Probing anion-metal interactions on aluminum and Al 2024 alloy by in situ and ex situ methods. A status report

摘要

We studied deposition processes, adsorption, incorporation, and precipitation, of solute ions on the surface of aluminum and aluminum alloy 2024-T3 using electrochemical, radiochemical and ultra-high vacuum spectroscopic techniques. The measurements were carried out at open circuit potential and in the electrode potential range on the negative side of the open circuit potential (cathodic polarizaiton conditions), at various pH. The focus was on sorption reversibility, the relationship between anion's surface concentration and pH, as well as on the effect of local reactions on ion depoision. We have found that ion deposition is primarily controlled by the solution pH on aluminum surfaces. The change in the alloy surface composition and morphology induced by the electrochemical treatment and ion deposition was monitored by scanning Auger microscopy and energy dispersive X-ray spectroscopy. We have found that both the solution pH and electrode polarization exhibit major influence on composition and stability of intermetallics as well as the ion surface coverage around these copper-rich centers. Specifically, the extent of ion deposition usually increased in the following order: S-phae particle>=Cu-Fe-Al intermetallics>bulk matrix in acidic solutions. The most reactive parts of the Al2024-T3 surface are the S-phase particles, which change their electrochemical character during solution exposure.