Wear behavior of al cma-type al3 mg2nanocomposites fabricated by mechanical milling and hot extrusion

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Wear Behavior of Al/CMA-type Al3Mg2Nanocomposites
Fabricated by Mechanical Milling and Hot Extrusion
H. Ramezanalizadeh
a
, M. Emamy
a
& M. Shokouhimehr
b
a
School of Metallurgy and Materials Engineering, College of Engineering, University of
Tehran, Tehran, Iran
b
School of Chemical and Biological Engineering, College of Engineering, Seoul National
University, Seoul, Korea
Accepted author version posted online: 01 Jun 2015.
To cite this article: H. Ramezanalizadeh, M. Emamy & M. Shokouhimehr (2015): Wear Behavior of Al/CMA-
type Al3Mg2Nanocomposites Fabricated by Mechanical Milling and Hot Extrusion, Tribology Transactions, DOI:
10.1080/10402004.2015.1050138
To link to this article: http://dx.doi.org/10.1080/10402004.2015.1050138
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Wear Behavior of Al/CMA-type Al3Mg2 Nanocomposites Fabricated by Mechanical
Milling and Hot Extrusion
H. Ramezanalizadeha*
, M. Emamya
and M. Shokouhimehrb
a
School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran,
Tehran, Iran.
b
School of Chemical and Biological Engineering, College of Engineering, Seoul National
University, Seoul, Korea.
*
Email: hralizadeh@ut.ac.ir
Abstract: In current research the wear behavior of an aluminum matrix nanocomposite material
prepared via mechanical milling and hot extrusion was investigated. The sample powders were
milled at different milling times up to 15 h to produce nanostructure powders. Mechanical
milling was used to prepare nanocomposite samples by the addition of 10 wt% of Al3Mg2
nanoparticles into the Al matrix. A pin-on-disk setup was used to evaluate the wear properties of
the hot extruded samples under dry condition. Hardness values were used for further explanation
of the observed results. Scanning electron microscopy (SEM) equipped with EDS analyzer was
used to analyze the worn surfaces. The results revealed a lower friction coefficient and a lower
wear rate for the unmilled nanocomposite sample in contrast to a commercial pure Al one. The
same pattern was also observed in the milled nanocomposite samples with respect to the base
matrix.
Keywords: Al metal matrix nanocomposite, Mechanical milling, CMA-type Al3Mg2, Extrusion,
Wear.
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Introduction
Due to higher mechanical performance of Al matrix composites reinforced with hard second
particles in comparison to the unreinforced Al alloys, many studies have recently been
concentrated on the study of the mechanical and wear properties of such materials (Kimura (1);
Raghumatham, et al. (2)). Due to their higher strength to density ratio and better wear
performance, these metal matrix composites (MMCs) are used as tribological parts in automotive
industry (Shibata, et al. (3); Chellman, et al. (4); Chawla, et al. (5)). This is primarily due to the
fact that hard second phases make the matrix alloy plastically constrained and improve the high
temperature strength of the base virgin alloy (Rohatgi, (6)). In addition, these second phases
prevent the matrix from severe contact with the counter surfaces (Sannino, et al. (7); Sharma, (8),
which in turn enhances the wear performance of the subjected composite with respect to the base
alloy (Jiang, et al. (9); How, et al. (10)).
Different types of materials, ranging from the typical ceramics, such as Al2O3 and SiC (Kainer,
(11); Slipenyuk, et al. (12); Tan, et al. (13)), to more unconventional types, such as metallic
glasses (Yu, et al. (14); Lee, et al. (15); Scudino, et al. (16); Scudino, et al. (17)) and
quasicrystals (Schurack, et al. (18); El Kabir, et al. (19); Tang, et al. (20)), have been
successfully used as reinforcing in MMCs. Other possible candidates as reinforcing agents in
MMCs are complex metallic alloys (CMAs), intermetallic compounds with giant unit cells,
comprising up to more than a thousand atoms per unit cell (Urban, et al. (21)). In particular,
CMAs display several attractive properties for reinforcement applications, such as high strength
to weight ratio, good oxidation resistance and high-temperature strength (Feuerbacher, et al.
