Abstract：With the continuous progress of science and technology and the continuous improvement of engineering application standards, more and more extreme conditions put forward more stringent requirements for welding technology. Firstly, the service conditions are divided into four aspects: ambient temperature, corrosion environment, wear condition and vacuum environment. The comprehensive performance changes of welded structures in these extreme environments are reviewed. At the same time, various coping methods and their mechanisms to overcome the negative effects of these extreme environments are compared. Secondly, based on the welded material structure, the technical problems and fatigue life evaluation of the two extreme size structural parts of the large structure and thin-walled structure are introduced. The problems and difficulties of welding technology under extreme conditions are summarized and sorted out, and its future development direction is prospected.
Abstract：With the increase in harsh environment and processing and manufacturing complexity, the comprehensive performance of ceramic/metal heterogeneous structures has become more demanding. Brazing technology is now widely used for ceramic-metal heterogeneous connections, and the challenge of residual stress relief in welded joints between the two materials is very difficult. Residual stresses have a significant impact on the performance of ceramic/metal joints and their magnitude is influenced by a variety of factors. Therefore, a systematic overview of the state and distribution of residual stresses in ceramic-metal welding, from the optimization of process parameters, the addition of intermediate layers, composite brazing materials and surface structure design of the four mitigation paths are systematically reviewed. Finally, the future opportunities and challenges of ceramic/metal heterostructure residual stress research.
Abstract：Laser brazing technology for dissimilar metals of aluminum alloy and steel is a technology that uses laser as welding heat source, under the premise of ensuring that the high melting point steel matrix does not melt, the low melting point aluminum alloy matrix is melted and a fusion welding joint is formed with the melted filler metal, and the liquid aluminum alloy matrix and the filler metal are spread on the steel surface that is not melted and form a brazing joint to realize the high-quality and high-strength metallurgical connection between aluminum alloy and steel. This paper reviewed the research results of aluminum alloy/steel dissimilar metal laser brazing technology at home and abroad from three aspects: interface wetting spreading of aluminum alloy and steel interface, micro-control of interface, and performance evaluation of brazing joint. It focuses on introducing the influence of metal coating, brazing agent and parent material thermal field on the interface wetting spreading of aluminum alloy and steel laser brazing process, summarizing the role of interface thermal field, auxiliary energy field, groove surface angle and alloy elements in the micro-control of aluminum alloy and steel laser brazing process, and summarizing the evaluation methods of aluminum alloy and steel laser brazing joint performance. At present, domestic and foreign scholars had done a lot of research work on aluminum alloy/steel laser brazing, and had achieved many creative technical achievements, but high-quality, efficient and reliable aluminum alloy steel dissimilar metal laser brazing technology still needs to solve the following four problems: precise and controllable wetting spreading of steel parent material surface brazing agent; precise and adjustable reaction of aluminum alloy/steel laser brazing interface; high strength and toughness design of aluminum alloy/steel laser brazing joint; and reliability evaluation of aluminum alloy/steel brazing joint performance.
Keywords：dissimilar metals of aluminum alloy/steel;laser brazing technology;coating;wetting;interface;joint performance
Abstract：Titanium alloys have been widely used in many fields such as aerospace, energy, automotive, construction, packaging, transportation, and other fields due to their excellent properties, such as low density, high temperature resistance, excellent creep and corrosion resistance. However, the high-temperature performance of traditional titanium alloys is relatively low. Connecting titanium alloys with ceramics to prepare composite structures can help to obtain components with light weight and excellent high-temperature performance. However, large differences in physical and chemical properties of dissimilar materials often lead to difficulties in joining. Brazing is one of the most widely used methods for connecting materials in the manufacturing industry, and is widely used in medical, power electronics, and automotive fields. Academics around the world believe that brazing is the most effective and promising connection method for ceramic/metal heterogeneous connections. This article summarizes the current research status of brazing titanium alloys to common ceramics such as Al2O3 and ZrO2, and ceramic matrix composites such as ZrB2-SiC and ZrC-SiC. It also introduces commonly used methods such as interlayer method to alleviate residual stress in titanium alloy ceramic joints, and summarizes the selection of reinforcing phases in interlayer and composite solder. Finally, the shortcomings in the research and development of titanium alloy/ceramic heterogeneous brazing technology are pointed out, and the future development direction of titanium alloy/ceramic heterogeneous brazing technology is prospected, providing theoretical basis and technical support for the related research and engineering application of titanium alloy/ceramic heterogeneous material bonding.
Keywords：titanium alloy;ceramic;brazing;residual stress;heterogeneous material
Abstract：With the increase in laser power, laser transmission is severely affected by plasma plumes, resulting in a one-time penetration depth of laser welding that is not proportional to laser output power, and the stability of weld formation cannot be reliably guaranteed. Research has found that laser welding can show different process characteristics in a vacuum environment, effectively suppressing plasma plumes, increasing weld penetration, improving weld pool stability, and obtaining high-quality welds. This provides a new process method and research idea for achieving high-quality and efficient welding of thick wall components. Based on a comprehensive review of research achievements at home and abroad, the development history of vacuum laser welding technology is introduced, then the characteristics of weld formation, weld pool and keyhole, and plasma plume during laser welding in vacuum environment is analyzed, and then the design of vacuum laser welding equipment and related applications of vacuum laser welding are combed through, the existing problems in the current research of vacuum laser welding technology are discussed and the future development direction of vacuum laser welding technology is prospected.
