Electrochemical Behavior of AZ31 Mg Alloy in Neutral Aqueous Solutions Containing Various Anions

Abstract

<p>This work was performed to characterize the electrochemical behavior of AZ31 Mg alloy in neutral aqueous solutions where Cl<sup>−</sup>, SO<sub>4</sub><sup>2−</sup>, PO<sub>4</sub><sup>3−</sup>, and F<sup>−</sup> ions were present and pH was adjusted to 6 to exclude the contribution of H<sup>+</sup> and OH<sup>−</sup> ions. Open-circuit potential (OCP) transient, electrochemical impedance spectroscopy (EIS) and potnetiodynamic polarization curves were employed. The OCP value appeared to decrease in the order of F<sup>−</sup> > Cl<sup>−</sup> > SO<sub>4</sub><sup>2−</sup> > PO<sub>4</sub><sup>3−</sup> ions while corrosion current density increased in the same order. Electrochemical impedance spectroscopy (EIS) data showed two capacitive arcs in all the solutions and one more inductive arc appeared in PO<sub>4</sub><sup>3−</sup>-containing solution. By fitting of two capacitive arcs, capacitance of dense film (C<sub>df</sub>), resistance of porous film (R<sub>pf</sub>) and double layer capacitance (C<sub>dl</sub>) and charge transfer resistance (R<sub>ct</sub>) beneath the porous films were obtained. A simplified model in which various thicknesses and coverages of dense and porous films are assumed to be present on the AZ31 Mg alloy surface, is suggested to explain the effects of four different anions on the electrochemical behavior of AZ31 Mg alloy.</p>

Corrosion and Formation of Surface Films on AZ31 Mg Alloy in Aqueous Solution Containing Sulfate Ions with Different pHs

“…After immersing the specimens for 30 min, EIS measurements were performed over a frequency range of 10 5 to 10 −1 Hz, with a signal amplitude of 10 mV. The obtained EIS results were fitted with EC-Lab software using equivalent circuit models, as suggested in a previous paper [26]. Both the OCP and the EIS measurements were repeated three times to ensure reproducibility.…”

“…The Nyquist plots in Figure 5 were fitted using the equivalent circuits suggested in previous studies [26]. The resistance and capacitance values of the porous and dense surface films obtained are shown in Figure 6 as a function of the pH of the solution.…”

“…In conclusion, it can be said that the surface films formed on AZ31 Mg alloy are denser and thicker with the increasing solution's pH, which effectively serves as a barrier against corrosion. The Nyquist plots in Figure 5 were fitted using the equivalent circuits suggested in previous studies [26]. The resistance and capacitance values of the porous and dense surface films obtained are shown in Figure 6 as a function of the pH of the solution.…”

“…We have reported the effects of chloride ion (Cl − ), sulfate ion (SO 4 2− ), phosphate ion (PO 4 3− ) and fluoride ion (F − ) in neutral aqueous solutions on the electrochemical and corrosion properties of the AZ31 Mg alloy [26,27]. An interesting aspect among the experimental findings was that no weight change was observed in the AZ31 Mg alloy during immersion in a neutral aqueous solution containing sulfate ions.…”