## 3 Results and Discussion
### Microstructure of Joint  
The formation of a PZ zone at the weld interface has occurred. It cannot be validated using an optical microscope due to its thinness (Figure 7). As demonstrated in Figures 8 and 9, based on the SEM picture of the fracture surface, there was still residual of SS 316 on the zinc-only side. To ensure that the interface between SS 316 and pure zinc is formed in the PZ zone as a result of the solid-state reaction between SS 316 and pure zinc during welding. Figures 8 and 9 illustrate the mapping of pure zinc SS 316 connector elements. At the weld interface, elements Fe and Cr diffused to form the PZ zone; whereas, O and C were measured through oxidation caused by the contact between two metals. To ensure that the interface between SS 316 and pure zinc formed in PZ zone as a result of the solid-state reaction between SS 316 and pure zinc during welding. Figures 8 and 9 depict the mapping of pure zinc SS 316 connector elements. At the weld interface, elements Fe and Cr are shown in Figure 8.  
Figure 7: Hardness distribution across the weld of SS 316-pure Zn from two samples with friction time of 35 s.  
Cr diffused to form the PZ zone. O and C were measured through oxidation caused by the contact between the two metals. According to [PERSON] et al. [45], the induction of friction between the two base metals resulted in larger carbide and oxide particles. At the interface of the pure zinc fracture side for the 35 s sample (Figure 8a) and 40 s sample (Figure 8b), the dark yellow, red, light yellow, and blue curves were scattered, respectively. The 45 s sample (Figure 8c) contained only the red and blue curves. For the fracture side interface of pure zinc in the preheat-treated sample at 35 s--100 \({}^{\circ}\)C (Figure 9a), red, light yellow, and blue curves can be observed. The 35 s--150 \({}^{\circ}\)C sample (Figure 9b) and the 35 s--200 \({}^{\circ}\)C sample (Figure 9c) showed scattered dark yellow, red, light yellow, and blue curves. Figure 10 is a point analysis (EDS) of the fracture surface resulting from the tensile test. For the 35 s and 40 s samples, EDS analysis (Table 2) showed the presence of approximately Zn, Fe, O, Cr, and C. On the other hand, EDS analysis for the 45 s sample only detected Zn, O, and C. This meant that with an increase in friction time, more oxide formed on the surface of the metal and prevented the diffusion process. As for the preheated samples, which showed 35 s--100 \({}^{\circ}\)C samples, EDS analysis showed the presence of Zn, O, Cr, and C. Meanwhile, for the 35 s--150 \({}^{\circ}\)C sample and 35 s--200 \({}^{\circ}\)C sample, EDS analysis detected all (Fe, Cr, O, and C). Table 2 also shows that by increasing the preheating temperature, there was a significant increase in O and C elements. The preheating process increased the interfacial bond strength by promoting film growth. [PERSON] et al. (1997) stated that the formation of an intermetallic phase at the weld interface is a necessary condition for achieving an adequate bond formation during friction welding of dissimilar materials [50]. This intermetallic phase is produced by the diffusion of the elements present in the welded metal. However, many of the weld strength qualities that resulted from the combination of alloy components are unacceptable. This occurs during friction welding of metals with a low affinity for oxygen. Meanwhile, metals with a strong affinity for oxygen will develop an oxide layer to prevent diffusion. The strength of the welded joint, according to [PERSON] et al. (2020) is greatly influenced by the formation of a hard and brittle intermetallic phase at the interface [51]. Recent research from [PERSON], [PERSON] et al. (2020) on forming nanoscale amorphous alloys at the Al-Fe interface is one of the offers for development in the design of amorphous new alloys and dissimilar metal joining techniques [52]. Good joints are also found in AA 6103-SS 202 with an average intermetallic zone width of 0.4 mm [30].