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Collision welding is a promising approach for joining conventional materials in identical or dissimilar combinations without heat-related strength loss, thereby opening up new lightweight potential. Widespread application of this technology is still limited by an insufficient state of knowledge with respect to the underlying joining mechanisms. This paper applies collision welding to a material combination of DC04 steel and EN AW 6016 aluminium alloy. Firstly, the welding process window for the combination is determined by varying the collision speed and the collision angle, the two main influencing variables in collision welding, using a special model test rig. The process window area with the highest shear tensile strength of the welded joint is then determined using shear tensile tests and SEM images of the weld zone. The SEM investigations reveal four distinct metallographic structures in the weld zones, the area fractions of which are determined and correlated with collision angle and shear tensile strength. [ABSTRACT FROM AUTHOR]

In this study, a novel embedded machine learning (ML) framework was employed to analyze interfacial characteristics in dissimilar-alloy impact welding. While keeping the substrates constant, i.e., stainless steel and Ti alloy, the influence of interlayer types on the resultant morphology of impact-welded bonds was also highlighted. The dataset was meticulously generated through numerical simulations, utilizing materials properties and processing parameters as primary inputs. These inputs were used to predict various interfacial features, including the extent of wave formation (L), specific welding zone area (S), average waveform amplitude (A), and maximum interface temperature (Tmax). Impressively, exceptional predictive capabilities were demonstrated by the ML model, with determination coefficients of 0.938, 0.924, 0.967, and 0.909 for S, L, A, and Tmax, respectively. Based on the results, strong dependencies between interfacial features and the weight functions of materials properties and processing parameters were unveiled. Intriguingly, as the weight function of materials properties for a specific output objective increased, a corresponding decrease in the weight function of processing parameter inputs was observed. These findings emphasize the complex connection between input parameters and output characteristics, revealing previously unexplored intricacies in the impact welding process, facilitated by our advanced ML methodology. [ABSTRACT FROM AUTHOR]

While high velocity impact welding is perceived as a solid-state joining process, localized or continuous melting on the weld interfaces has posed a significant challenge. Here we propose to overcome this challenge by introducing a nanocrystalline layer on the metal surface for impact welding of magnesium to aluminum. After surface nanocrystallization, melting and intermetallic (IMC) formation at the interface were suppressed, resulting in a 60% improvement in Mg-Al joint strength. This is because the surface nanocrystalline layer limited the plastic shearing deformation and deformation heat at the Mg-Al interface during impact welding. Meanwhile, the high density of grain boundaries in nanocrystalline Mg layer and the high density of dislocations inside the nanocrystalline provided short-circuiting paths for Al diffusion into Mg matrix, forming a diffusion layer of 30–45 nm thickness. This work provides a new approach to dramatically improve dissimilar impact welding strength via surface nanocrysallization. [Display omitted] [ABSTRACT FROM AUTHOR]

To explore the optimal method for simulating impact welding, we compared detailedly the smoothed particle hydrodynamics (SPH) and structured arbitrary Lagrangian-Eulerian (S-ALE) methods in predicting bonding interface. Based on the experimental results of Cu-Q235 steel atmospheric explosive welding, an in-depth analysis was presented. The results show that the SPH and S-ALE methods converged at element sizes of 2.5 and 2 μm, respectively. When the element size was further reduced to 0.5 % of the wavelength, the errors of both methods were less than 5 %. Benefiting from the gradient mesh, the efficiency of the S-ALE method was 2–4 times that of the SPH method at the same element size. With the addition of the gas medium, the S-ALE method derived the formation mechanism of the gap gas shockwave and indicated that the pressure distribution is not uniform. Furthermore, the local high pressure of the gas shockwave prevents the vortex closure during the wave formation, generating the pore. The calculated pressure and velocity of the wavefront were 20 MPa and 3500 m s−1, respectively. In conclusion, the SPH is suitable for fast previewing waveform interfaces, while the S-ALE method has the advantage of capturing fine waveform structures under various environmental conditions. [Display omitted] • Independent analyses of the impact welding process was carried out by the SPH and S-ALE methods. • The SPH and S-ALE methods revealed different reasons for describing the initial disturbance. • The two methods present their own advantages in facing different problems. • The S-ALE method can capture some defects generated by explosive welding in the atmosphere. [ABSTRACT FROM AUTHOR]

