Journal of Minerals & Materials Characterization & Engineering, Vol. 11, No.4, pp.335-352, 201 2
jmmce.org Printed in the USA. All rights reserved
335
Effect of Copper and Silicon Carbide C ontent on the Corr osion Resistance of
Al-Mg Alloys in Acidic and Alkaline Solution s
Ahmad T. Mayyas1,
∗
, Mohammad M. Hamasha2, Abdalla Alrashdan2, Adel M. Hassan2,
Mohammed T. Hayajneh2
1 Department of Automotive Engineering, Clemson University-International Center for
Automotive Research (CU-ICAR), 4 Research Drive, Greenville, South Carolina 29607 USA.
2 Center for Autonomous Solar Power, State University of New York at Binghamton,
Binghamton, NY 13850, USA
3 Department of Industrial Engineering, Faculty of Engineering, Jordan University of Science
and Technology, P.O. Box 3030, Irbid, 22110, Jordan
∗ Corresponding Author: [e-mail]
ABSTRACT
In this study, corrosion resistance of cast aluminum based alloys and composites reinforced with
silicon carbide has been investigated. Different Al-Mg-Cu alloys and Al-4wt.%Mg-Cu/SiC
composites reinforced with 5 or 10 vol.%SiC were subjected to corrosive media (acidic: 1.0M
HCl and alkaline: 1.0M NaOH) using weight loss method to evaluate their corrosion resistance.
The results show that introducing copper and silicon carbide have a negative effect on the
corrosion resistance of monolithic aluminum; however, Al-based composites still being
attractive materials to replace steel parts in automotive and aircraft industries and hence

336 A.T. Mayyas, M.M. Hamasha, A. Alra shd a n , A.M. Hassan, M.T. Hayajneh Vol.11, No.4
studying their corrosion resistance is of high importance. Scanning electron microscopy (SEM)
and Energy-dispersive X-ray (EDS) were used to show the degree of attack and of acidic and
alkaline solution on the surface of the investigated materials.
Keywor d s: Casting; Corrosion Testing; Metal Matrix Composites; Surface Engineering.
1. INTRODUCTIO N
Aluminum matrix composites (AMCs) refer to the class of light weight high performance
aluminum centric material systems. The reinforcement in AMCs could be in the form of
continuous/discontinuous fibers, whisker or particulates [1], in volume fractions ranging from a
few percent to 60%. Studying corrosion resistance of Al-based materials is important especially
for automotive and aircraft applications where the parts are prone to corrosive media like salt
water solutions, acidic and alkaline media. Aluminum based composites are usually reinforced
b y Al2O3, SiC, and C. The major advantages of AMCs compared to unreinforced materials are
as follows: greater strength, improved stiffness, reduced density, good corrosion resistance,
improved high temperature properties, controlled thermal expansion coefficient, thermal/heat
management, improved wear resistance and improved damping capabilities [1-6] . Nowadays, the
increased demand for light weight components, primarily driven by the need to reduce energy
consumption in a variety of societal and structural components, has led to an increase in the use
of aluminum. Among the various methods to fabricate metal matrix composites, stir casting
method has drawn keen attraction among the researchers due to its industrial feasibility.
The major limitation in many cases in fabricating metal matrix composites by liquid phase route
resides upon the incompatibility of the reinforcement and the matrix [ 1-3]. This problem in case
of Al-based metal matrix composite is due to the formation of stable tenacious oxide film,
resulting in poor wettability with the ceramic particle. One of the common practices to improve
wettability of an Al melt is through addition of small amount of reactive metals like magnesium
and titanium prior to the incorporation of ceramic particle [1,3]. However, in the present work, 4
wt% Mg was added to Al to improve wettability and argon flux was used during melting and
pouring tasks to reduce oxidation effect.

