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Cold welding refers to an effect related to space (vacuum). The heavy vibrations during a launch subject interfaces (hold down points) to oscillating motions which may lead to formation of a kind of “friction weld”. If so, these mechanisms may get stuck, and deployment will be hindered. This may endanger the functionality of the mission (instruments) or even the whole spacecraft (if solar panels do not open). Several studies have been done to characterize material combinations (including coatings) for their ability to cold welding in space. Meanwhile, also during launch grease free contacts are demanded. If grease hat to be omitted, the risk of cold welding under fretting was found to increase (when testing in high vacuum). To rate this risk under launch conditions, the test method was recently extended for testing under launch conditions. The new tests procedure consists of fretting applied in the sequence in air, low vacuum and high vacuum. The paper shall present first results gained with this new method of testing in launch conditions and compare them to previous studies done in vacuum. Following the need of space industry on mechanisms for launch and in-orbit life, a first set of combinations of materials and coatings were selected for this new test sequence where fretting is now applied in a sequence of air, low vacuum and high vacuum. Under this sequence, the measured levels of adhesion and it’s evolvement was found to differ strongly from tests done formerly. The paper outlines these first results and compares them to existing data.

Graphene (G) and its derivatives exhibit great potential as oil-based additives to enhance the anti-friction capacity of amorphous carbon (a-C) interface for industrial applications. However, due to the structural diversity of G derivatives and the limitation of experimental characterization, the difference of intrinsic G and its derivatives in improving the lubricity and the underlying tribochemical information is still unclear, leading to a lack of fundamental understanding of the friction mechanism. Here, we address these issues through the atomic-scale simulation and demonstrate that compared to the intrinsic G, its derivatives can further reduce the friction resistance at a-C surface, especially the chair-type graphane with the reduction of friction coefficient by 86%. Most importantly, the fundamental friction mechanism caused by G derivatives mainly attributes to the G-induced cross-linking and cold welding of mated a-C surfaces, although it is also affected by the passivation of the friction interface and the hydrodynamic lubrication of base oil. These outcomes can guide the R&D of advanced a-C/lubricant synergy systems for technical applications.

Effective fabrication methods of Cu-Ag core-shell nanowires network are of vital importance for their shining applications in stretchable electronics. In this study, molecular dynamics simulations are performed to study nanojoining of Cu-Ag core-shell nanowires by head-to-head cold welding, along with mechanical properties of obtained welding joints. Results show that Cu-Ag core-shell nanowires can be successfully connected by cold welding with high-efficiency and few defects owing to atomic interaction and diffusion of atoms. What's more, welding velocity and remaining deformation in nanowires will exert significant influence on mechanical properties of joints, including strength and plasticity. It is revealed that cold welding under pressure will somewhat cause internal compression of structures which can be alleviated by following tensile deformation of the two heads if possible. These findings deepen the understanding of nanoscale cold welding and are expected to provide practical reference for the bottom-up fabrication and assembly of Cu-Ag core-shell nanowires network.

There is represented the creation of a skid for manual contact welding. It consists of a metal structure of the skid itself and a movement carriage. Strength and stiffness calculations of the metal structure of the skid and of the carriage were performed. A full-scale sample of the skid assembly result is shown.

This article proves the advantage of gauze compared to the wire, tape, and powder materials as a filler material for electro contact welding. The gauze as a tape material consisting of wires has the advantages of wire (high adhesive strength and high fatigue life) and the tape advantages (high producibility, ease of use). The paper presents the coating study methods and results using gauze welding and the effect of this coating on the adhesive strength depending on electro contact welding modes, material and gauze parameters, residual stresses in coatings, and coating wear-resistance. During electro contact welding in rational modes, the woven gauze adhesive strength is 41% higher than the steel tape. When analyzing residual stress as a relation of the effective stress to the material yield strength of the sample or coating, it was found that residual stresses have a smaller effect in the woven gauze coating compared to the tape made of steel 45. A stainless steel woven gauze coating and a steel tape coating made from steel 45 are equal in wear resistance. Thus, a metal gauze can be used as filler material during electro contact welding on the surface of worn parts instead of steel tape made from a similar grade of steel applied to the worn parts' surface.

In immersed friction stir welding, the workpiece is fully immersed in the water during welding. This work illustrates the effect of welding speed on mechanical properties and microstructure. Friction stir welding joints were produced using AA2014-T6 at different welding speeds ranging from 80 to 125 mm/min with constant rotational speed of 1000 r/min in air and immersed water conditions. Results revealed that with an increase in welding speed, the tensile strength of joint increased, this is due to a reduction in heat input while using both air and immersed friction stir welding, which in turn reduces the dissolution of strengthening precipitates. Microstructure result showed that grain size decreased with an increase in welding speed due to less heat input at increased welding speed. The dissolution of strengthening precipitates weakened with an increase in welding speed in both air and immersed friction stir welding, leading to an increase in hardness value at the nugget zone. Maximum tensile strength was obtained at a welding speed of 100 mm/min in immersed friction stir welding and was around 17% higher compared with a maximum tensile strength obtained using air friction stir welding.

