R. PALANIVEL et al.: DEVELOPING A FRICTION-STIR WELDING WINDOW FOR JOINING ...
5–9
DEVELOPING A FRICTION-STIR WELDING WINDOW FOR
JOINING THE DISSIMILAR ALUMINUM ALLOYS
AA6351 AND AA5083
ISKANJE VARILNEGA OKNA ZA TORNO VRTILNO VARJENJE
PRI SPAJANJU RAZLI^NIH ALUMINIJEVIH ZLITIN AA6351 IN
AA5083
Ramaswamy Palanivel1, Rudolf Frans Laubscher1, Isaac Dinaharan1,
Nadarajan Murugan2
1University of Johannesburg, Department of Mechanical Engineering Science, Johannesburg 2006, South Africa
2Coimbatore Institute of Technology, Department of Mechanical Engineering, Coimbatore 641014, Tamil Nadu, India
rpelmech@yahoo.co.in
Prejem rokopisa – received: 2015-03-04; sprejem za objavo – accepted for publication: 2015-12-21
doi:10.17222/mit.2015.049
In this study a welding window was constructed for the relatively new welding process of friction-stir welding (FSW) to join the
6-mm-thick dissimilar aluminium alloys AA5083-H111 and AA6351-T6. The dissimilar joints were fabricated using different
combinations of tool rotational speeds and welding speeds. The effect of the process parameters on the macrostructure of the
joints was analysed and reported. Established along with the macrostructural analysis, a welding window was made. These
windows will act as reference maps for selecting the appropriate FSW process parameters to produce defect-free welds of
dissimilar aluminium alloys.
Keywords: friction stir welding, dissimilar joints, welding window, macrostructure
V {tudiji je bilo postavljeno varilno okno, za relativno nov postopek torno vrtilnega varjenja (FSW), za spajanje razli~nih
aluminijevih zlitin AA5083-H111 in AA6351-T6 debeline 6 mm. Zvari so bili izdelani s pomo~jo razli~ne kombinacije
rotacijskih hitrosti orodja in hitrosti varjenja. Analiziran je bil vpliv procesnega parametra na mikrostrukturo zvarov. Na podlagi
analize makro strukture je bilo postavljeno okno za varjenje. Ta okna slu`ijo kot referen~na pri izbiri ustreznih parametrov torno
rotacijskega varjenja razli~nih aluminijevih zlitin, za izdelavo zvarov brez napak.
Klju~ne besede: torno vrtilno varjenje, spoji razli~nih materialov, varilno okno, makrostruktura
1 INTRODUCTION
Environment friendly friction stir welding (FSW) is a
solid-state welding process invented by the The Welding
Institute (TWI) in 1991 in the UK to join metals, more
specifically aluminum alloys, which are used in trans-
portation industries, having a low melting point and
difficult to join with conventional techniques. FSW uses
a rotating tool with a pin travelling along the weld path
and plastically deforming the surrounding material to
make the weld. The warmth created by the rubbing bet-
ween the rotating tool and the plates encourages a local
increase in the temperature and softens the materials
underneath the tool shoulder and simultaneously the
plunged rotating tool pin moves and mixes the softened
materials by intense plastic deformation, joining both in
a solid-state weld. Attractive benefits of the FSW of alu-
minum alloys compared to fusion-welding processes are
less distortion, lower residual stresses, fewer weld
defects, no hot cracking and execution without a shield-
ing gas.1–3 The fine microstructure in friction-stir welds
produces good mechanical and metallurgical properties.
By developing such technology, one of the most im-
portant facts is the possibility of joining different alumi-
num alloys.4 The joining of dissimilar aluminum alloys
offers the potential to give the advantages of different
materials, often providing unique solutions to engi-
neering-industry requirements.
The foremost FSW process parameters that deter-
mine the joint strength and microstructure are the tool
rotational speed, welding speed, axial force and tool pin
profile.2 The effects of the tool rotational speed and
welding speed were investigated by various resear-
chers5–8 in order to obtain better mechanical and me-
tallurgical properties of the welded joints. S. A. Khodir
et al.9 studied the FSW of 2024 Al alloy plate to 7075 Al
alloy plate and observed that the rise in welding speed
tended to the formation of a kissing bond and pores.
A. Steuwer et al.10 quantified the effect of the tool rota-
tional speed and traverse speed on the residual stress of
3-mm-thick AA5083 and AA6082 joints. They reasoned
that the tool rotational speed was a useful process
variable to optimize the residual stress. The welding
speed determines the exposure time of this frictional heat
per unit length of weld and subsequently affects the grain
growth.11 M. J. Peel et al.12 noticed a 35 % drop in
microhardness in the HAZ of the AA5083 side of the
Materiali in tehnologije / Materials and technology 51 (2017) 1, 5–9 5
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967-2017) – 50 LET/50 YEARS
UDK 621.791:669.715:621.791/.792 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 51(1)5(2017)
dissimilar joint consisting of the aluminum alloys
AA5083 and AA6062. N. Shanmugasundaram and
N. Murugan13 developed a mathematical model to study
the effect of FSW parameters on the tensile strength and
elongation of dissimilar AA2024–AA5083 joints.