Vol.11, No.4 Effect of Copper and Silicon Carbide o n the Corrosion 337
Corrosion is the dissolution of a metal into an aqueous environment where the metal atoms
dissolve as ions. Since corrosion is always a function of the environmental conditions, control in
many cases is important in order to prevent the contact between metal and the surrounding
environment. The resistance of aluminum against corrosion in aqueous media can be attri but ed t o
a rapidly formed surface oxide film [4]. Therefore, aluminum has been known to exhibit widely
different electrochemical properties in different aqueous electrolytes [5]. Many researchers
studied pitting corrosion of aluminum alloys and aluminum composites since it is the dominant
corrosion type for these materials [e.g. 5-7]. Other researchers studied behavior of aluminum and
aluminum alloys under different acidic and alkaline solutions [e.g. 7-9]. Candan and Bilgic [10-
12] are among other researchers who studied pitting corrosion of Al-based composites in
different corrosive media. Their studies not only prove that Al-SiC composites are good
corrosion resistance materials, but also show that intermetallics resulted from the reaction
between Al and Si C particl e has a ben eficial effect o n corros ion res istan ce of t he comp osit es d ue
to interruption of the continuity of the metal matrix [12].
Other studies of corrosion resistance of aluminum materials are focusing on the methods and
materials that can help in improving corrosion resistance of such materials. Using inhibitors and
protective layers to improve corrosion resistance of aluminum have been investigated
thoroughly. For example, the effect of inhibitors and accelerators on the reaction kinetics of
corrodent solutions was studied by Abiola et al. [13] who examined the effect of mercaptoacetic
acid (MCA), on the corrosion behaviors of aluminum alloy in hydrochloric acid solutions. They
found that mercaptoacetic acid acts as corrosion accelerator of aluminum in HCl solutions. The
acceleratin g action o f mercaptoacetic aci d on alumin um corrosi on is ascribed to a catalytic effect
on the hydrogen evolution reaction. Oguzie et al. [14] studied the effect of addition methylene
blue (MB) dye on the electrochemical corrosion of aluminum in HCl solutions using gravimetric
techniques at 303 and 333 K. The results indicate that MB acts as an inhibitor in the acidic
corrodent. They also estimated the reaction rates and activation energies for different solutions
with and without inhibitors. Lunarska and Chernyayeva [15] s tudied the corrosion rate, hydrogen
permeation rate (hydrogen uptake) and stress corrosion cracking of Al in NaOH solutions, pure
and with the addition of H3BO3, EDTA, KMnO4 and As2O3. These chemicals known as the
corrosion inhibitors of Al in alkaline solutions [15] or as the hydrogen ingress promoter in

338 A.T. Mayyas, M.M. Hamasha, A. Alra shd a n , A.M. Hassan, M.T. Hayajneh Vol.11, No.4
electrolyte and the implantation of Al surface with B+ ions inhibited corrosion. Hydrogen uptake
was found to be promoted or inhibited by means of studied species, depending on the method of
their introduction into the base solution and on the applied polarization.
The different studies dealt with the effect of alloying elements on the corrosion resistance of
aluminum showed that magnesium tends to enhance corrosion resistance of aluminum while
copper has adverse effect on the corrosion resistance of aluminum [16-18]. It was proposed that
the concentrations of alloying elements, particularly copper, in Al solid solution are the key
factors which could influence the pitting corrosion. Such increase of copper in the aluminum
matrix increases the corrosion potential of aluminum matrix [16].
The present study is an attempt to investigate the corrosion behavior of Al-based alloys and
composites reinforced with SiC under chemical attacks of acidic and alkaline aqueous media. In
this study, two different aqueous solutions were used; namely: 1.0M HCl as acidic environment
and 1.0M NaOH as alkaline environment. Such kind of corrosive media might be similar to what
automotive and airplane parts face in their service lifetime.
2. EXPERIMENTAL SETUP AND PROCEDURE
2.1 Materials
The test materials studied in this work were a mixture of aluminum (commercial grade Al, ~99%
purity) and copper granules with an average particle size of 0.425 mm and ~97% purity as a
metal matrix. Silicon carbide particles ware added as reinforcement to the metal matrix. About
1000 g of commercial grade Al ingots and different weight percentages of copper powder (0, 1,
2, 3, 4, and 5 wt.%) were used to prepare the base metal matrix by stir casting method. Specific
quantities of silicon carbide powder with an average particle size of 75μm and purity exceeds
99.5% of 5 and 10 vol.% were added to the matrix alloy. Magnesium ingots (~99% purity) was
added in small quantities (fixed weight percentage 4wt.%) to promote wettability between metal
matrix and reinforcement particles [2, 10].

