Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 919-923
Published Online September 2012 (
The Effect of Ageing Time on Some Mechanical Properties
of Aluminum/0.5% Glass Reinforced
Particulate Composite
Aondona P. Ihom1*, Nyior G. Bem2, Emmanuel E. Anbua3, Joy N. Ogbodo4
1Department of M e t a l l urgy, National Metallurgical Development Center, Jos, Nigeria
2Department of Metallurgical and Materials Engineering, Ahmadu Bello University, Zaria, Nigeria,
3Department of Mechanical Engineering, Federal Polytechnic Bauchi, Bauchi, Nigeria
4Departmen t of Welding and Fabrication, Scientific Equipment Development Institute (SEDI), Enugu, Nigeria
Email: *
Received June 23, 2012; revised July 31, 2012; accepted August 22, 2012
A particulate-hardened composite usually known as cermets with aluminum matrix and reinforced with ceramic parti-
cles from broken bottles was used to investigate the effect of ageing time on hard ness and tensile strength. Th e samples
used for the work were produced using stir-cast method and the samples were cast in metal moulds to improve on the
surface finish and to obtain good cooling rate. The composite composition used was Al/0.5% glass particles. The sam-
ples were treated at 500˚C and quenched in water at 65˚C. They were then aged at various temperatures ranging from
150˚C - 210˚C. The result of the hardness test showed that within the range of the ageing time selected the hardness
increased with the ageing for all the ageing temperatures used. Variations were observed but this is normal in ageing,
particularly when coherent and incoherent precipitates are formed at a point in time, or when over-ageing occurs. The
plot of the tensile strength tests and the hardness tests, with ageing time showed the trend as observed. The highest
hardness value of 37.3 HRB occurred after 5 hours of ageing likewise the highest tensile strength value of 398.36
N/mm2 occurred after 5 hours of ageing at the same ageing temperature of 190˚C. The aged composite showed im-
proved hardness and tensile strength when compared to as-cast value of 23.7 HRB for hardness and 253.12 N/mm2 for
tensile strength respectively.
Keywords: Al/0.5% Glass; Ageing Time; Particulate; Composite; Mechanical Properties
1. Introduction
Composite materials are usually classified on the basis of
the physical or chemical nature of the matrix phase e.g.
polymer matrix, metal matrix, and ceramic composites.
According to surappa [1] the term “composite” refers to a
material system which is composed of a discrete con-
stituent (the reinforcement), distributed in continuous
phase (the matrix), and which derives its distinguishing
characteristics from the properties of its con stituent, from
the geometry and architecture of the constituents and
from the properties of the boundaries (interfaces) be-
tween different constituents. A composite can also be de-
fined as a material that consists of constituents produced
via a physical combination of preexisting ingredient ma-
terials to obtain a new material with unique properties
when compared to the monolith ic material p roperties [2].
Curran [3] pointed out that there are two main types of
metal matrix composites, namely powder reinforced and
fibre reinforced. In the production of metal matrix com-
posites, one of the subjects of interest when choosing the
suitable matrix/reinforcement is the interaction in its in-
terface. For their production, oxide reinforcements have
been used in particles or whiskers morphology, like
Al2O3, ZrO2, or ThO2 in aluminum, magnesium and other
metal matrix. Metal-matrix composites provide the opp-
ortunity to combine metallic properties of the matrices
with the ceramic properties of the reinforcements, lead-
ing to greater modulus, strength, wear resistance and
thermal stability. They are a new class of materials suita-
ble for advanced structures, aerospace, automotive, elec-
trical, thermal management and wear applications [4].
The transport of solutes through the matrix of a metal
is accomplished by diffusion. Diffusion follows Fick’s
first law:
J Dcx
where J is flux, or amount of diffusing substance that
passes through a unit cross-sectional area per unit time,
*Corresponding author.
Copyright © 2012 SciRes. JMMCE
D is the diffusion coefficient and δc/δx is the concentra-
tion gradient of the diffusing substance. The transport of
substance in the matrix depends on values for the diffu-
sion coefficient and the characteristics of the concentra-
tion gradient. The diffusion coefficient is in turn, a func-
tion of temperature and the solute concentration or the
particulate reinforcement in this case. At higher tem-
peratures the transport of substances within the matrix is
faster, while longer time is required for lower tempera-
ture [5]. To accomplish equilibrium in thermal ageing of
composites and alloys, lower temperatures are preferred
to avoid any negative effect on the hardness of the com-
posite [6]. Thermal ageing affects both the microstruc-
ture and the mechanical properties because it determines
the nature of precipitates and phases formed in the matrix
of the composite or alloy [7]. The work by Curran [3]
and Hassan et al. [8] have laid the foundation for this
current work, their respective works have highlighted the
effect of ageing time on mechanical properties and mi-
crostructure of metal based composites reinforced with
ceramics or oxide particulates. The morphology of phase
format i o n ha s also been explained by the autho r s.
