Laser techniques for dissimilar joining of aluminum alloys to steels: A critical review

The use of multi-materials structures is nowadays one of the most sought solutions to decrease weight and reduce both emission of greenhouse gases and fuel consumption in the automotive industry. Dissimilar joining of aluminum (Al) alloys to steels by fusion-based welding technologies is often difficult to achieve as a result of the significant mismatch in these materials' physical and chemical properties. Moreover, when mixed in the liquid state, hard and brittle intermetallic compounds are easily formed. Due to characteristics that include high processing speed, flexibility and energy density, multiple attempts have been made to join Al to steel using laser based processes. This thorough review article provides a comprehensive and exhausting analysis of the recent achievements and progress on joining of Al alloys to steel by various laser-based joining processes, including laser keyhole welding, laser welding-brazing, laser-arc welding, laser-assisted friction stir welding, laser roll pressure welding and joining based on laser additive manufacturing. This paper also evaluates the joining conditions, filler materials, phase constitution, microstructure, mechanical properties and joining mechanisms associated to each process. Furthermore, special emphasis is given to factors affecting the joint strength such as welding defects, joint geometry, intermetallic compounds formation and interfacial strength. The review is then concluded with an outlook providing the summary and future trends of this field.