Vol.11, No.4 Effect of Copper and Silicon Carbide o n the Corrosion 339
2.2 Processing
The synthesis of the particulate metal matrix composites used in the present study was carried
out by the stir casting method (compocasting method). Aluminum ingots and copper granules
melted together at 850 °C. The amount of SiC powder pre-oxidized at 900°C for about 30
minutes to form a layer of SiO 2 on their surface in order to improve their wettability with molten
aluminum were incorporated into the melt [1]. Magnesium was added to the melt in the final
stage prior to pouring. The pouring temperature was maintained at 580-600 °C in semisolid state.
Then the mould was left in air to cool down to room temperature. Finally the produced cast bars
were turned to small disks to get the required specimens to be used in corrosion test (specimen
dimensions were: 25 mm in diameter and 10 mm in thickness and each specimen has a hole of
8.5 mm in diameter.). The total surface area for each sample was 1920 mm2.
2.3. Weight Loss Measurements
For full immersion method the specimens were suspended in glass jar contains the corrodent
solution (1.0M solution of HCl or 1.0M solution of NaOH) using plastic string. The corrodent
solution was exposed to atmospheric air and its temperature was maintained at 23–25 °C. The
weight loss rates were determined by removing specimens from test solutions at 30 minutes
intervals with total testing time of 240 minutes. To avoid local crevice corrosion, the specimens
were firstly ground with #600 SiC abrasive paper, the specimens were then doubly rinsed under
running water, cleaned in ethanol to remove any remaining debris, and to ensure complete
dryness of the specimens, they were dried in oven at 70 °C for 20 minutes and then cooled to
room temperature prior to weighing using electronic balance having 0.1 mg accuracy. The
specimens were subsequently returned to the testing solutions and the procedure repeated
progressively for 240 minutes. Cumulative weight loss was established based on the original
weight of each specimen. New similar specimens were used in 1.0M NaOH solution to get a
relative comparison of the corrosion resistance of the specimens in both acidic and alkaline
solutions. The corroded surfaces were then examined using scanning electron microscope (SEM)
(Quanta 200) equipped with Energy dispersive X-ray spectroscopy (EDS) (EDAX).

