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Scientific Reports volume 14, Article number: 29418 (2024 ) Cite this article 6061 T6 Aluminum Plate
Magnetic pulse spot welding based on a field shaper can effectively achieve spot welding of dissimilar metal plates by using the multi-turn flat coil and magnetic gathering through the field shaper. Through existing experimental research, it has been found that when using this method for welding, there will be a serious bulging problem in the center of the welding area, which will affect the flatness and aesthetics of the welding area, thereby affecting its application range. To solve this problem, this work proposes two different welding methods for welding dissimilar AA1060 aluminum and SS304 steel plates with a thickness of 1 mm: one based on the center opening of the flying plate and the other based on the pre-deformation of the flying plate. The causes of bulging and the effects of discharge voltage, welding gap, and inner hole radius of the field shaper on bulging size were studied. The cross-sectional morphology and mechanical properties of welded joints obtained by two welding methods were studied through numerical simulation, cross-sectional analysis, and tensile testing. The results indicated that both welding methods can successfully eliminate the bulging problem, and the point welding method based on the center opening of the aluminum plate can also reduce the minimum welding energy required for effective welding and improve welding efficiency. In addition, microscopic analysis results showed that a waveform composite interface was formed at the welding interface of the joint, and the connection performance of the welded joint was good. These two welding methods can also be extended to the welding of other dissimilar metal plates, which is of great significance for the industrial application of magnetic pulse spot welding technology based on field shaper.
In the rapid development of society today, the demand for energy saving and environmental protection in all walks of life is getting higher and higher, and lightweight technology conforms to the needs of the times and is gradually becoming a hot spot in the field of advanced manufacturing technology research1,2. Lightweight technology is an effective measure for achieving energy conservation, emission reduction, and environmental protection in the automotive industry, aerospace, and other fields3. Studies have shown that long-range missiles can increase their effective range by 20 km for every 1 kg of weight reduction; The carrying capacity of an aircraft body can be increased by 10 kg for every 1 kg of weight reduction; 75% of the fuel consumption of an automobile is related to the weight of the entire vehicle, and for every 10% drop in the weight of an automobile, the fuel consumption will drop by 6-8%, and the corresponding carbon emissions will drop by 4%. As it was specifically pointed out by several researchers that the promotion and application of lightweight alloy materials such as magnesium alloys, aluminum alloys, titanium alloys, and other lightweight alloy materials is an important way to realize the lightweight of launch vehicles, aircraft, automobiles and so on4,5,6,7,8.
Magnetic pulse welding(MPW) technology is a new type of high-speed impact welding technology developed on the basis of electromagnetic forming technology. It drives two metals to collide at high speed through pulsed electromagnetic force, causing atomic diffusion of metal materials to achieve metallurgical bonding between dissimilar metals, avoiding the above welding problems. Its welding strength is high, and there is no need to add auxiliary materials or welding pollution, which can effectively achieve welding between dissimilar metals16,17,18,19.
At present, the MPW mainly includes two categories: pipe welding and plate welding16,20,21,22. Among them, the research on the MPW of pipe fittings is relatively early, the technology is also mature, and it has also had certain industrial applications23,24,25. Relatively speaking, the research on the MPW of plates started relatively late and the technology is not mature enough, and is still in the experimental research stage23,26,27,28. Magnetic pulse spot welding(MPSW) based on field shaper can effectively achieve spot welding of dissimilar metal plates by using the multi-turn flat coil and magnetic gathering through the field shaper, which can effectively ensure the strength of the coils and improve energy utilization, and has a wide range of application prospects. Deng et al.29 were the first to apply flat plate field shaper to the MPW of plates based on the principle of magnetic pulse forming, and designed a set of spot welding devices. By using the field shaper with a radial gap to converge the magnetic field generated by the coil, a local high-intensity magnetic field is established on the surface of the plate, generating pulsed electromagnetic force to drive plate collision and achieve welding. Although this welding method can effectively achieve spot welding of dissimilar metal sheets of aluminum and stainless steel plates, the welding samples obtained with this welding device suffered from serious center bulges. On this basis, Zhang et al.30,31 optimized the welding device and increased the welding area, but the problem of bulging in the center of the welding samples still existed.
