A novel multi-spot structure for joining aluminum and steel dissimilar thin-walled tubes by magnetic pulse crimping

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Lightweight manufacture for dissimilar thin-walled tube structures without additional liner support has always been a challenge. A novel magnetic pulse multi-spot joining structure was proposed for the non-weight gain mechanical connection of 6061 aluminum to SPCC (Steel Plate Cold-rolled Common) steel thin-walled tubes. Mechanical properties, microscopic features, and joining mechanism of the magnetic pulse crimping (MPC) joints were explored based on simulation and experiments. Under the geometric conditions of flyer tube with an outer diameter of 30 mm and a thickness of 1 mm, the optimal preformed groove depth and discharge energy for the MPC joints were 2 mm and 16 kJ, respectively. The corresponding maximum tensile and torsional strength were 10.6 kN and 131.2 N m, respectively. The corresponding relative thinning rate of aluminum outer tube was 13 %. The failure forms of the MPC joints were all pull out and torsion out failures. During the high-speed joining of aluminum tube to steel tube, stress concentration phenomena occurred successively at the circumferential bottom fillet, axial bottom fillet, and axial upper edge of the groove. This was due to a certain height difference between the circumferential and axial directions of the groove. It was related to induction distance, discharge energy, skin effect, proximity effect, and tip effect in the coupled field. The yielding and instability of the groove in the steel inner tube would lead to a decrease in the fitting area of the aluminum outer tube filled groove and the relative thinning rate of the aluminum outer tube. This caused a decrease in the mechanical interlocking force at the groove, which was detrimental to the mechanical properties of the MPC joints. This article provides a new approach and data support for the lightweight manufacture of dissimilar thin-walled tube structures.