S. Rajakumar et al.14 optimized the developed models
using the software expert to maximize the tensile
strength of the joints.
Despite the great quantity of published literature
about the FSW, insufficient information exists in the
selection of working ranges of the process parameters
based on macrostructural observations. Hence in this
investigation an attempt has been made in developing a
welding window based on the macrostructural obser-
vation to produce defect-free welds.
2 EXPERIMENTAL PART
Rolled aluminum-alloy AA6351 and AA 5083 plates
of size 100 mm × 50 mm × 6 mm were used in this
study. AA5083 and AA6351 were kept along the retreat-
ing side and advancing side of the joint line, respectively.
Due to better tensile properties15 the straight square tool
pin having a shoulder diameter of 18 mm, a pin diameter
of 6 mm and a pin length of 5.6 mm was used to fabri-
cate the joints. The manufactured FSW tool is shown in
Figure 1. The FSW line was parallel to the rolling
direction of AA5083-H111 and perpendicular to the roll-
ing direction of AA6351-T6. The dissimilar butt welding
was carried out on an in-house built FSW machine (M/s
RV Machine Tools, Coimbatore, INDIA) by combi-
nations of rotational speed (800 min–1 to 1200 min–1) and
welding speed (45 mm/min to 85 mm/min). Axial force
(15 kN) and tool tilt angle (01) were maintained constant
for all the joints. The single-pass welding procedure was
followed to weld the joints. The specimens were made as
per standard metallography procedures and etched with
concentric Keller reagent. The digital image of the ma-
crostructure of the etched specimens was captured
utilizing a digital optical scanner to read the quality of
the dissimilar joints produced by the various combina-
tions of FSW process parameters. The welding window
was made based on a macrostructural analysis for the
joining of dissimilar aluminum alloy by different com-
binations of rotational speed and welding speed.
Stoppage of material flow due to defects was observed
using a scanning electron microscope. A verification test
was made within the welding window region to validate
the results.
3 RESULTS
Effects of the process parameters on the macrostruc-
ture of dissimilar joints are presented in Table 1, with
the probable reason. Figure 2 shows the welding win-
dow of joining dissimilar aluminium alloys based on a
macrostructural analysis. The tool rotational speed and
R. PALANIVEL et al.: DEVELOPING A FRICTION-STIR WELDING WINDOW FOR JOINING ...
6 Materiali in tehnologije / Materials and technology 51 (2017) 1, 5–9
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967-2017) – 50 LET/50 YEARS
Figure 2: Welding window for dissimilar aluminium alloys
Slika 2: Varilno okno za razli~ne aluminijeve zlitine
Figure 1: Photograph of manufactured FSW tool
Slika 1: Posnetek izdelanega orodja za FSW
Figure 3: SEM images: a) defects of the joints and material flow
clogged due to the defects, b) macrostructure without defects and
proper material flow
Slika 3: SEM-posnetki: a) napake v spoju in prepre~en tok materiala
zaradi napak, b) makrostruktura brez napak in ustrezen tok materiala
R. PALANIVEL et al.: DEVELOPING A FRICTION-STIR WELDING WINDOW FOR JOINING ...
Materiali in tehnologije / Materials and technology 51 (2017) 1, 5–9 7
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967-2017) – 50 LET/50 YEARS
Table 1: Effect of process parameter on the macrostructure of dissimilar joints
Tabela 1: Vpliv procesnega parametra na makrostrukturo spojev razli~nih materialov
S.no Parameter Macrostructure Name of the defects Probable reason
Welding speed of 45 mm/min
Rotational speed, min–1 RS AS
1 700 Pinhole at advancing side ofthe weld zone Insufficient stirring action of tool
2 800 No defects Sufficient heat generation andinteraction of tool
3 900 No defects Sufficient heat generation andstirring action of the tool
4 1000 Tunnel at the bottom, ofweld zone High heat generation
Welding speed of 55 mm/min
5 700 Pinhole at retreating side Insufficient stirring action of tool
6 800 No defects Sufficient heat generation andinteraction of tool
7 900 No defects Sufficient heat generation andinteraction of tool
8 1000 PinholeAt advancing side High heat generation
Welding speed of 65 mm/min
9 700 Tunnel defects at weld zonecollapse
Insufficient heat and stirring
action of the tool
10 800 No defects Sufficient pulsating stirring actionand flow of plasticized material
11 900 No defects Sufficient pulsating stirring actionand flow of plasticized material
12 1000 No defects Sufficient pulsating stirring actionand flow of plasticized material
13 1100 Tunnel defects at thebottom of weld zone High heat generation
Welding speed of 75 mm/min
14 800 Tunnel defects at retreatingside of the weld zone Insufficient stirring action of tool
15 900 No defects Sufficient heat generation
16 1000 No defects Sufficient heat generation
17 1100 No defects Sufficient heat generation
18 1200 No defects Sufficient heat generation
19 1300 Tunnel defects at thebottom of the weld zone High heat generation
the welding speed that are considered, which contribute
remarkably to the generation of frictional heat during the
welding. During welding the combination of process
parameters that are having too high or too low heat input
produces defects due to improper material flow. The
rotational speed of 800 min–1 to 1200 min–1 yielded
defect-free joints depending on the welding speed used
and the welding speed in the range of 45 mm/min to 85
mm/min yielded defect-free joints depending on the
rotational speed used.
