D. MANICKAM et al.: EXPERIMENTAL INVESTIGATION OF LM25 ALLOY REINFORCED WITH SiC, Gr ...
395–398
EXPERIMENTAL INVESTIGATION OF LM25 ALLOY
REINFORCED WITH SiC, Gr AND MOA PARTICLES
EKSPERIMENTALNE RAZISKAVE NA Al ZLITINI LM25, OJA^ANI
Z DELCI SiC, GRAFITA IN PEPELA MORINGE
Dhanashekar Manickam, Senthil Kumar Velukkudi Santhanam
*
, Karthikeyan Sivagnanam
Anna University, Department of Mechanical Engineering, Chennai 600025, Tamil Nadu, India
Prejem rokopisa – received: 2018-03-09; sprejem za objavo – accepted for publication: 2018-12-20
doi:10.17222/mit.2018.038
An experimental investigation was performed on an LM25 aluminium alloy reinforced with silicon carbide (SiC), graphite (Gr)
and moringa oleifera ash (MOA) particles. The composites with different proportions such as 5 w/% of SiC, 5 w/% of SiC +
1 w/% of Gr, 5 w/% of SiC + 3 w/% of Gr, 5 w/%SiC+1w/% MOA, and 5 w/% of SiC + 3 w/% of MOA were produced with
the stir-casting method. The effects of the reinforcement particles on density, micro-hardness, grain size, porosity, particle
distribution and microstructure were studied. A characterization study was made using optical microscopy (OP) and scanning
electron microscopy (SEM). Based on the hardness and density results, the MOA-reinforced composites had better hardness and
decreased porosity when compared to the Gr-reinforced composites. The MOA particles exhibited a homogeneous distribution
in the matrix whereas the Gr particles had a few cluster formations.
Keywords: LM25 aluminium alloy, moringa oleifera ash, stir casting, mechanical properties
Avtorji opisujejo eksperimentalne raziskave na Al zlitini LM25, oja~ani z delci silicijevega karbida (SiC), grafita (Gr) in pepela
moringe (MOE, angl.: Moringa Oleifera Ash). Kompoziti so vsebovali razli~ne dele`e posameznih delcev, to je: 5 w/% SiC,
5 w/%SiCin1w/% Gr, 5 w/% SiC in 3 w/% Gr, 5 w/% SiC in 1 w/% MOA, 5 w/% SiC in 3 w/% MOA. Kompozite so izdelovali
s tehniko vme{avanja delcev v talino Al zlitine. Avtorji so nato raziskovali vpliv oja~itve (dodanih delcev) na gostoto,
mikrotrdoto, velikost kristalnih zrn, poroznost in ostalo mikrostrukturo zlitine. Analize so izvedli z opti~no (OP) in vrsti~no
elektronsko mikroskopijo (SEM) ter rentgensko strukturno analizo (XRD). Iz rezultatov meritev mikrotrdote in gostote
ugotavljajo, da imajo z MOA oja~ani kompoziti bolj{o trdoto in manj{o poroznost v primerjavi z Gr oja~animi kompoziti. Delci
MOA so enakomerno porazdeljeni v kovinski osnovi zlitine, medtem ko so se delci Gr zdru`evali oziroma tvorili skupke.
Klju~ne besede: zlitina na osnovi aluminija LM25, pepel moringe, postopek litja z vme{avanjem delcev v talino Al zlitine,
mehanske lastnosti
1 INTRODUCTION
Aluminium-based composites with bio-organic parti-
cles as the reinforcement are a topic of interest for the
researchers due to their low costs and improved mecha-
nical properties. To date, researchers have investigated
the effects of various natural wastes used as reinforce-
ment particles such as fly ash,
1,2
rice-husk ash,
3
bean-pod
ash,
4
bamboo-leaf ash, red mud, groundnut-shell ash,
5
melon-shell ash
6
and bagasse ash
7
as the substitutes for
the commercial reinforcement particles for producing
cost-effective and new composite materials. Mazahery
Ali et al.
