INFLUENCE OF THE COMPOSITION OF Zn-Al FILLER METAL ON THE INTERFACIAL STRUCTURE AND PROPERTY OF Cu/Zn-Al/Al BRAZED JOINT

The Cu/Al dissimilar metal joint is a compound structure that can efficiently decrease manufacturing costs, reduce product weight, and integrate the advantages of both metals. For the excellent comprehensive properties, the Cu/Al dissimilar metal joint has broad application prospects in air conditioners, refrigerators, cables, electronic components, solar collectors, et al. Brazing is considered as a promising method to join the Cu/Al dissimilar metal for lower residual stress, lower costs, higher precision and better adaption to the structure of joint. Meanwhile, the Zn-Al filler metal is considered as the relatively ideal filler metal due to better property of the Cu/Zn-Al/Al joint. However, the influence of the composition of the Zn-Al filler metal on the interfacial structure near Cu substrate and property of the Cu/Al joint has not been investigated. In this work, the Cu/Al joints were brazed by Zn-15Al, Zn-22Al, Zn-28Al, Zn-37Al and Zn-45Al filler metals, respectively. The influences of the composition of Zn-Al filler metals on the interfacial structure near Cu substrate of the Cu/Al joints were investigated, and the relationships of the composition of the Zn-Al filler metals, the interfacial structure and the shear strength of the Cu/Al joints were described systematically. It was found that the interfacial structure of the Cu/Zn-15Al/Al brazed joint was Cu/A14 2Cu32Zno2. For thinner A14.2Cu3.2Zn.2.2 layer (2-3 pm), the shear strength of the joint was higher (66.3 M Pa). With the increase of Al content of the filler metal, the thickness of A14.2Cu3.2Zn0,2 layer at the interface was increased for Cu/Zn-22A1/A1 joint, even some CuAl2 phase can be found nearby the A14.2Cu3.2Zn0.7 layer of Cu/Zn- 28A1/A1 joint, and the shear strength of the Cu/A1 joints were decreased correspondingly. When the Cu/A1 joint was brazed by the Zn-37A1 filler metal, the interfacial structure near Cu substrate was transformed into Cu/A14.2Cu3.2Zn0,2/CuAl2. For higher brittleness of CuAl2 layer, the shear strength of the joint was decreased obviously (34.5 MPa). Finally, the interfacial structure of the Cu/Zn-45A1/A1 joint was transformed into Cu/CuAl2, the interfacial structure lead to the lower shear strength of the joint, which is only 31.6 MPa.