The welding of dissimilar materials with variation in thickness and composition has been a focus in industries such as automotive, shipbuilding, and others. This is due to their complex design requirements that need to be strong and lightweight. Conventional fusion-based methods are unable to join dissimilar metals well due to physical and thermal material properties. Friction stir weldingFriction stir welding, a solid-state welding process, has been used to weld dissimilar materials, such as A572 steel and 6061-T6 aluminumAluminum. However, friction stir weldingFriction stir welding has often resulted in low joint efficiency, mainly because of root defects in butt welding and hook features in lap welding. To address these issues and to increase joint efficiency, this research utilizes a butt-lap configuration. After welding with this configuration, microstructural characterizationCharacterization and mechanical testing were performed on samples from the weld joints. The results reveal this configuration promotes uniform material mixing in weld nugget, leading to improved joint efficiency. The enhancement in mechanical propertiesMechanical properties may be attributed to the controlled interaction of the tool with steel, the formation of fragmented intermetallic compounds, a larger welding area, and superior interface quality.