In order to solve the problem of severe bulging at the center of the welding sample in the MPSW based on field shaper, the causes of the bulging problem were first analyzed in this work. On this basis, two new point welding methods were proposed: one based on the center opening of the flying plate and the other based on the pre-deformation of the flying plate. Among them, the method based on the center opening of the flying plate eliminates the problem of bulging by removing the area with insufficient deformation at the center of the flying plate, and the method can also reduce the minimum discharge energy required for effective welding and improve welding efficiency; The method based on pre-deformation of the flying board is to eliminate the problem of bulging by compensating for the insufficient deformation of the center of the flying board. Finally, the feasibility of the two welding methods was verified through numerical simulations and experiments. In the following chapters, principles and characteristics, numerical analysis, experimental research, and microscopic analysis are reported separately.
Figure 1 shows the working principle diagram of the MPSW based on the field shaper, mainly including charging and discharging system, coil, field shaper, flyer plates, target plate and cushion blocks. The plate field shaper can concentrate the magnetic field generated by the coil into a smaller range, thereby enhancing the local magnetic field strength and eddy current density, and achieving the goal of improving the collision speed of the plate. During operation, a sharply varying pulsed magnetic field is generated by discharging the coil. The rapidly changing magnetic field induces eddy currents on the upper surface of the field shaper, which flow through the radial gap to the lower surface, where the current on the lower surface further induces eddy currents on the surface of the fly plate. The eddy currents, under the action of the pulsed strong magnetic field, generate a huge Lorentz force on the surface of the flyer plate, which drives the flyer plate to deform and move at high speed, and finally collide with the target plate to realize welding.
Principle diagram of the MPSW based on the field shaper.
The electromagnetic force F on the coil, the field shaper and the flyer plate is determined by the induced eddy current density J and the magnetic flux density B, as shown in the following equation:
The flyer plate undergoes plastic deformation motion under the action of electromagnetic force, and its motion satisfies the following equation:
where σ is the stress tensor of the workpiece, Fv is the bulk density vector of the electromagnetic force, ρ is the workpiece density, and u is the displacement vector.
To study the causes of bulging problems in the MPSW based on field shaper and propose effective solutions, a magnetic pulse welding system was designed and built. The flyer and target plates for the welding experiments were AA1060 aluminum and SS304 stainless steel plates both with a thickness of 1 mm, respectively.
The welding system consists of a pulse power supply device and a magnet device. As shown in Fig. 2, it is the structural diagram of the welding magnet device. Figure 2a shows the main structure of the magnet device, which mainly consists of a discharge coil, a field shaper, and a field shaper tray, and is reinforced with epoxy end plates and bolts. The discharge coil was made of a single-layer multi-turn flat coil with epoxy as the skeleton and tightly wound with 5 × 3mm2 square purple copper enameled wire in cross-section. To ensure the insulating strength of the coil, a layer of high-voltage insulating tape was wrapped around the outside of the original insulating layer of the purple copper conductor, the distance between turns was about 0.8 mm, the number of turns was 8 turns, and the outermost layer was reinforced with Zylon fibers of high tensile strength. The field shaper was made of Cu-Cr-Zr, which has good electrical and thermal conductivity, high hardness, wear-resistant and explosion-resistant. To prevent the bottom edge of the field shaper from being too sharp and the current density is too high, which leads to stress concentration and high temperature and damages the field shaper, a 1 mm thick step was reserved at the bottom of the field shaper during the design and processing. To fix and prevent the field shaper from deformation, the design used the same thickness of high-strength stainless steel plate to make a tray. Figure 3 shows photographs of the discharge coil, field shaper, and tray.
