Welding Mechanism Research Articles

Reversible Schiff-base chemistry enables thermosetting smart composites with versatile properties

Fibre-reinforced polymer composites have become indispensable structural materials in modern life and global industry due to their superior specific properties and improved energy efficiency. However, the irreversibility of commercially available thermoset matrices, characterized by covalent cross-linking, poses challenges to both the recyclability and the enhancement of functionality. Herein, inspired by living tissues, we demonstrated recyclable, reprocessing, self-growing, and thermally/water modulated carbon fibre reinforced polyimine composites at low processing temperatures (≤110 °C, without any catalyst), realizing the intelligent composites. The tensile strength and average friction coefficients of our composites were 129.1 MPa and 0.52, respectively. Moreover, the chemical welding and self-growing mechanism of our system were deeply explored. The process enabled the recovery of clean and intact carbon fibres. We aim for this work to further deepen the understanding of dynamic polyimine networks with semi-aromatic skeleton, and facilitate the preparation of smart, adaptive and pluripotent composites.

Welding of glass and single crystal graphite film using a high repetition fs laser

In this paper, we successfully welded an ordinary glass and a single crystal graphite film without visible cracks by employing a high repetition femtosecond laser. The tensile strength of two welding samples exceeds those of the original films. Based on the SEM-EDS data and the Raman spectra data, two types of plasma welding regions can be clearly discriminated. The welding mechanism can be attributed to the mixture of graphite plasma and glass plasma and their resolidification. The energy density of single pulse at the interface is the most dominant factor because of this welding mechanism. From the Raman spectra data of the rear surface of the 20μm sample, how the shock wave influences the configurations of the C–C bonds in the graphite film can also be studied. Those results are helpful in understanding the dynamics of femtosecond laser welding and quickly optimizing laser parameters.

Micro-welding of non-optical contact sapphire/metal using Burst femtosecond laser

Recently, welding of dissimilar material, such as transparent material to metal material, is widely used in aerospace, microelectronic packaging, medicine, etc. Ultrafast laser welding provides a new method for high-performance dissimilar material welding, in which the non-optical contact dissimilar material welding has become a new research hot spot. In this paper, we report the effective welding of Fe-36Ni with roughness as high as 1.1 µm to sapphire, which, to our knowledge, is the roughest dissimilar material welding achieved in ultrafast laser. A 238 fs, 1035 nm, 200 kHz Burst mode femtosecond laser (4 sub-pulses with a total energy of 132.5μJ) yields a smooth and uniform interface with a welding strength up to 11 MPa. In this context, the welding performance and mechanism of Burst mode and single pulse mode ultrafast laser are systematically analyzed. The relevant research results are expected to provide theoretical guidance for the welding of high-strength and high-stability dissimilar materials.

Tuning residual stresses in welded structures by exploiting bio‐inspired suture interfaces

AbstractNature offers a valuable source of inspiration when designing optimized structures. For instance, when two or more shells are joined during growth processes, Nature prefers to exploit interlocking paradigms to enhance the strength of the bond—cranial sutures are one example. Mimicking this distinctive characteristic when welding thin metallic elements may offer some structural benefits. The present study theoretically investigates the possibility of mitigating the detrimental tensile residual stress that always originated by welding processes, by exploiting Computational Welding Mechanics. Specifically, two plates joined by laser welding following sinusoidal paths (i.e., wave‐like), alongside a linear one, will be studied and compared. Thanks to the distinctive temporal and spatial heat distributions of sinusoidal welding, both welding stress and strain develop in dissimilar ways compared with linear path welding—this is reflected to the resulting weldment distortion too. The results show that geometrically optimized sinusoidal welding can effectively reduce residual stress magnitudes compared with the linear configuration counterpart. The implications of these findings are of particular interest when dealing with the structural performance of welded structures, especially in fatigue contexts.

Study on Penetration Increase Mechanism of TIG Welding Using External Magnetic Field

Study on Penetration Increase Mechanism of TIG Welding Using External Magnetic Field

Oblique incidence of ultrafast laser for glass butt welding.

Lap welding restricts the connection state of glasses by vertically incident ultrafast laser at the interface to be welded, which cannot meet the increasingly flexible welding needs. In this Letter, glass butt welding is achieved by oblique incidence of an ultrafast laser, expanding the applicability of ultrafast laser glass welding. Furthermore, the propagation path of the laser beam after oblique incidence into a glass is solved based on geometric optics, the dynamic development of the molten pool in a glass is observed through a high-speed camera, and the mechanism of glass butt welding is elucidated. Finally, the influence of laser pulse energy, glass tilt angle, and defocus amount on welding strength is investigated, achieving a maximum shear strength of 11.5 MPa.

