Accepted Manuscript

Corrosion behavior of Mg-5Al-xZn alloys in 3.5 wt.% NaCl solution

Nguyen Dang Nam, Motilal Mathesh

PII: S0925-8388(14)01593-XDOI: http://dx.doi.org/10.1016/j.jallcom.2014.07.014Reference: JALCOM 31642

To appear in: Journal of Alloys and Compounds

Received Date: 28 November 2012Revised Date: 3 July 2014Accepted Date: 3 July 2014

Please cite this article as: N.D. Nam, M. Mathesh, Corrosion behavior of Mg-5Al-xZn alloys in 3.5 wt.% NaClsolution, Journal of Alloys and Compounds (2014), doi: http://dx.doi.org/10.1016/j.jallcom.2014.07.014

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1

Corrosion behavior of Mg-5Al-xZn alloys in 3.5 wt.% NaCl solution

Nguyen Dang Nam1,*, Motilal Mathesh2

1Petroleum Department, Petrovietnam University, Ba Ria City, Ba Ria - Vung Tau

Province 74000, Vietnam

2School of Life and Environmental Sciences, Deakin University, Geelong Waurn Ponds

Campus, Victoria 3220, Australia

*Corresponding author Tel.: Tel.: +84 643 738 879, Fax: +84 643 733 579

E-mail address: ndnam@pvu.edu.vn

ABSTRACT

Five types of Mg-5Al alloys with different weight percentages of Zn ranging from 0

to 4 wt.% were examined using electrochemical techniques and surface analysis. The

electrochemical results indicated that the Mg-5Al alloys containing Zn have a lower

corrosion and hydrogen evolution rates than the Mg-5Al based specimens with a

decrease of value being observed with the decrease in Zn content. Zn addition induced

the precipitation of Mg-Al and Mg-Zn phases in the Mg matrix along with grain

refinement and increased an interaction of Zn oxide with Mg and Al products serving as

a corrosion barrier.

Keywords: Mg alloys, Zinc, Microstructure, Grain refinement, Hydrogen evolution rate,

Corrosion resistance

2

1. Introduction

Mg and its alloys are used as engineering materials in automotive, aerospace and

electronic fields [1-3] that requires high specific toughness, high specific strength to

weight ratio and lightweight properties [4]. Magnesium alloys have superior physical

and mechanical properties which make them extremely attractive for applications in

field which have requirement of lightweight materials. Research activities on

magnesium alloys have increased significantly, which includes the development of:

computational materials science and engineering approaches in alloy development

together with thermodynamic and first-principles modeling; mechanistic understanding

and development of creep-resistant casting alloys; mechanistic understanding and

modeling of deformation, including mechanical twinning and dynamic recrystallization;

and texture modification via alloying and processing [5]. However, as one of the most

reactive metals, the poor intrinsic corrosion resistance of magnesium alloys has limited

their widespread application.

Improvements in the mechanical properties and corrosion resistance have led to

greater interest of magnesium alloys for aerospace and special applications. There have

been many attempts to improve the corrosion resistance of magnesium alloys by adding

certain alloying elements [6-15], refining its microstructure [16-21], anti-corrosion

coating [22-27], and control of the orientations [28,29]. At present, it has been

successfully used to enhance the strength and ductility of wrought magnesium alloys

produced via processes such as extrusion, rolling, forging, twin-roll strip casting and

equal channel angular pressing [30-36]. Among these techniques, extrusion is very

useful for its technical and economical advantages in the production of structural

3

components [37]. Several wrought magnesium alloys with stable secondary-phase

particles have been developed using grain size refinement by hot extrusion method [38-

46]. In these processes, grain growth could be inhibited due to the dispersion or

precipition of secondary-phase particles and an improved microstructure could be

achieved by thermomechanical processes.

