76
A. K. Choudhary and R. Jain
rates brought the peak temperature down to 400 °C and reduced the possibility of
intermetallic formation in the weld nugget. Weld efficiency of 97% was reported.
Habibnia et al. [156] investigated mechanical properties and microstructure of
FSW of 3 mm thick AA5050 with 304 stainless steel. Positioning Al alloy towards the
retreating side with variable tool offsets ranging from 0, 0.8, and 1.5 mm. Tungsten
carbide tool with a conical probe was employed with a 2° tilt angle. Defect-free
and improved joints were formed while decreasing the rotational speed from 710
to 500 rpm and increasing welding speed from 40 to 80 mm/min at a tool offset of
1.5 mm. Also, intermetallic compounds such as Al 13 Fe 4 and Al 5 Fe 2 were observed
in the stir zone.
Karakizis et al. [157] investigated FSW of 2 mm thick AA5754 and H114 strain
hardened mild steel. The tool pin geometry of a star-shaped polygon was used for
joining. Steel was kept at the retreating side with a tool offset of 0.2 mm. Experiments
were carried out at distinct input parameters. The rotational speed of 750 rpm and a
welding speed of 30 mm/min showed the best result. An increase in microhardness
at the SZ was reported because of the grain refinement.
Lan et al. [158] successfully welded high-strength TRIP 780 steel with aluminum
alloy AA 6061-T6 using FSW. Steel was kept toward the advancing side in butt
configuration. Tool material was tungsten carbide with 10% cobalt and pin geometry
was an non-threaded conical pin. The formation of the intermetallic Fe 3 Al or FeAl
layers thickness close to 1 μm was observed.
Yazdipour and Heidarzadeh [159] FSWed AA 5083-H321 with 316L stainless
steel plates in lap configuration. H13 tool steel with a tilt angle of 2.5° was employed
for joining two metals. The maximum weld strength of 238 MPa was obtained at
280 rpm and 160 mm/min. At lower tool rotational of 180 rpm resulted in tunnel
defect at the joint interface.
2.8.3 Tool Wear
Tool wear rate is a critical factor of tool design. It is majorly dependent on tool
rotation speed, welding speed, workpiece and tool material, and axial force. It is also
reported that the influence of these parameters is noteworthy only during the plunging
and the initial phase of the welding and tool wear drops considerably during the later
stage of welding [160]. The axial force is significantly high during the plunging
and this is one of the primary reasons for the tool failure/wear during that stage [8].
Generally, tool wear is reported to be directly proportional to the tool rotational speed
and welding speed. The tool undergoes self-optimization because, during the initial
stage, high-stress concentration gradients regions undergo maximum wear followed
by tool attaining a shape where the stress gradients reduce across the tool [41].
Investigation of the deformation behavior and load-bearing capacity of the tool
pin during the FSW process is important, as the tool pin is susceptible to more
deformation/failure as compared to the shoulder. The pin is the weakest module of
the tool as it undergoes severe stress conditions at elevated temperature and that
A. K. Choudhary and R. Jain
rates brought the peak temperature down to 400 °C and reduced the possibility of
intermetallic formation in the weld nugget. Weld efficiency of 97% was reported.
Habibnia et al. [156] investigated mechanical properties and microstructure of
FSW of 3 mm thick AA5050 with 304 stainless steel. Positioning Al alloy towards the
retreating side with variable tool offsets ranging from 0, 0.8, and 1.5 mm. Tungsten
carbide tool with a conical probe was employed with a 2° tilt angle. Defect-free
and improved joints were formed while decreasing the rotational speed from 710
to 500 rpm and increasing welding speed from 40 to 80 mm/min at a tool offset of
1.5 mm. Also, intermetallic compounds such as Al 13 Fe 4 and Al 5 Fe 2 were observed
in the stir zone.
Karakizis et al. [157] investigated FSW of 2 mm thick AA5754 and H114 strain
hardened mild steel. The tool pin geometry of a star-shaped polygon was used for
joining. Steel was kept at the retreating side with a tool offset of 0.2 mm. Experiments
were carried out at distinct input parameters. The rotational speed of 750 rpm and a
welding speed of 30 mm/min showed the best result. An increase in microhardness
at the SZ was reported because of the grain refinement.
Lan et al. [158] successfully welded high-strength TRIP 780 steel with aluminum
alloy AA 6061-T6 using FSW. Steel was kept toward the advancing side in butt
configuration. Tool material was tungsten carbide with 10% cobalt and pin geometry
was an non-threaded conical pin. The formation of the intermetallic Fe 3 Al or FeAl
layers thickness close to 1 μm was observed.
Yazdipour and Heidarzadeh [159] FSWed AA 5083-H321 with 316L stainless
steel plates in lap configuration. H13 tool steel with a tilt angle of 2.5° was employed
for joining two metals. The maximum weld strength of 238 MPa was obtained at
280 rpm and 160 mm/min. At lower tool rotational of 180 rpm resulted in tunnel
defect at the joint interface.
2.8.3 Tool Wear
Tool wear rate is a critical factor of tool design. It is majorly dependent on tool
rotation speed, welding speed, workpiece and tool material, and axial force. It is also
reported that the influence of these parameters is noteworthy only during the plunging
and the initial phase of the welding and tool wear drops considerably during the later
stage of welding [160]. The axial force is significantly high during the plunging
and this is one of the primary reasons for the tool failure/wear during that stage [8].
Generally, tool wear is reported to be directly proportional to the tool rotational speed
and welding speed. The tool undergoes self-optimization because, during the initial
stage, high-stress concentration gradients regions undergo maximum wear followed
by tool attaining a shape where the stress gradients reduce across the tool [41].
Investigation of the deformation behavior and load-bearing capacity of the tool
pin during the FSW process is important, as the tool pin is susceptible to more
deformation/failure as compared to the shoulder. The pin is the weakest module of
the tool as it undergoes severe stress conditions at elevated temperature and that