Effect of axial magnetic field on cold metal transfer arc-brazing of Ti6Al4V to 304L steel

Abstract

Magnetic intensities from 0 to 18.0 mT and CuNi10 wire were employed in Cold Metal Transfer (CMT) joining of Ti6Al4V to 304 L stainless steel. The axial external magnetic field (EMF) could improve the wetting behavior and modify the microstructure of arc-brazed joints. A rotated bell-shaped arc was formed owing to the Lorentz force acting during the welding process, resulting in short arc length, wide arc width, and low temperature of the melting pool. The liquid metal in the melting pool exhibited an incomplete circular motion on the surface owing to the pulsed plasma shear stress and Lorentz force caused by the radial current and axial magnetic field. With increasing magnetic intensity, the inner layer containing β + π + Ф (NiTi + NiTi2+CuTi) and π + ψ + Ф (NiTi2 + CuTi2 + CuTi) and outer layer containing γ + Δ ((Cu, Ni) + TiNiCu) became thinner and more uniform because of the intense flow and short reaction time at high temperature. The microstructure on the 304 L side of the joints changed from columnar dendrites to coarsened grains. With increasing magnetic intensity, the tensile strength of the joints increased from 270.7 to 387.8 MPa. All the samples fractured at the Ti6Al4V/seam interfacial layer of the joints.