# A Literature Survey on Electrical-Current-Assisted Friction Stir Welding
## 3 Various Types of EA-FSW  
There are three main categories for the EA-FSW. The first category is called the preheating model in EA-FSW (Figure 1a), the second category is called the heat treatment model in EA-FSW (Figure 1b), and the last one is known as the combination model in EA-FSW (Figure 1c).  
The classification in EA-FSW is related to the electrical current circuit. A power supply is used in the middle of the electrical line to create an electrical current flow into the joint line, on the side of the current attached to the FSW tool (usually positive side) and another side attached to a conductive strip. If the conductive strip is placed in front of the workpiece,  
Figure 1: EA-FSW in (**a**) preheating, (**b**) heat treatment, and (**c**) combination models.  
the electrical current is imported to the joint line by the tool and exits from the conductive strip in front of the tool. In this case, the electrical resistance heated the interfaces that were not welded, and electrical current could preheat the joint line before FSW (Figure 1a). In this type, the workpieces are preheated in front of the tool, which makes the joint line metal soft, and for this reason, this type is called preheating EA-FSW. For this reason, the welding force decreases sharply, the joining process time decreases, and the working life of the FSW tool is prolonged. The type one joint is suitable for hard materials that can be softened before the FSW tool mixes workpieces. In this case, the flowability during the stirring action increases with the decreasing shear strength of base metals. Greater flowability decreases the formation of root voids and prevents surface flash formation.  
In the second type of EA-FSW, the conductive strip is placed behind the joint line (Figure 1b). In this case, the electrical current path is behind the FSW tool and causes the welded joint-line temperature to increase after welding, due to the inner resistance of the joint line. In this case, the conducting circuit caused a heat treatment effect on the joint line. In the second type of EA-FSW, the resistance heat produced by the electrical current reduces the residual stress of the joint line and the hardness, and improves the formability of the joint line for the post-metal-forming process. In this case, the joining mechanism is similar to the regular FSW, but with this type, a post-heat treatment is applied on the joint line and helps the microstructural recovery of weldments. The third type is related to the dissimilar joints (Figure 1c). In this case, the electrical current passes through harder materials to be heated up by resistance heat. In this process, the harder material became softer, and the welding procedure made a sound and defect-free joint line [24]. This type of joint increases the stirring of the hard material during dissimilar joining. The lack of mixing between dissimilar materials on the macroscale could be improved. On the other hand, overheating herded materials may lead to thick intermetallic compounds (IMC) forming, decreasing the final joint strength. Controlling input current to prevent the formation of thick IMC is the negative side of this joint.