Cerium deposition on aluminum alloy 2024-T3 in acidic NaCl solutions

We analyzed the interaction of cerium ions with surface intermetallics on Al 2024-T3 in NaCl media under open circuit conditions at pH 3 using scanning electron microscopic, Auger-electron spectroscopic (AES), and energy dispersive X-ray techniques (EDX), as well as electrochemistry. The results indicate that cerium deposition in a pH 3.0 NaCl solution is strongly surface-site specific. The cerium deposition was the highest on the S-phase particles, lower on the (Cu, Fe, Mn) Al-6 sites, and minimal on the bulk matrix. In addition to the formation of a cerium-rich film on the intermetallics, we found that cerium incorporated into the porous structure of the dealloyed S-phase particles (Cu- Mg-Al intermetallics). Our analyses show that cerium does not prevent the dealloying of the intermetallic particles; in fact, the dealloying is necessary for local cerium deposition. AES and EDX data also revealed significant chloride enrichment on the cerium-rich sites. From our electrochemical measurements we conclude that the cerium-rich layer formed in acidic solution at short exposure times does not inhibit cathodic reaction on the intermetallics. (C) 2003 The Electrochemical Society.