A thinner film formation is featured by Al addition to Mg alloys which contains a

mixture of MgO/Al2O3 and/or Mg(OH)2/Al(OH)3 ameliorating its protective behavior

due to the presence of Al in the passive layer [47,48]. But, Al improves the corrosion

resistance of Mg alloys only at higher concentrations. In recent years, Zn has been

added to improve the mechanical properties [49-51]. The enhancement in the

mechanical properties of these magnesium alloys is due to formation of a long periodic

stacking structure [52-54]. It was reported that the addition of Zn element can

effectively increase the strength and improve the plasticity. In addition, Zn has been

showed to have a great potential for employment in manufacture of new generation

biodegradable implants [45-57]. Zn addition also significantly refined the grain size of

the extruded Mg-Mn alloy as well as enhanced the mechanical properties [58-60]. This

reveals that Zn addition as an alloying element enhances the mechanical property and it

is necessary to provide a base for the understanding of corrosion performance. In order

to determine the corrosion behavior of Mg-5Al alloys in corrosive solutions, this work

was carried out on, Mg-5Al, Mg-5Al-1Zn, Mg-5Al-2Zn, Mg-5Al-3Zn, Mg-5Al-4Zn

alloys and conducted on the basics of electrochemical measurements and surface

analysis.

2. Experimental

4

2.1. Specimen preparation

Pure Mg (99.9 %) ingot was melted in a stainless steel crucible under the protection of

gas mixture containing SF6 and CO2. The calculated amounts of 5 wt.% Al and 1, 2, 3,

and 4 wt.% Zn were added to the Mg melt. After solidification, the ingots were

subjected to homogenizing treatment at 400 ˚C for 14 h. The homogenized ingots were

machined, which were used as raw materials for extrusion. The extrusion of billets was

performed at 320 ˚C. In addition to this, extrusion ratio of 25:1 and speed of 0.15 mm/s.

were applied. The chemical compositions of tested alloys were determined by Optical

Emission Spectroscopy. Alloys with chemical compositions were 5.000 Al, 0.005 Si,

0.004 Fe, 0.003 Cu, 0.007 Ni, while the difference between measured and specified

composition of Zn is imperceptible. The specimens for electrochemical tests were first

cold-mounted on a mounting cup and then finished by grinding with 600-grit silicon

carbide paper.

2.2. Electrochemical investigation methods

All of the electrochemical experiments were performed at room temperature in 1000

ml of 0.6 M NaCl solution with aeration. The exposed area was 1 cm2. Potentiodynamic

polarization tests were performed using an EG&G PAR 263A potentiostat for the DC

measurements. A graphite counter electrode was used, with a saturated calomel

electrode as the reference. Prior to the potentiodynamic polarization test, the samples

were immersed in the solution for 1 h in order to stabilize the open-circuit potential. The

potential of the electrodes was swept at a rate of 0.166 mV/s in the range from initial

potential of -250 mV versus Ecorr to final potential of -1.3 VSCE. The electrochemical

impedance spectroscopy (EIS) and corrosion potential measurements were conducted

5

using a IM6e system with a commercial software program for the AC measurements.

The amplitude of the sinusoidal perturbation was 10 mV. The frequency range was from

100 kHz to 1 Hz. The hydrogen evolution rate of the alloys was investigated by

immersion tests. The specimens, with dimensions of 10 mm × 10 mm × 2 mm, were

prepared by grinding each side with 600-grid emery paper and degreasing the surfaces

with ethanol prior to corrosion testing. The hydrogen evolution rate was used as an

indicator of the corrosion rate which was monitored every 1 hour. Alloy specimens for

hydrogen gas collection, to characterize the corrosion rate during solution immersion,

were immersed in 1000 ml of 0.6 M NaCl solution with aeration. The hydrogen evolved

during the corrosion experiment was collected in a burette above the corroding

specimens. The overall magnesium corrosion reaction,

Mg + H+ + H2O = Mg

2+ + H2 (1)

shows that one molecule of hydrogen is evolved for each atom of corroded magnesium.

2.3. Surface analysis

The crystal structure of the specimens was investigated by XRD using Cu Kα radiation.

For the observation of the microstructure, optical microscope was used. The specimens

were mechanically sanded with sand paper (#220, 600, 1200, 2000, and 4000) and then

fine polished with 0.1 µm alumina powders. These specimens were then etched in a

mixture of solution containing acetic acid (10 ml), picric acid (5 g), distilled water (10

ml) and ethanol (70 ml of 95% purity). To investigate the relationship between the

electrochemical behavior and surface morphology, the specimens were examined by

SEM after 6 hours of immersion test. The surface products were examined by X-ray

photoelectron spectroscopy (XPS) after 1 h of the open-circuit potential.

