Volume 3, Issue 3, March– 2018 International Journal of Innovative Science and Research Technology

ISSN No:-2456-2165

Process Optimization of Preheated Friction Stir

Welded Ferrous and Non-Ferrous Materials
Prashant S Humnabad Dr. M S Ganesha Prasad
Research Scholar, Department of Mechanical Engineering Professor and Head, Department of Mechanical Engineering
Sir M Visvesvaraya Institute of Technology New Horizon College of Engineering,
Bengaluru, Karnataka, India Bengaluru, Karnataka, India

Abstract:- Joining of Ferrous and Non-Ferrous materials, have different thermal and mechanical properties. The sound
such as aluminum and steel alloys is very challenging joint is the highest concern through the design of the parts
which requires the efficient and economic processes. The especially for such places where the quality of the joints has
Al/Steel combination have wide range of industrial more priority than other concerns.
application especially in automotive sector looking for
It is assumed that the new replacement of the light
lightweight materials and provides good strength. As we
materials is that it will help to reduce the fuel consumption,
know aluminum and steel alloys have different
production cost and effectively reduces the amount of human-
metallurgical properties it is quite difficult to join them
elemental energies on the heavier materials. For instance, the
with fusion welding methods. Friction Stir Welding (FSW)
use of the aluminum/steel alloys and finding the surrogating
process (also referred as green joining technology) is most
material for some of the sensitive components is relatively
suitable technology to join dissimilar materials like
influenced by the controlling forces like current regulations to
Al/Steel, which was developed way back in 1991 by The
encounter fuel efficiency standards by decreasing vehicle
Welding Institute (TWI). Earlier FSW was used to join
weight [1, 2].
softer material such as aluminum alloys and the process
has been expanded to weld the materials having higher There are, however, numbers of works on the
strength. To join high strength materials large forces are application of different welding technologies to bond
required, due to this tool wear have become major issue. dissimilar alloys but the problem of losing the strength in the
To resolve this issue, an additional heating source is bond areas is always a big challenge because of the formation
introduced in front of the Friction Stir Welding tool which of the brittle intermetallics has not been solved [3,4].
softens the base material to be welded and reduces the load
on tool hence no mimized tool wear. Present work focused Subsidiary precipitates created during solidification,
to join Ferrous and Non-Ferrous materials like A6082-T6 different thermal properties, dissimilar thermal expansion, heat
capacity and thermal conductivity, large difference between
and Steel and evaluate the effect of parameters considered
the melting points (around 650 °C for Al alloy and 1457 °C for
on tensile strength. Taguchi parametric design approach
steel) and nearly zero solid solubility of iron in aluminum are
was used to determine process parameters, post welding
creating the large discrepancy between the metals leading to
the results are analyzed by using ANOVA statistical tools.
the reduction of the mechanical properties after the joining
The best welding quality is found out by comparing the
processes. Laser roll bonding [5], impact welding [6], friction
result obtained from tensile testing showed that due to
welding [7], ultrasonic welding [8], diffusion bonding [9],
preheating of base metal, increase in material flow and
explosive welding [10], laser brazing/welding [12, 13],
quality of the weld.
magnetic pulse welding [14] and laser pulse welding [15, 16]
Keywords:- Friction Stir Welding; Ferrous/Non-Ferrous are the typical welding processes that have been applied up to
Materials; Preheating; Optimization; SEM. now to join different grades of the steels to the aluminum
alloys.
I. INTRODUCTION In the present work Friction stir welding of A6082-T6
The current industrial requirements are joining of and Mild Steel plates with accepted strength is studied with
dissimilar materials which have numerous industrial the help of preheating. Steel plate is preheated to 100ᵒC, 150ᵒC
applications. This lead to the development of latest joining and 200ᵒ C before friction stir welding. Preheating improve
techniques capable to join dissimilar materials like aluminum mechanical properties such as tensile strength, cooling rate and
and steel, which are among the most significant materials that residual stress. From the investigation it is found that
are finding applications on the various industries from the preheating of base metals before welding will reduces the load
miniature assemblies to extremely large earth-moving on tool and tool wear. Also helps better mixing of the alloys at
vehicles, more viable and sustainable products. joint interface, which helps to get good joint strength.
Optimizing the process will help to get best combination of
However, there are a certain number of methods to parameters to achieve required objective.
join these dissimilar metals but no one could establish a
reliable or a sort of credible welding method for the industrial
applications while quality, cost, human resources and facilities II. LITERATURE REFERENCES
are taken into the main considerations.
As many of the metals, there are still many unsolved Watanabe and K. Kimapong [17] investigated
problems in the joining of different alloys which basically Friction Stir Welding of Aluminum Alloy with Mild Steel

