Finite element investigation on the effect of FSSW parameters on the size of welding subdivided zones in TRIP steels

In this study, the effect of friction stir spot welding (FSSW) parameters, including rotational speed, dwell time, and plunge depth on size of the subdivided zones, which are formed by heat and strain imposed by welding process during joining of transformation-induced plasticity (TRIP) steels, was determined using finite element modeling and response surface methodology (RSM). At first, the finite element results were validated with experimental data and then the RSM was applied for developing a mathematical model which can predict the main effects of the above parameters and their impacts on the size of stir zone, thermomechanically affected zone, and heat-affected zone in 1.2-mm-thick TRIP steel sheets using data which obtained by finite element simulations. The analysis of variance was performed to check the adequacy of the developed model. A comparison was also made between the predicted and actual results. Of the three investigated parameters, dwell time was found to have great influence on the size of welding zones followed by tool rotation speed and plunge depth, respectively. Also, it was found that the maximum stir zone (SZ) + thermomechanically affected zone (TMAZ) can be obtained when selecting a proper combination of the rotational speed at 1400-1500 rpm and plunge depth at 1.94-2.06 mm.