Abstract :
This article reports on a remarkable natural
ageing response observed for the first time in this work in
Mg–Zn-based alloys. In these alloys, hardness in the naturally
aged condition, generally, almost equals that in the
artificially aged condition. The time to maximal hardness in
the naturally aged condition can be dramatically reduced
from several months needed for a binary Mg–Zn alloy, to a
practical duration of a few weeks when some additional
alloying elements that act as accelerants are added. Examples
of such elements presented here are Cu and Ti.
Strengthening in the naturally aged condition of these alloys
is achieved through the formation of a very high density of
Guinier-Preston (GP) zone-type precipitates. Both Cu and
Ti also enhance the artificial ageing response by increasing
the number density of the strengthening precipitates. Unlike
Cu, Ti is not detrimental to the corrosion resistance and the
current results indicate that it also has a very pronounced
grain-refining effect on the Mg–Zn-based alloys.