Abstract：As an important technical means of manufacturing and remanufacturing, built-up welding technology is widely used in the manufacturing and repair of equipment parts, especially through high-quality refurbishment, life extension and other technical means to significantly reduce the resource and energy consumption and carbon emissions brought about by manufacturing new parts. The current development status of wear-resistant built-up materials and equipment in arc surfacing is summarized, as well as the typical engineering applications of plasma surfacing and laser surfacing. It briefly describes research development and typical applications of arc additives as digital built-up technology for large-scale components manufacturing and remanufacturing of irregular areas. In addition, the requirements of the development of built-up industry technology for high-end surfacing materials, full cycle theoretical research on surfacing and integration of control systems are also discussed, providing guidance for the research, technical improvement, and application of built-up welding technology.
Abstract：Polycrystalline diamond compact (PDC) is widely used in machining, energy mining, geological exploration and so on because of its excellent properties. However, PDC had high temperature sensitivity. At high temperature, the internal residual stress increases, the oxidation and graphitization of diamond layer occur, which leads to the tearing of PDC diamond skeleton, the peeling of diamond particles, and even the failure of composite sheet. the current status of PDC research at home and abroad this paper is reviewd from five aspects, including surface modification of PDC, binder optimization, PDC structure design, grain refinement and PDC brazing technology, the common problems of PDC are discussed and the future research direction is prospected.
Abstract：Molybdenum and its alloys have excellent high temperature performance, heat dissipation capacity and low thermal expansion coefficient. Graphite has a thermal expansion coefficient close to that of molybdenum alloy. In addition, graphite has very high specific heat capacity and heat dissipation capacity, but with very low strength. Generally, the combination of molybdenum alloy and graphite can meet the requirements of high temperature strength and high heat dissipation capacity. The reliable connection of molybdenum alloy with graphite is the basis of application. Based on the physical and chemical properties of molybdenum and graphite, the welding characteristics are analyzed. Besides, the welding methods, microstructures evolution of welding interface, and mechanical properties of TZM and graphite are reviewed. And the joint technology of molybdenum alloy and graphite is prospected.
Abstract：Transient liquid phase bonding was performed on TA2 titanium at 880 ℃ × 30 min using ZrCuNi interlayer with 0.01 mm Cu foil, 0.01mm Ni foil, 0.01 mm, 0.02 mm and 0.03 mm Zr foil. The mechanism of interfacial microstructure evolution, interlayer element diffusion and mechanical properties of the joint were studied. The results show that the interface structure of the joint is composed of the intermetallic compound (IMC) layer in the center and the eutectoid structure on both sides. A continuous band of (Ti, Zr)2(Cu, Ni) IMC with a thickness of about 10 μm is formed in the jonint center with 0.01 mm Zr interlayer. When the thickness of Zr interlayer increases to 0.02 mm and 0.03 mm, the eutectic structure containing (Ti, Zr)2(Cu, Ni) IMC is formed in the joint, and the thickness of the eutectic increases to 80 μm and then decreases to 37 μm. The microhardness of (Ti, Zr)2(Cu, Ni) IMC is above 500 HV0.1, which thickness decreasing is helpful to improve the joint strength. The decrease of the thickness of the brittle (Ti, Zr)2(Cu, Ni) is helpful to improve the joint strength. The shear strength of the joint is the highest with 0.01 mm Zr interlayer, and the mean value is 207 MPa. The cracks spread along the IMC layer and the eutectoid structure on both sides. The fracture features dimple and fluvial pattern, which is a composite fracture mode of toughness and brittleness. The shear strength of the joint is respectively 92 MPa and 135 MPa when the thickness of Zr interlayer increase to 0.02 mm and 0.03 mm. The crack extends along the eutectic structure, and the facet cleavage characteristics shown by the fracture morphology are typical of (Ti, Zr)2(Cu, Ni) IMC.
Abstract：The crack resistance of 20 mm thick Q1400E ultra-high strength steel is studied using a laser arc hybrid welding method. Through the crack sensitivity examination of the inclined Y-groove, it is found that welding cracks are easy to occur at the upper position of the weld center. Through metallographic examination, surface morphology examination, and EDS analysis, it is determined that the crack is a solidification crack. Causes of cracks: (1) insufficient shrinkage of liquid metal leading to shrinkage porosity; (2) micro segregation of harmful elements such as C, S and P occurs; (3) the base metal possesses a high hardenability and high binding strain at the pointed corners of the groove. The characteristics of deep penetration welding using laser hybrid welding and pre welding preheating measures are used to further reduce the welding restriction stress. The results reveal that when using welding parameters such as laser power 8 500 W, welding current 250 A, welding voltage 24 V, welding speed 1.2 m/min, and preheating 200 ℃, the welding crack problem of 20 mm thick Q1400 ultra high strength steel can be efficiently solved.