The welding magnet device: (a) main structure of the welding magnet device (Drawing software: Blender4.0, https://download.blender.org/release/Blender4.0/), and (b) detailed geometric parameters of the symmetric plane.
(a) Discharge coil, and (b) field shaper and tray.
A pulse power supply device was used in the laboratory’s existing capacitor-type power supply, this welding system used two 50 µF capacitors in parallel discharge, the rated voltage is 20 kV, the maximum charge and discharge energy can reach 20 kJ. Photographs of the charging and discharging system and the magnet device are shown in Fig. 4.
The welding system: (a) charging and discharging system, and (b) magnet device.
The process of the MPW is a high-speed dynamic process, and numerical modeling is undoubtedly a relatively easy and cost-effective method in order to analyze the plastic deformation behavior and collision process of the plates during the welding process. In this section, the LS-DYNA software will be used to build a 3D collision FEM-BEM model of the magnetic pulse welding process of the plates.
To simplify the modeling and save computational time, only necessary components such as coil, field shaper, flyer plate and target plate are selected for modeling the solid mesh, as shown in Fig. 5. The three-dimensional model completely reproduces the welding device used in the actual experimental process.
3D model of the MPSW device (Drawing software: LS-PrePost(R) V4.6.25, https://ftp.lstc.com/user/ls-prepost/4.6/win64/).
To save computational costs, in the electromagnetic field module, the experimentally obtained current curve can be directly loaded into the three-dimensional model for solving, and Fig. 6 shows the experimentally obtained current curve. The electromagnetic parameters of the materials used in the simulation are shown in Table 1.
Due to the high deformation rate of the aluminum plate during the welding process, this paper will select the Cowper Symonds model to characterize the effect of high strain rate on the high-speed deformation motion of the aluminum plate. The constitutive equation is expressed as follows:
where \(\sigma _{{qs}}\) denotes the stress-strain equation for AA1060-O aluminum sheet at quasi-static, \(\:{\epsilon\:}_{P}^{*}\) denotes the strain rate, and P and m denote the constants associated with the inverse and high strain rate effects, respectively, with values of 6500 and 0.2532.
As shown in Fig. 7, the real stress-strain curves of AA1060-O aluminum under quasi-static conditions were tested and fitted using a universal tensile test machine. The power exponential function is used to fit it33, and the stress-strain equation of AA1060-O aluminum plate under a quasi-static state is finally obtained as follows:
True stress-strain curve of AA1060-O aluminum under quasi-static conditions.
The stainless steel plate does not undergo high-speed plastic deformation during the welding process, so its constitutive model only needs to use the bilinear isotropic hardening model. In addition, this model is mainly used for the study of the macroscopic deformation behavior of the plates during the magnetic pulse welding process. Therefore, the mechanical strength of coil and field shaper was not taken into consideration during modeling, and it can be set as a rigid material. The structural parameters of the materials used in the simulation are shown in Table 2.
Finally, it is also necessary to set the contact surface and boundary conditions of the model by keywords. Fix the nodes at both ends of the aluminum plate and the lower surface of the stainless steel plate to restrict their movement, while maintaining free deformation in the middle of the aluminum plate.
A series of welding experiments were conducted to investigate the bulging problem. Figure 8 shows the welding sample and its cross-section obtained when the welding gap is 2 mm and the discharge voltage is 10 kV. It can be seen that the weld zone is nearly circular, while the center of the weld zone has a more severe bulging problem. The height of the bulge can even reach more than twice the thickness of the plate, and the diameter of the bulge zone exceeds half of the welding zone. wherein the bulge height is defined as the distance between the peak of the bulge and the upper surface of the aluminum plate, and the bulge diameter is defined as the diameter of the region where the bulge height is greater than zero.
Welding sample: (a) appearance diagram, and (b) sectional view.