Electromagnetic-mechanical response mechanism and microstructure evolution during Al-Mg electromagnetic pulse welding

Electromagnetic pulse welding technology can achieve effective bonding of different metals without intermetallic compounds and heat-affected zones. Current research primarily focuses on bonding interface and strength, neglecting the fact that the strength of the joint is also related to the performance of the plate itself. This study investigates the macro-microscopic responses, and relevant mechanisms of plates under electromagnetic-mechanical coupling effects are revealed by the integration of microscopic characterization, a finite element model, and mechanical tests. The results show that diverse crystal structures have different mechanical response behavior. The elongation of aluminum after pure pulsed electromagnetic field (EMF) treatment is 27% higher than the untreated specimen while the tensile strength remains the same. But magnesium alloys show an increase of 16%, and 23% for tensile strength, and elongation, respectively. Under a pure EMF, the movement and recombination of dislocations are promoted in aluminum alloy, which is beneficial to reducing the dislocation density of aluminum alloy. As for magnesium alloy, twinning and recrystallization are induced to realize grain refinement. Under the coupling of electromagnetic-mechanical, there is an interaction between the electromagnetic effect and strain rate hardening on dislocations. The tensile strength of the Al specimen increases first and then decreases with the discharge voltage rising. This is determined by the dislocation entanglement behavior. This paper can provide a reference for an in-depth understanding of the mechanism and welding process of electromagnetic pulse welding.

Study on the keyhole oscillation mechanism of laser welding based on electro-mechano-acoustical analogy theory

The acoustic emission phenomena generated by the laser welding process are closely related to the keyhole's forced oscillation and the dynamic pressure balance at the keyhole bottom. In this study, we constructed the mechanical equation of keyhole bottom pressure balance and used the “electro-mechano-acoustical” analogy theory to convert it into an acoustic equation, the acoustic resonant frequency as well as the magnification amplification factor of the keyhole oscillation in different penetration states were derived. A monitoring platform combining acoustic sensor and high-speed photography was established to obtain acoustic emission signals and lateral keyhole images. The acoustic and image features extracted from the monitoring data validated the derived formulas. Additionally, the acoustic phenomena of different frequency-energy components were explained according to the derived formulas in turn. The results demonstrated that the derived theory is compatible with experimental comparisons, showcasing its great interpretability and applicability. The introduced analogy theory effectively establishes a bridge between keyhole forced pressure and acoustic emission vibration, aiding in the understanding of keyhole oscillation characteristics. A novel model of keyhole oscillation was proposed and verified using process monitoring data in this study, which provides a new approach for the investigation of keyhole dynamic.

Microstructure investigation and optimization of process parameters of ultrasonic welding for Al–Cu dissimilar joints using design of experiment

Ultrasonic Metal Welding (UMW) employs high-power ultrasonic vibrations to join thin metal sheets of different materials, effectively addressing the thermal damage issues associated with traditional welding methods. This study aimed to optimize the joining of thin aluminum (Al) and pure copper (Cu) metal sheets using high-power ultrasonic vibration. The investigation focused on the effect of input parameters, including time, static pressure, and welding power, on the output parameter of joint strength. The results indicated that the welding time had the most significant effect on the load obtained from the Tensile-shear test. The optimal condition was determined to be a welding time of 0.98 s, a pressure of 2 bar, and a power of 85%, resulting in a maximum predicted tensile-shear test load of 753.3 N, with an error value of 11.4% obtained from the software. Microscopic images reveal that the welding mechanism in ultrasonic welding involves continuous plastic deformation, dispersion of oxide layers, and the formation and extension of micro-bonds along the weld line.

Temporal spatial transfer characteristics and cross-scale fusion behavior mechanism of interface temperature in induction welding of plain carbon fiber polyphenylene sulfide

