# A Literature Survey on Electrical-Current-Assisted Friction Stir Welding
## 5 EA-FSW of Similar Joints
### EA-FSW of Aluminium Alloys  
Aluminum alloys are widely used in various industries due to their lower melting temperature compared with other metals, outstanding mechanical performance, good weldability, and high corrosion resistance [46]. Until now, two pieces of literature considered EA-FSW of aluminum alloys. The lack of penetration (LOP) defects in the conventional FSW process appear at the bottom of the stir zone [47]. LOP is a common defect in the FSW of aluminum alloys that formed due to a slightly shorter pin length than the thickness of the weld metals. The LOP results from poor material flow at the bottom of base materials. The study on the effects of electrical current assistance on the LOP during the FSW of aluminum alloy was considered for the first time by [PERSON] et al. [28]. They performed 800A electrical current during FSW of the AA6082-T6 aluminum alloy sheet. The result shows that the electrical current during FSW effectively reduced the LOP defect at the root of the stir zone. The higher heat input in the stir zone caused the materials to flow and increase in the root of the stir zone. The electrical resistance of the joint line increased the internal heat, and the aluminum alloy was plasticized further. The higher plasticized phase means the softening and stirring actions to soften the metals are easier. [PERSON] et al. [29] investigated the EA-FSW of 4 mm-thick AA6082-T6 aluminum alloy. Root defects are common when aluminum alloys are welded using a friction stir welding process. The lack of penetration and the alignment of oxide particles and/or second-phase particles are common root defects in this case, where the latter is more difficult to detect and eliminate. Machining the root and double-sided welding using bobbin tool welding are examples presented in the literature to overcome these defects. The application of a high-density electrical current in FSW promotes viscoplasticity of the material, and the probability of the formation of root defects decreases as a result. [PERSON] et al. [30] investigated various input electric currents on the properties of the AA2219 aluminum alloy EA-FSW joint. They tested the 0-600 A direct current on the mechanical properties of the final joint. The first difference between the joint welded by FSW and EA-FSW was that the temperature difference in the advancing side (AS) and retreating side (RS) in EA-FSW was more than in the FSW case. The hardness of the joint welded by EA-FSW was also greater than the FSW case. In the electrical current range used by [PERSON] et al., the joint welded with 100-400 A has improved tensile strength by 2.74-7.38%, respectively, but the joint welded by 600A has significantly improved tensile strength by 17.11%. They also reported that it promoted hardness for weld zones, especially on the advancing side. Higher joint strength was achieved when higher current intensity was applied (500 A to 600 A). The bigger overall joint area and especially bigger thermo-mechanical affected zone (TMAZ) and heat affected zone (HAZ) and weld nugget zone (WNZ) were evident in the joints. The failure zone was the boundary of the nugget zone and TMAZ on the advancing side, and the nugget zone on the retreading side for FSW- and EA-FSW-welded joints, respectively. The discontinuity of different zones in the microstructure is the reason of starting failure in this zone. When a higher current intensity is used, the dimples are larger and deeper. Larger and deeper dimples are formed when the material represents more ductile behavior under loading. When a higher current is applied, the material is deformed in a higher temperature which maintains its ductility. A refinement of Al\({}_{2}\)Cu precipitates and more homogenous distribution of them are results of applying an electrical current. When an electrical current is introduced to the nugget, the material experiences a higher temperature, which makes it less strong, and with the application of a lower shear stress it is possible to flow the material.