Brazing of high-strength steels: Recent developments and challenges

Zinc-coated high-strength steels (HSS) and advanced high-strength steels (AHSSs) are widely employed in automobile body manufacturing owing to their impressive metallurgical and mechanical characteristics. However, acquiring defect-free and mechanically sound welding joints is still quite challenging due to the formation of various defects, namely porosity, loss of coating, and the evolution of undesired microstructural phases in both the heat-affected zone and the fusion zone. The higher heat input during conventional fusion welding processes tends to exacerbate these challenges. Brazing, sometimes referred to as weld-brazing, is a comparatively new joining process that offers the ability to join thin and zinc-coated steel sheets with a significantly lower heat input using a compatible lower melting temperature filler wire, has been proposed as an alternative to fusion-based joining techniques. However, under-matching, i.e., mechanically weaker brazing filler than that of the base metal, limits the widespread application of brazing. In this regard, several developments have been reported to overcome under-matching by changing the filler composition, coating composition, and joining methodology. This comprehensive review highlights the key challenges associated with steel-to-steel brazing, while offering a detailed survey of various methods that can be used to improve the performance of brazed joints.