## 2 Dissimilar FSW Experiments  
Copper and aluminum specimens were used for the FSW experiments. To simulate the FSW applied to the inverter housing of a real electric vehicle, a specimen with a mixture of butt and lap joints was used. A copper plate was FSWed to an aluminum casting, and 10 holes with a diameter of 1 mm were created to insert thermocouples at intervals of 5 to 10 mm from the weld centerline for temperature data measurement during FSW. To collect temperature data, K-type thermocouples were inserted into the hole and heat-resistant tape was used to securely fix the thermocouple. The welding tool is made of tungsten carbide material. When welding hard and soft materials in FSW, the position in which the materials are clamped affects the quality of the weld [5; 29; 30; 31]. In general, good weld quality is obtained when the hard material is clamped on the advancing side and the soft material is clamped on the retreating side [5; 29]. In addition, in the Al/Cu joint, the weld quality depends on the offset of the tool pin, and a high-quality weld face is obtained when it is offset to the Al side [32; 33]. [PERSON] et al. conducted a FSW study by fixing pure copper on the advancing side and Al 5086-H116 on the retracting side, and offsetting the tool pin to the Al side. The offset to the Al side was 0 to 0.4 mm, and the maximum weld strength was obtained at 0.2 mm offset [17]. [PERSON] et al. reported that in the FSW of pure copper and Al 1060, a good weld surface without defects could be obtained when the copper plate was fixed on the advancing side and the tool pin was offset by more than 2 mm towards the aluminum side [32]. [PERSON] et al. conducted FSW experiments on the joining of pure aluminum and copper by fixing the copper plate on the advancing side and the aluminum plate on the retracting side [33]. They reported that a sound weld surface was obtained when the tool pin was offset by 2 mm in the direction of the aluminum, and tunnel defects occurred when the tool pin was fixed in the center. Therefore, in this study, the copper plate was fixed on the advancing side and the aluminum plate was fixed on the retracting side. The welding tool was rotated clockwise and offset by 1.1 mm toward the aluminum plate so that the tip edge of the probe was located on the line where the dissimilar materials meet. Figure 2 shows a schematic and real of the overall FSW experiment. After performing the dissimilar material FSW, the cross-section was observed as shown in Figure 3. The cross-section after FSW shows a good joint at line 1 section, which is closest to the beginning of the weld. However, as the FSW progressed, internal tunneling defects were observed at 2 section, and unfilled areas on the weld surface appeared at lines 3 and 4 section. This was due to the different melting points and fluidity of the two materials, as well as the high temperature of the FSW tool, which caused the base material to stick to the tool as shown in Figure 4. The defects observed in Figure 3 are a result of the FSW tool probe no longer fulfilling its function as a stirrer and passing over the weld line. Figure 1: Flow diagram of the process. Figure 3: Specim and cross-section results after FSW. Figure 2: Schematic (**a**) and real (**b**) of the overall FSW experiment. To overcome the issue of the workpiece adhering to the FSW tool probe, a solution was devised whereby liquid nitrogen (LN\({}_{2}\)) at a temperature of \(-196\)\({}^{\circ}\)C was sprayed onto the side of the FSW tool. This was an effective method of reducing the temperature of the tool. As a result, the quality of the weld joint was visibly improved, as shown in Figure 5. Experiments were conducted under different rotational speeds and feed rates to obtain data for the construction and training of the ANN. The experimental conditions are shown in Table 1 and were performed in the order shown.