 179 J; under the condition of -40 ℃, the fusion line impact work of steel plate thickness center is 50~216 J, with an average value of 115 J. The impact performance of welded joints is good in all positions, which meets the requirements of impact performance of welded joints of EH36 steel plate.关键词：large heat-input welding;EH36 steel;double wire gas electric vertical welding;impact energy;oxide inclusion
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发布时间：2024-03-14
Important Issuse
- 摘要：In order to improve the performance of welded joints, the rail welding joint must be normalized after welding. Compared with the flame heating normalization method, the induction heating normalization method has the advantages of high degree of automation, stable normalizing quality, good working environment and so on. It is more and more recognized in rail field welding joint normalization. This paper focuses on the analysis of the PFM, PWM, PFM&PWM three AC side power regulation methods, the establishment of the mathematical model of the three control methods, and the use of MATLAB software to carry out three-dimensional visualization analysis of the mathematical model. The results show that the PFM&PWM control method has the advantages of less switching loss and less frequency change during power adjustment compared with the other two control methods. The control strategy of rail welding joint induction heating power supply based on PFM&PWM control method is proposed, and its control track is illustrated by combining with the three-dimensional mathematical model of rail welding joint induction heating power supply; The software and hardware based on TMS320F28335 are designed to realize the control waveform of the control strategy.关键词：rail welding joint;induction heating power supply;MATLAB;three-dimensional mathematical model;PFM & PWM
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发布时间：2024-03-14 - 摘要：The short-circuit transition type CO2 arc welding system is prone to spatter during the welding process, which is mainly due to the unstable arc energy and the undesirable transition state of the molten droplets during the welding process. In order to solve this problem, from the main circuit structure of the arc welding system, the mathematical model of two different control modes, namely, full inverter and rear stage adding chopper, is established. Under certain assumptions, the simulation model of these two control modes was established using the Simulink module in MATLAB, and the output waveforms under the two main circuit structures were compared and analyzed. The results show that the main circuit structure with chopper control in the back stage can more effectively meet the demand for low spatter in the short-circuit transition of CO2 welding. This control method can reduce the spatter during the welding process and improve the welding quality by adjusting the arc energy and the transition state of the melt droplet. In addition, the simulation results also show that the main circuit structure of the latter stage to join the chopper control in the reduction of spatter at the same time, but also effectively improve the stability of the welding process, improve welding efficiency. This has important theoretical significance and practical application value for optimizing the control mode of CO2 arc welding system and improving the welding quality.关键词：CO2 welding;short-circuit transition;Matlab simulation;low spatter
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发布时间：2024-03-14
Welding Equipment
- 摘要：The diamond film was brazed with copper alloy using Ag-Cu-Sn-Cr active brazing material. The study analyzed the effect of brazing temperature on the microstructure and mechanical properties of the joint. The results indicate that the interface between the brazing material and diamond is well bonded, and Cr in the brazing material reacts with diamond to form Cr3C2 carbides at the interface. The center of the brazing seam is mainly composed of Cu based solid solution, Ag based solid solution, Cu3Sn intermetallic compound, and Cr. When the brazing temperature is in the range of 780~840 ℃, as the temperature increases, the interface reaction layer gradually thickens, and the shear strength of the brazed joint first increases and then decreases. At the optimal brazing temperature of 820 ℃ and holding time of 15 minutes, the maximum shear strength of the joint reached 147 MPa. By optimizing the brazing temperature, reliable connection between diamond film and copper alloy has been successfully achieved. This method can provide new ideas and technical approaches for the connection between hard and brittle materials and metals in actual industrial production.关键词：diamond;brazing;copper alloy;microstructure;mechanical properties
