Effects of thermal distribution strategy on a Ti-6Al-4V/304L dissimilar joint fabricated using the variable polarity cold metal transfer arc-brazing method

Abstract

To suppress the amount of brittle TiFe intermetallics in Ti-6Al-4V/304L joints, this study adopts the variable polarity cold metal transfer arc-brazing method using ERCuSi-A wires. The effects of the thermal distribution strategy on the welding process, penetration ratio, microstructure, and tensile strength are investigated by varying the electrode positive/electrode negative (EP/EN) ratio. With the ratio decreasing, more energy is conducted to the wire, thereby decreasing the high-temperature holding time. When the ratio decreases from 8:1 to 1:8, the thickness of the Ti-6Al-4V/seam transition zone containing a TiCu interlayer and Ti5Si3 intermetallic layer decreases from 118 to 81 μm. Along with the decrease in the interlayer thickness, the joint tensile strength initially increases from 216.28 to 261.69 MPa and then decreases to 211.29 MPa. A high EP/EN ratio results in a thick Ti-6Al-4V/seam transition zone that includes a Ti5Si3 layer. A low EP/EN ratio results in a thin Ti-6Al-4V/seam transition zone that includes Ti5Si3 distributed in the grain boundary. Both conditions reduce the tensile strength of the joints. The highest tensile strength is obtained when the ratio is 8:8, under which a thin transition zone and concentrated Ti5Si3 intermetallic layer can be generated.