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Contact dynamic welding failure problems seriously limit the electrical lifetime of electromechanical relay. However, the welding behavior occurred in contact making and breaking process and relevant influencing factors are still unknown. In this article, a series of experiments are carried out in make only, break only, and make & break (M&B) operation modes individually to differentiate the effects of making and breaking processes on contact dynamic welding. The typical dynamic force and electrical waveforms of contact making and breaking processes are obtained and the statistical results of welding force are presented. The roles of bounce arc and molten bridge in welding force are interpreted explicitly by using the variations in electrical parameters such as bounce energy, contact resistance, molten bridge energy, break arc energy, and surface substructure morphologies. It is determined that the bounce arc plays a crucial role in the formation of weld nugget and strength, and the strongest welding occurs in the M&B operation mode.

Thin, sensitive skin electronics The properties of the human sense of touch, including high sensitivity to differences in temperature, pressure, or surface roughness, are challenging to replicate in robotics because skin materials must be highly conductive, stretchable, and thin. Jung et al . developed a process to assemble nanomaterials as a monolayer that is partially embedded in an ultrathin elastomer. The process works by depositing a mixed solvent containing nanostructured silver and/or gold, along with elastomer, onto deionized water. This results in a layer of nanoparticles residing at the interface coating with elastomer, which is further densified by the addition of surfactant. The process is scalable, and the resulting elastomer membranes can be transferred to other substrates. —MSL

Glass-forming ability is a long-standing concern in the field of metallic glasses (MGs), which greatly limits their maximum casting size and extensive applications. In this work, we report an ultrasonic-assisted rapid cold welding of bulk MGs without using any additives. MGs with various compositions are welded together under a 20,000-Hz high-frequency ultrasonic vibration without losing their amorphous nature. The ultrasonic technology offers the advantages of rapid bonding (< 1 s) at low temperature (near room temperature) and low stress (< 1 MPa). According to the phenomenon observed in the experiment, the activated fresh atoms diffuse through the broken channel port under continuous rupture of the oxide layer, and the ultrasonic vibration accelerates the atomic-diffusion process. Finally, stable bonding of the MG interface is realized. This universal ultrasonic-assisted welding process can realize the composition design of dissimilar MGs as well as tuning of new materials with new performance.

Cold welding technique at room temperature is the preferred option in nano-assembly and nano-jointing. In this study, the cold welding behavior and mechanical strength of Cu50Zr50 metallic glass nanowires (MGNWs) in head-to-head contact are investigated by molecular dynamics simulation based on the embedded atom method potential. Effects of welding velocity, operating temperature, and size of nanowires are discussed with the consideration of stress, shear strain, atomic deformation processes, and weld quality. Our simulation results demonstrate that a desirable weld quality can be obtained at room temperature. With an increase in welding velocity, the shear deformation zones of the welded MGNWs increase, leading to a decrease in mechanical strength. However, the effect of temperature on the weld quality is not pronounced. Besides, the elongation ability of the welded MGNWs increases with increasing diameters of nanowires. Smaller diameter results in better weld quality due to the size effect of metallic glass. For a pair of MGNWs with different diameters, the necking and fracture of the welded MGNWs occur in the regions of the nanowire with a relatively smaller diameter. This study carries major implications for the fabrication and structural assembly of metallic glass-based nanomaterials.

Characteristics of organosilicon sealant of VGO-1 brand, which is employed in the preparation of glue-welded joints through contact welding are considered. Preparation conditions of glue-welded joints are given and it is determined that there is a decrease in the magnitude of welding current and an increase in the time of welding and electrode contact pressure upon welding of steel specimens of 08kp brand by the VGO-1 sealant. Structural studies of the sealant after exposure at various temperatures show that the sealant possesses high frost resistance at –30°C in the air and a satisfactory frost resistance at –50°C in the liquid. The swelling degree of the sealant after 20 days of exposure in medical ethyl alcohol is less than 4.5%.

The results of tests aimed at estimating the microhardness of a cast nugget and the heat-affected zone are provided. It is established that dot welding along a layer of glue is attended by nonlinear changes in microhardness along the diameter of the cast nugget. In glueless contact welding, the microhardness level along the entire cast nugget is higher than with the application of glue. The greatest reduction in microhardness is observed in the middle of the cast nugget and reaches 15%. The procedure of applying similarity criteria in estimating adhesive and weldbonded joints for microhardness is exposed. The similarity coefficient values are determined, and it is shown that they are effective for use in trying out production procedures in case of replacing welding modes or used material, for example, with a different glue compound.

The features of the welded joint formation of palladium foil with stainless steel by using nickel foil as an intermediate layer at resistance welding are considered. It is shown that through the ch...

