Electrochemical and Corrosion Performance of Zinc-containing Tri-layer Aluminum Brazing Sheet AA7072/3003/4343 in OY Synthetic Water 2005-01-2035

This work focuses on the electrochemical behavior and corrosion performance of a tri-layer aluminum brazing sheet AA7072/3003/4343 in OY synthetic water. Post-brazed tri-layer sheet samples from four different brazing temperature cycles were subjected to the immersion corrosion test in OY synthetic water for 30 days at 88 ± 2°C to investigate the effect of brazing temperature and zinc diffusion on the corrosion performance of the material. Electrochemical measurement method was also used for examining the corrosion potentials and the galvanic corrosion currents for AA7072, AA3003 and AA4343 both before and after brazing in OY water. The results show that the zinc-containing AA7072 sacrificial layer corroded preferentially during the immersion corrosion tests in OY water. When the sample was brazed at 600°C or lower temperature, the zinc content is higher than 0.63% on the AA7072 external surface and higher than 0.20% at the AA7072/AA3003 interface, with only the general corrosion occurring on the AA7072 clad layer. However, when the sample was brazed at 620°C, the zinc remained lower than 0.40% on the AA7072 external surface and lower than 0.20% at the AA7072/AA3003 interface. The corrosion mode changed from general to localized corrosion. Pitting corrosion took place on the AA7072 clad layer and penetrated into the core AA3003, which indicates that the residual zinc is not sufficient to provide sacrificial protection to the core AA3003. This work reveals a correlation between the OY corrosion performance of AA7072 containing multi-layer material and the brazing temperature cycle as well as zinc diffusion within the material.