Butt-fusion welding is an effective process for welding polymeric pipes. The process can be simplified into two stages. In heat soak stage, the pipe is heated using a hot plate contacted with one end of the pipe. In jointing stage, a pair of heated pipes is compressed against one another so that the melt regions become welded. In previous works, the jointing stage that is highly related to the welding quality was neglected. However, in this study, a finite element simulation is conducted including the jointing stage. The heat and momentum transfer are considered altogether. A new numerical scheme to describe the melt flow and pipe deformation for the butt-fusion welding process is introduced. High density polyethylene (HDPE) is used for the material. Flow via thermal expansion of the heat soak stage, and squeezing and fountain flow of the jointing stage are well reproduced. It is also observed that curling beads are formed and encounter the pipe body. The unique contribution of this study is its capability of directly observing the flow behaviors that occur during the jointing stage and relating them to welding quality.

Welding is widely used as a joining method for thermoplastics, and it is imperative to ensure the joining quality, particularly for critical applications. In a previous work by the authors, an Eigen-line was found in the electrofusion joint of polyethylene (PE) pipes based on ultrasonic tests and it could be used to detect and assess cold welding defects. However, the nature of the Eigen-line and reasons for the Eigen-line's existence in ultrasonic images have not yet been fully understood, which limited its applications. In this paper, Eigen-lines were observed in other thermoplastics including polypropylene (PP), polyamide 6 (PA 6), polyoxymethylene (POM) and polyethylene terephthalate (PET), suggesting that Eigen-lines have common existence. Microindentation tests were conducted on specimens cut from electrofusion joints and butt joints of PE pipes. It was found that a significant change of elastic modulus exists around the Eigen-line, which can partly explain the appearance of an Eigen-line in ultrasonic images. Scanning electron microscopy (SEM) and reflective optical microscopy were also employed to explore the nature of the Eigen-line. The results showed that an Eigen-line is a thin layer with polymer chain orientation between base material and welded zone.

We report that twin-roll cast and subsequently heat-treated Mg–6Zn–1Mn–1Al alloy sheets with a thin thickness of 1 mm were successfully joined by surface-friction welding process. The welded sheet revealed several distinct weld zones, which are closely related to plastic flow and frictional heat generation during welding. Although large microstructural differences were found among the welded zones, the presence of thermally stable Al 8 Mn 5 particles pre-existing in the sheet appeared uninfluenced by the welding process. The role of the microstructural changes induced by the welding process in the hardness variation and tensile properties of the welded sheet is discussed.

Aluminum alloy 2219 is widely used in aerospace applications since it has a unique combination of good weldability and high specific strength. Furthermore, it can provide a high strength after heat treatment with superior properties in cryogenic environment so they have been widely used for cryogenic fuel tank of space launch vehicles. It is known that solid state welding like friction stir welding can improve the joint properties of this alloy. Friction stir welding is a solid state welding technology which two materials are welded together by the frictional heat due to the rotation of the tool. In this study, friction stir welding was performed on aluminum alloy 2219 sheets. The range of welding parameter is four rotation speeds from 350 to 800 rpm and six travel speeds from 120 to 420 mm/min. The results include the microstructural change after friction stir welding. The microstructure was characterized and material in the stirred zone experience sufficient deformation and heat input which cause the complete dynamic recrystallization. The present work represents the strength at each process condition and the optimum friction stir welding process parameters. The optimum weld efficiency obtained in this study was 76.5 %.

A new welding technique has been developed for manufacturing large aluminum chambers for an ultra-high vacuum (UHV) system. Combined with appropriate manufacturing processes, the aluminum chambers have an oil-free interior surface finished for an ultra-high vacuum environment before aluminum welding. An automatic welding system, which comprises six welding torches to implement simultaneously two longitudinal side welds of the asymmetric chamber, is introduced. In traditional manual welding, the key success factors focus on elimination as much as possible the distortions of structural assemblies. The six-torch welding and a clamp-free approach together address the issue of reducing distortion and minimizing residual stresses with a novel one-step welding process. From the beginning of CNC machining to the end of vacuum component assembly, deformations through all process sequences are measured and controlled under 0.35 mm. In this paper, both the manufacturing sequences and statistical analysis of deformation control are presented in detail.