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发布时间：2024-03-14 - 摘要：The 45 steel composite billet was sealed and fabricated by vacuum electron beam welding method. The microstructure and mechanical properties of the electron beam joint at different positions (1# arc, 2# middle and 3# arc closure) were analyzed by means of metallography microscope (OM), scanning electron microscope (SEM), Vickers hardness tester and impact testing machine. The results show that: When the welding position changes from the arc starting point to the arc retracting point, the joint penetration depth is almost constant, and the heat affected area decreases gradually. After welding, the cooling rate of the 1# joint is relatively slow, no crack occurs at the root of the weld, the structure is a mixture of acicular martensite and clumpy trotensite, the hardness (HV) is 588, the impact energy of the weld root is 25.7J, and the fracture is ductile. After welding, the cooling rate of the 2# and 3# samples is high, and obvious transgranular cracks appear at the root of the weld, and the microstructure is acicular martensite. With the acceleration of the cooling rate after welding, the number of martensite increases and the size becomes finer. The hardness (HV) increased to 674 and 729, respectively, and the impact property decreased to 18J and 13.7J, respectively, and showed a brittle fracture.关键词：45 steel composite billet;electron beam welding;joint organization;hardness;crack
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发布时间：2024-03-14 - 摘要：In this paper, the friction plug repair welding process and mechanical properties for the threaded hole on rail vehicle part were studied. The defect-free repair welding joints with optimized geometries of the plug/hole and welding parameters were obtained, and their microstructure, tensile properties, impact toughness and fatigue properties were analyzed. The results showed that incomplete penetration occurred in the bonding interface at high axial force. The defect-free joints were obtained with a rotation speed of 7 000 r/min, axial force 35 kN, thrust force 40 kN, and the plug feeding 18 mm. The microstructure near the bonding interface consists of pearlite, ferrite and some lath bainite, at the nugget zone is acicular ferrite, a large amount of grain boundary ferrite and a small amount of lath bainite. The defect-free joint has excellent mechanical properties, the tensile properties are equivalent to that of base metal, the fracture position of the joints are all located in the base metal at room temperature tensile test. In the fatigue test, the external thread of bolt always cracked precedes that of the internal thread of repair thread hole, The five million cycles fatigue strength of repair thread by plug welding reaches 142 MPa.关键词：low alloy high strength steel;threaded hole;friction plug repair welding;microstructure;mechanical properties
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发布时间：2024-03-14 - 摘要：SMA490BW weathering steel is usually joined by welding. Residual stress will be generated during the welding process, which has a great impact on engineering application. In industry, annealing heat treatment is often used to reduce residual stress. This paper establishes a finite element model of the welding process and post-weld heat treatment process of SMA490BW, the finite element simulation of the residual stress field of welding and post-weld heat treatment were carried out, and it was proven correct through test. By introducing the CREEP constitutive model of the material, the Norton-Bailey exponential equation is used to simulate the creep behavior of the material during post-weld heat treatment, and the effect of heat treatment on the welding residual stress is obtained. The research results show that: using the CREEP constitutive model, introducing the creep behavior of material can better simulate the stress and strain changes during the post-weld heat treatment of the welded workpiece, and the simulated residual stress values are in good agreement with the measured values.关键词：SMA490BW weathering steel;heat treatment;residual stress;numerical simulation
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发布时间：2024-03-14 - 摘要：In the construction process of large walled stainless steel composite plate pressure vessels, a complete set of new construction key technologies has been successfully formed through in-depth research on its technical points and difficulties, optimization of welding joint structure design. This technology not only optimizes the welding joint structure, but also innovates a series of construction methods, including cylinder heating and rolling, joint groove machining, TIG/FCAW automatic overlay welding of the corrosion-resistant layer on the inner wall of the connecting pipe, stainless steel lined pipe liquid nitrogen cooling sleeve, spherical head inner wall corrosion-resistant layer strip electrode submerged arc overlay welding, longitudinal ring seam narrow gap submerged arc welding, and saddle type submerged arc welding of the pipe joint. The application of these new key construction technologies not only improves the quality and effectiveness of pressure vessels, but also brings significant economic benefits, providing reference for the construction of similar equipment in the industry. In future research, the application of these technologies in other fields can be further explored to achieve broader technological exchange and cooperation. At the same time, for the construction of pressure vessels with large wall thickness stainless steel composite plates, it is still necessary to continuously study their material characteristics, process parameters, and construction methods in order to continuously improve the performance and safety of the equipment.关键词：large wall thickness;stainless steel composite plate;pressure vessel;key technology
