THE JOINING OF THREE DISSIMILAR METALLIC ALLOYS BY A SINGLE-PASS FRICTION STIR WELDING

1. International Symposium on Research in Innovation and Sustainability 2014 (ISoRIS ’14) 15-16 October 2014, Malacca, Malaysia
Special Issue
Sci.Int.(Lahore),26(4),1569-1574,2014 ISSN 1013-5316; CODEN: SINTE 8 1569
THE JOINING OF THREE DISSIMILAR METALLIC ALLOYS BY A
SINGLE-PASS FRICTION STIR WELDING
Sadiq Aziz Husseina, b
, S. Thirua
, R. Izamshaha,
*, Abd Salam Md Tahira
a
University Teknikal Malaysia Melaka (UTeM), Melaka, Malaysia.
b
Foundation of Technical Education, Baghdad, Iraq.
izamshah@utem.edu.my
ABSTRACT: A friction stir welding (FSW) is normally used to join two similar or dissimilar laps or butt
joints for alloys and/or materials. FSW produces good joint efficiency, especially for dissimilar ones as
compared to other welding methods. In the present study, a single-pass FSW is used for butt joining of the
5083 and 6061 aluminum alloy plates lap to steel (electro-galvanized steel) by employing the plunging and
diffusion assisted bonding techniques. The backscattered electron detector image obtained from a scanning
electron microscope showed the existence of an intermetallic reaction layer at the welded interface zone.
The compositions of the intermetallic layers were investigated by utilizing energy-dispersive X-ray
spectroscopy. The tensile tests were used to examine the joint efficiency of specimens welded by using
different welding parameters. It was found that at 900 rpm rotational speed and 20 mm/min welding speed,
the maximum joint efficiency was 73%.
Keywords: friction stir welding, intermetallic, single pass, three dissimilar, low weight products.
1. INTRODUCTION
Among the lightweight materials used to accommodate the
demand for sophisticated designs, aluminum alloys are the
most extensively used and are the focus of considerable
interest in the aviation, shipping, and automobile industries.
Moreover, the joining of dissimilar materials and alloys is
adopted in new designs to achieve low fuel consumption and
sustainability. An effective welding process remains difficult
to achieve because of the inappropriate combination of
materials and/or alloys with different properties. Recently,
advanced aviation and automobile design have started to use
friction stir welding (FSW), which is a solid-state joining
technique for dissimilar metal welding [1]. When Al/steel
component is used to replace the steel-made parts, an
approximately 25% weight reduction is achieved in the sub-
frames, thereby reducing the required energy by 50% [2, 3].
The overall process parameters and requirements of the
FSW, particularly for Al alloys have been well discussed in
the literatures [1–6]. Given that the method is solid-state, the
difficulties associated with fusion techniques can be
prevented. Thus, the method is suitable for welding
dissimilar materials [5]. Although the physical process,
structure, and properties of dissimilar welds are now
understood [5, 6], data about the characteristics of this joint
type is limited [4]. Shigematsu et al. [7] classified that 5083
and 6061 Al alloys joining as similar and dissimilar,
respectively. They found that for dissimilar 5083/6061 Al
alloy joint, the maximum joint efficiency (ζ) is 63%, which
is similar to that for 6061/6061 joints. Dissimilar Al/St FSW
has been given considerable research attention [3, 8–11].
The three main techniques used to generate distinct AlxFey
compound layers, which represent the main cause of
aluminum to steel joining, are plunging (the pin is touching
the bottom plate) [8, 10, 12], diffusion [3], and annealing
after welding[13].
To the best of our knowledge, the welding of 5083, 6061,
and steel by single-pass FSW has not been studied. In
addition, when two dissimilar 5083 and 6061 Al alloys are
welded to the steel frame, the joint efficiency may be
affected (decreased or increased). This weld type is
investigated in this study.
2. EXPERIMENTAL PROCEDURE
The two butt welded dissimilar base Al alloys used were the
5083-H112 and 6061-T6 (both 75 mm× 150 mm ×3 mm),
and they were lap welded together to electro-galvanized
steel (EG steel zinc coated) using single-pass FSW (Fig. 1).
The chemical and mechanical properties of the material and
alloys are shown in Table 1. Two stir pins made from
tungsten carbide were used, the shoulder was made from
tungsten carbide and hardened tool steel H13. The
dimensions are shown in Fig. 2. The pin lengths used were
2.9 mm for diffusion (no steel plate touching) and 3.1 mm
for plunging (inserted in the steel plate). A smooth
cylindrical pin profile was used. Thus, another objective is
achieved, that is, a process simplicity for three dissimilar
FSW. The rotational (N) and welding speeds (ν) used are as
shown in Table 2. The 6061 plates were placed on the
advancing side for the primary investigations. The position
was then reversed to study the effects on the results under
the same welding parameters.
After welding, tensile tests and microstructural
characterization were conducted. The specimens were drawn
perpendicular to the welding line. The tensile test was
conducted in accordance with ASTM E8/E8M-09 to
determine the ultimate tensile stress (σu) for the welded and
base Al alloys and steel.
.
EG Steel
AA5083
AA6061-T6
Figure 1: Schematic of FSW setup.

