Investigation of gap filling ability of Ag–Cu–In brazing filler metals

Abstract

In an attempt to develop cadmium-free silver brazing filler metals, the ternary Ag–Cu–In alloys were investigated. The effect of varying indium content on melting temperatures and brazeability of Ag–Cu–In alloys on copper was ascertained in this article. Additionally, microstructures, hardness, and shear strength of the brazed joints were investigated. Investigation of brazeability was carried out using a varying gap test piece method adapted from ISO 5179-1983. With this method, the capillary rise height at different joint gaps was used as a quantitative measure for brazeability. The results from differential thermal analysis showed that with the increase of indium content in Ag–Cu–In, the solidus and liquidus temperatures of the filler metals decreased. However, the increase of indium contents showed no significant improvement to the capillary rise height. The limits of capillary rise height of each filler metal corresponding to the joint gaps of 50 and 100 μm were approximately 45 and 28 mm, respectively. Increasing of indium content led to the increase of an intermetallic phase in the brazed layer which subsequently increased the joint hardness. However, this slightly reduced joint shear strength. The average shear strength of the joint brazed with 60Ag–15Cu–25In filler metal was about 11% lower than that brazed with 60Ag–35Cu–5In filler metal.