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 ribbons have been investigated using hydrogen evolution testing in 3% (0.51 M) solution and electrochemical techniques in 0.01 M NaCl. Open circuit potential measurements showed that the as-spun alloys were more electrochemically noble than that of pure Mg. Dissolution rate measurements showed that the corrosion rates of the partially crystallised samples were lower than that of the fully amorphous samples. Potentiodynamic polarisation results showed that although there was ennoblement in the corrosion potential E_corr, the corrosion current density i_corr was higher for the melt-spun alloy than for pure Mg. Comparison of the polarisation responses for the partially crystallised samples in 0.01 M 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 deterioration of corrosion resistance. The corrosion results have been discussed and correlated with the progress of crystallisation processes by means of XRD and TEM.