(22); Demange, et al. (23); Roitsch, et al. (24); Heggen, et al. (25)). Among the different CMAs,
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the β-Al3Mg2 phase (with 1168 atoms per unit cell) (Feuerbacher, et al. (22)) has been
investigated with particular attention to its structure as well as to its physical and mechanical
properties (Feuerbacher, et al. (22); Roitsch, et al. (24); Dolinsek, et al. (26); Bauer, et al. (27)).
The attractive properties such as low specific gravity of 2.25 g/cm3
(Feuerbacher, et al. (22))
(less than that of Al, 2.7 g/cm3
), high hardness and wear resistance (Achanta, et al. (28)), high-
temperature strength (~300 MPa at 573 K (Roitsch, et al. (24))), and high capacity for hydrogen
absorption (Fernandez, et al. (29)), make Al3Mg2 a likely candidate as a reinforcing in an Al
matrix composite.
Although, numerous studies have been conducted on the wear and friction characteristics of
ceramic particle–reinforced nanocomposites (Pradhan, et al. (30); (Lee (31); McElwain, et al.
(32); Eckels, et al. (33); Zhang, et al. (34); Beckford, et al. (35)), the literature data on
tribological properties of metal matrix nanocomposites (MMNCs) reinforced with CMAs-type
second phase are scarce (Achanta, et al. (28)). Due to their unique electronic structure, the
surface energy of complex metallic alloys is lower than the ones of metallic elements
constituting these alloys. A low surface energy means a low wetting tendency by polar liquids,
and a low friction that makes them suitable as the materials in tribological applications.
Nowadays, large efforts have been made to produce nanocrystalline materials for their superior
physical and mechanical properties as compared to their coarse grained counterparts (De Castro,
et al. (36)); Keblinski, et al. (37); Suryanarayana (38)). A powerful tool for composite fabrication
with the mentioned properties is mechanical alloying/milling (MA/MM). The MA/MM process,
using ball-milling techniques, has received much attention for the fabrication of several
advanced materials including equilibrium, nonequilibrium (e.g. amorphous, quasicrystals,
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nanocrystalline), and composite materials (Ramezanalizadeh, et al. (39). Also, MA/MM has
produced notable improvements in the strength, toughness, fatigue life, and corrosion resistance
of aluminum alloys (Suryanarayana (40)).
Although numerous studies have been conducted on the mechanical behavior of nanocrystalline
metals by standard hardness, compression or tension tests, mechanisms of friction and wear
properties have received less attention, perhaps due to the difficulties in production of bulk
nanocomposite samples to be suitable for the friction and wear tests (Kong, et al. (41)).
Previous studies have revealed that embedding of nanoparticles in a metal matrix has great
influence on the tribological performance of the metal matrix composites (MMCs) (Du, et al.
(42); Dao, et al. (43)). The amount of results in the respected field is still unsatisfying. Also there
are only a few studies for milling time effect on the wear properties of these materials.
Thus, the current study focuses on the tribological properties and wear performance of Al/10 wt.
% Al3Mg2 nanocomposites, produced via mechanical milling and hot extrusion processes. For
this, effect of Al3Mg2 nanoparticles and also milling time were investigated. For comparison, a
coarse grained Al matrix was used for better understanding of the wear and tribological
properties.
Experimental
In this study, pure Al and Mg metals (>99.9%) were used for melting in a well atmosphere
controlled furnace to prepare Al3Mg2 ingots. Then powders of Al3Mg2 were fabricated by
mechanical milling of the broken ingot using an attrition ball mill with rotation speed of 400 rpm
and ball to powder weight ratio of 12:1. The vial and balls were made of hardened chromium
steel. In all experiments stearic acid (2 wt. %) was also added to the powder mixture as a process
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control agent (PCA). The milling operation was pursued in pure argon atmosphere (99.999%) to
avoid the oxidation of the materials. Al powder, (63 μm, >99.9%), blended with 10 wt. % of β-
Al3Mg2 powders were synthesized through mechanical milling technique. Table 1 shows the
material compositions and milling conditions for this study. The phase compositions of milled
powders were investigated by X-ray diffraction analysis (XRD) using a „„Philips PW 1730‟‟ X-
ray diffractometer with CuKα filtered radiation and 2 deg/min scanning rate.
