## 4 Conclusions  
The mechanical properties and fatigue behaviour of RSW joints made from similar and dissimilar AISI 304 austenitic stainless steel and titanium grade 2 alloy with equal and unequal thicknesses of 0.5 and 1 mm were evaluated in the present study. The following conclusions can be drawn from this investigation:  
1. The shear tensile strength evaluations of the titanium RSW joint indicated that case B (0.5-0.5 mm) achieved the highest tensile strength of 613 MPa, while case A (1-1 mm) had the second-highest shear strength of 374.7 MPa. Case C (1-0.5 mm) had the minimum shear strength of 333.5 MPa. 2. The results regarding the shear strength of RSW joints for AISI 304 suggested that the peak shear strength of 526.8 MPa was recorded in case D (1-1 mm), whereas case G (0.5-0.5 mm) attained the second highest shear strength at 515.2 MPa. Nevertheless, the smallest shear strength for AISI 304 joints occurred in case H (1-0.5 mm), reaching 369.5 MPa. 3. The findings of the shear strength analysis of AISI 304/Ti grade 2 dissimilar joints demonstrated that case J had the highest strength of 183.9 MPa, while case E had the lowest strength of 115 MPa. The second- and third-highest shear strengths of 156 and 129 MPa, respectively, were identified in cases F and I. 4. SEM and XRD inspections proved that similar welded titanium joints are mostly made up of the alpha (\(\alpha\)) phase, with small amounts of the beta (\(\beta\)) phase as well. The XRD and SEM results of the similar AISI 304 joint proved that the \(\gamma\)-Fe and \(\delta\)-Fe phases were found in the welded joint. 5. The reduced grain size and the presence of \(\gamma\)-Fe in the welded junction are the reasons for the improvement in the shear strength of the Ti/AISI 304 dissimilar joint, as confirmed by XRD. 6. Case A (1-1 mm) had the greatest fatigue life of 1.39 \(\times\) 10\({}^{6}\) cycles, according to the fatigue life results of similar titanium welded joints. On the other hand, case B (0.5-0.5 mm) produced a maximum fatigue life of up to 7.37 \(\times\) 10\({}^{5}\) cycles. Case C (1-0.5 mm) has a maximum fatigue life of 7.69 \(\times\) 10\({}^{5}\) cycles. 7. The greatest fatigue life recorded for case G (0.5-0.5 mm) was 3.35 \(\times\) 10\({}^{6}\) cycles, whereas the maximum fatigue life of 4.56 \(\times\) 10\({}^{6}\) cycles was attained for case D (1-1 mm). It should be noted that a fatigue life of 7.39 \(\times\) 10\({}^{5}\) cycles was achieved by using an unequal thickness combination in case H (1-0.5 mm). 8. It was shown that the thickness combination has a significant impact on the fatigue life of welded joints made of titanium and stainless steel, particularly at the maximum applied stress of 0.9% UTS. Employing similar thicknesses resulted in a longer fatigue life compared to using uneven thicknesses. 9. Based on the findings of Ti/AISI 304 dissimilar joints, case J had the highest fatigue life (6.47 \(\times\) 10\({}^{5}\) cycles) before failure, whereas case E had the smallest fatigue life (3.7 \(\times\) 10\({}^{5}\) cycles). With values of 6.1 \(\times\) 10\({}^{5}\) and 4.11 \(\times\) 10\({}^{5}\) cycles, respectively, cases I and F were ranked second and third in terms of fatigue life. 10. The presence of dimples and slide bands on the fatigue-fractured surface of similar Ti welded joints exposed to the HCF regime suggests that ductile failure develops in this case. On the other hand, under the LCF condition, the fractured surface had brittle failure because it was non-uniform, with larger steps than in the HCF regime, and cleavage facets as well. 11. Under the HCF regime, the surface of the similar AISI 304 joint failed with a ductile fracture because of the shallow dimples and slips present. However, when exposed to the LCF condition, the failure behaviour was brittle because the fracture surface generated numerous quasi-cleavage facets and had a few fatigue striations. 12.