• Effects of hugoniot properties on the jet onset time, velocity and jetting side. • Jet initiates earlier at higher velocity if jetting side has higher shock parameter. • Jet initiates earlier at higher velocity if jetting side has higher sound velocity. • Jet initiates later and at lower velocity if jetting side has high density. • Effect of s-parameter and speed of sound is more profound than the density. Jets are the earliest ejected material from a hypervelocity impact event. Jets comprises of projectile and target's surface material and are ejected at velocities higher than escape velocity for Earth. Effects of Hugoniot properties of the projectile and target material on jet initiation are not well understood. We, therefore, developed a mathematical model that incorporated the limitations imposed by Hugoniot properties on jet initiation for hypervelocity impact. This model analysed the effects of changes in Hugoniot properties of the projectile and target on the jet onset time, jet onset velocity and jetting side (projectile or target). The results reveal that (i) jet initiates earlier and at higher velocity if the jetting side has higher value of shock parameter or higher velocity of sound in the material; (ii) jet initiates later and at lower velocity if jetting side has high density; (iii) effect of s-parameter and speed of sound in material is more profound than the effect of density. [ABSTRACT FROM AUTHOR]

Characteristic features of impact welding were investigated in a simple model system of colliding copper single crystals. Large grained sheets were used to approximate single crystal to single crystal impact. Optical microscopy and electron backscatter diffraction (EBSD) analyses showed multiple features of the weld interface, which include deformation twinning, adiabatic shear banding, localized melting, and dynamic recrystallization. To support the microstructural findings, numerical simulation based on smoothed particle hydrodynamics method was conducted to predict the local temperature, pressure, and strain distributions. The insights gathered here will aid in the design of materials combinations and systems for impact welding. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The microstructure of aluminum‐steel compounds fabricated by magnetic pulse welding are investigated. Electron backscatter diffraction, energy dispersive x‐ray spectroscopy and scanning electron microscopy revealed the existence of several different phases along the weld seam. While one layer could be identified as aluminum solid solution, a very thin layer close to the steel side of the compound eluded detailed characterization by scanning electron microscopy techniques. Transmission electron microscopy and selected area electron diffraction investigations of this layer revealed a mix of nanocrystalline and amorphous parts. When ambient pressure was reduced to 1 mbar during welding, no interlayers were observed in the samples. This suggests that the interlayers are precipitates of the jet that is formed during conventional impact welding. [ABSTRACT FROM AUTHOR]

This paper proposes a novel impact welding method named water-augmented vaporizing foil actuator welding, in which liquid water is introduced to alter the foil's vaporization process, thus altering the induced driving pressure and the final welding performance. A series of comparative experiments were performed to confirm the effectiveness of the process and to understand the underlying mechanism. The proposed process decreased the lower-bound required discharge energy by 58–69%, increased the peel strength by 30–60%, and significantly reduced the variability in the critical standoff distance at the lower bound of the weld window. In addition, the proposed process resolved the robustness issue by producing a much more regular and repeatable shape of the weld area compared to conventional VFAW. Furthermore, three potential mechanisms have been proposed to explain the process improvement: the added water 1) increased the electrical energy deposition, 2) introduced additional energy from the aluminum-water chemical reaction, and 3) provided a more efficient force-transfer medium. In summary, this paper introduces a novel impact welding method with much improved process capability and robustness compared to conventional vaporizing foil actuator welding. In addition, due to its simplicity, this method may be easily extended for other forms of impulse metalworking, which may stimulate a wide interest for the community of high velocity metalworking. [ABSTRACT FROM AUTHOR]

Explosive welding involves processes like the detonation of explosive, impact of metal structures and strong fluid-structure interaction, while the whole process of explosive welding has not been well modeled before. In this paper, a novel smoothed particle hydrodynamics (SPH) model is developed to simulate explosive welding. In the SPH model, a kernel gradient correction algorithm is used to achieve better computational accuracy. A density adapting technique which can effectively treat large density ratio is also proposed. The developed SPH model is firstly validated by simulating a benchmark problem of one-dimensional TNT detonation and an impact welding problem. The SPH model is then successfully applied to simulate the whole process of explosive welding. It is demonstrated that the presented SPH method can capture typical physics in explosive welding including explosion wave, welding surface morphology, jet flow and acceleration of the flyer plate. The welding angle obtained from the SPH simulation agrees well with that from a kinematic analysis. [ABSTRACT FROM AUTHOR]