Titanium alloys are widely used in the aerospace industry on account of their high strength, fatigue strength, impact strength, and corrosion resistance. Airplane components such as ribbed panels must satisfy strict requirements on the quality of weld joints and the dimensional precision. The welding of titanium alloys leads to the formation of flaws at the joint and impairs the performance of the part; their geometric dimensions are distorted on account of the welding stress; pores and microstress appear in the seam; and the mechanical and other characteristics are impaired. That calls for comprehensive analysis of the manufacture of ribbed titanium panels, all the way to the heat treatment of the final product, so as to discover the processes that are most likely to generate defects. The manufacture of the workpieces—including their preparation for welding, the welding conditions, and subsequent heat treatment—affects the static and cyclic strength of welded ribbed panels, with variation in the number of weld-seam defects and their total area. The results obtained in the present work permit prediction of the properties and reliability of welded structures and the maintenance of identical properties of the basic metal and the seam metal, with the guaranteed absence of external and internal effects, on the basis of the selected production processes. It is found that the properties and reliability of weld joints will match those of the basic VT20 titanium alloy in ribbed panels in the following conditions: welding with specific cooling rate in the phase-transition temperature range; final milling, turning, degreasing, and drying of the surface of the joined edges; light annealing after welding in air; subsequent sandblasting; and gas-laser layout cutting in a nitrogen or argon atmosphere, with or without milling.

The present study is a work on a single-pass full penetration hybrid laser-metal inter gas (MIG) welding of 8-mm-thick pure copper (T2) in butt joint configuration without any heat treatment before the welding process. The effect of process parameters and joint configuration on the geometry and integrity of the joint was studied and then analyzed with the aid of digital camera through high-speed imaging. The optimized joint configuration and optimal welding parameters were experimentally investigated. The fusion zone showed an aspect ratio of about 1.43, the ratio of plate thickness to weld width. Nondestructive X-ray inspection revealed that the joint could satisfy the requirement of a nondestructive test of pressure equipment standard JB/T4730–2005.

Silver nanowire (AgNW) films have been studied as the most promising flexible transparent electrodes for flexible photoelectronics. The wire–wire junction resistance in the AgNW film is a critical parameter to the electrical performance, and several techniques of nanowelding or soldering have been reported to reduce the wire–wire junction resistance. However, these methods require either specific facilities, or additional materials as the “solder”, and often have adverse effects to the AgNW film or substrate. In this study, we show that at the nanoscale, capillary force is a powerful driving force that can effectively cause self-limited cold welding of the wire–wire junction for AgNWs. The capillary-force-induced welding can be simply achieved by applying moisture on the AgNW film, without any technical support like the addition of materials or the use of specific facilities. The moisture-treated AgNW films exhibit a significant decrease in sheet resistance, but negligible changes in transparency. We have...

Laser beam welding is based on interaction between the laser beam and parent metals. Methods have been developed in recent years to produce joints of most light metals and their combinations. It provides good weld joint to simplify the structure and reduce the weight and cost to meet the main concerns of the aircraft industry. To achieve these, Ti6Al4V and AA2024 alloy sheets with a thickness of 1.0 mm have been welded with butt joint configuration using pulsed Nd:YAG laser beam welding without groove and filler metal. The weldment has been subjected to testings such as surface roughness, microstructure, hardness, tensile strength and distortion. Test results reveal that laser beam welding is very much suitable for joining Ti6Al4V/AA2024 alloys, while focusing from aluminium side.

Studies on bonding of aluminium alloys to steels are popular because these are structural materials widely used in a variety of industries. However, joining these dissimilar materials is difficult mainly because of the formation of brittle intermetallic compounds. This paper presents a study on welding aluminium to steel by resistance spot welding. Before the welding, steel surface was covered by cold spraying with the layer of aluminium, nickel and nickel–aluminium. This way, instead of the welding of dissimilar materials, the welding of aluminium to aluminium (or nickel) layer pre-deposited on the steel sample was performed. The feasibility of using interlayers for improving the welding of dissimilar materials was tested using SEM, EDX and XRD. Mechanical properties of welds were investigated by microhardness and shear strength tests. The results showed that the coating allowed to decrease hardness in the welding zone and to increase the shear strength of the weld.

A pile is a fundamental part of fixed type platform which commonly used to support superstructure rig in the offshore area. A seamless pipe is usually used as the pile structure. However, this seamless pipe is a high-priced pipe and scarce to find in Indonesia. ERW (Electric Resistant Welded) pipe can be used for an alternative selection of the seamless pipe for piling structure. However, ERW pipe production may have a defect in the form of a cold weld and a hook crack. This paper studies the possibility of ERW pipe utilization as the piling structure. A case study was conducted for ERW pipe NPS 24 and length of 6 m. This research conducted by using eta-FEMB and LS-DYNA software to examine the effective stress of the pile structure during installation. Numerical simulations were carried out on the pile structure with crack modelling and withstand multiple impact loading. The result was compared with failure criterion based on API RP 2A WSD. Those criteria include Axial Allowable Tensile Stress (AATS), Axial Allowable Compressive Stress (AACS) and Critical Hoop Buckling Stress (CHBS). Based on this preliminary analysis, we hypothesize that the ERW pipe with defect length up to 5 mm can be used for the piling structure. However, this analysis need further investigation in order to be a recommendation for substituting seamless pipe for piling structure.