4 DISCUSSION
Joining of aluminium alloys by fusion welding pro-
duces defects like hot cracking, porosity, slag inclusion,
etc. with the mechanical and metallurgical properties.
Usually, the friction stir welded joints are free from these
defects since the absence of melting during welding;
metals are joined in the solid state due to the heat gene-
rated by the friction and flow of metal by the stirring
action. However, FSW joints are likely to have other
defects like pinhole, tunnel defect, piping defect, kissing
bond, cracks, etc. due to the improper flow of metal and
insufficient consolidation of the metal in the weld zone.
A low welding speed and a high tool rotational speed
increases the frictional heat due to the increased residing
time of tool. Tool rotational speed results in stirring and
mixing of the material about the rotating pin, which in
turn increases the temperature of the metal. It seems to
be the most important process variable since it is given to
influence the weld speed. A low rotational speed to pro-
duce a low heat input. This low heat input results in lack
of stirring and yields defects. It is clear that in FSW, as
the rotational speed increases the heat input also in-
creases. Figure 3 shows SEM images of the macrograph
and mixing of the material of the joints. The material
flow of the FSW joint from advancing side to retreating
side and vertical movement (bottom to top) is collaged
due to the defects formation as shown in Figure 3a. Pro-
per mixing of the material due to the absence of defects
is shown in Figure 3b. More heat input destroys the
regular flow behaviour of plasticized material and a
higher rotational speed causes the excessive release of
stirred materials to the upper surface, which leaves voids
in the weld zone.16,17 The lowest and highest welding
speed produces defects due to the increased frictional
heat and insufficient frictional heat generated, respec-
tively.18 In general FSW at higher welding speeds results
in a short exposure time in the weld area with insuffi-
cient heat and poor plastic flow of the metal and causes
some voids, like defects, in the joints. Higher welding
speeds are associated with low heat inputs, which result
in faster cooling rates of the welded joint and hence
yields defects. The developed welding window was vali-
dated with verification tests and the results are presented
in Figure 4, having no defects within the welding-win-
dow regions.
R. PALANIVEL et al.: DEVELOPING A FRICTION-STIR WELDING WINDOW FOR JOINING ...
8 Materiali in tehnologije / Materials and technology 51 (2017) 1, 5–9
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967-2017) – 50 LET/50 YEARS
Figure 4: SEM image of the macro images of the dissimilar FSW
joints with in the welding window region: a) 70 mm/min and 900 min–1,
b) 80 mm/min and 1100 min–1
Slika 4: SEM-posnetek makro izgleda FSW-spoja razli~nih mate-
rialov, na podro~ju varilnega okna: a) 70 mm/min in 900 min–1,
b) 80 mm/min in 1100 min–1
Welding speed of 85 mm/min
20 1000 Pinhole at advancing side Insufficient heat generation
21 1100 No defects Sufficient heat generation
22 1200 Tunnel defects at nuggetcollapse Insufficient stirring action of tool
5 CONCLUSION
Defect-free dissimilar FSW joints were produced
under a wide range of rotational speeds and welding
speeds. The friction stir welding window was developed
to obtain defect-free welds.
The developed welding window will be applied as a
ready reference to select the appropriate rotational and
welding speeds to manufacture the defect-free joints.
