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ABSTRACT
This contribution discusses the microstructures observed in the bonding zone during electromagnetic impulse welding of similar and dissimilar alloys. Magnetic pulse welding (MPW) is accomplished by high-velocity impact between the two alloys. The impact has sufficient energy to cause the colliding metal surfaces to flow hydrodynamically when they intimately contact one another in order to promote metallurgical bonding, resulting permanent deformation with no springback. The origin of the MPW morphologies were studied by: light optical and scanning electron microscopy and the distribution of the alloying elements was measured by energy-dispersive spectrometry. The residues of metal jet emitted during MPW was also investigated and analyzed. The interface between the two components is typically wavy and displays an elevated microhardness. The interfacial zone displays discontinuities like inclusions, cracks and pores. No heat-affected zone was observed adjacent to the interface in alloys.
KEY WORDS: Magnetic Pulse Welding, Al couple, Al-Mg couple, jet, wavy interface
1. INTRODUCTION
Although not a recently developed welding technology, magnetic pulse welding (MPW) has lately gained the attention of the welding community because it enables joining similar as well as dissimilar materials in microseconds, without the need for any consumables [1]. Accordingly MPW has been growing since the 70's and there is an increasing interest in the welding process in several industrial high-volume applications, such as in the automotive and aircraft industries [2-6]. In MPW, a high intensity current (up to IMA for larger machines) discharged through a coil, initiates an eddy current in the conductive outer workpiece (Fig. 1) [6]. The result is a Lorentz force that produces repulsion between the coil and outer workpiece. Plastic deformation in the outer workpiece is initiated when the resulting stresses exceed the material's flow stress. Figure 2 shows the typical part geometry before and after the welding process. Note that the welded area is always accompanied by deformation of the outer component, as shown in the figures. The repulsion between the two magnetic fields accelerates the outer component across the standoff gap (1-3 mm), resulting in an impact at high collision velocity (>300 m/s) with the inner workpiece [1], [6]. The resultant impact creates very high-localized pressures (up to 10 GPa) which travel away from the collision point at the acoustic velocity of...