Joining processes by high speed impacts such as explosion welding and electromagnetic pulse welding offer great advantages compared to conventional joining methods, especially fusion welding. However, a comprehensive understanding of the mechanisms and phenomena does not exist yet and thus process design largely involves empirical data. The established high speed joining technologies have in common that their observability for basic research is limited. It is the aim to provide valid and process independent data on necessary weld conditions which can be transferred to any impact welding process. A special test rig is used for basic research under reproducible conditions. The impact area is observed with high spatial and temporal resolution. Both the impact angle and the impact velocity can be adjusted individually and are constant during the process: The impact angle can be adjusted and measured with an accuracy of ± 0.05°, the normal impact velocity can be set in steps of 0.03 m/s up to 262 m/s. This publication focusses on the acquisition and discussion of a process window for aluminium specimens. Investigations on the joint strength will be carried out. It will be shown that the findings are in good accordance to analytical explanations and earlier works in literature. [ABSTRACT FROM AUTHOR]

This paper investigates the development and evolution of various interfacial features during high speed impact welding processes using numerical simulations. Arbitrary Lagrangian - Eulerian (ALE) and Eulerian computations are performed and compared with experimental features of welded joints. ALE method reveals poor mesh quality while the interface experiences severe shear deformation. Therefore, ALE simulations cannot accurately capture the morphological transition toward a wavy shape and cannot compute the successive jet formation from the interface. But, the Eulerian method becomes a good alternative to overcome those limitations of the ALE method. Computed interfacial features using Eulerian simulations are agreed well with the experimental observations of various interfacial phenomena. The actual kinematics along the whole length of the weld including wavy pattern, localized plastic deformation and shear strain orientation are clearly reproduced. Eulerian simulation also provides understanding for the potential cause of defects that corresponds to the experimental observations, in terms of morphology and site occurrence. [ABSTRACT FROM AUTHOR]

Using transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDXS), we have investigated the microstructures of the bonding interface in Al/Fe clads fabricated by pulsed-magnetic-driven impact. A ∼10 nm thick interfacial layer of amorphous Al–Fe alloys has been observed to form at the interface of crystalline Al/Fe bimetallic system. Amorphization of polycrystalline Al takes place concurrently within the grain boundary triple junctions. It is suggested that amorphization at the bonding interface is initially driven by the collapse of the lattice during the high-strain-rate impact process and then followed by the interdiffusion reaction at temperature below the melting point. [ABSTRACT FROM AUTHOR]

Finite element simulations of high strain rate forming processes are of significant interest to industry, but are challenging due to the coupled physics and dynamic nature of the processes. For instance, in high velocity impact welding, extremely high plastic strain regions develop. Thus, a traditional pure Lagrangian analysis is not able to accurately model the process due to excessive element distortion near the contact zone. In this study, the Arbitrary Lagrangian-Eulerian method (ALE) was used to simulate an impact welding process for two Al6061-T6 plates. The ALE method was able to numerically predict the temperature at the interface as well as the necessary process parameters to achieve a wavy morphology at the interface of the materials which is assumed to be a characteristic of a quality impact weld. This allowed the prediction of a weldability window, including separate regions for melting and purely solid state welds. To validate the proposed numerical model and wavy morphology regions, experimental tests with a Vaporizing Foil Actuator Welding (VFAW) process were conducted including Photon Doppler Velocimetry (PDV) measurements of the impact velocity. The numerical results were in good agreement with the experimental tests including the temperature prediction and interfacial melting observed through microstructural analyses. [ABSTRACT FROM AUTHOR]

The objective of this study was to create impact welds between a Zr-based Bulk Metallic Glass (BMG) and copper at a laboratory scale and subsequently investigate the relationship between interfacial structure and mechanical properties. Vaporizing Foil Actuator (VFA) has recently been demonstrated as a versatile tool for metalworking applications: impact welding of dissimilar materials being one of them. Its implementation for welding is termed as VFA Welding or VFAW. With 8 kJ input energy into an aluminum foil actuator, a 0.5 mm thick Cu110 alloy sheet was launched toward a BMG target resulting in an impact at a velocity of nearly 600 m/s. For this experiment, the welded interface was straight with a few BMG fragments embedded in the copper sheet in some regions. Hardness tests across the interface showed increase in strength on the copper side. Instrumented peel test resulted in failure in the parent copper sheet. A slower impact velocity during a separate experiment resulted in a weld, which had wavy regions along the interface and in peel failure again happened in the parent copper sheet. Some through-thickness cracks were observed in the BMG plate and there was some spall damage in the copper flyers. TEM electron diffraction on a sample, cut out from the wavy weld interface region using a focused ion beam, showed that devitrification of the BMG was completely avoided in this welding process. [ABSTRACT FROM AUTHOR]