The objective of this paper is to d etermine the effect of
ageing time on some mechanical properties of Alumi-
num/0.5% glass reinforced particulate composite.
2. Materials and Methods
2.1. Materials
The materials used for the work included; pure aluminum
from electrical cables, waste bottles, magnesium alumin-
ium alloy, and water.
2.2. Equipment
The equipment used for the work were those of the Na-
tional Metallurgical Development Centre, Jos (NMDC)
and these included, metallurgical microscope, Rockwell
hardness tester, Denison universal strength testing ma-
chine, crucible furnace, gravity metal casting mould,
hacksaw, lathe machine and ball-mill.
2.3. Methods
The samples used for the work were those produced us-
ing stir casting method. The composite was produced
using pure aluminum (99.8%) which was melted and the
temperature was raised to 700˚C. 50 g of aluminium-
magnesium (50/50) alloy frit was added to introduce
magnesium to the melt. Broken bottles which were pul-
verized using ball-mill were classified, and 90 microns
passing sizes were introduced into the molten aluminum
in various compositions. The melt was stirred at the rate
of 315 rpm after which it was poured into the metal
moulds. After the castings had cooled they were removed
and cleaned. The composition used for this study was
that of Al/0.5% glass reinforced particulate composite.
2.3.1. A geing Treatment
After the cleaning of the cast specimens they were heated
to 500˚C and held for 45 minutes before quenching in
water at 65˚C. The round bars of 20 mm diameter and
350 mm length were then aged in the oven at different
temperatures ranging from 150˚C - 210˚C. The solution
treatment was carried out to enhance the homogenization
of the reinforcement particles in the matrix of the com-
posite. After the ageing treatment the specimens were
ready for hardness testing and tensile strength testing.
2.3.2. Hardness Testi ng
The samples were tested using Rockwell hardness tester.
A minor load of 10 kg was first applied to seat the speci-
men. Then the major load of 100 kg was used on the B
Scale, with a 1.6 mm diameter steel ball. The result was
then recorded automatically on the dial gauge in terms of
arbitrary hardness numbers. This was then recorded with
the value first and HRB at the end.
2.3.3. Tensile Strength Test
The specimens for the test were produced according to
“ASTM standard” (American Society for Testing and
Materials) as specified in standard method of tension
testing of metallic materials, ASTM Designation E 8-69.
The specimen was mounted on the Denison universal
strength testing machine. It was then operated and the
progressive results and tensile strength displayed as the
materials were failed.
3. Results and Discussion
3.1. Results
The results of the work are displayed in Figures 1- 8. The
as-cast composite has a hardness value of 23.7 HRB and a
tensile strength value of 253.12 N/mm 2.
3.2. Discussion
3.2.1. Analysis of Hardness Test Results
Figures 1-4 show the variation of ageing time with
hardness values of the composite at various temperatures
(150˚C - 210˚C). Figure 1 is the variation of ageing time
with hardness values of the composite (Al/0.5% glass
reinforced) at 150˚C. The plot shows that at 1hour of
ageing the hardness value was 33.9 HRB. The hardness
value dropped gradually to 24.4 HRB after 4 hours and
then rose up to 34.2 HRB after 5 hours of ageing. This
behavior is not uncommon with ageing and is normally
linked to the nature of precipitates that have been formed
at a particular time [6-8]. The variation in hardness can
Copyright © 2012 SciRes. JMMCE
A. P. IHOM ET AL. 921
Figure 1. Effect of ageing time on the hardness of Al/0.5%
glass reinforced composite at 150˚C.
Figure 2. Effect of ageing time on the hardness of Al/0.5%
glass reinforced composite at 170˚C.
Figure 3. Effect of ageing time on the hardness of Al/0.5%
glass reinforced composite at 190˚C.
Figure 4. Effect of ageing time on the hardness of Al/0.5%
glass reinforced composite at 210˚C.
Figure 5. Effect of the ageing time on the tensile strength of
Al/0.5% glass reinforced composite at 150˚C.
Figure 6. Effect of ageing time on the tensile strength of
Al/0.5% glass reinforced composite at 170˚C.
Figure 7. Effect of ageing time on the tensile strength of
Al/0.5% glass reinforced composite at 190˚C.
Figure 8. Effect of ageing time on the tensile strength of
Al/0.5% glass reinforced composite at 210˚C.