XRD data was also used to determine the crystallite size (D) and lattice strain (). The crystallite
size was determined from the broadening (B) of the diffraction lines 1 1 1, 2 0 0, 2 2 0 and 3 1 1
using following Scherrer equation (Scherrer (44); Sivasankaran, et al. (45)):
[1]
The lattice strain (ε) was also calculated for the same diffraction lines from the following
equation (Sivasankaran, et al. (45)):
ε = B/4tan θ [2]
where, � is wave length = 1.54059 Å (CuK� radiation), B is the full width at half maximum in
radians and θ is the Bragg angle.
Grain structure of the milled powder was investigated by utilizing transmission electron
microscopy (TEM, JEOL JEM-3010) operated at 200 kV. The mechanically milled powders
were then cold pressed, vacuum sintered and finally hot extruded with an extrusion ratio of 6:1.
The final product consisted of cylindrical bars with 12 mm in diameter. The reference Al sample,
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for comparison results, was prepared from the unmilled Al powder by the same cold pressing,
vacuum sintering and hot extrusion procedure.
Microhardness was measured using a microhardness tester with a Vickers indenter under a load
of 100 mN for 10s. An average of 30 indentations was considered as the Vickers microhardness
value.
The relative density and porosity of extruded bodies were measured by Archimedes method
according to ASTM: B962-13. Theoretical density of compacts was calculated using the simple
rule of mixtures, considering the fully dense values of aluminum and Al3Mg2. Dry sliding wear
properties of the prepared samples were examined using a pin-on-disk setup according to the
ASTM G99-05. The samples were used as pins of 10 mm diameter and 10 mm length produced
from as-extruded rods. The contact surfaces were ground using 800-grit SiC paper and cleaned
with alcohol. An AISI-O1 oil hardened tool-steel disc (63 HRC) was used as the counter face in
the pin-on-disk setup. The roughness of the counterface was 0.1 μm.
All the wear tests were conducted at room temperature with a rotational speed of the disk of 200
rpm under the applied load, respectively; of 10, 20, and 30 N. The radius of wear track and the
actual sliding speed were 13 mm and 0.27 m/s, respectively.
Sliding distance was set to 1000 m under lubricated condition. The samples were weighted after
each sliding distance of 250 m and, subsequently, the amount of mass loss was calculated at the
respected sliding distance, which was then converted into volume loss. For this reason, an
analytical balance with the precision of 0.0001 g was used.
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Wear rate is reported as the volume loss divided by the wear distance. Wear behavior of the
subjected samples was studied as a function of sliding distance and applied load. SEM and EDS
analyses were used to evaluate both the resulted wear surfaces.
Results and Discussion
Microstructural Observations
Fig. 1 shows the TEM micrograph of the mechanical milled composite powder of Al–10 wt%
Al3Mg2 for 15 h. As shown, Al3Mg2 particles are embedded in the ductile Al matrix due to
mechanical milling. EDX results are also provided which confirm the presence of Al matrix
reinforced with Al3Mg2 particles.
Fig. 2 shows the back-scattered electron SEM micrographs of the extruded composites as
unmilled and milled for 15 h. These images display the microstructure consisting of dark areas
(the β-Al3Mg2 CMA reinforcement) dispersed in the Al matrix (the gray regions). As shown in
Fig. 2a, some clustering and agglomerates of Al3Mg2 is observed in AC10-UM sample. The
distribution of β-Al3Mg2 particles become more homogenously and the distance between them
reduces with increasing milling time (Fig. 2b). Only few pores are visible, further corroborating
the high density of the consolidated specimens.