In order to investigate the cause of the bulging problem, the induced current density, magnetic field and electromagnetic force density distributions on the surface of the aluminum plate were first simulated, as shown in Fig. 9. It can be seen that in the MPSW based on the field shaper, the presence of the center hole of the field shaper results in both the induced current and the magnetic field on the aluminum plate in the corresponding region to be smaller, and the electromagnetic force applied is also smaller, which makes it difficult to drive the aluminum plate in the region to produce a plastic deformation movement.
Distribution cloud diagram: (a) induced current density, (b) magnetic field, and (c) electromagnetic force.
Then, the plastic deformation rate and deformation state of the aluminum plate during the magnetic pulse welding process were simulated and analyzed. Figure 10 shows the velocity distribution cloud diagram and deformation state of the aluminum plate along the direction of the gap of the field shaper during the plastic deformation movement with time under the action of the pulsed electromagnetic force when the discharge voltage is 10 kV and the welding gap is 2 mm. It can be seen that as time goes on, the aluminum plate in the corresponding area of the lower end face of the field shaper continues to accelerate deformation with the increase of electromagnetic force, with a maximum deformation speed exceeding 300 m/s. Eventually, it collides with the stainless steel plate to achieve welding. The deformation rate of the aluminum plate corresponding to the center hole area of the field shaper was almost zero, and only a small plastic deformation was produced by the surrounding aluminum plate, which eventually formed a bulge in the center of the welding zone.
Velocity distribution cloud and deformation state of aluminum plate: (a) 8 µs, (b) 14 µs, (c) 18 µs, and (d) 21 µs.
Based on the above analysis, it can be concluded that due to the presence of the central hole in the field shaper, the electromagnetic force on the aluminum plate in the corresponding area is also relatively small, which is not sufficient to drive the deformation movement of the aluminum plate in that area. Although the deformation in the surrounding area can drive some deformation in that area, the effect is not significant. In addition, due to the collision and tight integration in the peripheral area, the air in the central area cannot be eliminated, and the obstruction of deformation by the air will also affect the generation of the central bulge to a certain extent.
In the MPSW based on the field shaper, the discharge voltage will affect the electromagnetic force and collision speed, the welding gap will also affect the collision speed and bulge height, and the inner hole radius of the field shaper will affect the bulge diameter, all of which will have a significant impact on the bulge size in the welding area. To study the influence of these process parameters on the size of the bulge, longitudinal section cutting was performed on the welding sample, and the height and diameter of the bulge were measured under different process parameters, and a curve graph was drawn.
Figure 11 shows the height and diameter of the bulging area of the welding sample under different discharge voltages when the inner hole radius of the field shaper is 8 mm and the welding gap is 2 mm. It can be seen that the height of the bulge region only has a slight decrease as the discharge voltage increases, while the extent of the bulge region has a significant reduction. This is because as the voltage increases, the deformation speed of the corresponding area on the lower end face of the field shaper will increase, which will increase the area of the welding area, resulting in a decrease in the diameter of the central bulge area. However, the electromagnetic force in the central hole area has not been significantly strengthened, and the aluminum plate has not yet undergone significant deformation, so the height of the bulge area has not decreased significantly.
Size of bulging zone under different discharge voltages.
Figure 12 shows the height and diameter of the bulging area of the welding sample under different welding gaps when the inner hole radius of the field shaper is 8 mm and the discharge voltage is 10 kV. It can be seen that as the welding gap increases, the height of the bulging area also increases, while the diameter of the bulging area decreases. This is because with the increase of the welding gap, a larger acceleration distance is provided for the plate, and the plate will obtain a greater deformation speed. Therefore, a larger area will collide with the stainless steel plate to achieve welding, thereby reducing the bulging area. However, the problem of small electromagnetic force and insufficient deformation in the central area still exists, and a larger welding gap will inevitably lead to higher bulging. In addition, the increase in welding gap will also lead to an increase in the collision angle of welding, which is not conducive to the implementation of welding. Therefore, it is necessary to comprehensively consider the size of the welding gap. The welding gap used in the following studies is 2 mm.
