joints produced using
different friction pressure
values. It is convenient
to describe
the microstructural
features of these
joints using the
nomenclature employed
by Kang, etal.
(Ref. 9), namely, the
dynamically recovered
microstructure
at the weld interface
is region RI, the upset
region where the
original base material
grains are reoriented
by the forging stage in
friction joining is RII
and the undeformed
base material microstructure
is region
Rill- Fig. 3. Both dynamic
recrystallization
and dynamic recovery
have been
proposed as mechanisms
for the microstructural
evolution
of material at the
joint centerline (at
the contact region) in
rotary friction welds
and in the plasticized
region formed during
friction stir welding.
However, the most
recent research indicates
dynamic recovery
is the most likely
softening process in
6082-T6 and 7108-
T79 friction stir
welds.