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Friction Stir Welding on Aluminum Alloy 6063 Pipe

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In Friction Stir Welding (FSW) process, there is a substantial amount of research done on aluminum plate but very few are found for aluminum pipe due to its tubular shape. A specially customized Orbital Clamping Unit (OCU) was used and fixed on the Bridgeport 2216 CNC milling machine in order to weld an aluminum alloy 6063 pipe butt joint at several welding parameters. This OCU will hold the work pieces together tightly, rotate them at the required constant low speed, and ensure easy removal. This paper will investigate the effect of welding parameters on the tensile strength of joint produced by the FSW process. Several good samples of pipes joint were produced using the present experiment setting.
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Friction Stir Welding on Aluminum Alloy 6063 Pipe
Azman Ismail
1
, Mokhtar Awang
2
, Hasan Fawad
2
and Kamal Ahmad
1
1
Universiti Kuala Lumpur, Malaysian Institute of Marine Engineering Technology, Lumut, Malaysia.
2
Department of Mechanical Engineering, Universiti Teknologi PETRONAS, Tronoh, Malaysia.
E-mail: azman@mimet.unikl.edu.my
Abstract
In Friction Stir Welding (FSW) process, there is a
substantial amount of research done on aluminum plate but
very few are found for aluminum pipe due to its tubular
shape. A specially customized Orbital Clamping Unit
(OCU) was used and fixed on the Bridgeport 2216 CNC
milling machine in order to weld an aluminum alloy 6063
pipe butt joint at several welding parameters. This OCU
will hold the work pieces together tightly, rotate them at the
required constant low speed, and ensure easy removal. This
paper will investigate the effect of welding parameters on
the tensile strength of joint produced by the FSW process.
Several good samples of pipes joint were produced using
the present experiment setting.
Introduction
The Friction Stir Welding (FSW) is the state-of-the art
joining process which was invented and later patented by
The Welding Institute (TWI) in 1991 [1]. This is a solid
state joining process which uses heat from frictional work
to soften and join the material together through stirring
process. The schematic process is shown in Figure 1 [2].
This welding technique provides many advantages such as
it produces no fumes, no arc and requires no filler metal
[3]. Thus, this process can be regarded as an
environmental-friendly process.
Figure 1: Friction stir welding process
However, the experiment setting is the most critical part in
this process especially for joining aluminum alloy 6063
pipes. Good samples are needed before tensile testing. The
Orbital Clamping Unit (OCU) was developed and fixed on
the Bridgeport 2216 CNC milling machine. This OCU will
hold the pipes together tightly, rotate them at required
constant low speed, and ensure easy removal.
This application of FSW on pipes can be used for
petroleum, petrochemical, and natural gas industries which
in some studies, estimated to provide 25% and 7% cost
saving for offshore and onshore construction respectively
[4].
A substantial amount of research has been done on
aluminum plate but found very few for aluminum pipe due
to its tubular shape [5]-[12]. This paper will study the effect
of welding parameters on the tensile strength of the friction
stir welded aluminum alloy 6063 pipe butt joint.
Experimental setup
In this study, full-penetration friction stir welds are
performed on aluminum alloy 6063 pipe for butt joint
configuration as shown in Figure 2.
Figure 2: Orbital clamping unit for FSW experiment
The 89 mm outside diameter of aluminum alloy 6063 pipe
with 5 mm nominal thickness was used in this present
study. Chemical composition and mechanical properties are
Proceedings of the 7th Asia Pacific IIW International Congress 2013 (IIW 2013)
Copyright © 2013 IIW 2013 Organisers. All rights reserved.
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Proceedings of the 7th Asia Pacific IIW International Congress 2013 (IIW 2013)
shown in Table 1 and 2, respectively. The tool geometry
used for this study was made of high carbon steel with 20
mm diameter of shoulder, 5 mm and 3.8 mm of pin
diameter and length, respectively. The position of tool was
offset 6mm forward from centerline [2].
TABLE 1: CHEMICAL COMPOSITION [13]
TABLE 2: MECHANICAL PROPERTIES [13]
FSW for pipe posed unique challenge and the orbital
clamping unit (OCU) was vital in this current setting. Two
categories of welding parameters were used which can be
referred to in Table 3. The plunge depth and dwell time
used were 4mm and 30s respectively.
