Microstructures and mechanical properties of copper-stainless steel butt-welded joints by MIG-TIG double-sided arc welding

Abstract

Dissimilar copper/stainless steel metal joints with excellent double-sided forming can be obtained by MIG-TIG double-sided arc welding without grooving and preheating. The joints with welding-brazing and fusion welding modes based on the different joining mechanisms in the SS/weld interface can be found. The brazing stainless steel/weld interface shows a flat morphology, while the fusion SS/weld interface consists of a melted unmixed zone (MUZ) and shows a scraggy morphology. A joint free of cracks and pores can be obtained using the welding-brazing mode, which is attributed to the low heat input during welding and the homogeneous composition in the weld zone. Tensile tests show that fracture occurs at the heat-affected zone (HAZ) at the copper side in all joints, and the optimal tensile strength reaches 229 MPa. All joints exhibit lower tensile strength and larger elongation than the Cu base metal due to softening in the HAZ on the copper side. As the amount of the softening mainly depends on the heat input, the welding-brazing joint with low heat input shows high resistance to softening.