Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 704-708
Published Online July 2012 (
Studies on Mechanical and Wear Properties of
Al6061/Beryl Composites
Hosur Nanjireddy Reddappa1*, Kitakanur Ramareddy Suresh1, Hollakere Basavaraj Niranjan2,
Kestur Gundappa Satyanarayana3
1Department of Industrial Engineering & Management, Bangalore Institute of Technology, Bangalore, India
2HKBK College of Engineering, Bangalore, India
3Research & Development Centre, BMS College of Engineering, Bangalore, India
Email: *
Received March 25, 2012; revised May 10, 2012; accepted June 1, 2012
Beryl-Al6061 alloy composites having 2 - 12 wt% of beryl particles were fabricated by liquid metallurgy (stir cast)
method. The tensile and wear properties of beryl-Al6061 composites have been evaluated and compared with its base
alloy. The results revealed that the Al6061-10 wt% of beryl composites shows an improvement of 15.38% in tensile
strength and specific wear rate decreases by 8.9% at normal load of 9.81 N when compared to matrix i.e. base alloy.
Significant improvement in tensile properties and hardness are noticed as the wt% of the beryl particles increases. The
microstructures of the composites were studied to know the uniform dispersion of the beryl particles in matrix. It has
been observed that addition of beryl particles significantly improves ultimate tensile strength and hardness properties as
compared with that of unreinforced matrix.
Keywords: Tensile Strength; Hardness; Wear; Al6061; Beryl
1. Introduction
The aluminium alloys reinforced with ceramic particles
emerged as a new generation of engineering materials with
improved mechanical properties to weight ratio [1,2].
Aluminium matrix composites offer good mechanical and
superior wear resistance properties when compared to the
alloy irrespective of applied load and sliding speed. This
is primarily due to the fact that the hard particles like SiC,
WC and Al2O3 etc., when dispersoid in matrix which
makes the matrix alloy plastically constrained and im-
proves the high temperature strength of the base alloy [3].
Most of the researchers have investigated aluminium
composites by different processing routes [4]. Of all the
processing routes, liquid metallurgy method is the most
sought after owing to its several advantages such as eco-
nomical, mass production, near net shaped components
can be produced [5]. Hosking et al. reported in their re-
search work Al2024 alloy with 20 wt% of alumina shows
good wear resistance [6]. Wang and Rack reported that
although the wear rate of Al7091 alloy and Al7091-SiC
composites are almost the same at a sliding velocity of
1.2 m/s, but with increase in increasing sliding velocity
composites exhibit lower wear rate than that of unrein-
forced matrix [7]. The abrasive wear rate of Al6061-
alumina fiber composites was found to be much less,
indicating almost six times better wear resistance than
matrix alloy [8]. Use of TiO2 as reinforcement in alumi-
num alloys has received little attention although it pos-
sess high hardness and modulus with superior corrosion
resistance [4]. Of all the aluminum alloys, Al6061 is
quite popular choice as a matrix material to prepare metal
matrix composites owing to its better formability charac-
teristics and option of modification of the strength of
composites by adopting optimal heat treatment [9].
In recent years, aluminum alloy based metal matrix
composites (MMCs) are being explored as candidate
materials in several interesting applications such as pis-
ton, connecting rod, contactors, where sliding is a key
component [4]. Excessive wear, due to sliding, will ulti-
mately result in seizure of the mating parts sometimes
leading to catastrophic failure [10]. Hence, prediction of
the wear behaviour of the sliding components is of ut-
most importance avoiding huge economic losses. Tri-
bological characteristics of several MMC systems in-
volving glass, flash, SiC, graphite, mica, Al2O3 as dis-
continuous dispersoids have been reported [11-13]. Beryl-
silicate of aluminum and beryllium is one of the naturally
available mineral. As observed in various literatures, the
particle reinforced Aluminum composites shows rea-
sonably good wear resistance. However, there is very
*Corresponding author.
Copyright © 2012 SciRes. JMMCE
little work is reported with “beryl” being used as a rein-
forcing phase in aluminum matrix. Hence the aims of the
study are: 1) To standardize the beryl addition to liquid
aluminum alloy; 2) To examine the mechanical and wear
properties of these aluminum matrix composites.
2. Material and Experimental Procedures
2.1. Matrix Material
The matrix chosen for this work is ASM 6061 Al-Mg-Si
alloy. It has the highest strength and ductility of the alu-
minium alloys with excellent machinability and good
bearing and wear properties [14].