340 A.T. Mayyas, M.M. Hamasha, A. Alra shd a n , A.M. Hassan, M.T. Hayajneh Vol.11, No.4
3. RESULTS AND DISCUSSIONS
The presence of copper as alloying element in aluminum is essential component in formulating
the high strength aging alloys, it has been reported that copper seriously diminishes the corrosion
resistance of aluminum alloys although it [4-5]. Copper is dissolved in casting process in the
matrix phase of the alloy and is concentrated into a variety of second phase particles.
Predominant particles include Mg2S i, Al5Mg8Si6Cu2, Al2Cu and Al2C uMg [4, 16-17]. Also, the
formation of Al-Cu-Mg intermetallic particles promotes the cathodic reduction of oxygen and
then accelerates corrosion process [17]. Consequently the passive films formed on the Al-Cu-Mg
intermetallic particles were chemically different and less protective than those formed on the
aluminum matrix [5,17]. Copper and magnesium-rich intermetallics strongly influenced the
corrosion behavior of aluminum. According to Blanc et al. [17] the reactivity of Cu and Mg
intermetallics can be described by a three-step process consisting of homogeneous dissolution,
copper re-deposition followed by local dissolution of the surrounding matrix. Many other
researchers have discussed the importance of intermetallic particles as initiation sites for
corrosion [12,18-24].
Aluminum based composites tend to corrode in a localized manner; several studies on the
corrosion of aluminum and its composites in chloride-containing solutions showed that the origin
of localized attack depends highly on the alloy composition and microstructure (which is
affected by the processing method). Possible mechanisms include: microgalvanic coupling
between the matrix and reinforcement or between the matrix and intermetallics, failure of the
protective oxide film due to micro-segregation of the alloying elements or micro-crevices at the
matrix-reinforcement interface [13]. When the composites are fabricated by the melt route then
degradation mechanism might take place, especially for light metals such as Mg. Also there is a
possibility of degradation of SiC [8]; this is related to the potential attack of SiC by liquid
aluminum and the subsequent degradation according to the following reactions [15]:
3SiC(s) + 4Al(l) → Al4C3(s) +3Si(in 1 Al) (1)
Al4C3(s) +12 H2O(g) → 4Al(OH)3(s) + 3CH4(g) (2)
Al4C3(s) +18 H2O(l) → 4Al(OH)3(s) + 3CO2(g) +12 H2 (3)

Vol.11, No.4 Effect of Copper and Silicon Carbide o n the Corrosion 341
The intermetallic precipitates that may found during casting process are Al 4C3 and free Si- type
intermetallic, the contribution of such hard intermetallic precipitates is to increase corrosion rate
in monolithic aluminum alloys and matrix composites [2, 8]. The chemical reaction of Al4C3
with water (even with moisture in the atmosphere at room temperature) and other environments
such as HCl and NaOH is thermodynamically favorable and could be detrimental to the
composites properties [8,13].
Silicon dioxide (SiO2) as it formed from reaction between aluminum and oxidized silicon
carbide particles in Al/SiC composites would have various beneficial effects [8]: i) abating
processing costs, ii) preventing the formation of Al4C3 and iii) promoting in situ growth of
thermodynamically stable phases (MgO, MgAl 2O4) that may act as reinforcem ents, according to
[8] the following reactions may take place:
SiO2(s) + 2Mg(l) → 2MgO(s) + Si(in 1 Al ) (4)
Mg(l) +2Al(l) +2 SiO2(s) → MgAl2O4 (s) + 2Si (in l Al) (5)
4Al6Si2O13(s) +13 Mg(l) +2Al(l) → 13MgAl2O4 (s) + 8Si (in l Al) (6)
In addition to these reactions, the following chemical reaction between molten aluminum and
SiO2 is also thermodynamically possible [8]:
2
3
SiO2(s) + 2Al(l) → 2Al2O3(s) +
2
3
Si(in 1 Al) (7)
Although the rejection of a certain amount of silicon into the alloy matrix is useful to prevent the
formation of Al4C3, it may represent a potential problem. Reaction of Si in the alloy (or that
formed as a by-product) with magnesium might produce Mg 2S i during solidification of the alloy
matrix in the composites. The intermetallic Mg2Si has been reported to be electrochemically
active and may enhance localized corrosion [8]. On the other hand, high dislocation densities
have been ob served at the Al -SiC matrix interfaces as a result of differential thermal contraction
between SiC p arti cles and the Al mat rix [9] . A ls o t he prot ruded S iC part i cles increase t he s urface
area which becomes in contact with corroding solution and hence increase the susceptibility of
the surface to be corroded.

