## 4 Conclusions  
Previous studies have investigated WAAM-bimetal and WAAM-rolling separately. This study examined the variable-pressure rolling effects on wire arc additively manufactured Inconel625-SS308L bimetallic structures. Characterizations, including Vickers microhardness testing, tensile testing, SEM, and EDS, were carried out to assess the mechanical and metallurgical properties. Based on the Ferrite-Austenite mode, the solidification of 308L stainless steel commenced with the primary \(\delta\)-ferrites originating from the liquid phase, which were subsequently replaced by \(\gamma\)-austenite phases due to swift cooling. As evident in Figure 4a, under non-pressure conditions, the SS308L microstructure was characterized by dominant dendritic austenite, accompanied by residual \(\delta\)-ferrite traces, and demonstrated a shift in the dendrite growth direction with an increase in SS308L's height. This configuration was attributed to WAAM's directional cooling, which led to the appearance of columnar grains aligned to the build direction. Primarily ferritic in nature due to the filler wire's low carbon content, the SS308L microstructure witnessed a decrease in grain directionality and refinement with elevated loads. Contrarily, the Inconel625 region, illustrated in Figure 4d,e, remained entirely austenitic, a characteristic feature of Ni-base alloys. Both specimens exhibited dendritic grain growth patterns: continuous columnar grains, as shown in Figure 4d, and discontinuous dendrites, as shown in Figure 4e, both of which were affected by the rolling process. The Scanning Electron Microscope (SEM) images and elemental mapping data for SS308L and Inconel625 are depicted in Figure 5. The data showed that, among all the elements, only Chromium (Cr) had a consistent distribution across the interface, attributable to the similar weight proportions in both materials. Meanwhile, elements such as Nickel (Ni), Niobium (Nb), and Molybdenum (Mo) were mainly found on the Inconel625 side, whereas Iron (Fe) and Manganese (Mn) were dominant in SS308L. Some Fe was also detected on the Inconel625 side near the interface. Figure 6 visually represents the EDS elemental mapping across the interface, emphasizing the progressive transition of elements without any segregation. Despite the fusion welding of different alloys often leading to liquation cracks in the partially melted zone (PMZ), none were found in this study. Increases in Nb and Mo on the Inconel 625 side were observed. Figure 7's SEM image showed precipitates within the Inconel 625 layer, dispersed between the dendritic arms instead of forming continuously. The EDS analysis revealed higher Mo and Nb concentrations, indicating the presence of a laves phase, a typical feature in welded Inconel 625 layers. This laves phase had a hexagonal structure, made up of (Ni, Cr, Fe)\({}_{2}\) (Nb, Ti, Mo). In all the experimental conditions, the bimetallic structure exhibited a uniformly constructed layer, free of defects such as delaminations and cracks. Pressure application improved the hardness of both SS308L and Inconel625. Figure 8 displays the hardness profiles for all the experimental cases, including the bimetallic interface. SS308L had a hardness ranging from 139 to 188 HV, while Inconel625 ranged from 187 to 222 HV. In Case 1, with no pressure applied, the hardness was notably low. When 10,000 N was applied to the Inconel section in Case 2, only a minor increase in hardness was noticed in the SS308L section. As the pressure progressed from Case 1 to Case 3, SS308L's hardness increased by an average of 20 HV for each step. Inconel625's hardness rose by about 22 HV on average from Case 1 to Cases 2, 3, and 4. As the pressure increased, there was a more prominent increase in the hardness of the SS308L region in comparison to that of Inconel625.