Self-corrosion, galvanic corrosion and inhibition of GW103 and AZ91D Mg alloys in ethylene glycol solution

Abstract

The self-corrosion and galvanic corrosion of magnesium based alloys Mg–10Gd–3Y–0·5Zr (GW103) and AZ91D coupled to carbon steel and Cu in ethylene glycol (EG) solution with and without inorganic–organic inhibitor packages Na3PO4+SDBS and Na3PO4+benzoate were investigated through measuring their open circuit potentials, coupling potentials, potentiodynamic polarisation and galvanic current densities. It was found that these two inhibitor packages effectively inhibited the self-corrosion of GW103 and AZ91D but accelerated the dissolution of the carbon steel and Cu in the EG solution. When the Mg alloys were coupled with the carbon steel or Cu, their galvanic current densities were also inhibited if the Na3PO4+benzoate inhibitor package was used in the EG solution. It is surprising that the addition of Na3PO4+SDBS accelerated the galvanic corrosion. Based on the mixed potential theory, it is believed that the variation in Ecorr difference between the anode and cathode and the change of their Tafel slopes after inhibitor addition should be responsible for the galvanic corrosion behaviour of these couples.