2. 1570 ISSN 1013-5316; CODEN: SINTE 8 Sci.Int.(Lahore),26(4),1569-1574,2014
The tensile test machine used was Instron’s universal testing
machine with 1 mm/min cross-head speed. All of the
specimens (Fig. 3) were obtained using the water jet cutting
machine, which helps to prevent stress and/or heat
generation on the interface during cutting. To specify the
significant zones of the interface near the Al/St joint line, an
optical device with small magnifications (×1 to ×2) was
used. Then, the scanning electron microscope (SEM) was
used, and the back-scattered electron detector (QBSD) was
employed. This process minimizes the time and cost needed
to specify the significant zones. The energy-dispersive X-ray
spectroscopy (EDS) was used to identify the generated
intermetallic compound (AlxFey) type, where x and y are the
weight ratios of the aluminium and iron respectively in this
compound.
3. RESULTS AND DISCUSSION
For dissimilar FSW, the stir zone (onion shape) did not
occur [6]. This finding corresponds with the optical
macrograph results for the three dissimilar materials, in
which the interface line between AA5083 and AA6061 is
clearly observed (Fig. 4). At the same time, the line between
the steel and Al alloys was also observed. The high forces
associated with the use of 900 rpm decreased by employing
1,200 rpm. As such, 1,200 rpm was adopted for the plunging
experiments. For weld no. S1 (Table 3), free defect at the
weld zone was observed. The three selected zones in Fig. 4-a
were investigated further using SEM; Fig. 5 shows the
reaction layer at the weld zone. The EDS results are shown
in Fig. 6 which provides the weight
ratios of Al and Fe. By contrast, the tunnel defect can be
observed for weld no. S2 because of the parameters used
[10]. Weld no. S3 did not provide enough adhesion force
between the steel part and Al alloys. Separation also
happened during the tensile sample preparation (cutting)
using the water jet machine. This occurance can be related to
the high welding speed (90 mm/min). Haghshenas et al. [3]
reported that “reducing the welding speed improves
mechanical properties of the Al 5754/DP600 joints”. Weld
no. S4 shown in Figs 4-c exposed the steel fragment inside
the aluminum matrix, which decreased the joint efficiency
and caused fractures at this zone: This was observed
previously by Kimapong and Watanabe [14].
Rotational
speed
(rpm)
Welding
speed
(mm/min)
Pin
length
(mm)
Assisted
technique
used
900 20, 45, 90 2.9 Diffusion
1200 50 3.1 Plunging
Table 2: Welding parameters.
Figure 3: Tensile test specimen.
Steel
6061
5083
Tool steel H13
Tungsten carbide
12 10 4
Figure 2: Tool schematic used in the experimental work.
Table 1: Chemical composition and tensile stress of AA5083, AA6061 and steel.
Al Alloy
fvvvv Chemical composition wt% ultimate tensile
strength σu (MPa)
5083 0.08 Si, 0.27 Fe, 0.03 Cu, 0.65 Mn, 4.71 Mg, 0.08 Cr, 0.04 Zn,
0.02 Ti, balance Al
319
6061 0.67 Si, 0.32 Fe, 0.32 Cu, 0.014 Mn, 1.06 Mg, 0.21 Cr, 0.007
Zn, 0.02 Ti, other 0.05, balance Al
311
EG Steel 0.0204 C, 0.027 Si, 0.199 Mn, 0.0079 P, 0.0083 S. Zinc coated
weight is 19 g/m2
on both surfaces
328

