Effect of filler metals on microstructure and properties of T2 copper/316L stainless steel GTAW joint

T2 copper/316L stainless steel dissimilar joints were produced by gas tungsten arc welding with Cu filler wire and 307Si filler wire, respectively. The effect of filler metals on microstructure, mechanical properties and corrosion resistance of the joints was investigated. The microstructure of copper/steel weld was largely affected by liquid phase separation between iron and copper. When Cu filler wire was used, Fe-rich spherulites formed by Fe-Cu primary liquid phase separation distributed in the weld. Inside the Fe-rich spherulites, minority Cu-rich spheres formed by secondary liquid phase separation. However, when 307Si filler wire was used, the primary liquid phase separated Cu-rich spherulites showed no characteristic of secondary liquid phase separation. The tensile specimens achieved by both filler wires fractured at HAZ on the copper side, and the strength of each joints reached at least 80% of Cu base metal. Dimples and stretched zone were distributed on the fracture, showing the ductile fracture mode. Compared to the joint achieved by 307Si filler wire, the joint achieved by Cu filler had larger corrosion depth and corrosion current density, showing an inferior corrosion resistance.