Electromagnetic Pulse Welding Research Articles

Microstructure and formation mechanism of the transition layer at the interface of Al–Cu EMPW joint

In the dissimilar metal welding field, electromagnetic pulse welding (EMPW) is a kind of potential technology. To further reveal the bonding mechanism of EMPW, this work carried out a Cu–Al sheet EMPW experiment with a discharge voltage of 15 kV and a gap of 1.5 mm. It analyzed the microstructure and formation mechanism of the Cu–Al EMPW joint bonding interface transition layer in detail by SEM, EDS, TEM, and FIB. The transition layer was found at the vortex zone, and there was an isolated long strip Cu particle separated from the main body of the Cu sheet. The tested results showed that the transition layer contained Al-rich intermetallic compound (IMC) Al2Cu, and some bulk particles in the transition layer were Cu-rich IMCs Al4Cu9 and AlCu4. There were Cu-rich IMCs Al4Cu9, AlCu4, and AlCu between the long strip Cu particle and the IMC transition layer. In the violent impact process between the Cu sheet and Al sheet, the Cu rapidly diffused in the Al matrix to form the Al-rich IMC (Al2Cu) as the primary transition layer, and the interface was high temperature and high pressure, forming a plastic flow and vortexes swirling. Some Cu particles separated from the Cu sheet and became the vortex piece during the plastic flow process, and continued to interact with the Al2Cu primary transition layer to form the secondary transition layer. This work could provide a basis for revealing the structure composition and formation mechanism of the Cu–Al EMPW joint interface transition layer.

Effect of DH-shaped coil symmetry coefficient on EMPW process

ABSTRACT The coil is used for electrical connection and energy conversion in the electromagnetic pulse welding (EMPW) process, so its structure affects the welding effect. In this work, for the dual H-shaped (DH) coil, the influence of the symmetry coefficient on the Cu-Al sheets EMPW was studied through the simulation and experiment. When the voltage was 7 kV and the symmetry coefficient g was 0.75, 1, and 1.33, the V c-β trajectory curve contained by the simulation combined with the welding window curve (WWC) to analyze the dynamic process and welding effect. The relative impact speed was the fastest and the corresponding weld seam length was the longest when g was 1.33. The welding experiment results were consisted with the simulation results, it was beneficial to weld the Cu-Al sheets when g was 133. The symmetry coefficient could change the impact speed and angle to affect the welding effect. This work is of great significance for DH coil design.

Microstructure characterisation of electromagnetic pulse welded high-strength aluminium alloys

Electromagnetic pulse welding is a high-velocity impact joining process employed with the intention of forming fast and effective solid-state bonds. Electron microscopy techniques, including SEM and TEM, revealed that bonding was not fully accomplished in the solid state; instead, local melting can occur. These locally melted areas likely occur around the point of first contact during the welding process and are associated with a debonded region that runs alongside or through the centre of melted zones. Microstructural characterisation showed dispersoid-free regions, columnar grains, epitaxial growth, and localised increases in O, Fe, Si, and Mn content in locally melted areas. This region contrasts with the solid-state bonded region, in which the interface exhibited sub-micron grains.

Phase transformation mechanisms of NiTi shape memory alloy during electromagnetic pulse welding of Al/NiTi dissimilar joints

The phase transformation mechanisms of NiTi shape memory alloy (SMA) during electromagnetic pulse welding (EMPW) of Al/NiTi dissimilar alloy joints were studied. Two types of amorphization behaviors were observed in the NiTi SMA of the Al/NiTi dissimilar joint. These are: i) fast cooling-induced amorphization of the joint interfacial reaction layer; and ii) severe deformation-induced amorphization. Additionally, the martensitic transformation was observed in the NiTi SMA during the high strain rate plastic deformation imposed by the EMPW process. The study shows that the formation of B19' martensite during high strain rate plastic deformation of NiTi SMA is influenced by both the strain rate and the peak pressure of the deformation during welding.

Intermetallic compounds growth and morphology evolution of Al6061/SS304 electromagnetic pulse welding joint interface during post-weld heat treatment

The effects of heat treatment on the intermetallic compounds (IMCs) and morphology at the interface of stainless steel 304 bonded to aluminum 6061 by electromagnetic pulse welding (EMPW) were investigated in this study. A thin discontinuous non-uniform wavy transition layer with an average thickness of 1.144 μm was formed at the interface of the as-welded joint. After heat treatment, the average grain size of the Al/SS304 interface grew from 6.85 μm to 7.42 μm. The thickness of the transition layer increased significantly, reaching an average thickness of 4.109 μm after heating at 210 °C for 4 h. In addition, the wavy interface grew gradually and became smooth with increasing heating temperature, suggesting the growth rate of the IMCs at the trough was greater than that at the adjacent crest. Then the effect of heating time on the growth of IMCs was studied. According to the characteristics of the transition layer and the diffusion law, the IMCs grew faster at the trough than at the crest of the transition layer. Differences in element concentration, crystal deformation, grain boundaries, dislocation density, and energy storage were observed at the trough and crest of the interface as a result of the different growth rates of the IMCs.

