S. CHINNAIYAN et al.: SYNTHESIS AND FORMING BEHAVIOUR OF AA7075-TiC POWDER-METALLURGY COMPOSITES
809–812
SYNTHESIS AND FORMING BEHAVIOUR OF AA7075-TiC
POWDER-METALLURGY COMPOSITES
SINTEZA IN FORMIRANJE AA7075-TiC P/M KOMPOZITOV
Saravanan Chinnaiyan
1
, Subramanian Karuppazhagi
2
, Anandakrishnan Veeramani
3
,
Sathish Shanmugam
3
1
Department of Mechanical Engineering, University College of Engineering, Bharathidasan Institute of Technology Campus, Anna University,
Tiruchirappalli-620024, Tamil Nadu, India
2
Department of Mechanical Engineering, Government College of Engineering, Srirangam-620012, Tamil Nadu, India
3
Department of Production Engineering, National Institute of Technology, Tiruchirappalli-620015, Tamil Nadu, India
csaravananauto5@gmail.com
Prejem rokopisa – received: 2017-11-15; sprejem za objavo – accepted for publication: 2018-08-02
doi:10.17222/mit.2017.189
Aluminium 7075 is frequently used in aircraft structures. Aluminium metal-matrix composites with0%T iC( w/%),8%T iC
and 16 % TiC were produced using the powder-metallurgy technique. Metallurgical studies, such as X-ray diffraction (XRD)
and scanning electron microscopy (SEM), were made to confirm the occurrence of reinforcements. A cold-upset test was
conducted on the synthesized composites and different stress parameters were calculated to study the forming behaviour of the
produced composite in the tri-axial stress-state condition. The values of the stresses were found to be highest for the aluminium
composite reinforced with AA7075 + 16 % TiC.
Keywords: AA7075, metal-matrix composite, cold upsetting, formability
Najbolj pogosto uporabljana aluminijeva zlitina za letalske strukture je Al zlitina 7075. Avtorji v tem ~lanku opisujejo izdelavo
kompozita z Al matrico z 0 % TiC (w/%), 8 % TiC in 16 % TiC s postopkom metalurgije prahov. Izvedli so metalur{ke preis-
kave, kot sta rentgenska difrakcija (XRD) in vrsti~na elektronska mikroskopija (SEM), da bi potrdili navzo~nost oja~itvene faze.
Izvedli so hladni kova{ki test nakr~evanja na sintetiziranih kompozitih. Da bi lahko raziskovali obna{anje materiala med tvorbo
kompozita, so izra~unali razli~ne napetostne parametre v pogojih triosnega napetostnega stanja. Ugotovili so, da najvi{je
napetosti nastajajo pri formiranju Al kompozita AA7075 s 16 % TiC.
Klju~ne besede: AA7075, kompozit s kovinsko (Al) matrico, hladni kova{ki (kr~ilni) preizkus, oblikovalnost
1 INTRODUCTION
Composite material is the term that made a paradigm
shift in the field of material science. It introduces a new
engineered material with improved properties for re-
quired applications. In the area of composites, metal-
matrix composites have wider applications owing to their
enhanced material properties. Aluminium metal-matrix
composites have their own place, particularly in the field
of aerospace, and the marine and automotive indus-
tries.
1,2
Reinforcements of different types and forms are
available; they can be selected based on the required
property and the modes of fabrication. Aluminium-based
composites will generally be processed through casting
and the powder-metallurgy route. Powder metallurgy is a
technique that is used to synthesize a material with a
near net shape.
3
There are six considerations when de-
signing with powder metallurgy, i.e., material systems,
size, properties, complexity, quantity, cost and tole-
rances. There are two broader classifications in the
processing technique: one is the conventional pressing-
sintering process and the other is the full-density
process. The most common is the conventional press-
ing-sintering technique.
4
Several reinforcements like
silicon carbide, boron carbide, alumina, titanium carbide,
titanium dioxide, titanium diboride, zirconium diboride
etc. are available and titanium carbide has its exceptional
properties, such as low density, high hardness, high
stability and good wettability.
5
In order to evaluate the
potential of failure for any material, it is necessary to
conduct a workability study along with its failure crite-
rion.
6
Many research works were carried out with
metal-matrix composites, and some of them are
discussed. Hassani et al. synthesized a porous aluminium
composite reinforced with silicon carbide particles using
the powder-metallurgy technique and studied the in-
fluence of milling time on the metallurgical and me-
chanical properties of the composite.
7
Jeyasimman et al.
synthesized an aluminium nano-composite reinforced by
multi-walled carbon nanotubes and studied the
metallurgical and workability behaviour of the produced
composite.
8
Lee et al. studied the influence of a homo-
genization treatment on the mechanical properties and
the workability of the AlMg
5
Si
2
Mn alloy.
9
Liu et al.
made a hot-compression test at different temperatures
and strain rates and obtained the optimum condition
through a processing map.
