Effect of element content of AgCuMnNi brazing filler metal on microstructure and properties of brazed joints

Three kinds of AgCuMnNi brazing filler metal were designed. Solidus-liquidus line temperature of the three kinds of brazing filler metal was 750～792 ℃, and as-cast microstructure of brazing filler metal was mainly composed of Ag-rich phase and Cu-rich phase. With the increase of Ag content and the decrease of Ni and Mn content, proportion of Ag-rich phase in as-cast microstructure of brazing filler metal increased gradually. Vacuum brazing of YG6X/GH4169 was performed with three kinds of brazing filler metal at 860 ℃ for 10 min, and average tensile strength of Ag-3(AgCuNi4Mn8) brazed joints was 432.8 MPa, which was higher than that of both Ag-1 (AgCuNi11.5Mn21.5) and Ag-2(AgCuNi4Mn11.5) brazed joints. Cu-rich phase and Ag-rich phase were evenly distributed in microstructure of Ag-3 brazed joints, while high Mn oxidation zone was formed in brazing process of Ag-1 and Ag-2 due to high Mn content, which weakened mechanical properties of brazed joints.