342 A.T. Mayyas, M.M. Hamasha, A. Alra shd a n , A.M. Hassan, M.T. Hayajneh Vol.11, No.4
Figures 1 and 2 show the cumulative mass loss of different specimens in 1.0M HCl solution and
1.0M NaOH solution, respectively. The non-uniformity and non-linearity of the plots suggest
that the Al corrosion by HCl and NaOH environments is heterogeneous processes. In acidic and
alkaline environments the heterogeneous process involving several phases: in the first phase the
hard oxide film is damaged by corrodent and in the second phase with increased exposu re time a
steady state will be reached as the corrodent reaches the oxide-free matrix; hence it allows
equilibrium in the kinetics of dissolution of the outer porous layer and build-up of an inner
compact l ayer to be reached aft er an i nt erval of time. Pitting is the predominant form of localized
corrosion in this step [6, 9, and 16]. Similar observations have been also noticed in the present
study for corrosion of Al in NaOH solution.
Fig. 1 Cumulative mass loss of: a) Al-4wt.%Mg-Cu alloys, and b) Al-4wt.%Mg-SiC
composites in 1.0M HCl
Fig. 2 Cumulative mass loss of: a) Al-4wt.%Mg-Cu alloys, and b) Al-4wt.%Mg-SiC
composites in 1.0M NaOH

Vol.11, No.4 Effect of Copper and Silicon Carbide o n the Corrosion 343
3.1. Thermodynamics Of Corrosion
The dissolution of Al- based alloys and composites have shown stronger affection by acidic
solution of HCl compared to alkaline solution of NaOH. To compare the effect of dissolution
kinetics of Al-based alloys/composites in alkaline and acidic solutions the first order Arrhenius
equation:
)
RT
E
exp(- A.
a
=K
(8)
Where Ea is the apparent activation energy which depends on type of material, corrodent and
temperature, R is the ideal gas constant (8.314 J.mol-1.K-1), and T is absolute temperature. In its
original form the pre-exponential factor A and the activation energy Ea are considered to be
temperat u r e-independent. The rate constants can be calculated according to the following
equation [13]:
)ln(
t
1
K
f
i
w
w
=
(9)
wi represents the initial weight of specimen and w f represents t he final weight o f specimen aft er
immersion in corrodent solution for 240 minutes and t is time in minutes (i.e. 240 minutes). The
half-time (t1/2) was calculated from the first order Arrhenius equation [13]:
K
t693.0
2/1 =
(10)
When ln(wi –Δw) is plotted against time a linear plot is obtained which confirms first order
Arrhenius equation as shown in Fig. 3. Arrhenius first order equation was used to estimate the
kinetic data like rate constant (K) and half time (t1/2) as shown in Table 1. Fig. 4 has been
plotted to manifest the relative corrosion thermodynamics data in Table 1. Fig.4 shows the rate
constant and half-time (t1/2) for different alloys and composites in 1.0M HCl and 1.0M NaOH
solutions, respectively. The first observation from these figures indicates that the average
corrosion rates of Al-based materials in alkaline environment is lower than corrosion rate in
acidic environment, however, severe damaged is resulted from the acidic environments. Also,
from these figures one can observe that the rate constant varies considerably for Al-based
specimens used in 1.0M HCl solution compared to the specimens used in 1.0M NaOH ( in 1.0M
HCl rate constant range from 95.98X10-4 for Al-4wt.%Mg to 250.63X10-4 (min-1) for Al-
4wt.%Mg-5wt.%Cu-10vol%SiC which can be compared to the corresponding values in 1.0M

344 A.T. Mayyas, M.M. Hamasha, A. Alra shd a n , A.M. Hassan, M.T. Hayajneh Vol.11, No.4
NaOH as they ranged from 91.63X10-4 for Al-4wt.%Mg to 120.65X10-4 for Al-4wt.%Mg-
5wt.%Cu-10vol%SiC). Hence it is clear that the acidic solution has stronger effect on the Al-
based surfaces when compared to NaOH solutions.
Fig. 3 Variation of log (wi -Δw) with time for different samples in: a) 1.0M HCl solution,
and b) 1.0M NaOH solution.
Fig. 4 Rate constant (K) and half time (t 1/2) for different alloys and composites in: a) 1.0M HCl
solution, and b) 1.0M NaOH solution

