Microgalvanic Current Mapping of Magnesium / Aluminum Galvanic Couple by Scanning Vibrating Electrode Technique (SVET)

Many magnesium alloys exhibit microgalvanic corrosion due to anodic and cathodic reactions that occur at discrete phases. We used the scanning vibrating electrode technique (SVET) to map the local corrosion current distribution profile of specially designed magnesium and aluminum galvanic couples. We studied the effect of anode (Mg) to cathode (Al) area ratio (A/C = 1:9, 3:7 and 1:1) and the effect of electrolyte concentration (sodium chloride solutions, 10, 30, and 280 mM). The galvanic current density is mapped for different immersion time intervals (t= 0 and 1 hour). The SVET response clearly showed that anodic and cathodic current densities on the magnesium and aluminum (Mg-Al) galvanic couple, respectively.  The current density decreased with increasing anode to cathode surface area ratio, and at a given ratio, increased with increasing concentration of the sodium chloride solution. Out results showed that SVET can provide finite current/potential details of the microgalvanic activities within magnesium alloys, which are not possible with conventional electrochemical measurements, and it is an excellent measurement tool for understanding microgalvanic corrosion of magnesium alloys.