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Atmospheric Pitting Corrosion of AA7075-T6 Under Evaporating Droplets

Morton, Sean C
http://rave.ohiolink.edu/etdc/view?acc_num=osu1367585533

Abstract Details

2013, Master of Science, Ohio State University, Materials Science and Engineering.
Pitting corrosion of polished and etched AA7075-T6 in the presence of 3.5 wt % NaCl electrolyte was investigated both with standard full immersion testing, and with the application of evaporating electrolyte droplets in a fixed humidity environment. Testing included the addition of chromate-, vanadate, and cerous-based corrosion inhibiting salts in concentrations of 3 mM, 0.3 mM and 0.03 mM. A Scanning Kelvin Probe (SKP) was used to investigate the in situ corrosion potential behavior of the electrolyte droplets. In immersion testing, widespread pitting at intermetallic particles was observed in uninhibited solution. Similar but less severe attack was observed with additions of 0.03 mM vanadate and cerous ions. At higher concentration of vanadate, small numbers of very large pits were found, while higher concentrations of cerous ions provided very good inhibition. Chromate provided nearly complete inhibition of corrosion in all concentrations of immersion testing. In all cases of immersion testing, the measured corrosion potential was found to be pinned near to the pitting potential. In droplet testing, corrosion potentials measured by SKP were indicative of a range of behaviors, including metastable pitting, inhibition/passivation, and a form of corrosion attack in which pitting at the edge of the test droplet resulted in the formation of an adjacent, secondary droplet. This secondary droplet effect, observed in uninhibited NaCl droplets as well as with 0.03 mM concentration of both vanadate and cerous ions, was investigated in more detail with SKP. The attack progresses by large-scale separation of anodic and cathodic regions under the droplet, with the anodic region initiating near the edge of the droplet. A model is described for the formation of the secondary droplet and associated attack, by deliquescence of water vapor due to an excess of ions from the anode diffusing to the edge of the droplet.
Gerald Frankel, PhD (Advisor)
Rudolph Buchheit, PhD (Committee Member)
67 p.
Materials Science
corrosion; 7075; aluminum corrosion; atmospheric corrosion; corrosion inhibition

Recommended Citations

Citations

  • Morton, S. C. (2013). Atmospheric Pitting Corrosion of AA7075-T6 Under Evaporating Droplets [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1367585533

    APA Style (7th edition)

  • Morton, Sean. Atmospheric Pitting Corrosion of AA7075-T6 Under Evaporating Droplets. 2013. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1367585533.

    MLA Style (8th edition)

  • Morton, Sean. "Atmospheric Pitting Corrosion of AA7075-T6 Under Evaporating Droplets." Master's thesis, Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1367585533

    Chicago Manual of Style (17th edition)

osu1367585533
1,190
© 2013, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.