Size of bulging zone under different welding gaps.
To study the effect of the inner hole radius of the field shaper on the bulge size, field shapers with different inner hole radii were designed and fabricated. Figure 13 shows the height and diameter of the bulging area of the welding samples obtained using field shapers with inner hole radii of 4 mm, 6 mm, and 8 mm at a welding gap of 2 mm and a discharge voltage of 10 kV. Figure 14 are cross-sectional views of the corresponding welding samples taken along the direction perpendicular to the gap of the field shaper. It can be seen that as the radius of the inner hole of the field shaper decreases, the height and diameter of the bulging area will also decrease. In addition, the reduction of the inner hole radius of the field shaper will also lead to a decrease in the amplitude of the magnetic pressure on the surface of the plate, requiring a larger discharge voltage to ensure the welding strength of the plate. Therefore, it is necessary to select an appropriate inner hole radius based on the actual situation. The inner hole radius of the field shaper used in the following studies is 8 mm.
Size of bulging zone under different inner hole radii.
Cross section of bulging zone under different inner hole radii: (a) 4 mm, (b) 6 mm, and (c) 8 mm.
Through the above analysis of the bulging problem and the study of the influence of process parameters on the size of the bulge, it can be seen that the main factor leading to the bulge in the center of the welding area is still the smaller electromagnetic force on the aluminum plate corresponding to the center hole area of the field shaper, which leads to insufficient plastic deformation of the plate and the obstruction of the internal air. In view of this, this section proposed two spot welding methods, based on the center opening of the flying plate and based on the pre-deformation of the flying plate., with a view to solving the bulging problem in the center of the welding area.
This method eliminates the bulging problem in the center of the welding area by removing the aluminum plate with insufficient deformation in the welding center area in advance. By pre- opening a circular hole on the aluminum plate, the hole is placed concentric with the center hole of the field shaper during welding. When the radius of the circular hole reaches a certain value, the area with insufficient deformation at the center of the aluminum plate can be precisely removed, solving the bulging problem at the center of the welding area. In addition, due to the holes on the aluminum plate, the air inside can be discharged, eliminating the obstruction of air.
To investigate the effectiveness of the spot welding method based on the center opening of aluminum plate in solving the bulging problem, numerical simulations were first conducted to study the method from the perspective of dynamic plastic deformation collision process. Figure 15 shows the dynamic deformation collision process during welding of an aluminum plate with a center opening. t can be seen that compared with the dynamic deformation collision process during welding with unperforated aluminum plates, the deformation collision morphology of the aluminum plate is basically the same in the early stage of the welding process. However, as the collision progressed, the center area of the perforated aluminum plate gradually adhered to the stainless steel plate, and the protrusion in the center of the welding area was basically eliminated. This is due to the presence of the central hole in the field shaper, which results in a smaller electromagnetic force on the central area of the aluminum plate, which is insufficient to drive the deformation movement of the aluminum plate in that area. When the aluminum plate is not perforated, the electromagnetic force in the surrounding area is concentrated, rapidly deforming to form a weld bead, while the central area forms a bulge due to insufficient deformation; After the aluminum plate is perforated, due to the excavation of the area with insufficient deformation in the center, the aluminum plate near the center can also adhere to the stainless steel plate under the driving force of the surrounding deformation area, eliminating the problem of central bulging.
Dynamic deformation collision process during welding.
