Electrochemical behaviors of quad-layer aluminum brazing sheet composite for automotive applications

The cross-sectional depth corrosion potential profiles for a quad-layer aluminum brazing sheet composite AA4045/ 7072/3003/4045 (UNS A94045/A97072/A93003/A94045) in both the pre- and post-brazed-forms have been established using ASTM G69-97 standard test method. Galvanic corrosion behaviors between the AA 7072 (UNS A97072) layer and the nonzinc-containing AA3003 core alloy and AA4045 clad alloy also have been investigated in ASTM G69-97 solution by galvanic current measurement method. The effect of zinc and other major alloying elements on the corrosion potential was analyzed. The electrochemical studies show that there are significant potential differences (greater than or equal to100 mV) and galvanic currents (similar to2 to 8 x 10(2) muA/cm(2)) between the AA7072 layer and the other nonzinc-containing core and clad layers both before and after brazing. A zinc-containing AA7072 layer appears to be able to provide a sacrificial protection to both core alloy AA3003 and high-silicon braze clad layers such as AA4045 in ASTM G69-97 solution. The zinc distribution across the brazing sheet material was derived from the relative corrosion potential measurements. The distribution of zinc within the material can be related to the diffusion of zinc during the brazing process.