6

3. Results and discussion

Fig. 1 compares the microstructures of the Mg-5Al alloys with different amounts of

Zn content. The microstructures consisted of only the α-Mg matrix. The addition of Zn

decreased the grain size of the Mg-5Al alloy and also showed appearance of an

increased amount of new fine grains at the grain boundary due to the recrystallization.

In general, the microstructure included primary α grains surrounded by new fine grains.

The specimens had relatively smaller α-Mg grains with increasing Zn content which

may influence the corrosion performance since uniform corrosion product is expected to

act as a barrier. The phase compositions of the specimens were examined by XRD as

shown in Fig. 2. There is no significant difference in the α-Mg peaks between the Mg-

5Al and Zn-containing specimens. The results also show the well-defined peaks of Mg

and Mg17Al12 with an additional peak close to the reflections by Mg2Zn. The intensity

of the Mg2Zn diffraction peaks increases with increasing Zn content due to an increase

reaction between Mg and Zn.

Fig. 3 (a) shows the hydrogen evolution rate and Fig. 3 (b) shows the corrosion rate of

the alloys calculated by hydrogen evolution rate. All specimens exhibited an increase in

hydrogen evolution rate with increasing immersion time during 7 h. The hydrogen

evolution rate for Mg-5Al based alloy increased strongly with exposure time and were

significantly larger than that of Zn-containing specimens. The hydrogen evolution

volume of Mg-5Al-xZn alloys in Fig. 3 (a) can be ranked in a decreasing series as: Mg-

5Al > Mg-5Al-4Zn > Mg-5Al-3Zn > Mg-5Al-2Zn > Mg-5Al-1Zn. The result showed

that the corrosion rate of the Zn-containing samples was stable during 7 h immersion time,

while it increased quickly in case of Mg-5Al based alloy. The result suggested that

7

hydrogen evolution rate of a corroding magnesium alloy at its open current potential is

equal to its corrosion rate and reflects to some degree the electrochemical activity of Mg

alloy. In addition, hydrogen evolution rate allows studying the variation in corrosion

rate with immersion time.

Fig. 4 shows the polarization curves of the Mg-5Al alloys as a function of Zn content

in 0.6 M NaCl solution. All alloys demonstrated active corrosion behavior, as the

current density increased continuously with increasing potential. The corrosion current

density increased with increase in Zn content. Table 1 lists the corrosion properties

observed from potentiodynamic polarization. The corrosion rate was determined using

the Tafel extrapolation method, based on Faraday’s law [61-63]:

Corrosion rate (cm/y)ρ××

×××=

Fz

Micorr

71016.3

(2)

where icorr is the corrosion current density (A/cm2), M is the molar mass of the metal

(g/mole), z is the number of electrons transferred per metal atom, F is the Faraday’s

constant, and ρ is the density of the metal (g/cm3). Polarization resistance (Rp) value

was obtained from eq (2) [64]:

)(3.2 cacorr

cap

iR

ββ

ββ

+×= (3)

where βa and βc are the anodic and cathodic Tafel slope, respectively. The corrosion

current density of the alloys was calculated using Eq. (3) under the assumption that βa

and βc are equal to 0.1 V/decade. Similarly, corrosion rate of the alloys was calculated

from the EIS measurements by using Eq. (2).

Fig. 5 (a) and (b) present the Nyquist and Bode plots after immersion for 1 h at Ecorr.

The high spectra are used to detect the local surface defects, whereas the medium and

8

low frequency spectra detect the processes within the corrosion product and at the

metal/corrosion product interface, respectively. The impedance spectrum of the Mg-

5Al-xZn alloy exhibits a capacitive loop in the high frequency range and an inductive

loop in the low frequency range. The aperture of impedances and impedance modulus

|Z| of the Zn-containing alloys are greater than that of the Mg-5Al based alloy which

increase with a decrease of Zn content. These results confirmed the increase in

impedance gained via the addition of Zn due to the formation of a corrosion product

layer. The electrochemical response to the impedance tests for these materials was best

simulated with the equivalent circuits as shown in Fig. 5 (c) [65], in which Rs represents

the solution resistance between working electrode and reference electrode. Rc represents

resistance of corrosion product layer, Cc represents capacitance of corrosion product

layer, CPE represents the constant phase element for the double layer capacitance, Rct

represents the charge transfer resistance during electrochemical reaction. A constant-

phase element representing a shift from an ideal capacitor was used instead of the

capacitance itself, for simplicity. The impedance of a phase element is defined as:

