Influence of spot time on solidification behavior in cold gas tungsten arc welding of copper–stainless steel joints

Welding copper to stainless steel is inherently challenging due to their contrasting thermophysical properties and the immiscibility of the Cu-Fe system. This study introduces a novel Cold Gas Tungsten Arc Welding (CGTAW) technique, featuring reduced heat input and controlled arc shutdown, to improve the quality of dissimilar copper-stainless steel joints. A full-factorial experimental design evaluates the effects of spot time, welding speed, and takt time on material intermixing and defect formation. Results show that spot time critically influences fluid flow and weld pool stability, while takt time and welding speed modulate the intensity of mixing and defect development. Complete arc shut-off mitigates solidification cracking and porosity by promoting rapid solidification and minimizing copper dilution. The microstructure shows steep concentration gradients with spherical gamma-phase inclusions in the fusion zone. The shape and arrangement of these inclusions are primarily influenced by fluid flow during welding. The mechanical performance primarily depends on the balance in the distribution and shape of the gamma-phase within the welds. These insights underscore the role of thermal cycles and fluid dynamics in determining weld quality in CGTAW.