Lap joining of TC4 titanium alloy to 304 stainless steel with fillet weld by GTAW using copper-based filler wire

TiFe and TiFe2 intermetallic compounds (IMCs) were effectively suppressed with copper-based filler wire when joining TC4 titanium alloy to 304 stainless steel by gas tungsten arc welding (GTAW). A Ti/Cu reaction zone, consisting of various IMCs like Ti2Cu, AlCu2Ti, TiCu, Ti3Cu4 phases, formed between TC4 substrate and the weld. Increasing welding heat input induced the formation of TiFe, TiFe2 and complex TiCuAlFe IMCs in the Ti/Cu reaction zone. The highest shear fracture load occurred at welding heat input of 2.34 kJ/cm reached 341 N/mm corresponding to 107 MPa in shear strength, and the microhardness in the Ti/Cu reaction zone was about 619 HV. Further increasing welding heat input deteriorated the shear fracture load and increased the microhardness in the Ti/Cu reaction zone. All joints fractured at the Ti/Cu reaction zone with cleavage characteristics on the fracture surface due to the brittle IMCs and micro cracks generated in the Ti/Cu reaction zone.