ZCPE = [C(jω)n]-1

(4)

where C is capacitance; j is the current; ω is the frequency and -1 = n = 1. The value of

n seems to be associated with the non-uniform distribution of current as a result of

roughness and surface defects. The n value of a CPE indicates: capacitance, Warburg

impedance, resistance and an inductance when n=1, 0.5, 0, -1 respectively. In the

present study, n was consistently maintained near 0.8, as a result of the deviation from

ideal dielectric behavior. The low frequency inductance loop is described with Rdiff

(inductance resistance) and L (inductance). In this case, the polarization resistance, Rp,

is calculated from the equivalent circuit in Fig. 4 (c) as shown in the equation:

9

Rp = Rs + Rct + Rdiff (5)

The fitting results are presented in Table 2. It indicates that resistances of Zn-containing

specimens are much higher than that of Mg-5Al based alloy which increases with

decrease of Zn content.

Fig. 6 compares the average corrosion rate for alloys obtained from hydrogen

evolution rate measurement and electrochemical methods. The corrosion rate in the case

of the electrochemical measurements can be inferred from the corrosion current density,

based on Faraday’s law. In addition, the hydrogen evolution volume rate, VH (ml/cm2.d)

can be related to the corrosion rate according to the equation [66]:

PH (cm/y) = 0.2279 VH (6)

The average corrosion rate of the alloys using the above methods was ranked in the

following order: Mg-5Al > Mg-5Al-4Zn > Mg-5Al-3Zn > Mg-5Al-2Zn > Mg-5Al-1Zn.

It indicated that Zn-containing Mg-5Al alloy have lower corrosion rates than Mg-5Al

based alloy, and the corrosion rate decreases with decreasing Zn content. In summary,

the electrochemical and hydrogen evolution rate measurements showed that the

corrosion resistance of Mg-5Al alloy can be improved significantly by Zn addition.

Fig. 7 shows SEM images of the surface morphology after the hydrogen evolution test

for 7 h immersion at Ecorr. A severe corrosion was observed on the Mg-5Al based alloy

due to large number of hydrogen bubbles, while less corrosion was observed in case of

Zn containing specimens, especially for Mg-5Al-1Zn.

Fig. 8 shows XPS results of the specimen surfaces after exposing the alloys to the 0.6

M NaCl solution for 1 h at room temperature. This figure shows that the peaks of Mg,

Al, Cl, Zn and O exist. Oxygen KVV correspond to peak in the region near 1100 eV.

The narrow XPS spectra for Mg 2p, Al 2p, Zn 2p, Cl 2p, and O 1s regions are shown in

10

Figs. 8 (b, c, d, e and f), respectively. The spectra of Mg 2s, 2p and Al 2p corresponds to

MgO/Mg(OH)2 and Al2O3/Al(OH)3 on the surface of the alloys. When specimens are

immersed in 0.6 M NaCl solution, the corrosion attack on magnesium is severe due to

easy penetration of the oxide/hydroxide products by Cl‾ ions and the formation of a

basic chloride salt (MgCl2), which is readily accommodated in the layered structure of

MgO/Mg(OH)2 and Al2O3/Al(OH)3. The O 1s spectra were composed of two peaks

corresponding to the signals from oxygen in the oxide at 530.05 eV and oxygen in the

hydroxyl groups at 531.70 eV. In addition, a small Cl peak was observed in the Mg-5Al-

1Zn specimen. This figure also shows the appearance of Al 2p and O 1s peaks which are

enriched with decreasing Zn content, while lesser intensity Mg peak was obtained in the

case of Mg-5Al alloy. The binding energy of Zn 2p was approximately 1020 eV as

shown in Fig. 8 (f). The presence of ZnO on the surface of the Zn-containing alloys

decreased the corrosion rate due to a decrease in the hydrogen evolution rate. Compared

to the Zn 2p oxide peaks in Fig. 8 (f), the alloy contribution for the 1 wt.% Zn-

containing alloy has higher peaks than the peaks from other alloys. The results indicated

that the enriched Mg, Al and Zn products played an important role in improving the

corrosion products of magnesium alloys, thereby providing better corrosion protection

which inhibited the adsorption of Cl- ions.