Abstract：In response to the issue of weak flowability of AgCuNiMn filler metal on the surface of superalloys, in the YG6X/AgCuNiMn/GH4169 brazing system, the wetting morphology and final wetting angle of the brazing materials on the GH4169 surface with or without nickel coating were compared, and the effect of nickel plating on the wetting performance of the brazing materials on the GH4169 surface was analyzed; and with the help of SEM, the microstructure of the brazed joint with nickel coating was analyzed, and combined with the tensile performance test results of the joint, the influence of the nickel coating on the microstructure and mechanical properties of the joint was revealed. The study found that nickel plating on the surface of GH4169 can significantly improve the wetting and spreading performance of the solder on the alloy surface. After nickel plating, the minimum wetting angle of AgCuNiMn solder on the alloy surface can reach 4 °, and there is about 20 μm reaction zone at the interface between the solder and the superalloy. The presence of the reaction zone can improve the wettability of the solder and prevent the diffusion of elements such as Fe, Cr, and Nb from the base metal of the superalloy into the solder joint region, thereby reducing the tensile strength of the joint, with an average tensile strength of 631.6 MPa.
Abstract：Intermetallic compounds (IMCs) distributed at the interface reduce the bonding strength of MnCuAl alloy/430 stainless steel (430SS) brazed joints, and then reduce the performance of welding structure. Ni layer is electroplated on 430SS surface to inhibit the formation of IMC in the joint, then the effect and mechanism of Ni layer with different thickness on joint structure and IMC are investigated. The results show that there is no obvious defect at the interface between the Ni plating and the substrate, and the Ni plating can be well combined with the 430SS substrate. For the brazed joint without Ni plating, γ-(Fe, Mn) solid solution layer is distributed at the interface of the 430SS side, and there are continuous distribution IMCs between the reaction layer and the center of the brazing seam on both sides, accompanied by the brazing flux residue. When 8 μm Ni layer is electroplated, the Ni layer completely dissolves after welding, γ-(Fe, Mn) solid solution layer is still distributed at the interface of the 430SS side, but IMCs disappeare and only a few brazing flux remaines. When the plating is 20 μm, there is a residual Ni plating layer on the 430SS side after welding, no γ-(Fe, Mn) solid solution layer is found, IMCs disappeare, and no residue of brazing flux is observed. It is concluded that Ni plating can inhibit the formation of IMCs by alloying and blocking when its thickness is 8 μm and 20 μm respectively.
Keywords：MnCuAl damping alloy;430SS;dissimilar metal brazing;electroplated Ni layer;intermetallic compound;interface
Abstract：The effects of laser power, welding speed, defocus, scanning amplitude and scanning frequency on backside forming of 8 mm carbon steel were systematically studied by using the penetrating scanning laser without opening welding method. The results show that under the conditions of welding speed of 0.9 m/min and 1.2 m/min, the weld pool is balanced by surface tension and gravity under the action of scanning laser, and the weld with uniform forming and continuous back, good root penetration and proper back residual height is obtained. With the change of defocusing distance from -10 mm to +10 mm, negative defocusing distance is more continuous and uniform than positive defocusing distance, and the residual height of back is from 1.2 mm to 1.5 mm. When the welding power, welding speed and defocusing distance were fixed and only scanning mode was changed for comparison test, liner (vertical) scanning mode obtained the best effect under several scanning modes in comparison experiment. Scanning amplitude and scanning frequency were changed, and the weld was partially penetrated or not penetrated when scanning frequency was greater than 300 Hz and the amplitude was greater than 2 mm. Scanning amplitude is 200 Hz, scanning amplitude is 1 mm when the forming is better, and the weld back forming effect welding heat input > defocusing distance > scanning frequency > scanning amplitude. Therefore, by increasing the welding speed, choosing the defocusing distance between -10 mm and 0 mm, liner (vertical) scanning mode, 200 Hz scanning frequency, 1 mm or 2 mm scanning amplitude, uniform, continuous and well-integrated single-side welding back shape of 8 mm carbon steel plate can be obtained.
Keywords：10 kW laser;scanning welding;single-side welding back forming;medium-thick plate;back more than high
Abstract：To improve the wettability of solder on the substrate surface, T2 copper was selected as the substrate and two types of linear grooves and reticulated grooves with different array spacing were prepared on the surface of the copper using the HG100-20W laser marking machine. Wettability tests were carried out on the T2 copper surface using BAg25CuZnSn electrodes and BCu93P-A powder as the brazing material, and the effect of the surface fabric and the spacing of the fabric on the wettability of the brazing material on the T2 copper substrate was investigated. The experimental results show that the surface texture of the T2 copper substrate increases the spreading area of the solder. When the solder is BCu93P-A and the groove texture array spacing is 100 μm, the maximum spreading area is 322.4 mm2. With the decrease of the texture array spacing, the spreading area of the two solders gradually increases, and the wettability of the linear textured substrate is smaller than that of the grid textured substrate.
Keywords：laser processing technology;surface texture;wettability;spreading area