(1.Northwest Institute for Nonferrous Metal Research, Xian 710016, China) (2.College of Material Science & Engineering, Xian University of Technology, Xian 710048, China)
In recent years, with the development of manufacturing industry, the raw materials used in heat exchange are also being updated. This has prompted the development of new Ag based brazing filler. Cu3Ag0.5Zr alloy has high thermal conductivity and strength, and is used to make new high performance heat exchangers. But too high brazing temperature will reduce the strength of the alloy. The elements such as Ga, In and Sn can significantly reduce the brazing temperature of Ag based filler metal and effectively improve the strength of Cu3Ag0.5Zr alloy after brazing. In this paper, AgCuGaInSn was designed and prepared by adding Ga, In and Sn elements to base alloy AgCu28. The effects of Ga, In and Sn elements on the phases and melting properties of the filler metal were studied. Afterwards, Ag61.2Cu23.8Ga3In10.5Sn1.5 was optimized for brazing Cu3Ag0.5Zr alloy, and the brazing performance of AgCuGaInSn filler to Cu3Ag0.5Zr alloy was evaluated by investigating microstructure and mechanical property of joints. The results show that when the total mass fraction of Ga,In,Sn increases to 15%, the liquidus points of fillers decrease to below 700 ℃. When the total mass fraction of Ga,In,Sn is 15% and the atomic ratio of Ga∶In is 2∶7, that is, the optimal filler Ag61.2Cu23.8Ga3In10.5Sn1.5 liquidus point is the lowest, 675 ℃. And this filler has good processability with which filler can form strips with 0.05～0.2 mm thickness after rotary forging, annealing, cold rolling. The joints of CuAgZr alloy with gap width of 0.2 mm can be brazed successfully by Ag612Cu23.8Ga3In10.5Sn1.5 filler at 675～735 ℃. The joints have two different varies of microstructures, which are Ag-rich phase+Curich phase and Ag-rich phase+Cu-rich phase+AgCu eutectic structure respectively. The shear strength is around 275 MPa in joints brazed at 675 ℃ with 0.2 mm gap width, and the fracture is ductile fracture. The microstructure characterization and shear properties tests of the joints show that the AgCuGaInSn brazing filler is suitable for the brazing of Cu3Ag0.5Zr alloy.