The precipitation sequence responsible for the age-hardening behaviour
of a cast Mg-1.3 wt% rare-earth alloy has been investigated by analyt
ical electron microscopy. Very fine intermediate precipitates formed a
t an early stage of ageing. Plate-shaped Mg(3)MM beta' precipitates (M
M = misch metal) and hexagonal prism-shaped Mg(12)MM beta precipitates
were primarily responsible for age hardening. Precipitate morphologie
s, crystal structures and crystallographic orientation relationship we
re determined for the various types of precipitates that formed during
ageing at different temperatures.