8
examined the impact of nano-SiC particles
incorporated in the A356 alloy and concluded that SiC
particles enhanced the mechanical properties of compo-
sites. Liang-Jing Fan
1
studied the behaviour of fly-ash
particles in the Al–3Mg melt at 850 °C and various
durations such as (0, 10, 20, 30 and 40) h, and observed
that the Si released from the fly ash and Mg undergoes a
reduction reaction to form the Mg
2
Si phase. During a
longer reaction, porous fly-ash particles decompose
completely and decrease the porosity. Rajan
2
examined
the significance of fine-ash particles in an aluminium
alloy at a very high temperature of 1200 °C; he found
that the fly-ash particles undergo interfacial reactions
with SiO
2
and Al
2
O
3
, yielding the MgAl
2
O
4
phase.
Atuanya
4
utilized the bean-pod ash as the reinforcement
and showed there was a better interparticle bond strength
in an Al–Cu–Mg alloy. Kenneth
5
investigated the effects
of groundnut-shell ash (GSA), rice-husk ash and bam-
boo-leaf ash along with silicon carbide as the rein-
forcement particles in an Al–Mg–Si alloy. GSA com-
posites produced the highest mechanical properties
among the ash particles. Abdulwahab
6
utilized the
melon-shell ash with 5, 10, 15, and 20-% additions using
the vortex method and observed a refined surface and
better particle-matrix interface bond. Mohammed Imran
7
attempted a study with sugarcane bagasse-ash and
graphite particles as the reinforcement in the Al7075
alloy and observed an increase in the hardness with an
increase in the reinforcement. A composite with natural
waste used as the reinforcing particles needs to have the
proper mix ratio to obtain improved properties. In this
experimental study, the stir-casting method was em-
ployed to manufacture particle-reinforced composites. To
the best of the author’s knowledge, moringa oleifera ash
particles have not been used as the reinforcement
Materiali in tehnologije / Materials and technology 53 (2019) 3, 395–398 395
UDK 620.1:669.715:546.281’261 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 53(3)395(2019)
*Corresponding author e-mail:
vssk70@gmail.com (Senthil Kumar Velukkudi Santhanam)

particles with an LM25 alloy. Based on a literature
survey, we can say that meagre information is available
on multiple particles used with the LM25 alloy and the
use of MOA as reinforcement particles. An experimental
investigation was conducted on the LM25 alloy rein-
forced with two different secondary reinforcements, i.e.,
Gr and MOA particles, and a comparative study of their
effects on the physical, microstructural and mechanical
properties of the composite materials was made.
2 EXPERIMENTAL PART
The LM25 alloy was selected as the matrix; its che-
mical composition is specified in Table 1. Silicon car-
bide (SiC), graphite (Gr) and moringa oleifera ash
(MOA) particles were the primary and secondary
reinforcements. Dried moringa oleifera was calcined at
750 °C for 5 h. The ash obtained was mixed with a
2.5 mol NaOH solution and boiled at 75 °C for 3 h with
magnetic stirring. Then the filtered precipitate was dried
andmixedwitha2%HClsolution, refluxing at 75 °C
for 4 h. Finally, the precipitate was collected, cleaned
and dried at 110 °C for 10 h.
4
The synthesized ash
particles were free from impurities and surface treated.
The key elements present in the moringa oleifera ash
were analysed and their values in w/% are shown in
Table 1. The LM25 alloy was melted to 800 °C in an
electric furnace and a hexachloroethane degasser was
used to remove dissolved hydrogen.
9
Particle wettability
in the melt was improved with an inclusion of 1 w/% of
pure Mg. The reinforcement particles were preheated to
250 °C to remove moisture and a chromium-coated
A310 stainless-steel stirrer was added at periodic inter-
vals, stirring the melt at a varying speed of 450–700 min
–1
.
A higher stirring speed caused a homogeneous distri-
bution of the particles
10
and a variation in the speed
helped to limit the particle settlement at the bottom. The
steel die was preheated to 250 °C to maintain a uniform
cooling rate. Specific notations were determined for the
composites such asA–(5w/% SiC),B–(5w/% SiC + 1
w/%MOA),C–(5w/% SiC + 3 w/%MOA),D–(5w/%
S i C+1w/ %G r )a n dE–( 5w/% SiC + 3 w/% Gr).
