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Materials Science and Engineering A 459 (2007) 718
Influences of pin profile and rotational speed of the tool on the formationof friction stir processing zone in AA2219 aluminium alloy
K. Elangovan, V. Balasubramanian
Department of Manufacturing Engineering, Annamalai University, Annamalai Nagar 608002, Tamil Nadu, India
Received 23 October 2006; received in revised form 13 December 2006; accepted 27 December 2006
Abstract
AA2219 aluminium alloy has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to-weight ratio.
Compared to the many fusion welding processes that are routinely used for joining structural aluminium alloys, friction stir welding (FSW) processis an emerging solid state joining process in which the material that is being welded does not melt and recast. The welding parameters and tool pin
profile play a major role in deciding the weld quality. In this investigation an attempt has been made to understand the influences of rotational speed
and pin profile of the tool on friction stir processed (FSP) zone formation in AA2219 aluminium alloy. Five different tool pin profiles (straight
cylindrical, tapered cylindrical, threaded cylindrical, triangular and square) have been used to fabricate the joints at three different tool rotational
speeds. The formation of FSP zone has been analysed macroscopically. Tensile properties of the joints have been evaluated and correlated with
the FSP zone formation. From this investigation it is found that the square tool pin profile produces mechanically sound and metallurgically defect
free welds compared to other tool pin profiles.
2007 Elsevier B.V. All rights reserved.
Keywords: AA2219 aluminium alloy; Friction stir welding; Rotational speed; Tool pin profile; FSP zone; Tensile properties
1. Introduction
AA2219 is most widely used material for the construction of
liquid cryogenic rocket fuel tanks. It has a unique combination
of properties such as good weldability, high strength-to-weight
ratio and superior cryogenic properties [1]. The preferred weld-
ing processes for AA2219 aluminium alloy are frequently gas
metal arc welding (GMAW) and gas tungsten arc welding
(GTAW) due to their comparatively easier applicability and bet-
ter economy [2]. However, plasma arc welding (PAW) with a
positive polarity electrode and high welding current allows alu-
miniumcomponents to be joinedeconomically with an excellent
weld quality [3]. In comparison with the TIG and MIG arcs,
the electron beam is characterized by higher power density and
thus permits the single pass welding of square butt joints with
thickness up to approximately 8 mm in the flat position [4].
Corresponding author. Tel.: +91 4144 239734;
fax: +91 4144 239734/4144 238275.
E-mail addresses: [email protected](K. Elangovan),
[email protected] (V. Balasubramanian).
ThoughAA2219 hasgot anedge over its6000and7000seriescounterparts in terms of weldability, it also suffers from poor as
weldedjoint strength.Thejoint strength is only about 40%when
compared to the base metal strength in T87 condition. This is
true both in autogenous welds as well as those welded with the
matching filler 2319, which contains slightly higher contents of
Ti and Zr. The loss of strength is due to the melting and quick
resolidification, which renders all the strengthening precipitates
to dissolve and the material is as good as a cast material with
solute segregation and large columnar grains [5].
Compared to many of the fusion welding processes that are
routinely used for joining AA2219 aluminum alloy, friction stir
welding (FSW) is an emerging solid state joining process in
which the material that is being welded does not melt and recast
[6]. Friction stir welding (FSW) was invented at The Welding
Institute (TWI), UK in 1991. Friction stir welding is a contin-
uous, hot shear, autogenous process involving non-consumable
rotating tool of harder material than the substrate material [7].
Fig. 1 explains the working principle of FSW process. Defect
free welds with good mechanical properties have been made in
a variety of aluminium alloys, even those previously thought
to be not weldable. When alloys are friction stir welded, phase
transformations that occur during cool down of the weld are of a
0921-5093/$ see front matter 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.msea.2006.12.124
mailto:[email protected]:[email protected]://dx.doi.org/10.1016/j.msea.2006.12.124http://dx.doi.org/10.1016/j.msea.2006.12.124mailto:[email protected]:[email protected]8/7/2019 Influ of tool pin and rotation speed on Al alloy
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8 K. Elangovan, V. Balasubramanian / Materials Science and Engineering A 459 (2007) 718
Fig. 1. Schematic representation of FSW principle.
solid state type. Due to the absence of parent metal melting, the
new FSW process is observed to offer several advantages overfusion welding [8].
