Deformation mechanisms in magnesium alloy Elektron™ 675.

Magnesium is a very lightweight and strong material and thus is of particular interest to
industries such as aerospace and automotive. Elektron™ 675 is a new alloy developed
by Magnesium Elektron Ltd. and based on the magnesium-gadolinium-yttrium system.
This gives particularly high strength and high temperature stability but currently proves
more difficult to process than conventional magnesium alloys. The objectives in the
current work were to study the deformation behaviour with particular emphasis on the
flow behaviour during rolling and the deformation mechanisms that are operating.
To study the deformation behaviour over a wide range of conditions, plane strain
compression (PSC) tests were carried out in a matrix between 380°C and 520°C and Is-1
and 10s-1 strain rates, similar conditions to those experienced in industrial rolling. The
tests showed similar behaviour at all conditions with a rise to a peak stress followed by
continuous softening and constitutive equations of flow stress were developed. Further
PSC tests were used to study behaviour such as static recrystallisation during annealing
and the effect of non-isothermal rolling with cold rolls.
Following deformation, the microstructures were studied using various microscopy
techniques, the most common being electron backscatter diffraction (EBSO). It was
found that {loT 2} twinning was very prevalent in the early stages of deformation,
particularly in the tests deformed at low temperatures or high strain rates. Slip occurred
predominantly on the basal plane but was also observed on prismatic planes and there
was strong evidence that <c+a> pyramidal slip was also active. Dynamic
recrystallisation was observed in necklace formations around grain boundaries and is
thought to have formed by the continuous dynamic rotation recrystallisation
mechanism.
This study has provided new information on the deformation mechanisms that operate
in high strength magnesium alloys and has calculated a viable process window in which
Elektron 675 can be rolled.