## 2 Materials and Methods
### RSW Process  
Resistance spot welding is a joining process in which workpieces are joined by heating the interfaces to a suitable welding temperature at which they lose their metallurgical continuity during the welding cycle. This welding process is carried out across the workpieces to be joined in the overlap configuration while they are held between two electrode tips under a certain mechanical force to overcome the electrical contact resistance at the interface and to provide a reliable current flow path [68; 69]. This mechanical force is applied through one or both of the electrodes of the welding electrode assembly, which is realised in an arrangement similar to a spot in shape due to the conductive tips of the respective electrodes. The welding cycle is generally divided into three phases in the resistance spot welding process. These are the preheating, welding, and cooling phases, respectively. Electrode force is applied in the first phase of the welding, i.e., the preheating phase, to establish a deformation resistance across the workpieces [21; 70]. \begin{table}
\begin{tabular}{c c c c} \hline
**Thickness (mm)** & **Length (mm)** & **Width (mm)** & **Overlap Region (mm)** \\ \hline
0.5 & 76 & 16 & 16 \\
1 & 100 & 25 & 25 \\ \hline \end{tabular}
\end{table} 
Table 1: Dimensions of the RSW specimens. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline
**Property** & **Ultimate Tensile Strength, UTS** & **Yield Strength** & \multirow{2}{*}{**Poisson’s Ratio**} & \multirow{2}{*}{**Young’s Modulus**} & \multirow{2}{*}{**Elongation** (**GPa)**} & \multirow{2}{*}{**(\%)**} \\  & & **(MPa)** & & & & & & & & \\ \hline Ti grade 2 & 428 & & 318 & 0.37 & 113 & 28 \\ AISI 304 & 505 & & 215 & 0.29 & 193 & 40 \\ \hline \end{tabular}
\end{table} 
Table 2: Mechanical properties of Ti grade 2 and AISI 304 steel. Figure 1: Schematic illustration of the tensile RSW sample. The welding current, which should be greater than the melting current of the interface to realise heat generation at the transient interface, is subsequently applied to heat the parent materials of the workpieces in the welding phase. When the interface reaches a melting temperature, a certain amount of the molten zone is generated that can be further joined metallurgically in the following welding cooling phase. The quality of the resistance spot welded joint generated mainly depends on various process parameters affecting the thermal and mechanical conditions of these three phases. Additionally, the electrical conductivity and thicknesses of workpiece materials also have more pronounced effects on the resistance spot weld quality. This study conducted RSW experiments using a dome-shaped electrode on an RSW machine set. Group A, class 2, type B chromium zirconium copper alloy was its composition. Its circular contacting area was 4 mm. To generate the pressure, a pneumatic supply was used. The digital screen linked to the machine allowed the operator to set the welding machine with the RSW process parameters, which included the welding current, welding pressure, pulse welding, squeezing welding, and holding times. The experiments were carried out at the typical temperature of a laboratory. The distribution of RSW specimens is as follows: The 30-sample titanium sheet welding experiment, based on optimal findings reported in [44], the 10-sample sheet welding experiment with an equal thickness of 1 mm, the 10-sample sheet welding experiment with an equal thickness of 0.5 mm, and the 10-sample sheet welding experiment with unequal sheet thicknesses of 0.5 and 1 mm are all included in this distribution. Similarly, 30 samples of AISI 304 sheets with thicknesses of 0.5 and 1 mm were welded according to the ideal parameters found in [6] and labelled with D, G, and H. The ideal results in [71; 72] were used to make the dissimilar RSW samples between AISI 304 and Ti grade 2 alloy. A total of 40 samples were used, with each case including 10 specimens and labelled E, F, I, or J.