Stability of the bulk glass-forming Mg65Y10Cu25 alloy in aqueous electrolytes

The corrosion behaviour of the amorphous Mg65Y10Cu25, alloy was studied in aqueous alkaline electrolytes and compared with that of the corresponding multiphase crystalline alloy and of magnesium. Alloy samples were prepared by melt-spinning and die-casting and characterised concerning their microstructure and thermal stability by X-ray diffraction, optical and scanning electron microscopy and differential scanning calorimetry. In 0.3 m H3BO3/Na2B4O7 buffer solution with pH = 8.4 and 0.1 m NaOH solution with pH=13 the samples were electrochemically investigated by recording Tafel plots and by performing potentiodynamic polarisation tests and current transient measurements at anodic potentials. Potentiostatically formed surface layers were characterised with Auger electron spectroscopy and scanning electron microscopy. For both, the amorphous and the multiphase crystalline Mg-Y-Cu alloy, differences in anodic surface layer growth mechanisms in the two investigated electrolytes were detected which are explained by the effect of the constituent copper. In the two electrolytes, the amorphous ahoy showed the lowest corrosion rates and the highest passivation ability also in comparison with earlier investigated Mg-Y alloys. Differences between the corrosion behaviour of the amorphous and the multiphase crystalline alloy are mainly attributed to heterogeneity effects rather than to an effect of the amorphous structure. (C) 2001 Elsevier Science B.V. All rights reserved.