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Research on the corrosion resistance of Cu-Al joints brazed with flux-cored Zn-2Al filler metal

In this paper, the corrosion resistance of the Cu-Al joint brazed with flux-cored Zn-2Al filler metal was investigated, comparing with that of the joint brazed with traditional Zn-2Al filler metal. Results showed that Zn-Al eutectic and α-Al were susceptible to the corrosion attack due to lower galvanic potential than other phases. The corrosion product of the Zn-Al eutectic was η-Zn and the α-Al dissolved after immersing for 48 h due to the galvanic corrosion. The corrosion resistance of the Cu-Al joint was improved by decreasing the area of phases, which was susceptible to the corrosion, when replacing traditional filler metal by flux-cored filler metal. The excessive Al dissolution resulted in lattice distortion and numerous microvoids, which in turn led to the formation and propagation of cracks. Residual oxides and flux in Cu-Al joints could also be the crack sources due to the generation of stress concentration in the process of corrosion. The shear strength of the joint brazed with flux-cored filler metal reached 34.5 MPa after immersing in 3.5 wt% NaCl solution for 18 days, which is higher than that of the joint brazed with traditional filler metal because of two aspects of decreasing brazing time and controlling brazing flux content.