Dissimilar Resistance Spot Welding of Steel and Aluminium Alloy Using Ni Interlayer for Automobile Structure

A lightweight multi-material combination of steel and aluminium alloy (Al) is becoming a novel approach towards environmentally sustainable transport systems. Studies show that 10% reduction of vehicle weight results into 3-7% reduction in specific fuel consumption in IC engines and a 13.7% improvement in electric range for electric vehicles. However, dissimilar welding of Al/steel is a key challenge because of incompatible thermo-physical properties (melting point, thermal conductivity, and coefficient of thermal expansion) and low miscibility between Al and steel. The formation of brittle and hard Al-steel intermetallic compound (IMC) at the joint interface is the major concern for dissimilar welding of Al/steel. In this work, efforts are made to check the feasibility of Ni interlayer to control IMC formation at the interface of Al/steel dissimilar welded joint. Resistance spot welding is used to join low carbon steel CR01 and Al AA6061-T6 with pure Ni interlayer. Microstructure and IMC morphology of welded joints are investigated by optical and scanning electron microscope. The mechanical performance of welded joints is evaluated by tensile shear strength (TSS), failure energy and failure mode. Ni-interlayer does not have major effect on physical aspects of weld such as electrode indentation, Al thinning and steel bulging height. Two separate interfaces namely, Ni/Al and Ni/steel are formed with Ni interlayer. Higher amount of expulsion is taken place at the Ni/Al interface, resulting into lower TSS for dissimilar welding with Ni-interlayer compared to without interlayer.