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Int. J. Electrochem. Sci., 7 (2012) 2846 - 2859
International Journal of
ELECTROCHEMICAL SCIENCE
www.electrochemsci.org
Corrosion Passivation in Natural Seawater of Aluminum Alloy
1050 Processed by Equal-Channel-Angular-Press
El-Sayed M. Sherif 1,3,*
, Ehab A. El-Danaf 2 , Mahmoud S. Soliman
2 , Abdulhakim A. Almajid
1,2
1 Center of Excellence for Research in Engineering Materials (CEREM), College of Engineering, King
Saud University, P. O. Box 800, Al-Riyadh 11421, Saudi Arabia 2 Department of Mechanical Engineering, College of Engineering, King Saud University, P.O. Box
800, Al-Riyadh 11421, Saudi Arabia 3 Electrochemistry and Corrosion Laboratory, Department of Physical Chemistry, National Research
Centre (NRC), Dokki, 12622 Cairo, Egypt * E-mail: [email protected]
Received: 7 February 2012 / Accepted: 11 March 2012 / Published: 1 April 2012
The corrosion and corrosion passivation of aluminum alloy 1050 (AA 1050) that was fabricated by
equal-channel angular press (ECAP) after different pass time numbers, namely, 0, 1, 2, and 4, in
Arabian Gulf water (AGW) have been reported. The study was carried out using cyclic
potentiodynamic polarization (CPP), chronoamperometric current-time (CT), and electrochemical
impedance spectroscopy (EIS) measurements after 20 min and 10 days immersion in the AGW
solutions. CPP experiments showed lower corrosion rate and higher corrosion resistance for the
ECAPed alloy than annealed one; this effect increases with increasing the number of pass time. CT
curves at ‒630 mV vs. Ag/AgCl and EIS spectra indicated that the increase of pass time highly
decreases both uniform and pitting corrosion. Results collectively proved that the corrosion rate
decreases and resistance for uniform and pitting attacks increases with increasing the number of pass
time and the best performance was obtained for ECAPed AA 1050 alloy after 4 passes. For that the
behavior of the cast alloy was compared to the ECAPed one after 4 passes was also reported after 10
days immersion before measurements.
Keywords: Aluminum alloy 1050; natural seawater; corrosion measurements; ECAP; electrochemical
measurements
1. INTRODUCTION
The microstructure of metals can be significantly changed by subjecting the material to severe
plastic deformation through procedures such as equal channel angle pressing (ECAP) and high
Int. J. Electrochem. Sci., Vol. 7, 2012
2847
pressure torsion. These procedures lead to substantial grain refinement so that the grains are reduced to
the submicrometer or even the nanometer range [1,2]. ECAP is a processing procedure whereby an
intense plastic strain is imposed by pressing a sample in a special die. The die consists of two channels
equal in cross section, intersecting at an angle ɸ, which is a subject of research in ECAP usually
ranging from 90 o to 157
o [3]
. There is also an additional angle, which defines the arc of curvature at
the outer point of intersection of the two channels, and also it has been a subject of research. A
schematic of the die can be seen in Fig. 1.
Of the various procedures that impose severe deformation, ECAP is especially the most
attractive processing technique. ECAP have been utilized not only to obtain ultrafine-grained (UFG)
materials but also to produce extraordinary mechanical and physical properties without remarkably
changing the geometry of a bulk material. Materials processed with ECAP become superior to that of
conventional coarse-grained materials [4-9]. The significant feature of ECAP is that because the billet
retains the same cross-sectional area so that repetitive pressings are feasible, materials processed by
ECAP may be deformed to very high strains wherein the subgrain boundaries evolve into high-angle
boundaries through the absorption of dislocations, thereby producing arrays of ultrafine grains
separated by high-angle grain boundaries. By contrast, this evolution cannot be achieved in more
conventional metal-working processes because of the natural limit imposed on the total strain
introduced during deformation [10].
Protecting aluminum from being corroded has been investigated either by adding other alloying
elements and/or by decreasing the aggressiveness of its surrounding corrosive environments.
