Effect of copper on anodic activity of aluminum-lead model alloy in chloride solution

This paper investigates the effect of alloying element Cu on the anodic activation of aluminum by trace element Pb in chloride solution based on a comparison of the surface and electrochemical properties of a model AlPb alloy, containing 20 wt-ppm Pb, and an AlPbCu alloy, containing 0.5 wt% Cu and 20 ppm Pb. Anodic activation of AlPb occurs by the formation of a nanosized metallic Pb-rich film at the thermal oxide - aluminum substrate interface as a result of heat treatment at 600°C. Activation by Pb was reduced in the presence of Cu, although the Pb film was still formed by heat treatment independent of the presence of Cu in solid solution. While the anodic polarization behavior and corrosion mechanism were similar for the binary and ternary alloys, the corrosion rate at identical applied anodic potentials was significantly reduced by the presence of copper in the alloy. Copper became enriched at the surface as a result of selective corrosion of the more active aluminum component. Thus, the increased passivity of the surface by the presence of Cu was attributed to the ennobling effect of Cu countering the activating effect of Pb.