It is well known that, the first requirement for superior performance of a composite material is
the homogeneous distribution of the reinforcing phase. In particulate-reinforced composites; any
agglomeration of the reinforcement particles deteriorates the mechanical properties. Differences
in particle size, densities, geometries, flow or the development of an electrical charge during
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mixing all contribute to particle agglomeration. A decrease of the reinforcing particle size brings
about an increase in the mechanical strength of the composite, but the tendency of particle
clustering also increases (Fig. 2a) (Fogagnolo, et al. (46)). In powder metallurgy, the matrix and
reinforcement mixing process is the critical step towards a homogeneous distribution of
reinforcement particles throughout the matrix. One of the methods that can be used to achieve
homogeneity of particle distribution throughout the matrix and also reduce their size during the
process is MA (Fig. 2b) (Suryanarayana (40)). Also, in MMCs, hot extrusion tends to eliminate
the clustering of reinforcement particles and therefore a better distribution through the metal
matrix (Lu, et al. (47)). So, as both MA and hot extrusion processes were used in the present
study, the final distribution of Al3Mg2 nanoparticle would be uniform (Fig. 2b).
Relative density and porosity
The effect of milling time of composite powders on relative density and porosity of the extruded
samples is shown in Table 2. As expected, the theoretical density of AC10 MMC (2.655 g/cm3
)
is lower than that of Al density (2.7 g/cm3
). The relative density of the extruded samples
increases with increasing milling time. This increasing in density is high probably due to the
large surface area of the fine particles, which induces high reactivity, i.e., particles with small
mean size values are easily densified as bigger particles under the same compaction conditions.
Increasing the density with increasing the milling time has also been reported in several works
(Kwon, et al (48); Linn, et al. (49)).
On the other hand, it is believed that extrusion can decrease the number of pores and improve the
density of composite materials. In general, the presence of oxide layers on the surface of the
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aluminum powders can substantially degrade the solid-phase-sintering ability as a diffusion
barrier (note that it is solid phase-sintering at 448 o
C in the present study). Flumerfelt (50)
indicated that external applied stress can break up the oxide layer, and thus improve the solid-
phase-sintering ability and decrease the volume fraction of the pores.
Microhardness measurements
The microhardness values of the materials in this study are presented in Fig. 3. As shown in Fig.
3, hardness markedly increases with the addition of second hard particles as a combined effect of
load share between the matrix and reinforcing phase (due to their high module, reinforcement
particles can withstand higher amount of stress before they start deforming plastically, helping
the softer metallic matrix) and their effect on flow obstruction of dislocation during deformation,
acting like micro barriers. Given that the hardness of Al3Mg2 is much more than that of
aluminum, increase of hardness as a result of Al3Mg2 is not unexpected. This could also be
analyzed simply based on mixture rule (Rahimian, et al. (51)). Therefore, it is clear that hardness
of unmilled Al/Al3Mg2 sample is more than pure Al sample. Hardness increasing as a result of
reinforcing particles addition is attributed to dispersion strengthening. Because the addition of
Al3Mg2 to aluminum matrix increases the number of barriers across dislocations movement (their
movement delay), as a result hardness increases.
This hardness improvement varies as a function of preparation conditions reaching a maximum
for AC10-15HM. It means that increasing the milling time will increase the composite hardness,
which its main reason, according to Hall–Petch relationship, is microstructural refinement during
mechanical milling:
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H = H0 + KHP/√D [3]
where, H0 is the hardness of annealed coarse grained sample, D is grain size and KHP is a Hall-
Petch constant number (Rahimian, et al. (51); Razavi Tousi, et al. (52)).
The profound high hardness of composite powders produced by the mechanical milling method
may be due to work-hardening effect of the milling operation, the effect of reinforcing phase
(Fogagnolo, et al. (46); Zhang, et al. (53)) and nano-structured alloy with higher dissolved
alloying element, much higher than the equilibrium content (Wang, et al. (54)).
According to Fig. 3, rate of microhardness increasing at lower milling time is more than the
longer milling times. In other word the ΔHV/hour of milling is about 15-16 HV/hr of milling
near 2 hours of milling but becomes nearly constant and remain close to 6-7 HV/hr of milling at
higher milling times. The hardness increment is caused by the increase of the dislocation density
as well as the crystallite refinement, Fig. 3 (Fogagnolo, et al. (55)). Slower rate in microhardness
increasing at longer milling time may be attributed to the completion of milling and dynamic
recovery due to high work hardening effects of deformed Al powders. It may be even ascribed to
static recovery of high deformed Al matrix with local increase of temperature in particles during
collisions.
