Optimization and evaluation of mechanical properties of RSW joints between SS 304 and DSS 2205 using TOPSIS

As the automotive industry explores the increasing use of stainless steel (SS), joining different grades of them in a two-sheet configuration becomes essential. Given the joining complexities possessed by the differing physical and metallurgical properties of SS 304 and duplex SS 2205, this study investigates double-spot resistance spot welding (RSW) as a potential solution, examining its effects on mechanical and microstructural characteristics. The tensile strength, hardness and microstructural characteristics of the joints were examined. A series of experiments were conducted using various combinations of welding parameters (power supply: 25–35 A, squeeze time: 25–29 ms, weld time: 25–29 ms, hold time: 2 s), double-spot orientations (vertical, horizontal, and diagonal) and spot distance (7 , 8 , 9 mm). A peak tensile strength of 897 N/mm 2 and a hardness of 297.47 HV were observed. The microstructure in the nugget region exhibited needle-like β-phase dendrites which significantly influenced the mechanical properties of the joint. Further, technique for order preference by similarity to ideal solution (TOPSIS) was used to optimize the RSW parameters and a combination of welding current (35 A), squeezing time (29 ms), weld time (29 ms), hold time (2 s), vertical orientation and a distance of 7 mm between spots was identified to be optimal. The corresponding tensile strength of 627 N/mm 2 , and a hardness of 278.52 HV were higher than the standards.