Effects of corrosive media on the localized corrosion forms of Mg-3Zn alloy

Mg-3Zn alloy presents filiform corrosion in NaCl solution but pitting corrosion in Na2SO4 solution.The mechanisms for those different localized corrosion forms were investigated using SEM,XPS and electrochemical measurements.It is found that surface films and different features of Cl– and SO42–determine the corrosion forms of Mg-3Zn alloy.The surface film formed in Na Cl solution is porous,and Cl–ions are enriched in the filament heads,resulting in propagation of corrosion along the horizontal direction to form filiform corrosion.However,the surface film formed in Na2SO4 solution is compact,and SO42– anions are aboundant at the bottom of corrosion pits,resulting in the propagation of corrosion along the vertical direction to form pitting corrosion.Corrosive media play a key role in the initiation and propagation of corrosion,further resulting in the different corrosion forms of Mg alloys.