2.2. Reinforcing Materials
Beryl, a naturally occurring mineral having the formula
(Be3Al2(SiO3)6) was used as the reinforcing material,
while Al6061 alloy has been used as the matrix. The
beryl particles used were of 45 - 60 μm size. They have a
density of 2.6 - 2.8 g/mm3 which is almost on par with
that of Al6061 and has hardness of 7.5 to 8 on Mho’s
scale and a hexagonal structure [15,16]. The chemical
composition of beryl particles are shown in the Tabl e 1.
A liquid metallurgy route has been adopted to prepare
the cast composites as described in our earlier works [9].
Al6061 has been chosen as the matrix alloy. Preheated
beryl particle of size 53 - 75 μm was introduced into the
vortex of the molten alloy after effective degassing. Me-
chanical stirring of the molten alloy for duration of 10
min was achieved by using ceramic-coated steel impeller
with a speed of 300 rpm was maintained. A pouring
temperature of 710˚C was adopted and the molten com-
posite was poured into cast iron moulds. The extent of
incorporation of beryl in the matrix alloy was varied
from 2 to 12 wt%.
The cast composites and matrix were machined to ob-
tain tensile, hardness and wear specimens; the tensile test
was carried out on samples according to ASTM-E8. All
the composites were tested for strength, samples were
loaded till fracture. Three trials were carried out for the
purpose of repeatability and the average of them is pre-
sented here. Hardness has some influence on the wear
behavior on any material. Hence, the hardness was
measured for the composite samples as well as squeeze
cast alloy. The hardness tests were carried out as per
ASTM-E-10-93 standard. The tests were conducted on
three locations on the sample to counter the possibility of
indenter resting on hard particle, which may result in
anomalous value.
Wear tests were carried out using a pin-on-disc appa-
G99-95 standard under varying applied pressure and
sliding distance at a fixed sliding speed of 1.66 m/s.
against an EN32 steel disc. The specimen samples were 8
mm diameter and 25 mm length. The surface of the
specimen sample and the steel disc were ground using
emery paper (grit size: 240) prior to each test. The sam-
ples were cleaned with acetone. The wear losses of sam-
ple specimens were measured as height loss in microns
which was recorded using an LVDT transducer of accu-
racy of 1 μm. The measurement of wear loss of the
specimen was used to evaluate the volumetric loss, which
in turn was used to compute the specific wear rate of the
composites. Lastly, wear surface were studied with SEM
to determine the wear mechanism undergone by the ma-
3. Results and Discussions
3.1. Morphology
The microstructure of Al6061 and Al6061-10 wt% of
beryl composite are shown in Figures 1(a) and (b). The
microstructure clearly indicates fairly uniform distribu-
tion of beryl particles in the matrix along with evidence
of minimal porosity in both the base alloy and the com-
posite. Further, an excellent bonding between the matrix
and the reinforcement particles was observed.
3.2. Tensile Strength
The properties of composites samples reinforced with
“beryl” particles were evaluated and compared with that
of matrix material, to see the effect of addition of parti-
cles. The results are reported below. The addition of
beryl particles enhances the tensile strength of the base
material as can be seen from Figure 2. However, peak
tensile strength is for an addition of 10% by weight of
The presence of hard beryl particles may be responsi-
ble for the improvement in strength. Theses particles
impede the advancing dislocation front [17-21]. The ad-
dition of these particles may have given rise to large re-
sidual compressive stress developed during solidification
due to difference in coefficient of expansion between
ductile matrix and brittle ceramic particles [22-26]. The
enhancement in strength may also be attributed to closer
packing of reinforcement and hence small interparticle
spacing in the matrix, at the same time it may be due to
Table 1. Chemical composition of beryl particles.
Element SiO2 Al2O3 BeO Fe2O3 CaO MgO Na2O K2O MnO
Composition (%) 65.4 17.9 12.3 0.8 1.34 0.48 0.55 0.004 0.05
Copyright © 2012 SciRes. JMMCE
Figure 1. Microstructure of (a) Al6061 (200×); (b) Al6061-
10% beryl composite (200×).
Beryl particle content
Ultimate tensile strength (MPa)
(wt %)
Figure 2. Ultimate Tensile Strength (UTS) of Al6061/beryl
composite’s ability to exhibit internal ductility to redis-
tribute high localized internal stresses [27].
