Numerical simulation of the molten pool in laser spiral spot welding of Al/Fe dissimilar metals

Laser spiral spot welding (LSSW), with precisely adjustable energy distribution, effectively increases bonding interface density and controls intermetallic compounds (IMCs) formation, serving as a key method for welding Al/Fe dissimilar structures. In this study, a three-dimensional multi-phase transient numerical model of Al/Fe LSSW was developed to elucidate the temperature evolution process and the molten pool flow mechanism during welding. The results demonstrate that the molten pool maintains an inverted triangular pyramidal morphology with curved edges, and its radius expands along the scanning path. The enhanced Marangoni stress in the outer region constrains the molten pool radius to be smaller than the scanning path radius. The flow velocity is higher in the inner ring, with a peak value near the keyhole wall. Peclet numbers are predominantly between 2 and 41 indicating that the convective heat transfer dominates the thermal transport within the molten pool. Furthermore, the molten pool of Fe, driven by the evaporation recoil pressure, impinges on the Al layer, causing partial melting and extrusion of Al into a U-shaped liquid film, which is the key mechanism for the formation of the Al-rich U-shaped solute band. In addition, thermal history analysis provides valuable insights into the solidification characteristics of the joint.