Evidence for Cu ion formation by dissolution and dealloying the Al2CuMg intermetallic compound in rotating ring-disk collection experiments

Rotating ring-disk collection experiments and stripping voltammetry have be en used to detect Cu ions generated by dissolution of the Al2CuMg intermeta llic compound in aqueous chloride solutions. Cu ions are generated under op en-circuit conditions (open-circuit potential -0.930 V-SCE), or by slight a nodic or cathodic polarization (+/- 0.050 V from the open-circuit potential ). In all cases, Cu ion generation occurs even though the electrode potenti al is hundreds of millivolts negative of the equilibrium potential, Ec, Res ults show that Cu ion generation is strongly dependent on the degree of sol ution aeration, indicating a role fur Cu oxidants in the liberation process . Copper chloride-complex formation and local surface curvature effects can shift the Cu equilibrium potential in the active direction, but neither ph enomenon appears to play a primary role in oxidation of Cu from the interme tallic compound. Rather, the results of this study support the notion that Cu ion generation involves (i) dealloying of the intermetallic compound, (i i) nonfaradaic liberation of mechanically and electrically isolated metalli c Cu clusters by physical coarsening of the dealloyed particle, and (iii) o xidation of the electrically isolated Cu clusters. This Cu ion generation m echanism is believed to be a significant factor contributing to the poor co rrosion resistance and poor conversion coating characteristics of Al2CuMg-b earing alloys. (C) 2000 The Electrochemical Society. S0013-4651(99)01-012-5 . All rights reserved.