*1.2. Magnetic Pulse Welding*

In MPW, the sudden discharge of a capacitor generates very high electric currents through a coil, leading to a very high magnetic field pressure that accelerates toward one another the parts to be welded. Welding of a wide range of similar and dissimilar materials in different MPW configurations have been reported. For example, Okagawa and Aizawa [7] proposed a parallel MPW configuration that led to seam welds between 1 mm thick aluminum sheets. They experimentally studied the seam weld shearing strength and observed its dependence on the kinetic energy of the sheets before the collision and magnetic pressure after the collision. Watanabe et al. [8] obtained lap joints for aluminum flyer plates and iron, nickel, and copper base plates. They reported that exceeding a certain level of discharge energy resulted in a decrease in amplitude and wavelength of material interflow at the weld interface. Lee et al. [9] produced lap joints between 1.2 mm thick aluminum flyer plates and 1 mm thick low-carbon steel plates using MPW. They observed a slight flattening of the grains of aluminum plates in the vicinity of the weld after impact, but no change was apparent in the grain structure of the steel plates. Their nano-indentation hardness tests revealed increased hardness in the intermediate layer between the plates. Ben-Artzy et al. [10] showed that, in tubular MPW joints, reflected shock waves generate interference waves along the weld interface, and that the wavelength of interference waves is proportional to the free path of the shock wave propagation (the first path between front face and back surface) on the interior side of the weld. Göbel et al. [11] made a comparison between the physics involved in EXW and MPW. They reported that in MPW the impact velocity and angle changes along the weld, and that wave creation is possible at lower velocities in MPW compared to EXW. This allows for different welding windows (in terms of impact angle and velocity) in MPW and EXW. Raoelison et al. [12] performed an Eulerian simulation of MPW assuming a linear flyer velocity distribution having a mean value of 600 m/s for aluminum workpieces. They predicted thermomechanical material flow in the form of particle jetting. Cui et al. [13] proposed a method for MPW of 1.4 mm thick carbon-fiber-reinforced plastic and 1 mm thick aluminum tubes. They numerically imitated the MPW process using a coupled electromagnetic and mechanical simulation with constant stress elements.

### *1.3. Vaporizing Foil Actuator Welding*

In VFAW, a sudden capacitor-discharge generates a very high current through a thin conductor foil, vaporizing it almost instantaneously. This creates a very high-pressure plasma, which accelerates the flyer plate towards the target plate. The technique was introduced by Vivek et al. [14] in 2013. They successfully welded copper to titanium, copper to steel, aluminum to copper, aluminum to magnesium, and titanium to steel. Moreover, they quadrupled the weld strength of the titanium/steel combination by introducing a thin nickel interlayer. Hahn et al. [15] attempted an experimental comparison of VFAW and MPW and achieved success only for VFAW. Using the same charging energies of the pulse generator, with VFAW they reached velocities three times those for MPW. Vivek et al. [16] demonstrated two VFAW experiments to join copper sheets with 3 mm thick zirconium-based bulk metallic glass (BMG). In one experiment, the 0.5 mm thick copper sheet was directly launched towards the BMG, resulting in a straight welded interface. In the other experiment, a 0.5 mm thick titanium sheet was first launched towards a 0.25 mm thick copper sheet, consequently launching it towards the BMG, which resulted in a wavy weld interface and no devitrification of the BMG. Nassiri and Kinsey [17] created 2D simulations for VFAW of 2 mm thick flyer and 3 mm thick base plates of aluminum using ALE and SPH methods. In both methods, an initial constant flyer velocity and impact angle were assumed. While the SPH method was able to simulate material jetting, it was found to be less accurate compared to ALE. Nassiri et al. [18] conducted a similar comparison study for VFAW of 0.5 mm thick titanium flyer and 1 mm thick copper plates. They validated the ALE and SPH simulation results through VFAW experiments. ALE was deemed incapable of mimicking material vorticities. Chen et al. [19] machined slanted grooves in 6.3 mm thick steel plates at different angles ranging from 8 to 28 degrees and joined them to 0.508 mm thick aluminum flyers using VFAW. They used this technique to control the impact angle, and thus obtained various morphologies at the weld interface. In a separate study [20] that implemented this procedure, aluminum flyer plates of the same thickness were welded to 1.905 mm thick titanium plates. Gupta et al. [21] applied the same technique and similar foil thicknesses in VFAW of copper to titanium, and vice versa. They created an explicit thermomechanical Eulerian simulation with no slip in contact of Eulerian parts but again assuming a constant initial flyer velocity. It was shown that for capture of interfacial waves, sufficient mesh refinement must be implemented. Groche et al. [22] designed an experiment for process window acquisition in HVIW. They used 2 mm thick aluminum workpieces and reached total normal impact velocities up to 262 m/s (131 m/s for each workpiece). It was shown that in cases where the collision point velocity exceeds the speed of sound in aluminum, jetting would not occur, resulting in no bonding.
