V. [PADA et al.: INVESTIGATION OF THE MECHANICAL PROPERTIES OF AlSi9Cu3(Fe)/MWCNT NANOCOMPOSITES ...
601–606
INVESTIGATION OF THE MECHANICAL PROPERTIES OF
AlSi9Cu3(Fe)/MWCNT NANOCOMPOSITES PREPARED BY HPDC
RAZISKAVA MEHANSKIH LASTNOSTI AlSi9Cu3(Fe)/MWCNT
NANOKOMPOZITOV, PRIPRAVLJENIH S POSTOPKOM HPDC
Vedrana [pada
1*
, Davor Stani}
2
, Ivan Brnardi}
3
1
METRIS Materials Research Centre of Region of Istria, Zagreba~ka 30, 52100 Pula, Croatia
2
CIMOS, P.P.C. Buzet d.o.o., Most 24, 52420 Buzet, Croatia
3
University of Zagreb, Faculty of Metallurgy, Aleja narodnih heroja 3, 44000 Sisak, Croatia
Prejem rokopisa – received: 2019-01-05; sprejem za objavo – accepted for publication: 2019-03-11
doi:10.17222/mit.2019.006
In this research, an often-used high-pressure die-casting (HPDC) AlSi9Cu3(Fe) alloy was chosen as the matrix for an
Al-alloy/MWCNT nanocomposite material that could be, in the case of targeted mechanical properties, used for the production
of lighter car parts. In the industrial experiment, nanocomposite samples were prepared by a HPDC machine from a base
AlSi9Cu3(Fe) alloy with three different mass ratios of MWCNTs placed on two different positions inside the casting machine.
The structure and thermal stability of the used MWCNTs were visually confirmed by scanning electron microscopy (SEM). The
microstructural and metallographic properties were studied using an optical microscope. The mechanical properties (tensile
strength, elongation at break and hardness) were investigated using a universal testing machine and a Vickers hardness tester.
The experimental results of this research showed that the HPDC-prepared Al-alloy matrix nanocomposite material had
significantly changed mechanical properties even with small MWCNT contents. The elongation at break and the tensile strength
of the Al-alloy/MWCNT nanocomposite were increased in comparison with the base alloy. The finest microstructure was shown
by samples with 0.05 w/% MWCNTs, which was in correlation with the most significant change in the mechanical properties.
Keywords: metal-matrix nanocomposites, AlSi9Cu3(Fe) alloy, multi-walled carbon nanotubes (MWCNT), high-pressure die
casting (HPDC)
Avtorji opisujejo raziskavo izdelave nanokompozitnega materiala s kovinsko osnovo iz zlitine AlSi9Cu3(Fe). Za oja~itveno fazo
so uporabili ve~stenske ogljikove nanocev~ice (MWCNT). Za izdelavo kompozita so uporabili visokotla~no brizganje taline v
kovinsko orodje oz. deljivi model (HPDC). Ta postopek se najbolj pogosto uporablja za izdelavo lahkih avtomobilskih delov s
specifi~nimi mehanskimi lastnostmi. Izvajali so industrijske preizkuse na HPDC stroju in pri tem uporabili kovinsko talino
AlSi9Cu3(Fe) s tremi razli~nimi dodatki MWCNT, ki so jih postavili na dve razli~ni mesti v votlini orodja. Strukturno in
termi~no stabilnost uporabljenih MWCNT so potrdili s preiskavo ulitkov pod vrsti~nim elektronskim mikroskopom (SEM).
Nadalje so izvedli {e metalografske preiskave mikrostrukture pod opti~nim mikroskopom. Mehanske lastnosti izdelanih
materialov, natezno trdnost in raztezek po prelomu, so dolo~ili na univerzalnem trgalnem stroju, medtem ko so trdoto dolo~ili na
standardnem Vickersovem merilniku. Eksperimentalni rezultati te preiskave so pokazali, da so se mehanske lastnosti s
postopkom HPDC izdelanega nanokompozita na osnovi Al zlitine znatno spremenile `e pri dodatku dokaj malih koli~in
MWCNT. Natezna trdnost in raztezek po prelomu nanokompozita MWCNT/Al-zlitina sta v primerjavi z osnovno Al zlitino
narasla. Najbolj drobnozrnato mikrostrukturo so imeli vzorci z dodatkom 0,05 masnih dele`ev MWCNT, kar se je ujemalo z
najve~jo spremembo mehanskih lastnosti.
