2 Fundamentals of Friction Stir Welding, Its Application, and Advancements
69
and better mechanical outcome as compared to the threaded cylindrical pin. The
reason could be credited to the high eccentricity present in square pin and dynamic
pulsation effect which results in a higher amount of plastic deformation and greater
heat dissipation in the weld. At the nugget zone, square and threaded cylindrical pin
resulted in fine recrystallized grains of 10 and 15 microns, respectively.
Heidarzadeh et al. [126] developed the optimized process parameter windows
for the welding of copper alloy. Rotational speed (700–1100 rpm), welding speed
(50–100 mm/min), and axial force (1.5–2.5 kN) produced defect-free weld and
better strength. Hardness value showed a direct relationship with welding speed
and inversely varies with rotational speed and axial force.
Sun et al. [49] welded CuNiCrSi and CuCrZr alloy in butt configuration. A fixed
welding velocity of 150 mm/min with a varying rotating speed of 800, 1100, 1400,
1700, and 2100 rpm was used. They reported that 1400 and 1700 rpm resulted in
a sound quality joint. Cr precipitates in the weld matrix show proper dissolution to
increase the mechanical and microstructural properties of the stir zone. Microhardness at the SZ and weld strength decreased with the increase in rotational speeds due
to the formation of larger grain size.
Sahlot et al. [127] studied FSW of pure copper. A tungsten carbide tool with 12%
cobalt with a flat shoulder and tapered cylindrical profile was used. Heat dissipation was studied during the process. Results show that tool rotation speed directly
influences the peak temperature and weld strength.
2.8.1.3 Mg Welding
Welding of magnesium alloy is difficult because of high flammability. In recent years,
FSW has been effectively applied for the welding of magnesium alloy [128]. Pan
et al. [129] FSWed Mg-5Al-1Sn alloy in butt configuration. The influence of tool
rotational speed on weld properties has been investigated. The H13 tool steel with
a concave shoulder and a threaded cylindrical pin was employed for welding with
a tilt angle of 2.5°. Microstructural observation reveals equiaxed and fine grains at
the nugget because of adequate heating and intense plastic deformation. Hardness
distribution showed the lowest value between NZ and TMAZ, due to the extended
deformed grains. Weld strength of 258 MPa was obtained at 800 rpm resulting in
91% of weld efficiency.
Pareek et al. [130] FSWed 3.175 mm thick AZ31-H24 magnesium alloy. The
influence of rotational and welding speed on metallurgical evolution was studied.
It reveals that dynamic recrystallized grains and the beginning of growing grains in
some regions of the weld nugget. Partially recrystallized grains were also identified towards (TMAZ). During the tensile test, all weld specimens failed from
the advancing side of the workpiece. Weld efficiency of 75% was obtained at a
combination of 2000 rpm and 204 mm/min.
Wang et al. [131] investigated the welding of AZ31 using FSW. The experiment was done by varying rotational speeds from 800 to 1600 rpm at a constant
welding speed of 120 mm/min. Hardened H13 tool steel with a threaded pin was
69
and better mechanical outcome as compared to the threaded cylindrical pin. The
reason could be credited to the high eccentricity present in square pin and dynamic
pulsation effect which results in a higher amount of plastic deformation and greater
heat dissipation in the weld. At the nugget zone, square and threaded cylindrical pin
resulted in fine recrystallized grains of 10 and 15 microns, respectively.
Heidarzadeh et al. [126] developed the optimized process parameter windows
for the welding of copper alloy. Rotational speed (700–1100 rpm), welding speed
(50–100 mm/min), and axial force (1.5–2.5 kN) produced defect-free weld and
better strength. Hardness value showed a direct relationship with welding speed
and inversely varies with rotational speed and axial force.
Sun et al. [49] welded CuNiCrSi and CuCrZr alloy in butt configuration. A fixed
welding velocity of 150 mm/min with a varying rotating speed of 800, 1100, 1400,
1700, and 2100 rpm was used. They reported that 1400 and 1700 rpm resulted in
a sound quality joint. Cr precipitates in the weld matrix show proper dissolution to
increase the mechanical and microstructural properties of the stir zone. Microhardness at the SZ and weld strength decreased with the increase in rotational speeds due
to the formation of larger grain size.
Sahlot et al. [127] studied FSW of pure copper. A tungsten carbide tool with 12%
cobalt with a flat shoulder and tapered cylindrical profile was used. Heat dissipation was studied during the process. Results show that tool rotation speed directly
influences the peak temperature and weld strength.
2.8.1.3 Mg Welding
Welding of magnesium alloy is difficult because of high flammability. In recent years,
FSW has been effectively applied for the welding of magnesium alloy [128]. Pan
et al. [129] FSWed Mg-5Al-1Sn alloy in butt configuration. The influence of tool
rotational speed on weld properties has been investigated. The H13 tool steel with
a concave shoulder and a threaded cylindrical pin was employed for welding with
a tilt angle of 2.5°. Microstructural observation reveals equiaxed and fine grains at
the nugget because of adequate heating and intense plastic deformation. Hardness
distribution showed the lowest value between NZ and TMAZ, due to the extended
deformed grains. Weld strength of 258 MPa was obtained at 800 rpm resulting in
91% of weld efficiency.
Pareek et al. [130] FSWed 3.175 mm thick AZ31-H24 magnesium alloy. The
influence of rotational and welding speed on metallurgical evolution was studied.
It reveals that dynamic recrystallized grains and the beginning of growing grains in
some regions of the weld nugget. Partially recrystallized grains were also identified towards (TMAZ). During the tensile test, all weld specimens failed from
the advancing side of the workpiece. Weld efficiency of 75% was obtained at a
combination of 2000 rpm and 204 mm/min.
Wang et al. [131] investigated the welding of AZ31 using FSW. The experiment was done by varying rotational speeds from 800 to 1600 rpm at a constant
welding speed of 120 mm/min. Hardened H13 tool steel with a threaded pin was