Ti2AlNb alloy is an attractive material for advanced aerospace applications. Welding of the alloy can lead to severe distortion, influencing dimensional precision of the welded workpiece and structural integration. In this study, the effect of welding parameters on the weld shape of the Ti2AlNb alloy jointed by electron beam welding was investigated. A three-dimensional thermal-elastic-plastic finite element method was developed to simulate the welding distortion. The simulation results agreed with experimental measurements very well. It showed that the developed computational approach has sufficient accuracy and can be used to predict welding distortion. Because of the low longitudinal shrinkage force, the workpiece was bent to a concave-concave shape. When welding without fixture, the bead-on-plate joint has less distortion than butt weld. Also, it was found that focus current can significantly change the weld shape, resulting in various of transverse shrinkage distributions, consequently determining transverse bending deformation. When welding heat input is kept constant, the nail-shaped weld made with a certain negative defocusing electron beam will have minimum angular distortion. Keywords: Ti2AlNb alloy, Welding distortion, Numerical simulation, Electron beam welding

Stitch welding of plate covered skeleton structure of Ti–6Al–4V titanium alloys has a variety of applications in aerospace vehicle manufacture. The laser stitch welding of Ti–6Al–4V titanium alloys was carried out by a 4 kW ROFIN fiber laser. Influences of laser welding parameters on the macroscopic geometry, porosity, microstructure and mechanical properties of the stitch welded seams were investigated by digital microscope, optical microscope, scanning electron microscope and universal tensile testing machine. The results showed that the three-pipe nozzle with gas flow rate larger than 5 L/min could avoid oxidization, presenting better shielding effect in comparison with the single-pipe nozzle. Porosity formation could be suppressed with the gap between plate and skeleton less than 0.1 mm, while the existing porosity can be reduced with remelting. The maximum shear strength of stitch welding joint with minimal porosity was obtained by employing laser power of 1700 W, welding speed of 1.5 m/min and defocusing distance of +8 mm.

The work addresses microstructure–property relationships of hot-rolled complex phase steel sheets subjected to various conditions of dual beam laser welding. The article also contains a comparison between single-spot and twin-spot laser welding. Test-related joints were made using a Yb:YAG disc laser having a maximum power of 12 kW and a welding head enabling the focusing of a laser beam on two spots. The tests involved investigating the effect of power distribution on the macrostructure, microstructure and mechanical properties of joints. Microscopic investigations revealed the stabilisation of some fraction of retained austenite in the intercritical heat affected zone (ICHAZ) of joints. The application of the second beam resulted in tempering-like effects in the martensite of the fusion zone and in the HAZ, favourably reducing the hardness of the joint. The use of bifocal welding enabled the obtainment of a 10% hardness reduction in the fusion zone as against single-spot laser beam welding.

激光堆焊可以获得高耐磨性、高耐腐蚀性等优异性能的合金堆焊层，在冶金、机车、船舶等领域展现了诱人的应用前景。与埋弧焊、电渣焊、等离子焊等传统堆焊工艺相比，激光堆焊具有组织较细、堆焊层厚度较大、热变形较小，以及堆焊层与基体呈冶金结合、堆焊层成分及稀释率可控、易实现选区堆焊和工艺自动化等优势。本文对激光堆焊的基本原理及其工业应用几个方面做了简单介绍；阐述了激光加工过程中裂纹、气孔产生的主要原因；为了解决激光加工产生的裂纹、气孔等缺陷，本文对激光与电场、磁场、超声振动场的复合协同发展趋势做了分析预测。在此基础上，本文从裂纹、气孔缺陷的抑制以及避免马氏体组织出现等方面探讨了机车车轮、铁轨激光堆焊修复的可行性及可能面临的挑战，为机车轮芯、轮毂等机车零部件的激光修复工业化应用提供参考。 High hard-wearing, high corrosion resistant and other excellent beam welding alloyed coating can be achieved by laser beam welding, which demonstrates promising applications in the fields of metallurgy, locomotive and boats, etc. Compared with the traditional beam welding technologies, laser beam welding exhibits finer microstructures, thicker welded coating and smaller thermal deformation advantages, as well as good metallurgical bonding between welded coating and substrate, controllable component and dilution of welded coating, selective area welding and automation technology characters. The basic mechanism and technological application of laser beam welding were introduced in this paper, in which the main reasons of crack and porosity of laser processing were clarified. In order to solve the crack and porosity problems of laser processing, the compounded cooperation development trend of laser with electric field, magnetic field and ultrasonic field was analyzed and predicted. Moreover, the possibility and challenge of beam welded repairing for locomotive wheel and rail were analyzed, based on the crack and porosity avoidance and martensite microstructure control, which will provide new ideas for the industrial application of laser repairing of wheel center, wheel flange and other locomotive parts.

