The Influence of Incubation Time on the Passive Film Breakdown of Aluminum Alloys in Seawater.
Research and development rept.,
DAVID W TAYLOR NAVAL SHIP RESEARCH AND DEVELOPMENT CENTER ANNAPOLIS MD SHIP MATERIALS ENGINEERING DEPT
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Potential-controlled electrochemical methods were used to characterize the pitting behavior of 6061 alloy aluminum in synthetic ocean water. Irreproducible breakdown potentials E sub bd and reproducible repassivation potentials E sub rp were determined from cyclic anodic polarization CAP. Reproducible breakdown and repassivation potentials were found from the quasi-stationary anodic polarization method however, the breakdown potential values were shifted in the electronegative direction relative to the CAP method due to the allowance of a longer incubation time. These results support the theory that with sufficient incubation time, pit initiation and propagation will occur at potentials at or slightly above the repassivation potential, and that the repassivation potential value is the only characteristic potential for aluminum. The quasi-stationary anodic polarization method used for E sub rp determination provides a reproducible electrochemical method for obtaining E sub rp after minimal pit growth or surface damage. Cyclic anodic polarization can also be used for determining a representative potential if surface damage subsequent to pit initiation is minimized.
- Properties of Metals and Alloys