Effects of Electric Current Intensity on Microstructure and Mechanical Properties of Steel-Aluminum Electric Assisted Pressure Welding Joints

Using electric assisted pressure welding technology, axial pressure and pulse current are simultaneously applied between 45 steel and 6061-T6 aluminum alloy, providing mechanical plastic deformation and rapid Joule heating to the local area of the welding joint, achieving efficient and controllable welding of the welded joint. The effect of welding current intensity on the microstructural transformation and mechanical properties of the welded joints was studied. The relationship between welding process, microstructure, and mechanical properties was analyzed through microscopic analysis, mechanical testing, and combined with ABAQUS thermal-electric-mechanical multi-field coupling simulation. The findings reveal that increasing welding current intensity markedly accelerates interdiffusion rates at the steel-aluminum interface, fostering the formation and evolution of interfacial metallic compound layers. At a current level of 1.85 kA, the welded interface primarily comprises Fe₃Al, FeAl, and Fe₂Al₅ intermetallics. However, when elevating the current to 1.95 kA, the type of interfacial compounds has transformed into Fe₃Al, FeAl₂ and FeAl₃. The fracture load of the welded joint first increases and then decreases with the increase of welding current intensity. Under the current of 1.90 kA, the welded joint exhibits a maximum peak fracture load of 2.7 kN. However, excessive high current intensity promotes the dissolution of strengthening phases in the 6061-T6 aluminum alloy, diminishing the base metal's strength and ultimately resulting in ductile fracture of the Al alloy base metal during tensile test, with a fracture tensile strength of roughly 289 MPa.