As it is known, titanium alloys due to a number of features (high specific strength, fatigue resistance, fracture toughness and corrosion resistance) are widely used in aerospace engineering, including ribbed panels. For products of this kind it is necessary to meet high requirements of quality of welded joints and dimensional accuracy of the construction. Fusion welding of titanium alloys results in the formation of inhomogeneities in the connection zone and in the reduction of technological and operational performance. The geometric dimensions of design are distorted due to occurrence of welding stresses, pores and microcracks appear in the weld metal, mechanical properties and other parameters are reduced. These facts require a comprehensive analysis of the manufacturing process of titanium ribbed panels: from the manufacturing of semi-finished products to the final stage of heat treatment of the finished product from the point of detection of the most significant in relation to defects in operations. The blank manufacturing operations, including their preparation for welding, welding and subsequent heat treatment regimes affect the cyclic and static strength of welded ribbed titanium panels depending on the number and total area of welding defects. The article presents the research that allows to predict the properties and reliability of welded structures and to achieve identity of the properties of basic metal and weld metal with the lack of a guarantee of both internal and external defects, depending on the choice of the complex technological measures. It is shown that a certain welding cooling rate in the range of phase transformation temperatures, finish milling, running and cleaning (degreasing and dehydration) of the surface of abutting edges, low annealing after welding in the air and subsequent sand cleaning; GLC in the auxiliary gas medium of nitrogen or argon or the combined GLC blanks and cutting by milling determine correspondence of properties and reliability of the welded joints of base metal of ribbed panels from VT20 alloy.

Low alloy steel and 304 LN austenitic stainless steel pipes were welded together by gas tungsten arc and narrow gap welding. The aim of investigation was to identify particular welding technique, which may able to deliver better joint quality over the other considering mechanical properties of assemblies. Welding consumable was IN82 for both of them. Multilayered buttering was done over low alloy steel prior to welding for conventional GTAW. Microstructural characterisation was done and tensile strength was determined through in-situ deformation of miniature samples for welded joints. Low alloy steel consisted of heat affected zone close to interface. Near fusion boundary between low alloy steel and IN82, islands of martensite, complex alloy carbides, Types-I and II boundaries were formed. Width of heat affected zone and martensite layer was more for conventional welding in comparison to narrow gap welding. During in-situ tensile testing crack was initiated from stress concentration site and propagated through IN82. Joint strength and strain hardening co-efficient for narrow gap welded specimen was higher than conventional welded sample. This indicated better formability of narrow gap welded assembly with respect to gas tungsten arc welded specimen.

The resistance welding technique for thermoplastic composites (TPCs) entails melting the TPC polymer at the joint interface using heat generated by resistive (Joule) heating of a conductive mesh or heating element placed between the surfaces to be welded. The continuous resistance welding (CRW) is an automated large-scale resistance welding technique that consists of a moving voltage source along the heating element creating a continuous weld along its path. This paper presents a transient model that is developed to predict the heat transfer in TPCs in all three dimensions during the CRW process. The model is finite element in nature and includes both the resistive and thermal conductivity behaviors of the material involved. The significance of this modeling approach is that it captures the movement of the electrical connection, as well as the nonuniform distribution of the current and resistive heating along the length and width of the weld seam. The modeling results are compared with experimental data obtained by thermocouples and an infrared camera, and exhibit solid conformance for predicting the trend of variations in weld temperature.

Nowadays, the railways in the Russian Federation are moving to the path of seamless construction. The development of technologies to ensure the possibility of continuous welded rail track with the desired quality characteristics is the actual direction now. One of the key technologies for the construction, repair and maintenance of a seamless path is welding of rails, for which various methods have been developed and are used, such as: electric-contact, gas-press, induction, laser welding, friction welding, aluminothermic, electric arc electrodes, in the environment of protective gases, electroslag, powder wires, etc. The article describes the advantages and disadvantages of the main types of welding rails that are most widespread today: resistance flash welding and aluminothermic welding. It is shown that as the primary method of rails welding in Russia, electric-contact welding is used. However, in connection with the inability to weld rails in the zones of turnouts by contact machines, the use of aluminothermic welding of rails started on the railways of Russia. It has been shown that the most important factors that determine the quality and reliability of welded rails are metallurgical and welding technologies, as well as subsequent processing methods that reduce the impact of high temperature effects. The technological features of these methods, advantages and disadvantages of modern methods of solving problems in welding, as well as economic costs were considered taking into account operational properties of joints. Experience has shown that during the exploitation of welded joints made by aluminothermic method on the railway and at testing on the experimental ring of JSC All-Russian Scientific Research Institute of Railway Transport, their quality is slightly inferior of electric-contact welding. Special attention is paid to the peculiarities of welding technology for differentially thermally strengthened rails. The analysis of existing methods of rails welding allows working out the main directions of research to solve this problem.