Decreasing the corrosivity of the environments can be done mostly by using corrosion inhibitors [11-
17] or protective coatings [18, 19]. The inhibition of the alloy surface is usually obtained by inorganic
oxidants such as chromate, molybdate, and tungstate [20-23] or organic compounds having polar
groups, such as oxygen, sulfur and nitrogen as well as heterocyclic compounds containing functional
groups and conjugated double bonds [11-17]. ECAP is considered as one of the very useful methods
for producing ultra-fine microstructures of Al-based alloys with significantly improved mechanical
properties and higher corrosion resistance [24-26]. In addition, some ultra-fine grained Al-based alloys
produced by ECAP showed a superplastic forming capability [27, 28].
The objective of this work was to study the effect of ECAP pass time number that varied from
1 to 4 on the corrosion of the annealed aluminum alloy 1050 (AA 1050) in Arabian Gulf water. A
particular attention was paid to the effect of pass time number on the pitting corrosion of the AA 1050.
The study was achieved by using different electrochemical techniques such as cyclic potentiodynamic
polarization, chronoamperometric current-time variations, and electrochemical impedance
spectroscopy.
2. EXPERIMENTAL PROCEDURE
2.1. Fabrication of the ECAPed AA 1050
The die, Fig. 1, was manufactured from hot work tool steel. The die angles were designed and
manufactured to have: =0 and ɸ=90 o . Route BC, where the sample was rotated by 90
o between
Int. J. Electrochem. Sci., Vol. 7, 2012
2848
subsequent pressings was adopted in the present study. Commercial purity aluminum (AA 1050)
containing the following impurities, Fe–0.40% min, Si–0.25%, Cu–0.05%, Mn–0.05%, Mg–0.05%,
Cr–0.05%, Zn–0.05%, V–0.05%, Ti–0.03%, others 0.03% and Al–balance) with purity of 99.5% was
used in this study. The material was supplied as cold rolled plates of 15 mm thickness. Cylindrical
samples were machined parallel to the rolling direction, and then annealed at a temperature of 600 o C
for 8 hours, to give an average grain size of about 600µm. The annealed samples were lubricated using
graphite based lubricant and pressed in the ECAP die. The Vickers microhardness (kg/mm 2 ) was
measured using a Buehler micromet hardness tester at a load of 300 g and the reported value is the
average of 20 readings. Samples of about 6 mm in length were cut from the ECAP processed samples
and pressed in a direction parallel to the extrusion direction to document the yield strength.
Figure 1. Schematic representation of the ECAP process showing the billet axes system xyz and the
reference shear axis system x’y’z’.
2.2. Corrosion tests
2.2.1. Chemicals and electrochemical cell
The natural sea water was brought from the Arabian Gulf at the eastern region (Jubail,
Dammam, Saudi Arabia) and was used as received. An electrochemical cell with a three-electrode
configuration was used for electrochemical measurements. Annealed and ECAPed AA 1050 rods were
used in this study. The AA 1050 rod, a platinum foil, and a Metrohm Ag/AgCl electrode (in 3 M KCl)
were used as working, counter, and reference electrodes, respectively.
The AA 1050 rods for electrochemical measurements were prepared by welding a copper wire
to a drilled hole was made on one face of the rod; the rod with the attached wire were then cold
mounted in resin and left to dry in air for 24 h at room temperature. Before measurements, the other
face of the Al electrode, which was not drilled, was grinded successively with metallographic emery
paper of increasing fineness of up to 800 grits. The electrodes were then washed with doubly distilled
water, degreased with acetone, washed using doubly distilled water again and finally dried with tissue
paper. In order to prevent the possibility of crevice corrosion during measurement, the interface
x
y
z
Int. J. Electrochem. Sci., Vol. 7, 2012
2849
between sample and resin was coated with Bostik Quickset, a polyacrelate resin. The total exposed
surface area of the working electrode was 1.0 cm 2 .
