Utilization of a Partially Non-aqueous Electrolyte for the Spatial Mapping of Mg Corrosion Using a Model Mg–Al Electrode

In-situ techniques to spatially map micro-galvanic corrosion are particularly important for alloys with heterogeneous microstructures. In particular, scanning electrochemical microscopy (SECM) has been utilized to map microstructural features on Mg which may control the corrosion rate. However, rapid corrosion rates of Mg in fully aqueous environments interfere with mapping capabilities. A mixed aqueous and non-aqueous electrolyte, containing methanol and H₂O, is proposed which is capable of mapping the active corrosion on Mg with time. However, thorough understanding the effect of methanol additions on the corrosion rate was required. Therefore, the intrinsic corrosion rates of Mg in varying amounts of methanol (0–100 wt%) were investigated using electrochemical impedance spectroscopy (EIS) by exploring the corrosion rate on an Al wire embedded in Mg as a galvanic couple. The nature of the non-aqueous electrolyte on the EIS response is discussed. The evolution of this intrinsic corrosion behavior at the galvanic couple was investigated using a combination of optical microscopy, SECM and mixed potential theory.