Effect of Brazing Temperature on Electrochemical Performance and Zinc Diffusion of AA7072 Clad in Tri-layer Aluminum Brazing Sheet AA7072/3003/4343

A tri-layer aluminum brazing sheet AA7072/3003/4343 is used for the manufacture of concentric oil cooler (ACOC) at Dana Corporation. The effect of brazing temperature cycle on corrosion potential and zinc diffusion of this tri-layer material was investigated in ASTM G69-97 standard solution by electrochemical technique. The galvanic corrosion currents between the zinc-containing AA7072 clad and the nonzinc-containing AA3003 and AA4343 were also examined in this solution. The cross-sectional corrosion potential profiles were established for this tri-layer material brazed at four different brazing temperature cycles. The zinc distribution across the brazing sheet both before and after brazing was derived from the corrosion potential measurements. The studies show that there are significant potential differences and galvanic currents between the AA7072 clad and those non-zinc containing alloys both before and after brazing. This indicates that the zinc-containing AA7072 layer can potentially provide a sacrificial protection to both AA3003 core alloy and AA4343 braze clad alloy. The zinc contents are not constant within the AA7072 clad layer in both the as-received and post-brazed conditions, which can be related to the diffusion of zinc during the clad manufacturing and the brazing process. The results provide valuable information on the understanding of the corrosion performance and mechanism of the multi-layer aluminum brazing material with zinc containing clad. The electrochemical measurement method could potentially be used to predict the brazing temperature and the zinc distribution within the materials.