FSW joints usually consist of four different regions as shown
in Fig. 2. They are: (a) unaffected base metal; (b) heat affected
zone (HAZ); (c) thermo-mechanically affected zone (TMAZ)
and (d) friction stir processed (FSP) zone. The formation of
above regions is affected by the material flow behaviour under
the action of rotating non-consumable tool. However, the mate-
rial flow behaviour is predominantly influenced by the FSW
tool profiles, FSW tool dimensions and FSW process param-
eters [9,10]. The available literature focusing on the effect of
welding parameters and tool profiles on FSP zone formation in
AA2219 aluminum alloy is very scant. Hence, in this investiga-tionanattempt has beenmade to understand the effectof tool pin
profiles and rotational speed on FSP zone formation. This paper
presents the relation between the FSP zone formation and ten-
sile properties of friction stir welded AA2219 aluminium alloy
joints.
2. Experimental Work
The rolled plates of 6 mm thickness, AA2219 aluminium
alloy, were cut into the required size (300mm 150mm) by
power hacksaw cutting and grinding. Square butt joint con-
figuration, as shown in Fig. 3 was prepared to fabricate FSW
joints. The initial joint configuration was obtained by securing
the plates in position using mechanical clamps. The direction of
welding was normal to the rolling direction. Single pass weld-
Fig. 2. Different regions of FSW joint: (a) unaffected base metal; (b) heat
affected zone (HAZ); (c) thermo-mechanically affected zone (TMAZ); (d) fric-
tion stir processed (FSP) zone.
Fig. 3. Dimensions of square butt joint.
Fig. 4. FSW tool dimensions.
Table 1a
Chemical composition (wt%) of base metal
Cu 6.7
Mn 0.27
Si 0.01
Zn 0.04
Ti 0.05
Fe 0.13
Zr 0.12
Mg 0.01
Al Bal
ing procedure was used to fabricate the joints. Non-consumable
tools made of high carbon steel were used to fabricate the joints.
The tool dimensions are shown in Fig. 4. The chemical com-
position and mechanical properties of base metal are presented
in Table 1. An indigenously designed and developed machine
(15HP; 3000 rpm; 25 kN) was used to fabricate the joints. Five
different tool pin profiles, as shown in Fig. 5 were used to fab-
ricate the joints. Using each tool, 3 joints were fabricated at 3
different rotational speeds and in total 15 joints (5 3) were
fabricated in this investigation. Trial experiments were carried
out to find out the working limits of welding parameters. Three
differentwelding speeds (0.32 mm/s, 0.76 mm/s and1.25 mm/s)
and three different axial force levels (10 kN, 12 kN and 14 kN)
were used to fabricate the joints. Then the joints were visually
inspectedfor exteriorwelddefects andit was foundthat thejoints
Table 1b
Mechanical properties of AA2219-T87
Yield strength (MPa) 310
Ultimate tensile strength (MPa) 408
Elongation (%) 23
Vickers hardness (0.5 kg) 140
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K. Elangovan, V. Balasubramanian / Materials Science and Engineering A 459 (2007) 718 9
Fig. 5. FSW tool pin profiles.
Table 2
Welding parameters and tool dimensions
Process parameters Values
Rotational speed (rpm) 1500, 1600, 1700
Welding speed (mm/s) 0.76
Axial force (kN) 12
D/dratio of tool 3.0
Pin length (mm) 5.7
Tool shoulder diameter, D (mm) 18
Pin diameter, d(mm) 6
Tool inclined angle () 0
Shoulder deepness inserted into the surface
of base metal (mm)
0.2
Included angle of taper pin 7.5
Pitch (mm) and included angle () of
threaded pin
1 and 60
fabricated at the welding speed of 0.76 mm/s and axial force of
12 kN was free fromany externaldefects. Similar welding speed
was used by the other investigator [8] also to weld AA2219 alu-
minium alloy. The welding parameters and tool dimensions are
presented in Table 2.