Using lighter materials like Aluminium(Al) is also a common practice for producing prosthetic devices. This method not only provides less weight but also gives freedom to the designer to design customized devices. But Al can not be used in its pure form as it lacks strength, toughness, rigidity. A common way to overcome these issues is the use of composite materials. In this paper, we have studied how mechanical milling can be used to disperse hard ceramic particles and Carbon nanotube homogenously in Al matrix. We have also demonstrated how changes in different process parameters affect the properties of this composite and how a uniform dispersion can be achieved by the use of the specialized technique. In this paper, we have also suggested methods to avoid clustering and cold welding of reinforcements.

The purpose of this work is to develop a methodology for determination of the total level of multifrequency magnetic field (MF) at the working area of welder by studying the dependences of the magnetizing force of its individual harmonic components to the electrical characteristics of the MF source and welding modes. The study was carried out at a wide frequency range of the MF action for the researching of dependences to MF technological parameters of the contact welding machine and the distance to it. An induction magnetic field sensor and a digital recording oscilloscope with a fast Fourier transform function were used for experimental studies of MF magnetizing force and their spectral ranges. Based on the analysis of the obtained MF oscillograms and spectrograms, the shape and magnitude of the MF magnetizing force signals in different frequency ranges were established. Since it is impossible to quantify the overall level for a multifrequency MF with taking into account all the harmonic components of the MF simultaneously, the generalized magnetic field level indicator (MFI) was proposed, which became the basis for its use as a methodology for the assessment of MF impact on human body. The use of the proposed methodology allowed to establish that it is generated MF with harmonic components in the frequency ranges 5-50 and 50-1000 Hz at working area under contact spot welding, which may exceed their maximum allowed levels, leading to the respective increase of MFI level. It was established that any changes in the mode of contact spot welding, compared to the mode of welding with one batch of full-phase pulses of welding current, lead to the increase in MFI with exceeding of maximum allowed level at a distance of 800-1000 mm from the axis of contact welding machine electrodes; modelling of the front and trailing edges of the pulse lead to the reduction of MFI level, while increasing the angle of phase control of the heating mode leads to the increase of MFI level. The proposed methodology can be applied as universal both for hygienic assessment of the electromagnetic environment during arc welding and for other electrical equipment. The developed methodology gives possibility to assess the overall impact of multifrequency MF on human body. It is based on the known laws of electrodynamics using a new generalized indicator - magnetic field level indicator MFI.

Modularity in total hip arthroplasty allows a surgeon to have intraoperative versatility, allowing for fine adjustments of the femoral offset, leg length, and version. However, modularity can be a source of multiple complications. This case report describes a novel intraoperative solution for the problem of cold welding of a neck-stem junction using sterile ice to cryogenically disengage the modular components.

Problem of generation of local hardened areas in weld metal d ing rails welding in production of continuous welded rails is solved by using local heat treatment of weld joint. As a result, appearance of quenching structures is excluded. However, new zones of thermal influence with reduced hardness may appear. During operation, such rails are characterized by increased wear of the rolling surface in these areas and collapse of the head at welded joint. It is the main reason for removing rails from the track earlier than time guaranteed. Application of new technology based on dependences of dispersion degree of the structural components (primarily perlite and carbide particles formed during obtaining welded butt joints of rails) on steel composition and rails cooling conditions is proposed. Cooling rate has a decisive influence on the degree of dispersion of ferritic-cementite structure formed during decomposition of austenite. When welding rails in a butt weld, generation of granular perlite is possible in the areas with temperature between Ac 1 and Ac m points. To determine these critical temperatures, thermodynamic calculations were performed using Thermo-Calc ® software (TCFE database) taking into account chemical composition of the samples obtained by spectrometry. Fe – C state diagrams for 76KhSF rail steel were modeled with the minimum and maximum content of alloying elements according to the state standard GOST R 51685 – 2013. To obtain minimal volume of sections with reduced hardness, it is possible to conduct rails welding in hard conditions by electrocontact method using pulsating reflowing. To prevent formation of defective sections with quenching structure, it is possible to control cooling of welded joint using contact heating. Measurement of the temperature distribution during welding according to the given modes and controlled cooling confirms theoretical conclusions.

The dislocation model of welding joint formation during the process of cold welding is proposed. The relations were obtained and the estimated grade of tendency of a number of metals to cold welding was performed on the grounds of the hypothesis of active centers limiting sizes. Relations for the estimated grade of the required for cold welding plastic deformation are obtained.

The features of the formation of microconnections in electronic modules on an aluminum-polyimide basis by the method of ultrasonic welding, which allows to obtain reliable mounting joints of different thickness aluminum without preliminary removal of oxide films where the use of contact welding and soldering are practically difficult or impossible, are investigated. The influence of technological modes (power of an ultrasonic generator, oscillation amplitude of a welding tip (tool), welding force and welding time) on the reliability of mounting microconnections is considered

In order to analyze the making arc characteristics of AgSnO2 contact, experiments were carried out with a self-developed experimental equipment. It was found that contact resistance had no obvious change with the increase of the number of experiments.In the later stage of the experiment, the contact bounces occurred during the contact closing process, which not only prolonged the making arc duration, but also increased making arc energy. When the contact was eroded to a certain extent by arc, making welding occurs.