In order to investigate the effect of the central opening radius of aluminum plates on the dynamic plastic deformation collision process, numerical simulations of the collision process during welding of aluminum plates using different opening radii were carried out. Figure 16 shows the initial collision morphology and displacement distribution cloud map of the aluminum plates under different opening radii at the center of the aluminum plate. It can be seen that as the radius of the center opening increases, the initial collision morphology of the aluminum plate also changes, and the deformation displacement of the center region of the aluminum plate increases. When the radius of the aperture is increased to 8 mm, the initial collision attitude of the aluminum plate is also changed, and the position of the collision point is shifted toward the center, and the collision starts at the edge of the aperture and proceeds to the outside, which helps to eliminate the bulge.
Initial collision morphology and displacement distribution for different opening radii: (a) 4 mm, (b) 6 mm, and (c) 8 mm.
The effect of the opening radius on the collision velocity was further analyzed, and Fig. 17 shows the initial collision velocity variation curve of the plates with different opening radii. It can be seen that the spot welding method based on the center opening of the aluminum plate can not only effectively eliminate the bulging problem, but also increase the collision speed of the plate, and the increase in collision speed becomes more and more significant with the increase of the opening radius. This is due to the fact that the aluminum plate with insufficient deformation in the center is gouged out, reducing the impediment of that portion of the plate to the deformation collision of the aluminum plate in the effective welding area. In addition, the increase in collision velocity can also reduce the discharge voltage to some extent, thus improving the welding efficiency. Table 3 shows the initial collision position and velocity at different opening radii, where the collision position is the distance from the center.It can be seen that as the opening radius increases, the initial collision position gradually moves towards the center, while the collision speed increases, which is beneficial for eliminating the problem of central bulging.
Initial collision velocity curves for plates with different opening radii.
To verify the effectiveness and feasibility of this welding method, it will be further investigated by experiments in this section. Aluminum plate center opening radius is an important factor in determining the final welding effect of the method, to study its effect on the welding effect, a series of welding experiments were carried out using aluminum plates with different opening radii at different discharge voltages. In this case, the opening radii of the aluminum plates were 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, and 8 mm, respectively; and the discharge voltages of the experiments were set from 7 kV to 10 kV, with each 0.5 kV as a level, according to the existing studies. Keeping the welding gap constant at 2 mm, welding experiments were carried out at different discharge voltages using aluminum plates of each opening radius and three repetitions were performed to avoid chance factors.
The appearance of the welding samples obtained experimentally using aluminum plates with different opening radii at a discharge voltage of 10 kV is shown in Fig. 18. It can be seen that the bulge in the center of the weld area gradually becomes flat as the opening radius increases. When the opening radius reaches 5 mm, the bulge is basically avoided.
Welding samples with different opening radii: (a) 2 mm, (b) 3 mm, (c) 4 mm, (d) 5 mm, (e) 6 mm, (f) 7 mm, and (g) 8 mm.
In order to observe the effect of opening radius on the height of the bulge more intuitively, cross-sectional analysis was carried out on welding samples with different opening radii under a discharge voltage of 10 kV, as shown in Fig. 19. It can be seen that there is a significant bulging problem in the welding sample obtained from experiments using unperforated aluminum plates, while the heights of the bulge of the welding samples obtained from experiments using aluminum plates with central openings gradually decrease with the increase of the opening radius until they are eliminated. When the radius of the openings is small, the size of the bulge decreases slightly, due to the fact that the openings both reduce the obstruction of the surrounding deformed area by the central undeformed aluminum plate and eliminate the influence of internal air on the deformation. As the radius of the opening increases, the aluminum plate in the region of insufficient deformation in the center decreases and gradually fits with the stainless steel plate driven by the surrounding deformed aluminum plate. When the opening radius increases to 5 mm, the aluminum plate in the welding area is basically completely adhered to the stainless steel plate, and the welding center area is relatively flat, and the bulging problem is also solved.
Cross sectional views of welding samples with different opening radii: (a) 0 mm, (b) 2 mm, (c) 3 mm, (d) 4 mm, and (e) 5 mm.