The welded joints were sliced using power hacksaw and
then machined to the required dimensions to prepare ten-
sile specimens as shown in Fig. 6. American Society for
Testing of Materials (ASTM) guidelines were followed for
preparing the test specimens. Tensile test was carried out
in 100 kN, electro-mechanical controlled Universal TestingMachine. The specimen was loaded at the rate of 1.5 kN/min
as per ASTM specifications, so that tensile specimen under-
goes deformation. The specimen finally fails after necking
Fig. 6. Dimensions of tensile specimen.
and the load versus displacement was recorded. The 0.2%
offset yield strength, ultimate tensile strength and percentage
of elongation were evaluated. Vickers microhardness testingmachine (Make: Matzusawa, Japan and Model: MMT-X7) was
employed formeasuringthehardnessacrossthe joint with 0.5kg
load.
Macro- and microstructural analysis was carried out using
a light optical microscope (VERSAMET-3) incorporated with
an image analyzing software (ClemexVision). The specimens
for metallographic examination were sectioned to the required
sizes from the joint comprising FSP zone, TMAZ, HAZ and
base metal regions and polished using different grades of
emery papers. Final polishing was done using the diamond
compound (1m particle size) in the disc polishing machine.
Specimens were etched with Kellers reagent to reveal the
macro- and microstructures. The fractured surface of the ten-
sile tested specimens was analysed using digital scanner at
low magnification to study the general mode of fracture pat-
tern to establish the relationship between FSP zone and the
fracture.
3. Results
3.1. Macrostructure
In fusionwelding of aluminiumalloys, thedefects like poros-
ity, slag inclusion, solidification cracks, etc. deteriorates the
weld quality and joint properties. Usually, friction stir weldedjoints are free from these defects since there is no melting takes
place during welding and the metals are joined in the solid
state itself due to the heat generated by the friction and flow of
metal by the stirring action. However, FSW joints are prone to
other defects like pinhole, tunnel defect, piping defect, kissing
bond, cracks, etc. due to improper flow of metal and insuffi-
cient consolidation of metal in the FSP region. All the joints
fabricated in this investigation are analysed at low magnifica-
tion (10) using optical microscope to reveal the quality of FSP
regions.
The macrostructure of the joints and the observations (FSP
zone shape, FSP zone height (H), FSP zone width (W) at three
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10 K. Elangovan, V. Balasubramanian / Materials Science and Engineering A 459 (2007) 718
Table 3
Effect of rotational speed on macrostructure of the joints fabricated by straight cylindrical pin profiled tool
Rotational
speed (rpm)
Macrostructure Size of FSP
zone (mm)
Shape of
FSP zone
Name of the
defect and
location
Quality of
weld metal
consolidation
Probable reasons
RS AS W H
1500 8.7 5.9 Inverted
trapezoidal
Tunnel in the
bottom of the
weld in the
retreating side
(RS)
Poor Insufficient heat
input and flow of
the plasticized
metal
6.1
4.1
1600 9.2 5.9 Tunnel in the
root of the weld
in the retreating
side
No vertical flow
of the metal6.3
3.9
1700 11.1 5.8 Pinholes in the
retreating side
and the root of
the weld
6.2
4.6
different locations, quality of the FSP zone, etc.) made from the
macrostructure are presented in Tables 37. All the three joints
fabricated using straight cylindrical pin profiled tool (Table 3)
and tapered cylindrical pin profiled tool (Table 4) are found
to be defective irrespective of rotational speeds used. In the
case of threaded cylindrical pin profiled tool (Table 5) and tri-
angular pin profiled tool (Table 7), the joints fabricated at a
rotational speed of 1500 rpm are found to be defective. On the
Table 4
Effect of rotational speed on macrostructure of the joints fabricated by tapered cylindrical pin profiled tool
Rotational
speed (rpm)
Macrostructure Size of FSP
zone (mm)
Shape of FSP
zone
Name of the
defect and
location
Quality of
weld metal
consolidation
Probable
reasons
RS AS W H
1500 7.4 5.8 Inverted
trapezoidal
Tunnel in the
bottom of the
weld in the
retreating side
Poor Insufficient heat
input and flow
of the
plasticized metal
5.1
3.1
1600 8.4 5.9 Pinhole in the
middle of the weld
in the retreating
side
No vertical flow
of the metal6.1
4.3
1700 11.3 5.9 Tunnel in the
bottom of the
weld in the
retreating side
6.7
5.1
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K. Elangovan, V. Balasubramanian / Materials Science and Engineering A 459 (2007) 718 11
Table 5
Effect of rotational speed on macrostructure of the joints fabricated by threaded cylindrical pin profiled tool
Rotational
speed (rpm)
Macrostructure Size of FSP
zone (mm)
Shape of FSP
zone
Name of the
defect and
location
Quality of
weld metal
consolidation
Probable reasons
RS AS W H
1500 8.1 5.9 Inverted
trapezoidal
No defect Good Screw thread generate
more heat and exerts
an extra downward
movement to the
plasticized metal
4.3
3.1
1600 10.3 5.8 No defect Good 5.2
3.9
1700 11.2 5.9 Pinhole in the
middle of the
weld
Poor Excess turbulence of
the plasticized metal
due to higher
rotational speed
8.3
7.1
other hand, the joints fabricated using square pin profiled tool is
found to be free from defects (Table 6). From the macrostruc-
ture analysis, it can be inferred that the formation of defect
free FSP zone is a function of tool profile and rotational speed
used.
