Effect of ERNiCr-3 and ER70S-G Filler Metals on Mechanical and Microstructural Properties of TIG-Welded SS 409–Cu C11000 Joints

Welding ferritic stainless steel to copper is well known to be challenging because of the large mismatch in their thermal conductivities and metallurgical behaviors. Dissimilar joints are required in a range of energy, automotive, and metallurgical applications. In this study, TIG welding of SS 409 to copper C11000 was performed using ERNiCr-3 (Ni-based) and ER70S-G (Mn-based) filler metals under controlled DCEN conditions to evaluate their mechanical and microstructural performance. Tensile testing, microhardness mapping, and microstructural observations using scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDS) were performed after the welding process. The results show that the joints welded with ERNiCr-3 exhibited a higher ultimate tensile strength, reaching approximately 220 MPa, along with an elongation of approximately 10%. In comparison, ER70S-G joints achieved a tensile strength of approximately 160 MPa and exhibited lower ductility, with an elongation of approximately 6%. A smoother hardness transition across the weld interface was observed for ERNiCr-3, whereas ER70S-G produced a more localized hardness peak close to the fusion boundary. SEM-EDS analysis indicated sound fusion for both filler metals, with limited formation of interfacial compounds. Based on these results, ERNiCr-3 remains the preferred filler when a higher mechanical performance is required. However, ER70S-G can be considered a practical and economical alternative to TIG-welded SS 409–Cu C11000 joints in applications where moderate strength is sufficient.