Effect of Sn content on microstructure and mechanical properties of BAg5CuZn-0.3 wt.%La brazing material

This article studies the effects of different Sn contents on the melting characteristics, microstructure, and mechanical properties of brazed joints of low-silver BAg5CuZn-0.3wt.%La brazing material. A differential thermal analyzer (HCR-1) was used to measure the solid-liquidus temperature of BAg5CuZn-0.3wt.%La-xSn brazing material. The results show that the addition of Sn element effectively reduces the solid-liquidus temperature of BAg5CuZn-0.3wt%La brazing material. Microstructural characterization was conducted using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), etc. Analysis reveals that progressive aggregation and precipitation of Cu-Sn intermetallic compounds occur with increasing Sn content, leading to microstructural coarsening. Notably, severe grain coarsening is observed when the Sn content reaches 4 wt.%. Shear testing of the BAg5CuZn-0.3wt.%La-xSn brazing joints reveals a non-monotonic trend in joint strength: as Sn content increases, the shear strength initially improves but subsequently deteriorates after reaching an optimal value.