The Influence of Microstructure on the Corrosion of Magnesium Alloy ZEK100

The corrosion behavior of Mg alloy ZEK100 was investigated in water and in chloride-containing environments. The alloy is composed of an α-Mg matrix and a wide-spread dispersion of a Mg-Zn-Nd phase and Zr-rich particles. Potentiodynamic polarization measurements showed the corrosion resistance of the ZEK100 alloy improved with decreasing chloride content. Intermittent immersions in 0.16 wt% sodium chloride (NaCl) showed corrosion occurred preferentially by tracking along the surface, interlinking the secondary phase particles. Some of the particles acted as strong cathodes microgalvanically coupled to the α-Mg matrix. Of the three main types of secondary phase identified, i.e., Mg-Zn-Nd, Zr, and Fe-containing Zr particles, the latter were the dominant active cathodes. This was demonstrated by experiments in deionized water (18.2 MΩ cm) where the tracking of corrosion across the surface was absent and active cathodes could be identified by a small surrounding zone of corroded α-Mg and an accumulated dome of corrosion product over the top of the active particle.