Application of response surface methodology for weld strength prediction in FSSWed TRIP steel joints

The effect of friction stir spot welding (FSSW) parameters on microstructure and mechanical properties of transformation-induced plasticity (TRIP) steel joints was investigated. The microstructure of the base metal and welding zone (stir zone, thermomechanically affected zone, and heat-affected zone) was examined using OM, SEM, EBSD, and XRD. The results of fractography of joints show that the microstructure and size of bonding ligament are the main parameters affected on the weld strength. The influence of FSSW parameters such as rotational speed, dwell time, and plunge depth on the strength of the TRIP steel joints was investigated using response surface methodology and considering bonding ligament of joints. The results of analysis of variance (ANOVA) show that the mathematical model was in good agreement with actual amounts of joints strength. Analysis of variance also determined that the plunge depth was a more effective parameter than other parameters. By optimization of the parameters, it was found that the maximum strength (9.42 kN) can be achieved by choosing of the rotational speed at 1218 rpm, dwell time at 1.65 s, and plunge depth at 0.19 mm.