Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 695-703
Published Online July 2012 (
Some Studies on Wear and Corrosion Properties of
Al5083/Al2O3/Graphite Hybrid Composites
V. N. Gaitonde1*, S. R. Karnik2, M. S. Jayaprakash1
1Department of Industrial and Production Engineering, B. V. B. College of Engineering and
Technology, Hubli, India
2Department of Electrical and Electronics Engineering, B. V. B. College of Engineering and
Technology, Hubli, India
Email: *,,
Received March 14, 2012; revised April 28, 2012; accepted May 17, 2012
Advanced technology has put an increasing demand on the composite materials, particularly more in the areas of dy-
namic structures. Among the several types of aluminum alloys being used, Al5000 series are widely used in marine and
aerospace applications due to their superior corrosion resistance, excellent formability and good welding characteristics.
Al5083, a non-heat treatable high Mg-Al wrought alloy, is extensively used for the marine applications. Hence, an at-
tempt has been made in the proposed work to study the effects of Graphite (Gr) and Aluminium oxide (Al2O3) on alu-
minum hybrid composites involving both hard and soft reinforcements on wear and corrosion properties. The synthesis
of hybrid metal matrix composite used in the present study has been carried out by stir casting method. The effects of
reinforcement, time duration and particle size on prepared samples of composites have been studied on slurry erosive
wear. The static and accelerated corrosion tests have been performed and the microhardness of the developed compos-
ites was also investigated. The experimental results on Al5083-Al2O3-Gr hybrid composites revealed that the addition of
reinforcement improves the hardness and reduces corrosion and wear rates.
Keywords: Al5083-Al2O3-Gr Hybrid Composites; Microhardness; Slurry Erosive Wear; Corrosion
1. Introduction
Aluminum based metal matrix composites (AMCs) are of
lightweight high performance material systems. Among
the several types of aluminum alloys being used, Al5000
series are extensively used in marine and aerospace ap-
plications because of their superior corrosion resistance,
excellent formability and good welding characteristics.
Al5000 series are broadly used for the construction of
ship buildings/structures; however due to low strength
and poor wear resistance the application of this series is
limited. The addition of reinforcement to aluminum ma-
trix drastically alters mechanical, tribological and corro-
sion properties. The reinforcement in AMCs could be in
the form of continuous/discontinuous fibers, whiskers or
particulates. The hybrid composites have been prepared
by incorporating different types of fibers into a single
matrix. Due to two or more fibers in the hybrid compos-
ite, the advantages of one type of fiber could complement
with what are lacking in the other. The properties of hy-
brid composite primarily depend upon fiber content,
length of individual fibers, orientation, extent of inter-
mingling of fibers, fiber to matrix bonding and arrange-
ment of the fibers.
Several authors have reported on slurry erosive wear
and corrosion behavior of metal matrix composites. The
slurry erosion can be defined as a type of wear or loss of
material experienced by a component, when exposed to
high velocity stream of slurry mixture of solid particles
in a liquid [1], which is a serious problem in many engi-
neering applications. When the components are entrained
in such environments, the design life of the component is
significantly reduced, resulting in huge economic losses.
The areas in which components suffering from this prob-
lem include, mining machinery components, hydraulic
transport of solids in pipelines, marine, oil gas and power
generation industries [2-5].
Caron et al. [6] studied the slurry erosive wear behave-
ior of 5083-Al2O3 composites and found that slurry ero-
sive wear of composites increases with increase in alu-
minium oxide (Al2O3) content in the matrix material.
Ramachandra and Radhakrishna [7] reported that the
slurry erosive wear resistance increases with increased
silicon carbide (SiC) content in Al/SiC composites. It
was observed that the formation of passive layers on sur-
*Corresponding author.
Copyright © 2012 SciRes. JMMCE
face of slurry erosive specimens decreases wear loss by
forming protective layers against the impact of slurry.
Ramachandra and Radhakrishna also [8] analyzed the
slurry erosive wear behavior of Al-12wt%Si alloy rein-
forced with fly ash composites and it was noticed that the
flyash enhanced the slurry erosion wear resistance of the
developed composites. Li et al. [9] have investigated the
effect of time duration on slurry erosive wear of alumi-
num alloy and found that the wear rate increases with
increase in test time duration.