2.2.2. Electrochemical methods
Electrochemical experiments were performed by using an Autolab Potentiostat (PGSTAT20
computer controlled) operated by the general purpose electrochemical software (GPES) version 4.9.
The CPP curves were obtained by scanning the potential in the forward direction from -1800 to -500
mV against Ag/AgCl at a scan rate of 3.0mV/s; the potential was then reversed in the backward
direction. Chronoamperometric current-time experiments were carried out by stepping the potential of
the AA 1050 rods at – 630 mV versus Ag/AgCl; in some experiments this potential value was applied
after stepping the potential of Al to -1000mV vs. Ag/AgCl for 20 min. EIS tests were performed at
corrosion potentials (ECorr) over a frequency range of 100 kHz – 100 mHz, with an ac wave of 5 mV
peak-to-peak overlaid on a dc bias potential, and the impedance data were collected using Powersine
software at a rate of 10 points per decade change in frequency. ZSimpWin software was used to fit the
EIS data to best equivalent circuit for Al rods in AGW. All the electrochemical experiments were
recorded after the electrode immersion in the test solution for 20 min and in some cases the electrodes
were immersed for 10 days before measurements. All measurements were also carried out at room
temperature in freely aerated stagnant solutions.
3. RESULTS AND DISCUSSION
3.1. Cyclic potentiodynamic polarization (CPP) data
In order to study the effect of the number of ECAP pass time on the corrosion behavior of AA
1050 in AGW solution, CPP experiments were carried out. The CPP curves for (1) 0 pass, (2) 1 pass,
(3) 2 passes, and (4) 4 passes ECAPed AA 1050, respectively after 20 min immersion in AGW
solutions are shown in Fig. 2. It has been reported [12, 13] that the cathodic reaction for Al in aerated
near neutral pH solutions is the oxygen reduction followed by its adsorption i.e.
)1(4OH 4O2H O 22
e
The presence of oxygen enhances the cathodic reaction due to oxygen reduction and transforms
aluminum to aluminum hydroxide as follows,
)2(3 Al(OH) 3OH Al ads.3,(S)
e
The aluminum hydroxide, Al(OH)3, is transformed to Al2O3.3H2O,
Int. J. Electrochem. Sci., Vol. 7, 2012
2850
)3(O.3HOAl 2Al(OH) 232ads.3,
The formed 32
OAl is of a dual nature and consists of an adherent, compact, and stable inner
oxide film covered with a porous, less stable outer layer, which is more susceptible to corrosion [21,
29, 30].
10 -1
10 0
10 1
10 2
10 3
10 4
j /
A c
m -2
j /
A c
m -2 (b)
(a)
10 -1
10 0
10 1
10 2
10 3
10 4
-1.8 -1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4
E / V (Ag/AgCl)
E / V (Ag/AgCl)
(d)(c)
-1.8 -1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4
Figure 2. CPP curves obtained for (a) annealed, (b) 1 pass, (c) 2 passes, and (d) 4 passes ECAPed AA
1050 electrode, respectively after its immersion in AGW for 20 minutes.