Vol.11, No.4 Effect of Copper and Silicon Carbide o n the Corrosion 345
Table 1 Thermodynamic data of different alloys and composite specimens used in this study
in 1.0M HCl
in 1.0M NaOH
Sample No.
Cu
(wt.%)
SiC
(vol%)
K (X10
-6
)
t1/2 (hr)
K (X10
-6
)
t1/2 (hr)
1
0
0
65.979
175.056
91.636
126.042
2
0
5
75.879
152.217
87.564
131.904
3
0
10
99.089
116.562
93.363
123.711
4
1
0
84.411
136.831
68.624
168.308
5
1
5
109.317
105.656
81.351
141.978
6
1
10
128.060
90.192
94.562
122.142
7
2
0
129.828
88.964
82.622
139.793
8
2
5
157.082
73.528
79.662
144.987
9
2
10
184.172
62.713
93.947
122.942
10
3
0
134.560
85.836
82.957
139.228
11
3
5
141.363
81.704
80.997
142.599
12
3
10
255.595
45.189
97.746
118.1638
13
4
0
135.549
85.209
88.432
130.609
14
4
5
162.062
71.269
118.966
97.086
15
4
10
252.646
45.716
117.499
98.298
16
5
0
171.297
67.427
92.827
124.425
17
5
5
205.143
56.302
114.287
101.061
18
5
10
250.630
46.084
120.648
95.733
3.2. Surface Characterization
The specimens were exposed to corrodent solutions for 240 minutes before they examined using
scanning electron microscope (SEM) and energy dispersive X-ray (EDS). Fig. 5 shows
photographs of the surface of some corroded specimens investigated in this work. Visual
inspection with the aid of this figure shows that the HCl solution has stronger effect on the
surface of Al-based materials than the NaOH solution. However, such kind of subjective
judgment is rather important, but at least it gives us a feeling of what is happening in the
corrosion test. During the testing period and especially in the initial periods, pitting corrosion is
the dominant type of corrosion followed by formation of white and light-gray powders on the
specimen surfaces. The amount of that powder was observed significantly in the 1.0M NaOH
solution. However, polished surfaces were obtained after the termination of the corrosion test in
1.0M NaOH as shown in Fig. 5. In 1.0M HCl solution it was observed continuous pitting
corrosion of surface with decreasing corrosion rate due to the etching effect of acidic solutions.

346 A.T. Mayyas, M.M. Hamasha, A. Alra shd a n , A.M. Hassan, M.T. Hayajneh Vol.11, No.4
The etched layer forms some anti-corrosion film which enhances corrosion resistance of interior
matrix [5].
Fig . 5 Photos showing corroded surface of: a) Al-4wt.%Mg-4wt.%Cu alloy in 1.0M HCl; b) Al-
4wt.%Mg-10vol%SiC composite in 1.0M HCl; c) Al-4wt.%Mg-4wt.%Cu alloy in 1.0M NaOH;
d) Al-4wt.%Mg-10vol%SiC composite in 1.0M NaOH
The second parts of Fig's 6-11 show the EDS spectrum of the corroded region, revealing the
presence of the different elements which form the alloy/composite. The presence of silicon for
example is due to the natural formation in the alloy and/or composite in trace amounts or may
reject from reactions (5) and (6). On the other hand, the presence of oxygen is attributed to
hydrated aluminum oxide and possibly to the presence of Mg(OH)2 [8]. The EDS analysis of
some Al-4wt.%Mg-Cu alloys shows small amounts of copper in the corroded surfaces although
it was added on predetermined quantities (for example 4wt.% in Fig.8 ). The EDS spectra
indicat e that there was o nly a very slight enrichm ent of copper i n the corroded area as compared
to the uncorroded surface. However, a very significant enrichment of Cu was observed locally in
the form of copper-rich or possibly pure copper particles. It should also be noted that no copper-
containing particles were observed on uncorroded areas of the sample. This can be attributed to
the stronger electrochemical behavior of copper which makes it easily to dissolute from the

