Interfacial behavior and galvanic corrosion challenges in dissimilar aluminum–steel welding for automotive lightweight applications

Steel and Aluminum for structural purposes are very important for lightweight automobiles that achieve high fuel efficiency and limit air pollution. Due to incompatibility of these metals, galvanic corrosion can occur at the junction of these metals. In domains like aviation, electric mobility, and structural engineering types of connections are equally critical. Compared to conventional brazing and fusion welding, ultrasonic welding has higher performance regulation and microstructure. Cold Metal Transfer (CMT) has emerged as an advanced modification of traditional metal inert gas (MIG) technologies for the processing of metallic materials, offering the possibility of joining similar to and dissimilar metals, with a lower thermal consumption. These differences in mechanical and corrosion properties by process parameters are defined regarding the basic processes of welding and metallurgical change in alloys. The effects of shielding gases on the mechanical properties and morphology of beads are analyzed in diverse environments. In this paper, we emphasize metallurgical, electrochemical, and industrial aspects of dissimilar welding of aluminum and steel, with a special focus on the long-term durability aspects in automotive applications. The subject involves how the mechanisms to develop intermetallic compounds (IMCs), galvanic interactions, crevice effects, surface treatments, and coatings have been devised. In order to reduce the chances of the formation of intermetallic compounds (IMCs) and improve metals’ corrosion resistance, we assess advances in solid-state techniques such as diffusion bonding, explosive welding, Friction Stir Welding (FSW), and Friction Stir Spot Welding (FSSW). The review concludes with fresh research directions for enriching ultrasonic welded dissimilar connections. For corrosion investigations of high-nickel alloys and stainless steel in pure liquid chloride salts, there are significant variations between electrically coupled and isolated specimens in degradation rates. The proximity influence may indicate corrosion effects during the operation of molten salt systems despite no direct electrical contact, therefore indicating the existence of the galvanic and non-galvanic corrosion processes. The challenge could be remedied by using interlayer materials, better junction design, processing, protective coatings, and rapid testing. The research discussion concludes with a review of techniques for developing strong and corrosion-resistant multi-material vehicle structures. It also notes some urgent concerns, such as how lifecycles can be integrated, predictive corrosion-mechanical modelling, and whether solid-state processes will be scalable to mass production.