Friction Coefficient
Fig. 4a and Fig. 4b shows the variation of friction coefficient (FC) and average FC as a function
of sliding distance (under applied of 10 N) and normal loads, respectively, for the subjected
samples. As seen, the value of average FC for the AC10-UM is smaller than that of the
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unreinforced Al sample. As shown in Fig. 4, similar trend also exists for the milled
nanocomposite samples in contrast to the unmilled sample. It is seen that the increase in the
milling time decreases the value of FC for the nanocomposite samples. These observations reveal
the positive effect of Al3Mg2 incorporation and milling time on the friction properties of the
respected samples, the later is more effective which can be attributed to the specific
characteristics of the mechanically milled nanocomposites, namely clean interface (free of
reaction products at the interface between the matrix and reinforcement, Fig. 5), and improved
dispersion of the nanoparticles. Thakur, et al. (56) reported that proper dispersion of the
dispersoids beside stronger and cleaner matrix/reinforcement interface reduces the value of FC.
Wear Behavior
By considering the significant influence of high energy milling and incorporation of Al3Mg2
nanoparticles on the hardness value and subsequently the wear rate, the wear rate of samples was
investigated. As result of the deformation induced by the milling process, refinement of Al grains
occurred and thus the internal lattice strain increased. Fig. 6 shows the grain size and lattice
strain of the tested samples obtained using broadening of XRD peaks, indicating that the crystal
size decreases with increasing milling time, according to the Eq. [4] (Suryanarayana (40)):
D = Kt -2
[4]
Where D is the grain size (nm), K is a constant and t is the milling time (s).
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The results showed that the effect of milling process on the refinement of Al grains is more
significant at the presence of Al3Mg2 nanoparticles. Similar results were found by Prabhu, et al.
(57) for Al-Al2O3 nanocomposite powders prepared via high energy milling.
Different factors such as uniform distribution, fine grain size of both matrix and reinforcement
and strong interfacial bonding can greatly improve the hardness of the mechanically milled
composites. Confirmation to this, one can mention to the results obtained by Durai, et al. (58)
and Rao, et al. (59).
The wear rates of unreinforced Al, unmilled nanocomposite and milled nanocomposite samples
at different times with the content of 10 wt% of Al3Mg2, respectively, are shown in Fig. 7a.
As can be seen, the wear rate of the unreinforced Al sample is not higher than that of the
unmilled nanocomposite sample. It also does not change with the increase in the milling time up
to 2 h. An interesting point is that increasing the milling time to 15 h decreases the wear rate
vigorously. This can be attributed to the high hardness and also the strong interfacial bond
between the Al3Mg2 and Al matrix in 15 h milled nanocomposite in comparison to other
samples, which in turn improves the load transfer from the matrix to the hard particles. In these
circumstances, it could be mentioned that pure Al sample experiences a severe wear. Grain
refinement of aluminum and adding Al3Mg2 have positive effects on the wear behavior, so that
unlike pure aluminum, under a load of 10 N, severe wear does not occur.
As shown in Fig. 7a, the wear rate of AC10-UM sample under a load of 10 N is almost the same
as pure Al sample. By milling the composite to 2 and also 15 h, its wear rate, comparing to pure
aluminum decreases 8.08 %, and 38.42 %. So, it can be concluded that mechanical milling is
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more effective than just adding the second phase to the matrix on reducing wear rate. That is due
to grain refinement and hardness increment. The well known Archard equation (Archard (60))
describes the influence of hardness on the wear rate:
Q = KW/H [5]
where Q equals to wear rate, W is the applied force, H equals to hardness of worn material and K
is the wear coefficient. According to the above relation, the higher the hardness is in worn
surface, the lower the wear is in material. As mentioned before, mechanical milling process
decreases the grain size and increases the hardness. According to the Archard law, wear rate has
reverse relationship with material hardness (Hutching (61)), therefore, increase of the AC10
sample hardness decreases the wear rate, as a result of grain refinement. Studies conducted on
wear behavior of metal based composites show that the presence of reinforcement particles
increases the hardness and therefore improve the wear resistance. Moreover, reinforcement
particles reduce the tendency of adhesive bonding to the counterface (Sirinivasan, et al. (62)).
