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This paper focuses on the nanoscale characterization of a welded Al/Cu interface produced by magnetic pulse welding. Welding tests were performed using three field shapers with similar dimension but having strongly different electrical conductivity. Other welding parameters were strictly the same. The three tests produce similar welded joints that consist of a similar morphology of wavy interface at the macroscopic scale. Thus, the Al to Cu transition zone across the location of an interfacial wave is identified as a suitable repetitive site that enables for repetitive fine-scale characterization across a distance less than 1 µm. Transmission Electron Microscopy (TEM) observations of the welded Al/Cu interface reveal a gradient of nanostructures which consists of an amorphous AlxCuy nanolayer (∼30 nm) and then, a nanocrystalline layer with a thin thickness of a few tens of nanometres at the Cu side and at the Al side as well. This hierarchical nano-featured structure is confined within a very short total distance of about 200 nm. Outside these confined nanostructures, the interface exhibits a crystalline structure. These nanofeatures were observed at the interface of the Al/Cu welded joint produced by three different field shapers, that shows a reproducibility of the interface structure at the nanoscale level. A thermomechanical analysis of the high strain process at a collision point allows for depicting the mechanism of microstructure formation confined at the Al/Cu interface. The shear strain rate across the interface shows peaks where the temperature distribution also reaches a peak beyond the melting point of Al. The thermal kinetics within the molten zone is characterized by a high cooling rate up to 103 °C/ns during the melting/solidification stage that explains the observation of the amorphous nanolayer revealed by the TEM observation. The formation of nanocrystalline structure confined at both sides of the amorphous layer can be explained by a nucleation of crystals at a very early stage governed by the thermal kinetics at the boundaries (Al side and Cu side) of the melted zone, and by a dynamic recrystallization governed by the gradient of shearing at high strain rate confined at the collision point. Together, these processes of highly transient thermomechanical responses confined at the Al/Cu interface explain the formation mechanism of interface microstructure that results in the hierarchical nanostructure as identified by TEM characterizations.

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.

This paper investigates the transformation of Mg-Si precipitates formed at an interface of an Al-Mg-Si alloy joint, welded by the high strain-rate collision during magnetic pulse impact welding. The Transmission Electron Microscopy (TEM) and Energy dispersive X-Ray (EDX) analysis of the precipitates reveal a nucleation of circular shape AlFeMnSiCr precipitate (size of ∼100 nm) from the dissolution of the native β″ (needle-shaped) precipitate. The AlFeMnSiCr phase can also reach a size up to several microns and grows into diverse shapes (rod-shaped, polygonal-shaped, ovoid-shaped). Based on the microstructural characterizations and on observations available in the literature including relevant data of Lodgaard and Ryum, the transformation sequence due to the high-speed collision can be described as follows: β″-Mg-Si (needle-shaped) → β’-Mg2Si (rod-shaped) ‘u-phase’ → Al(MnCrFe)Si (round-shaped) → Al(MnCrFe)Si +(+: Cr; Cu and/or Ni, rod-shaped, polygonal-shaped, ovoid-shaped). The comparison of samples welded at three different impact conditions (low impact intensity, intermediate impact intensity, high impact intensity) shows that the area fraction of the precipitates decreases with the increase of the impact intensity. The identification of the crystal structure of these different precipitates, from the nucleation to the final complete formation of the precipitation, can further enrich the transformation sequence in this paper. The role of the high strain kinematics on the deformation of the Al lattice and on the diffusion rate of alloying elements is also a perspective that can further explain this new observation of precipitation during magnetic pulse welding.

This study demonstrates that the thickness of the target and its backing condition have a powerful effect on the development of a wave structure in impact welds. Conventional theories and experiments related to impact welds show that the impact angle and speed of the flyer have a controlling influence on the development of wave structure and jetting. These results imply that control of reflected stress waves can be effectively used to optimize welding conditions and expand the range of acceptable collision angle and speed for good welding. Impact welding and laser impact welding are a class of processes that can create solid-state welds, permitting the formation of strong and tough welds without the creation of significant heat affected zones, and can avoid the gross formation of intermetallic in dissimilar metal pairs. This study examined small-scale impact using a consistent launch condition for a 127 µm commercially pure titanium flyer impacted against commercially pure copper target with thicknesses between 127 µm and 1000 µm. Steel and acrylic backing layers were placed behind the target to change wave reflection characteristics. The launch conditions produced normal collision at about 900 m/s at the weld center, with decreasing impact speed and increasing angle moving toward the outer perimeter. The target thickness had a large effect on wave morphology, with the wave amplitude increasing with target thickness in both cases, peaking when target thickness is about twice flyer thickness, and then falling. The acrylic backing showed a consistently smaller unwelded central zone, indicating that impact welding is possible at a smaller angle in that case. Strength was measured in destructive tensile testing. Failure was controlled by the breakdown of the weaker of the two base metals over all thicknesses and backings. This demonstrates that laser impact welding is a robust method for joining dissimilar metals over a range of thicknesses.

