Microstructural analysis and discontinuities in the brazed zone of copper tubes

Abstract

In this study, ISO Cu-DHP tubes were brazed using different filler metals such as AWS BCuP-2, BCuP-3, BCuP-5, BAg-16, and DIN L-CuP7 and L-Ag40Cd. The microstructures of the brazed zone of tubes were examined with optical and scanning electron microscopic studies. Hardness measurement and leak-tight tests were conducted. The discontinuities in the brazed zone were determined. The microstructures of the brazed zone of the filler metals generally included two or three different regions. The zones of BCuP-2 and LCuP7 consisted of round phosphorus poor dendrites in a matrix of Cu–P. Ag poor dendrites were observed in a silver rich matrix of BAg-16 filler metal. On the other hand, the microstructures of the BCuP-3, BCuP-5 and L-Ag40Cd consisted of three distinct regions. For instance, dendrites of copper solid solution, Ag–Cu–P eutectic and silver rich dendrites were observed in the brazed zone of BCuP-5 filler metal. Some discontinuities such as porosities, insufficient penetration and positioning errors were observed in the brazed zone of the different filler metals. It was observed that the positioning errors in joints strongly influenced the penetration of filler metal. Silver content decreased the ductility of the brazed zone.