## 2 Materials and Methods
### Welding Setup, Parameters, and Quality Assurance
These parameters were selected based on manufacturer recommendations, standard guidelines, and preliminary calibration tests. A summary of all applied welding conditions is provided in Table 5, which consolidates the key parameters across all six test configurations (samples 3-3, 3-5, 6-3, 6-5, 9-3, and 9-5). Previous studies confirm that stud diameter and welding current are the most critical parameters influencing mechanical strength [21]. The mechanical performance of stud welded joints is strongly influenced by the selected stud diameter and welding current [22]. To ensure comprehensive quality evaluation, both non-destructive and destructive testing methods were applied. Visual inspection was performed first to detect surface-level discontinuities such as undercuts, cold laps, lack of fusion, excessive spatter, and angular misalignment, serving as the initial quality control step. Bend tests were conducted at angles of 30\({}^{\circ}\) or 60\({}^{\circ}\), depending on the expected thermal gradients and mechanical loads, to assess ductility and weld-root integrity through plastic deformation. Radiographic testing (X-ray or gamma-ray) was employed to identify internal defects, including porosity, slag inclusions, or incomplete fusion, which are not visible on the surface. Metallographic analysis involved sectioning and mounting welded studs from representative test plates, followed by grinding, polishing, and etching to reveal microstructural features such as heat-affected zone morphology, grain boundary integrity, and possible phase transformations. This approach provides valuable insights for diagnosing failure mechanisms and validating process qualification. By combining non-destructive and destructive testing, including detailed microstructural characterization, the weld quality assurance process becomes more robust, enhancing the prediction of in-service performance and long-term reliability. Effective quality assurance is essential for detecting weld defects and verifying compliance with applicable process standards [23]. Optimization of welding parameters for high-strength steels and \begin{table}
\begin{tabular}{l l l l l l l l l l} \hline \hline
**Sample** & **Method** & **Material** & **Stud** & **I (A)** & **L (mm)** & **P (mm)** & **tw (ms)** & **SRM (mA)** & **Gas Flow** \\ \hline
3-3 & CF & Steel 1.0038 & M12 \(\times\) 70 A2-50 RD & 684 & 1.4 & 3.0 & 390 & - & - \\  & & (S235R + N) & M12 \(\times\) 70 A2-50 RD & 684 & 1.4 & 3.0 & 390 & - & - \\
3-5 & CF & Steel 1.4301 & M12 \(\times\) 70 A2-50 RD & 684 & 1.4 & 3.0 & 390 & - & - \\
6-3 & SG & Steel 1.0038 & M12 \(\times\) 70 A2-50 PD & 760 & 2.1 & 2.0 & 190 & - & 4 L/min \\
6-5 & SG & Steel 1.4301 & M12 \(\times\) 70 A2-50 PD & 772 & 2.0 & 2.0 & 201 & - & 4 L/min \\
9-3 & SRM & Steel 1.0038 & M12 \(\times\) 40 A2-50 HZ-1 & 772 & 1.3 & 3.5 & 200 & 270 & 4 L/min \\
9-5 & SRM & Steel 1.4301 & M12 \(\times\) 40 A2-50 HZ-1 & 772 & 1.3 & 3.5 & 203 & 270 & 4 L/min \\ \hline \hline \end{tabular}
\begin{tabular}{l l l l l l l l l} \hline \hline
**Sample** & **Method** & **Material** & **Stud** & **I (A)** & **L (mm)** & **P (mm)** & **tw (ms)** & **SRM (mA)** & **Gas Flow** \\ \hline
3-3 & CF & Steel 1.0038 & M12 \(\times\) 70 A2-50 RD & 684 & 1.4 & 3.0 & 390 & - & - \\  & & (S235R + N) & M12 \(\times\) 70 A2-50 RD & 684 & 1.4 & 3.0 & 390 & - & - \\
3-5 & CF & Steel 1.4301 & M12 \(\times\) 70 A2-50 RD & 684 & 1.4 & 3.0 & 390 & - & - \\
6-3 & SG & Steel 1.0038 & M12 \(\times\) 70 A2-50 PD & 760 & 2.1 & 2.0 & 190 & - & 4 L/min \\
6-5 & SG & Steel 1.4301 & M12 \(\times\) 70 A2-50 PD & 772 & 2.0 & 2.0 & 201 & - & 4 L/min \\
9-3 & SRM & Steel 1.0038 & M12 \(\times\) 40 A2-50 HZ-1 & 772 & 1.3 & 3.5 & 200 & 270 & 4 L/min \\
9-5 & SRM & Steel 1.4301 & M12 \(\times\) 40 A2-50 HZ-1 & 772 & 1.3 & 3.5 & 203 & 270 & 4 L/min \\ \hline \hline \end{tabular}
\begin{tabular}{l l l l l l l l l} \hline \hline
**CF = ceramic ferrule; SG = shielding gas; SRM = radially symmetric magnetic field; I = welding current, L = lift, P = plunge depth; tw = welding time.**  
\end{table}