It is clearly seen from Fig. 2, curve 1, that the anodic reaction of Al started from the corrosion
potential (‒1285 mV vs. Ag/AgCl) towards the less negative potential values to show a passive region
at an average current density of 62.2 µA/cm 2 , extending from −1150 to −680 mV. In this potential
range, aluminum oxide is formed on the surface according to reaction (3). After which the current
shows an abrupt increase in its values with increasing the applied potential due to the breakdown of the
formed oxide film and the occurrence of pitting corrosion, accordingly the dissolution of aluminum
can be expressed by the reaction [11-13, 31, 32];
)4(3e .Al Al 3
This occurs under the influence of the attack of the aggressive chloride ions that present in the
seawater to the aluminum in the flawed areas of the oxide film, which leads to the formation of the
soluble aluminum chloride complex;
Int. J. Electrochem. Sci., Vol. 7, 2012
2851
Al 3+
+ 4Cl ‒ = AlCl4
‒ (5)
Here, there are two points of views explaining the mechanism of pitting corrosion at this
condition. The first claims [32, 33] that a salt barrier of AlCl3 is formed within the pits on their
formation, which could lead to the formation of AlCl4 − as repersented by Eq. 5, and diffuses into the
bulk of the solution. While, the second [34] has proposed that the chloride ions do not enter into the
oxide film but they are chemisorbed onto the oxide surface and act as a reaction partner, aiding the
oxide to dissolve via the formation of oxy-chloride complexes as follows:
Al 3+
(in crystal lattice of the oxide) + 2Cl ‒ + 2OH
‒ = Al(OH)2Cl2
‒ (6)
The occurrence of pitting corrosion was also indicated by the appearance of the hysteresis loop
on reversing the potential scan in the backward direction towards the more negative values. This loop
appeared due to higher current values in the reverse scan than the forward values. The bigger the area
of the loop the more severe is the pitting corrosion.
The CPP curves of ECAPed alloy show almost similar behavior but with lower corrosion rates
and higher corrosion resistances. This was indicating by recording the values of the corrosion potential
(ECorr), corrosion current (jCorr), cathodic (βc) and anodic Tafel slopes (βa), passivation current (jPass),
protection potential (EProt), pitting potential (EPit), polarization resistance (RP), and corrosion rate
(KCorr), obtained from CPP curves (Fig. 2) for the annealed and ECAPed AA 1050 alloys after their
immersion in AGW solutions for 20 min and shown in Table 1. The values of the corrosion potential
and corrosion current were obtained from the extrapolation of anodic and cathodic Tafel lines located
next to the linearized current regions. The pitting potential was determined from the forward anodic
polarization curves where a stable increase in the current density occurs. The protection potential was
determined from the backward anodic polarization curve at the intersection point with the forward
polarization curve. The values of RP and KCorr were calculated from the polarization data as reported in
our previous work [35-44].
It is seen from Fig. 2 and Table 1 that the AA 1050 alloy pressed by ECAP shifted the values of
ECorr to less negative values, lowered the values of jCorr, jPass, and KCorr, and increased the values of RP.
This effect is significantly increased with increasing the number of pass time to reach its maximum
after 4 passes. For that CPP behavior of the annealed AA 1050 alloy was compared to the fabricated
alloy by ECAPed for 4 passes after 10 days immersion in sea water before measurements as
repersented by Fig. 3a and Fig. 3b, respectively. The corrosion parameters obtained from Fig. 3 are
shown in Table 1. Fig. 3 and Table 1 show that the ECAPed alloy recorded lower corrosion rate and
higher corrosion resistance than the annealed alloy and both of the alloys showed better performance
compared to their CPP behavior when the immersion time was only 20 min. This indicates that the
increase of immersion time decreases the corrosion of annealed and ECAPed AA 1050 alloys.
According to Chung et al. [6] the increase of ECAP pass number increases the corrosion resistance of
AA 1050 due to the decreasing of the size of the Si-containing impurities on the alloy surface. Where,
the presence of these Si-containing impurities induced the micro-galvanic reaction by its reaction with
the Al matrix and also between the Al matrix and the Si-containing oxide.
Int. J. Electrochem. Sci., Vol. 7, 2012
2852
-1.8 -1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 10
-1
10 0
10 1
10 2
10 3
10 4
(b)
(a)
10 -1
10 0
10 1
10 2
10 3
10 4
-1.8 -1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4
j /
A c
m -2
E / V (Ag/AgCl)
j /
A c
m -2
Figure 3. CPP curves obtained for (a) annealed and (b) 4 passes ECAPed AA 1050 electrode after its
immersion in AGW for 10 days before measurement.
Table 1. Corrosion parameters obtained from polarization curves shown in Fig. 2 and Fig. 3 for AA
1050 after 20 min and 10 days of the electrode immersion in Arabian Gulf water.