Cu–(20 wt %)Cr alloys with a layered structure are synthesized by liquid phase impregnation of chromium powder with copper melt. In synthesizing the alloys, the corresponding composites are subjected to pre-crystallization vibrational treatment. The layers of composites are enriched in chromium to different extents (from ~2 to 90 vol %). The layer composition and structure are shown to depend on the temperature and duration of vibrational treatment, as well as on the degree of pre-synthesis compaction of chromium powder. We study the phase composition of prepared alloys, the element composition of phases, and their microhardness. Our experiments show for the first time the formation of Cr core–(Cr + Cu) shell structures on the basis of chromium particles. These structures have a gradient distribution of the elements in the shell and form at the initial stages of interaction between Cu and Cr. At advanced stages of interaction, chromium particles are permeated with copper completely. In electron microscopy images in backscattered electrons, these formations appear as being greatly blurred and shapeless. In this way, precursors to crystallization of chromium dendrites are formed. The dendrite crystallization takes place in upper layers of the melt provided copper is present at the necessary and sufficient concentration (or at considerable superheating). The morphology of dendrites in which crystallization from precursors was incomplete is studied. The contact area of α-Cu is anticipated to be greatly reduced by the precursors that spread in the copper matrix during arcing. At the same time, contact welding will be considerably reduced, compared to similar composites with purely copper matrices (e.g., Cu–W).

Algorithms for current stabilization in the control of contact welding are considered. The proposed method for specifying and maintaining the welding current permits correction of the thyristor firing angle by means of an approximate formula taking account of the measured current-pulse parameters in phase regulation. The proposed method simplifies the equipment and increases the efficiency of regulation.

Compared with other metal materials, the welding performance of lightweight materials is obviously lower, which seriously hinders the industrial application of such materials. In order to improve the welding effect of lightweight materials, the overall design scheme of cold welding power source (low energy input gas metal arc welding inverter power source) was designed. The proposed scheme adopts a bipolar soft switch control system on the of voltage and current waveforms for the hardware, to effectively reduce the switching energy consumption. Besides, A welding expert system is designed for the software. The expert system adopts a Newton interpolation welding parameter self-adjusting algorithm to realize fine adjustment of output control, which can not only eliminate splash factors, but also significantly reduce arc energy consumption. The Welding experiment results show that the welding process is stable and the weld joint is well formed. That’s to say, the cold welding power source based on the expert system is effective in welding lightweight materials, such as aluminum and magnesium sheets.

The contact welding failure of general-purposed relay closely relates to alternating current (AC) arc erosion. In this paper, AC arc behavior is investigated by a general-purpose relay firstly. The typical waveforms of arc voltage and current during contact making and breaking are presented, then the effects of point-on-wave (POW) at break on arc energy is analyzed explicitly. Based on the degradation processes of contact opening time and making heat occurred in the electrical endurance experiment, the possible physical mechanism of contact welding failure for general-purposed relay is proposed.

For long-serviced pressure equipment that is under severe working conditions such as a high temperature, high pressure, and corrosion, the material properties and structure will be unavoidably damaged or degraded, especially cracks and other damages at key positions such as welded joints, which seriously threaten the safe operation of the equipment. In order to promote the sustainable development of industries such as the chemical and petrochemical industries, remanufacturing technology has emerged worldwide, and various surface repair processes have also rapidly developed. As an important branch of surface repair technology, the high energy spark deposition (HESD) process is a new pulse cold welding repair technology developed from electro-spark deposition, which combines the advantages of multiple surface repair processes. The HESD process has the characteristics of a smaller heat affected zone and lower welding residual stress. It is a new type of repair method that is worthy of popularization and application. The process has been initially applied in the fields of surface modification and die steel repair. In this paper, the application of the HESD process to the repair of welded joints was introduced, the mechanical properties of the joints and the residual stress distribution after welding were analyzed, and the feasibility of HESD as a repair welding method for pressure structures was discussed. First, a numerical simulation of the temperature and stress field of HESD was proposed by using ABAQUS and the related subprograms, and the validity of the simulation results was verified by the residual stress test with the indentation strain method. Due to the precise control of the heat and pulse discharge working mode, the heat-affected zone and deformation caused by the HESD were extremely small, and the residual stress that was generated was low and only concentrated on the repair welding seam. Second, according to the numerical simulation and the test results of the mechanical properties of the welded joint, the optimal repair welding process parameters were obtained through the orthogonal experiment: peak current 45 A, pulse width 90 ms, and output voltage 10 V.

