Microstructure of localized corrosion front on Mg alloys and the relationship with hydrogen evolution

Actively propagating localized corrosion fronts on pure Mg, Mg-Zn-Ca-Mn, and Mg-Y alloys in NaCl aqueous solutions were investigated by site-specific characterization techniques. Regardless of alloy microstructure and polarization conditions, rising streams of hydrogen bubbles were observed predominantly at the propagating corrosion fronts. Localized corrosion propagated inside the alloys, underneath a surface corrosion film, and exhibited a finger-like morphology at the corrosion region/alloy interface. Hydrogen evolution was found to be related to the formation of corrosion products and followed local anodic dissolution of Mg. Localized corrosion morphology strongly varied with the underlying Mg alloy microstructure and chemistry.