An Experimental Study on Deposition Mechanism of High-Speed Spraying Cu Coating Based on Electromagnetic Pulse Welding Technology

An Experimental Study on Deposition Mechanism of High-Speed Spraying Cu Coating Based on Electromagnetic Pulse Welding Technology

Research Progress of Aluminum Alloy Welding/Plastic Deformation Composite Forming Technology in Achieving High-Strength Joints.

Fusion welding causes joint deterioration when joining aluminum alloys, which limits the use of aluminum alloy components in high-end equipment. This paper focuses on an overview of how to achieve high-strength aluminum alloy welded joints using welding/plastic deformation composite forming technology. The current technology is summarized into two categories: plastic deformation welding and plastic deformation strengthening. Plastic deformation welding includes friction stir welding, friction welding, diffusion welding, superplastic solid-state welding, explosive welding, and electromagnetic pulse welding. Plastic deformation strengthening refers to the application of plastic deformation to the weld seam or heat-affected zone, or even the whole joint, after welding or during welding, including physical surface modification and large-scale plastic deformation technology. Important processing parameters of plastic deformation welding and their effects on weld quality are discussed, and the microstructure is described. The effect of plastic deformation strengthening technology on the microstructure and performance evolution, including the hardness, tensile strength, fatigue property, residual stress, and hot cracking of aluminum alloy welded joints, and its evolution mechanism are systematically analyzed. Finally, this paper discusses the future development of plastic deformation strengthening technology and anticipates growing interest in this research area.

Decouple the effect of the horizontal and vertical components of the collision velocity on interfacial morphology in electromagnetic pulse welding

Decouple the effect of the horizontal and vertical components of the collision velocity on interfacial morphology in electromagnetic pulse welding

Mechanism of the discharge behavior in electromagnetic pulse welding: Combination of electron emission and electric field

The analysis of transient phenomena in electromagnetic pulse welding is of great interest for unraveling the underlying principles. This research systematically investigates the mechanism of the discharge phenomenon by integrating finite element modeling with surface morphology analysis. The results revealed that the discharge area is discretely distributed on the surface, primarily concentrated around the welding area where the severe collision occurs. In contrast, when the collision is eliminated, the discharge is confined only to the edge. Given a fixed input energy, the discharge ablation on the surface is more pronounced for materials with a low work function. The research further establishes that both electron emission and the intense electric field contribute to the discharge behavior. This discharge behavior subsequently leads to high temperatures in the discharge area, facilitating element diffusion and shock wave generation. However, intermetallic compounds are not observed due to the brief duration of the discharge. This study illuminates the adverse effects of the collision and provides profound insights into the dynamic behaviors during welding. The findings offer valuable theoretical guidelines for the development and optimization of welding processes.

Interfacial microstructure of multi-layered Al–Cu joint by electromagnetic pulse welding

The necessity of the multi-layered aluminium (Al) tabs to copper (Cu) busbars for electric vehicle (EV) batteries is increasing. Electromagnetic pulse welding (EMPW) is applicable to the welding of conductive dissimilar/similar materials. In this work, three Al sheets and a single Cu sheet are joined by the EMPW technology. The layer-wise tensile lap shear properties of the multi-layered Al–Cu EMPW joint are evaluated. The layer-wise interfacial microstructures of the joint parallel to and perpendicular to the welding direction are studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS). The results showed that every layer achieved metallurgical bonding. The Al sheets were formed to be whole. There were three types of interfaces at the Al–Cu interface parallel to the welding direction: flat interface, wave interface, and irregular wave interface. The transition zone is found at the Al–Cu interface perpendicular to the welding direction. Due to the impact, the grains near the Al–Cu interface and Al–Al interface are both refined. Thus, the well-bonded multi-layered Al–Cu joint is successfully obtained via EMPW. The results can offer help in the manufacturing of EVs.