3.2. Tensile properties
Transverse tensile properties of FSW joints such as yield
strength, tensile strength, percentage of elongation and joint
efficiency were evaluated. Three specimens were tested at each
Table 6
Effect of rotational speed on macrostructure of the joints fabricated by square pin profiled tool
Rotational
speed (rpm)
Macrostructure Size of FSP
zone (mm)
Shape of FSP
zone
Name of the
defect and
location
Quality of
weld metal
consolidation
Probable reasons
RS AS W H
1500 10.1 5.8 Inverted
trapezoidal
No defect Good Sufficient working of the
plasticized metal due to
the pulsating action of the
pin profile
4.1
4.0
1600 10.0 5.9 5.7
3.3
1700 12.1 5.9 Excess working of the
plasticized metal with
wider FSP due to high
rotational speed
8.4
6.8
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12 K. Elangovan, V. Balasubramanian / Materials Science and Engineering A 459 (2007) 718
Table 7
Effect of rotational speed on macrostructure of the joints fabricated by triangular pin profiled tool
Rotational
speed (rpm)
Macrostructure Size of FSP
zone (mm)
Shape of FSP
zone
Name of the
defect and
location
Quality of
weld metal
consolidation
Probable reasons
RS AS W H
1500 7.4 5.9 Inverted
trapezoidal
Pinhole in the
retreating side
Poor Insufficient heat
input and flow of
the plasticized
metal
4.8
3.3
1600 8.6 5.9 No defect Good Adequate heat
input and flow of
the plasticized
metal
5.8
4.3
1700 9.1 5.9 No defect Good
5.9
3.4
condition and average of the results of three specimens is pre-
sented in Fig. 7. From the figure, it can be inferred that the
tool profile and tool rotational speed are having influence on
tensile properties of the FSW joints. Of the five joints, the
joints fabricated by square tool profile exhibited superior tensile
properties compared to other joints, irrespective of tool rota-
tional speed. Similarly, the joints fabricated by threaded pin
profiled tool are also showing almost matching tensile prop-
erties to that of square tool profile. But the joints fabricated by
straight cylindrical tool profile exhibited inferior tensile proper-
Table 8
Effect of rotational speed on fracture surface of the joints fabricated by straight cylindrical pin profiled tool
Rotational speed (rpm) Fracture surface Location of
fracture
Fracture surface
appearance
Orientation of defects
1500 Between FSP
and HAZ of
retreating side
Coarse granular
appearance with
concave surface
Groove corresponding
to the tunnel in the
weld cross section
1600 Uneven surface with
mixed mode pattern
1700 Irregular surface with
dull grey fibrous
appearance
Groove corresponding
to the pinhole in the
weld cross section
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K. Elangovan, V. Balasubramanian / Materials Science and Engineering A 459 (2007) 718 13
Fig. 7. Effect of rotational speed on tensile properties: (a) tensile strength; (b) yield strength; (c) percentage of elongation; (d) joint efficiency.
tiescompared to theircounterparts, irrespectiveof toolrotational
speed.