TABLE 3: WELDING PARAMETERS
FSW
sample
Welding parameters Remarks
Rotation
speed
(rpm)
Travel
speed
(mm/s)
FSW1 900 1.2 Vary in rotation
speed but constant
in travel speed
FSW2 1200 1.2
FSW3* 1500 1.2
FSW3* 1500 1.2 Vary in travel
speed but constant
in rotation speed
FSW4 1500 1.8
FSW5 1500 2.4
*with same welding parameters
Visual inspection was conducted to detect for possible
voids or imperfections such as crack, excessive flash,
surface tunnel, wormhole and lack of penetration according
to AWS D17.3 [14]. Tensile tests were performed
according to ASTM E8M-04 [15]. Three tensile samples
were prepared for each weld. The tensile tests were
conducted at specific parameters, by using servo controlled
universal testing machine. Macro tests were prepared based
on ASTM E340 [16]. The optical microscope was used
during the macro structural analysis with 10x of
magnification and the etchant used was Keller's reagent.
Results and discussion
a) Visual Inspection
Table 4 shows the surface finishing for each FSW sample.
The FSW1 and FSW2 give smooth weld surface with some
lateral flash; meanwhile FSW3, FSW4 and FSW5 show
smooth weld surface condition. With the increase of
rotation speed, the lateral flash was minimized while
increasing the travel speeds, no such lateral flash occurred.
Therefore, it was discovered that the external surface
behavior may depend on the welding parameters as stated
in the previous study [12].
TABLE 4: WELD SURFACE FINISHING
FSW
sample
Weld surface finishing Remarks
FSW1
Smooth
weld surface
with lateral
flash
FSW2
Smooth
weld surface
with lateral
flash
FSW3
Smooth
weld surface
FSW4
Smooth
weld surface
FSW5
Smooth
weld surface
b) Macrostructures and weld defects
Table 5 shows the cross sectional macrostructure for five
pipe specimens at different welding parameters. For FSW1
-FSW4, the specimens show defect free samples but defect
formed in FSW5 sample. This may due to excessive
turbulence caused by higher travel speed which affects the
formation of defect. This was agreed that the higher
parameters will cause excessive turbulence due to different
plastic deformation degrees and temperatures [5]-[6].
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Proceedings of the 7th Asia Pacific IIW International Congress 2013 (IIW 2013)
TABLE 5: CROSS SECTION MACROSTRUCTURES
FSW
sample
Advancing
side
Retreating
side
Remarks
FSW1
Defect free
FSW2
Defect free
FSW3
Defect free
FSW4
Defect free
FSW5
Crack line and
very small pin
hole were
detected.
c) Tensile properties.
Tensile strength may vary depending on its welding
parameters [12]. The tensile strength is plotted based on
actual strength. Figure 3 shows the tensile strength for each
FSW sample. The increment in rotation speed (FSW1,
FSW2 and FSW3) increase the tensile strength up to
126MPa then decrease to 121MPa. Similar pattern goes to
sample FSW3, FSW4 and FSW5. The tensile strength
increase up to 132 MPa before it starts decreasing to
114MPa.
Table 6 shows the fracture section for each FSW sample.
As detected on FSW1, there was defect free as shown in
Table 5 but it breaks on the weld centerline. This weak
joint shows the lowest tensile strength at 104MPa.
Meanwhile, the FSW2, FSW3 and FSW4 samples give
better joint strength as it breaks on the base metal either on
advancing or retreating side. It is a bit different from the
previous study which found that the fracture location was
on the retreating side and applicable for certain grade of
aluminum [6]. For FSW5 sample, it is clearly observed by
using the optical microscope, the hairline crack and small
pin hole affect the strength of the joint as it breaks on the
weld centerline. It also gives the lower tensile strength with
the value of 114MPa.
Figure 3: Tensile strength for FSW sample.
TABLE 6: FRACTION SECTION
FSW
sample
Advancing
side
Retreating
side
Remarks
FSW1
Breaks on
centerline
FSW2
Breaks on
retreating side
FSW3
Breaks on
advancing side
FSW4
Breaks on
retreating side
FSW5
Breaks on
centerline
Conclusions
From the results of the present study, several conclusions
can be drawn:
1) High rotation speed of 1500rpm for various travel
speed (1.2, 1.8 and 2.4 mm/s) gives better weld surface
finishing without lateral flash.
