Effect of combined addition of Sn and Ce elements on the microstructure and properties of the joints brazed with BAg5CuZn filler metal

The effects of Sn and Ce combined addition on the melting characteristics, spreading ability of BAg5CuZn filler metal, the microstructure and mechanical properties of their corresponding brazed joints were studied respectively. The results showed that the solidus and liquidus temperatures of the filler metals decreased significantly, and the spreading areas of the filler metals on the base metal increased with the combined addition of Sn and Ce elements. However, when the mass fraction of Ce element was higher than 0.15%, the spreading performance of the filler metals deteriorated. The addition of appropriate amount of Sn and Ce elements could significantly improve the microstructure of the joints brazed with BAg5CuZn filler metals. When the mass fractions of Sn and Ce elements reached 2% and 0.15% respectively, the microstructure of the joint was obviously refined, which the most uniform distribution was obtained. However, excessive Ce addition in the filler metal tended to form complex intermetallic compounds with Ag and Sn elements, and precipitate at the grain boundary, which significantly worsened the uniformity of the joint microstructure. When mass fractions of Sn and Ce elements in the filler metal were reached 2% and 0.15% respectively, the shear strength obtained the maximum value of 495 MPa, which was 23.1% higher than that of the joint brazed with BAg5CuZn filler metal.