Li-Sn alloys are of considerable interest in the design of plasma facing systems for nuclear fusion reactors. This letter reports the production of Li-Sn alloys by mechanical alloying, followed by cold pressing. Li atomic concentrations below 25 at.% were studied. Powder morphology during milling evolves from cold welded, rugose powders, to spherical or faceted smoother powders, and finally to thin large discs. Cold-welding and alloying are the predominant mechanisms observed up to 24 h milling. An out of equilibrium distribution of LixSny intermetallic particles with sub-micrometric size forms. Milled powders could be formed into pellets by cold pressing due to its ductility and cold welding behaviour. Contamination free Li-Sn alloys, with 5, 15 and 25 at.% Li, were successfully produced by this method. The main phases identified are β-Sn, Li2Sn5 and LiSn. Phase composition evolves with annealing, with LiSn decrease and Li2Sn5 increase.

In order to clarify the contact welding failure mechanism of DC electromagnetic relay, a series of electrical endurance tests are carried out with the use of silver tin oxide material under resistive and capacitive load conditions. The typical waveforms of contact voltage and contact current during making and breaking resistive load and capacitive load (load capacitance of 1mF, 1.5mF, 2mF and 2.5mF) are obtained by the designed model switch. Further, the variations of sensitive electrical parameters such as bounce energy, contact resistance, static contact force and break arc energy during electrical endurance test are analyzed explicitly. It is found that the variations in sensitive electrical parameters is closely related to the electrical load type. In particular, under the capacitive load conditions, the sharp increase of each sensitive electrical parameter in the end of lifetime prognosticates the dynamic welding failure of silver tin oxide contact material. Finally, with the help of SEM (Scanning Electron Microscope) pictures of failed contacts, the surface erosion features of contact materials are mainly determined by the competition between the cathode arc and the anode arc. And the material transfer and distribution are the root reason for the contact welding failure of DC electromechanical relays.

Flame spraying was applied to prepare aluminum (Al)-reduced graphene oxide (rGO) composite coatings for the first time using ball-milled composite powders. The microstructure, tribological and electrochemical properties of the rGO-Al composite powders and coatings were investigated. Microstructural characterization for the composite powders reveals that rGO nanosheets adhered to Al particle surfaces after milling. Flattening and cold welding phenomena of Al particles were also recognized. The structure evolution of rGO as a function of the time of ball milling was also revealed. The results of coating microstructure investigation show that the rGO nanosheets were uniformly distributed in the coatings after coating deposition. The result of ball-on-disk testing shows that the addition of 0.3 wt.% rGO in the composite coatings brought about significantly enhanced lubricant performance. We believe that the results gained in this research would give insight into producing novel rGO-metal anti-friction materials.

The effects of contact interference, crystal orientation, and material type on the cold nanowelding mechanism and mechanics are studied using quasi-continuum simulations. These effects are investigated in terms of atomic trajectories, strain distribution, and the stress–strain curve. The simulation results show that welding using a contact interference of 0 nm leads to the formation of the fewest defects inside the material during cold welding, and that the number of defects increases with increasing contact interference. For the Ni–Ni welding pair, welding using a contact interference of 0 nm with the structural orientation [110] versus [001] has the largest ultimate strength and longest elongation during tensile testing due to the formation of fewer defects during welding. The welding quality obtained with the Ni–Ni welding pair is higher than that obtained with Ni–Cu and Cu–Cu welding pairs. During the tensile deformation process, dislocations nucleate from the free surface, propagate along the close-packed plane, and then terminate at the other free surface.

Carbon nanomaterials are desirable candidates for lightweight, highly conductive, and corrosion-resistant current collectors. However, a key obstacle is their weak interconnection between adjacent nanostructures, which renders orders of magnitude lower electrical conductivity and mechanical strength in the bulk assemblies. Here we report an "epitaxial welding" strategy to engineer carbon nanotubes (CNTs) into highly crystalline and interconnected structures. Solution-based polyacrylonitrile was conformally coated on CNTs as "nanoglue" to physically join CNTs into a network, followed by a rapid high-temperature annealing (2800 K, overall ∼30 min) to graphitize the polymer coating into crystalline layers that also bridge the adjacent CNTs to form an interconnected structure. The contact-welded CNTs (W-CNTs) exhibit both a high conductivity (∼1500 S/cm) and a high tensile strength (∼120 MPa), which are 5 and 20 times higher than the unwelded CNTs, respectively. In addition, the W-CNTs display chemical and electrochemical stabilities in strong acidic/alkaline electrolytes (6 mol/L) when potentiostatically stressing at both cathodic and anodic potentials. With these exceptional properties, the W-CNT films are optimal as high-performance current collectors and were demonstrated in the state-of-the-art aqueous battery using a "water-in-salt" electrolyte.

