The effect of dynamic oxide film on interface characteristics of Al-Mg dissimilar hybrid heating-electromagnetic pulse welded joints

Al/Mg dissimilar metal welded structures are widely used in vehicle manufacturing due to their lightweight and high-strength advantages. Electromagnetic pulse welding of Al/Mg dissimilar metals encounters challenges such as a narrow process window and the difficulty in balancing welding quality and efficiency. This paper investigates the impact of the Al/Mg interface layer's state on enhancing interface performance through substrate preheating treatment. It also explores the interface control mechanism of intermetallic compounds (IMCs) in heating-electromagnetic pulse hybrid welding. The interface of Al/Mg dissimilar joints appears wavy if the substrate is not preheated. Preheating the substrate results in a flat interface and a significantly thicker IMCs layer compared to when preheating is not used. For Al/Mg dissimilar joints, preheating the substrate increases the maximum tensile force to 3.28 kN, roughly three times higher than without preheating. The analysis of the fracture morphology shows that the hybrid joint fractures at the necking point of the flyer plate. However, without preheating the substrate, the effective weld length is only 43%. In summary, the IMCs interface control in Al/Mg dissimilar metal hybrid welding is divided into two stages. During the IMCs generation stage, the substrate is preheated, and the flyer plate is rapidly moved to the substrate by electromagnetic force. The surface oxide film is broken by the combined effects of the metal jet from the electromagnetic force and high-temperature heat, allowing direct contact between the dissimilar metals and the formation of IMCs. In the IMCs growth stage, preheating enhances the atomic diffusion rate between the substrate and the flyer, increasing the thickness and uniformity of the IMCs layer. Simultaneously, the plastic deformation of the substrate decreases, creating a flat interface. This reduces the hindrance to the impact stress wave energy, increases the effective weld length, and ultimately enhances process stability and joint shear strength.