## 2 Dissimilar FSW Experiments
The experimental conditions to obtain data for training the ANN were set with rotational speeds ranging from 1000 to 1600 rpm and feed rates from 25 to 1000 mm/min, and the experiments were conducted under a total of 24 cases. As mentioned before, the temperature was measured in 10 channels during the FSW process. Since the FSW tool was offset by 1.1 mm from the aluminum specimen during welding, the highest temperature values were measured in the channel closest to the weld line of the aluminum specimen. Table 2 shows the maximum temperature values measured using thermocouples for each process condition. The results for the 1200 RPM-25 mm/min and 1600 RPM-300 mm/min conditions were excluded because the temperature values were not measured properly during the experiment. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Rotation Speed**} & \multicolumn{6}{c}{**Feed Rate (mm/min)**} \\ \cline{2-7}  & **1000** & **500** & **300** & **100** & **50** & **25** \\ \hline
1000 & \#1 & \#5 & \#9 & \#13 & \#17 & \#21 \\
1200 & \#2 & \#6 & \#10 & \#14 & \#18 & \#22 \\
1400 & \#3 & \#7 & \#11 & \#15 & \#19 & \#23 \\
1600 & \#4 & \#8 & \#12 & \#16 & \#20 & \#24 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: FSW experiment condition for training set. Figure 4: Base material sticks to the tool probe: (**a**) before FSW; (**b**) after FSW. Figure 5: Dissimilar FSWed joint results: (**a**) FSW process without LN\({}_{2}\); (**b**) FSW process with LN\({}_{2}\). In previous studies, the temperature trend according to rotation speed and feed rate showed that when the rotation speed is constant, the temperature tends to increase as the speed of the feed rate decreases [34; 35; 36]. However, in this study, the temperature measured here shows that the lower the feed rate of the tool, the lower the temperature. Based on this result, it is believed that the lower temperature gradient as the tool feed rate decreased was caused by the increased time the FSW tool was exposed to LN\({}_{2}\) as the feed rate decreased. In addition, as shown in Figure 6, the actual FSW experiment showed that the weld surface cracked as the feed rate decreased, which is believed to be caused by heat loss due to cracking of the weld during FSW. The experimentally measured temperature data were used as heat source values in the heat transfer analysis of the finite element analysis. The tensile test was conducted using an Instron-type tensile tester (SHIMADZU, AG-IS, 5 Ton, Kyoto, Japan) at a crosshead speed of 1 mm/min at room temperature. The test specimens, which adhered to ASTM-E8 specifications, were machined using electric discharge perpendicular to the welding line, as illustrated in Figure 7. For each FSW condition, three tensile specimens were made and the tensile strength was measured as shown in Figure 7. The average value of the three tensile strengths was used as output data for machine learning in Section 4. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Rotation Speed** & \multicolumn{5}{c}{**Feed Rate (mm/min)**} \\ \cline{2-7}
**(RPM)** & **1000** & **500** & **300** & **100** & **50** & **25** \\ \hline
1000 & 367.77 & 264.9 & 219.45 & 248.04 & 145.43 & 147.3 \\
1200 & 321.66 & 251.07 & 262.96 & 216.37 & 176.81 & X \\
1400 & 362.51 & 245.92 & 210.7 & 202.24 & 188.74 & 190.52 \\
1600 & 284.9 & 261.07 & X & 168.72 & 199.82 & 157.44 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Maximum temperature data of FSW experiment condition. Figure 6: Surface results after FSW experiment with LN\({}_{2}\): (**a**) 1000 RPM-1000 mm/min; (**b**) 1000 RPM-25 mm/min.