Evolution of the surface chemistry of hot dip galvanized Zn–Mg–Al and Zn coatings on steel during short term exposure to sodium chloride containing environments

Editors' Choice—Dealloying of MgZn2Intermetallic in Slightly Alkaline Chloride Electrolyte and Its Significance in Corrosion Resistance

“…They found that on the Zn-Al-Mg alloy coating, a stable protective film of Zn 6 Al 2 (CO 3 )(OH) 16 · 4H 2 O layer decreased further corrosion on the surface. Duchoslav et al 10 surveyed the evolution of corrosion products on the surface of Zn-2 wt% Al-2 wt% Mg hot-dip galvanized alloy during short term exposure to standardized salt spray test. It was concluded that a rapid formation of layered double hydroxides (LDH) stabilized the surface pH and hindered further surface alkalization as compared to the standard Zn coating during the initial corrosion attack.…”

“…3,[8][9][10][11][12][13][14] The improved corrosion stability of the Zn-Mg alloy has been attributed the formation of a compact simonkolleite (Zn 5 (OH) 8 Cl 2 · H 2 O) layer, on the Zn-Mg coating serving as a barrier to oxygen diffusion. 8,9 Further, it has been suggested that the precipitation of alkali-resistant Mg(OH) 2 is responsible for the reduced oxygen activity at the Zn cathode.…”

Utilization of chemical stability diagrams for improved understanding of electrochemical systems: evolution of solution chemistry towards equilibrium

“…2,18,[30][31][32][33][34] The work by Plagemann et al will be used here to exemplify the utility of chemical stability diagrams. 18 Most notably, a thermodynamic framework is needed to explain the observed disparity in corrosion product (unidentified) formation as a function of different Mg-Zn pigment compositions exposed to constant salt spray exposure testing.…”

“…2,30,[32][33][34] Whereas this case study examined the effect of changing the nature of the dissolving interface 2,18 on the final state of equilibrium, the next section will investigate the effect of changing the nature of the electrolyte on final chemical equilibrium.…”

“…As is common for outdoor exposure, and as was found in this Mg-Li study, carbonate compounds are formed and can be considered along with the usual oxide/hydroxide compounds. 2,24,30,[32][33][34][36][37][38] The stability of a carbonate compound depends on the concentration of the carbonate ion as a function of pH, as the carbonate ion can participate in proton exchange reactions according to the stability of its variously protonated species as a function of pH. 39 The total concentration of each carbonate species present as a function of pH can be calculated as expressed by Eq.…”