Density measurements were made using the Archime-
dean principle and comparing the weights of the samples
immersed in air and distilled water.
8
The rule-of-mix-
tures relation, as given in Equations (1, 2), was applied
to calculate the theoretical density and porosity %,
respectively. The hardness was measured using a Vickers
hardness-testing machine operated at a load of 200 gm,
and the average of ten measurements from different
points on a sample was taken. An XRD peak analysis
performed with an X’PERT-PRO X-ray diffractometer
operated at a scanning rate of 0.02 °min
–1
, wavelength of
0.15406 nm, generator setting of 45 kV and 40 mA was
used to study the metallurgical changes. The composites
were mirror polished and etched using Keller’s reagent
prior to optical and SEM examinations.
d
th
= d
m
× V
m
+ d
r1
× V
r1
+ d
r2
× V
r2
(1)
Porosity =
dd
d
th mc
th
−
×100 (%) (2)
Here d
th
,d
mc
,d
m
,d
r1
,d
r2
stand for the theoretical den-
sity, measured density, matrix density, reinforcement 1
density and reinforcement 2 density while V
m
,V
r1
,V
r2
stand for the volume fraction of the matrix, reinforce-
ment 1 and reinforcement 2, respectively.
3 RESULTS AND DISCUSSION
3.1 Density, porosity and Vickers hardness
An addition of moringa oleifera ash particles to the
composites decreases the density but the porosity forma-
tion is minimal when compared to the graphite-mixed
composites. An increase in the addition of Gr particles
leads to an increase in the porosity %, which agrees with
the result of the study by Mishra.
11
From Table 2,itis
clear that the porosity increases as the w/% of graphite
increases owing to the poor wettability and the graphite
particles being clustered near the silicon carbide parti-
cles. On the contrary, the MOA particles exhibit a better
wettability with the matrix; thereby the porosity % is
minimal. From Table 2, it is clear that the hardness de-
creases with an increase in the graphite and MOA
particles. Single-reinforcement composite A exhibits a
higher hardness compared to the ones with dual rein-
forcements. The MOA-reinforced composites have a
higher hardness than the Gr-reinforced ones because of
the formation of the strengthening phase Mg
2
Si and the
microstructural refinement. This grain refinement is
ascribed to the increase in the hardness of the MOA-rein-
forced composites.
3.2 Microstructural characterization
Figure 1 (a–f) shows the microstructures of the
LM25 alloy and composites A, B, C, D and E, respect-
ively, consisting of Al dendrites and eutectic Si. The
microstructure examination reveals the dispersed MOA
particles at the primary  -aluminium grain interface.
Composites B and C show no evidence of a cluster
formation of the MOA particles. The average grain size
D. MANICKAM et al.: EXPERIMENTAL INVESTIGATION OF LM25 ALLOY REINFORCED WITH SiC, Gr ...
396 Materiali in tehnologije / Materials and technology 53 (2019) 3, 395–398
Table 1: Chemical compositions of the LM25 alloy and MOA particles
Elements Cu Si Mg Mn Fe Ti Ni Zn Pb Sn Al
LM25 alloy (w/%) 0.02 6.99 0.48 0.02 0.22 0.18 0.01 0.04 <0.001 0.001 Balance
Elements SiO 2 Al 2O 3 Fe 2O 3 TiO 2 P 2O 5 CaO MgO Na 2OK
2OS O
3
MOA particles (w/%) 1.22 0.024 0.045 <0.001 0.03 0.33 0.24 0.11 1.07 0.19

and circularity were measured using the ImageJ analysis
software
12
and the values are given in Table 2. The
circularity value is high for the MOA-particle-reinforced
composites when compared to the base alloy and the
other composites. The circularity is used to define the
roundness of the grains (cylindrical shape) and a higher
value provides a better strength. The grain shape has an
effect on Young’s modulus due to the difference between
the volume fractions of the grain boundaries with
different grain shapes.