The joints fabricated at the rotational speed of 1500 rpm have
shown lower tensile strength and elongation compared to the
joints fabricated at a rotational speed of 1600 rpm and this trend
iscommonfor allthe tool profiles.Similarly, thejoints fabricated
at therotational speed of 1700 rpmhavealso shownlowertensile
strength and elongation compared to the joints fabricated at a
rotational speed of 1600rpm. The effect of rotational speed is
concerned, the joints fabricated at a rotational speed of 1600 rpm
areshowing superior tensile properties compared to other joints,
irrespective of tool profiles. The fractured surfaces of the tensile
test specimens were scanned using a digital scanner and the
fracture patterns of all the joints and observations made from
the fractured surface are presented in Tables 712. From the
fractured surface analysis, it can be inferred that the defect free
welds are showing uniform deformation across the weld before
failure (Table 11).
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14 K. Elangovan, V. Balasubramanian / Materials Science and Engineering A 459 (2007) 718
Table 9
Effect of rotational speed on fracture surface of the joints fabricated by tapered cylindrical pin profiled tool
Rotational speed (rpm) Fracture surface Location of
fracture
Fracture surface
appearance
Orientation of
defects
1500 Between FSP
and HAZ of
retreating side
Irregular surface
with fibrous
appearance along
with striations at
the top
Groove
corresponding to
the tunnel in the
weld cross section
1600 Uneven surface
with fibrous dull
grey appearance
Insufficient
consolidation
corresponding to
the pinhole in the
weld cross section
1700 Flat surface with
coarse granular
appearance
Groove
corresponding to
the tunnel in the
weld cross section
4. Discussion
From the experimental results (macrostructure, tensile prop-
erties and fracture surface), it is found that the joint fabricated
using square pin profiled tool at a rotational speed of 1600rpm
exhibited superior tensile properties compared to other joints.
The reasons for the better performance of these joints are
explained below.
4.1. Effect of tool pin profile
The primary function of the non-consumable rotating tool
pin is to stir the plasticized metal and move the same behind
it to have good joint. Pin profile plays a crucial role in mate-
rial flow and in turn regulates the welding speed of the FSW
process [11,12]. The pin generally has cylindrical plain, frus-
tum tapered, threaded and flat surfaces. Pin profiles with flat
Table 10
Effect of rotational speed on fracture surface of the joints fabricated by threaded cylindrical pin profiled tool
Rotational
speed (rpm)
Fracture surface Location of
fracture
Fracture surface
appearance
Orientation of
defects
1500 Between FSP and
HAZ of retreating
side
Flat and smooth
surface with bright
granular appearance
No defect
1600 Irregular surface with
fibrous dull grey
appearance
No defect
1700 Uneven surface with
fibrous appearance
along with striations
at the top
Groove
corresponding to
the pinhole in the
weld cross section
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K. Elangovan, V. Balasubramanian / Materials Science and Engineering A 459 (2007) 718 15
Table 11
Effect of rotational speed on fracture surface of the joints fabricated by square pin profiled tool
Rotational
speed (rpm)
Fracture surface Location of
fracture
Fracture surface
appearance
Orientation of defects
1500 Between FSP
and HAZ of
retreating side
Coarse granular
appearance with striations
at top and bottom
No defect
1600 Concave surface with
granular appearance (like
cup and cone fracture)
1700 Granular appearance with
striations at the bottom
Table 12
Effect of rotational speed on fracture surface of the joints fabricated by triangular pin profiled tool
Rotational
speed (rpm)
Fracture surface Location of
fracture
Fracture surface
appearance
Orientation of defects
1500 Between FSP
and HAZ of
retreating side
Uneven surface with
coarse granular
appearance along with
striations at the bottom
Groove corresponding to
the pinhole in the weld
cross section
1600 Flat surface with bright
granular appearance
No defect
1700 Irregular surface with dull
grey fibrous appearance
along with striations at
the bottom
No defect
Fig. 8. Effect of pin profiles on FSP zone hardness.
faces (square and triangular) are associated with eccentricity.
