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 (RP) over time, as evaluated from EIS at the low
frequency limit incorporating full consideration of the pseudoinductive
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.