Corrosion Phenomenon Evaluation of Mg Alloys using Surface Potential Difference Measured by SKPFM

Abstract

Magnesium is easy to be corroded because it has small standard electrode potential (SEP). In magnesium alloys, the corrosion resistance of dispersoids hasn’t yet evaluated quantitatively as the SEP of dispersoids wasn’t almost investigated. This study surveyed the surface potential difference (SPD) between α-Mg in AZ91D magnesium alloy and the dispersoids in that alloy by using Scanning Kelvin Probe Force Microscope (SKPFM). The corrosion resistance was evaluated and correlated with SPD, where this measured SPD represents the difference of work function between α-Mg and the dispersoid. At this experiment, it was obtained that the difference of SEP generally increases as the SPD increases. The good correlation between difference of SEP and SPD was obtained. The SPD between α-Mg and Mg17Al12 or Al6Mn in AZ91D Mg alloy is measured. In addition, in order to obtain the reference of SPD, the area of α-Mg only and the interface area between Fe and α-Mg were respectively scanned. The result shows that Mg17Al12 has small SPD to α-Mg and that the SPD between Mg17Al12 and α-Mg is mostly the same as that in α-Mg. Therefore, Mg17Al12 is considered of no effect on corrosion. On the other hand, Al6Mn degrades corrosion resistance because the SPD between Al6Mn and α-Mg is as large as that between Fe and α-Mg.