Dealloying and corrosion of Al alloy 2024-T3

We present results of a comprehensive electrochemical study aimed at determining the factors that control the corrosion evolution of the important structural alloy Al 2024-T3. An important aspect of corrosion in this alloy is copper redistribution. The redistributed copper serves to enhance the kinetics of the corrosion process and presents some major difficulties with respect to development of new families of conversion coatings. Two major sources of "mobile" copper are discussed, the Al₂CuMg S-phase and copper in solid solution. In each case, a dealloying mechanism is responsible for liberating copper that becomes available to redistribution by solid state and/or liquid phase transport mechanisms. This work is concerned with identifying the relative importance of these sources of copper and the active transport mechanisms. In order to decouple the sources of copper, we designed "synthetic" 2024 alloys that emulate the oxygen reduction kinetics of the real alloy. Our results indicate that, in principal, both sources of copper are operative during redistribution and, for the particular alloy that we examined, both contribute about equally to the amount of redistributed copper.