Process Parameter Optimization in Refill Friction Stir Spot Welding of Dissimilar AA5754 and Electro Galvanized DP600 Joints

The present study features analytical and experimental results of AA5754/DP600 dissimilar joints produced by the refill friction stir spot welding of 1.5-mm-thick sheets. The selection of proper parameters for this process, such as tool rotational speed (RS), welding time (WT), tool plunge depth (PD), welding force (WF) and backing plate material played an important role in assuring weld strength. In this work, experimental tests were carried out based on the welding conditions according to Taguchi method, in order to determine optimal welding parameters and investigate the effect of those in the joint’s mechanical properties. Analysis of variance (ANOVA) was also applied to determine the individual importance of each parameter on the lap shear strength (LSS). The results showed that the use of a backing plate with high conductivity during the welding process is a critical factor for control the formation of intermetallic layer on the interface of the joints and consequently increase the mechanical properties of the joints. Additionally, the results based on lap shear strength indicated that tool rotational speed was the parameter with the largest influence on the joint shear resistance. In contrast, DT was shown to have no significant influence on the joints performance for the selected range tested.