Corrosion behaviors in the brazed seam of Al/Cu dissimilar joints brazed by Zn-Al alloys

Cu/Al composite structures have considerable prospect for applications in refrigeration, automotive, power plant, and aerospace industries. The corrosion resistance of the Cu/Al joints is crucial to these applications. In this paper, corrosion behaviors of the Cu/Al joints brazed with three kinds of commercial Zn-Al filler metals were evaluated by salt spray test. The microstructure and composition of the brazing seam before and after corrosion were investigated and compared. The results showed that there were two kinds of corrosions in the joints, i.e., pitting corrosion at exposed brazing seam and corrosion cracks inside brazing seam. The pitting corrosion occurred at the massive Zn-rich precipitates and can be impeded by staggered CuAl2 phases. The corrosion cracks propagated along the diffusion layer or Zn-rich precipitates. Thick diffusion layer and massive Zn-rich precipitates accelerated the propagation of the corrosion crack. The joint brazed with Zn-15Al, Zn-22Al, and Zn-28Al lost 45%, 38%, and 30% the initial strength after 36 h salt spray corrosion, respectively. In general, the increase of Zn content in the filler metals resulted in drastic decline of the joint corrosion resistance.