As there has been an increasing demand for cold welding methods recently, this offers the chance and possibility to use the potential of magnetic pulse technology to its full extent. This is especially the case when joining different materials (steel–aluminum sheet metal welds) and having to adhere to the specific requirements of lightweight constructions, thus, giving this welding method a particular role. In this paper and the oral presentation, results of a publicly funded project will be presented (AiF-Nr. 18290 N/P1029). The focus lies on the weldability of mixed-material combinations through magnetic pulse technology and its reproducibility. Tests showed that, aside from the influence of the surface properties, it is the mechanical properties and chemical composition of the materials that are especially important for the process stability. The generated process window illustrates the aforementioned, whereby the lower curve—surface preparation—can be adapted to meet fluctuations and tolerances in the production. On a secondary level, the robustness of the process is shown as regards fluctuations and tolerances of the process. The results show relevant differences, especially for the alignment of the welding partners as even a change in the discharge energy influences the weld results. The influence of deviations from the angle for a parallel alignment of the metal sheets, the influence of fluctuations in the gap, and the increase in discharge energy are determined and characterized through destructive tests with fragmentation pattern analyses. In sum, the results show the high potential of magnetic pulse welding for the joining of mixed materials and show a high reproducibility of the welding results.

Mechanical bearings in a flywheel energy storage system (FESS) may experience unique wear patterns due to the vacuum condition that such systems operate under. The FESS discussed herein uses an aluminum flywheel rotor hub with an integrated shaft and full silicon nitride ceramic bearings. The bearings experienced fretting wear, as is common to many bearing–shaft systems, which eroded the naturally forming oxide layer on the surface of the shaft which was not replaced due to the lack of oxygen. This exposed the soft aluminum surface below creating the opportunity for material transfer between the surfaces and cold welding between components to occur. The existence of fretting and material transfer is demonstrated, and the opportunity for cold welding between components is discussed. The effects of these processes on system components are described. Recommendations to avoid or mitigate fretting and adhesion damage to the system are made for the studied FESS in particular, and, more generally, similar systems operating in vacuum conditions.

Autogeneous laser beam welding is an efficient process to join ferritic-martensitic dual-phase steels without large dimensional distortions. Localized softening may occur in the heat affected zone, particularly in DP1000 steel with a high martensite volume fraction. DP1000 steel was welded in bead-on-plate configuration varying the welding power between 0.4 and 2.0 kW and the welding speed between 20 and 150 mm/s. Light optical microscopy, scanning electron microscopy, and X-ray diffraction were used to perform the microstructural characterization of the welded joints. High-quality laser beam welds of thin sheets of DP1000 steel can be produced using appropriate welding parameters. The optimal welding condition was a nominal laser power of 2.0 kW and a welding speed of 150 mm/s. This condition minimizes the amount of softening of prior martensite and yields a narrow heat affected zone and a small volume fraction of retained austenite in the weld.

Cold Metal Transfer technology has revolutionized the welding of dissimilar metals and thicker materials by producing improved weld bead aesthetics with controlled metal deposition and low heat-input. In this study, the process, weld combinations, laser-CMT hybrid welding and applications of CMT welding are critically reviewed. Microstructure and other weld characteristics have been discussed at length for various base metal combinations. Particularly, the welding of aluminium and steel with better results has been possible with CMT Welding. The results reviewed in this article indicate that the CMT-Laser hybrid welding is more preferable to Laser or Laser hybrid welding. CMT welding has found applications in automobile industries, defence sectors and power plants as a method of additive manufacturing.

Disk laser beam welding technique is used to fabricate 2-mm 2A14-T6 aluminum alloy plates under different welding parameters. Effects of welding parameters on microstructures and mechanical properties of the weld are investigated. Grain size and porosity ratio in the disk laser welds firstly decrease, then increase with the increase of the heat input. Hardness at the fusion line and in fusion zone, tensile strength and elongation firstly increases, then decreases with the increasing heat input. When laser power is 2500 W, welding velocity is 2.0 m/min and heat input is 75 kJ/m, the finest microstructures, the minimum porosity ratio, the highest hardness and the maximum tensile strength are obtained. The fracture type in all samples is defined as a ductile fracture, and the maximum tensile strength reaches up to 261.7 MPa, about 61.2% of that of the base metal.

In order to solve the problem of large deformation, low production efficiency and high tendency of hot cracking in welding 19.05 mm thick plates of Fe36Ni Invar alloy, laser-MIG hybrid multi-layer welding technique (LMHMW) has been developed. To investigate the influence of different welding parameters on the joint properties, optical microscope observation, SEM, EDS and microhardness measurement were conducted. Experimental results illustrated that different matching of welding parameters significantly affected the depth-to-width ratio, formation of defects and HAZ width. Besides, weld zone were consisted of two regions according to the different grain shape. The region near center of weld seam (region 1) was columnar dendrite induced by laser, while the region far away from weld seam center (region 2) was cellular dendrite which was mainly caused by MIG arc. The peak value of microhardness appeared at the center of weld seam since the grains in region 1 were relatively fine, and the lowest hardness value was obtained in HAZ. In addition, results showed that the sheets can be welded at optimum process parameters, with few defects such as, surface oxidation, porosity, cracks and lack of penetration in the welding seam: laser power of backing weld P = 5500 W, welding current I = 240 A, welding speed v = 1 m/min. laser power of filling weld P = 2000 W, welding current I = 220 A, welding speed v = 0.35 m/min. laser power of cosmetic weld P = 2000 W, welding current I = 300 A, welding speed v = 0.35 m/min.

