Assessing the Corrosion of Commercially Pure Magnesium and Commercial AZ31B by Electrochemical Impedance, Mass-Loss, Hydrogen Collection, and Inductively Coupled Plasma Optical Emission Spectrometry Solution Analysis

The corrosion of commercially pure magnesium (Mg) and AZ31B-H24 with simultaneous measurements of electrochemical impedance (EIS) and hydrogen gas evolved over a 24 h immersion period was studied in solutions of three chloride concentrations. The corrosion rate was determined from the Stern-Geary approach. The integral electrochemical-based mass loss was compared to the gravimetric mass loss and inductively coupled plasma optical emission spectrometry (ICP-OES) solution analysis of the total Mg concentration released. The use of ICP-OES to support the other assessment methods has not been previously reported. Assuming Mg dissolves as Mg²⁺, there was agreement using these four unique measures of Mg corrosion. The integration of the polarization resistance (R_P) over time, as evaluated from EIS at the low frequency limit incorporating full consideration of the pseudo-inductive impedance behavior of Mg, provided excellent correlation to the cumulative mass loss, ICP-OES solution analysis, and volume of hydrogen collected for commercially pure Mg and reported for the first time for AZ31. The choice of using the Tafel slope in the Stern-Geary approach, as well as the subsequent comparison of results to corrosion rate data in the literature, are discussed.