The intricate multiphysics coupling conditions and nonlinear characteristics inherent in carbon fiber composite induction welding render the temperature transfer properties of the interface and the fusion connection mechanism across different scales ambiguous. In this study, a transient 3D finite element model was developed to simulate the induction welding process of carbon fiber reinforced polyphenylene sulfide (CF/PPS) composites, utilizing an electromagnetic-thermal multiphysics coupling mechanism. This investigation revealed that the electromagnetic effect leads to the accumulation of magnetic flux and spatial constraints, thereby triggering an eddy current concentration effect at the interface, which serves as an additional influencing factor in induction welding's edge effect. Simultaneously, the temperature distribution at the induction welding interface exhibits a gradient characteristic over both time and space: fluctuations in the current heat source result in a pronounced gradient distribution pattern of 225 %-680 % in welding interface temperature differences, accompanied by a 43.29 % reduction in shear strength. Notably, this study delves into the intricate origin of the induction welding heat source, elucidating that the generation of induced current in the magnetic field by carbon fiber overlap contributes to volumetric heat induction. This facilitates the welding process to some extent, despite the significantly lower heat contribution compared to thermally conductive wire meshes. In conclusion, to gain deeper insights into the impact of heat input on the fusion behavior of the bonding interface, SEM analysis was conducted on the experimental samples to examine the fusion morphology of the induction welding interface. Additionally, the method of EDS elemental analysis has also been used to investigate the generation and fusion mechanisms of welding defects. The amalgamation of numerical simulation technology and multi-scale material characterization serves as a methodological guide for researching the welding mechanisms of composite materials and even extends to investigations within the domain of metal connections. Furthermore, it paves the way for exploring a multidimensional research horizon in the realm of material joining and molding.

INFLUENCE OF WELDING PARAMETERS ON THE PERFORMANCE CHARACTERISTICS OF THE THERMOCATODES

Methods of controlling welding parameters, physical and physico-chemical transformations that occur during welding are considered in the work. The physico-chemical mechanism of welding is considered - the deformation of the crystal lattice, the transfer of metal on the contacting surfaces, the mixing of deformation products, diffusion, phase transformations, the appearance of new chemical compounds - intermetallics, oxides, carbides. Studies of the influence of the main parameters of friction welding on the formation of the structure of the welded joints of the investigated alloys have been carried out. The microstructures of welded joints OT4 + VN-2AE and VT6 + VN-2AE are given. The obtained dependence of the relative strength of the OT 4 + VN-2AE connection on the parameters of the welding process. The given microstructures were obtained by SEM from the surface of OT 4 + VN-2AE and VT6 samples, based on which it was determined that the destruction begins with the formation of microcracks in the contact zone on the side of the VN-2AE niobium alloy. It was determined that a layer saturated with oxygen is formed in the diffusion zone due to which the β-modification of Ni2O5 with a significant specific volume is formed, which causes high internal stresses and the formation of microcracks. The reason for the decrease in the mechanical properties of the welded joint OT 4 + ВН-2АЕ was established - the formation of a phase (Ti-Nb) with an orthorhombic lattice, the degree of curvature of which determines the degree of strengthening of the layer and depends on the niobium content. These data are confirmed by X-ray structural analysis. The analysis of the concentration curves of niobium and titanium shows that titanium does not diffuse into the narrow contact zone of the niobium alloy, and niobium forms a wide diffusion zone in the contact zone of the OT 4 alloy. It was established that niobium contributes to the increase in the solubility of aluminum in λ-titanium, which leads to increase in weldability plasticity and corrosion resistance. It was determined that the low mechanical properties of the welded joints of the VN-2AE alloy with the OT-4 and VT-6 titanium alloys are due to the same nature - the oxidation of the niobium alloy at the welding temperature. It was established that the weak link of the welded joint is the surface of the niobium alloy.

Welding of Steel - Its Mechanism and Applications in Multiple Sectors

Among different metals steel can be easily welded and welded steel has required strength, good ductility and sufficient resistance to general corrosion media. Since steel welding is being used in all types of fabrication industries, the mechanism of steel welding has been explored for different types of steel along with its multiple applications.

Experimental and numerical study on the mechanism of interlayer explosive welding

Currently, a gap in understanding the mechanism of interlayer explosives exists. This study systematically investigated this mechanism using TP 270C/SUS 821L1 to fill this knowledge gap. By comparing the outcomes of direct and interlayer welding through methods such as optical microscope (OM), computed tomography (CT), electron probe micro-analysis (EPMA), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), nanoindentation, and tensile shear test, it was found that an interlayer can significantly lessen the energy at the target interface. This was further evident when comparing welds with varying interlayer thicknesses, showing that thinner interlayers lead to less energy transfer between the flying plate and the interlayers. Notably, at an interlayer thickness of 0.1 mm, the welding interface appeared irregular. The smoothed particle hydrodynamics (SPH) method was employed to simulate the welding, highlighting the interlayer's impact on factors like pressure, jet, temperature, and melting. This simulation also explained why the 0.1 mm interlayer had an irregular interface due to jetting affecting the welding between the flyer plate and interlayer. The study also analyzed the weldability window in interlayer explosive welding, noting how the interlayer influenced its upper and lower limits. The relation between interlayer thickness and the constant k in the lower limit was examined, along with the minimum velocity needed for the flyer plate to generate a jet VP. Their relationship satisfied exponential functions in the detonation velocity range of 1800–3000 m/s. This study thus established a link between traditional and interlayer explosive welding.

