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 m ultiphase crystalline alloy and of magnesium. Alloy samples were prepared b y melt-spinning and die-casting and characterised concerning their microstr ucture and thermal stability by X-ray diffraction, optical and scanning ele ctron microscopy and differential scanning calorimetry. In 0.3 m H3BO3/Na2B 4O7 buffer solution with pH = 8.4 and 0.1 m NaOH solution with pH=13 the sa mples were electrochemically investigated by recording Tafel plots and by p erforming potentiodynamic polarisation tests and current transient measurem ents at anodic potentials. Potentiostatically formed surface layers were ch aracterised with Auger electron spectroscopy and scanning electron microsco py. For both, the amorphous and the multiphase crystalline Mg-Y-Cu alloy, d ifferences in anodic surface layer growth mechanisms in the two investigate d electrolytes were detected which are explained by the effect of the const ituent copper. In the two electrolytes, the amorphous ahoy showed the lowes t corrosion rates and the highest passivation ability also in comparison wi th earlier investigated Mg-Y alloys. Differences between the corrosion beha viour of the amorphous and the multiphase crystalline alloy are mainly attr ibuted to heterogeneity effects rather than to an effect of the amorphous s tructure. (C) 2001 Elsevier Science B.V. All rights reserved.