Microstructures and mechanical properties of laser-arc hybrid welded dissimilar pure copper to stainless steel

Laser-cold metal transfer hybrid welding was applied to the butt-welding of T2 copper/304 stainless steel (Cu/304SS) dissimilar joint by deviating the laser beam from the edge of the weld seam to the Cu plate. Under the optimal laser offset (ΔD = 0.5-1.0 mm), an acceptable weld with uniform surface morphology and free of visible defect was obtained. All the joints obtained at the optimal ΔD fractured at the Cu side, with the maximum tensile strength reached up to 215 MPa, approximately to that of T2 copper (200-240 MPa). The variations of the weld mechanical properties were well corresponding to the observed microstructure changes. Too small ΔD (<0.5 mm) resulted in the excess melting of 304SS and formation of the macrosegregations of the Fe-rich peninsula and islands in the fusion zone, which deteriorated the weld mechanical properties. While increasing the ΔD decreased the amount of the melted 304SS, and benefited to from the Cu-rich matrix and inner uniformly distributed Fe-rich particles, which strengthened the weld. However, excess ΔD (>1.0 mm) weakened the weld because only coarse Cu columnar grains formed.