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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
, Mokhtar Awang
, Hasan Fawad
and Kamal Ahmad
Universiti Kuala Lumpur, Malaysian Institute of Marine Engineering Technology, Lumut, Malaysia.
Department of Mechanical Engineering, Universiti Teknologi PETRONAS, Tronoh, Malaysia.
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.
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
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)
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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].
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.
Welding parameters Remarks
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].
Weld surface finishing Remarks
weld surface
with lateral
weld surface
with lateral
weld surface
weld surface
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].
Proceedings of the 7th Asia Pacific IIW International Congress 2013 (IIW 2013)
Defect free
Defect free
Defect free
Defect free
Crack line and
very small pin
hole were
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
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.
Breaks on
Breaks on
retreating side
Breaks on
advancing side
Breaks on
retreating side
Breaks on
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.
The authors would like to acknowledge the Universiti
Kuala Lumpur for providing the conference grant, 160-
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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... Heat generation is influenced by tool rotation speed and tool shoulder diameter. An increase in tool rotation speed enhances tensile strength up to a certain limit, after which tensile strength decreases [24,25]. Several modelling approaches have also been investigated in order to determine the optimum FSW pipe welding process parameters. ...
... For instance, Khourshid and Sabry [25] analysed the effect of rotational speed on FSW of AA6063 pipes and reported an increase in tensile strength with the rise in tool rotational speeds. Ismail et al. [24] also included the effect of tool traverse speed for the AA6063 alloy pipes of 89 mm outer diameter and 5 mm thickness in their study. A rigid visco-plastic model has also been developed to elucidate the temperature distribution and force variation for pipe FSW [26]. ...
With the elimination of solidification defects, friction stir welding becomes the most effective process for joining flat and curved surfaces. Tool geometry (tool pin profile, shoulder diameter) and tool rotation speed mainly contribute to the overall weld quality. The study evaluates the simultaneous effect of tool geometry, rota-tional speed, base offset and double pass Friction Stir Welding (DP-FSW) on the defect formation and the mechanical properties. Micro-structure and macro-structure have been analysed for weld strength and hardness characterisation, and found, at high tool rotation speed maximum hardness is achieved in the Stir Zone (SZ). A small tunnel present near the middle proved to be more detrimental than the large one at the bottom. Grain refinement in the SZ was 87.2% while augmentation in hardness was 21.3 HV. Maximum tensile strength of approximately 103% with decent bead profile is obtained, using taper cylindrical tool at 710 rpm with 14 mm shoulder diameter. Fractography of the fractured surface revealed a pure ductile failure. It has been discovered that with base offset the strength of the weld is increased. However, reduction of 4.8% was obtained with DP-FSW. Better weld profile gives better strength. With DP-FSW, a significant improvement in bead surface is obtained.
... In addition, conventional friction welding is not compatible with thin-walled pipes. By controlling the relative motion of the tool, friction stir welding (FSW) can be used to join thin-walled pipes to avoid defects encountered in conventional welding processes [16]. Previous investigations have referred to pip-pipe welding using friction welding techniques [17,18,19], and few types of research have been done on FCW [20,21]. ...
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... Another study reported the welding of AA6063 pipes with v ranging from 900 to 1500 rpm and v from 72 to 144 mm/min. [5][6][7] The welded sample was characterized by joint strength and hardness. The maximum and minimum joint strength efficiency were observed to be 54% and 45% with 1500 rpm and 108 mm/min, and 900 rpm and 72 mm/min, respectively. ...
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... Friction welding has two groups classified as the relative motion increasing the tool rotation speed. Other investigations on aluminum alloys 6063 were carried the properties of friction welding by using orbital clamping unit system (OCUS) [10,11]. The OCUS defined as a system to rotate the work piece parts at the same time around its axis by mandrel/ shaft connected with external motor. ...
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... Khourshid and Sabry (Khourshid and Sabry 2013) studied the effect of process parameters on FSW of 6063 aluminum alloy and reported that both tool rotational speed and weld speed had a combined effect on the weld joint efficiency. Ismail et al. (Ismail et al. 2013) performed full penetration FSW of 6063 aluminum pipes and concluded that high tool rotational speed of 1500 rpm and weld speed of 144 mm/min gave defect-free welds. Even though these works try to portray the effects of process parameters, they lack the optimal results. ...
