Effects of In and Ga on Spreading Performance of Ag10CuZnSn Brazing Filler Metal and Mechanical Properties of the Brazed Joints

Ag-based brazing filler metals are preferred in many industries, but the high price of Ag restricts their wider application. Therefore, developing novel low-Ag brazing filler metals has aroused extensive interest. In this study, the effects of the In and Ga elements on the melting behavior and spreading property of Ag10CuZnSn filler metal and the microstructure and strength of the brazed joints were investigated. The results show that both In and Ga can significantly decrease the solidus and liquidus temperatures of the filler metal. The In element can dissolve into the liquid filler metal and the Ga element can decrease the surface tension of the melted filler metal, which, in turn, improves the spreading area. The In element prefers to dissolve into the Ag-rich phase, and the Ga element prefers to dissolve into the Cu-rich phase; both improve the strength of the filler metal through solid-solution strengthening. The shear strength of the 304 stainless-steel brazed joint reached a peak value of 396 MPa when the Ag10CuZnSn-1.5In-2Ga (wt%) filler metal was used. However, the excessive addition of In and Ga forms brittle intermetallic compounds (IMCs) in the brazing seam, which decreases the strength of the brazed joint.