1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME
AND TECHNOLOGY (IJMET)
ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
Volume 4, Issue 5, September - October (2013), pp. 295-300
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IJMET
©IAEME
MICROSTRUCTURE AND MECHANICAL PROPERTIES OF MILD STEELCOPPER JOINED BY FRICTION WELDING
Dalip Kumar1, Antariksha Verma2, Sankalp Kulshrestha3, Prithvi Singh4
1
(Department of Mechanical Engineering, Delhi Technological University/Formerly Delhi College of
Engineering, Main Bawana Road -Delhi India)
2, 3
(Department of Mechanical Engineering, Jodhpur Engineering College & Research Centre /
Jodhpur National University Jodhpur – Rajasthan, India)
4
(Department of Mechanical Engineering, Shridhar University Pilani - Rajasthan, India)
ABSTRACT
Joining of dissimilar metals is one of the most essential needs of industries.Dissimilar metal
mild steel-copper been investigated in the present work.In friction welding of two dissimilar
materials, two rods are welded together by holding one of themstill while rotating the other under the
influence of an axial load which creates frictional heat in theinterface. The tensilestrength of the
joints was determined, using a conventional tensile test machine.Ultimate tensile strength, percentage
elongation of the welded joints and hardness variations across the weld interface has been reported.
The integrity of the joint has been investigated using scanning electron microscopy.
Keywords: Friction welding, mechanical properties, microstructure.
1.
INTRODUCTION
Friction welding is a solid state process for joining materials, especially dissimilar materials,
which involves generation of heat by the conversion of mechanical energy into thermal energy at the
interface of the work pieces without using electrical energy or heat from other sources during
rotation under pressure [1].Copper has excellent ductility, corrosion resistance, thermal and electrical
conductivity, and has been widely used to produce engineering parts such as electrical component
and radiator.Many ferrous and non-ferrous alloys can be friction welded. Friction welding can be
used to join metals of widely differing thermal and mechanical properties. Of-ten combinations that
can be friction welded cannot be joined by other welding techniques because of the formation of
brittle phases which make the joint poor in mechanical properties. The sub-melting temperatures and
short weld times of friction welding allow many combinations of work metals to be joined [2].Main
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2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME
advantages of friction welding are high material saving, low production time and possibility of
welding of dissimilar metals or alloys [3].Sahin et al. [4] joined steel and copper using friction
welding process in their studies. They determined that maximum heat is away from the center, close
to but not exactly at the surface during the welding process.However, due to the difference of
chemical, physical and mechanical properties between the components to be welded, the welding of
dissimilar materials is generally more difficult than that of homogeneous materials. High-quality
Copper and mild steel dissimilar joint is hard to be produced by fusion welding techniques due to the
large difference of melting points, brittle intermetallic compounds existence and crack formation [57].Mohammadet al. [8] joined alumina and mild steel using friction welding at low rotational steel.
They concluded that the strength of alumina–steel bonding is much dependent on the wet ability of
the alumina surface by the partially molten aluminum interlayer and the existence of mechanical
interlocking between the interlayer and mild steel. Many authors have recently conducted
extensive investigation into the friction welding of dissimilar materials. The main reasons for
dissimilar joining are due to the combination of good mechanical properties of one material
and the low specific weight, good corrosion resistance, and good electrical properties of a
second material. During the friction welding of dissimilar materials, significant cost saving is
possible because engineers can design bimetallic parts that use expensive materials only
where needed. Expensive forgings and castings can be replaced with less expensive forgings
to bar steel, tubes, plates and suchlike.Duffin and Bahrani [9] carried out a series of experiments
on the friction welding of mild steel tubular specimens to study the variations in resisting torque,
axial force, and axial shortening when the angular speed and axial force are varied.
In this work, dissimilar friction welding of commercial pure copper and mild steel rods was
carried out, and the microstructure and mechanical properties of the dissimilar joints were
investigated. Based on the experimental results, the formation of the dissimilar joints was discussed.
2.
EXPERIMENTAL PROCEDURE
2.1
Materials
Commercially available pure copper and mild steel were used, and the chemical compositions
of the experimental materials are listed in Table 1.The materials used in the experiments were mild
steel and copper rods both measuring 10mm in diameter and 50mm in length. Before welding, the
surfaces of the sheets were ground with grit paper to remove the oxide film and then cleaned with
ethanol.
Material
C
Si
Mn
Ni
Cr
Cu
Fe
Zn
Mild Steel
0.175
0.118
0.394
0.016
0.02
0.022
99.1
-------
Pure Copper
-----
-----
-----
0.009
-----
99.957
0.009
0.025
Table 1 Chemical compositions of Mild steel andpure copper
2.2
Welding set-up
A friction welder capable of operating at 200kN maximum load was designed and
manufactured to carry out the experiment (Figure 1).