To evaluate the effect of the center opening of the aluminum plate on the mechanical properties of the welding joints, tensile experiments were carried out on the welding joints obtained by welding aluminum plates with a center opening radius of 5 mm at different discharge voltages, and the tensile results are shown in Fig. 20. When the discharge voltage is low, the joint fails by pulling off. As the discharge voltage increases, the failure mode of the joint differs from that of the unopened welding joint in that the aluminum plate breaks away from the open hole. This is due to the opening causing a decrease in the strength of the aluminum plate at that location. As the discharge voltage continues to rise, the failure mode of the welding joint shifts to fracture of the base material, at which point the tensile strength of the joint is greater than that of the base material and can satisfy the needs of the weld.
Tensile curves of welding samples at different discharge voltages.
Through welding experiments and tensile tests on the welding samples, the welding windows at different discharge voltages and opening radii were established after the results were tallied, as shown in Fig. 21. It can be seen that when the opening radius is small, the welding situation is basically the same as when there is no opening. As the opening radius increases, the minimum discharge voltage required for effective welding decreases. This is because under the same discharge voltage, the opening reduces the obstruction of the central undeformed area to the deformed area, and the collision speed of the plate is increased, thereby reducing the minimum discharge voltage required for effective welding and improving welding efficiency.
Welding window of discharge voltage (energy)—opening radius.
The spot welding method based on the center opening of the aluminum plate can eliminate the bulging problem in the center of the welding area, but it also damages the integrity of the aluminum plate to a certain extent. In view of this, this section also proposes a spot welding method based on pre-deformation of an aluminum plate, which compensates for areas of insufficient deformation by means of pre-deformation of the aluminum plate, thereby eliminating the problem of bulging in welding.
In order to determine the size of the pre deformation of the aluminum plate, it is necessary to first determine the pre-deformation contour of the aluminum plate. The bulging section of the welding joint obtained when the discharge voltage is 10 kV and the welding gap is 2 mm was analyzed, and the outer contour dimension of the bulging area was measured and drawn, as shown in Fig. 22. It can be seen that the contour of the bulging area is approximately a conical shape with a smooth transition at the top. Next, a set of pre-deformed molds was made based on the contour dimensions of the bulging area, including stainless steel concave molds and matching convex molds. The diameter of the concave mold is about 13 mm and the height is about 2.5 mm, as shown in Fig. 23a. The aluminum plate is pre-deformed using the pre- deformation mold, and a concave groove is pre formed on the aluminum plate, as shown in Fig. 23b. Finally, the pre-deformed treated aluminum plate is used for welding experiments, in which the pre-deformed groove on the aluminum plate is placed concentrically with the center hole of the field shaper, so as to compensate for the deficiency of the center deformation of the aluminum plate through the pre-deformed dents on the aluminum plate, thus eliminating the bulging problem in the center of the welded area.
Outline dimensions of the bulging area.
Pre-deformation processing: (a) pre-deformed mold, and (b) pre-deformed aluminum plate.
The effect of different pre-deformation heights on the bulge size during actual welding was further investigated. The aluminum plates were first pre-deformed with different heights using the pre-deformation die. Then a series of welding experiments were carried out on aluminum plates with different heights of pre-deformation under a discharge voltage of 10 kV and a welding gap of 2 mm, and the cross sections of the welded samples are shown in Fig. 24. It can be seen that the center of the welding sample obtained by welding aluminum plate without pre-deformation treatment has a serious bulging problem. When welded with pre-deformed aluminum plate, the height of the bulge in the center of the welding area decreases gradually with the increase of the pre-deformed height. When the pre-deformation size is comparable to the size of the bulge contour, the pre-deformation is just able to compensate for the region of insufficient deformation of the aluminum plate, as shown in Fig. 24d, it can be seen that the central bulge area has been basically eliminated.
Cross sections of welding samples at different pre-deformation heights: (a) 0 mm, (b) 0.6 mm, (c) 1.2 mm, and (d) 1.8 mm.
