The dissimilar brazing of Kovar alloy to SiCp/Al composites using silver-based filler metal foil

Abstract

Aluminum metal matrix composites with high SiC content (60 vol.% SiCp/Al MMCs) were surface metallized with a Ni–P alloy coating, and vacuum brazing between the composites and Kovar alloy were performed using rapidly cooled Ag–22.0Cu–15.9In–10.86Sn–1.84Ti (wt%) foil. The effects of Ni–P alloy coating and brazing parameters on the joint microstructures and properties were researched by SEM, EDS, and single lap shear test, respectively. Results show that Ag–Al intermetallic strips were formed in the 6063Al matrix and filler metal layer because of diffusion, and they were arranged regularly and accumulated gradually as the brazing temperature was increased (T/°C = 550–600) or the soaking time was prolonged (t/min = 10–50). However, excessive strips would destroy the uniformity of seams and lead to a reduced bonding strength (at most 70 MPa). Using a Ni–P alloy coating, void free joints without those strips were obtained at 560 °C after 20 min soaking time, and a higher shear strength of 90 MPa was achieved. The appropriate interface reaction (~2 μm transition layer) that occurred along the Ni–P alloy coating/filler metal/Kovar alloy interfaces resulted in better metallurgical bonding. In this research, the developed Ag-based filler metal was suitable for brazing the dissimilar materials of Ni–P alloy-coated SiCp/Al MMCs and Kovar alloy, and capable welding parameters were also broadened.