Ijciet 08 04_223

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International Journal of Civil Engineering and Technology (IJCIET)
Volume 8, Issue 4, April 2017, pp. 1967–1976 Article ID: IJCIET_08_04_223
Available online at http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=4
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
© IAEME Publication Scopus Indexed
EVALUATION OF ELECTRO-MECHANICAL
PROPERTIES OF FRICTION STIR WELDED AL
/ CU BIMETALLIC LAP JOINTS
Dr. M. Satya Narayana Gupta
Professor, Department of Aeronautical Engineering,
MLR Institute of technology, Hyderabad, India
K. Shiva Shankar
Assistant Professor, Department of Aeronautical Engineering,
MLR Institute of Technology, Hyderabad, India
ABSTRACT
Friction stir welding Processes (FSWP) is a sophisticated solid state welding
technology to join dissimilar and similar materials. Commercially pure Aluminium and
Copper plates were joined using FSWP and the mechanical and electrical properties
of bimetallic lap joints have been evaluated by changing the input processes
parameters. Number of experiments was performed to obtain the optimum joint
properties by adjusting angle of tool tilting, rotational and welding speeds. The
experiments were carried out using design of experiments (DoE) to minimize number
of experiments. The present paper provides a very valuable information on electro-
mechanical behavior of Al to Cu dissimilar joints used for a critical application i.e.
heat sinks, high voltage bus bars and heavy duty earthing strips, etc. It has been
observed that high quality welds are obtained at low rotational and welding speeds
irrespective of tilting angle. The maximum value of tensile shear strength is 70 MPa.
The hardness is uniform throughout the joint. In manufacturing condition the resistance
of the joint is negligible.
Key words: Friction Stir Welding, Dissimilar Metals, Lap Joints, Mechanical
Properties, Electrical Resistance.
Cite this Article: Dr. M. Satya Narayana Gupta and K. Shiva Shankar, Evaluation of
Electro-Mechanical Properties of Friction Stir Welded Al / Cu Bimetallic Lap Joints.
International Journal of Civil Engineering and Technology, 8(4), 2017, pp. 1967-1976
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=4

Dr. M. Satya Narayana Gupta and K. Shiva Shankar
1. INTRODUCTION
Due to the rapid increase in Copper cost, the manufacturers of electronics and electrical
equipment manufactures prefer to replace the Cu with Al in many applications [1] like heat
shinks, heavy duty busbars, high duty earthing strips, panel boards etc. Different parameters
influence the selection of conductor material for heavy duty current bus systems. Generally, Al
is taken for one side of the system and Cu for another side. The transition have been made,
where the two conductors meets. Originally, bolted joints were used to made transition pieces
[2, 3]. Because of difficulty in making electrically reliable and stable bolted joints in between
Al and Cu metals, in last decade most of the researchers were focused on making transitions
using bonded Cu to Al materials.
Welding of Al/Cu is generally utilized as a transition piece as a part of high current transport
frameworks to transmit the current. From the perspective of the welding procedure, Al and Cu
are incongruent metals to welding since they have a high fondness to each other, at a
temperature more than 120 0C and create fragile intermetallics [4, 5] that is mechanically and
electrically shaky, in light of the fact that these intermetallic mixes have a nonmetallic
covalence band. Hence, an endeavor to weld Al to Cu by routine means through the use of heat
energy, to dissolve and fuse, the two metals can bring about a temperamental weld. The regular
procedure to achieve this metallic bond has been to plate Al with another metal. This practice
includes many stages, is environmentally not friendly and is utilized for only little joints.
Explosion welding, friction and friction stir welding have been considered as the qualified
welding procedure of these metals because of reliable joint interface and little intermetallic
development.
Friction stir joining is a lot of versatile, compared to all or any different solid state joining
methods, in welding parts rather massive or complex in shape [6]. This welding method is a
novel solid state welding method in which the metal that is being welded doesn’t melt and
recast7. In this joining process, the plates to be welded are firmly clamped in position. FSW
tool is a rotating non-consumable tool with specially designed pin and shoulder. This tool
penetrates into the two parts to be joined until the tool shoulder touches the top overlap part
and moves along the required weld seam as represented in figure1.
Figure 1 Schematic representation of single lap joint
This method have many merits such as less lead time, great material saving and used to
weld different metals and alloys in different thicknesses. Therefore, friction stir welding can
minimize the formation of the brittle intermetallic compound at the interface because it is
carried under melting temperature, high pressure and shorter process time.

