Evaluation of the role of process parameters of CMT welding and their statistical behaviour on the tensile properties of weld joint of novel aluminium hybrid composite

The present study investigates the cold metal transfer (CMT) welding of a novel hybrid aluminium composite (AA6061-T6/ 2wt.% TiB₂/ 0.5wt.% La₂O₃) fabricated via stir casting. It analyzes the effect of welding parameters, i.e. current, travel speed, and gas flow rate, on the tensile strength of the composite’s weld joint using response surface methodology (RSM). Also, a dedicated study of the microstructure and mechanical properties of weld joints at optimal parameters has been conducted. Results indicate that current significantly affects tensile strength, followed by travel speed and gas flow rate. The optimal parameters identified are 142 A current, 9 mm/s travel speed, and 14 L/min gas flow rate for maximizing tensile strength. Welds at optimal parameters displayed no solidification cracking and minimum porosity. The microstructural analysis confirmed the presence of reinforcements in the composite with the formation of finer grains in the fusion zone (FZ) compared to the heat-affected zone (HAZ). Microhardness tests showed the highest values in the FZ and the lowest in the HAZ, while tensile tests showed reduced strength at HAZ compared to the FZ and base composite, with dominant brittle behaviour. Post-weld heat treatment improved ductility, as indicated by deeper dimples and tear ridges with fewer cleavage facets in fracture analysis.