The electrochemical characteristics of bulk-synthesized Al2CuMg

An S-phase intermetallic compound (Al2CuMg) was synthesized in bulk form to characterize its, electrochemical behavior by conventional techniques. Lar ge S-phase crystals, suitable for analysis, were formed in an Al-Cu-Mg ingo t. The structure of Al2CuMg was verified by electron-backscatter Kikuchi pa tterns and X-ray diffraction. The composition of Al2CuMg was verified by el ectron-probe microchemical analysis. Open-circuit potential and potentiodyn amic polarization measurements were conducted in aerated and deaerated 0.5 M NaCl solutions. Bulk S-phase electrodes exhibited steady-state open-circu it potentials ranging from -0.920 to -0.930 V-SCE, which did not vary signi ficantly with changes in solution aeration. In aerated solutions, the phase dissolved vigorously at modest anodic polarizations, and no passive respon se was detected. Limiting cathodic current densities on the order of 1.0 mA /cm(2) were measured for small cathodic polarizations, probably due to the development of a porous, catalytic surface. Overall, the S phase supports r apid anodic and cathodic reaction kinetics, which contribute to the instabi lity of the compound and subsequent Liberation of Cu. These results implica te the presence of S-phase intermetallic particles as a key contributor to the poor corrosion resistance of Al-Cu-Mg alloys. (C) 1999 The Electrochemi cal Society. S0013-4651(99)01-011-3, All rights reserved.