Figure 7b shows the influence of the applied load on the wear rate of the respected samples. For
all samples, the wear rate does not change significantly with an increase in the applied load. This
observation that wear rate (expressed as wear volume per sliding distance) does not vary with
normal load is more interesting, and thus contradicts Archard law that would describe it not only
increasing weakly but instead increasing in proportion to normal load.
Wear Mechanisms
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Fig. 8a shows the SEM micrographs of worn surface of pure Al sample after being worn under a
load of 10 N. As it is clear, the worn surface of aluminum consists of large delaminated area
along abrasion region. Delaminating wear is the state in which, the wear particle shape is likely
to be thin flake-like sheets and that the surface layer undergoes large plastic deformation. It also
predicts the number of observed phenomena. For instance the differences of experimentally
fretting wear rate on displacement amplitude are predictable (Suh (63)).
The results of EDS line scan analysis of this sample‟s surface from abrasive to delaminated areas
are shown in Fig. 8b. Presence of a considerable amount of oxygen and iron in chemical
composition of these areas indicates the formation of an oxide tribological layer on the surface.
In terms of wear properties, formation of this layer on the surface can be useful, because it
avoids establishing of direct contact between pure aluminum (pin) and disc (steel) and occurring
adhesive mechanism and in addition to wear rate decreases, delays transformation to severe wear
(Bing, et al. (64)). Considering EDS line scan analysis of tribological layer of pure Al sample,
after being worn under a load of 10 N, the chemical composition of layer is roughly the same in
abrasive to delaminated areas. Therefore, it could be said that sample wear is controlled by
delamination mechanism. Therefore, delamination mechanism of tribological layer is the
dominant wear mechanism of pure Al sample under a normal load of 10 N.
Fig. 9 shows the SEM micrograph of worn surface of AC10-UM sample under a load of 10 N.
EDS analysis of worn surface areas shows a considerable amount of oxygen and iron or
formation of a tribological layer on worn surface. Microscopic image analysis of worn surface
also approves the presence of tribological layer.
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According to the results of wear rate (Fig. 7a), it could be concluded that only the presence of
Al3Mg2 particles does not have a significant effect on the wear resistance, so that the wear
property of AC10-UM sample seems to be similar to the pure Al. In the other word, the AC10-
15HM sample has a much better wear resistance than pure Al, AC10-UM and even AC10-2HM
samples, because the increasing of milling time along with addition of Al3Mg2 particles to the
matrix increases the hardness and strength. As a result, in comparison with pure Al, the
tribological layer stability increases which leads to the enhancement in the wear resistance of
nanocomposite, comparing to pure aluminum and also unmilled composite increases (Mousavi
Abarghouie, et al. (65)).
Fig. 10 shows the worn surface (a) and also the result of EDS line scan analysis (b) of AC10-
15HM nanocomposite sample under a normal load of 10 N. The microscopic image of worn
surface under a load of 10 N confirms the presence of tribological layer. As can be seen, the
mentioned layer demonstrates a good integration. As can be seen, the tribological layer maintains
its stability on the surface and the amount of crater on the nanocomposite surface, comparing to
pure Al and AC10-UM samples under the same amount of load, is smaller and the mentioned
layer is more integrated. As can be seen, the amount of crater on the surface of this AC10-15HM
sample, in comparison with pure aluminum and AC10-UM samples under the same amount of
load, is smaller. However, under the same amount of load, pure aluminum does not have the
ability to keep the mentioned layer on the surface. Since mechanical milling leads to grain
refining, hardness and strength increase, the stability of tribological layer increases and wear
properties improves. The analysis of this sample‟s worn surface indicates the presence of a
considerable amount of iron and oxygen on surface or formation of a tribological layer on
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nanocomposite surface. Considering the craters and abrasions on the surface of AC10
nanocomposite samples, it could be mentioned that the abrasive mechanism and the delamination
mechanism of tribological layer are the dominant mechanisms. Presence of stable and pressed
tribological layer on the surface, not only increases the wear resistance of material, it also avoids
its wear mechanism change with force in the studied load scope and transformation to severe
wear conditions.
