The influence of heat treatment on the corrosion behaviour of amorphous melt-spun binary Mg-18 at.% Ni and Mg-21 at.% Cu alloy

The corrosion behaviour of melt-spun amorphous Mg82Ni18 and Mg79Cu21 ribbon s have been investigated using hydrogen evolution testing in 3% (0.51 M) so lution and electrochemical techniques in 0.01 M NaCl. Open circuit potentia l measurements showed that the as-spun alloys were mere electrochemically n oble than that of pure Mg. Dissolution rate measurements showed that the co rrosion rates of the partially crystallised samples were lower than that of the fully amorphous samples, Potentiodynamic polarisation results showed t hat although there was ennoblement in the corrosion potential E-con, the co rrosion current density i(corr) was higher for the melt-spun alloy than for purl Mg. Comparison of the polarisation responses for the partially crysta llised samples in 0.01 hi NaCl showed that the passivation current density i(p) was lower than for the as-spun amorphous sample. With; prolonged heat treatment duration, fully crystallised samples exhibit a marked deteriorati on of corrosion resistance. The corrosion results have been discussed and c orrelated with the progress of crystallisation processes by means of XRD an d TEM. (C) 2001 Elsevier Science B.V All rights reserved.