For decades, post-welding magnetic treatment has been used to reduce residual stress of welds by improving the crystal structure of solid-state welds. In this paper, we propose a new magnetic treatment method, which can reduce the time-dependent thermal stress field in situ and reduce the final residual stress of welds by simply exerting an assisted weak magnetic field perpendicular to the welding direction and workpiece during laser welding. A new finite-element model is developed to understand the thermal–mechanical physical process of the magnetic-assisted laser welding. For the widely used 304 austenite stainless steel, we theoretically observed that this method can reduce around 10 pct of the time-dependent thermal stress field, and finally reduce approximately 20 MPa of residual stress near the heat-affected zone with a 415-mT magnetic field for typical welding process parameters. A new mechanism based on magneto-fluid dynamics is proposed to explain the theoretical predications by combining high-speed imaging experiments of the transient laser welding process. The developed method is very simple but surprisingly effective, which opens new avenues for thermal stress reduction in laser welding of metals, particularly heat-sensitive metallic materials.

Copper electrodes are commonly employed in micro-resistance spot welding (MRSW), a dominant process used to join ultra-thin metallic sheets. During welding, some copper from the electrodes inevitably diffuses into the spot welds, changing the chemical compositions and properties of the resulting welded joints. In this study, 0.05-mm-thick Ti alloy metallic sheets were welded via MRSW under various combinations of welding parameters (ramping time, welding time, holding time, welding current, and electrode force). The effects of these welding parameters on electrode elemental diffusion were investigated via elemental analysis. Elemental composition of welded joints was measured via energy-dispersive spectrometry after tensile-shear tests. No copper was detected in the heat-affected zone or base material, but the amount of copper in the welding nuggets varied significantly with the welding parameters. Moreover, comparing copper element and hardness maps in weld nugget, the welding nugget hardness increased when more copper diffused into it.

Although lap joint laser welding is in great demand in practice, very limited numerical studies have been performed to investigate the hot cracking behavior in this welding configuration. This is because the traditional numerical methods are ineffective in simulating lap joint welding processes, which requires consideration of the discontinuous thermomechanical fields across the metal sheet interface prior to joining and the complicated contact conditions that evolve with material phase transitions during the welding process. The aim of the present study is to introduce a new irreversible melting state variable into the thermomechanical coupled computational model to account for the melting state effects on the mechanical and thermal properties at the welding interfaces. Under this framework, the calculation of thermal conductance and frictional coefficient depends on both temperature and the melting state variable. This allows the proper thermal and mechanical contact conditions to be captured at various melting states during the whole welding process. The proposed melting state-based model has been applied to the simulation of lap joint laser welding for the numerical investigation of the critical crack initiation location as well as the influence of various processing parameters on the cracking susceptibility and the cracking mechanism during heating-cooling processes.

Joining of metals and aluminium hybrid metal matrix composites has significant applications in aviation, ship building and automotive industries. In the present work, investigation is carried out on Friction Welding of AISI 1030 steel and hybrid AA6063-6SiC p -3Gr p composite, that are difficult to weld by fusion welding technique. Silicon carbide and graphite particle reinforced AA6063 matrix hybrid composite was developed successfully using stir casting method and the joining feasibility of AISI1030 steel with AA6063-6SiC p -3Gr p hybrid composite was tried out by friction stud welding technique. During friction stage of welding process, the particulates (SiC & Graphite) used for reinforcement, tend to increase the viscosity and lead to improper mixing of matrix and reinforcement. This eventually results in lower strength in dissimilar joints. To overcome this difficulty AA1100 interlayer is used while joining hybrid composite to AISI 1030 steel. Experimentation was carried out using Taguchi based design of experiments (DOE) technique. Multiple regression methods were applied to understand the relationship between process parameters of the friction stud welding process. Micro structural examination reveals three separate zones namely fully plasticized zone, partially deformed zone and unaffected base material zone. Ultra fine dynamically recrystallized grains of about 341 nm were observed at the fully plasticized zone. EDX analysis confirms the presence of intermetallic compound Fe 2 Al 5 at the joint interface. According to the experimental analysis using DOE, rotational speed and interlayer sheet thickness contribute about 39% and 36% respectively in determining the impact strength of the welded joints. It is found that joining with 0.5 mm interlayer sheet provides efficient joints. Developed regression model could be used to predict the axial shortening distance and impact strength of the welded joint with reasonable accuracy.

