Jump to main content
Jump to site search

Volume 180, 2015
Previous Article Next Article

In situ monitoring of corrosion mechanisms and phosphate inhibitor surface deposition during corrosion of zinc–magnesium–aluminium (ZMA) alloys using novel time-lapse microscopy

Author affiliations

Abstract

In situ time-lapse optical microscopy was used to examine the microstructural corrosion mechanisms in three zinc–magnesium–aluminium (ZMA) alloy coated steels immersed in 1% NaCl pH 7. Preferential corrosion of MgZn2 lamellae within the eutectic phases was observed in all the ZMA alloys followed by subsequent dissolution of Zn rich phases. The total extent and rate of corrosion, measured using time-lapse image analysis and scanning vibrating electrode technique (SVET) estimated mass loss, decreased as Mg and Al alloying additions were increased up to a level of 3 wt% Mg and 3.7 wt% Al. This was probably due to the increased presence of MgO and Al2O3 at the alloy surface retarding the kinetics of cathodic oxygen reduction. The addition of 1 × 10−2 mol dm−3 Na3PO4 to 1% NaCl pH 7 had a dramatic influence on the corrosion mechanism for a ZMA with passivation of anodic sites through phosphate precipitation observed using time-lapse image analysis. Intriguing rapid precipitation of filamentous phosphate was also observed and it is postulated that these filaments nucleate and grow due to super saturation effects. Polarisation experiments showed that the addition of 1 × 10−2 mol dm−3 Na3PO4 to the 1% NaCl electrolyte promoted an anodic shift of 50 mV in open circuit potential for the ZMA alloy with a reduction in anodic current of 2.5 orders of magnitude suggesting that it was acting primarily as an anodic inhibitor supporting the inferences from the time-lapse investigations. These phosphate additions resulted in a 98% reduction in estimated mass loss as measured by SVET demonstrating the effectiveness of phosphate inhibitors for this alloy system.

Back to tab navigation

Supplementary files

Publication details

The article was received on 08 Dec 2014, accepted on 21 Jan 2015 and first published on 21 Jan 2015


Article type: Paper
DOI: 10.1039/C4FD00251B
Author version available: Download Author version (PDF)
Citation: Faraday Discuss., 2015,180, 361-379
  •   Request permissions

    In situ monitoring of corrosion mechanisms and phosphate inhibitor surface deposition during corrosion of zinc–magnesium–aluminium (ZMA) alloys using novel time-lapse microscopy

    J. Sullivan, N. Cooze, C. Gallagher, T. Lewis, T. Prosek and D. Thierry, Faraday Discuss., 2015, 180, 361
    DOI: 10.1039/C4FD00251B

Search articles by author

Spotlight

Advertisements