Characterisation of precipitates in an aged Mg–Zn–Ti alloy

Up to about 0.2 at.% of Ti may be dissolved in the solid magnesium in the presence of Zn (in Mg–2.4 at.% Zn alloy) which is orders of magnitude higher than the solubility of this element in the pure solid magnesium. The presence of Ti does not modify significantly the constituent particles which are compositionally and morphologically similar to the eutectic phase and contain up to about 0.1 at.% of Ti. Ti is exceptionally effective in promoting the nucleation of the precipitates during ageing. The precipitates formed during ageing in Mg–Zn–Ti alloy were generally similar to those forming in the binary alloy, although the results indicate that Ti promotes favourable nucleation of some precipitate species thus changes the relative fractions of the precipitates present in the microstructure. The greatest level of hardening in Mg–Zn–Ti alloy can be produced by ageing at about 70 °C due to the formation of a dense dispersion of at least five types of precipitates observed also in the binary alloy.