Vol.11, No.4 Effect of Copper and Silicon Carbide o n the Corrosion 347
matrix and rejected into the electrolyte solution. EDS analysis indicates that the bright spots are
copper enriched particles [17-20]. For example, Fig's 8, 10 and 11 show such copper-enriched
spots indicated by white arrows. Hard attack was observed in the Al/SiC composites as appear in
SEM analysis by darker spots due to hard etching of the SiC particles and their surrounding
matrix in both acidic and alkaline solutions, but generally the harder attack was observed in
acidic solution.
Fig. 6 a) SEM micrograph of corroded surface of Al-4wt.%Mg alloy in 1.0M HCl solution after
240 minutes, and b) Corresponding EDS analysis showing the attacked surface and chemical
composition of corroded surface
Fig. 7 a) SEM micrograph of corroded surface of Al-4wt.%Mg-10 vol.%SiC composite in 1.0M
HCl solution after 240 minutes, and b) Corresponding EDS analysis showing the attacked
surface and chemical composition of corroded surface.

348 A.T. Mayyas, M.M. Hamasha, A. Alra shd a n , A.M. Hassan, M.T. Hayajneh Vol.11, No.4
Fig. 8 a) SEM micrograph of corroded surface of Al-4wt.%Mg-4 wt.%Cu alloy in 1.0M HCl
solution after 240 minutes, and b) Corresponding EDS analysis showing the attacked surface and
chemical composition of corroded surface.
Fig. 9 a) SEM micrograph of corroded surface of Al-4wt.%Mg alloy in 1.0M NaOH solution
after 240 minutes, and b) Corresponding EDS analysis showing the attacked surface and
chemical composition of corroded surface.

Vol.11, No.4 Effect of Copper and Silicon Carbide o n the Corrosion 349
Fig. 10 a) SEM micrograph of corroded surface of Al-4wt.%Mg-4 wt.%Cu alloy in 1.0M NaOH
solution after 240 minutes, and b) Corresponding EDS analysis showing the attacked surface and
chemical composition of corroded surface.
Fig. 11 a) SEM micrograph of corroded surface of Al-4wt.%Mg-4 wt.%Cu-10 vol%SiC
composite in 1.0M NaOH solution after 240 minutes, and b) Corresponding EDS analysis
showing the attacked surface and chemical composition of corroded surface.
4. CONCLUSIO N
The major type of corrosion of aluminum-based materials in HCl and NaOH solutions is pitting
corrosion. In the present work, it was found that the addition of copper and silicon carbide into

350 A.T. Mayyas, M.M. Hamasha, A. Alra shd a n , A.M. Hassan, M.T. Hayajneh Vol.11, No.4
Al-4 wt.%Mg alloy tend to diminish the ex cellent corrosion resistance of pure aluminum in both
acidic and alkaline media. The addition of SiC particles will also diminish the corrosion
resistance of Al-4wt.%Mg alloy since that it is difficult to achieve very good bond-ability
between ceramic and metal. On the other hand, during corrosion tests in extremely alkaline or
acid solutions, Cu surface enrichment likely occurs by particle dissolution and de-alloying and
possible de-alloying of the matrix phase. It was found that both Al-based alloys and their
associated composites have fewer tendencies to corrode in NaOH compared to HCl environment.
SEM analysis shows that the corrosion effect on the silicon carbide containing composites is
more sever compared to corresponding Al-4wt.%Mg-Cu alloys. When conducting EDS analysis
the absence of copper on the corroded surfaces is attributed to the high chemical activity of
copper eit her by formation of the hard intermetallic particles which are usually very active or by
dissolution in corrodent.
ACKNOWLEDGEMENTS
The authors gratefully acknowledge the assis tance of t he commit tee of scien tific r esearch/ J ord an
University of Science and Technology for its support of this research (grant No. 29/2007). The
authors would like also to gratefully acknowledge the use of Machine shop and the laboratory
facilities at Jordan University of Science and Technology, Irbid, Jordan
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