While investigating the influence of an alloying element on the corrosion properties of a metal, materials scientists and engineers typically fabricate an array of samples with increasing concentrations of the alloying element in order to build up a gradient of substrates suitable for corrosion testing. The resulting series of substrates can consist of many samples, which can be time consuming to test and hence slow to reveal the effects of the alloying element’s concentration. In this work, we present a fast, simple, and reliable methodology on an ideal model system for monitoring the effect of one of the most commonly used alloying elements in Magnesium alloys, aluminum, on magnesium’s corrosion behavior using a single Mg-Al diffusion couple sample and the scanning micropipette contact method. The use of ethylene glycol as the solvent was carried out to enhance the stability of the micro electrochemical setup. The corrosion potentials and currents of pure Mg and Al as well as the intermetallic regions were collected using micro polarization measurements without the influence of grain boundaries and inclusion size. Similar measurements performed across the interfacial region of Al diffusion into Mg revealed a threshold value of Al wt% on the corrosion potentials measured. Such methodology proved to be reproducible and therefore is a good way to measure the effects of various alloying elements for any metal in question.