In many respects, the advantages of the hybrid welding process Plasma-MIG are explained by the interaction of the arc discharges, which make up it: a plasma discharge and an arc with a consumable electrode (MIG). Knowledge and understanding of the laws of this interaction is very important for the implementation of the process and obtaining good results. The theoretical analysis of the influence of the plasma discharge temperature with non-consumable electrode on the melting of the electrode wire was carried out. The dynamics of the melting of the electrode wire and dynamics of circuit with consumable electrode arc were been investigation. Estimates of the maximum value of the temperature of plasma discharge have been made. These results were used to select welding modes and for carrying out the technological experiments.

The high-pressurized zinc vapor, which was developed at the interface of the two metal sheets due to the lower boiling point of zinc (around 906 °C) than the melting point of steel (over 1500 °C), led to the formation of macro-blowholes. Vacuum-assisted laser welding was a powerful approach to obtain a defect-free weld bead. The laser welding process was simulated to observe the dynamic or zinc vapor. The stability of laser welding was analyzed according to simulated results. The zinc distribution which was measured by EDS experiment also represented the influence of ambient pressure on welding stability. The bearing load for weld beads under different ambient pressure was measured by shear strength test. A defect-free continuous laser weld bead could be obtained under 3 kPa ambient pressure.

Laser beam welding of 4.5-mm-thick sheets of maraging steel 250 using a 4-kW ytterbium fiber laser was studied. Maraging steel 250 is widely used in the aerospace industry in applications that require high strength. Therefore, in order to join two parts made of maraging steel 250, it is essential to produce a high-quality weld that meets weld bead geometry requirements, without any porosity formation in the weld that may lead to premature fatigue failure. In order to achieve a reliable and repeatable welding process, we investigated the influence of welding parameters on the welded process responses, i.e., weld penetration depth, bead width, and potential formation of porosity. A complete model was developed using multiple regression analysis. Based on this model, we developed a method for selecting welding parameters that assure production of porosity-free welds with the required geometry. We used this method to automate the industrial welding process of a part-family of maraging steel 250 cylinders.

Laser beam welding technique offers obvious advantages over other fusion welding processes in terms of joining titanium alloy. The microstructure of welded seam and heat affected zone resulted from diverse welding speeds and laser powers were investigated after simulating welding heat treatment. The analysis of the thermal transport properties successfully explained the morphology. Optimal process parameters were obtained. The simulation results were consistent with the corresponding experimental observations.

Results of studying the processes of diffusion welding of similar (steel) and dissimilar (steel and bonze) materials through interlayers in the form of thin foil of porous nickel and copper are considered. Thin foils of porous structure were produced by vapour phase condensation on the substrate in electron beam evaporation of elements in vacuum. Application of such foils as interlayers not only promotes formation of defect-free joints, but also leads to lowering of temperature and pressure of diffusion welding, compared to welding without an interlayer. Correlation of the change of parameters of diffusion welding through porous foil and lowering of the temperature of its transition into the superplastic state that is accompanied by the change of characteristics of foil porous structure, suggested that the processes running in the interlayer may promote establishment of physical contact between the surfaces being welded and accelerate the diffusion processes in the joint zone.

Laser beam welding (LBW) was used to join Ti–22Al–25Nb/TA15 dissimilar titanium alloys. The microstructure and mechanical properties of the welded joints under single and dual beam welding were analyzed and compared. In the mode of single laser beam, the fusion zone only consisted of B2 phase because of existence of β-phase stabilizer and rapid cooling rate of LBW. However, O phase was formed in the fusion zone while applying dual-beam laser welding due to decrease of the cooling rate. The microhardness distribution of the welded joint in dual-beam welding mode was consistent with that in single mode, but the hardness of the weld under dual laser beam was higher than that of single laser beam. In room-temperature tensile tests, the fractures all occurred in the weld, but the morphology exhibited a quasi-cleavage feature in single mode while the morphology was dimple fracture in the mode of dual laser beam. The tensile strength and elongation were both increased under dual-beam laser welding compared with those under single-beam laser welding.

Due to the low welding energy efficiency of ultrasonic composite welding, preheating is proposed to concentrate the welding energy to joining interface. By analyzing the maximum shear load, fracture surface, and microstructure of the joint cross-sections, it is found that preheating can localize welding pressure because of the softening of the welding layers, which can further concentrate weld area and reduce the generation of welded edges. Preheating enhances the welding energy efficiency, reflected by improved weld attributes (weld area and the degree of bonding) and joint quality as preheating temperature increased. With extended preheating time, the maximum shear load increases, and then drops owing to the porosity generated in the weld layer when the joints are over-heated.

