The Effects of Chloride Implantation on Pit Initiation in Aluminum

High-purity aluminum samples were implanted with 35 keV Cl + then polarized in both Cl - -containing and Cl - -free electrolytes in order to ascertain corrosion behavior as a function of Cl - content in the oxide. Implant fluence between 5 × 10 15 and 2 X 10 16 Cl + cm -2 resulted in little or no localized attack. Implant fluences of 3 X 10 16 and 5 X 10 16 Cl + cm -2 resulted in significant pitting in a Cl - -free electrolyte with the severity scaling as a function of implant fluence. The low variability in the pitting behavior of the 5 X 10 16 Cl + cm -2 sample suggests that this implant dosage results in a critical Cl - concentration in the oxide for pit nucleation. The passive current density (i pass ) decreased with increasing implant fluence. A space-charge effect is proposed to account for this phenomenon, although effects from defect interactions and possible oxide thickening are still under consideration.