Conclusions
The main results of this study can be summarized as follows:
1. The results of wear rate of unreinforced Al, unmilled Al- Al3Mg2 nanocomposite and milled
Al-Al3Mg2 nanocomposites showed that mechanical milling and incorporation of Al3Mg2
particles decreases the wear rate of pure Al severely, however the effect of mechanical milling is
more significant due to the structural refinement.
2. The results showed that although milling time improves the hardness, the different loads do
not have any remarkable effect on wear rate. These results that wear rate does not change with
normal load are interesting and contradict Archard law.
3. For nanocomposite samples, abrasive mechanism and delamination mechanism of tribological
layer are the dominant mechanisms. Presence of stable and pressed tribological layer on the
surface not only increases wear resistance of material but also avoids its wear mechanism change
with force in the studied load scope and transformation to severe wear conditions.
Acknowledgements
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The authors gratefully acknowledge University of Tehran for lab facilities and Iran National
Science Foundation for financial support of this work.
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Table 1. Materials composition and milling conditions used in this study.
Materials
label*
Matrix Al3Mg2
(wt %)
Milling
time (h)
Al Al 0 0
AC10-UM Al 10 0
AC10-2HM Al 10 2
AC10-5HM Al 10 5
AC10-7HM Al 10 7
AC10-10HM Al 10 10
AC10-15HM Al 10 15
AC10-20HM Al 10 20
*The symbol: “A” represents Al; the second
symbol: “C” represents Composite, the third
symbol: “H” represents Hour and the last
symbol: “M” represents Milling. The first two
digits designate the amount of Al3Mg2 and the
next digits designate the milling time. The UM
means Unmilled.
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Table 2. Effect of milling time on relative density and apparent porosity of AC10 composite.
Sample Theoret
ical
Density
(g/cm3
)
Archim
edes
Density
(g/cm3
)
Relati
ve
densit
y (%)
Appare
nt
porosit
y (%)
Al 2.7 2.68 99.25 0.75
Al3Mg2 2.25 - - -
AC10-
UM
2.655 2.609 98.3 1.7
AC10-
2HM
2.655 2.6119 98.38 1.62
AC10-
5HM
2.655 2.6149 98.49 1.51
AC10-
7HM
2.655 2.6188 98.64 1.36
AC10-
10HM
2.655 2.6239 98.83 1.17
AC10-
15HM
2.655 2.6297 99.05 0.95
AC10-
20HM
2.655 2.63 99.06 0.94
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Fig. 1. a) TEM image the milled AC10-15HM powder sample, b) typical EDX analysis of
nanocomposite.
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Fig. 2. a) FESEM micrographs for the extruded material a) AC10-UM and b) AC10-15HM.
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Fig. 3. Microhardness variation versus milling time for AC10 samples.
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Fig. 4 a) Variation of friction coefficient with sliding distance at load 10 N and b) average
friction coefficient as a function of the normal load for unreinforced Al and Al-Al3Mg2
nanocomposites.
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Fig. 5 (a) Bright field TEM image of AC10-15HM sample and (b) HRTEM image from the area
enclosed by a rectangle in (a) showing the Al3Mg2 lattice linked with Al matrix directly and also
Al3Mg2/Al interface is metallurgically clean.
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Fig. 6. Crystallite size and lattice strain of extruded AC10 samples at different milling time.
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Fig. 7. a) Comparison of wear rate of unreinforced Al, AC10-UM and AC10-15HM
nanocomposite, b) Variation of wear rate as a function of normal load.
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Fig. 8. (a) SEM micrograph of worn surface of unreinforced Al sample under a normal load of
10 N, (b) EDS line scan analysis of selected area in fig 8 (a).
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Fig. 9. (a) SEM micrograph of worn surface of AC10-UM sample under a normal load of 10 N,
(b) EDS analysis of area in 1 and (C) EDS analysis of area 2.
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Fig. 10. (a) SEM micrograph of worn surface of AC10-15HM sample under a normal load of 10
N, (b) EDS line scan analysis of selected area in fig 10 (a).
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