This eccentricity allows incompressible material to pass aroundthe pin profile. Eccentricity of the rotating object is related to
dynamic orbit due to eccentricity [13]. This dynamic orbit is
the part of the FSW process. The relationship between the static
volume and dynamic volume decides the path for the flow of
plasticized material from the leading edge to the trailing edge of
the rotating tool. This ratio is equal to 1 for straight cylindrical,
1.09 for tapered cylindrical, 1.01 for threaded cylindrical, 1.56
for square and 2.3 for triangular pin profiles. In addition, the
triangular and square pin profiles produce a pulsating stirring
action in the flowing material due to flat faces. The square pin
profile produces 100pulses/s and triangular pin profile produces
75 pulses/s when the tool rotates at a speed of 1500 rpm. There
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16 K. Elangovan, V. Balasubramanian / Materials Science and Engineering A 459 (2007) 718
Fig. 9. Effect of tool pin profiles on FSP zone microstructure: (a) straight cylindrical; (b) taper cylindrical; (c) threaded cylindrical; (d) square; (e) triangular.
is no such pulsating action in the case of cylindrical, tapered and
threaded pin profiles.
During tensile test, most of the specimens failed in the FSP
region but the exact location of failure is either at the retreating
side (RS) or at the advancing side (AS) and it is also evident
from the fracture surface analysis. Hence, microhardness mea-
surement and microstructural analysis have been carried out in
the FSP region of all the joints. Fig. 8 shows the microhardness
values and Fig. 9 displays themicrostructure of FSPregionof all
the joints fabricated at a rotational speed of 1600rpm for com-
parison purpose. Of the five joints, the highest hardness value
of 105 Hv has been recorded in the joint fabricated using square
pin profiled tool and the lowest hardness value of 82 Hv has
been recorded in the joint fabricated using straight cylindrical
pin profiled tool. Similarly, the FSP region of the joint fabri-
cated using square pin profile tool contains finer grains (Fig. 9d)
compared to other joints. The higher number of pulsating action
experienced in the stir zone of square pin profiled tool produces
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K. Elangovan, V. Balasubramanian / Materials Science and Engineering A 459 (2007) 718 17
finer grained microstructure and in turn yields higher strength
and hardness.
4.2. Effect of tool rotational speed
Rotational speed appears to be the most significant process
variable since it also tends to influence the translational velocity.
Veryhighrotationalspeeds (>10,000 rpm)couldraisestrain rate,
andthereby influence therecrystallisationprocess;whichin turn
could influence the FSW process [14]. Higher tool rotational
speed resulted in a higher temperature and slower cooling rate
in the FSP zone after welding. A higher rotational speed causes
excessive release of stirred materials to the upper surface, which
resultantly left voids in theFSP zone. Lowerheat input condition
dueto lowerrotational speed resulted in lack of stirring.Thearea
of the FSP zone decreases with and decreasing the tool rotation
speed and affect the temperature distribution in the FSP zone
[15].
As the rotational speed increases, the strained region widens,
and the location of the maximum strain finally moves to theadvancing side from the original retreating side of the joint.
This implies that the fracture location of the joint is also affected
by the rotational speed [16]. The tensile properties of the joints
madewithdifferentwelding conditionsresulted in lowest tensile
strength and ductility at lowest spindle speed for a given tra-
verse (welding) speed. As the spindle speed increased, both the
strength and elongation improved, reaching a maximum before
falling again at high rotational speeds. It is clear that, in FSW,
as the rotational speed increases, the heat input also increases.
However, the calculated maximum temperatures are nearly the
same in all the rotational speeds. This phenomenon can be
explained by the following two reasons: first, the coefficient offriction decreases when a local melt occurs, and subsequently
decreases when a local input; secondly, the latent heat absorbs
some heat input.
Moataz and Hanadi [17] have opined that at very high rota-
tional speeds, second phase (strengthening) particles would
suffer more fragmentation and leads to segregation of par-
Fig. 10. Effect of rotational speed on FSP zone hardness (tool profile: square
pin).
ticles in other parts of the TMAZ. As the rotational speedis decreased, and the temperature within the nugget becomes
lower and the volume fraction of coarse second phase particles
increases. Hence, the tool rotation speed must be optimized to
getFSPregionwith fineparticlesuniformlydistributedthrough-
out the matrix. Of the three different tool rotational speeds,
the joints fabricated at a rotational speed of 1600 rpm exhib-
ited superior tensile properties, irrespective of tool pin profiles.
