Parametric Dependence and Characterization of Laser Brazed Copper-Stainless Steel Joints

Joining of dissimilar metals leading to better material utilization with improved functionality encouraged the research thrust on various dissimilar material joining processes including laser brazing. This paper reports the development of laser brazing joints and their characterization for 3 mm thick Cu sheet with 3 mm thick AISI 316L stainless steel sheet in butt joint configuration using 63Ag-35.25Cu-1.75Ti active brazing foil as filler metal. Comprehensive experiments were carried out to identify the optimum processing parameters for controlled simultaneous heating of the filler metal and sheets by laser beam resulting in melting of the filler metal without melting Cu and SS sheets. Using this methodology, a number of brazed joints were successfully prepared at different set of processing parameters. The brazed joints were subjected to various non-destructive (visual and dye-penetrant test) and destructive (microscopic examination, energy dispersive spectroscopy, four point bend testing etc.) characterization techniques. The results demonstrated that laser energy per unit length of 100 J/m is threshold limit for feasibility of brazing process for selected metal and thickness combination. Microscopic studies of transverse section of laser brazed joint showed full penetration across the thickness without the melting of parent metals. Energy-dispersive X-ray spectroscopy studies showed the diffusion of filler material (Ag) more towards the Cu sheet as compared to that of stainless steel sheet. Four point bend test showed that the alignment of laser beam-metal joint was critical for the brazing joint strength and improved joint strength was achieved when the beam was at the centre of the brazing joint. A maximum joint strength of 343.7 MPa was achieved for laser power of 550 W at scan speed of 3 mm/min.