The Tafel plot which you can see in the picture below, is the most ideal polarization curve that can be. It was built with the data points computed by the Butler-Volmer equation for the following parameters: T = 298K, nc = na = 2 electrons, α = 0.5, io = 10-11 A. Any real polarization curve is 'worse' from the point of view of Tafel analysis.
Two postgraduates (each in the framework of his/her research) had to compare corrosion rates of magnesium alloys in salt water measured by several techniques. Both obtained weird results, which can be summarized as follows:
1. Virtually any Al-containing Mg alloy consists of two main phases (the very important influence of minor additives is ignored at this stage):
α-phase: essentially pure magnesium
β-phase: Mg17Al12 (calculated 55.7wt% Mg)