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发布时间：2024-03-14 - 摘要：As the core material for high-speed, high-efficiency, and high-capacity hydropower generator units, the strengthening mechanism and welding characteristics of hydropower steel are currently the focus of research. This paper summarizes the recent development of hydropower steel, deeply analyzes its chemical composition, microstructure, and properties, as well as the impact of various strengthening mechanisms on its strength. It is found that fine-grain strengthening, solid-solution strengthening, dislocation strengthening, and second-phase strengthening can effectively enhance the strength of hydropower steel. Additionally, this paper discusses in detail the crack tendency of welded joints of hydropower high-strength steel, the matching mechanism of weld metal and base metal's strength and toughness, as well as the performance changes in the heat-affected zone. This research not only provides theoretical support for optimizing the performance of hydropower steel, but also provides strong support for technological advancements in related fields.关键词：steel for water and electricity;microstructure and properties;strengthening mechanisms;weldability characteristics
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发布时间：2024-03-14 - 摘要：Tensile test are conducted after the brazing VT for end ring and bar joints of squirrel cage rotor of a certain type of traction motor. It is found that part of the bar is pulled off from the end ring and bar joint beam, this result cannot satisfy the tensile strength requirement. In order to solve this problem, micro-cracks, undense filler metal filling and delamination were found in the brazing interface between the inner side of the end ring and the conductor bar through penetration testing and macroscopic testing. It is pointed out that the unreasonable design of end-ring and conductor bar structure and the insufficient duration of high temperature brazing are the main factors leading to the pull-out problem. In view of these two factors, the improvement scheme is put forward: the depth of the end ring groove is changed from 6 mm to 4 mm, the inner chamfer of the end ring groove is increased by 45°, and the holding time of 450 ℃ is extended to 90 s in winter brazing. After the improvement, the tensile test proved that the problem of pulling out of the conductor bar was solved successfully and the product quality was guaranteed..关键词：squirrel cage rotor;brazing;bar tensile failure;cause analysis;structure improvement
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发布时间：2024-03-14
Welding Technology
- 摘要：ENiCrMo-2 nickel-based welding rod alloy cladding metal was prepared using SMAW. The microstructure of the cladding metal was studied by optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) methods. The grain boundary morphology, precipitate phase composition, and precipitate phase morphology characteristics were studied. The tensile test was conducted on the cladding metal, and the fracture morphology was analyzed to study the effect of Mn content on the microstructure and mechanical properties of the cladding metal. The results showed that the microstructure was mainly columnar austenite, and the increase in Mn content changed the width of the segregation zone, but had no significant effect on the precipitate phase. The precipitate phase included Cr-rich carbides (M7C3) and Mo- and Cr-rich carbides (M23C6), with partial precipitates being M7C3 encapsulated by M23C6. With the increase in Mn content from 0.16 wt.% to 0.91 wt.%, the ductility and crack resistance of the cladding metal were improved, and the mechanical properties of the cladding metal were good. Through fracture analysis, it was found that when the Mn content was 0.16 wt.%, there was a weak tendency for crystal cracks and high-temperature ductile cracks. The increase in Mn content weakened the crack tendency, and the dimple morphology on the fractured surface along with grain boundaries became gradually deeper and more uniform. Therefore, appropriately increasing Mn content can optimize the microstructure and mechanical properties of ENiCrMo-2 nickel-based welding rod alloy cladding metal. When the Mn content is increased to 0.91 wt.%, the mechanical properties of the cladding metal are optimal.关键词：welding electrode of nickel alloy;deposited metal;Mn content;microscopic organization;precipitated phase;mechanical properties;crack tendency
