Microstructure and brazing properties of a novel Ag–Cu-Ga solder

Abstract

In this study, a novel low-silver Ag-xCu-5Ga (x = 28, 34, 39, 49 and 55) solder with high strength was designed and prepared. The effect of element composition on microstructure evolution, thermal behavior, and the mechanical performance of Ag–Cu-Ga solders were investigated in detail. The results indicated that the melting temperature of Ag–Cu alloy could be reduced effectively with Ga addition, and the typical joint consisted of the block-shaped Cu-rich phase in the welded seam and the ribbon-shaped Cu-rich phase adjacent to the interface. The shear strength of joints brazed with Ag-xCu-5Ga (x = 28, 34, 39 and 49) filler metals can be improved significantly compared to that of commercial Ag–28Cu solder, with a maximum value of approximately 445 MPa in Ag–39Cu–5Ga solder. The best mechanical properties are obtained as the second-phase strengthening and interfacial strengthening reach a balanced coexistence state, determined by the block-shaped Cu-rich phase in the welded seam and the ribbon-shaped Cu-rich phase adjacent to the interface, respectively. This study can provide insights to investigate strengthening mechanisms and develop high-strength solders for vacuum brazing.

Keywords

• Vacuum brazing
• Ag–Cu-Ga alloy
• Shear strength
• Interfacial microstructure