Evaluation of Electro-Mechanical Properties of Friction Stir Welded Al / Cu Bimetallic Lap Joints
The main aim of this paper is to test the weldability of Cu/Al lap joints fabricated by FSW
and to evaluate the electro-mechanical properties of the weld by changing input parameters
such as rotational speed of tool, speed of welding and the tilting angle.
2. EXPERIMENTAL PROCEDURE
The pure Copper and Aluminium plates of size 150mm x 100mm x 3mm were used to fabricate
FSW Cu/Al lap joints.
Tables 1a and 1b represents the mechanical and chemical properties of the parent materials.
The relative positions of Cu and Al plates for FSW are shown in figure2. In this work, single
pass welding processes used for fabrication of lap joints. High speed tool M2 of hardness Rc62
has been used for welding. The taper pin tool geometry and material chemical composition is
given in table 2a and 2b. The friction stir welding machine is shown in figure4. This machine
has an arrangement for adjustment of angle of tilt, welding speed, rotating speed of tool,
frictional time and speed of plunging.
Table 1a Parent metal mechanical properties
Base metal
Mechanical properties
Y.S (MPa) T.S (MPa) %Elongation T.S.S(M.Pa)
(0.6xT.S)
Pure Aluminium 95 119 16.7 71.4
Pure Copper 108 200 52.62 100
Y.S: yield strength; T.S: tensile strength; T.S.S: tensile shear strength
Table 1b Parent metal chemical composition (Wt %)
Base metal Chemical compositions (Weight %)
Pure
Aluminium
Al Si Mn Cr Ti Cu Zn Mg Fe
99.64 0.18 0.04 0.001 0.002 0.012 0.001 0.001 0.1
Pure Cupper
Cu Ag Sn Sb Pb As Zn Bi Fe
99.98 0.002 0.001 0.001 0.001 0.002 0.002 0.001 0.002
Table 2a Tool Geometry
Si. No. Tool Geometry Dimension (mm)
1 Shoulder Diameter 15
2 Maximum Diameter of pin 5
3 Minimum Diameter of pin 3.5
4 Length of pin 5.7
Table 2b Tool Material Chemical compositions (in Wt %)
Tool material Chemical compositions (Weight %)
HSS(M2)
C Si Mn Cr Mo W V
0.8 0.4 0.4 4.15 5 6.1 1.9

Figure 2. Relative Position of Copper and Aluminium Plates
Figure 3 Non-Consumable Rotating Tool
Figure 4 FSW Machine
The three welding process parameters chosen are tool rotational speed, traverse speed and
tilting angle, which are generally considered to be the variables controlling quality in FSW.
The other parameters- plunging speed, tool sinking and frictional heating time are maintained
constant at appropriate levels. Trial experiments are conducted to fix the working range of the
input process variables. The range of feasible processes variables has been taken in such a way
that, to keep the welds free from noticeable outer defects. The important factors that affect the
strength of the welds and their working limits are represented in table3. Due to the wide range
of factors, it has been decided to use only 3 factors, two levels, full factorial
Design matrix to optimize the experimental conditions. Table 4 shows the 8 (23) sets of
coded conditions used to form the design matrix. For convenience of recording and processing
experimental data, upper and lower levels of the factors have been coded as +1 and -1
respectively.

Table 3 Important factors and their levels.
S.No Parameter
Factor
Designation
Unit
Design Levels
-1 (lower) +1(upper)
1
2
3
Rotational speed
Welding speed
Tool tilting angle
N
V
A
Rpm
mm/min
Degrees
1500
30
0
2500
80
3
Constant parameters: plunging speed is 10 mm/min, tool sinking is 5.8mm and frictional
heating time is 10sec.
Table 4 Design matrix and experimental results
Experiment
number
Factors Tensile shear
strength(MPa)
Fracture
location
Weld bead
N V A
L1 _ _ _ 70 Al base metal
L2 + _ _ 41 Interface
L3 _ + _ 55 Interface
L4 + + _ 52 Interface
L5 _ _ + 68 Al base metal
L6 + _ + 46 Interface
L7 _ + + 30 Interface
L8 + + + 40 Interface
As specified by the design matrix, eight lap joints have been fabricated. The welded joints
are sliced using a shear cutting machine and then machined to the required size as shown in
figure 5. The tensile shear specimens are prepared as per the ASTM D-1002 standard to
evaluate the tensile shear strength of the welded joints. Tensile shear strength of the FSW lap
joints is evaluated by conducting shear test on universal testing machine (UTM). The
consistency of the results has been checked by repeating the experiment L1 four times. The
standard deviation and variance were calculated for these four experiments as 1.515 and 2.296
respectively. This value is much less than the standard deviation of eight treatment
combinations i.e 13.88

