Dealloying corrosion of anodic and nanometric Mg41Nd5 in solid solution-treated Mg-3Nd-1Li-0.2Zn alloy.

[Display omitted] • The Volta potential of Mg 41 Nd 5 phase is more negative than that of α-Mg. • The dealloying mechanism of Mg 41 Nd 5 is proposed. • Nd-rich films endow the alloys good corrosion resistance. • T4 treatment led to a shift from pitting corrosion to uniform corrosion. • The "ring-shaped" corrosion is discussed. The microstructure and chemical compositions of the solid solution-treated Mg-3Nd-1Li-0.2Zn alloy were characterized using optical microscope, scanning electron microscope (SEM), transmission electron microscope (TEM), electron probe micro-analyzer (EPMA) and X-ray photoelectron spectroscopy (XPS). The corrosion behaviour of the alloy was investigated via electrochemical polarization, electrochemical impedance spectroscopy (EIS), hydrogen evolution test and scanning Kelvin probe (SKP). The results showed that the microstructure of the as-extruded Mg-3Nd-1Li-0.2Zn alloy contained α -Mg matrix and nanometric second phase Mg 41 Nd 5. The grain size of the alloy increased significantly with the increase in the heat-treatment duration, whereas the volume fraction of the second phase decreased after the solid solution treatment. The surface film was composed of oxides (Nd 2 O 3 , MgO, Li 2 O and ZnO) and carbonates (MgCO 3 and Li 2 CO 3), in addition to Nd. The as-extruded alloy exhibited the best corrosion resistance after an initial soaking of 10 min, whereas the alloy with 4h-solution-treatment possessed the lowest corrosion rate after a longer immersion (1 h). This can be attributed to the formation of Nd-containing oxide film on the alloys and a dense corrosion product layer. The dealloying corrosion of the second phase was related to the anodic Mg 41 Nd 5 with a more negative Volta potential relative to α-Mg phase. The preferential corrosion of Mg41Nd5 is proven by in-situ observation and SEM. The solid solution treatment of Mg-3Nd-1Li-0.2Zn alloy led to a shift in corrosion type from pitting corrosion to uniform corrosion under long-term exposure. [ABSTRACT FROM AUTHOR]