The Effect of Grain Size on the Corrosion Behavior of Mg-RE Alloy ZE10A

Mg-RE alloy Electron717 (ZE10A, UNS M11600) has a nominal composition of 1.2wt % Zn, 0.25wt% Zr, <0.5%Zr, 0.007wt%Mn, 0.004wt %Fe, 0.001wt%Ni and balance Mg. The alloy was investigated in three different heat-treated conditions such as (1) as received (AR) (average grain size dav = 7.90 µm), (2) solution treated at 525°C for 8 hours (ST8 with dav: 26.24 µm) and (3) solution treated at 525°C for 24 hours (ST24 with dav: 41.37 µm). Anodic and cathodic polarizations were carried out in three different electrolytes (pH unadjusted) such as: a) 0.6M NaCl, b) 0.5M NaNO3, and c) 0.1 M Na2SO4. The results are compared with commercial purity magnesium with an average grain size of 16 μm. The effect of grain size on the corrosion rate was observed for ZE10A alloy in the 0.1 M NaNO3 solution. Increase in the grain size increased the corrosion current density. The grain size effect diminished when polarized to high anodic potentials. Commercial purity magnesium showed lower corrosion current density than the ZE10A specimens in all the solutions tested in this study.