13
Figure 2 (e, f) depicts SEM images of the compo-
sites, displaying the formation of particle clusters for the
graphite-reinforced composites. Figures 2c and 2d show
a better wettability of the MOA particles with the matrix,
which hinders the growth of the secondary dendrite arm
spacing; as a result, finer grains are formed. The MOA
particles act as grain refiners and similar results were
observed by Kanth et al.
14
who studied the effect of fly
ash/SiC particles reinforcing Al-Zn alloy based compo-
sites fabricated with the stir-casting method. As shown in
Equation (3), Si and Mg react to form Mg
2
Si strength-
ening precipitates in the MOA composites, which was
confirmed with an XRD analysis as shown in Figure 3.
The composites reinforced with SiC and Gr particles
favour the formation of a brittle Al
4
C
3
compound accord-
ing to Equations (4, 5), and graphite particles have a
weak interface bonding with the matrix, which ultima-
tely decreases the material properties.
Si + 2Mg  Mg
2
Si (3)
4Al+3C Al
4
C
3
(4)
D. MANICKAM et al.: EXPERIMENTAL INVESTIGATION OF LM25 ALLOY REINFORCED WITH SiC, Gr ...
Materiali in tehnologije / Materials and technology 53 (2019) 3, 395–398 397
Figure 1: Optical microstructures of the stir-cast alloy and composites a) LM25 alloy, b) composite A, c) composite B, d) composite C, e)
composite D, and f) composite E at 500 × mag./25 μm (the insert graph at a magnification of 100 ×/100 μm)
Figure 2: SEM images of the LM25 alloy and composites: a) LM25
alloy, b) composite A, c) composite B, d) composite C, e) composite
D, and f) composite E
Table 2: Density, porosity, micro-hardness, grain size and circularity values for the LM25 alloy and the composites
S. No. Composite
Theoretical
density (g/cm
3
)
Measured density
(g/cm
3
)
Porosity
(%)
Vickers hardness
(Hv)
Average
Grain size in μm
2
Circularity %
1 LM25 alloy 2.66 2.7 0.54 67.5 47.78 0.24
2 A 2.70 2.68 0.71 91 40.3 0.62
3 B 2.45 2.42 1.41 84 35.68 0.66
4 C 2.06 1.99 3.21 77 34.78 0.66
5 D 2.62 2.5 4.41 80.5 48.05 0.57
6 E 2.51 2.32 7.62 71 38.1 0.53

4Al + 3SiC  Al
4
C
3
+ 3Si (5)
Figure 3 shows XRD plots for the prepared compo-
sites and the patterns exhibit a complete particle distri-
bution in the matrix. From the XRD results, it is
observed that the moringa ash particles influenced the
aluminium phase as the peak intensity is reduced and the
overall intensity peaks are reduced in Composites B and
C. The XRD results also confirm that there was no for-
mation of secondary phases. The aluminium peaks for
Composites B and C (with moringa oleifera ash parti-
cles) are shifted to higher 2 values in comparison to the
LM25 alloy. This result is similar to that obtained by
Praveen
15
who fabricated aluminium-matrix composites
with bamboo leaf ash particles.
4 CONCLUSIONS
Moringa oleifera ash reinforced composites enhance
the evolution of Mg
2
Si precipitates and grain refinement.
Graphite reinforced composites contain Al
4
C
3
precipi-
tates, which retard the material properties because of
their brittle nature. The moringa oleifera ash reinforced
composites exhibit a decrease in the porosity % when
compared to the graphite reinforced composites. The po-
rosity of the moringa oleifera ash reinforced composites
was reduced by 81.5 % compared to the graphite rein-
forced composites. Composite A with a single reinforce-
ment shows a higher hardness of 91 Hv, followed by
Composite B with MOA particles. An increase in the se-
condary reinforcement particles decreased the hardness
of the composites.
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D. MANICKAM et al.: EXPERIMENTAL INVESTIGATION OF LM25 ALLOY REINFORCED WITH SiC, Gr ...
398 Materiali in tehnologije / Materials and technology 53 (2019) 3, 395–398
Figure 3: XRD patterns of the LM25 alloy and composites: a) LM25
alloy, b) composite A, c) composite B, d) composite C, e) composite
D, and f) composite E