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Volume 3, Issue 3, March– 2018 International Journal of Innovative Science and Research Technology
ISSN No:-2456-2165
plate. This study investigated the effects of pin rotation speed, III. METHODOLOGY
position of the pin axis, and pin diameter on the tensile
strength and microstructure of the joint. The main results A. Design of Experiment
obtained are as follows: Butt-joint welding of an aluminum
alloy plate to a steel plate was easily and successfully The process parameters identified for the
achieved. Many fragments of the steel were scattered in the investigations are shown in Table I such as Preheating
aluminum alloy matrix, and fracture tended to occur along the Temperature, Tool Rotation Speed and Tool Travel Speed.
interface between the fragment and the aluminum matrix. A This is the design of experiment by which the present work
small amount of intermetallic compounds was formed at the has been carried out. Table II gives Friction Stir Welding tool
upper part of the steel/aluminum interface, while no details
intermetallic compounds were observed in the middle and
bottom regions of the interface. A small amount of
intermetallic compound was also often formed at the interface Sl.
Process Parameters
between the steel fragments and the aluminum matrix. No.
Tool Rotational Speed
M. Merklein et. al. [18] mentioned it is difficult to 1 1000 1400 2000
(rpm)
join steel-aluminium, since intermetallic phases appear during Tool Travel Speed
welding. Because of these phases joint may fail due to load. 2 16 20 25
(mm/min)
Laser assistance for preheated friction stir welding of steel is Preheating Temperature
adapted in order to enhance the weldability as well as the 3 100 150 200
(°C)
welding feed and to reduce the wear at the tool.
Antonio José Ramirez Londoño et. al. [19] studied TABLE I. FSW PROCESS PARAMETER
dissimilar joining of 2 mm thick butt joint involving AISI
1020 mild steel and aluminum alloy 6063-T6. To understand
the effect of welding parameters on the joint microstructural Tool Material Tungsten-Carbide
evolution and mechanical performance of such welded joint. Pin Profile Cylindrical Tapered
Avinash S. et. al. [20] carried out a review on Shoulder Diameter 20 mm
Optimization of Process Parameters by using Taguchi Pin Top Diameter 5 mm
experiment design technique for maximizing tensile strength Pin Bottom Diameter 3 mm
of friction welding Al (6061) and steel 304.An orthogonal Pin Length 3.4 mm
array of L9 was; Using ANOVA and signal to noise ratio of Shoulder Length 30 mm
robust design, effect of tensile strength of friction welding
process parameter (Rotational speed, forging force, time) is TABLE II. FRICTION STIR WELDING TOOL DETAILS
evaluated and optimum welding condition for maximizing
tensile strength is determined. Sundaravel Vijayan et. al. [21]
Carried research on Multi objective Optimization of Friction B. Taguchi’s Method
Stir Welding Process Parameters on Aluminum Alloy AA Taguchi approach attempts to extract maximum
5083 Using Taguchi-Based Grey Relation Analysis. The L9 important information with minimum number of experiments.
orthogonal array of Taguchi experimental design is used for Taguchi techniques are experimental design optimization
optimizing the FSW process parameters on tensile strength of techniques which use standard Orthogonal Arrays (OA) for
FSW welds and total input power required for the process. forming a matrix of experiments. Using an OA to design the
experiment helps the designer to study the influence of
Elena Scutelnicu. et. al. [22] studies shows that multiple controllable factors on the average of quality
adding additional source of heat to preheat base metal provides
characteristics and the variations in a fast and economic way.
added advantages such as quick and better plastic deformation
OA’s allow screening out few important main effects from the
of base material, also minimized tool failure and quality of
many less important ones.
weld would be better.
In the present work operating parameters, each at
Maulik kumar Patel. et. al. [23] studied, Friction stir three levels are selected to evaluate strength of the joint are
welding of Al 6061T-6 plate with accepted strength is studied mentioned in Table III. Based on Taguchi method, the L27-
with the help of preheating heat source of the al 6061 T-6 OA was constructed. The reason for using L27-OA is to
plate. Al 6061 T-6 plate is preheated to 100ᵒC, 125ᵒC and150ᵒ
evaluate the significance of interaction terms. Interaction
C before friction stir welding. Preheating of friction stir means the influence of an operating variable on the effect of
welding joints is welded completely without any un-welded other operating variable.
zone resulting from smooth material flow by equally
distributed temperature in two sides of Al plates. Preheating
C. Anova Analysis
improve mechanical properties such as tensile strength,
cooling rate and residual stress. Preheating in friction stir Analysis of Variance (ANOVA) is a statistical
welding help to improve welding speed, penetration depth, method which is used to discuss the relative importance of the
heat affected zone. entire control factor. They are also used to find the
contribution of each parameter. F-test proposed by Fisher is