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... Underfill defect on the advancing side of the tubular welds of 2024-T3 alloy resulted in about 75% decrease in elongation [8]. Ismail et al. [9] obtained orbital friction stir welds without lateral flash at a high rotational speed and travel speeds by using a specially customized orbital clamping unit. ...
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This work aims at studying the effect of triflute pin tools on single-pass orbital friction stir lap welding of AA5456-H321/AA5456-O alloys by varying pin length, tool rotational, and travel speeds. The mechanical properties of welds were examined while the microstructures and fracture modes of welds were observed and analyzed via the aid of an optical microscope, scanning electron microscope, and energy dispersive X-ray spectroscopy. The results show that upward-thrust flow and intermingling of the alloys are directly improved with an increase in tool rotational speed. Strengthening precipitate dissolution (AA5456-H321) and grain size strengthening (AA5456-O) occur in the stir zones. Weld samples without volumetric flow defect/microvoids are obtained as the tool rotational speeds are increased. Optimum weld strength of 303 MPa was obtained at tool rotational and travel speeds of 900 rpm and 45 mm/min, respectively. Fracture location and nature of dimples are influenced by the level of tool rotational speed.
Since the start of welding, fusion welding has been the key contributor to welding materials. Due to the shortcomings of fusion welding, friction stir welding emerged as an alternative to fusion welding. Aluminum and magnesium which were considered un-weldable by conventional welding processes now can be easily welded by the friction stir welding technique. Much work has been done on friction stir welding of aluminum, magnesium, and copper plates. Various welding parameters like tool rotation rate, tool traverse speed, tilt angle, and tool geometry affect the texture and mechanical properties of FSW alloys. In addition to the above parameters plunge depth also greatly affects the welding characteristics and quality. The present work addresses a review of the current understanding of the effect of plunge depth on various facets of welding of aluminum pipes especially considering the role and effects of plunge depth as a parameter affecting welding characteristics.
This study has attempted to employ a novel hybrid welding technique to overcome root defects during the joining of aluminium pipes using friction stir welding (FSW) process. Hybrid weld technique is accomplished by combining FSW process along with tungsten inert gas (TIG) welding process to complete the weldment. Aluminium 6063-T6 pipes, with outer diameter 500 mm and 5 mm thickness, are first welded on the root side using TIG welding to a calculated depth of 1 mm, which is followed by FSW on the face side to the remaining depth of 4 mm. Radiography tests are carried out to identify the presence of root defects. Hybrid welded pipes are compared with pure friction stir welded pipes for mechanical properties. Taper cylindrical tool at a rotational speed of 2000 rpm and welding speed of 0.6 rpm exhibited a superior weld strength of 176 MPa, which is 73% of base metal strength and 87.2% of pure friction stir welded pipes. Microstructural attributes have also been discussed.
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Friction stir welding of pipes is gaining research interest as it delivers high performance weld joints when compared to fusion welding techniques. Mechanical testing of such welded pipes will yield only results about mechanical behaviour but cannot detect the defects. An attempt has been made in employing non-destructive techniques in analysing the defects in Aluminium Alloy 6063 pipe joint obtained using friction stir welding. Three different tool pin profiles have been used in this study. The non-destructive testing methods employed helped to show the variation in the quality of the welds achieved through the three different tool pin profiles. Dye penetrant testing has been used in assessing the surface defects where solvent removable penetrant SKL-SP1 has shown evident results. Radiographic testing has been used in assessing root side defects. Tool with taper cylindrical pin along with tool rotational speed of 2000 rpm and weld speed of 0.6 rpm has produced weld with minor defects based on liquid penetrant and radiographic test results. Also the capability of non-destructive techniques in analysing the defects produced through friction stir welding has also been evaluated and presented.
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Description Friction Stir Welding (FSW) is a relatively new joining process that has exhibited many advantages over traditional arc welding processes, including greatly reducing distortion and eliminating solidification. The present work aims to determine the feasibility to weld two pieces of aluminum pipe by friction stir welding process and study the effect on the mechanical properties of welding joints. Special welding fixture fixed on conventional milling machine has been conducted to attempt this welding and group of welding parameters. Three tool rotational speeds (500, 630, 800 rpm) with four welding speeds (0.5, 1, 2, 3 mm/sec) for each rotational speed had been used to study the effect of each parameters (tool rotation, weld speed) on mechanical and microstructure properties of welded joints. Mechanical properties of welded joints were investigated using different mechanical tests including non destructive test (visual inspection, X-ray) and destructive test (tensile test, microhardeness and microstructure). Based on the stir welding experiments conducted in this study the results show that aluminum pipe (AA 6061-T6) can be welded by (FSW) process with a maximum welding efficiency (61.7%) in terms of ultimate tensile strength, using 630 (RPM) rotational speed, 1 (mm/sec) traveling speed.