Setsuo et al. [10] discussed the effect of impact veloc-
ity and sand concentration on erosive wear of eutectic
alloys and observed that increase in sand concentration
and impact velocity increases the wear rate. Candan and
Bilgic [11] in their study reported that the addition of SiC
particles to Al-4wt%Mg could improve the corrosion
resistance of the composites over that of the base alloy in
3.5 wt% NaCl solution. On the other hand, Kiourtsidis
and Skolianos [12] noted that although SiC is not directly
responsible for the enhanced pitting corrosion of alumi-
num AA2024 composites in 3.5 wt% NaCl solutions,
intermetallic phases surrounding the particles initiated
pitting attack of the material.
Saxena et al. [13] explained the inferior seawater cor-
rosion resistance behaviour of a 4xx.x cast aluminum
alloy (LM-13 alloy), containing 3 wt% graphite particles,
to galvanic corrosion between the cathodic graphite par-
ticles and active aluminum matrix. However, the 4xx.x
cast aluminum-graphite composites displayed excellent
corrosion resistance in SAE-40 engine oil at 150˚C. Nath
and Namboodhiri [14] observed that Al-Mg and Al-Cu
composites exhibit superior corrosion resistance than the
composites reinforced with mica particles. The inferior
corrosion resistance of the mica-reinforced composites
was attributed to the distortion of the passive protective
films and provision of pit nucleation sites by the mica
particles. Nunes and Ramanathan [15] studied the corro-
sion behaviour of alumina-aluminium and SiC-Al in so-
dium chloride solution. Immersion and anodic polariza-
tion corrosion tests have been carried out and these
composites exhibit lower corrosion resistance when com-
pared to matrix alloy. The formations of pits in the ma-
trix near the particle matrix interface have been ob-
served by Paciej and Agarwala [16], which lead to the
pull out of the particle.
Mclnyre et al. [17] in their research reported that the
precipitation behavior and consequently the pitting sus-
ceptibility of heat treatable matrix alloys vary in the
presence of SiC particles. Ahmad and Aleem [18] de-
scribed the corrosion behavior of aluminum metal matrix
composites in salt water. Al6013-20%SiC composite
showed good resistance to corrosion in salt spray tests. It
was reported by Greene and Mansfield [19] that casting
defects, the particle size of the reinforcing phase, the
processing route, the amount of alloying element present
in the matrix alloy are the factors which determine the
pitting corrosion behavior of MMCs. Tazaskoma et al.
[20] found that the pitting susceptibility was same for the
composite and the matrix alloy except for the 2024 alloy.
The general corrosion of these alloys was affected more
by the presence of oxygen than by the silicon carbide
Although there are several studies reported in the lit-
eratures on wear behavior of aluminum metal matrix
composites, no published work has been seen on the ef-
fect of reinforcement on erosive wear of Al5000 series
MMCs. Hence, the present research work has been un-
dertaken, with an objective to explore the use of alumin-
ium oxide (Al2O3) with graphite (Gr) as reinforcing ma-
terials in Al5083 alloy.
2. Experimental Details
The base matrix is used in the present investigation is
Al5083 alloy; the chemical composition is presented in
Table 1. The base alloy was melted in the electric fur-
nace and different castings were taken. Aluminium oxide
(Al2O3) and graphite (Gr) are used as reinforcing materi-
als in Al5083 alloy. Aluminium oxide is chosen as rein-
forcement owing to its high hardness and low co-effi-
cient of thermal expansion, highly wear resistant, good
mechanical properties, high temperature strength and
thermal shock resistance. Graphite is a solid lubricant,
which permits high corrosion resistance and almost re-
duces the friction coefficient, disintegrates the wear prod-
ucts, accelerates heat abstraction and increases seizure
resistance. The properties of aluminium oxide (Al2O3)
and graphite (Gr) are summarized in Tables 2 and 3 re-
spectively. The different types of hybrid composites have
been prepared with three different compositions. The
designations of the proposed composites are given in
Table 4. The reinforcements aluminium oxide (Al2O3)
and graphite (Gr) of partical size in the range of 20 - 60
µm are varied in the range of 3 wt% to 6 wt% of base
The synthesis of hybrid metal matrix composites used
in the present study has been carried out by stir casting
method. Al5083 alloys in the form of ingots were used
for the preparation of specimens. The cleaned metal in-
gots were then melted to the desired super heating tem-
perature of 800˚C in the graphite crucibles under a cover
of flux layer in order to minimize the oxidation of molten
metal. A three-phase electrical resistance furnace with
temperature controlling device was used for the melting
purpose. The graphite (Gr) and aluminum oxide (Al2O3)
particulates preheated to around 500˚C and added to
molten metal and then stirred continuously by a me-
chanical stirrer at 720˚C. The stirring time maintained in
Copyright © 2012 SciRes. JMMCE
Copyright © 2012 SciRes. JMMCE
Table 1. Chemical composition of base metal Al5083 (weight percentage).
