Study and Selection of the Most Appropriate Filler Materials for an Al/Cu Brazing Joint in Cooling Circuits

Five dissimilar commercial filler alloys with four fluxes were used in the aluminum to copper diffusion brazing process. The filler metal alloys composition comprised AlSi12, ZnAl 96/04, ZnAl 98/02, AlSi12 + ZnAl 98/02, and AlSi12 + ZnAl 85/15 alloys. The use of these filler alloys on the assembly of piping for cooling circuits has been analyzed. Brazing aluminum to copper is difficult, principally due to the substantial differences between their thermal properties and the generation of intermetallic compounds in the joint, especially when certain mechanical strength of the joint is needed. Pipes of Al 1350 and Sf-Cu R220 were brazed using five brazing alloys, and the section of the joint was analyzed after polishing and etching. Microhardness tests were also carried out. Furthermore, the microstructure and phase constitution for the copper to aluminum brazing were exhaustively studied by means of metallography, electron probe microanalyzer (EPMA), and X-ray diffraction (XRD). The experiment results obtained indicated that the ZnAl 96/04 filler alloy represents the optimum solution due to the low microhardness, homogeneous microstructure and lack of defects (pores and cracks) shown.