High Pressure Torsion (HPT) is historically the first and is currently most common process of the severe plastic deformation (SPD). HPT is used for producing nanocrystalline structures in metals and alloys, as well as for cold welding of powders. The result of the HPT treatment is determined by the flow kinematics and the stress state of a material under deformation. P. Bridgman proposed a simple model for the initial assessment of shear strain in the sample during HPT. A number of recent investigations show that the true plastic flow during HPT can differ significantly from the simple model. We present in our report results of the FEM investigation of different types of flow during HPT. We propose a hypothesis that the vortex formation during the SPD process is caused by the local blocking of simple shear in a material under deformation.

Friction-stir welding (FSW) is a solid-state joining process (meaning the metal is not melted during the process) and is used for applications where the original metal characteristics must remain unchanged as far as possible. This process is primarily used on aluminium and most often on large pieces which cannot be easily heat treated post weld to recover temper characteristics. The rotating tool “stirs” the material, softened by the frictional heat generated, and consolidates the stirred material behind the tool. This process has several advantages when compared to conventional fusion welding process. The present paper introduces the welding process and the welding of metal matrix composites. The welding was carried out on a CNC milling machine that was adopted for this work. Under Experimental condition of the study, mechanical strength, maximum temperature between the edge of the stir zone and the top surface, and effect of force against the tools are investigated. The micro hardness was also found to slightly increase with increased feed rate of the tool.

Metal transfer process in underwater flux-cored welding are investigated by X-ray transmission method for welding velocity from 0.5 mm/s to 9.5 mm/s. The metal transfer mode of underwater flux-cored wire welding is the mixed transfer mode mainly composed of four fundamental transfer modes i.e. wide-angle globular repelled transfer mode, small-angle globular repelled transfer mode, surface tension transfer mode and short-circuit transfer mode. The category and proportion of fundamental modes constituting the mixed mode depend strongly on the welding velocity owing to the variation of force condition on droplet. With increasing welding velocity, the proportion of the wide-angle globular repelled transfer mode increases continually while that of the surface tension transfer mode and short-circuit transfer mode decreases, and the proportion of the small-angle globular repelled transfer increases firstly and then decreases gradually. The welding appearance and cross-sectional macrostructure of weld specimens at different welding velocities are also investigated. When the welding velocity increases from 0.5 mm/s to 3.5 mm/s, the weld width decreases from 20 mm to 12 mm and the weld penetration increases rapidly from 0.8 mm to 3.7 mm, completely different from in-air welding.

A tungsten inert gas (TIG)-cold metal transfer (CMT) hybrid welding process is proposed. Compared with the conventional TIG-metal inert gas/metal active gas (MIG/MAG) hybrid welding method, the characteristic of TIG-CMT welding process is that there is no interaction between the two arcs. The addition of TIG can improve the wettability of molten metal. The microstructure in hybrid joint is coarser than that in conventional CMT joint, and the microhardness in weld metal (WM) of hybrid joint is higher than that of conventional CMT joint. In TIG-CMT hybrid welding process, the TIG current plays an important role in changing contact angle and the dilution of weld bead. Fine equiaxed grains have been observed in partially melted zone (PMZ) and coarsened equiaxed grains exist in heat-affected zone (HAZ). The width of PMZ increases with the increase of heat input. More heat input can also lead to the coarser columnar dendrite. In all weld joints, the microhardness in HAZ remains at a low level, and the microhardness in PMZ always has a sharp decrease from WM to HAZ. The outcome of this work shows that the TIG-CMT hybrid process is suitable for the multi-passes welding of aluminum alloy.

The synthesis of composite nanowires has recently emerged to be an important topic in the field of low-dimension nanostructures, and molecular dynamics (MD) simulation proves an effective way to figure out their mechanical properties and is thus adopted to explore the cold welding process of gold nanowires with single-crystalline, fivefold twinned and particularly polycrystalline structure. Four samples of nanowires were successfully welded through limited loadings with similar stress-time responses toward cold welding. The stress shows a low average value during welding with oscillations, indicating the existence of relaxation stages. Herein, the number of defects in the welded nanowires could be controlled by varying the loading time. These findings are expected to open an avenue towards the use of cold welding technology, including welding between materials with various properties, for the bottom-up nanofabrication and nanoassembly techniques without introducing defects.

