Microstructural Evaluation of Copper Brazed Joints Using Silver-Based Filler Metal

Abstract

The oxy-acetylene torch brazing of copper tubes using silver-based filler metals (Ag-Cu-Zn-Cd) was investigated in this study. Filler metals containing silver content of 15% and 35%, designated by BR15 and BR35, were used to assess the influence of the silver content in the microstructure and mechanical performance of brazed joints. The brazed joints microstructure was analyzed by means of optical microscopy, scanning electron microscopy, and energy-dispersive spectroscopy. The microstructures of the BR15 and BR35 samples were composed mainly of Ag–Cd-rich phase, solid solution of Cu–Zn, and a eutectic structure of Ag and Cu. The increase in the Ag content changed the solidification mode from cellular to dendritic and caused an increase in the eutectic phase volume fraction. The tensile strength of the Ag–Cu–Zn–Cd filler and the phos–copper filler metals was compared. The tensile strength of silver-based filler metal was slightly higher than the phos–copper filler metal brazed joints.