54
A. K. Choudhary and R. Jain
Tool tilt angle is another important parameter that governs the forging action
during FSW, minimizes flash formation and improves mechanical properties of the
weld [53]. A non-zero angle facilitates the better flow of the plasticizing material
around the tool. Increasing the tilt angle increases the downward force and frictional
heat during welding, resulting in higher plasticization and material softening [54].
An optimized tool tilt angle governs the weld quality [55]. A higher tilt angle may
damage the pin from the weld root resulting in defective or damaged welds. So, an
optimized tool tilt angle leads to efficient transport of the material from the front side
to the rear side of the pin resulting in the defect-free weld. Therefore, the selection
of appropriate tool tilt angle value along with a suitable combination of other input
parameters ie. tool rotation and welding speed is necessary. It is also observed that
the tool tilt angle increases stress towards the leading edge of the tool within the
workpiece because increasing tilt angle results in the increase in temperature and
decrease in stress value is seen as material flow in the rear advancing side is observed.
It also improves material stirring action at trailing edge towards the advancing side
[56]. Chauhan et al. [57] studied the effect of the tool tilt angle on defect formation.
They varied the tilt angle from 0° to 2°. A 0° tilt angle resulted in a defective weld.
A tilt angle of 1° resulted in a tunnel defect along the weld line. The tilt angle of
2° resulted in a defect-free weld because of an increase in the axial force value.
Weld efficiency for 0° and 1° was 35 and 50%, respectively due to defects. A weld
efficiency of 90% was recorded for a 2° tilt angle. Mehta and Badheka [58] studied the
influence of tool tilt angle during the FSW of aluminum alloy with copper. Tilt angles
varied from 0° to 4° at an interval of 1° at a constant rotational speed and welding
speed of 1300 rpm and 40 mm/min, respectively. The tilt angle of 0° and 1° resulted
in defective weld while 2°, 3°, and 4° showed a defect-free weld. A maximum weld
strength of 117 MPa was obtained at a 4° tilt angle. Maximum macro-hardness 186
HV was reported for 4° tilt angle while minimum macro-hardness 58 HV for 0° tilt
angle.
2.4 Output Mechanical Responses of FSW
2.4.1 Temperature Distribution/heat Generation
The study of evolution of temperature in and nearby the NZ has a direct impact
on the weld microstructure [59, 60]. It influences grain size, nature of new grains,
coarsening and mixing of precipitates with the base metal and resultant mechanical
properties of the welds [61, 62]. Temperature measurement in the stirred zone with a
thermocouple is difficult as plastic deformation of the material will break and wash
away the thermocouple [63]. Therefore, temperature distribution has been either
estimated from the history of the weld microstructure or measuring it near to the
shoulder, i.e., outside the stirred zone [64]. Microstructural observation related to
grain size and its distribution reveals the thermal history. Fine-grain size is an outcome
A. K. Choudhary and R. Jain
Tool tilt angle is another important parameter that governs the forging action
during FSW, minimizes flash formation and improves mechanical properties of the
weld [53]. A non-zero angle facilitates the better flow of the plasticizing material
around the tool. Increasing the tilt angle increases the downward force and frictional
heat during welding, resulting in higher plasticization and material softening [54].
An optimized tool tilt angle governs the weld quality [55]. A higher tilt angle may
damage the pin from the weld root resulting in defective or damaged welds. So, an
optimized tool tilt angle leads to efficient transport of the material from the front side
to the rear side of the pin resulting in the defect-free weld. Therefore, the selection
of appropriate tool tilt angle value along with a suitable combination of other input
parameters ie. tool rotation and welding speed is necessary. It is also observed that
the tool tilt angle increases stress towards the leading edge of the tool within the
workpiece because increasing tilt angle results in the increase in temperature and
decrease in stress value is seen as material flow in the rear advancing side is observed.
It also improves material stirring action at trailing edge towards the advancing side
[56]. Chauhan et al. [57] studied the effect of the tool tilt angle on defect formation.
They varied the tilt angle from 0° to 2°. A 0° tilt angle resulted in a defective weld.
A tilt angle of 1° resulted in a tunnel defect along the weld line. The tilt angle of
2° resulted in a defect-free weld because of an increase in the axial force value.
Weld efficiency for 0° and 1° was 35 and 50%, respectively due to defects. A weld
efficiency of 90% was recorded for a 2° tilt angle. Mehta and Badheka [58] studied the
influence of tool tilt angle during the FSW of aluminum alloy with copper. Tilt angles
varied from 0° to 4° at an interval of 1° at a constant rotational speed and welding
speed of 1300 rpm and 40 mm/min, respectively. The tilt angle of 0° and 1° resulted
in defective weld while 2°, 3°, and 4° showed a defect-free weld. A maximum weld
strength of 117 MPa was obtained at a 4° tilt angle. Maximum macro-hardness 186
HV was reported for 4° tilt angle while minimum macro-hardness 58 HV for 0° tilt
angle.
2.4 Output Mechanical Responses of FSW
2.4.1 Temperature Distribution/heat Generation
The study of evolution of temperature in and nearby the NZ has a direct impact
on the weld microstructure [59, 60]. It influences grain size, nature of new grains,
coarsening and mixing of precipitates with the base metal and resultant mechanical
properties of the welds [61, 62]. Temperature measurement in the stirred zone with a
thermocouple is difficult as plastic deformation of the material will break and wash
away the thermocouple [63]. Therefore, temperature distribution has been either
estimated from the history of the weld microstructure or measuring it near to the
shoulder, i.e., outside the stirred zone [64]. Microstructural observation related to
grain size and its distribution reveals the thermal history. Fine-grain size is an outcome