Figure 5 Schematic Diagram of Tensile Specimen
The test specimens for measurement of electrical resistance are cut from the friction stir
welded Al /Cu bimetallic lap joints and had a dimension of 3mm x 20mm x 170mm. The contact
resistance across interface of friction stir welded Al/Cu was measured using the high-precision
nano-voltmeter (KEITHLEY 2182) and DC current source (KEITHLEY 6220) with a
resolution of 10 nano - ohms. Figure 6 shows the simplified schematic of the assembly used to
measure resistance of Al/Cu lap joints. Figure 7 shows the resistance test arrangement during
measuring the resistance of Al/Cu lap joints. By measuring the potential between the two ends
of the specimen, the specimen resistance was calculated from Ohm’s law (V=IR). The
specimen resistance was determined by averaging 10 resistance measurements made across this
interface after selected time interval.
Figure 6. Simplified Schematic Representation of The Setup Used to Measure Resistance Of Al/Cu
Bimetallic Lap Joints
Figure 7 Resistance Test Arrangement

3. RESULTS AND DISCUSSION
3.1 Mechanical Properties
3.1.1. Tensile Shear Strength
The tensile shear strength of friction stir welded lap joints of aluminium and copper has been
experimentally determined using UTM. The tensile shear test results weld bead and fracture
location at various treatment combinations are given in table 4. The test results indicated that
the high-quality welds are observed at low rotational speed and welding speed irrespective of
tilting angle. The maximum value of tensile shear strength obtained was 70MPa. It is about
100% of base metal Aluminium and 70% of base metal Copper. The maximum tensile shear
strength obtained was much more than the maximum shear strength obtained by the previous
studies [8].
As can be seen in table 4, there are some conditions in which failure has been occurred in
the base metal, sufficiently far from the jointed area as shown in figure 8 and therefore, it is
possible to achieve the optimum shear tensile strength of joint by adjusting the rotational speed,
welding speed. On other hand, most of the specimens failed on the advancing side because
formation of intermetallic compounds is likely to occur in advancing side because of higher
amount of temperature and strain in this side. High rotational and welding speeds decreases the
shear loads because the higher rotational speed increases the amount of intermetallic
components and lack of vertical flow of material at high welding speeds.
(a)
(b)
Figure 8 Failure locations at a) N =1500 rpm, V=30 mm/min and A = 00
b) N =1500 rpm, V=30
mm/min and A = 30
3.1.2. Surface Hardness
In order to get experimental indications of the temperature distribution during the friction stir
welding processes and in particular of the effects of the heat fluxes on the mechanical
characteristics of base metal, micro-hardness tests have been measured along the transverse
section of the joints using a load of 500 g. The results from the hardness measurements are
shown in Figure 9. The vertical line represents the position of the tool pin during welding. The
hardness varied between 36 and 44 HV0.5 and between 62 to 69 HV0.5 for Aluminium and
copper plates respectively. The minimum hardness in Aluminium and copper was found in the

heat affected zone (HAZ) of both the advancing and retreating side. This shows the local
softening of the material in HAZ, because of the thermal action of the welding processes. The
hardness of the nugget was higher than that of HAZ and the base metal. This may be attributed
to the formation of brittle and hard intermetallic compound and very fine recrystallized grains
in the nugget zone and grain growth in HAZ[9,10] .
Figure 9 Micro hardness distribution for the joint produced by N=1500rpm and v = 80 mm/min
The hardness in longitudinal direction also performed near interface and top of the plates
in order to know uniformity of the joint. The measurement results in longitudinal direction are
shown in the figure10 and figure11. The hardness results indicate that the hardness has been
uniform throughout the joint. This indicates that the joint is uniform from the beginning to the
end of the joint. At some point’s high hardness (120 and 168) has been observed this is due to
the inter-metallic compound Al3Cu9.
Figure10 Hardness distribution of longitudinal section in Al plate near interface and top of the plate