3. International Symposium on Research in Innovation and Sustainability 2014 (ISoRIS ’14) 15-16 October 2014, Malacca, Malaysia
Special Issue
Sci.Int.(Lahore),26(4),1569-1574,2014 ISSN 1013-5316; CODEN: SINTE 8 1571
5083
Steel
6061
Steel
Steel
5083
6061
Figure 5: The QBSD micrographs of weld no. S1at the (a)
5083/St, (b) 5083-6061/St, and (c) 6061/St interfaces.
Fig. 6-a
Fig. 6-b
(a)
(b)
(c)
Figure 4: Optical macrograph for the weld cross section with different
welding parameters (a) 900 rpm, 20mm/min, diffusion (b) 900 rpm,
45mm/min, diffusion, and (c) 1200 rpm, 50mm/min, plunging.
AA6061
AA5083
Tunnel
defect
Steel
Fig. 5: a, b, & c
AA6061
AA5083
Steel
Steel
fragments
Steel
AA6061
AA5083
(a)
(b)
(c)

4. 1572 ISSN 1013-5316; CODEN: SINTE 8 Sci.Int.(Lahore),26(4),1569-1574,2014
High forces were generated using the 900 rpm speed. As
such, 1200 rpm was used to prevent the generation of high
forces when the pin plunges into the bottom plate (steel). All
of the specimens showed that the steel plates separated at the
AA6061 side, whereas the steel plates remained joint to the
AA5083. Failures normally occur in all of the tests at the
6061 side exactly at the heat-affected zone, even when the
defect is at the stir zone. This may be related to the existence
of the intermetallic compound, which enhances the joint
strength by adding a shear resistance force. Moreover, the
steel atoms that diffuse inside the aluminum matrix are
sufficient to weld the steel plate to the Al alloy plates. Fig. 7
shows the joint efficiency for the different welding
parameters, in which the joint efficiency is obtained by
dividing the ultimate tensile strength (σu) of the welded
specimen by the AA6061 one. The maximum joint
efficiency is 73% without the need to plunge into or touch
the steel plate (diffusion), it is better as compared to the
literature (63%) so far [7]. The plate place arrangements
(advancing and retreating) effect was examined; high defect
was observed as shown in Fig. 8 when the 6061 is placed on
the retreating side. For the lap joining of soft (upper plate) to
hard (lower plate), high wear on the pin will occur in case of
pin insertion (plunging). Therefore, diffusion technique is
the best choice to avoid the wear as well as the high
generated forces for such weld with good joint efficiency.
.
Weld No. Rotational
speed
(rpm)
Welding
speed
(mm/min)
Ultimate
tensile strength
σu (MPa)
Joint
efficiency
ζ (%)
Pin length
(mm)
S1 900 20 226.44 73 2.90
S2 900 45 179.25 58 2.90
S3 900 90 179 58 2.90
S4 1200 50 197.1 63 3.10
Table 3: The tensile test results for joining of three dissimilar materials.
Point 1 Point 2
Figure 6: The peaks of EDS result for weld S1.
(b), EDS peaks result of point 2
(a), EDS peaks result of point 1
AA5083 AA6061
Steel Steel

5. International Symposium on Research in Innovation and Sustainability 2014 (ISoRIS ’14) 15-16 October 2014, Malacca, Malaysia
Special Issue
Sci.Int.(Lahore),26(4),1569-1574,2014 ISSN 1013-5316; CODEN: SINTE 8 1573
4. CONCLUSION
Three dissimilar materials (AA5083, AA6061, and steel) are
successfully welded together by single-pass FSW. For
different rotational and welding speeds, the maximum joint
efficiency recorded was 73% using 900 rpm rotational
speed, 20 mm/min welding speed, and the diffusion
technique. This finding may be related to the existence of the
intermetallic compound (FexAly), which enhanced the joint
efficiency by adding shear force resistance at the weld zone.
The diffusion technique used in this study also generated the
intermetallic compound which was weld with the three
dissimilar materials without making contact with the steel
surface (plunge). Meanwhile, 1200 rpm was used to prevent
the occurrence of the high forces associated with the first
rotational speed (900 rpm) for the plunging technique, which
resulted in low joint efficiency caused by the steel fragments
inside the aluminum matrix.
ACKNOWLEDGMENT
The authors are grateful to the technicians of Faculties of
Mechanical, Technology, and Manufacturing Engineering,
University Teknikal Malaysia Melaka (UTeM) who
participated in this work.
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Table 4: Summary of EDS results for the
points 1 & 2 of Fig. 6 at %.
Al Fe Zn
Point 1 55.58 38.85 5.57
Point 2 43.74 48.02 8.24
AA6061
AA5083
Defects
Figure 8: Defect presence due to the placing of the
AA6061 plate on the retreating side.
Figure 7: Effect of welding parameters on the tensile
test results.

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