Optimization of dissimilar joining between AA 5052 and G3101 galvanized steel using pulsed cold metal transfer spot weld-brazing

In this work, pulsed cold metal transfer spot weld-brazing was used to determine the optimal conditions for dissimilar joining AA 5052 and G3101 galvanized steel. The optimal weld-brazing conditions provided the maximum weld-brazing tensile-shear strength, minimum bead height, and minimum intermetallic compound (IMC) thickness. The weld-brazing variables were the current, filler wire speed, and torch distance. Each experiment was conducted at three levels using a central composite design. A mathematical model was derived using the response surface methodology and the maximum-response desirability function. The optimal conditions for weld brazing were as follows: a current of 80 A, a filler wire speed of 6 m/min, and a torch distance of 7 mm. The tensile-shear strength was 330.0498 MPa, the bead height was 2.0103 mm, and the IMC thickness was 2.1110 µm, with prediction errors of 7.554%, 3.004% and 5.688% for the tensile-shear strength, bead height, and IMC thickness, respectively. An FeAl₅ intermetallic compound layer was observed between the filler metal and the steel substrate. The α-Al solid solution and Al-Si eutectic phases were present in the fusion of the filler metal. In addition, an Al‒Si eutectic phase occurred at the grain boundaries of the α‒Al solid solution. The best welded-brazed joint, a refinement in grain size and the eradication of substrates porosities were achieved. The extensive fusion zone aids in the efficient elimination of gas pores and prevents the occurrence of voids near the IMC layer. The fusion zone of the weld displayed diffusion of the Fe element from the steel substrate, resulting in a more considerable hardness value in comparison to the heat-affected zone and the base metal. The weld-brazing fracture mechanisms play a crucial role. The failure of the weld-brazing joint was related to fusion zone and the weld-brazing interface.