Galvanic Corrosion and Inhibition of GW103 and AZ91D Mg Alloys Coupled to an Al Alloy in an Ethylene Glycol Solution at Ambient and Elevated Temperatures

Abstract

The galvanic corrosion of GW103 and AZ91D coupled to an Al alloy (Al 7005 [UNS A97005]) in an ethylene glycol (EG [C 2 H 6 O 2 ]) solution at ambient (25°C) and elevated temperatures (90°C) was investigated using open-circuit potential (OCP), coupling potential (CP), galvanic current density, potentiodynamic polarization curve, and electrochemical impedance spectroscopy (EIS). Moreover, weight-loss measurement and scanning electron microscopy (SEM) also were used to investigate the galvanic corrosion damage of the coupled Mg alloys. The galvanic corrosion behaviors of the couples were compared in the EG solution before and after a combination of inorganic inhibitor sodium phosphate (Na 3 PO 4 ) and organic inhibitor sodium dodecylbenzenesulfonate (C 18 H 29 NaO 3 S) was added to the solution. It was found that both the general corrosion and galvanic corrosion of the Mg alloys were mitigated by the organic-inorganic inhibitor package. The most interesting finding was that the anode and cathode of the Mg alloy-Al alloy couples were reversed by adding inorganic and organic inhibitors into the blank EG solution. The anode-cathode reversal can be attributed to the OCP changes of the anode and cathode after inhibitor addition. The measured galvanic behavior was in good agreement with the mixed-potential theory predictions.

Review of Recent Developments in the Field of Magnesium Corrosion

“…Inhibition was ascribed to a synergistic influence of the organic and inorganic compounds. Inhibition of the inhibitor combination decreased dramatically when a Mg alloy was coupled with other metals . In some cases, the inhibitor combination worsened the galvanic corrosion of the Mg alloys .…”

“…In some cases, the inhibitor combination worsened the galvanic corrosion of the Mg alloys . In another case, it caused a reversal of the anode and cathode . Huang et al found that some organic inhibitors, such as piperazine and pyrazine, without mixing with an inorganic compound, can also act as an inhibitor for a Mg alloy in an ethylene glycol solution.…”

Corrosion behavior and prevention strategies for magnesium (Mg) alloys

“…Basically, modifi cation of the environment includes increasing the pH value, reducing the concentration of aggressive species and adding passivators or inhibitors (Song, 2007a ;. Recently, some organic and inorganic inhibitors as well as combinations thereof have been developed for Mg alloys (Hu et al ., , 2012aHuang et al ., , 2012. Due to the high electrochemical activity and the presence of the corrosion product fi lm, identifi cation of a highly effi cient inhibitor for Mg is currently still diffi cult.…”