It is difficult to obtain a quality joining of steels to aluminum alloys by fusion welding processes due to the large difference between melting temperatures and the formation of thick brittle Al/Fe intermetallic compounds at the joint interface. In this study, lap welds between Al 1100 and St37 steel were performed by solid-state friction stir welding with different tool rotation and welding speeds. FeAl and Fe 3 Al with thicknesses of up to 93 μm were the intermetallic compound layers formed at the joint interfaces. Shear tensile test and Scanning Electron Microscopy results showed that Fe-rich intermetallic compounds are not detrimental to joint strength and some defects, like voids, are responsible for the deteriorated weld strength. The welding parameters determine bond properties by controlling the distribution of welding energy as heat or mechanical work. At low welding speeds, mechanical work is the dominant factor. The optimum tensile strength is achieved at low welding speeds and high rotation speeds, where both factors of heat input and mechanical work are in equilibrium.

Multi-pass gas metal arc welding was carried out for Al 5083 alloy plate with thickness 30 mm. During multi-pass welding of thick plate, the former welding pass experienced multiple thermal cycles that came from subsequent welding passes. This work focused on the effect of thermal cycle on metallurgical characteristics and mechanical properties. Different from what had long been recognized that welding thermal cycle was harmful, the results indicated that multiple thermal cycles caused the partial transition from columnar grains to equiaxed grains, which finally contributed to the refinement of microstructure. Increased precipitated particles resulted in the improvement of strengthening effect. These beneficial effects of microstructure and precipitated phase led to the increase of micro-hardness and the improvements of tensile strength and ductility. As the progress of welding process, overall properties of the welded joint improved. Conclusion could be made that appropriate thermal cycles were beneficial during multi-pass welding of Al 5083 alloy.

Recently, trends in lightweight materials and their fabrication process have been focused on reducing global warming and environmental pollution. Therefore, the demand for aluminum is increasing as representative lightweight material. In general, a fusion welding process, such as high-speed GTA (Gas tungsten arc) welding, is used to join aluminum sheet, or for mechanical joining which accomplished using a rivet process. However, it is difficult to ensure a high-quality joint, given that various defects are often reported. Therefore, in this study, we propose not only welding aluminum sheets using a MPW (Magnetic pulse welding) process, but also analyzing characteristics of these joints through experimental and numerical analyses. In order to achieve this objective, a proper coil type was selected after preliminary testing in which a MPW process was performed using 0.5 mm thick A5052 sheets. After the welding, the characteristics on joint were analyzed using a peel test and optical microscope. Although there was an overlapping zone, and the coil shape was quadrangular, a circular joint shape was achieved with no evidence of welding in the center of the joint. These tests confirmed that nonuniform distributions of electromagnetic forces cause the only overlapping zone, located on the adjacent edge of the coil.

Aluminium alloy AA2219 reinforced with graphene/MWCNT nanocomposites having near theoretical densities has been successfully fabricated by high-energy ball milling followed by vacuum hot pressing. Effect of varying graphene and MWCNT content was studied on different aspects of processing of the composites. The particle size increases during milling due to cold welding; but the presence of reinforcement restricts and the resultant microstructures exhibited a layered morphology with graphene/MWCNT between particle boundaries. The composite with 0.5 wt.% reinforcement (graphene/MWCNT) content exhibited peak hardness, and further additions led to a decrease in hardness owing to the agglomeration of reinforcement at particle interfaces. The present study reveals that graphene is a better reinforcement compared to MWCNTs in aluminium matrix. This is attributed to the sheet-like morphology of graphene which covers the matrix powder particles more effectively compared to tube-like MWCNTs in providing more matrix–reinforcement contact points leading to better sintering.

Experimental results confirm that deep penetration welding with oscillations of the laser beam influences formation of the structure, shape and quality of a welded joint. The results of metallographic studies are used to determine the values of the oscillation parameters of the laser beam at which the risk of formation of defects in the welded joint is reduced. The results of mechanical tests and microhardness measurements of the welded joints produced by laser welding with an oscillating beam in 10KhSND steel are presented.

The effect of the method of welding on the mechanical properties of the welded joints of the 1565chM alloy is studied at room, high, and low temperatures.

The inertial friction welding of similar PM FGH96 superalloy was investigated. The inertial friction welding introduced steep thermal gradients of welding zone for PM FGH96 superalloy, the whole welding process only needed several seconds, therefore, it’s a fast heating and cooling completely recrystallization process. Dramatic changes in the microstructure were observed over a narrow weld zone, which across the weld interface was measured to be about 1.0-1.2mm. Significant changes in the secondary and tertiary γ′ distribution can be observed over the first 2mm from welding line, while very fine tertiary γ′ particles precipitated in a unimodal size distribution and in a high density at welding line. The fine secondary re-precipitated γ′ under fast cooling was spherical in shape, which gradually transformed into elliptical, cube with the distance from welding line. No significant texture or grain distortion was observed in the extensively plastically deformed region due to recrystallization.