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发布时间：2024-03-14 - 摘要：In order to investigate the reasons of product failure resulting from a lot of pores and inclusions at the interface of brazing joints during induction brazing motor rotors using the same grade filler metals produced by different manufacturers, the oxygen content, microstructure and tensile strength of domestic and Indian brazing materials were compared, and the effects of different brazing materials combinations on wettability and brazing joint strength were investigated. The results showed that the average tensile strength of the domestic filler metal was 382.7 MPa, which was 3.8% higher than that of the Indian filler metal. The Indian filler metal with high oxygen content was more likely to form oxidation inclusions with Ca, Fe, P and other inclusion elements in the raw materials, resulting in a significant decrease in the strength of the filler metal. Furthermore, the average wetting area of domestic brazing materials was 286.96 mm2, which was 36.7% higher than that of Indian brazing materials. During brazing with Indian brazing materials, numerous residues containing F and K as well as oxidized slag were present in the braze zone, resulted reduced joint strength.Therefore, it was crucial not only to select clean filler metal with excellent fluidity and performance during brazing, but also consider choosing an appropriate flux exhibits high activity levels.关键词：silver based brazing filler metal;flux;oxygen content;microstructure;tensile strength
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发布时间：2024-03-14 - 摘要：The effects of argon refining process parameters on the hydrogen contents in ER4043 aluminum melt and the resulting solid alloy wires were investigated. Experimental results show that reducing the argon flow rate during gas refining can significantly reduce the hydrogen content of melt and decrease the number and size of pores on the longtitudinal section of the samples prepared by reduced pressure test. When the argon flow rate was at 8~10 mL/min, the hydrogen content in melt reached the minimum value. Bulk hydrogen of solid ER4043 alloy wires can be obtained accurately by the LECO RHEN602 hydrogen determinator. Similarly, when the flow rate of argon during smelting was controlled at 8~10 mL/min, the bulk hydrogen in solid alloy wire reached the lowest value of 0.17~0.18 mL/100g Al, which could meet the technical requirements of low hydrogen aluminum alloy wire production. In addition, under the same argon refining process, the bulk hydrogen content in solid alloy wire was higher than the hydrogen content in melt, and the ratio of the former to the latter was kept between 1.7 and 2.1.关键词：aluminum alloy wires;argon refining;hydrogen in melt;hydrogen in solid alloy
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发布时间：2024-03-14 - 摘要：In this paper, the ball milling time in the production of steel-bonded cemented carbide was selected as the research object. The effects of ball milling time of 20 h, 24 h and 28 h on the microstructure and properties of TiC high manganese steel-bonded cemented carbide were studied. The results show that the ball milling time increases from 20 h to more than 24 h and 28 h, the proportion of the particle size distribution of the mixture over 600 mesh increases from 44.51% to 80% and 83%, the particle size distribution is finer, the microstructure pores of the alloy decrease, and the bending strength increases from 833 MPa to 932 MPa and 1008 MPa.The more pores in the alloy lead to a decrease in density because the CO and CO2 gases produced in the redox reaction stage of the sintering process cannot be discharged from the sintered body in time.In actual production, by appropriately increasing the ball milling time, the microstructure of TiC high manganese steel bonded carbide can be improved, its performance can be improved, and higher quality products can be obtained.关键词：ball milling time;TiC high manganese steel bonded carbide;Mircostructure;performance
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发布时间：2024-03-14
Welding Material
- 摘要：In order to meet the needs of new Engineering education for cultivating new engineering talents, improve the teaching quality of materials forming and control engineering (welding) majors, consolidate students' theoretical basis in the subject, and cultivate students' professional theoretical analysis capabilities, the project-based teaching research was conducted to reform the course on numerical analysis of welding thermal processes. Integrating welding thermal process theory with fluid dynamics (CFD) theory and tool software, a project-based teaching exploration that integrates theoretical learning and virtual simulation experiments was conducted. Taking the Gas Tungsten Arc Welding molten pool as the analysis object, a numerical simulation model of the molten pool was designed, and the thermal process of the molten pool was analyzed from the aspects of material properties, process parameters, heat source model, etc., and data analysis and theoretical discussion were completed. The project-based teaching strengthens the whole-process interaction between students and teachers, drives students' to learn independently, and cultivates students' ability to use advanced tools and software to solve practical welding engineering issues, which is conducive to cultivate welding talents with a solid theoretical basis and practical ability.关键词：project-based teaching;practice capability;weld pool thermal processes;numerical simulation
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发布时间：2024-03-14
Education & Training
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