Highlights: [•] A novel test rig to examine the principles of impact welding has been developed. [•] Numerical analyses of the impact conditions have been performed. [•] Microscopic investigation of the welded samples has been conducted. [•] The joints of the test rig and the real process are comparable. [•] The test rig can represent all stages of electromagnetic pulse welding. [Copyright &y& Elsevier]

Abstract: Three complementary impact welding technologies are described in this paper. They are explosive welding, magnetic pulse welding, and laser impact welding, which have been used to provide metallurgical bonds between both similar and dissimilar metal pairs. They share the physical principle that general impact-driven welding can be carried out by oblique impact but are used at different length scales from meters to sub-millimeter. The different length scales require different kinds of systems to drive the process, and the scales themselves can give different weld morphologies. Metallographic analysis on cross-sections shows a wavy interface morphology which is likely the result of an instability associated with jetting, which scours the surfaces clean during impact. The normalized period and amplitude of the undulations increase with increasing impact energy density. Microhardness testing results show the impact welded interface has a much greater hardness than the base metals. This can lead to weldments that have strengths equal to or greater than that of the weakest base material. [Copyright &y& Elsevier]

Abstract: This paper presents an experimental study and a numerical simulation of impact welding of single and double aluminium plates using a gas gun. The study shows the differences in the bonding quality of the two impacting flyer plates. In general the bonded area between the two flyer plates is less than that between the leading flyer and the target. The simulations show that the back surface of the leading plate flyer exhibits an increase in roughness after impacting onto the target. The numerical modelling in agreement with the experiment shows that the contact surface between two flyers at the time of the contact is not flat. [Copyright &y& Elsevier]

Abstract: The paper reports a study of high-speed oblique collision of non-flat metal plates with fixed target blocks. The main aim of the study was to improve the understanding of the industrial process of explosive welding. The results of tests with flat, V- and U-shaped flyer plates were presented. The effect of flyer shape on the area of bonding was examined and three-dimensional numerical modeling was used to identify and relate mechanical parameters, such as plastic strain and shear stress to the quality of welding. Effective plastic strain (PEEQ) and shear stress in the flyer plate were shown to be criteria in determining weld quality. The study has shown that the shape and amplitude of the waves in the interface between flyer plate and target block are dependent on the shape of the flyer plate. Both the numerical modelling and the experimental tests showed that the largest area of weld was produced with flat flyer plates. [Copyright &y& Elsevier]

Impact welding has been carried out using a projectile having a diameter of 11 and 5 mm at an impact velocity of 200 m/s or more. A large projectile regardless of the slenderness ratio, was welded to a stainless steel target. However, only a small projectile with a slenderness ratio less than 1.2 was welded to the same target. In order to examine the effect of the diameter of the projectile on the weldability, the temperature elevating process in two cylindrical projectiles subjected to a longitudinal impact was evaluated numerically using LS-DYNA. The numerical results indicated that since the deformation mechanism of a projectile with a slenderness ratio less than 1.0 is different of that of the projectile with the slenderness ratio more than 1.5, the small projectile with the slenderness ratio less than 1.0 can be welded to the target. [ABSTRACT FROM AUTHOR]

