Interlayers in Resistance Spot-Welded Lap Joints: A Critical Review

This paper presents a review of various interlayers employed to enhance the properties of similar and dissimilar materials welded by resistance spot welding (RSW). The commonly used base materials are steel, Al alloys/steel, Al/Al alloys, Al/Ti alloys, Al/Mg alloys, etc., and the interlayers proposed by various researchers include Zn, Ni, Sn, galvanised steel, SS304, Al–Mg, AlSi12, graphene, carbon nanotube, etc. Microstructural changes due to the incorporation of various interlayers were observed, and the enhancement of different mechanical and surface properties was studied focusing on the weld joint. It also includes weld bonding, the role of different process parameters on the properties of the weldment, failure modes observed in tension or lap shear tests. Studies have shown that increasing the welding parameters and incorporating suitably selected materials in between the mating surfaces of the lap joint can significantly enhance the quality of the joint. For the dissimilar RSW of Al/steel, the usage of optimised morphology of the electrodes, RSW with the incorporation of cover plates, and the usage of various interlayers were observed to subdue the brittle intermetallic compounds formation and enhance the quality of joint in case of Al/Mg alloys.