Mechanical and microstructural properties of dissimilar copper and stainless-steel butt welds prepared using zigzag and circular fiber laser oscillation methods

Abstract

Dissimilar copper and stainless-steel butt welds are prepared using zigzag and circular laser beam oscillation welding methods. The tensile strengths, microhardness values, and weld bead morphologies of the joints are evaluated and compared for various values of the oscillation amplitude and frequency. The optimal laser oscillation parameters are found to be a laser power of 1550 W, an oscillation frequency of 15 Hz, and an oscillation amplitude of 1 mm. Under these optimal processing conditions, the tensile strengths of the joints produced using the zigzag and circular oscillation welding modes are 232.6 MPa and 235.7 MPa, respectively. The superior strength of the weld produced using the circular oscillation method is attributed to a more uniform mixing of the alloying elements in the weld zone and a greater penetration depth. The addition of a thin Ni interlayer to the joint is found to improve the tensile strength to 240 MPa for the zigzag oscillation mode and 242 MPa for the circular oscillation mode. By contrast, the addition of a Ti interlayer reduces the tensile strengths of the joints to around 163 MPa and 198 MPa, respectively. The reduction in the tensile strength is the result mainly of a more brittle fracture mode within the heat affected zone (HAZ). Nonetheless, the circular oscillation welding mode results in a higher tensile strength than the zigzag mode due to a greater suppression of intermetallic compound (IMC) phase in the weld area and a reduction in the number of pores and cracks. Compared to conventional straight-line welding, the zigzag and circular oscillation modes reduce the grain size by around 32% and 52%, respectively, and enhance the mechanical properties accordingly.