Effect of Sn on the microstructure and properties of Cu-Sn-Ti brazing filler metal

In order to reveal the regulation of Sn on the microstructure and mechanical properties of Cu-Sn-Ti brazing filler metal, Cu-xSnxTi10 brazing filler metals were prepared by vacuum non-self-consumption melting method, and the effects of Sn on the microstructure, microhardness, shear strength and fracture morphology of Cu-Sn-Ti brazing filler metals were investigated by using scanning electron microscopy (SEM), X-ray diffractometer (XRD), energy spectrometer (EDS), and universal material testing machine, etc. the results showed that:the microstructure evolution of the solder with the increase of Sn content was as follows : dendritic primary α-Cu matrix phase + eutectic tissue + intergranular tissue → primary α-Cu matrix phase + eutectic tissue → eutectic tissue → primary CuSn₃Ti₅ phase + coarsened eutectic tissue + α-Cu matrix phase (Sn-rich) + Cu₄₁Sn₁₁ phase + SnTi₃ phase, in which the intergranular tissue was a mixed structure of α-Cu phase and CuSn₃Ti₅ phase + a small amount of SnTi₃ + CuTi phase + Cu₃Ti phase. With the increase of Sn content, the microhardness of filler metal increases first and then decreased, the shear strength of filler metal decreasing gradually, and the fracture morphology changed from the quasi-cleavage fracture to the mixture of cleavage fracture and quasi-cleavage fracture. The increase of Sn content promoted the formation of coarsened CuSn₃Ti₅ phase and eutectic tissue in the filler metal, which was the main reason for the decrease of shear strength of brazing metal.