Klju~ne besede: nanokompoziti s kovinsko osnovo, zlitina AlSi9Cu3(Fe), ve~stenske ogljikove nanocev~ice (MWCNT),
visokotla~no litje v kovinsko orodje (HPDC)
1 INTRODUCTION
Modern material research is more and more dedica-
ted to nanocomposites with polymer and metal matrixes
because of their great potential to reduce fuel consump-
tion and carbon dioxide (CO
2
) emissions through lighter
parts and a reduction of the total car weight. Recent
investigations showed that carbon nanotubes (CNTs),
especially multi-walled carbon nanotubes (MWCNTs),
could be used as nanofillers for strengthening light metal
Al-alloy matrix composites because of their high
strength, low mass, great active surface, and good
thermo-mechanical stability. Such nanocomposites
produced by different industrial procedures showed a
significant improvement in mechanical properties
compared to a clean matrix, even with a small mass ratio
of added nanotubes.
Modern research in the field of material science and
the development of new materials for different uses is
devoted to the preparation and characterization of nano-
composites based on polymer and metal matrixes with
fillers.
1–23
Nanofillers have an important role as they
improved the chemical, physical and mechanical pro-
perties of the nanocomposites, which could then replace
commonly used materials for a wide spectra of industrial
applications, and also products made from that new
material could be reduced in mass and/or thinner, which
is an absolute "must" nowadays. One of the most com-
monly used and investigated nanofillers for composite
materials are carbon nanotubes (CNTs) because of their
Materiali in tehnologije / Materials and technology 53 (2019) 4, 601–606 601
UDK 620.1:67.017:620.3 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 53(4)601(2019)
*Corresponding author's e-mail:
vedrana.spada@centarmetris.hr

high Young’s modulus,
24
which often results in an im-
provement of the nanocomposite’s mechanical properties
compared to the pure matrix. For the preparation of
metal matrix nanocomposites, multi-walled carbon
nanotubes (MWCNTs) were used because of their lower
price and industrial scale availability.
25–29
The literature shows that in modern scientific
research, polymer-matrix nanocomposites still dominate
over metal-matrix nanocomposites.
1–5
The reason for this
situation in material science can be found in the high
melting temperature of metals, which destructively
effects CNTs through thermal degradation. Also, there
were problems with how to introduce, mix and homo-
geneously disperse CNTs in a metal matrix, which most
certainly had a crucial influence on the final mechanical
properties of the produced nanocomposites. The
approach in this industrial research was directed to
producing light metal-matrix nanocomposite material
from an AlSi9Cu3(Fe) alloy with MWCNTs, avoiding
the thermal degradation of nanofillers and overcoming
the inhomogeneous distribution, followed by better
mechanical properties than the matrix itself. Usually,
agglomeration caused the formation of micro-aggregates
in metal matrix nanocomposites, i.e., "weak spots", re-
sulting in losing the CNT strengthening potential. Some
researchers solved these problems with different
approaches and methods for nanocomposite preparation.
Li et al. prepared Al-5 % CNT reinforced light metal
composites produced by melt stirring.
6
Uozumi et al.
used a squeeze casting fabrication process for carbon
nanotube/light metal matrix composites.
7
Laha et al. pro-
duced carbon nanotube reinforced aluminium nanocom-
posite via plasma and high-velocity oxy-fuel spray
forming.
8
Hao et al. studied the effect of mechanical
alloying time and rotation speed on the evolution of
CNTs/Al-2024 composite powders.
9
The aim of this work was to prepare nanocomposite
material with a commonly used alloy and an important
industrial production method. The high-pressure die
casting (HPDC) of Al car parts production is very often
used in the automotive sector, so it became of great im-
portance to successfully prepare Al-alloy nanocomposite
material of smaller weight, but better mechanical pro-
perties, by using exactly that process and also optimizing
it along the way (matrix, nanofillers, and MWCNT con-
tent, parameters of casting).
In this industrial experiment, nanocomposites from
the AlSi9Cu3(Fe) alloy and multi-walled carbon nano-
tubes (MWCNTs), with varying mass ratios, were
prepared using a high-pressure die casting (HPDC)
process. Samples were prepared in two different ways,
placing three mass ratios of MWCNTs in two different
positions of the HPDC machine. The stability and the in-
fluence of MWCNT (w/% and position) on the mecha-
nical properties and microstructure of the nanocom-
posites and base alloy were investigated.
2 EXPERIMENTAL PART
The nanofillers were obtained from Chengdu Organic
Chem. Co. The characteristics of the industrial
MWCNTs were: outside diameter from 5 nm to 30 nm,
purity >95 % and length from 10 μm to 30 μm. The
morphology and diameter of the used MWCNTs were
determined by a secondary-electron detector of a
field-emission scanning electron microscope (FE-SEM)
at different magnifications (Figure 1).
The base alloy AlSi9Cu3(Fe) for car parts production
in the Croatian metallurgy and foundry company CIMOS
– P.P.C. Buzet Ltd. was used as the metal matrix. The
chemical composition of the used alloy in the industrial
experiment obtained by optical emission spectrometer
with a glow discharged source LECO 500A (OES-GDS)
was compared with the required chemical composition
according to the norm EN 1706
29
and showed no
deviations.
