Electrochemical Impedance Spectroscopy is a useful technique to evaluate the corrosion properties of organic and inorganic coatings on metals and alloys. I have used this technique to study the effect of micro arc oxidation on corrosion behavior of Mg AZ31 alloy. Now I am planning to investigate the corrosion properties of some dissimilar weldments. Can I use EIS for corrosion studies of welds?
There are other methods for different approaches in terms of corrosion resistance of surface coatings: potentiodynamic polarization curves, method of polarization resistance and method of electrochemical noise. I think the first is an effective and simple method
Impedance measurements only provide an average electrochemical response over the whole exposed surface. Thus, if you are wanting to study the change in response of a localised effect, you either need to shield the rest of the surface so that only the area of interest is active, or you need to choose a different investigation technique.
This comment would apply equally to the use of polarization curves, the analysis of which would probably need to be more 'intuitive' (i.e. you would need to have more experience looking at them before you would be able to interpret what they are telling you, which if fine if you're used to using polarization scans but not so helpful if you've done more impedance work as EIM plots give more mechanistic information.
It is difficult to offer more advice on what technique might be the most effective without greater knowledge of your experimental set-up, but some of the more informative results on differential weld corrosion behavior have been obtained using the multiple ZRA type approach.
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