10
Narayan et al. produced
aluminium composites reinforced with4%ofTiC,WC,
Fe
3
C and Mo
2
C through powder metallurgy and found a
higher densification for the TiC-reinforced composite.
11
Materiali in tehnologije / Materials and technology 52 (2018) 6, 809–812 809
UDK 620.1:669.715:620.168 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 52(6)809(2018)

Anandakrishnan et al. synthesized in-situ AA7075–TiC
composites using the stir-casting technique and studied
the formability behaviour of the composite.
5
Devi et al.
synthesized in-situ AA 7075/Al
2
O
3
composites through
the powder-metallurgy technique and studied its corro-
sion behavior.
12
Narayanasamy et al. synthesized in-situ
Cu–TiC composites through the powder-metallurgy
technique and studied the effect of copper addition and
the aspect ratio on the formability behavior.
13
Ravichan-
dran et al. synthesized an aluminium metal-matrix
composite with titanium dioxide as the reinforcement
using the powder-metallurgy technique and studied its
workability behavior.
14
Govindan and Gowthanithan-
kachi synthesized aluminium composites with ZrO
2
to
investigate their tensile behaviour and found an
improved strength for 12 % of ZrO
2
.
15
Ravichandran et
al. produced hybrid aluminium metal-matrix composites
reinforced with titanium dioxide and graphite through
the powder-metallurgy technique and studied the effect
of titanium dioxide and graphite additions on the
densification and deformation behavior.
3
Narayanasamy
et al. manufactured an aluminium metal-matrix compo-
site with alumina as the reinforcement using the
powder-metallurgy technique and studied the mecha-
nisms involved in the geometric and matrix work
hardening.
16
Bensam raj et al. manufactured an alumi-
nium metal-matrix composite with silicon carbide as the
reinforcement using the powder-metallurgy technique
and studied the effect of the sintering temperature on the
workability behaviour of the produced composite.
17
Moazami-Goudarzi et al. manufactured an aluminium
metal-matrix composite with nano silicon carbide as the
reinforcement using the powder-metallurgy technique
and found the addition of nano SiC improved the hard-
ness and the densification of the composite.
18
Ravindran
et al. studied the metallurgical, mechanical and tribolo-
gical behaviours of a hybrid aluminium composite with
silicon carbide and graphite as the reinforcement.
19
Ma et
al. fabricated a Ni – 30 % SiC (x/%) composite using the
powder-metallurgy technique and found that the pro-
perties of the coated SiC particles are improved effec-
tively.
20
Ilayaraja et al. manufactured a copper-matrix
composite with TiO
2
and graphite as the reinforcement
using the powder-metallurgy technique to investigate the
formability behaviour and found the addition of the
reinforcement improved the true stresses.
21
Elango et al.
manufactured a hybrid aluminium-matrix composite with
TiO
2
and silicon carbide to investigate its tribological
behaviour and observed an increased hardness with
increased reinforcement additions.
22
With reference to
the earlier studies, an attempt was made to synthesize an
aluminium metal-matrix composite AA7075 with TiC as
the reinforcement for different weight percentages, i.e.,
0 %, 8 % and 16 %, using the powder-metallurgy tech-
nique and to study the formability behaviour of that
composite.
2 EXPERIMENTAL PART
Aluminium 7075 powder was taken as the matrix
material and TiC was taken as the reinforcement. The
powders were weighed in a precise weighing machine to
obtain the required proportions of AA7075, AA7075 +
8%T iC( w/%) and AA7075 + 16 % TiC. The weighed
powders were blended in a ball mill to achieve the
homogenous powder mixtures. Then the powders were
compacted in a hydraulic machine to realize the green
compacts, after which they were sintered in a furnace at
a temperature of 600 °C and allowed to cool to room
temperature.
4
From the sintered composite, samples for
the cold upsetting and metallographic analyses, such as
X-ray diffraction and scanning electron microscopy,
were made and the analyses was made in a Rigaku
Ultima and a Vega 3 Tescan, respectively. The initial
dimensions of the cold upset samples, i.e., top diameter,
bottom diameter, bulge diameter and height, were
measured and recorded. Then the samples were sub-
jected to a compressive incremental load of 2 t, between
the mirror-polished flat dies, in the hydraulic machine
until the vicinity of the crack at the periphery of the
sample surface. Then the dimensions of the samples
were measured and recorded at each and every incre-
mental load. Based on the theoretical relationships, as
stated in Equations (1–5), different upsetting parameters
were calculated under the tri-axial stress-state condition.
3
Axial stress,  z
=
Applied Load
Contact Area
(1)
Axial true strain,  z
n
h
h
=
⎛ ⎝ ⎜ ⎞ ⎠ ⎟ l
f
0
(2)
Hoop stress, 
0
12
2
=
+∝
+∝
⎛ ⎝ ⎜ ⎞ ⎠ ⎟ ()
()
z
(3)
Hydrostatic stress,  
 m
=
+
⎛ ⎝ ⎜ ⎞ ⎠ ⎟ z
2
3
(4)
Effective stress,()  
      eff
=+−+
zz
22 () (5)
3 RESULTS AND DISCUSSION
3.1 X-ray diffraction (XRD) analysis
The X-ray diffraction analysis of the composite
AA7075+8%T i Ci ss h o w ni nFigure 1. From the
analysis the peaks corresponding to the aluminium
matrix material and the reinforcement titanium carbide
are identified. It also shows successful fabrication of
composite using the powder-metallurgy technique.