The nanocomposite samples were prepared on a
Buhler 42D HPDC machine (Figure 2) at a temperature
of 690 °C, a pressure of 800 bar, by 58 s cycles in a
specially designed tool containing six samples with
different diameters and 0.950 kg of total weight.
V. [PADA et al.: INVESTIGATION OF THE MECHANICAL PROPERTIES OF AlSi9Cu3(Fe)/MWCNT NANOCOMPOSITES ...
602 Materiali in tehnologije / Materials and technology 53 (2019) 4, 601–606
Figure 1: SEM images of MWCNTs with diameter marks at a) 100 k×;
b) 200 k× magnification

The weight of the MWCNTs was measured to
prepare the nanocomposites with three different mass
ratios of 0.05 %, 0.1 % and 0.2 % by wrapping the exact
mass in commercially available aluminium foil. The
nanocomposite samples were prepared in two different
ways: firstly by placing the wrapped MWCNTs in the
chamber in front of the piston (position 1), and secondly
by putting the wrapped MWCNTs at the beginning of the
casting cavity (position 2) for exact shape casting
formation. Also, reference samples from the base alloy
were also cast for comparison. The melted alloy was
poured into the chamber and then pushed into the tool by
the piston. When the tool opened, the casted samples
were cooled in the air, marked and separated for
subsequent tests (Figure 3).
Every sample was cast five times with an exact
procedure and was named as proposed: R (reference
sample – base alloy), C1-0.05, C1-0.1, C1-0.2, C2-0.05,
C2-0.1 and C2-0.2 (composite CX-Y, X stands for the
position of the wrapped MWCNTs adding 1 in front of
piston, 2 at the beginning of the casting cavity and Y
stand for w/% of MWCNT).
Mechanical measurements (elongation at break and
tensile strength) were performed on a Messphysik BETA
250 testing machine, in the uniaxial tension mode at
25 °C. At least three specimens were tested for the
sample, according to the HRN EN ISO 6892-1 standard.
The hardness was also tested using a Vickers Duramin 2
device at HV1. The stability and existence of the
MWCNTs and the microstructure of the fractured
surfaces after the mechanical testing were analyzed with
a scanning electron microscope (SEM) in the form of a
FEG SEM Quanta 250 FEI microscope. The metallo-
graphic investigations were conducted with an optical
metallographic microscope BX51 OLYMPUS. Prior to
the analysis the samples were metallographically
polished and etched with Keller’s etchant for 15 s. All
the experiments were performed on casted samples with
an 6.4 mm diameter.
3 RESULTS AND DISCUSSION
The results of the tensile testing and the hardness of
the prepared nanocomposites were summarized in Table
1. Three of the five tested samples were chosen based on
deviations.
Table 1: Mechanical properties of the base Al alloy and the Al alloy
with different contents of MWCNTs
Samples
Elongation
(%)
Ultimate tensile
strength (MPa)
Hardness
(HV1)
R 1.93±0.12 263.2±2.9 95.1±2.2
C1-0.05 2.50±0.16 274.7±2.9 93.3±3.1
C1-0.1 2.24±0.20 262.1±3.7 89.0±4.8
C1-0.2 2.28±0.51 271.9±4.8 88.5±3.4
C2-0.05 2.36±0.16 273.6±3.8 89.1±2.0
C2-0.1 2.46±0.15 273.1±10.9 88.8±4.1
C2-0.2 2.57±0.25 251.4±7.0 94.3±5.9
The nanocomposite samples prepared with 0.05 w/%
of MWCNTs, placing them at position 1 (in front of the
piston) in the HPDC machine, showed the best results
regarding improving the mechanical properties of the
base alloy: breaking elongation by  30 % and tensile
strength by  4.4 %.
The results for the nanocomposites prepared by
adding MWCNT at the position 2 in the HPDC machine
(C2) showed a larger discrepancy. The hardness was
slightly different in the prepared nanocomposites
compared to the base alloy.
Furthermore, some samples prepared at position 2
showed micro- and macro-agglomerates of MWCNTs on
the fracture surface, which can be correlated to the short
period for the melting of the wrapped foil with the hot
base alloy, resulting in a non-homogenous distribution,
which is in correlation with a larger discrepancy of the
mechanical results that can be seen in Table 1.
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Materiali in tehnologije / Materials and technology 53 (2019) 4, 601–606 603
Figure 2: Buhler 42D HPDC machine
Figure 3: Nanocomposite samples as casted

Figure 4 shows the micro (C2-0.1-SEM image) and
macro (C2-0.2-photo image) agglomerates in the
samples achieved using position 2, which visually
explained the poorer mechanical results of the position 2
prepared nanocomposites shown in Table 1.