Si Cu Fe Mg Mn Zn Ti Cr Al
0.4% 0.1% 0.4% 4.0% - 4.9%0.4% - 1.0%0.25% 0.15% 0.05% - 0.25% Balance
Table 2. Properties of aluminium oxide.
Density (g/cm3) Modulus of
elasticity (GPa) Poisson’s ratio Tensile strength
Fracture toughness
Coefficient of
thermal expansion
3.9 380 0.22 282 - 551 4.2 - 5.9 7.4 39
Table 3. Properties of graphite.
Bulk density 1.3 - 1.95 g/cc
Porosity 0.7% - 53%
Modulus of elasticity 8 - 15 GPa
Compressive strength 20 - 200 MPa
Coefficient of thermal expansion 1.2 - 8.2 × 106 C
Thermal conductivity 25 - 470 W/m˚K
Specific heat capacity 710 - 8130 J/m˚K
Electrical resistivity 5 × 106 - 30 × 106 ·m
Table 4. Designation of hybrid composites.
Composites Composition
C1 Al5083 + 3wt%Al2O3 + 3wt%Gr
C2 Al5083 + 6wt%Al2O3 + 3wt%Gr
C3 Al5083 + 3wt%Al2O3 + 6wt%Gr
between 5 and 8 minutes and the impeller speed was kept
constant at 250 rpm. The melt with the reinforced par-
ticulates was poured into the dried, coated, cylindrical
permanent metallic mould of 80 mm in diameter and 175
mm height and the pouring temperature was maintained
around 680˚C. The melt was then allowed to solidify in
the moulds. For the purpose of comparison, the base al-
loy was cast under similar processing conditions.
The hardness, slurry erosive wear and corrosion resis-
tance tests of the prepared cast matrix and the hybrid
composite were carried out as per ASTM standards. The
hardness measurements were made using Vickers micro
hardness tester. The slurry erosive behavior of Al5083
base alloy and the developed hybrid composites was
studied using slurry wear tester. The slurry was prepared
by adding 20 liters of normal water with 700 gms of so-
dium chloride (NaCl). The sand particles of size up to
650 µm were added in the slurry at the rate of 100 gms/
ltr. The specimens were cleaned with acetone before and
after testing and the corresponding loss of weight was
measured using a digital weight balance (0.001 gm accu-
racy). The immersion tests were carried out for base al-
loy as well as developed hybrid composites as per ASTM
G31 test procedure. The polished samples of Al5083
matrix alloy and its hybrid composites were immersed in
3.5% NaCl solution for duration of 60 days. The polari-
zation studies were conducted and the standard reference
was calomel electrode while the working electrode was
the cast composite prepared as per ASTM standard G 69
- 81. The potentiodynamic measurements were made at
room temperature. The salt spray test was conducted in
salt spray chamber. The specimens were subjected to salt
spray test for 20 hours. The weight loss was measured for
every four hours. At the end of the test, the specimens
were taken out of the chamber, rinsed thoroughly and
then dried. The dried specimens were then weighed.
3. Results and Discussion
Figure 1 shows the scanning electron micrograph (SEM)
photographs of Al2O3 and graphite as reinforcements.
