The effect of vanadate, phosphate, fluoride compounds on the aqueous corrosion of magnesium alloy AZ31 in dilute chloride solutions

Zhiyuan Feng, Jichao Li, Zi Yang, Rudolph Buchheit

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


The anodic polarization response of magnesium alloy AZ31 was first characterized during exposure to aerated 0.1 M NaCl solutions with millimolar additions of NaVO3, Na3PO4, Na2HPO4, NaF and various pairings to assess their ability to inhibit corrosion kinetics and retard localized corrosion. Each of the candidate inhibitors reduced the corrosion rate of the alloy to some degree. A Na3PO4-NaVO3 pair produced a good inhibiting effect decreasing the corrosion rate to about 10-7 A/cm2, which was two orders of magnitude lower than the uninhibited control case. A Bliss Independence assessment indicated that this inhibitor pair acted synergistically. A Na2HPO4-NaVO3 pair reduced the corrosion rate to 10-6 A/cm2 but was not assessed to be acting synergistically. The NaVO3-NaF pair did not reduce the corrosion rate significantly compared to the control case and was an antagonistic pairing. SEM imaging showed film formation due to exposure, which appears to be the origin of the observed inhibition. The resistance to localized corrosion was assessed as the difference in the breakdown potential and the corrosion potential, with larger values indicating a lower probability of localized corrosion during free corrosion exposures. The effects of the inhibitors on this characteristic were mixed, but each of the inhibitor pairs yielded potential differences in excess of 100 mV. A conceptual conversion coating process based on a mixture of vanadate and phosphate compounds were demonstrated. A fluoride-bearing formulation produced coatings whose total impedance was increased by a factor of two compared to an uncoated control. A fluoride-free formulation produced coatings whose corrosion resistance was increased by more than a factor of three.

Original languageEnglish
Article number1325
Issue number6
StatePublished - Mar 1 2020

Bibliographical note

Funding Information:
Funding: This research was funded by The Army Research Laboratory, grant number W911NF-14-2-0004. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Laboratory or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation herein.

Publisher Copyright:
© 2020 by the authors.


  • Conversion coating
  • Corrosion
  • Fluoride
  • Inhibition
  • Light alloys
  • Magnesium
  • Phosphate
  • Vanadate

ASJC Scopus subject areas

  • Materials Science (all)
  • Condensed Matter Physics


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