Thermal degradation of the MWCNTs did not occur
in all the prepared AlSi9Cu3(Fe)/MWCNT nanocompo-
sites, which was confirmed by the SEM analysis (Figure
4a). Therefore, the HPDC method for introducing the
MWCNT in the metal matrix can be used and the
MWCNT are well-chosen nanofillers for HPDC. In
addition, the low discrepancy of the results of the me-
chanical properties shown in Table 1 could mean the
homogenous distribution of the MWCNTs in the metal
matrix at position 1 for 0.05 w/% (best mechanical
results) is also in correlation with the SEM secondary-
electron detector images of the fracture surface of the
C1-0.05 sample in Figures 5a and 5b.
The influence of the MWCNTs on the microstructure
of the base Al-alloy was examined under an optical
microscope. Figure 6 shows the microstructure of the a)
base alloy and b-e) nanocomposite samples with 0.05
w/% and 0.1 w/% of added MWCNTs in positions 1 and
2. The samples with 0.2 w/% were obviously inhomo-
geneous and also without an improvement of the mecha-
nical properties, so they were not metallographically
investigated. As can be seen, the microstructure, as
expected, changed under the influence of the MWCNTs
and the prepared Al-nanocomposites had a finer-grained
structure of the primary Al grains than the base alloy,
which is in correlation with the better mechanical
properties.
19–21
The finest microstructure of the primary
Al grains is, as expected, found in the 0.05 position 1
samples (Figure 6b), where the Al grains are smaller
than the base alloy and the grain boundaries are fine
distributed and clear. Also observed is the correlation
with the improvement of the mechanical properties.
Other nanocomposites, even position 1 (w = 0.01 %)
(Figure 6d), showed some black areas on the grain
boundaries and nevertheless presented MWCNTs
between the finer Al grains than in the base alloy.
Regarding all the results, position 1 with 0.05 w/%
MWCNT content was the best for the preparation of
homogenous Al-alloy/MWCNT nanocomposite samples
with HPDC. Such properties could result in thinner and
smaller dimensions of different car parts that could
reduce the total car weight, the consumption of raw ma-
terials and energy in the production process. Success in
this research means a great step forward in the deve-
lopment of nanocomposite materials for a wide spectrum
of applications and specifically follows trends of more
and more strict standards in the automotive sector, along
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604 Materiali in tehnologije / Materials and technology 53 (2019) 4, 601–606
Figure 5: SEM images of sample C1 – 0.05 fracture surface (Al-alloy
and MWCNT) showing MWCNTs at a magnification of: a) 30 k×, b)
120 k×
Figure 4: a) SEM image of MWCNTs agglomerated in the C2-0.1
sample, b) photograph of easily visible agglomerate in the mechani-
cally poor C2-0.2 sample

with conditions of reducing the CO
2
footprint already in
the parts production by developing materials that
decrease the vehicle’s weight and fuel consumption.
We can assume that the process of adding MWCNTs
to the base alloy for HPDC needs some improvement. In
an aim to overcome the agglomeration and the non-
homogenous distribution, future research will focus on
finding new ways of introducing MWCNTs into the Al
matrix, for example, adding MWCNTs in the pre-furnace
of the HPDC machine with mechanical mixing under an
inert atmosphere and the addition of alloying elements
for an improvement of the interphase wetting.
4 CONCLUSIONS
MWCNTs were used as fillers for the preparation of
nanocomposites based on an AlSi9Cu3(Fe) matrix
(3 different MWCNT contents and 2 different positions
of adding). The SEM analysis visually confirmed the
thermal stability of the MWCNTs in the Al-matrix
nanocomposite samples prepared by the HPDC method.
Experimental testing showed increased mechanical
properties, especially for nanocomposites with 0.05 w/%
MWCNT (position 1): elongation at break by 30 % and
tensile strength by 4.4 %. The homogenous distribution
of the MWCNTs for the best C1-0.05 sample was also
confirmed by the low discrepancy of the mechanical
results and the SEM imaging at a magnification of 30k ×.
The finest microstructure (smaller size of Al primary
grains) also showed samples with 0.05 w/% MWCNT at
position 1 (in front of the piston in the HPDC machine),
which is in correlation with the largest improvement in
the mechanical properties.
Altogether, the main reason for some of the observed
inhomogeneous results in the nanocomposite samples
can be found in the agglomeration of the MWCNTs
caused by a small surface activity between the MWCNTs
and the base alloy, which should be overcome, probably
V. [PADA et al.: INVESTIGATION OF THE MECHANICAL PROPERTIES OF AlSi9Cu3(Fe)/MWCNT NANOCOMPOSITES ...
Materiali in tehnologije / Materials and technology 53 (2019) 4, 601–606 605
Figure 6: Micrographs of the a) base alloy, and b-e) nanocomposites samples

by active alloying elements and mixing under an inert
atmosphere.
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