Background. Electromagnetic Pulse Technology (TEM) is a non-contact pulse process with great potential for connecting dissimilar materials. This method uses pulsed electromagnetic fields to form and connect metals with high conductivity, such as aluminum or copper. This process makes it possible to perform connections with geometric closure and tension due to compression or expansion of profile structures of alloys with a closed cross section, as well as metallurgical welds. Despite the technological advantages and potential, only a modest introduction into industrial applications has been found. This scientific article aims to reveal the industrial interest and applicability of electromagnetic pulse technology in various subsectors of the microelectronic industry, promoting lightweight and highprecision engineering components. Materials and methods. Based on numerical and experimental studies, copper-copper and copper-aluminum electrical connections are produced by electromagnetic pulse crimping. The main parameters are determined and their influence on the connection process and the achievable strength of the connection is analyzed. Attention is paid to the development of electromagnetic drives. The fundamentals of the theory of magnetic and pulsed welding are applied. Results. Conclusions and instructions on the design of the manufacture of compounds using electromagnetic pulse technology are given. A simplified approach to modeling is presented for numerical studies. This unrelated approach makes it possible to successfully develop the process and design of the connection for electromagnetic pulse crimping. Various welding parameters are indicated, which determine the different morphology of the surface, the section with different mechanical strength. The influence of the mandrel surface on the quality of the joint is evaluated. Conclusions. The weldability criteria for copper and aluminum compounds have been experimentally determined. The influence of several parameters of the experimental welding process, namely the discharge energy, gaps and holes, is evaluated using destructive tests.

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.

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.

Collision welding is a joining technology that is based on the high-speed collision and the resulting plastic deformation of at least one joining partner. The ability to form a high-strength substance-to-substance bond between joining partners of dissimilar metals allows us to design a new generation of joints. However, the occurrence of process-specific phenomena during the high-speed collision, such as a so-called jet or wave formation in the interface, complicates the prediction of bond formation and the resulting bond properties. In this paper, the collision welding of aluminum and copper was investigated at the lower limits of the process. The experiments were performed on a model test rig and observed by high-speed imaging to determine the welding window, which was compared to the ones of similar material parings from former investigation. This allowed to deepen the understanding of the decisive mechanisms at the welding window boundaries. Furthermore, an optical and a scanning electron microscope with energy dispersive X-ray analysis were used to analyze the weld interface. The results showed the important and to date neglected role of the jet and/or the cloud of particles to extract energy from the collision zone, allowing bond formation without melting and intermetallic phases.

Collision welding is a high-speed joining technology based on the plastic deformation of at least one of the joining partners. During the process, several phenomena like the formation of a so-called jet and a cloud of particles occur and enable bond formation. However, the interaction of these phenomena and how they are influenced by the amount of kinetic energy is still unclear. In this paper, the results of three series of experiments with two different setups to determine the influence of the process parameters on the fundamental phenomena and relevant mechanisms of bond formation are presented. The welding processes are monitored by different methods, like high-speed imaging, photonic Doppler velocimetry and light emission measurements. The weld interfaces are analyzed by ultrasonic investigations, metallographic analyses by optical and scanning electron microscopy, and characterized by tensile shear tests. The results provide detailed information on the influence of the different process parameters on the classical welding window and allow a prediction of the different bond mechanisms. They show that during a single magnetic pulse welding process aluminum both fusion-like and solid-state welding can occur. Furthermore, the findings allow predicting the formation of the weld interface with respect to location and shape as well as its mechanical strength.

Collision welding processes are accompanied by the ejection of a metal jet, a cloud of particles (CoP), or both phenomena, respectively. The purpose of this study is to investigate the formation, the characteristics as well as the influence of the CoP on weld formation. Impact welding experiments on three different setups in normal ambient atmosphere and under vacuum-like conditions are performed and monitored using a high-speed camera, accompanied by long-term exposures, recordings of the emission spectrum, and an evaluation of the CoP interaction with witness pins made of different materials. It was found that the CoP formed during the collision of the joining partners is compressed by the closing joining gap and particularly at small collision angles it can reach temperatures sufficient to melt the surfaces to be joined. This effect was proved using a tracer material that is detectable on the witness pins after welding. The formation of the CoP is reduced with increasing yield strength of the material and the escape of the CoP is hindered with increasing surface roughness. Both effects make welding with low-impact velocities difficult, whereas weld formation is facilitated using smooth surfaces and a reduced ambient pressure under vacuum-like conditions. Furthermore, the absence of surrounding air eases the process observation since exothermic oxidation reactions and shock compression of the gas are avoided. This also enables an estimation of the temperature in the joining gap, which was found to be more than 5600 K under normal ambient pressure.

High-velocity impact welding is a kind of solid-state welding process that is one of the solutions for the joining of dissimilar materials that avoids intermetallics. Five main methods have been developed to date. These are gas gun welding (GGW), explosive welding (EXW), magnetic pulse welding (MPW), vaporizing foil actuator welding (VFAW), and laser impact welding (LIW). They all share a similar welding mechanism, but they also have different energy sources and different applications. This review mainly focuses on research related to the experimental setups of various welding methods, jet phenomenon, welding interface characteristics, and welding parameters. The introduction states the importance of high-velocity impact welding in the joining of dissimilar materials. The review of experimental setups provides the current situation and limitations of various welding processes. Jet phenomenon, welding interface characteristics, and welding parameters are all related to the welding mechanism. The conclusion and future work are summarized.