Figure11 Hardness distribution of longitudinal section in Cu plate near interface and top of the plate
3.2. Electrical Resistance of the Joint
Electrical resistance of the friction stir welded Al/Cu bimetallic joints, fabricated at optimum
conditions, was measured using the nano-Ohm meter. Table 5 presents the resistance
measurement for 3mm x 20mm x 100mm specimens of the pure Al and Cu. In service, the
electricity path is through the thickness of the Al/Cu joint. The electrical resistance through the
thickness of joint is the sum of resistances of Al and Cu
Rjoint = RAl + RCu
Where Rjoint = Resistance of Al/Cu joint
RAl = Resistance of Al
RCu = Resistance of Cu
Table 6 presents the calculated resistance of Al/Cu bimetallic test specimens (3mm x 20mm
x 170mm) compared with the experimentally measured resistance of the stranded Al/Cu
bimetallic test specimens. The data in table 7 shows that the measured resistance of the Al/Cu
joints is approximately equal to the sum of the resistances of Al and Cu. This indicates that the
bond zone resistance is essentially negligible as in manufactured condition. The measured
resistance is slightly more than the calculated resistance. This is because of intermetallic
formation in nugget zone [11].
Table 5 Measured Resistance of Al and Cu (each 3mm x 20mm x 100mm)
S. No Material Electrical Resistance (µΩ)
1 Aluminium 27.08
2 Copper 41.08
Table 6 Measured Vs Calculated Resistance
Si. No Joint
Resistance in Micro-Ohm’s
Measured Resistance
Calculated
Resistance
Bond Zone
Resistance
1 L1 59.55 58.14 1.41
2 L5 59.85 58.14 1.71

4. CONCLUSIONS
Sound lap joints of Al/Cu have been successfully obtained by friction stir welding technology.
Joint fabricated at low rotational speed and low welding speed yielded superior tensile shear
strength irrespective of tilting angle and the failure was in base metal Aluminum. The
maximum value of tensile shear strength was 70 MPa. It is about 100% of base metal
aluminium and 70% of base metal Copper. The minimum hardness in Al and Cu was found in
the heat affected zone (HAZ) of both the advancing and retreating side. The joint is uniform
from the beginning to the end of the joint. The joint resistance is essentially negligible as in
manufactured condition
5. ACKNOWLEDGEMENTS
The authors would like to acknowledge the help by M/S DMRL, Hyderabad and M/S BHEL
R&D, Hyderabad for giving permission to conduct experiments on friction stir welding
machine and to measure joint resistance respectively.
REFERENCES
[1] P.K. Rohatgi and C.Weiss, Technology forecasting for commodity projections: A case
study on the effect of substitution by Aluminium on the future demand for Copper,
Technology forecasting and social change volume 11, 1977, 25-46.
[2] William F.Olashaw, Aluminum- copper electrical joint, United States patent, June 1, 1980.
[3] William E. Veerkamp, Copper-to-Aluminum transitions in high DC bus system, IEEE
transactions on industry applications 1997, Vol.33, No 4.
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copper plates by explosive welding method, Materials and design Volume 29, 2008, 29, 75-
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[5] Bekir S. Yilbas, Ahmet Z. Shin, Friction welding of St-Al and Al-Cu materials, Journal of
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thicknesses”, Material Science and Engineering, 2007, A 459, 209-215.
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[8] A. Abdollah-Zadeh, T. Saeid, B.Sazgari, Microstructure and mechanical properties of
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[9] C.J. Hang, C.Q. Wang, M. Mayer, Y.H. Tian, Y. Zhou, H.H. Wang “Growth behavior of
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[10] Arun Nishchal Guleria and Sandeep Salhotra, Effects of Silica Fume (Micro Silica or Nano
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[11] P. Xue, D.R. Ni, D. Wang, B.L. Xiao, Z.Y. Ma , “Effect of friction stir welding parameters
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Ijciet 08 04_223

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Ijciet 08 04_223