The microscopic interface structure of welded joints is closely related to the mechanical properties of welded joints, which are further analyzed. As shown in Fig. 25, the micro-interfacial structure of the welded samples was observed at a weld gap of 2 mm and a discharge voltage of 10 kV. It can be seen that a waveform interface is characterized at the welded interface, and the presence of interface waves and their amplitude contributes to the mechanical properties of the welded joints.
Micro-interfacial structure of the welded samples.
The presence of an elemental transition zone was also observed at the weld interface, as shown in Fig. 26. It can be seen that a clear transition zone is generated at the weld interface, and the thickness of the transition zone is slightly smaller than the interface wave amplitude. A line scan of the interface was performed using an EDS energy spectrum analyzer, and the results are shown in Fig. 27. It can be seen that the two elements produce a clear cross over within the transition zone. The existence of the transition zone is due to the atomic migration and diffusion of the Al and Fe elements on both sides of the interface during the collision. The existence of the elemental transition zone also further indicates that the magnetic pulse welding realizes the metallurgical bonding of dissimilar metals.
Elemental transition zone elemental transition zone.
Element distribution in transition zone.
In this work, an analysis was conducted on the serious bulging problem in the welding center area of the MPSW based on the field shaper. On this basis, two new MPSW methods for dissimilar metal plates based on the center opening of the flying plate and the pre-deformation of the flying plate were proposed. The principle and characteristics were introduced, and the feasibility of two welding methods was verified through numerical simulation and experiments, and the microstructure of the welding interface was analyzed. The main results and conclusions are as follows:
The problem of severe bulging in the welding center area of the MPSW based on field shaper is due to the existence of the center hole of the field shaper, which results in a relatively small electromagnetic force on the aluminum plate in the corresponding area, which is not sufficient to drive the deformation movement of the aluminum plate in that area.
The impact of discharge voltage on the bulging area is relatively small; As the welding gap increases, the height of the bulging area will increase, but the diameter of the bulging area will decrease; As the radius of the inner hole of the field shaper decreases, the height and diameter of the bulging area will also decrease.
The welding method based on the center opening of the flying plate can eliminate the bulging problem by removing the area with insufficient central deformation, and this method can also reduce the minimum discharge energy required to achieve effective welding, improving the efficiency of welding.
The welding method based on the pre-deformation of the flying plate can eliminate bulging problems by compensating for insufficient deformation in the central area. When the pre-deformation size is equivalent to the contour size of the bulge, the pre-deformation can compensate for the insufficient deformation of the aluminum plate, thereby eliminating the bulge problem.
Microscopic analysis shows that a waveform composite interface is formed at the welded joint, and an element transition zone is also observed in the composite interface layer, indicating that magnetic pulse welding has achieved metallurgical bonding of dissimilar metals.
Data is provided within the manuscript or supplementary information files.
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This work was supported by the Natural Science Foundation of Henan province (Grant Numbers 222300420239), also supported by the National Natural Science Foundation of China (Grant Numbers 51821005).
College of Energy Engineering, Huanghuai University, Zhumadian, 463000, People’s Republic of China
Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan, 430074, People’s Republic of China
Xiaoxiang Li, Quanliang Cao & Hongfa Ding
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Hongfa Ding and Quanliang Cao supervised the team activity. All authors contributed to the study’s conception and design. Material preparation, data collection, and analysis were performed by Hang Zhang and Xiaoxiang Li. The first draft of the manuscript was written by Hang Zhang and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.
Correspondence to Hang Zhang or Hongfa Ding.
The authors declare no competing interests.
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Zhang, H., Li, X., Cao, Q. et al. Field shaper-based solutions to the bulging problem in magnetic pulse spot welding of dissimilar metal plates. Sci Rep 14, 29418 (2024). https://doi.org/10.1038/s41598-024-81135-1
DOI: https://doi.org/10.1038/s41598-024-81135-1
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