## 3 Results and Discussion
### Continuous Welding Process and Electrode Sticking
In the case of the as-received electrode, the sticking of the electrode was alleviated by increasing the electrode force, as shown Figures 11 and 12. However, in the case of the abraded electrode, sticking at different electrode forces did not change significantly, as shown in Figures 13 and 14. Under the conditions of this study, this may be because the effect of the electrode surface roughness on the sticking of the electrode was greater than that of the electrode force. The difference in sticking between the (\(+\)) and (\(-\)) electrode faces was attributed to the fact that the electrode surface roughness on the sticking of the electrode was not affected by the effect of the electrode surface roughness on the sticking of the electrode. Figure 10: Measured tensile shear strength during continuous RSW under the electrode force of 600 kgf. Figure 9: Measured tensile shear strength during continuous RSW under the electrode force of 400 kgf. the thermoelectric effect, such as the Peltier effect, which causes a difference in the amount of heat generated, depending on the current direction when the current flows in the contact region between dissimilar metals [11]. More specifically, when a direct current (DC) flows through the two metals in contact with each other, a temperature difference occurs between the positive pole and the negative pole. This effect is referred to as the Peltier effect, results in wearing or sticking of the electrode, and can lead to the formation of irregularly shaped nuggets. Since the Peltier effect occurs when the current flows in only one direction, it can be solved by applying an alternating current (AC). Electrode sticking occurred because the nugget melted more rapidly in the thickness direction than in the radial direction of the base material during the continuous RSW process. Therefore, the effect of the electrode surface type on the growth of nuggets in the thickness direction of the base material was investigated. Figure 11: Carbon imprints of the as-received electrode at the electrode force of 400 kgf during continuous RSW. Figure 12: Carbon imprints of the as-received electrode at the electrode force of 600 kgf during continuous RSW. Figure 13: Carbon imprints of the abraded electrode at the electrode force of 400 kgf during continuous RSW. Figures 15 and 16 show the nugget height and cross-section measurement results of welds produced with both the as-received and the abraded electrodes at different electrode forces during the continuous RSW process. At 400 kgf, the height of the nuggets produced with the as-received electrode was mostly 2.5 mm and it slightly increased at certain weld numbers. On the other hand, for the welds produced with the abraded electrode, the nugget height was about 1.7 mm at weld number 2, at 400 kgf and it gradually increased with increasing weld numbers; the height was about 2.6 mm at weld number 47. When the electrode force was increased to 600 kgf, the height of the nuggets produced with the as-received electrode was around 2.5 mm, except at weld number 37. For the welds produced with the abraded electrode, the nugget height was about 1.7 mm at weld number 2, similar to that measured under the electrode force of 400 kgf; however, the nugget height increased with the increase of the weld number, and its value was similar to that obtained using the as-received electrode at weld number 32. In the case of the as-received electrode, sticking occurred due to the nugget growth in the thickness direction and the melting of the base material over the entire thickness, as the weld number increased. In contrast, as shown in Figure 16, when the abraded electrode was used, the growth of the nugget in the thickness direction was slower compared to that observed for welds produced with the as-received electrode; therefore, the probability of sticking was reduced compared to the as-received electrode, because a molten layer did not develop on the surface of the base material.