Abstract
ABSTRACT In-situ crack tip pH measurements for corrosion fatigue (CF) cracks in sensitized AA5456-H116 loaded under low loading frequencies show that cathodic polarization has the ability to arrest actively growing stress corrosion (SCC) and CF cracks and produce a local alkaline crack tip pH. A method for measuring crack tip pH in-situ was developed. For AA5456-H116 under a single level of high sensitization, CF experiments while loading in the Paris regime at a loading frequency of 0.1 Hz were conducted under freely corroding conditions and a cathodic polarization of −1.3 VSCE. Results show that under freely corroding conditions the crack actively grows, and the crack tip pH is slightly acidic, while at −1.3 VSCE an alkaline crack tip develops with a pH of 10-12. The findings of this study support the earlier published hypothesis that crack arrest of SCC and low loading frequency CF cracks is due to corrosion-induced blunting after the development of highly alkaline conditions that causes corrosion of the crack tip region blunting and halting the crack.
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