Study on microstructure and mechanical performance of copper/brass brazing joint with Ag brazing fillers

Abstract

Ag is used as a useful alloying element in brazing filler metals. It is clear that the addition of Ag has a positive effect on the melting temperature, wettability, conductivity and mechanical property of the filler metals. For this reason, although Ag is very expensive, it is still widely used in many research and production. In this study, it was focused on obtaining both high strength and cost-effective brazing joints by using filler metals containing different levels of Ag. Melting-solidification temperatures, mechanical properties and microstructures of brazing joints obtained with filler metals containing different levels of Ag-Cu-Zn and Cd were investigated. In this study, the appropriate Ag content in brazing processes of pipes and caps used as copper-brass material pairing in cooling-heating devices in the air conditioning system was investigated in detail. When the typical microstructure of the joints was examined, it was observed that it mainly consisted of solid solutions and eutectic phases. The interfaces in the copper and brass regions were affected by both Ag content and melting temperatures. As a result of the burst test, the maximum stress value at which the brazed material pairs were damaged was found to be 345 MPa, and the damage was reported to occur in the copper pipe. In addition, it has been reported that the final product is damaged from the brazed zone when Ag-free solder wire is used. It was found that 5%Ag content provides sufficient performance in the final product due to the fact that the strength of the braze joint with low-Ag content is higher than the copper tube. The results also showed that the micro-hardness increased with the increase of Ag-addition, the hardness of the joint with the filler metal containing 5%Ag increased by 21%. The joint hardness obtained with filler metal containing 40% Ag showed an increase of up to 57%. This showed that the addition of Ag improves the strength, but its 5% Ag content provides sufficient performance in the brazing joint.