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A 2219-T6 aluminum alloy was friction stir welded in the present study. The results indicate that the recrystallized grains in the weld nugget zone (WNZ) of the joints exhibit the largest size in the middle part and the smallest size in the lower part. Furthermore, the void defect is formed in the joint when the rotation speed or welding speed is quite high. As the rotation speed or welding speed increases, the tensile strength of the joint firstly increases to a maximum value and then sharply decreases due to the occurrence of void defect. During tensile test, the defect-free joints welded at lower rotation speed are fractured in the WNZ, while those welded at relatively high rotation speed tend to be fractured in the heat affected zone (HAZ) adjacent to the thermal mechanically affected zone (TMAZ) on the retreating side.
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The maximum strain and strain rate experienced during friction stir welding/processing (FSW/P) has remained quite unclear, despite various efforts. Knowledge of strain and strain rate is important for understanding the subsequent evolution of grain structure, and serves as a basis for verification of various models as well. In the present study, we facilitated the breaking and embedding of the pin into the workpiece of cast Al-Si-Mg alloy during FS to obtain "frozen" samples for analysis. Metallographic evidence has indicated that in the leading transitional zone the strain gradient increased rapidly before entering into the thread space. Analysis of the deformed dendrites has suggested that the strain was ~ 3.5 and the strain rate was ~ 85 s-1 when the deforming material entered the thread space. The heavily deformed material then formed a rotational zone confined within thread spaces rotating largely with the pin, depositing a large part on the trailing side of the pin. Thus, once into the thread spaces, further strain is low and strain rate should decrease considerably.
Pipelines have long been a key component in the transportation and distribution of petroleum resources. Reducing the cost of pipelines to improve the economics of transportation is critical to the cost effective development of resources in remote locations. This paper addresses the economics of using friction stir welding (FSW) for pipeline construction and also documents a study concerning the welding of line pipe steels. An economic analysis of pipeline construction costs was conducted to compare FSW to construction using conventional gas metal arc welding (GMAW). Both offshore and onshore pipeline construction scenarios were considered in the study. Several assumptions were made during the study with respect to factors such as FSW tool cost and welding productivity. It is estimated that FSW offers about 25% and 7% construction cost savings for offshore (J-lay) and onshore construction, respectively. Several line pipe steels were welded using different process parameters. Weld properties were evaluated using microhardness tests, all-weldmetal tensile tests and crack tip opening displacement (CTOD) tests. Prior austenite grain size in the stir zone was calculated from electron back-scattered diffraction (EBSD) patterns. Of the X65 linepipe steels tested, all showed good strength and toughness properties; CTOD values were greater than 0.27 mm at-20°C. A computational fluid dynamics model was developed and used to understand the effect of process parameters on flow patterns in the weld stir zone. Effects of welding process parameters on weld defects are discussed in this paper. Copyright © 2011 by the International Society of Offshore and Polar Engineers (ISOPE).
Friction stir welding (FSW) of high-temperature alloys has been successfully demonstrated on flat plate. This was achieved using a system comprised of a polycrystalline cubic boron nitride (PCBN) tool, liquid cooled tool holder, telemetry system, and proper equipment controls. The knowledge and data generated from this system was used to friction stir weld X65 pipe. A portable FSW machine to weld surface pipeline was designed and fabricated based on the X65 pipe welding results. The method and requirements to friction stir weld pipe is discussed herein. Copyright © 2004 by The International Society of Offshore and Polar Engineers.
Friction stir welding (FSW) is a powerful joining process which is limited by its range of application and processing rate. Here the range of application is extended to small-diameter butted pipe sections and high processing rates are applied for increased productivity in manufacturing. Full penetration friction stir welds are performed on butted sections of alumin-ium alloy 6061-T6 pipe. These pipe sections are relatively small in diameter (4.2 inches) and relatively thin walled (0.2 inches). The small radius of curvature distinguishes this weld config-uration geometrically from a butted plate configuration and presents unique challenges. This work confronts these challenges using experimental and numerical methods. An FSW process method producing acceptable pipe joints is demonstrated.
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.
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.
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.
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.