Interface formation and defect elimination mechanism of T2/304L interface during electromagnetic pulse welding process

Experimental and numerical methods are carried out to analyze the interface formation and defect elimination mechanism during electromagnetic pulse welding T2 to 304L tube by changing the inner tube morphology from original scheme to stage scheme, ramp stage, and location stage. When the original scheme is operated with 13mm lap length, the morphology of interface is divided into four zones containing end unwelded zone, first welded zone, central unwelded zone, and second welded zone due to the different impact velocity and angle during the initial impact process, parallel impact process, and final impact process. The parallel impact leads to the formation of the central unwelded zone, containing (Cu, Fe) solid solution, oxides, nano grains, and amorphous phase. By providing a suitable impact angle, the ramp scheme (α = 7°) and location scheme (L = 6.5 mm) can eliminate the defect in the central unwelded zone.

Interfacial defects evolution of Al 6061 / SS304 electromagnetic pulse welding joints during post welding isothermal treatment

Defects such as pores and crack are often observed at electromagnetic Pulse Welding (MPW) Al/Fe dissimilar alloys joint interface. These defects are harmful to the mechanical properties and structural integrity of the Al/Fe dissimilar alloys joints. Hereby, the formation mechanism, evolution behavior of these defects at MPW Al/Fe dissimilar alloys joint interface were systematically investigated by experimental and molecular dynamic simulation. The results indicated that the original pores at the interface due to the shrinkage of the local melting, grew and expand rapidly under the combination of temperature and stress. When heated at 150 ℃, there is annexation of the pores and passivation of the cracks. When the temperature reached 180 ℃, the pores grow severely, the cracks expanded to the radial and circumferential directions along the pores within the interface. The defects deteriorated further at 210 ℃. The MD numerical simulation was used to testify the healing and propagation of the defects.

Fatigue behavior of Al-CFRP spot-welded joints prepared by electromagnetic pulse welding

In this study, the fatigue performance of magnetic pulse welding (MPW) joints of AA5052 aluminum alloy and T300 carbon fiber reinforced polymer (CFRP) with sandwich structure was systematically investigated. Mechanical property tests and microscopic observations were used to evaluate joint performance and damage to the CFRP. The results showed that satisfactory tensile strength (up to 92.24% of the tensile strength of the base material) was obtained by optimization of discharge energy. However, the samples in the fatigue test exhibited more sensitive properties to the fatigue environment. The higher fatigue cycle life was demonstrated only when the stress amplitude Sa ≤ 20.41 MPa. The fatigue test data were analyzed by Weibull distribution to fit the S-N curves under different reliability levels, which can be used for reliability assessment and life prediction in practical applications. The CFRP surfaces in different states were studied by scanning electron microscope (SEM). It was found that MPW would not damage the surfaces, while delamination and cracking would gradually occur during the fatigue process.

Atomic diffusion behavior in electromagnetic pulse welding

• Establish molecular dynamics model to investigate the interface diffusion behavior. • A narrow diffusion zone of amorphous layer was found at the bonding interface. • Improve the theoretical basis on the bonding mechanism at the atomic level. This paper investigates the atomic diffusion behavior and bonding mechanism in a Cu-Al joint fabricated by electromagnetic pulse welding. The molecular dynamics simulation is proposed to investigate the atomic diffusion behavior. The equation of diffusion layer thickness is deduced to calculate the diffusion layer thickness according to the simulation results. The welding and transmission electron microscope experiments are carried out, and the simulation results are in good agreement with the experiments. There is a diffusion zone of amorphous layer at the bonding interface, but the diffusion thickness is narrow. So this work reveals that the inter-atomic bonding is not a major factor in electromagnetic pulse welding.

Microstructure Evolution Mechanism and Numerical Simulation of Steel-copper Joint Fabricating by Electromagnetic Pulse Welding

Microstructure Evolution Mechanism and Numerical Simulation of Steel-copper Joint Fabricating by Electromagnetic Pulse Welding

An accelerated analytical method for predicting workpiece velocity and displacement during electromagnetic forming

