Lap Joint of 6061 Aluminum Alloy Sheet and DP590 Steel Sheet by Magnetic Pulse Welding and Characterization of Its Interfacial Microstructure

Abstract

Lap joint sheets of 6061-T6/SPCC and 6061-T6/DP590 (Dual phase) steel were fabricated by magnetic pulse welding (MPW). Strong lap joints were achieved at discharge energy W of >2.0 kJ and gap length d of 1.0 mm for the 6061-T6/SPCC, and W of 3.0 kJ and d of 1.4 mm for the 6061-T6/DP590 steel, respectively. This result suggested that the high-collision speed is required for lap joint of the 6061-T6/DP590 steel compared with that of the 6061-T6/SPCC. Weld interface showed wavy joint interface and weld width of the lap joint sheets tend to increase with increasing of discharge energy for MPW. An intermediate layer consisted of FeAl, Fe₂Al₅ and FeAl₃ was recognized at the weld interface discontinuously, due to localized melting and a subsequent high rate cooling of molten Fe and Al confined to the weld interface. Furthermore, work hardening by accumulated plastic strain and grain refinement of Al and Fe at the welded interface were recognized by SEM-EBSD. From microstructure observation, strong lap joint of the 6061-T6/DP590 steel by MPW was thought to be due to an increase in weld width, an anchor effect, and strengthening of the weld interface by work hardening and grain refinement.