In a current laser welding production process of components of stainless steel, a butt joint configuration may lead to failures in the form of blowouts, causing an unacceptable welding quality. A study to improve the laser welding process was performed with the aim of solving the problem by designing a suitable pattern of multiple small laser spots rather than a single spot in the process zone. The blowouts in the process are provoked by introducing small amounts of zinc powder in the butt joint. When the laser heats up the zinc, this rapidly evaporates and expands, leaving the melt pool to be blown away locally. Multiple spot pattern designs are tested. Spot patterns are produced by applying diffractive optics to a beam from a single mode fiber laser. Results from welding while applying spot patterns both with and without trailing spots are presented. Data showing the power ratio between a trailing spot and two main spots as a function of spot distance is also presented. The results of the study show that applying multiple spots in the welding process may improve the process stability when welding materials with small impurities in the form of zinc particles.

This study finds the comparison of AA 5083-T4 properties on Tungsten Inert Gas welding (TIGW) and Friction Stir Welding (FSW) processes. Generally all welding processes are aimed at obtaining welded joint with the desired weld-bead parameters, superior mechanical properties with minimum distortion. Welding input parameters play a very significant role in determining quality of weld. The weld quality can be determined in the terms of properties such as weld bead geometry, mechanical properties and distortion. The potential of FSW and TIGW for joining similar metal has been evaluated and compared. Different joint configurations from TIGW and welding speeds/feeds of FSW were used to study the effect of welding parameters on weld quality and properties

In aluminum welding, the grain structure of produced seams is an essential factor with respect to the seam properties. In the casting technology the effect of mechanical vibrations on the grain growth during the solidification of liquid metals is known as a refinement method. In this paper, the transferability of this approach from comparatively long-time processes in the field of casting to the short-time process of laser deep penetration welding is investigated. Therefore, specimens were sinusoidal vibrated with frequencies up to 4 kHz during bead-on-plate full-penetration welding experiments. The resulting grain size was determined by applying the circular intercept procedure on the center of a cross-section micrograph of each weld. The results show that grain refinement is in general achievable by mechanical vibrations in the audible frequency range during laser full penetration keyhole welding of the aluminum alloy EN AW-5083.

An improved method for calculating the minimum permissible electron beam welding (EBW) speed with continuous penetration is described. Calculations are carried out to construct nomograms for determ...

The aim of the work was to produce laminated structures consisting of Ti–6Al–4V alloy and AA2519 plates and to investigate their microstructure and mechanical properties with an emphasis on the role of an additional AA1050 interlayer. Explosive welding was selected as a joining technology. The microstructure and chemical composition of the explosively joined samples were investigated. Mechanical properties were evaluated in the tensile testing and by microhardness analysis.The results demonstrated that explosive welding is an effective way to produce Ti/Al laminates. Both Ti6Al4V/AA2519 and Ti6Al4V/AA1050/AA2519 laminated plates exhibit good quality of bonding without voids and major delamination. The explosive welding produced metallurgical bonding with a nanostructured zone consisting of Al3Ti and Al2Ti phases. This zone is thicker in the joint with additional AA1050 interlayer when compared to direct AA2519/Ti6Al4V bonding. In the latter, SEM and STEM analysis reviled the presence of net-like structure in the collision zone. Advanced EDX analysis shows the enrichment of grain boundaries in copper. The formation of this structure is widely discussed. In addition, the explosive welding introduces large plastic deformation which induces the process of grain refinement in aluminium plates. Tensile testing confirms that joining section is not the weakest element of the cladded plates. Keywords: Explosive welding, Interface, Aluminium alloys, Ti6Al4V, Microstructure, Chemical analysis

Large scale integration of 2D crystals and metal nanowires (NWs) with low junction resistance has been a long time challenge for functional structures. Herein, roll to roll printing technique was utilized to directly produce graphene oxide (GO) nanoplatelets stack laminated with metal NWs. This 2D/1D laminated structure activates high pressure between AgNWs, enables localized fusion, and opens a new way to tackle with local nanojunction resistance. Molecular dynamic simulations reveal that this cold nanojoining originates from high localized pressure activated isolated metal atoms, which possess high mobility, flow over nanojunction and recrystallize to form nanojoints. Compared with bare AgNWs network, the GO laminated counterparts achieve excellent performance ( 17 Ω / sq , 93 % @ λ = 550 nm ), which enlightens optoelectronics applications. The cross nanowire junction resistance decrease is verified by classical percolation theory and experimental characterizations. Haze measurements show that the scattering is significantly reduced. Laminated structure has been engineered layer by layer to accomplish quasi-3D hybrid film, which demonstrated application in flexible supercapacitors with high specific capacitance of 109 F g −1 . This hybrid 2D/1D nanomaterial thin film also demonstrated excellent stability during cyclic foldability, stretchability, high temperature and oxidation tests. These investigations provide insight for layered manufacturing of 2D crystals/1D NWs structure and quasi-3D hybrid film for energy storage applications.