Al2O3 particles are found to be uniform and spherical in
shape with size ranges from 10 - 30 m. On the other
hand, the graphite particles are angular in shape with
sharp edges. The largest particle size appears to be
around 50 - 60 m. The graphite powder appears to have
a flaky morphology as depicted in Figure 1. Figure 2
illustrates the optical micrographs of Al5083 base alloy
and Al5083-Gr-Al2O3 hybrid composites. It is observed
that the distribution of Gr and Al2O3 particles in base
matrix alloy is fairly uniform. The microphotographs al-
so reveal an excellent bond between the matrix alloy and
the reinforcement particles. The microstructure showed
the fine particles dispersed along the grain boundary in
the matrix of aluminium solution and for alloy it has fine
precipitates of alloying elements uniformly dispersed in
Al solid solution. The analysis of the results and the in-
fluence of various parameters on the properties are sum-
marized in the following sections.
3.1. Microhardness Test
The experimental results of icrohardness are presented m
(a) (b)
(c) (d)
Figure 1. Scanning electron micrographs of Al2O3 (a) and (b) and graphite (c) and (d).
in Figure 3. It is observed that there is a significant im-
provement in microhardness with addition of graphite
(Gr) and aluminium oxide (Al2O3) particles in matrix
alloy. An improvement of hardness is noticed in Al5083
+ 3%Gr + 6%Al2O3, Al5083 + 6%Gr + 3%Al2O3 and
Al5083 + 3%Gr + 3%Al2O3 hybrid composites. Further,
there is a large difference in co-efficient of thermal ex-
pansion of Al5083 alloy and reinforcement particles
leading to thermal mismatch between matrix alloy and
reinforcement. This factor increases the density of dislo-
cations in the material resulting in higher hardness value.
The higher hardness is always associated with lower po-
rosity of metal matrix composites.
3.2. Slurry Erosive Wear Analysis
The effect of reinforcement on slurry erosive wear resis-
tance of developed hybrid composites is shown in Figure
4. There is a significant reduction in the slurry erosive
wear rate of the developed composites with increased
percentage weight of reinforcement. This can be attrib-
uted to the higher hardness and excellent corrosion and
wear resistance of the composite. In general, higher the
hardness better the erosive wear resistance of the materi-
als. The results revealed that a slurry wear resistance
increases with both Al2O3 and Gr content. When com-
pared to base metal, the composite with 3%Al2O3 +
6%Gr show less weight loss. The presence of Gr parti-
cles effectively improves the wear resistance. The de-
crease in weight loss may be due to the formation of a
passive layer on the surface of the specimen acts as a
protective layer. This passive layer, as long as it is not
broken, protects the matrix from direct contact with the
slurry and lowers the rate of weight loss.
Figure 5 illustrates the effect of impinging particle
size on developed composites. As the particle size in-
creases, the wear rate of composites also increases. In-
creased mass loss with increase in silica sand concentra-
tion in slurry is because, the small sized particles tend to
deviate near the surface of the target material due to their
lower mass and lower impact energy. Further, at constant
slurry concentration, the number of particles available at
the surface of the target material is higher in case of
small sized particles when compared to large sized parti-
cles because of retardation after impact and inters colli-
sion among them.
Copyright © 2012 SciRes. JMMCE
25 μm
25 μm
(a) (b)
25 μm
25 μm
(c) (d)
Figure 2. Optical microstructure of composites. (a) Al5083 alloy; (b) Al5083 + 3%Gr + 3%Al2O3; (c) Al5083 + 6%Gr +
3%Al2O3; (d) Al5083 + 3%Gr + 6%Al2O3.
Figure 3. Microhardness of composites.
The slurry erosive wear of developed hybrid compos-
ites with different time duration at constant slurry rota-
tion of 900 rpm is exhibited in Figure 6. As can be seen
from Figure 6, the sample with 3%Al2O3 + 6%Gr shows
the minimum mass loss. It is observed that increased
time duration results an increased slurry erosive wear for
both base alloy and composites studied. However, in-
creased content of reinforcement in matrix alloy reduces
the slurry erosive wear for all the time duration. This is
because of the higher hardness of composites when
compared with matrix alloy.
3.3. Immersion Test
Figure 7 shows the variation of mass loss of Al5083
matrix alloy and its hybrid composites. It is observed that
Copyright © 2012 SciRes. JMMCE
Figure 4. Effect of reinforcement of composites on slurry
Figure 5. Effect of impinging particle size on slurry wear.