3.2 Scanning electron microscopy analysis
Figure 2 shows a scanning electron microscopy
image of AA7075+8%T iC.Itclearly reveals the pre-
sence of the reinforcement titanium carbide and their
distributions are found to be homogenous over the matrix
S. CHINNAIYAN et al.: SYNTHESIS AND FORMING BEHAVIOUR OF AA7075-TiC POWDER-METALLURGY COMPOSITES
810 Materiali in tehnologije / Materials and technology 52 (2018) 6, 809–812

material. In addition, the presence of TiC particles in the
form of hexagonal shapes is confirmed in the microsco-
pic analysis.
3.3 Forming behaviour
Figure 3 shows the true axial stresses vs. true axial
strain of the aluminium composite AA7075, AA7075 +
8 % TiC and AA7075 + 16 % TiC for a 0.75 aspect ratio.
Figure 3a clearly revealed that the true axial stress is
increased with respect to the increase in the true axial
strain. It also showed that the true axial stress at any
given axial strain is found to be higher for the 16 % of
TiCandlowerforthe0%ofTiC,whereas the true axial
stress for the8%ofTiCf alls within the0%ofTiCand
16 % of TiC. With the true axial stress strain graph and
the Ludwik equation,
3
as stated in Equation (6), the
values of the strength coefficient and the strain-hard-
ening index are attained, as shown in Table 1. The maxi-
mum value of the strength coefficient and the strain-
hardening index were found to be 0.1283 MPa and
250.61 MPa for the higher reinforcement of 16 % TiC.
The table also shows the value of the strength coefficient
increased with the addition of TiC, whereas the
strain-hardening index decreased with the addition of
TiC. It clearly shows that the addition of TiC improves
the strength of the material. The strain-hardening index
is found to be less for the higher percentage of rein-
forcement, which means the material is highly suitable
for the further processing of materials, such as cold
working and forming. The composite failure was iden-
tified through the visibility of cracks on the sample
peripheries, due to the shear band formation during the
cold upset tests, which is very much governed by the
friction factor in between the sample and the die.
Table 1: Strain-hardening index and strength coefficient of the
materials
Material
Strain hardening
index
Strength coefficient,
MPa
AA7075 0.2675 185.86
AA7075+8%TiC 0.2119 236.76
AA7075 + 16 % TiC 0.1283 250.61
S. CHINNAIYAN et al.: SYNTHESIS AND FORMING BEHAVIOUR OF AA7075-TiC POWDER-METALLURGY COMPOSITES
Materiali in tehnologije / Materials and technology 52 (2018) 6, 809–812 811
Figure 1: X-ray diffraction analysis of AA7075+8%TiC
Figure 3: True axial stresses vs. true axial strain a) Axial stress,
b) Hoop stress, c) Effective stress, d) Mean stress Figure 2: Scanning electron microscopy image of AA7075+8%TiC

Figure 3b shows a graph of the true hoop stress vs.
the true axial strain and it shows that the true hoop stress
is increased with an increase in the true axial strain. It
also showed that the true hoop stress at any given axial
strain is found to be higher for the 16 % of TiC and
lower for the 0 % of TiC, whereas the hoop axial stress
forthe8%ofTiCf alls within the0%ofTiCand16%
of TiC. Figure 3c and 3d shows the true effective stress
and true mean stress with respect to the true axial strain.
Similar to the axial stress and the hoop stress, the
effective stress and the mean stress are increased with an
increase in the true axial strain and also the higher values
of stresses are attained at 16 % of TiC, whereas the lower
stresses are attained at0%ofTiC.From the deformation
results, it was observed that the increased percentage of
TiC enhances the load-bearing capacity of the compo-
site, which leads to a higher densification and defor-
mation of the composite with 16 % of TiC.
4 CONCLUSIONS
Aluminium metal-matrix composites of AA7075,
AA7075+8%T i Ca n dAA7075 + 16 % TiC were
manufactured by the powder-metallurgy route. The
presence of the reinforcements was confirmed by x-ray
diffraction and scanning electron microscopy. From the
cold upsetting, it was observed that the addition of TiC
improved the value of stresses, i.e., the true axial stress,
true hoop stress, true effective stress and true mean stress
for a given axial strain. The highest values of the stresses
are obtained for the composite AA7075 + 16 % TiC in
all stresses with the true axial strain.
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S. CHINNAIYAN et al.: SYNTHESIS AND FORMING BEHAVIOUR OF AA7075-TiC POWDER-METALLURGY COMPOSITES
812 Materiali in tehnologije / Materials and technology 52 (2018) 6, 809–812