AA 1050 alloy
Parameter
βc / mV
dec -1
ECorr/ mV
jCorr/
Acm -2
βa/ mV
dec -1
jPass/
Acm -2
EProt/
mV
EPit/
mV
Rp/
Ωcm 2
KCorr/ mmy
-1
0 pass (20 min) 100 -1285 27 110 62.2 -720 -655 0.84 0.294
1 pass (20 min) 105 -1270 22 115 50.0 -710 -645 1.10 0.240
2 pass (20 min) 110 -1260 18 120 49.9 -705 -643 1.37 0.196
4 pass (20 min) 110 -1255 15 125 42.1 -710 -640 1.70 0.164
0 pass (10 days) 135 -1225 19 153 89.7 -680 -610 1.64 0.207
4 pass (10 days) 140 -1210 13 155 61.6 -680 -620 2.46 0.142
3.2. Chronoamperometric current-time (CT) measurements
In order to shed more light on the effect of ECAP pass time on the pitting corrosion of Al AA
1050 after 20 min and 10 days immersion in AGW at more anodic constant potential value,
chronoamperometric experiments were carried out. Fig. 4 represents the variation of the measured
dissolution currents versus time at ‒630 mV vs. Ag/AgCl for the annealed (1) and ECAPed (2) 1 pass,
(3) 2 passes, and (4) 4 passes AA 1050 alloy, respectively after 20 min immersion in AGW. The same
experiments were conducted on the different Al rods after applying ‒1000 mV (this potential was
chosen from the CPP curves, where it allows the alloy to develop a compact passive layer) for 10 min
Int. J. Electrochem. Sci., Vol. 7, 2012
2853
before stepping the potential to ‒630 mV and the curves are shown in Fig. 5. It is seen from Fig. 4 that
the highest current values were recorded for the annealed alloy (curve 1), where the current increased
upon applying the potential in the first hundreds of seconds, the current then decreased slightly with
time for the whole time of the experiment. For the ECAPed alloys, the current-time curves showed the
same behavior with lower absolute currents. This effect increases with increasing the pass time
number, where the ECAPed alloy fabricated at 4 passes showed the lowest absolute current with time.
This behavior indicates that the increase of pass time number to 4 passes decreased the uniform
corrosion of AA 1050 in AGW.
0
1
2
3
4
5
6
0 500 1000 1500 2000 2500
2
time / sec
j /
m A
c m
-2
4 3
1
Figure 4. Chronoamperometric curves obtained for (1) annealed, (2) 1 pass, (3) 2 passes, and (4) 4
passes ECAPed AA 1050 electrode after its immersion in AGW solutions for 20 minutes
followed by stepping the potential to ‒630mV vs. Ag/AgCl.
The current-time curves depicted in Fig. 5 showed similar behavior to those shown in Fig. 4 at
the same potential, with possible occurrence of pitting corrosion due to the attack of the aggressive
ions present in the AGW to the flawed area of the passive layer that was formed at ‒1000 mV. From
the chronoamperometric experiments the annealed alloy showed the worst corrosion resistance, while
the best performance was recorded for the ECAPed alloy after 4 passes, for that the CT curves at ‒630
mV for (1) annealed and (2) 4 passes ECAPed AA 1050, respectively after 10 days immersion in the
AGW were carried out as shown in Fig. 6. The current for annealed alloy recorded very low values at
the few seconds of the measurement due to the formed corrosion products and oxide layer on the
surface during the 10 days immersion. The current then started to increase rapidly accompanied by
large fluctuations, which indicate on the occurrence of severe pitting corrosion. On the other hand, the
current for the ECAPed alloy recorded very low current values (few microamperes) for the whole time
of the experiment, which indicate that the formed passive layer during the immersion time was
compact enough to protect the surface from being pitted and attacked by the corrosive species that
present in the Gulf water at the applied potential. This also agrees with the work reported by Chung et
al. [6] that the increase of ECAP pass time number increases the pitting resistance of the alloy.