Figure 6. Effect of test duration on slurry wear.
Figure 7. Effect of reinforcement in immersion test.
increased content of reinforcement in the matrix alloy
decreases the mass loss during immersion test. The de-
crease in the mass loss with increased content of rein-
forcement is due to the fact that an increased content of
reinforcement decreases the exposure of matrix area to
the corrosive solution. Further, both Gr and Al2O3 exhibit
excellent corrosion resistance, which decreases the mass
loss with increase in their content in the matrix alloy.
The effect of immersion duration on mass loss of
Al5083 alloy and developed hybrid composites is dis-
played in Figure 8. It is observed that initially mass loss
increases with increase in immersion and then becomes
stable. This can be attributed to the formation of a stable
passive layer of Al(OH)3, which is formed over the alu-
minum alloy and the Al(OH)3 protective oxides forma-
tion of such oxides results in less corrosion reaction over
a period of time. The saturation of solution with anodic
ions and also formation of relatively more stable passive
oxide layer, a steady state condition is arrived after few
days irrespective of the materials. Further, in all the cases
studied when compared with the matrix alloy the devel-
oped hybrid composites shows a decrease in the weight
3.4. Salt Spray Test
The inspections of the samples were placed in the cham-
ber for an interval of every four hours. The white corro-
sion product (white rust) and red corrosion product (red
rust) have been observed. Initially, the white rust appears
on the surface and as and when time progresses the red
rust appears. The formation of Al2O3 oxide layer resists
the white rust formation and this oxide layer slowly van-
ishes due to corrosion pits. As seen form Figure 9, the
Copyright © 2012 SciRes. JMMCE
Copyright © 2012 SciRes. JMMCE
Figure 8. Effect of immersion duration. Figure 9. Effect of test duration in salt spray test.
(a) (b)
(c) (d)
Figure 10. Polarization scan generated in potentiostat. (a) Al5083 Alloy; (b) Al5083 + 3%Al2O3 + 3%Gr; (c) Al5083 + 3%Al2O3 +
%Gr; (d) Al5083 + 6%Al2O3 + 3%Gr. 6
sample having 6%Gr content shows much resistance to
3.5. Polarization Studies
The polarization scan generated through potentiostat is
shown in Figure 10, which indicates the corrosion po-
tential of prepared composites. Figure 11 gives the effect
of corrosion density on developed hybrid composites. It
is observed that corrosion density, which is an indication
of the extent of corrosion of material increases gradually
with increased content of percentage of reinforcement in
the matrix alloy, resulting in material removal. It is evi-
dent that the composites reinforced with maximum per-
centage of graphite have exhibited reduced corrosion
current density when compared with the alumina rein-
forced composites. The corrosion density increases with
increase in percentage of reinforcement, which indicates
the improvement in the corrosion resistance of the com-
posites. From, Figure 12 it is also evident that in case of
the composites reinforced with 6% of Graphite, the
maximum corrosion resistance is observed.
4. Conclusions
The experimental investigations of wear and corrosion
behaviour of Al5083-Al2O3-Gr hybrid composites led to
the following conclusions:
The metallographic studies clearly revealed the uni-
formity in the distribution of reinforcements and ex-
cellent bond between the matrix and the reinforce-
The microhardness of hybrid composites are higher
when compared to matrix alloy. An increased content
Figure 11. Effect of corrosion density on sa mples p repared.
Figure 12. Effect of corrosion rate on samples p repared.
of hard reinforcement in the hybrid composites leads
to the enhancement in microhardness of hybrid com-
The slurry erosive wear of hybrid composites is less
when compared to unreinforced matrix alloy. An in-
creased content of reinforcement leads to improve-
ment in the slurry erosive wear and improves the re-
sistance of hybrid composites.
The immersion test on developed hybrid composites
indicated that addition of graphite and Al2O3 in to the
matrix have reduced mass loss under identical test
The salt spray test shows the formation of white and
red rust formation; the red rust appears due to forma-
tion of pit in aluminium matrix. Increased graphite
particles reduce the corrosion rate under identical test
The hybrid composites possess marginally inferior cor-
rosion resistance in 3.5% NaCl medium when com-
pared with matrix alloy.
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