Copper Phosphorous Brazing Filler Alloys with Low Melting Temperature (Report I)

Effect of Tin Addition

Abstract

A new copper phosphorous self-fluxing brazing filler alloy usable at 650°C has been developed by the addition of tin to Cu-Ag-P alloy. The influence of tin and phosphorous content on the brazability at 650°C has been investigated by evaluating the penetration length of filler alloy between two copper plates of 0.1 mm lap joint clearance. Differential thermal analysis and metallographic observation were also carried out to define the temperature ranges of melting and the phase Changes. Within the range of this investigation, the available filler alloy composition was found to be Ag/Cu(15/65)-15%Sn-(3-3.5)%P. The solidus and liquidus temperatures of the alloys were about 475°C and 620-650°C, respectively. The alloys of more than 3.5%P content havingprimary Cu₃P phase showed poor penetration length because phosphorous content in coexistingliquid decreased due to the formation of Cu₃P. On the other hand, the alloys of less than 3.5%P content crystallized primary Cu(a) phase, and then the coexisting liquid contained more phosphorous than the nominal concentration. Accordingly, the alloys exhibited excellent fluxing action.