6 REFERENCES
1 R. S. Mishraa, Z. Y. Ma, Frictions stir welding and processing,
Materials Science and Engineering R, 50 (2005) 1–2, 1–78,
doi:10.1016/j.mser.2005.07.001
2 R. Nandan, T. DebRoy, H. K. D. H Bhadeshia, Recent advances in
friction-stir welding process, weldment structure and properties,
Progress in Material Science, 53 (2008) 6, 980–1023, doi:10.1016/
j.pmatsci.2008.05.001
3 Y. Uematsu, K. Tokaji, H. Shibata, Y. Tozaki, T. Ohmune, Fatigue
behavior of friction stir welds without neither welding flash nor flaw
in several aluminium alloys, International Journal of Fatigue, 31
(2009) 10, 1443–1453, doi:10.1016/j.ijfatigue.2009.06.015
4 T. Saeid, A. Abdollah-Zadeh, B. Sazgari, Weldability and
mechanical properties of dissimilar aluminum–copper lap joints
made by friction stir welding, Journal of Alloys and Compounds,
490 (2010) 1–2, 652–655, doi:10.1016/j.jallcom.2009.10.127
5 M. Ericsson, R. Sandstrom, Influence of welding speed on the
fatigue of friction stir welds and comparison with MIG and TIG,
International Journal of Fatigue, 25 (2003)12, 1379–1387,
doi:10.1016/S0142-1123(03)00059-8
6 P. Cavaliere, G. Campanile, F. W. Panella, A. Squillace, Effect of
welding parameters on mechanical and microstructural properties of
AA6056 joints produced by friction stir welding, Journal of Material
Processing Technology, 180 (2006) 1–3, 263–270, doi:10.1016/
j.jmatprotec.2006.06.015
7 C. Leitao, R. M. Leal, D. M. Rodrigues, A. Loureiro, P. Vilaca,
Mechanical behaviour of similar and dissimilar AA5182-H111 and
AA6016-T4 thin friction stir welds, Materials and Design, 30 (2009)
1, 101–108, doi:10.1016/j.matdes.2008.04.045
8 H. J. Aval, S. Serajzadeh, A. H. Kokabi, Evolution of microstructures
and mechanical properties in similar and dissimilar friction stir
welding of AA5086 and AA6061, Materials Science and Engineer-
ing A, 528 (2011) 28, 8071–8083, doi:10.1016/j.msea.2011.07.056
91 S. A. Khodir, T. Shibayanagi, Friction stir welding of dissimilar
AA2024 and AA7075 aluminum alloys, Materials Science and Engi-
neering B, 148 (2008) 1–3, 82–87, doi:10.1016/j.mseb.2007.09.024
10 A. Stewart, M. J. Peel, P. J. Withers, Dissimilar friction stir welds in
AA5083–AA6082: The effect of process parameters on residual
stress, Materials Science and Engineering A, 441 (2006) 1–2,
187–196, doi:10.1016/j.msea.2006.08.012
11 T. Sakthivel, G. S. Sengar, J. Mukhopadhyay, Effect of welding
speed on microstructure and mechanical properties of friction stir
welded aluminum, International Journal of Advanced Manufacturing
Technology, 43 (2009) 5–6, 468–473, doi:10.1007/s00170-008-
1727-7
12 M. J. Peel, A. Stewart, P. J. Withers, Dissimilar friction stirs welds in
AA5083-AA6082 Part II: Process parameter effects on micro-
structure, Metallurgical and Materials Transactions A, 37 (2006) 7,
2195–2206, doi:10.1007/BF02586139
13 N. Shanmugasundaram, N. Murugan, Tensile behavior of dissimilar
friction stir welded joints of aluminum alloys, Materials and Design,
31 (2010) 9, 4184–4193, doi:10.1016/j.matdes.2010.04.035
14 S. Rajakumar, C. Muralidharan, V. Balasubramanian, Predicting ten-
sile strength, hardness and corrosion rate of friction stir welded
AA6061-T6 aluminium alloy joints, Materials and Design, 32 (2011)
5, 2878–2890, doi:10.1016/j.matdes.2010.12.025
15 R. Palanivel, P. Koshy Mathews, The tensile behavior of friction-stir
welded dissimilar aluminium alloys, Mater. Tehnol., 45 (2011) 6,
623–626
16 K. Elangovan, V. Balasubramanian, Influences of tool pin profile and
welding speed of the formation of friction stir processing zone in
AA2219 aluminium alloy, Journal of Materials Processing Tech-
nology, 200 (2008) 1–3, 163–175, doi:10.1016/j.jmatprotec.
2007.09.019
17 K. Elangovan, V. Balasubramanian, Influences of pin profile and
rotational speed of the tool on the formation of friction stir
processing zone in AA2219 aluminum alloy, Materials Science and
Engineering A, 459 (2007) 1–2, 7–18, doi:10.1016/j.msea.2006.
12.124
18 R. Palanivel, P. Koshy Mathews, I. Dinakaran, N. Murugan, Mecha-
nical and metallurgical properties of dissimilar friction stir welded
AA5083-H111 and AA6351-T6 aluminum alloys, Transaction of the
Non Ferrous Metal Society China, 24 (2014) 1, 58–65, doi:10.1016/
S1003-6326(14)63028-4
R. PALANIVEL et al.: DEVELOPING A FRICTION-STIR WELDING WINDOW FOR JOINING ...
Materiali in tehnologije / Materials and technology 51 (2017) 1, 5–9 9
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967-2017) – 50 LET/50 YEARS