2 Fundamentals of Friction Stir Welding, Its Application, and Advancements
75
Zhao et al. [150] investigated dissimilar FSW of aluminum alloy 6013 and magnesium alloy AZ31. The joints were made in underwater and conventional conditions.
H13 tool steel with a concave shoulder and 2.5° tilt angle was used for welding. The
optimized parameter was found at 1200 rpm and 80 mm/min. Water-assisted FSW
resulted in better joint quality and improved the joint strength close to 152 MPa
which was higher as compared to air-assisted which was 131 MPa. Water leads to
faster cooling of the FSW process resulting in lower thermal gradients. It showed
no cracks as faster dissolution of intermetallic inclusions in the weld. Also, in water
appearance of the joint was smoother and brighter than in air. In case of air cooling,
microhardness was higher as compared to the water cooling due to a strong stirring
effect and better thermal cycles.
Somasekharan et al. [151] FSWed 1.75 mm thick plates of AA6061 and Mg
AZ91D was carried at 800 rpm and 90 mm/min. Intermetallic phases of Mg with
Al were observed as a result of swirls and vortexes within the weld zone. It is due
to dynamically recrystallized regions formed due to extensive plastic deformation
and high temperature. SZ consists of a fine homogeneous microstructure. Due to the
presence of dislocation substrates and precipitates, it resulted in high weld strength.
Sato et al. [152] conducted dissimilar joint of Mg alloy AZ31with AA1050 using
FSW. It resulted in an excessive quantity of intermetallic compound Al 12 Mg 17 . Due
to which an appreciably higher hardness was observed in the weld nugget. The
experiment was carried out at 2450 rpm with 90 mm/min and 3° tool tilt angle. The
author has reported that intermetallic was formed because of constitutional liquation
during dissimilar welding.
2.8.2.3 FSW of Aluminum and Steel
Tanaka et al. [153] FSWed 3 mm thick mild steel sheet with AA1050 aluminum
alloy at 1800 rpm and 100 mm/min. Aluminum was placed at RS. The steel plate
was kept on AS with a probe contact width of 0.2 mm for better material flow.
K-type thermocouple was employed to reveal thermal history. Investigation of the
intermetallic compound was extensively studied as they later resulted in defects and
cause a significant reduction in weld strength. The intermetallic compound is formed
due to excessive heat generation.
Chen [154] carried out FSW on 6 mm thick AA6061-T651 with low-carbon SS400
steel using a tool tilt angle of 3°. Weld at 550 rpm and 54 mm/min, yielded excellent
impact strength and a satisfactory tensile strength. This weld specimen has been bent
to 150° without breaking.
Derazkola and Khodabakhshi [155] carried out underwater FSW of 5 mm thick
AA5083 with A441 AISI steel. Tungsten carbide tool with a frustum probe with a
conical diameter was employed for joining the base metals. The tool tilt angle of 2°
with a 0.4 mm plunge depth and tool offset of 1.5 mm towards the aluminum alloy
side was provided. The welding took place by immersing the workpiece into the
water at three different temperatures of 0, 25, and 50 °C. Optimized input processing
parameters of 1500 rpm and 25 mm/min was set for all conditions. Increasing cooling
75
Zhao et al. [150] investigated dissimilar FSW of aluminum alloy 6013 and magnesium alloy AZ31. The joints were made in underwater and conventional conditions.
H13 tool steel with a concave shoulder and 2.5° tilt angle was used for welding. The
optimized parameter was found at 1200 rpm and 80 mm/min. Water-assisted FSW
resulted in better joint quality and improved the joint strength close to 152 MPa
which was higher as compared to air-assisted which was 131 MPa. Water leads to
faster cooling of the FSW process resulting in lower thermal gradients. It showed
no cracks as faster dissolution of intermetallic inclusions in the weld. Also, in water
appearance of the joint was smoother and brighter than in air. In case of air cooling,
microhardness was higher as compared to the water cooling due to a strong stirring
effect and better thermal cycles.
Somasekharan et al. [151] FSWed 1.75 mm thick plates of AA6061 and Mg
AZ91D was carried at 800 rpm and 90 mm/min. Intermetallic phases of Mg with
Al were observed as a result of swirls and vortexes within the weld zone. It is due
to dynamically recrystallized regions formed due to extensive plastic deformation
and high temperature. SZ consists of a fine homogeneous microstructure. Due to the
presence of dislocation substrates and precipitates, it resulted in high weld strength.
Sato et al. [152] conducted dissimilar joint of Mg alloy AZ31with AA1050 using
FSW. It resulted in an excessive quantity of intermetallic compound Al 12 Mg 17 . Due
to which an appreciably higher hardness was observed in the weld nugget. The
experiment was carried out at 2450 rpm with 90 mm/min and 3° tool tilt angle. The
author has reported that intermetallic was formed because of constitutional liquation
during dissimilar welding.
2.8.2.3 FSW of Aluminum and Steel
Tanaka et al. [153] FSWed 3 mm thick mild steel sheet with AA1050 aluminum
alloy at 1800 rpm and 100 mm/min. Aluminum was placed at RS. The steel plate
was kept on AS with a probe contact width of 0.2 mm for better material flow.
K-type thermocouple was employed to reveal thermal history. Investigation of the
intermetallic compound was extensively studied as they later resulted in defects and
cause a significant reduction in weld strength. The intermetallic compound is formed
due to excessive heat generation.
Chen [154] carried out FSW on 6 mm thick AA6061-T651 with low-carbon SS400
steel using a tool tilt angle of 3°. Weld at 550 rpm and 54 mm/min, yielded excellent
impact strength and a satisfactory tensile strength. This weld specimen has been bent
to 150° without breaking.
Derazkola and Khodabakhshi [155] carried out underwater FSW of 5 mm thick
AA5083 with A441 AISI steel. Tungsten carbide tool with a frustum probe with a
conical diameter was employed for joining the base metals. The tool tilt angle of 2°
with a 0.4 mm plunge depth and tool offset of 1.5 mm towards the aluminum alloy
side was provided. The welding took place by immersing the workpiece into the
water at three different temperatures of 0, 25, and 50 °C. Optimized input processing
parameters of 1500 rpm and 25 mm/min was set for all conditions. Increasing cooling