Characterisation of rotary friction welding process and mechanism of heat-treated Scotch pine

Rotary friction welding of wood to heat-treated lumber from Scotch pine is feasible and the strength of the joint exceeds that of glued and hammered joints. This study investigated the rotary friction welding process parameters and its welding mechanism applicable to heat-treated Scotch pine. Untreated Scotch pine served as the control. The one-way test revealed the tenon/bore ratio of 1.5, rotational speed of 2000 to 3500 r/min, and feed rate of 15 to 20 mm/s as the ideal process parameters for heat-treated Scotch pine. Under the same conditions, heat-treated material had weld strength up to 63.2% higher than untreated material. The portion of the weld zone with better weld strength was larger in size, had a full surface, and was darker in color, according to ultra-depth-of-field microscopic examinations. The internal wood components melted and cooled after the welding was finished and re-polymerized to form a tightly wrapped structure, linking the dowel rods to the substrate, according to the results of scanning electron microscopy.

Laser shock-enabled optical–thermal–mechanical coupled welding method for silver nanowires

Silver nanowires (AgNWs) are recognized as highly promising materials for flexible and transparent electrode applications. However, existing material-processing methods fail to achieve uniform and reliable AgNWs junctions. In this study, we propose a new method using the laser shock effect combined with the laser heating effect, for creating AgNW junctions within thin films. We explored the welding mechanism of AgNWs through optic-thermal welding, laser shock-enabled mechanical welding, and laser-shock-enabled optical-thermal-mechanical (LS-OTM) experiments, as well as numerical simulations, and the results demonstrate that the innovative mechanism of the LS-OTM process lies in its utilization of laser shock to adjust the gap between the nanowire junctions, which in turn achieves a fine control of the thermal effect of the heating laser localised surface plasmon resonance, and the atomic diffusion in the solid state at intermediate temperature under the action of the impact force is the mechanism of the formation of high-quality junctions. We prepared flexible transparent conductive films and studied their transmittance, conductivity, and thermal properties, the results show that the flexible transparent conductive films prepared by LS-OTM welding method have excellent transmittance, conductivity, and thermal properties, this verifies the feasibility and effectiveness of this processing strategy. The LS-OTM method is a viable solution for manufacturing transparent, conductive films from AgNWs for emerging applications such as flexible heated films, flexible displays, and wearable medical devices.

Microstructure evolution and mechanical properties analysis in dissimilar ultrasonic metal welding of aluminum to copper

Ultrasonic metal welding is a solid-state welding process being widely employed for joining the interconnections of lithium-ion batteries in hybrid and plug-in hybrid vehicles. Examining the microstructure of the joint is of crucial importance to evaluate the performance. This analysis allows a comprehensive understanding of the phenomena influencing the joint strength. In this study, ultrasonic welding was utilized to join copper to aluminum sheets of 0.3 mm thickness, and then the macro- and microstructural characteristics of the weld cross-section and interface were thoroughly investigated. Finally, the microstructural changes at different values of ultrasonic welding parameters were correlated with the mechanical strength characteristics. This research identified mechanical interlocking and interface diffusion as the primary welding mechanisms. With an increase in welding time from 0.2 to 0.8 s, the bond density rose, the post-weld thickness decreased, and the average Vickers hardness at various points along the weld interface decreased by 10%.

Powder-metallurgical construction of graphene-like nanosheet network reinforced Cu composites towards balanced high-performance

