A strategy to achieve weight reduction that is receiving more and more attention in the car industry is the combination of materials with different properties. Multi-material design leads to weight savings and cost reduction. Thus, it is necessary to develop the joining of dissimilar materials to provide multi-material design feasibility as happens with aluminum and steel.

The process of joining steel and aluminum remains a complex challenge, primarily due to the notable disparities in their melting points, thermal expansion coefficients, and thermal conductivity, as well as the virtually negligible solubility of iron in aluminum. This limited solubility results in the formation of brittle intermetallic compounds (IMCs) at the interface of aluminum and steel, which can significantly impair the mechanical integrity of the joint. Laser welding emerges as a highly competitive technique, offering elevated energy densities that lead to moderate heat input, coupled with enhanced productivity and adaptability. However, despite its successful application in joining aluminum to steel, the high complexity and associated costs continue to hinder widespread industrial adoption of this technology. This article provides a concise overview of the latest advancements and challenges in the laser joining of aluminum alloys to steel. Furthermore, it introduces a novel method for achieving butt joints between aluminum and steel, followed by an in-depth microstructural and mechanical analysis of the resulting connections.