The work addresses modified methods of twin-spot laser welding of complex phase steel sheets and investigates the effects of laser beam distribution on the macrostructure, microstructure and hardness. The research-related results were obtained for the beam power distributions of 50%-50%, 60%-40% and 70%-30%. Test joints were made using a Yb:YAG disc laser with a maximum power of 12 kW and a welding head by means of which it was possible to focus a laser beam on two spots. It was found that the change in the laser beam distribution affects geometrical features of the joint. The application of the second beam of lower power enables obtaining tempering-like effects, which finally lead to the beneficial hardness reduction both in the fusion zone and in heat-affected zone. The identification of various microstructural constituents in different zones of the joint was performed using light microscopic micrographs and scanning electron images.

Based on the laser-driven flyer micro forming and laser high-speed impact welding, this paper put forward the laser high-speed impact synchronous welding and forming new process, and builds the compound welding experiment platform. The three-dimensional deep field digital microscope of KEYENCE VHX-1000C was used to measure the surface morphology and the maximum deformation depth of the welding and formingsamples. By observing the surface morphology of the sample, it was found that strong plastic deformation occurred on the surface of the materials and well reproduced the shape of the mold. When the laser energy was below 4.5J, the maximum deformation depth of the samples increased with the laser energy. However, the maximum deformation depth decreased due to the spring back phenomenon when the laser energy was larger than 4.5J. The Axio CSM 700 confocal microscope was used to measure the morphology of the welding interface. The cross profile of the welding interface showed that most regions had been welded and the welding interface was nearly flat.

The metallization of alumina samples was performed using ultrasonically assisted shot impact equipment. The alumina plate was pre-coated with a mixture of Cu-Ni-W powders and was then shot treated. The treatment resulted in the formation of a composite Cu-Ni-W layer that was cold welded to the alumina plate. The coating exhibited a nanolaminated composite structure consisting of various combinations of elemental lamellae in the stack. A nanolaminated morphology formed during the micro-forging process of the powder materials under localized compressive forces induced via shot collisions. During this process, the adjoining metallic components were flattened and shaped together. Cold welding between the metallic components occurred when different components co-deformed and moved in parallel layers. Cold welding of the metallic components was assisted by mechanically induced interdiffusion. Amorphous interdiffusion zones were observed at the Cu/W interface. The formation of transition layers and local amorphization of the alumina plate were detected at the metal/alumina interface. The alumina substrate was locally fractured under shot impact. When the metallic materials flowed, the ceramics fragments were transported over the surface along with plasticized metallic components. The alumina particles were spaced along the interlamellar regions.

The results of mechanical and other types of tests of metal of welded joints in pipe blanks of 15Kh5M martensitic steel, produced by friction welding with rotation, are presented. On the basis of the analysis of the test results it is concluded that 15Kh5M can be efficiently welded by friction welding and that the method can also be used for producing the tube–tube plate sections of heat exchangers made of 15Kh5M steel with appropriate modernization of welding equipment.

Investigations were carried out into the quality of welded joints in submerged-arc welding and also the problems of consumption of electrode material at higher currents. Methods for improving the quality of permanent joints when using tungsten electrodes are outlined.

Due to continually rising fire-safety standards, the use of plastics containing flame-retardant additives has increased strongly in recent years and is continuing to increase. The flame-retardant reaction of these materials prevents flames and the associated thermal energy from using the polymer as a source of flammable material, thus suppressing and slowing the spread of the flames. This, however, works (so to speak) against the energy needed to melt the polymer, which in turn can cause a reduction in weld strength. In this study, the behavior of flame-retardant plastics is examined for the four standard welding processes hot plate welding, vibration welding, ultrasonic welding, and laser welding. During the experiments, both a halogen and a nitric flame retardant are investigated in Polyamide 6.6, Polyamide 6, and polybutylene terephthalate, and their effect on weld strength was determined. It transpired that the activation of the flame retardant and the directly related loss of weld strength in the joint depend considerably on the welding process and its parameters. For hot plate welding, the temperature of the heated tool as well as the heating time is of considerable significance for the joint quality. Reaching a temperature above the activation temperature of the flame retardant resulted in notable reductions in weld strength, caused by the activated additive. These weld strength reductions can be to some extent held in check by suitable process parameters; in this case, there are boundary levels of activation which must not be exceeded, in order to ensure a sufficiently high joint strength. This behavior varies, however, from that shown in ultrasonic welding. Here, no activation of the flame retardant was observed, meaning that the flame-retardant additive acts only as a filler material on the joint strength. For vibration welding, there is an observable effect resulting from concentrations of flame retardant; this effect can be partially or entirely neutralized by a suitably high joining pressure, which pushes the concentrated areas into the welding bead and thus reduces or eliminates the damage to the weld itself. Laser welding leads to a high degree of activation in the flame retardant and therefore results in a significant drop in joint strength. To briefly summarize, it can be said that welding processes with external heat sources are to be more critically evaluated than processes with internal energy generation when welding flame-retardant polymers.