Abstract: To reveal the internal mechanism of the radial clearance between the inner and outer tubes on the microstructure of the electromagnetic pulse welding joint interface, the formation and evolution mechanism of interface microstructure are studied by changing the radial clearance between the 304L stainless steel and T2 copper tube combined with microscopic characterization and numerical simulation. The study shows that the interface presents a wave shape, which is due to the Kelvin-Helmholtz interfacial instability effect caused by the high-speed collision. As the radial clearance increases from 1.65 mm to 2.15 mm, magnetic intensity maximum, impact speed, impact angle, the length of the wavy unbonded region and the wavelength of the wavy interface increase. Meanwhile, the stress distribution appears S shape. The interface element distribution is a combination of local high-temperature melting and element interdiffusion at less high-temperature. And the formation of the steel-copper electromagnetic pulse welding joint includes the arcing of upper surface of the outer tube, the fragmentation of the end of the outer tube, the generation of unbonded areas and the generation of bonded areas. The reason is that the outer tube undergoes different plastic deformation under the combined effect of the propagation direction, the sound wave, and the reflected wave of the shock wave.

Key words: electromagnetic pulse welding, stainless steel, copper, wave-like interface, microstructure