The size and grain conformality of the metallurgical precursor powder significantly affect the comprehensive properties of metal matrix composites. To address this challenge, homogeneous hybrids of graphene-like nanosheets coated Cu (GLNs@Cu) particles with controllable sizes are synthesized through an in-situ decomposition of cupric tartrate. Subsequently, graphene-like nanosheet network reinforced Cu (GLNN/Cu) composites are prepared by a powder-metallurgical method from the GLNs@Cu particles based on a thermal-pressing welding mechanism. The 3D-GLNN are uniformly dispersed throughout the Cu matrix, creating an isolation structure over the Cu grains, and acting as a barrier to grain fusion resulting in grain conformality of the composites. Simultaneously, the 3D-GLNN distributes along the Cu grain boundaries establishing inter-connected pathways for the electrons, thereby maintaining high electrical conductivity while refining the grain size of the Cu composites. It is precisely because of this, the GLNN/Cu composites exhibit a tensile strength of ∼500 MPa, approximately 3 times higher than that of the pure Cu. In addition, the interlinked 3D-GLNN provides an electron transport channel for the Cu composite as well as an isolation structure from the corrosive medium, which makes the Cu composite maintain an electrical conductivity even higher than the pure Cu and a corrosion rate of 48.9 % compared with the pure Cu.

Electric-thermal-mechanics modeling for in-process phenomena during micro resistance spot welding spark plug of Pt and Inconel600

The spark plug is one of the important components in the gasoline engine's combustion chamber. To reduce vehicle emissions, the platinum spark plug is selected due to its good performance. Due to the high productivity of resistance spot welding (RSW), a micro-scale RSW process is employed to assemble the platinum tip to Inconel600 part in the production of spark plugs. In order to understand the electric-thermal-mechanics phenomena during micro resistance spot welding spark plug for controlling the welding quality and saving electric energy, a three-dimensional simulation model and the in-house finite element program JWRIAN-RSW3D were developed. The potential history and upper electrode displacement results were verified with experiments. Numerical case studies were made to investigate the influence magnitude of welding current on the electric-thermal-mechanics phenomena. The developed model reveals inside phenomena to clearly understand the welding mechanism for potential, current density, temperature, electrode displacement and their distribution/history as well as the molten zone. The comprehensive phenomena of maximum temperature distribution on both base metals and Inconel600 were clarified using a top perspective, revealing differences in distribution on the contact surface between horizontal and vertical sections. To achieve a complete welding joint, the molten zone on the contact area is required carefully in order to facilitate the bonding of both base metals. Based on simulation results for three welding conditions, the alternating current at the magnitude of 1.2 kA with the welding time of 0.1 s is recommended to obtain the welded joint with minimized energy consumption in production.

Microstructure characterization and solid welding mechanism of TiB2/6061Al composite profile fabricated by porthole die extrusion

The TiB2/6061Al composite profile with sound welding quality and good mechanical properties was fabricated by porthole die extrusion. The effects of TiB2 particles on the microstructure evolution and mechanical properties were investigated, and the welding mechanism was clarified. The results indicated that the weld seam in both 6061Al and TiB2/6061Al profiles disappeared as porthole die extrusion progressed. TiB2 particles refined the grain structure by promoting the occurrence of dynamic recrystallization through particle stimulated mechanism (PSN-DRX) and inhibiting the grain growth. The interface between TiB2 particles and 6061Al matrix was in good bonding status and modified by MgAl2O4 phase. The welding mechanism in the area far away from TiB2 particle is mainly the nucleation and growth of discontinuous dynamic recrystallization (DDRX) initiated by the bulging mechanism. In the vicinity of TiB2 particle, the nucleation of DDRX is suppressed due to the formation of particle deformation zone containing high-density dislocations, and the nucleation and growth of PSN-DRXed grains become the dominated welding mechanism. The strong β-fiber texture and relatively weak α-fiber texture were observed in both 6061Al and TiB2/6061Al profiles, while the addition of TiB2 particles greatly reduced the intensity of main textures, which in turn weakened the differences in tensile strength at different locations. TiB2 particles also contribute to better mechanical performances due to the effects of grain refining, load transfer and dislocation strengthening.

Numerical Analysis of Thermal Flow Dynamics of Arc Plasma and Molten Pool in Hollow Cathode Arc Welding with Oxygen Content

The mechanism of the pulsed hollow cathode arc welding (HCAW) process was revealed using a fully coupled model with a hollow cathode. We solved the governing equations with the Marangoni effect to study the dynamic behaviors of a molten pool with a square pulsing current (200~400 A, 900 Hz) and varying O2 content; the dynamics of the arc plasma and the weld pool in the HCAW process were investigated quantitatively. The results show that the intensity of the arc plasma was more significantly weakened by the design of the hollow cathode in HCAW than that in GTAW with a solid hollow cathode. We could obtain a stable molten pool even with a large pulsing current section (200 A–400 A) at higher frequencies. The flow dynamics of the molten pool were mainly dominated by the Marangoni effect with varying oxygen content, and we could promote penetration by increasing O2 content in HCAW.