Effect of heat treatment on the corrosion behaviour of amorphous Mg-18 at% Ni alloy

The effect of heat treatment on the corrosion resistance of rapidly solidified amorphous Mg₈₂Ni₁₈ ribbons has been studied by hydrogen evolution testing in 3% NaCl solution and potentiodynamic scanning in 0.01 M NaCl solution. The results show that the dissolution rate for the partially crystallised sample obtained after 4 min heat treatment at 160°, was lower in comparison to the fully crystalline or fully amorphous samples. Comparison of the polarisation responses of the samples showed that, for the partially crystallised samples, passivation current density was lower than that of the fully amorphous sample, although passivation behaviour was weaker. With prolonged heat treatment duration, fully crystallised samples exhibited a marked deterioration of corrosion resistance. The corrosion results were discussed and correlated with the progress of crystallisation processes by means of XRD, DSC, TEM and SEM.