Copyright © 2012 SciRes. JMMCE
also be linked to diffusion of the reinfo rcing agent as the
ageing time progresses. This last explanation agrees with
the fact that after ageing for 5 hours the hardness values
peaked at 34 HRB. This same observation has been made
by Hassan et al. [8] in precipitation hardening character-
istics of Al-Si-Fe/SiC particulate composites. Figure 2
shows that the highest hardness value of 34.4 HRB was
attained after 3 hours of ag eing as against as against 34.2
HRB in Figure 1 attained after 5 hours. This is not sur-
prising because the ageing process is a diffusion con-
trolled pro ocess and is controll ed by thi s e q uat i on:
DDе (2)
where D is the diffusion rate, DO is the diffusion coeffi-
cient, Q is the activation energy required to move an
atom, R is the gas constant and T is the temperature in
Kelvin. At higher temperatures the movement of solute is
faster because the activation energy required is met
quickly [5,6]. Fick’s law has also explained that the
quantity of the substance passing through a unit cross-
sectional area in a unit time is proportional to the con-
centration gradient (δc/δx) along the x-direction which is
perpendicular to this cross-section as in Equation (1).
Where D stands for coefficient of diffusion and de-
pends on the type of alloy, the type of solid solution,
grain size, and so much on the temperature as in the pre-
ceding equation. Martin [6] has also predicted that the
growth of spherical precipitates should obey an equation
of the form r = α(Dt)1/2. Where, r is the particle radius
after time t, D (assumed independent of composition) is
the volume diffusion coefficient and α is a function of the
super saturation. A similar calculation made for the
growth of planar precipitates again predicted a parabolic
relationship between thickness and time [5,6]. All these
have helped in explaining the attainment of higher hard-
ness at shorter time at higher temperatures and the
growth of precipitates with time. Ageing takes place
faster at higher ageing temperature but there is a problem
of equilibrium and stability at h igh temperatures [7]. This
could result into reduced hardness as can be seen in Fig-
ures 3-4 compared. The aged composite has shown im-
proved hardness from Figures 1-4 compared with the
as-cast hardness value of 23.7 HRB. Figure 3, where
ageing took place at 190˚C, however, had the highest
hardness values with increase in ageing time [11,12].
3.2.2. Tensile Strength Test
The test has taken into consideration the ultimate strength
of the composite at various ageing temperatures and age-
ing time. Figure 1 showed that the composite at 150˚C
ageing temperature had a tensile strength of 362.05
N/mm2 after been aged for 1 hour. This gradually de-
creased to 260.59 N/mm2 and peaked again at 265.26
N/mm2 after 5 hours. The trend is in teresting and may be
interpreted in terms of the progressive dispersion of pre-
cipitates from the solid solution of the alloy with time
[7,9]. The Martin equation also explains this [6]. The
process is diffusion-controlled process and can also be
observed from Figures 2-4. Figure 3, which ageing took
place at 190˚C has high tensile strength when compared
to the others. The highest tensile strength of 398.36
N/mm2 occurred at the ageing temperature of 190˚C after
5 hours. This may be due to higher or more homogene-
ous dispersion of precipitates with time [8-12]. As the
ageing time was increased the tensile strength was also
increasing with a slight drop after 4 hours, but continued
rising to peak at 398.36 N/mm2 after 5 hours, indicating
that the tensile strength increases with the ageing time at
a constant temperature of 190˚C. This agrees with Has-
san et al. [8] in precipitation hardening characteristics of
Al-Si-Fe/SiC particulate composites. Comparing the ten-
sile strength of the age hardened composite at various
temperature and time regimes it can be seen that most
ageing times showed improved tensile streng th as against
the as-cast tensile strength [11]. The as-cast tensile
strength of the composite is 2 53.12 N/mm2 and the high-
est tensile strength of 398.36 N/mm2 of the aged hard-
ened composite occurred at 5 hours of ageing at 190˚C.
This still confirms that ageing time has effect on this
mechanical property of the composite. The general trend
in Figures 1-4 is that the tensile strength increased with
the ageing time of the composite at different tempera-
tures covering the range 150˚C to 210˚C. This can be
linked to the precipitation of a second phase during age-
ing of the composite giving rise to increased tensile
strength [8]. The strength is due to solid solution metal-
ceramic bond formed at the interface leading to increased
tensile strength.
4. Conclusions
The study has been conducted and the following conclu-
sions were drawn from the study:
1) The mechanical properties of the composite (Al/
0.5% glass reinforced) are higher in the age-hardened
samples than in the as-cast samples, most likely due to
the precipitation of a second phase during ageing which
cover the surface at the particles-matrix interfaces.
2) The hardness increased with ageing time.
3) The tensile strength of the composite also increased
with ageing time.
4) The study has established that this grade of com-
posite responded to ageing as shown in the improved
mechanical properties tested.
5) The composite is a cermet composite with the in-
creased strength arising from solid solution bonding at
Copyright © 2012 SciRes. JMMCE
Copyright © 2012 SciRes. JMMCE
the interface.
5. Acknowledgements
The authors are seriously indeb ted to the management of
the National Metallurgical Development Centre, Jos for
providing their facilities for this research work.
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