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3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME
Figure 1 Experimental Set – Up
The friction welding machine operates with high precision and excellent repeatability of weld
parameters. The spindle is driven by an AC motor. The axial force was applied with the help of a
hydraulic group. Friction and axial forces are read by a load cell connected to machine. All relevant
data of every weld is recorded. The spindle motor is of 25 HP, 3Phase AC and operating speed can
be varied from 1 to 1500 RPM.During the weld the speed of rotation was kept constant at 900 RPM
and up-set force of 120 KN was applied. Once the resulting welds were obtained, tests were carried
out determine mechanical and metallurgicalcharacteristics of the weld joint.In first part the
mechanical properties of the resulting welds, tensile testing and micro hardness of the weldcrosssection were carried out. However, on the second part the metallurgical changes during welding were
examined using scanning electron microscope.
3.
RESULTS & DISCUSSION
3.1
Hardness
The representative section of Vickers hardness profiles of dissimilar weld were measured
along the length of specimen Figure2.
250
Hardness (HV)
200
Copper
Mild steel
150
100
50
0
-500
-400
-300
-200
-100
0
100
200
300
Distance (Micrometer)
Figure 2 Hardness profiles of the welded mild steel-copper
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4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME
It is obvious that the hardness at the mild steel side is higher than that at the copper side.The
hardness of mild steel increased towards the heat affected zone. The increase in hardness towards
HAZ in copper was less.This increase in the hardnessresulted in the formation of cracks at the edge
of hardness indentation. Higher hardness in all the welds can be attributed to the strain hardening
effect due to up-set force.It can be seen that at around the interface, the hardness of the copper
increases slightly. However, slight decrease in the hardness of the steel is observed. This is due to the
steel reaching the annealing temperature during the welding process, which in turn reduces hardness
on the steel side. On the other hand, copper exhibits hardening due to its high thermal conductivity
and fast cooling behaviour.
3.2
Tensile properties
Tensile properties of parent metals and weld joints are presented inTable 2. Mild steelcopper is an insoluble system. Joints formed here were very brittle in nature and exhibited drop in
strength with an increasein HAZof the weld region. Diffusivity of mild steel is higher than that of
copper and hence a reaction layer is formedtowards copper side and the failure has taken place in this
zone[10].Although the thermo physical properties of the two parts are quite different the tensile
strengths of welds close to those of the individual parts are obtained.
Mild Steel
Average Tensile
Strength (MPa)
390
Elongation
%
22
Yield Strength
(MPa)
287
Location of
Failure
-----
Copper
240
14
209
-----
Material
Weld Joint
215
3
----Table 2 Tensile properties of base metal and welded samples
Weld
3.3
Micro-structural characterization:
As the rotational phase continues, irregularities in the two faces are smoothed outby frictional
contact and pressure.When the heat generated at the interface increases the materials become plastic
and a condition of full-face intimate contact can be achieved. However, atless rotational speed,
impurities such as surface oxides, grease or oil, can remain trapped and, hence, do not permit the
close interface contact necessary to give full bonding.The small interface impurity can cause weaken
the weld join. The speed of rotation affects the intermetallic layer thickness such that a low speed of
rotation results in less intermetallic layer thickness.
Figure 3 (A) Microstructure of weld zone of dissimilar metal at 50X (B) Microstructure of weld
zone of dissimilar metal at 100X
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5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME
The microstructures of the welded joints, taken at 50X and100X using the scanning electron
microscope. The weld joints are seen to be continuous and the deformation zone being very different.
However, there is a distinction between the microstructures developed near the interface in the two
parts joined (Fig. 3a). The micrographs show diffusion at the interface of the joining.The temperature
developed in the outer region close to the free surface of the sample is higher than that corresponds
to the central region of the sample, during welding process. This results in relatively large melting
and heat-affected zones developing in this region. Small grains in the copper side indicate hardening,
whilst no significant variation is observed in the grain size on the steel side (Fig. 3b).
4.
CONCLUSIONS
1. Mild steel and pure copper are jointed successfully through friction welding with pin offset
technique under a rotation rate of900rpm and a set-up load of 120 KN.
2. The hardness at the mild steel side of the joint is higher than that at the copper side. The welded
materials have lower hardness compared to their parent materials due to thermal effects of the
friction welding.
3. The welded rods show lower tensile strength compared to their parent rods.The average tensile
strength and elongation of the dissimilar joints are 215 MPa and 3%, respectively, and the
dissimilar joints fail in a ductile-brittle mixed fracture mode.
4. Microstructure shows that the weld joint between mild steel-copper accompanied by the
diffusion of copper into mild steel.
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