Corrosion behaviour of the amorphous Mg65Y10Cu15Ag10 alloy

The corrosion behaviour of the amorphous (MgY10Cu15Ag10)-Y-65 alloy as well as of its crystalline multiphase counterpart was studied in alkaline electrolytes and compared with that of the amorphous Mg65Y10Cu25 alloy. Electrochemical investigations were carried out in 0.3 M H3BO3/Na2B4O7 buffer solution with pH = 8.4 and in 0.1 M NaOH solution with pH = 13. Tafel plots were recorded and cyclic potentiodynamic polarisation tests were conducted, transients were measured at anodic potentials. Potentiostatically formed surface layers were characterised by Auger electron spectroscopy and atomic force microscopy. Changes in the corrosion behaviour were noticed which are attributed to the presence of silver. The passive layers formed in the two electrolytes were quite different in the composition as well as in morphology. The layer growth mechanisms also showed some variation presumably mainly due to the presence of silver, though copper still seems to play a dominant role in the passivation of this alloy in the weakly alkaline solution. The amorphous alloys displayed superior corrosion behaviour compared to the crystalline alloy, because of the absence of the heterogeneties existing in crystalline alloys. (C) 2002 Elsevier Science Ltd. All rights reserved.