For comparison purpose, the microhardness and microstructure
of FSP regions produced by square pin profiled tool at different
rotational speedsarepresented in Figs. 10 and 11. Higher micro-
hardness and finer grain diameter have been obtained at the FSP
region of the joint fabricated at 1600 rpm using square pin pro-
filed tool. The combined effect of higher number of pulsating
stirring action during metal flow and an optimum tool rotational
speed may be the reason for superior tensile properties, higher
hardness and finer microstructure at the FSP region of the joint
fabricated at a rotational speed of 1600rpm using square pin
profiled tool.
Fig. 11. Effect of rotational speed on microstructure of FSP zone (tool profile: square pin).
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18 K. Elangovan, V. Balasubramanian / Materials Science and Engineering A 459 (2007) 718
5. Conclusions
In this investigation an attempt has been made to study the
effect of tool pin profile and tool rotational speed on the forma-
tion of friction stir processing zone in AA2219aluminium alloy.
From this investigation, the following important conclusions are
derived:
(i) Of the five tool pin profiles used in this investigation to
fabricatethe joints, squarepinprofiled tool produced defect
free FSP region, irrespective of rotational speeds.
(ii) Of the three tool rotational speedsused in this investigation
to fabricate the joints, the joints fabricated at a rotational
speed of 1600 rpm showed better tensile properties, irre-
spective of tool pin profiles.
(iii) Ofthe15 jointsfabricatedin this investigation, thejointfab-
ricated using square pin profiled tool at a rotational speed
of 1600 rpm showed superior tensile properties.
Acknowledgements
The authors are grateful to the Department of Manufacturing
Engineering, AnnamalaiUniversity, AnnamalaiNagar, Indiafor
extendingthefacilitiesof Metal Joining Laboratory andMaterial
Testing Laboratory to carryout this investigation. The authors
wish to place their sincere thanks to Aeronautical Research &
Development Board (ARDB), New Delhi for financial support
rendered through a R&D project No. DARO/08/1061356/M/I.
References
[1] C. Huang, S. Kou, Weld. J. 79 (5) (2000) 113s120s.
[2] G.I. Dance, Weld. Met. Fabrication 24 (1994) 216222.[3] J.A. Hartman, R.J. Beil, T.G. Hahn, Weld. J. 66 (1987) 73s83s.
[4] Y.P. Yang, P. Dong, J.Z. Zhang, X. Tian, Weld. J. 79 (2000) 9s17s.
[5] S.R. Koteswara rao, R. Madhusudhana Reddy, G. Srinivasa rao, K. Kama-
raj, M. Prasad Rao K, Mater. Charact. 40 (2005) 236248.
[6] W.M. Thomas, Friction stir welding, International Patent Application no.
PCT/GB92/02203 and GB Patent Application no. 9125978.8, December
1991, US Patent no. 5,460,317 (1991).
[7] C.J. Dawes, Weld. Met. Fabrication (1995) 12.
[8] G. Cao, S. Kou, Weld. J. (2005) 1-s8-s.
[9] Yingchun Chen, Huijie Liu, Feng Jicai, Mater. Sci. Eng. A 420 (2006)
2125.
[10] H.J. Liu, Y.C. Chen, J.C. Feng, Scripta Mater. 55 (2006) 231234.
[11] A. Oosterkamp, L. Djapic Oosterkamp, A. Nordeide, Weld. J. (2004)
225s231s.
[12] W.M. Zeng, H.L. Wu, J. Zhang, Acta Metall. Sinica 19 (1) (2006) 919.[13] W.M. Thomas, E.D. Nicholas, Mater. Des. 18 (1997) 269273.
[14] V.F. Olga, Scripta Mater. 38 (5) (1998) 703708.
[15] B.L. Won, Yun FY.M., J.B Seung, Mater. Trans. 45 (5) (2004) 17001705.
[16] H.J. Liu, H. Fuji, Sci. Technol. Weld. Joining 8 (6) (2003) 450454.
[17] M.A. Moataz, G.S. Hanadi, Mater. Sci. Eng. A 391 (2005) 5159.