Numerical Modeling of the Inclusion Behavior during AC Flash Butt Welding

The entrapment of inclusions in the solidified weld zone is detrimental to its mechanical properties. In an AC flash welding process, the upsetting rate, the initial temperature of the weld pool, and the size of inclusions may affect the final distribution of the inclusions. Additionally, the concentration of sulfur may induce Marangoni convection in the weld pool, which possibly affects the pushing and engulfment of inclusions by the solid at the solid-liquid interface. In the present work, a two-dimensional numerical model based on Computational Fluid Dynamics (CFD) has been developed to investigate the behavior of alumina inclusions during the AC flash welding of a thin SPFH590 steel plate. The Volume of Fluid (VOF) numerical model was coupled with the dynamic mesh model for the motion of plates, discrete phase for inclusion particles and solidification model. The simulation results show that the upsetting parameters significantly affect the overall inclusion motion. A high upsetting rate pushes the inclusions away from the welded joint. The high initial flash temperature does not affect the removal of inclusions from the weld zone. A similar outcome has been noted with respect to the increase in the diameter of the inclusions. Furthermore, the predicted results show that inclusions are prone to engulfment by the solidification front under the influence of higher interfacial tension between the inclusions and melt. Nevertheless, the inclusion displacement under the influence of an interfacial tension gradient is diminutive because of the rapid solidification rate of the weld pool.