9307308 Hebert This research examines the mechanism of surface pitting in aluminum alloys. Surface impurity concentration is varied by annealing and surface dissolution treatments to asses the effect on pit density. Surface impurity and defect concentrations are monitored through surface analytical techniques, including Rutherford Backscattering Spectroscopy, Secondary Ion Mass Spectroscopy, and positron annihilation measurements. Relationships between the importance of candidate defects (e.g., vacancy/impurity clusters, dislocations, surface roughness) as corrosion sites are sought. Early stages of pit initiation are examined through the interaction of chloride ions with aluminum oxide films. The positron measurements are carried out as a function of temperature in order to provide defect migration or bonding energies so that the atomic structure of the defects can be characterized. These measurements are performed on high purity aluminum doped with impurity elements to determine how various impurities behave as corrosion sites. %%% Practical information should result from this research that will assist in controlling corrosion of aluminum and its alloys. ***
