Effect of Silver on the Corrosion Resistance of Copper Phosphorus Brazing Filler Metals

Copper tubes used in heat exchangers were joined by brazing using copper phosphorus brazing filler metals. Leakage due to the progression of groove-like corrosion near the joints of copper tubes using copper phosphorus brazing filler metals became a problem. In addition to copper, copper phosphorus brazing filler metals also contained phosphorous and silver. In this study, we investigated the effects of silver on the corrosion resistance of copper phosphorus brazing filler metals. Observation and analysis of the metallographic structure of the copper phosphorus brazing filler metals revealed uneven distributions of phosphorus and silver components. Electrochemical measurements of anodic polarization curves showed that the current density of the copper phosphorus brazing filler metals with silver at high potentials was higher than that without silver. Furthermore, on the surface of the brazing material after the test, part of the structure of the silver-containing brazing material was observed to be corroded in the form of black dots. Therefore, the silver contained in the brazing material was considered to have effect on corrosion resistance of copper phosphorus brazing filler metals.