## 3 Results and Discussions
Figure 5: **(a)**The micrograph of \(\alpha 0\) using SEM with a 50x magnification, **(b)** 300x magnification, **(c)** color composite of SEM/EDS maps (backscattered electron), **(d)** map of O, **(e)** map of C, **(f)** map of F, **(g)** map of Cu, **(h)** map of Zn using EDS., **(i)** Elements composition of welded joint. SEM/EDS photos for the interface of the \(\alpha\)2 specimen are shown in Figure 7. There are many porosity, voids, and bubbles. The high O element provides the local corrosion. Compared to \(\alpha\)0, only bubbles exist in \(\alpha\)2 and no pits are available. The bubbles certainly cause the joint to become porous and fragile. To evaluate the porosity, the analysis of the surface photo is shown in Figure 8. In the \(\alpha\)2 specimen, the tapered surface of brass makes it easier to melt and coalesce to the steel surface. By nature, the steel (Fe) easily reacts with the oxygen in the HNO\({}_{3}\)[26]. These two phenomena can trap the air in the interface. The higher Fe content in \(\alpha\)2 specimen increases the possibilities of the air trapped in the joint. The lesser amount of porosities, voids, and bubbles in \(\alpha\)1 compared to \(\alpha\)2 specimens confirms the stronger joint of the tapered steel configuration (\(\alpha\)1). The quantitative analysis of pores was carried out using Phenom Photometric analysis which is attached as Supplementary Materials of this paper. The mean pore size of \(\alpha\)0, \(\alpha\)1, and \(\alpha\)2 are 44.7 \(\upmu\)m, 42.5 \(\upmu\)m, and 39.8 \(\upmu\)m, respectively. Many pores are found in the \(\alpha\)2 specimen with the lowest diameter. The distribution can be seen in Figure 8. \(\alpha\)0 exhibits 22 pores with an average pore area ratio of 9.09%, calculated for one image. Observing the \(\alpha\)1 image, six pores with an average pore area ratio of 1.13% are found, calculated for one image; whilst 23 pores are found for \(\alpha\)2 with an average pore ratio of 4.96%, calculated for one image. The higher pore area ratio indicates the weaker welding joint. The \(\alpha\)0 specimen shows a big amount of porosity since no melting existed at the steel and brass interfaces. Gaps on the interfaces take place in pore forms. The existence of a gap indicates that there is trapped air that forms visible pores. Big porosity on the welded joint enables a long crack in form of a line, and the product of corrosion spread over the joint surface. Based on microphotograph only, the strongest  
Figure 6: Micrograph of \(\alpha\)1 using SEM with (**a**) 50x magnification, (**b**) 300x magnification, (**c**) color composite of SEM/EDS maps (backscattered electron), (**d**) map of O, (**e**) map of C, (**f**) map of F, (**g**) map of Cu, (**h**) map of Zn using EDS, (**i**) Elements composition of welded joint. joint may be provided by the \(\alpha 1\) specimen since this joint has the smallest porosity ratio. This confirms the macrophotograph of Figure 4 and the SEM/EDS analysis of Figure 3.0 On the \(\alpha 2\) specimen, more porosity can be seen compared to \(\alpha 1\). Although melting takes place at the interface of steel and brass, higher porosity and impurity decrease the strength of the joint. The decreased diameter and lower melting point of brass produces more brass deposit on \(\alpha 2\) than on \(\alpha 1\). In short, it can be said that the result of the SEM/EDS and porosity analysis supports the results of the SCC test: the strongest joint is obtained from the \(\alpha 1\) configuration followed by \(\alpha 2\) and \(\alpha 0\), sequentially. Figure 3.1 Porosity diameter and distribution of the welded joint with varied surface configuration. Figure 3.2 (**a**) The micrograph of \(\alpha 2\) using SEM with a 50x magnification, (**b**) 300x magnification, (**c**) color composite of SEM/EDS maps (backscattered electron), (**d**) map of O, (**e**) map of C, (**f**) map of F, (**g**) map of Cu, (**h**) map of Zn using EDS, (**i**) Elements composition of welded joint.