3.3. Hardness
The dispersion of beryl particles enhances the hardness
of the matrix, since beryl particles being harder than
aluminum alloy, render additional hardness to the matrix
[28]. The hardness shows a linear relationship with the
quantity of particle addition. The composite with 12%
weight particle has hardness, enhanced nearly by 36.64%
when compared to the base alloy (Figure 3).
3.4. Dry Sliding Wear
The specific wear rate of test specimens in mm3/N-m
obtained from the height loss of the specimens during
sliding is plotted against sliding distance for a applied
load of 9.81 N. The specific wear rates of unreinforced
alloy and six different composite specimens with varying
volume percentage of particle reinforcement (2% to 12%)
are shown in Figur e 4.
It may seen from the Figure 4 that for any given wear
sliding distance the increased addition of beryl particles
results in a decrease in the specific wear rate of the
specimen. This inverse relationship may be directly re-
lated to the improvement in the hardness of the compos-
ites as the amount of beryl is raised.
Beryl, wt.%
Figure 3. Variation of hardness of Al6061/beryl composites
with increased content of beryl.
1000 2000 3000 4000 5000 6000
0% beryl
2% beryl
4% beryl
6% beryl
8% beryl
10% beryl
12% beryl
Specific wear rate*10-5,mm3/N-m
Slding distance,m
Figure 4. Specific wear rate (Sliding speed: 1.66 m/s, Load:
9.81 N) for different sliding distances.
Copyright © 2012 SciRes. JMMCE
Figure 5. Worn surface of (a) Al6061 alloy; (b) Al6061-10%
beryl composite (Load: 9.81 N, Sliding speed: 1.66 m/s).
The specific wear rate of beryl reinforced composites
decreases with increase in beryl content in the dry-sliding
wear tests. The asperities of both the pin and counter face
which were in contact with each other were subjected to
relative motion under the influence of sliding distance.
Initially, both the surfaces are associated with a large
number of sharp asperities and contact between the two
surfaces takes place primarily at these points.
In the present case, a number of reinforcements were
observed on the asperities on the pin. Under the influence
of increased sliding distances, the asperities in each sur-
face came in contact with each other and they were either
plastically deformed or remained in elastic contact. As
the asperities were very sharp in nature, the effective
stress on these sharp points might have been more than
the elastic stress and then all these sharp asperities were
plastically deformed at their contact points except the
plastically projected points of the reinforcement due to a
moderate increase in temperature of contact surface. This
is because of continuous sliding motion for a longer du-
ration on increased distance. The plastically deformed
surface would then fill the valley of the material both in
specimen and disc surface during the course of action
and there was a possibility of fracture a few asperities on
both the surfaces leading to very fine debris [29].
The Figures 5(a) and (b) depicts the worn worn sur-
faces of both matrix-Al6061 alloy and Al6061-10% beryl
composite. The examination of the worn surfaces shows
that the composite exhibited generally much rougher
surface than that of the Al6061 alloy. In the case of
composite, cavities and large grooved regions were ob-
served on the worn surface. The fact that the ceramic
particles were found inside the cavities indicates that
some particles were broken and pulled out from the sur-
face. This suggests an abrasive wear mechanism, which
is essentially due to exposure of hard ceramic particles
on the worn surface and loose fragments between two
surfaces [30]. As the ceramic particles resist the delami-
nation process, the wear resistance is more in the case of
composites alloy [31].
4. Conclusions
Based on the experimental observations made in the pre-
sent research, the following conclusions have been drawn.
Al6061 alloy matrix composites have been success-
fully developed with fairly uniform dispersion of
beryl particles.
Tensile strength of Al6061/10%. Wt. of beryl com-
posites shows 15.38% more when compared to Al6061
base alloy.
The sliding wear weight loss of the Al6061/beryl
composites shows an inverse relationship with the
quantity of addition of beryl particles.
Specific wear rate was observed to be approximately
8.9% less when compared to base alloy.
5. Acknowledgements
One of the authors (Mr. H. N. Reddappa) acknowledges
Vokkaligara Sangha, Bangalore for financial support. Al-
so, the authors sincerely thank the Management of Ban-
galore Institute of Technology and BMS College of En-
gineering with which the authors are associated presently
for their support and encouragement for this work.
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