2) High rotation speed of 1500rpm and travel speed of
2.4 mm/s cause void defect to form in the joint.
3) The increment of rotation speed will increase the
tensile strength up to maximum value of 126 MPa and
then starts decreasing to 121 MPa.
4) The increment of travel speed will increase the tensile
strength up to maximum value of 132 MPa and then
starts decreasing to 114 MPa.
5) The lowest rotation speed of 900 rpm and travel speed
of 1.2 mm/s give the weakest joint strength of 104MPa
while the highest rotation speed of 1500 rpm and travel
speed of 2.4 mm/s give defects in the joint with a bit
higher strength of 114MPa.
Acknowledgements
The authors would like to acknowledge the Universiti
Kuala Lumpur for providing the conference grant, 160-
80
Proceedings of the 7th Asia Pacific IIW International Congress 2013 (IIW 2013)
520435-003 and the Department of Mechanical
Engineering, Universiti Teknologi PETRONAS for
providing the required facilities and assistances.
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Friction stir welding process is a promising solid state joining process with the potential to join low melting point materials, particularly aluminum alloys. The most attractive reason for this is the avoidance of solidification defects formed during conventional fusion welding processes. Tool rotational speed and the welding speed play a major role in deciding the weld quality. In the present work an effort has been made to study the effect of the tool rotational speed and welding speed on mechanical and metallurgical properties of friction stir welded joints of aluminum alloy AA6082-T651. The micro hardness profiles obtained on welded zone indicate uniform distribution of grains in the stir zone. The maximum tensile strength obtained is 263 MPa which is about 85% of that of base metal. Scanning electron microscope was used to show the fractured surfaces of tensile tested specimens.
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The joining of dissimilar Al–Cu alloy AA2219-T87 and Al–Mg alloy AA5083-H321 plates was carried out using friction stir welding (FSW) technique and the process parameters were optimized using Taguchi L16 orthogonal design of experiments. The rotational speed, transverse speed, tool geometry and ratio between tool shoulder diameter and pin diameter were the parameters taken into consideration. The optimum process parameters were determined with reference to tensile strength of the joint. The predicted optimal value of tensile strength was confirmed by conducting the confirmation run using optimum parameters. This study shows that defect free, high efficiency welded joints can be produced using a wide range of process parameters and recommends parameters for producing best joint tensile properties. Analysis of variance showed that the ratio between tool shoulder diameter and pin diameter is the most dominant factor in deciding the joint soundness while pin geometry and welding speed also played significant roles. Microstructural studies revealed that the material placed on the advancing side dominates the nugget region. Hardness studies revealed that the lowest hardness in the weldment occurred in the heat-affected zone on alloy of 5083 side, where tensile failures were observed to take place.
Article
Lap joints of 1060 aluminum alloy and commercially pure copper was produced by friction stir welding and the effect of welding speed on interface morphology, microstructure, and joint strength was investigated. The experimental results revealed that in the aluminum close to the Al/Cu interface, a dark area was formed. In this area the intermetallic compounds of Al4Cu9 and Al2Cu, and some microcracks were detected. The frequency of such microcracks decreased with increasing welding speed.On the other hand, at higher welding speeds of 118 and 190 mm/min, the cavity defects were formed inside the joints as a result of insufficient heat input. The results of tensile shear test revealed that the maximum tensile shear strength of joint was obtained at welding speed of 95 mm/min. At this welding speed, no cavity defects, and few microcracks were observed in the weld.
Chapter
Friction stir welding/processing (FSW/P) is an innovative solid-state joining/processing technique (Thomas et al. 1991; Mishra and Ma 2005). The basic concept of FSW/P is very simple, as shown in Fig. 21.1 (Park et al. 2003a). A specially designed tool rotating at high speed is plunged into work pieces to be joined/processed and then is traversed along the weld seam, or in a direction of interest in the case of friction stir processing (FSP). The rotating tool produces frictional heat which softens the material so that it is readily extruded around the tool. The simultaneous rotational and translation motion of the tool forces the material to flow around the tool, filling a cavity at the rear of the tool and thus creating a solid-state joint. During the flow, the material undergoes extreme levels of plastic deformation and thermal exposure, which drastically changes the microstructure in the center of the processed zone. © Springer Science+Business Media, LLC 2009. All rights reserved.