Int. J. Electrochem. Sci., Vol. 7, 2012
2854
0
1
2
3
4
5
0 500 1000 1500 2000 2500
4
-630 mV
time / sec
3 2
j /
m A
c m
-2
1
-1000 mV
Figure 5. Chronoamperometric curves obtained for (1) annealed and (2) 1 pass, (3) 2 passes, and (4) 4
passes ECAPed AA 1050 electrodes after their immersion in AGW solutions for 20 min
followed by stepping the potential to ‒1000 mV for 10 minutes and finally fix it to ‒630mV vs.
Ag/AgCl.
0
1
2
3
4
5
6
0 10 20 30 40 50 60
time / min
j /
A c m
-2
2
1
Figure 6. Chronoamperometric curves obtained for (1) annealed and (2) 4 passes ECAPed AA 1050
rods after their immersion in AGW for 10 days before stepping the potential to ‒630mV vs.
Ag/AgCl.
3.3. Electrochemical impedance spectroscopy (EIS) measurements
The EIS has successfully employed to explain the corrosion and corrosion inhibition of several
metals and alloys in chloride media [45-55]. The method was used to determine kinetic parameters for
electron transfer reactions at the alloy/electrolyte interface. The EIS Nyquist plots obtained for (1)
annealed, (2) ECAPed 1 pass, (3) ECAPed 2 passes, and (4) ECAPed 4 passes AA 1050 alloy,
respectively after 20 min immersion in AGW are shown in Fig. 7. The Nyquist (a), Bode (b) and phase
Int. J. Electrochem. Sci., Vol. 7, 2012
2855
angle (c) plots for (1) annealed and (2) ECAPed 4 passes AA 1050 alloy, respectively after 10 days are
also shown in Fig. 8. The EIS data of the Nyquist spectra shown in Fig. 7 and Fig. 8a were analysed by
fitting to the equivalent circuit model shown in Fig. 9. The parameters obtained by fitting the
equivalent circuit are listed in Table 2. Here, RS represents the solution resistance between the alloy
surface and the counter (platinum) electrode, Q the constant phase elements (CPEs) and contain two
parameters; a pseudo capacitance and an exponent (an exponent of less than unity indicates a
dispersion of capacitor effects [12, 13]), the RP1 accounts for the resistance of a film layer formed on
the alloy surface, Cdl is the double layer capacitance, Cdl is the double layer capacitance, and RP2
accounts for the charge transfer resistance at the alloy surface, i.e. the polarization resistance.
0 2 4 6 8 10 12
0
1
2
3
4
5
6
-Z " /
k
c m
2
Z' / kcm2
4
3 2
1
Figure 7. Nyquist plots obtained for (1) annealed, (2) 1 pass, (3) 2 passes, and (4) 4 passes ECAPed
AA 1050 electrode at an open circuit potential after its immersion in AGW for 20 min.
Nyquist spectra shown in Fig. 7 and Fig. 8a with the parameters recorded in Table 2 clearly
revealed that the values of RS, RP1 and RP2 increased with increasing the pass time number for the AA
1050 alloy. This is attributed to the formation of a passive film and/or corrosion products, which gets
thicker with time and could lead to the decrease in jCorr and KCorr and also the increase in RP values we
have seen in polarization data (Fig. 2, Fig. 3 and Table 1) under the same conditions. The semicircles
at high frequencies in Fig. 7 and Fig. 8a are generally associated with the relaxation of electrical
double layer capacitors and the diameters of the high frequency semicircles can be considered as the
charge transfer resistance (RP = RP1 + RP2) [37].
The polarization resistance measured by EIS is a measure of the uniform corrosion rate as
opposed to tendency towards localized corrosion. The decrease Cdl values with ECAP pass time is due
to the reduced access of charged species to the surface suggest that the dissolution of the alloy via
mass transport decreases. The CPEs (Q) with their n values > 0.5 and close to 1.0 represent double
Int. J. Electrochem. Sci., Vol. 7, 2012
2856
layer capacitors with some pores; the decrease of CPEs with the increase of number of ECAP passes
provides another indication on the increased passivation of AA 1050.