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Volume 3, Issue 3, March– 2018 International Journal of Innovative Science and Research Technology
ISSN No:-2456-2165
used as an auxiliary tool of inspection. Thus, the larger the IV. EXPERIMENTAL PROCEDURE
value of f-test the more dominant the parameters are.
Following are the processes carried out during Friction Stir
D. S/N Ratio Welding:
Taguchi also recommended to analyse the values
using S/N ratio. It involves conceptual approach which graphs
the effect and identifies the significant values. A. Cutting
The required base metals Aluminum alloy 6082-T6
and Mild-Steel materials are cut as per the dimensions 100
L27 Variable/levels Tensile
mm x 50 mm x 4 mm.
Test SN Ratio
Array x1 x2 x3 (MPa) B. Preparation of Job
1 16 1000 100° 208.02 46.2902 The edges of the faces were cleaned by using
2 16 1000 150° 214.60 47.3831 different grain size emery paper to remove oxide layers or any
surface contamination and washed with acetone just before
3 16 1000 200° 228.01 46.97762 each experiment started. Then the plates are secured in a
position firmly using mechanical clamps.
4 16 1400 100° 227.65 47.15601
C. Welding
5 16 1400 150° 264.64 47.42072
All the experiments are carried out at almost same
6 16 1400 200° 245.60 47.15853 room temperature and other parameters selected are kept
constant for all the experiments (such as machine operator,
7 16 2000 100° 234.02 48.12907
dwell time, plunge depth, tool offset, tool profile etc…).
8 16 2000 150° 274.32 48.76485 The direction of welding is normal to the rolling
9 16 2000 200° 223.31 46.99108 direction. Single pass welding procedures are used to fabricate
the joints. Non-Consumable cylindrical tapered tool is made
10 20 1000 100° 207.23 46.33292 up of tungsten carbide is used to fabricate the joints. A non-
consumable rotating tool is specially designed by pin and
11 20 1000 150° 213.65 46.97762
shoulder to insert into the abutting edges of sheets or plates
12 20 1000 200° 224.65 47.15601 (offset towards steel to get better joint strength) which have to
be joined. The primary functions of the tools are: Heating the
13 20 1400 100° 223.34 47.80541 work piece and Movement of material to form joints
14 20 1400 150° 245.60 48.45085 In the present work, additional source for heating the
base material is introduced with conventional Friction Stir
15 20 1400 200° 228.00 46.97762
Welding (FSW) process which is used to preheat steel plate to
16 20 2000 100° 224.56 47.38310 different temperature levels. Preheat source located in front of
the tool in the welding direction provides adequate metal flow
17 20 2000 150° 255.01 48.16890 around the tool and simultaneously prevents formation of a
18 20 2000 200° 213.66 46.36100 large amount of brittle aluminum – steel intermetallic
compounds. The mechanical properties of the welded joints
19 25 1000 100° 204.33 46.27643 are analyzed for selected process parameters
20 25 1000 150° 208.02 46.58302 Due to the friction produced between the rotating tool
and the work piece plastic deformation of the work piece is
21 25 1000 200° 215.33 46.36461 achieved. Preheating and the high heat which is produced
22 25 1400 100° 208.03 47.14601 softens material around the pin and shoulder. The combined
effect of tool rotation and translation leads to movement of
23 25 1400 150° 235.02 47.81541 materials from front to the back of the pin (visa-versa).
24 25 1400 200° 224.63 47.02868 The formation of rings are observed on the line of
joining, thus a solid joint is formed. During FSW process the
25 25 2000 100° 223.31 47.40804 material undergoes a plastic deformation at high temperature
26 25 2000 150° 253.35 48.12807 which results in generation of fine and equaled re-crystallized
grains. It is expected that preheating of material not only
27 25 2000 200° 207.34 46.32291 reduces the forces acting during welding by softening the base
metal but also minimizes the chances of tool wear. Also helps
TABLE III. SHOWS THE DIFFERENT EXPERIMENTS CONDUCTED better mixing of the materials and provides better welding
BASED ON TAGUCHI’S L27 ORTHOGONAL ARRAY AND TEST results interms of improved welding efficiency and weld joint
RESULTS. quality.

