Real-time in situ observation of the corrosion process of die-cast AZ91D magnesium alloy in NaCl solutions under galvanostatic polarization

In situ observations of the filiform corrosion process of die-cast AZ91D magnesium alloy were carried out in 0.1 and 0.01 M NaCl solutions (pH 8.0) through a microscale polarization technique. The changes in morphology were observed in real-time using an optical microscope. Filiform corrosion proceeded in lamellar α + β structures adjacent to β phases and sometimes in the α phase grains. The β phases remained intact after filiform corrosion. • Filiform corrosion process of die-cast AZ91D was observed in real-time. • Filiform corrosion proceeded in lamellar α + β structures adjacent to β phases. • Corrosion resistance of coarse lamellar α + β structures may be better than that of dense structures. • Two corrosion morphologies were found for the α phase: spreading in grain and proceeding linearly in grain.