The lap welding of titanium sheet and mild steel sheet was performed with Cu-base filler foil as an insert metal using a seam welding method. The weldability was investigated in comparison with seam welds without the use of the insert metal. Without the insert metal, the seam welds were easily peeled off at the weld interface between the titanium and the mild steel. On the other hand, with the insert metal, the sound welds were produced at all welding conditions applied in this study. Therefore, it was concluded that the formation of intermetallic compounds, such as FeTi and Fe2Ti, were suppressed by using the insert metal. The result of the tensile shear test showed that the fractures occurred at the weld interface between the titanium and the mild steel, and the values of maximum tensile shear strength were approximately 100 to 120 MPa independent of the welding conditions. The XRD and EDX analyses on the fractured surfaces after performing the tensile shear test revealed that a very small amount of the insert metal remained at the weld interface between the titanium and the mild steel and also CuTi, Cu2Ti and β-Ti were formed at the interface. Consequently, the very small amount of the insert metal that remained at the weld interface between the titanium and the mild steel prevented the formation of brittle intermetallic compounds such as FeTi and Fe2Ti.