[Display omitted] • Vaporizing foil actuator welding was for the first time used to weld 7075 Al to a SiC-reinforced 8009 aluminum metal matrix composite. • 7075Al/8009 Al MMC dissimilar impact welds exhibited wavy interfaces with no apparent heat affected zone or melting. • SiC-depleted and SiC-rich bands were alternately distributed with consistent plastic flow patterns along the wavy interface. • Peel test yields a nugget failure on the AA7075-T6 indicating high strength of the weld. Vaporizing foil actuator welding (VFAW), an impact welding method, was used for the first time to produce high strength welds between SiC-reinforced 8009 aluminum metal matrix composite (MMC) (8009/SiC/11p) and 7075 aluminum alloy (AA7075). Microscopic characterization of the dissimilar impact weld revealed multiple heterogenous microstructural zones including an unbonded zone at the center, a flat interface, a wavy interface, and a trapped jet zone at the corner. SiC-depleted and SiC-rich bands were alternately distributed with consistent plastic flow patterns along the wavy interface. Microhardness tests prove that little or no heat or mechanically affected zones were formed in the dissimilar impact weld. Peel test yields a nugget pullout on the AA7075-T6 indicating high strength of the weld. VFAW process provides a solution to join the Al MMC with dissimilar metals in the applications of automotive and aerospace products. [ABSTRACT FROM AUTHOR]

This paper mainly demonstrates an advanced type of the vaporizing foil actuator welding (VFAW) process between GPa-grade steel (TRIP1180) and aluminum alloy (AA5052-H32) without applying standoff. To secure a flying distance during the VFAW process, the preformed target sheet shaped like a circular indentation has been utilized. It is necessary to optimize process parameters integrated with geometrical design of the preform since the welding strength can be decreased beyond the optimum input energy in the standoff-free VFAW process. The welded surface was evaluated by SEM-EDS, XRD, EBDS, and TEM to analyze the welding mechanism and composition at the welding interface. The diffusion zone including the AlFe3 phase was observed at the welded interface which has high grain density due to the high-speed impact by increasing the welding strength, which leads to the perfect welding between the dissimilar materials. [ABSTRACT FROM AUTHOR]

The effective weight reduction in the automotive industry by the wide adoption of lightweight magnesium (Mg) alloys demands high-quality joint between magnesium alloys and massively-used steels in order to wring the excess weight with strength and safety assurance. However, Mg-steel joint is difficult to achieve because there is no mutual solubility between magnesium and steel and huge disparity in physical properties. An impact-based welding method recently showed successful Mg-steel joining. In this work, the characteristics of Mg-steel interface joined by the impact welding method were investigated. Synchrotron high-energy X-ray computed tomography and diffraction were applied to characterize the microstructure across Mg-steel interface. Results revealed a deposit layer formed at the joint interface where Fe-rich particles spread deep into the Mg matrix. High-resolution 3D morphology of Mg-steel interface demonstrated the trapped pores and cracks inside the deposit layer. The formation of the deposit layer and the void/cracking evolution were analyzed by using finite element models. These findings provide insights into the immiscible Mg-steel joining process. [ABSTRACT FROM AUTHOR]

Introduced is a comprehensive numerical modeling framework that includes microstructure when simulating the laser impact welding (LIW) of metals to study the transient phenomena that occur during weld formation. Such transient phenomena include evolution of shear stresses, plastic strains, thermal response, and material jetting. Inhomogeneous microstructures for two dissimilar foils (aluminum 1100 and stainless steel 304) are first predicted using the Dynamic Kinetic Monte Carlo (KMC) method to simulate laser-based powder bed fusion (PBF-LB) additive manufacturing (AM). These microstructures are subsequently incorporated into an Eulerian finite element (FE) simulation of the LIW process, enabling prediction of grain elongations that result from the varying yield surfaces, stacking fault energies, and grain-boundary sliding effects. Trends in the predicted microstructure deformation patterns show strong agreement with those from experimental images in the literature. Compared to existing homogeneous models, the new framework with inhomogeneous AM microstructure reveals higher collision velocities at the weld interface, resulting in increased plastic strain rates, greater plastic heat dissipation, and increased material jetting with higher jet temperatures. The framework allows for new opportunities to study correlations between grain topography (as well as polycrystalline metal texture) and the transient process phenomena occurring at the impact weld interface. Unlabelled Image • Presented is a novel comprehensive modeling framework that captures inhomogeneous microstructure-driven anisotropic effects during simulation of laser impact welding • The findings reveal grain elongation and alignment resulting from grain-boundary sliding, which confirms the development of adiabatic shear banding • By capturing microstructure, increased plastic strain rates along the weld interface are revealed, resulting in greater plastic heat dissipation • Unlike existing homogeneous models, findings with the new framework reveal increased jetting with higher temperatures, even at lower collision velocities [ABSTRACT FROM AUTHOR]