0 10 20 30 40 0
20
40
60
80
10 -1
10 0
10 1
10 2
10 3
10 4
10 5
10 1
10 2
10 3
10 4
10 5
10 -1
10 0
10 1
10 2
10 3
10 4
10 5
0
15
30
45
60
75
90
1
2
2
1
(c)
(b)
(a) 2
-Z " /
k
.c m
2
Z' / k.cm 2
1
|Z |
.c m
2
Frequency / Hz
Frequency / Hz
P h
a se
o f
Z (
d e g
)
Figure 8. Nyquist (a), Bode (b) and phase angle (c) plots for (1) annealed alloy and (2) 4 passes
ECAPed AA 1050 electrode at an open circuit potential after its immersion in AGW for 10
days.
Figure 9. The equivalent circuit model used to fit the experimental data presented in Fig. 7 and Fig.
8a. See text for symbols used in the circuit.
Int. J. Electrochem. Sci., Vol. 7, 2012
2857
Table 2. EIS parameters obtained by fitting the Nyquist plots shown in Fig. 7 and Fig. 8a with the
equivalent circuit shown in Fig. 9 for AA 1050 electrodes after 20 min and 10 days of
immersion in Arabian Gulf water.
AA 1050 alloy
Parameter
RS /
Ω cm 2
Q RP1 /
k Ω cm 2
Cdl /
µF cm -2
RP2 /
k Ω cm 2 YQ/ µF cm
-2 n
0 pass (20 min) 6.23 32.89 0.83 0.201 26.14 5.51
1 pass (20 min) 8.81 25.34 0.80 0.860 19.01 7.75
2 passes (20 min) 9.45 14.30 0.80 2.86 16.75 9.19
4 passes (20 min) 11.28 5.48 0.76 1.731 13.07 11.39
0 pass (10 days) 8.90 0.56 0.80 1.91 2.79 9.58
4 passes (10 days) 12.49 0.19 0.88 3.28 1.89 23.98
Increasing the immersion time from 20 min to 10 days also enhances the values of RS, RP1, and
RP2 and decreases the values of CPEs and Cdl, which means the alloy surface gets more passivated as
the exposure time before measurements increases. Elongation of immersion period leads to
accumulation of corrosion products and protective oxide layers on the alloy surface and thus decreases
the uniform corrosion. This was also confirmed by the increase in the impedance of the interface (Fig.
8b) and the maximum phase angle (Fig. 8c) with increasing the immersion time. In general, EIS results
agree with CPP and CT measurements that the corrosion AA 1050 decreases with increasing the ECAP
pass time number as well as the immersion time of the alloy in the test solution before measurement.
4. CONCLUSIONS
A series of aluminum alloy 1050 was fabricated by using ECAP process after 0, 1, 2, and 4
passes. The electrochemical behavior of the annealed and the ECAPed AA 1050 in Arabian Gulf water
was investigated using variety of electrochemical methods. Cyclic polarization tests after 20 min and
10 days immersion in AGW indicated that the increase of ECAP passes time as well as immersion time
decrease the uniform corrosion of the alloy. The variation of current against time at – 630 mV vs.
Ag/AgCl after 20 min and 10 days also revealed that the dissolution of AA 1050 decreased with
increasing the pass time number, while increasing the exposure time increases the pitting corrosion of
the annealed alloy. Electrochemical impedance spectra proved that the solution and polarization
resistances decreased with increasing the pass time number up to 4 and immersion intervals. The
results together were internally consistent with each other, indicating clearly that the dissolution of the
alloy decreased with increasing the number of ECAP pass time and the best performance was shown
by 4 passes ECAPed AA 1050 and this effect increased with increasing the immersion time from 20
minutes to 10 days.
ACKNOWLEDGEMENT
The authors are grateful to the Center of Excellence for Research in Engineering Materials (CEREM)
for the financial support.
Int. J. Electrochem. Sci., Vol. 7, 2012
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