This paper presents complementary analytical analyses, experiments, and numerical simulations of the electromagnetic tube compression (EMTC) process using a multi-turn axisymmetric coil with a field shaper. In earlier contributions, we proposed an analytical model capable of predicting the magnetic pressure, radial velocity, and radial displacement for EMTC. In the present paper, our understanding of EMTC is expanded with the aid of a modified analytical model, a series of experimental tests with various materials, and 3D coupled electromagnetic-mechanical numerical simulations. First, the analytical model was improved by generating elements across the entire landing area of the field shaper. This modification provided a more accurate induced magnetic pressure in the analytical model. In addition, the experimentally measured coupling coefficients between the coil, field shaper, and workpiece tube were directly incorporated into the analytical model as opposed to utilizing them as correction factors during the magnetic pressure calculation in the previous studies. In the proposed analytical model, at each time increment, the magnetic field geometry is updated in response to the tube deformation. Second, to assess the proposed analytical model, experimental tests with Photon Doppler Velocimetry (PDV) were carried out for three different materials with different thermo-mechanical properties, i.e., Al6061-T6, Cu101, and Cu260 (Brass). Third, to compare the computational cost of the analytical model and to determine the accuracy of the proposed analytical model compared to the existing software packages in the market, a 3D coupled electromagnetic-mechanical finite element model was used. To investigate the influence of discharge energy on tube deformation, all three methods were examined at three different charging energies, i.e., 2.4, 3.6, and 4.8 kJ. Reasonably good agreement between all three approaches validates the ability of the analytical model to accurately capture the deformation velocity and displacement for this complex multi-physics manufacturing process in a computationally cost-effective manner. Such an analytical model can be used as a base model for predicting the impact velocity during electromagnetic pulse welding and crimping processes prior to performing expensive and time-consuming experimental tests or numerical simulations.

Evaluation model of electromagnetic pulse welding effect based on Vc-β trajectory curve

As a non-heat input solid-state joining technology, electromagnetic pulse welding (EMPW) has many advantages in the connection of dissimilar metals. Finite element (FE) methods are often used to design the EMPW equipment, explore the parameters and analyze the transient process. However, it is difficult to reflect the welding effect directly. This work proposed a welding effect evaluation model based on the welding window theory and the Vc-β trajectory curve obtained in the FE simulation. A FE model coupling the circuit-magnetic-structure field was established in COMSOL software to simulate the EMPW process of the Cu plate and Al plate. The Vc-β trajectory curve and welding traces were obtained according to the simulation results. An experimental platform WD-28 was used to carry out the welding experiments of Cu–Al plates at different discharging voltages. The welding traces were measured through SEM method and compared with the simulation results. According to the comparative result, the empirical constant of the calculation formula for the lower boundary of the welding window was adjusted into 1.6, so that the evaluation result was consistent with the experimental result. This work can provide a new method for evaluating directly the welding effect through the FE simulation results.

Electromagnetic pulse welding on a magnesium–aluminum joint: role of angle of welding

ABSTRACT Electromagnetic pulse welding technology shows a wide range of applications in welding dissimilar metals. In this work, the effect of the angle between the magnesium sheet rolling route and welding direction on the magnesium–aluminum joint has been studied. An electromagnetic pulse welding equipment WD-28 was used to weld the magnesium sheet and aluminum sheet. The angle was set to 0º, 45º, and 90º, and the discharge energy was set from 10.08 kJ to 17.92 kJ. The mechanical property of the magnesium–aluminum joints was compared. Scanning electron microscope and energy dispersive spectrometer were used to observe the microscopic morphology and element distribution of the bonding interface. Results show that the tensile strength of the joint is the highest when the angle is 0º under the same conditions. The tensile strength of the magnesium sheet, the movement of the collision point, and the metal jet during the electromagnetic pulse welding process were affected by the angle, causing the difference in the thickness of the diffusion layer, the morphology of the wavy interface, and the length of the welded zone. Moreover, the quality of the joints with different angles can be improved by increasing discharge energy.

Study on residual stress distribution of Al/Cu dissimilar metal joint manufactured by electromagnetic pulse welding

Electromagnetic pulse welding (EMPW) is a cold-welding technology to connect materials by driving the flyer plate with electromagnetic force to impact the target plate at high speed and it has been adopted to join dissimilar metals. In the present study, a dissimilar metal (2024 aluminum alloy and pure copper) joint was prepared with the EMPW. The contour method was used to get the full map of longitudinal stress distribution in the joint. The stress variation across the thickness was analyzed. The results show that the tensile stress appears at the side of aluminum alloy, and compressive stress occurs at the side of pure copper. The peak tensile stress (260 MPa) appears in the aluminum alloy plate at the location with 0.2 mm from the welding interface. The peak compressive stress in the copper plate is −254 MPa, occurring at the location with 0.1 mm from the welding interface. Within 0.3 mm, the peak tensile stress changes to the peak compressive stress, indicating a steep stress gradient across the EMPW joint. Instantaneous temperature variation, the difference between the coefficient of thermal expansion of aluminum and copper, and the metal-plastic flow induced by impact within the thin welding zone cause the steep stress gradient.

Spatial-Temporal Characteristics, Mechanism, and Suppression of Micro-Gap Discharge in Electromagnetic Pulse Welding

Spatial-Temporal Characteristics, Mechanism, and Suppression of Micro-Gap Discharge in Electromagnetic Pulse Welding