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Volume 3, Issue 3, March– 2018 International Journal of Innovative Science and Research Technology
ISSN No:-2456-2165
Fig. 1 shows Friction Stir Welding appearance to join be observed that aluminum material deposited on the tool
Dissimilar Materials, the process is started with edge shoulder and change in pin profile or pin completely broken.
preparation of the plates of A6082-T6 and Mild-Steel alloys to
make sure both the edges meet each other then they are
clamped firmly by using suitably designed clamping setup
which is fixed on the table of the machine, with the help of
preheating torch which is a preheating heat source is
positioned at an angle of sixty degree w.r.t. base metal at
standard distance. It was made sure that less arc effect on the
tool and softer material.
Then the process is followed by rotating a specially
designed FSW tool at predefined speed (rpm) before it is Fig. 2:- Tool Profile (a) New Tool (b&c) Pin broken and
inserted into wild line of the plates to be joined. A vertical Deformed Metal sticks the tool shoulder
force (z-axis load) is applied perpendicularly to the joint line,
driving the rotating pin into the work piece (01 mm offset V. RESULTS AND DISCUSSION
towards advancing side). Frictional heat is generated at two
points: one at the top surface of the workpiece under the FSW A. Tensile strength
tool shoulder and second is in the base material at the interface
with the pin. Tensile strength or ultimate strength is the maximum
stress that a material can withstand while being stretched or
pulled before failing or breaking. The value of the test
specimen does not depend on the size of the work piece but it
depends on factors like surface finish, temperature of the test
environment etc. Tensile testing of material was carried out at
ASTM E8M-04.Thus we need larger tensile strength to make
the material withstand when stretched or pulled. Thus we use
Larger the better to calculate S/N ratio.

B. Analysis of Variance

TABLE IV. ANALYSIS OF VARIANCE FOR SN RATIOS

Fig. 1:- Friction Stir Welding appearance to join Dissimilar
Materials

A lateral force (x-axis load) is applied in the direction

of travel, after sufficient dwell time (to allow for homogeneous
heating and softening of the material). Both z- and x-axis loads
act on the rotating welding tool as it traverses along the joint
line, sweeping the softened material along the periphery of the
pin and depositing it in the tool’s wake.
This “stirring” action, along with the pressure and
restraining forces induced by both the tool and fixturing,
creates a heavily deformed region of material which upon
cooling defines a strong metallurgical joint which will be
having fine-grained with no entrapped oxides or gas porosity.
Fig. 3:- Main Effect Plot For SN Ratio
Fig. 2a shows the new tool profile before welding and
Fig. 2 (b&c) shows the status of the tool after welding, it can

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ISSN No:-2456-2165
C. Interaction Plot magnification the transferred composition of steel over
aluminium is observed. In 2000X it is clearly seen that there is
Whether interactions between factors exist or not can be much traces of aluminium particles over the steel, very near to
shown by plotting a matrix of interaction plot. However, the the interface.
interaction plot doesn't tell if the interaction is statistically
significant.
To visualize interactions during DOE, interaction plots are
used most often. Matrix of interaction plot for means and
signal to noise ratios are shown in Fig. 4.
Sl. No. Level X1 X2 X3
1 1 47.411 46.591 46.751
2 2 47.017 47.335 47.580
3 3 46.812 47.346 46.970
4 Delta 0.581 0.770 0.830
5 Rank 2 3 1

TABLE V. RESPONSE TABLE FOR SN RATIOS

Fig. 5:- SEM Images at various Magnification (a) 200X (b)

500X
(c) 1000X (d) 2000X

VI. CONCLUSION

In the present work, Taguchi method was used to

obtain optimal condition for Friction Stir Welding of A6082-
T6 and Mild Steel, then the experimental results were
Fig. 4:- Interaction Plot for Signal to Noise (SN) Ratios evaluated using ANOVA.
The results can be draw as follows:
D. Interpretation of Interaction Plots
To get good weld strength, Tool Pin offseted 1 mm
towards steel (at joint interface).
The interaction plots show that the interaction between
Preheat temperature and Rotational Speed is major important It is observed that Preheating Temperature was the major
factor. The other two-factor interpretations do not appear to be factor affecting the Tensile strength.
important though they are significant. The maximum Tensile Strength was exhibited by the
Friction Stir Welded joints with the optimized parameters of
E. SEM Microstructural Investigation Preheating Temperature 150°C, Traverse Speed 16 mm/min,
and Rotational Speed 2000 rpm.
To understand material in clear way Scanning Electronic
Microscope (SEM) method is used. The atomic number of It’s better to withdraw the FSW-Tool from joint line (when
aluminium is 13 and atomic number of steel is 26. If atomic it reaches other end of the joint) while still it is in rotation, else
number is more then brightness of the material is more, if pin may break.
atomic number is less then brightness of material is less in
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ISSN No:-2456-2165
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