Mechanical and microstructural characterization of cold metal transfer (CMT) spot aluminium-steel weld-brazed joints

The aim of this work is to optimize the process parameters and to analyze the evolution of mechanical and microstructural properties during CMT spot weld-brazing of dissimilar materials aluminium-steel. In doing so, process parameters including hold time, hole diameter and pre-setting gap were optimized using Taguchi orthogonal design and then the microstructure of the interfacial region was characterized using optical microscopy, scanning electron microscopy and X-ray diffraction. Shear-tensile testing was performed to evaluate the load-bearing capacity of the joints. It was observed that the strength of spot weld-brazed joints is primarily dependent on the interfacial area and intermetallic compounds at the interface. High hold time and wider hole diameter resulted in poor joint strength due to excessive intermetallic formation and an unfilled region in the joint. In addition, Cyclogram revealed that the joining process was comparatively unstable for the wider hole and high hold time due to the formation of zinc fumes. The provision of a pre-setting gap in between the sheets showed a positive impact on the joint strength.