School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
Cite this article:
Zhiwei NIU,Zheng YE,Kaikai LIU,Jihua HUANG,Shuhai CHEN,Xingke ZHAO. Microstructure and Property of Cu/Al Joint Brazed with Al-Si-Ge Filler Metal. Acta Metall Sin, 2017, 53(6): 719-725.
Cu/Al brazing has good prospect for applications in the air conditioning and refrigeration industry. A suitable filler metal is the key of Cu/Al brazing. The chemical and physical properties of the filler metal have great influence on the brazing process and parameters. And the strength of the brazing joint is closely related to the properties of the filler metal and the brazing process. While the previous studies have not developed a kind of Cu/Al brazing filler metal which can achieve a tough joint at a low brazing temperature. In this work, the Al-5.6Si-25.2Ge filler metal was first used to braze Cu/Al dissimilar metals, and the melting characteristics of the filler metal, spreading wettability, Cu interfacial structure and strength of brazed joint were investigated systematically. Additionally, the common Zn-22Al filler metal was also used for comparison. The results show that the Al-5.6Si-25.2Ge filler metal possesses low melting temperature (about 541 ℃) and excellent spreading wettability on Cu and Al base metals. The interfacial structure of Al-5.6Si-25.2Ge/Cu was CuAl2/CuAl/Cu3Al2. The thickness of planar CuAl and Cu3Al2 phases was only 1~2 μm, and the thickness of cellular CuAl2 phase was about 3 μm. The interfacial structure of Zn-22Al/Cu was CuAl2/CuAl/Cu9Al4, but the average thickness of the CuAl2 layer was up to 15 μm. The test results of the shearing strength show that the shearing strength of the Cu/Al joint brazed with Zn-22Al filler metal was only 42.7 MPa, but the shearing strength brazed with Al-5.6Si-25.2Ge filler metal was higher (53.4 MPa).
Fig.2 SEM images (a, c) and XRD spectra (b, d) of Al-5.6Si-25.2Ge (a, b) and Zn-22Al (c, d) filler metals
Fig.3 DTA curves of filler metals
Fig.4 SEM images (a, c) and EDS element line scanning along the lines in Figs.4a and c (b, d) of Cu/Al joints brazed with Al-5.6Si-25.2Ge (a, b) and Zn-22Al (c, d) filler metals
Position in Fig.4
Atomic fraction / %
Phase
Al
Cu
Ge
Si
A
67.15
32.85
-
-
CuAl2
B
48.22
51.78
-
-
CuAl
C
41.41
58.59
-
-
Cu3Al2
D
-
-
78.54
21.46
Ge solid solution
E
69.09
30.91
-
-
CuAl2
F
51.17
48.83
-
-
CuAl
G
29.43
70.57
-
-
Cu9Al4
Table 1 EDS results of phases in the interfacial zones of the Cu/Al joints in Fig.4
Fig.5 SEM images of the fracture surface of the Cu/Al joints brazed with Al-5.6Si-25.2Ge (a) and Zn-22Al (b) filler metals
Fig.6 Typical SEM image of the fracture position of the Cu/Al joint
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