70
A. K. Choudhary and R. Jain
used. Microstructural investigation reveals that grain size in the SZ increases with
an increase in tool rotation. A joint efficiency of 90.2% was obtained at 1200 rpm. It
showed an increase in hardness value within the SZ because small grains attributes
to higher grain boundary and act as an obstacle for slip dislocation. This dislocation
acts as resistance to deformation.
Also, the peak temperature at SZ was reported as 495 °C. It was calculated by the
finite element model as it is difficult to obtain experimentally because of the wash
away of thermocouple in the stir zone.
Forcellese et al. [132] investigated the effect of input parameters on vertical force
and temperatures during FSW of magnesium alloy AZ31 sheets. Experiments were
carried from 1200 to 2500 rpm and 30 to 100 mm/min. Forces and temperature were
measured by a dynamometer and K-type thermocouple, respectively.
Mironov et al. [133] studied material flow behavior during FSW of AZ31 magnesium alloy. Also, the influence of temperature on material flow was examined. It
employed tool steel with a concave shoulder having a diameter of 15 mm with a
threaded cylindrical pin. Increasing the tool plunge depth increases welding temperature resulting in more stirring and material flow beneath the shoulder. Observation
of transitional material flow due to the presence of a small temperature gradient
within the stir zone showed that it resulted in a weld defect near the weld root.
Asadi et al. [134] investigated FSW of magnesium alloy plates using a FE
model. The developed model can predict the nucleation process and grain growth
through dynamic recrystallization. A combination of rotational and traverse speeds of
(710 rpm with 50 mm/min) and (1400 rpm with 25 mm/min) was employed as input
weld parameters to produce joints. The result shows that new grains nucleate and
grow from the region of high dislocation density because of temperature evolution
and plastic deformation.
Richmire et al. [135] studied FSW of magnesium alloy with a triangular tapered
pin. The magnesium AM60 cast alloy applicable to frames for the seat, steering
wheels, instrument panels, and brackets for the automobile company. It is ductile and
has significant toughness as compared to AZ91 Mg alloy. Microstructural evolution
revealed the presence of equiaxed fine grains in SZ and elongated tilted grains at
TMAZ. The results could be attributed to dynamic recrystallization, followed by
the grained refinement. Various defects like porosity and void are observed at a
low rotational speed. Also, insufficient heat resulted in inadequate material flow.
High rotation speed and low travel resulted in too much heat dissipation resulting in
local melting and grain growth due to softening. The presence of intermetallic i.e.
Al 12 Mg 17 is one of the possible reasons for void defects.
2.8.1.4 Steel
FSW is also used for welding hard alloys like steel and titanium. Steel is widely used
as a structural component and it is a universal material. FSW application on steel is
limited due to its high hardness, strength, high loading force, and severe wear of the
tool. Also, the manufacturing of tool materials for steel is complex and expensive.
A. K. Choudhary and R. Jain
used. Microstructural investigation reveals that grain size in the SZ increases with
an increase in tool rotation. A joint efficiency of 90.2% was obtained at 1200 rpm. It
showed an increase in hardness value within the SZ because small grains attributes
to higher grain boundary and act as an obstacle for slip dislocation. This dislocation
acts as resistance to deformation.
Also, the peak temperature at SZ was reported as 495 °C. It was calculated by the
finite element model as it is difficult to obtain experimentally because of the wash
away of thermocouple in the stir zone.
Forcellese et al. [132] investigated the effect of input parameters on vertical force
and temperatures during FSW of magnesium alloy AZ31 sheets. Experiments were
carried from 1200 to 2500 rpm and 30 to 100 mm/min. Forces and temperature were
measured by a dynamometer and K-type thermocouple, respectively.
Mironov et al. [133] studied material flow behavior during FSW of AZ31 magnesium alloy. Also, the influence of temperature on material flow was examined. It
employed tool steel with a concave shoulder having a diameter of 15 mm with a
threaded cylindrical pin. Increasing the tool plunge depth increases welding temperature resulting in more stirring and material flow beneath the shoulder. Observation
of transitional material flow due to the presence of a small temperature gradient
within the stir zone showed that it resulted in a weld defect near the weld root.
Asadi et al. [134] investigated FSW of magnesium alloy plates using a FE
model. The developed model can predict the nucleation process and grain growth
through dynamic recrystallization. A combination of rotational and traverse speeds of
(710 rpm with 50 mm/min) and (1400 rpm with 25 mm/min) was employed as input
weld parameters to produce joints. The result shows that new grains nucleate and
grow from the region of high dislocation density because of temperature evolution
and plastic deformation.
Richmire et al. [135] studied FSW of magnesium alloy with a triangular tapered
pin. The magnesium AM60 cast alloy applicable to frames for the seat, steering
wheels, instrument panels, and brackets for the automobile company. It is ductile and
has significant toughness as compared to AZ91 Mg alloy. Microstructural evolution
revealed the presence of equiaxed fine grains in SZ and elongated tilted grains at
TMAZ. The results could be attributed to dynamic recrystallization, followed by
the grained refinement. Various defects like porosity and void are observed at a
low rotational speed. Also, insufficient heat resulted in inadequate material flow.
High rotation speed and low travel resulted in too much heat dissipation resulting in
local melting and grain growth due to softening. The presence of intermetallic i.e.
Al 12 Mg 17 is one of the possible reasons for void defects.
2.8.1.4 Steel
FSW is also used for welding hard alloys like steel and titanium. Steel is widely used
as a structural component and it is a universal material. FSW application on steel is
limited due to its high hardness, strength, high loading force, and severe wear of the
tool. Also, the manufacturing of tool materials for steel is complex and expensive.