## 3 Results and Discussion
To study the chemical composition of samples, the EDS analysis of these regions shown in Figure 6 was performed from places indicated by the green circle in Figure 5. The EDS spectrum of sample A was depicted in Figure 6a, and the results suggest that this pink region is composed of a Mg-Al\({}_{12}\)Mg\({}_{17}\) eutectic compound. The EDS analysis of the continuous LMC layer of sample B in Figure 6b shows that the liquefaction zone formed a eutectic phase which is composed of Mg and Al\({}_{12}\)Mg\({}_{17}\) and a continuous layer consisting of Al\({}_{12}\)Mg\({}_{17}\) and Al\({}_{12}\)Mg\({}_{2}\) was formed adjacent to the Al layer. The EDS spectrum of sample c, as shown in Figure 6c, provides confirmation that at the interface of AA1050 and AZ91, the presence of Al\({}_{3}\)Mg\({}_{2}\) has been detected, indicating the formation of a continuous layer. The EDS analysis of sample D, Figure 6d, revealed that Al\({}_{12}\)Mg\({}_{17}\) was formed at the interface of AA1050 and AZ91. Moreover, fragments of AA1050-AZ91 intermetallic phases are dispersed in AZ91 matrix, whereas in AA1050 matrix dispersion of AA1050-AZ91, intermetallic phases cannot be detected. The formation of a brittle intermetallic compound (IMC) layer at the boundary between the base metals is the most critical issue that limits the strength of the dissimilar FSW joint between AA1050 and AZ91. The tensile test results, as a function of displacement, are presented in Figure 7a and the highest obtained UTS for samples is presented in Figure 7b. An illustration of the fracture path was schematized in Figure 7c. A great difference can be observed in some samples indicating that welding parameters influence the fracture strength. The fracture samples were precisely examined, and the fracture area was schematically shown in Figure 7c for all samples. It is noticeable that the fracture for  
Figure 5: The SEM images of (**a–d**) sample A–D, respectively. The continuous layer, liquefaction region, and eutectic structure were marked in the panels. In panel (**d**), a formed cavity is highlighted in orange. sample A took place across the eutectic zone. Similar to sample A, the fracture in sample B was placed in the eutectic zone as shown schematically in Figure 7c. Despite the presence of a continuous layer of intermetallic compounds, the fracture did not occur through this layer due to a low thickness of this continuous IMC layer. In this sample, the liquidation during welding caused a decrease in the friction coefficient which in turn decreased the heat generation during welding [34]. Furthermore, the formation of a eutectic microstructure impeded the growth of a thick IMC layer due to hindering diffusion and activity of elements which is consistent with another study [37]. Thus, it could be concluded that a lower local temperature during welding and eutectic formation leads to the formation of a thinner intermetallic compound at the interface. The illustration of the fracture place for sample C demonstrates that the fracture took place at the interface of Al\({}_{3}\)Mg\({}_{2}\) and Mg. According to Figure 7c, for sample D, it can be seen that the fracture was propagated at the interface of Al\({}_{12}\)Mg\({}_{17}\) and Mg. Some brittle regions at the fracture surface can be observed which is due to the dispersion of intermetallic phases in Mg matrix as seen in Figure 5d. It is documented that the fracture location (Figure 7c) occurred through the bonding interface which is mainly attributed to presence of brittle IMCs at the Al/Mg interface, adversely affecting the joint quality. Meticulous investigation of tensile test of samples (Figure 7a) revealed that three types of trends can be derived: (1) when tool rotational speed is steady (i.e., samples A and B), a sample with lower welding traverse speed (sample A) shows a higher, ultimate tensile strength (UTS); (2) at constant welding traverse speed (i.e., samples A and C), the lower rotational speed (sample C) resul  
Figure 6: (**a–d**) The EDS spectrum of A–D, respectively.