4. Conclusions

The addition of Zn caused a decrease in grain size of the α-Mg solid solution phase.

The corrosion and hydrogen evolution rates of Zn-containing alloys were lower than

that of Mg-5Al based alloy which increased with increasing Zn content. EIS showed

11

that the semicircle was less depressed in case of Zn-containing specimens. In addition,

the total resistance also decreased with increasing Zn content. Zn addition to Mg-5Al

alloys facilitates the formation and interaction of Mg, Al, and Zn oxides on the alloy

surface. In addition, the amount of chloride in the surface products decreases with

decreasing Zn content, indicating a more adherent corrosion products on the Mg-5Al-

1Zn alloy surface.

Acknowledgement

The authors are grateful for the support of Vietnam Oil and Gas Group, PetroVietnam

University and the National Foundation for Sciences and Technology Development

(NAFOSTED 2014).

12

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17

Figure captions

Fig. 1. Optical microscope of (a) Mg-5Al, (b) Mg-5Al-1Zn, (c) Mg-5Al-2Zn, (d) Mg-

5Al-3Zn, and (e) Mg-5Al-4Zn alloys.

Fig. 2. XRD patterns of (a) Mg-5Al, (b) Mg-5Al-1Zn, (c) Mg-5Al-2Zn, (d) Mg-5Al-

3Zn, and (e) Mg-5Al-4Zn alloys: a; α-Mg, b; Mg17Al12, and c; Mg2Zn.

Fig. 3. (a) Hydrogen evolution and (b) Corrosion rate of the Mg-5Al-xZn samples

immersed in 3.5 wt.% NaCl at room temperature as function of immersion time.

Fig. 4. Potentiodynamic polarization curves of Mg-5Al as a function of Zn content.

Fig. 5. Impedance spectra on (a) Nyquist plots and (b) Bode plots and (c) equivalent

circuit for fitting the EIS data.

Fig. 6. Average the corrosion rate calculated using potentiodynamic polarization, EIS,

and the hydrogen evolution measurements in 3.5 wt.% NaCl at room temperature.

Fig. 7. SEM images of the specimens tested after 6 h immersion in 3.5 wt.% NaCl at

room temperature: (a) Mg-5Al, (b) Mg-5Al-1Zn, (c) Mg-5Al-2Zn, (d) Mg-5Al-3Zn, and

(e) Mg-5Al-4Zn alloys.

Fig. 8. XPS peak analysis for the surface products of the Mg-5Al-xZn alloys: (a) survey

scan spectra and narrow scan spectra of (b) Mg, (c) Al, (d) Zn, (e) Cl, and (f) O.

18

(a)

(b)

19

(c)

(d)

20

(e)

Fig. 1.

21

20 30 40 50 60 70 80

(a)

Inte

nsi

ty (

Arb

.un

its)

2θ (Degree)

(b)

(d)

(c)

c b aaa aaaaabb

aaaa(e)

Fig. 2.

22

0 1 2 3 4 5 6 7 80

2

4

6

8

10 Mg-5Al

Mg-5Al-1Zn

Mg-5Al-2Zn

Mg-5Al-3Zn

Mg-5Al-4ZnV

olu

me

of

H2 (

ml/

cm2)

Time (hr)

(a)

0 1 2 3 4 5 6 7 80

2

4

6

8 Mg-5Al

Mg-5Al-1Zn

Mg-5Al-2Zn

Mg-5Al-3Zn

Mg-5Al-4Zn

Corr

osi

on R

ate

(cm

/yr)

Time (hr)

(b)

Fig. 3.

23

10-6

10-5

10-4

10-3

10-2

10-1

-1.8

-1.7

-1.6

-1.5

-1.4

-1.3

-1.2

Pote

nti

al

(VS

CE)

Current Density (A/cm2)

Mg-5Al

Mg-5Al-1Zn

Mg-5Al-2Zn

Mg-5Al-3Zn

Mg-5Al-4Zn

Fig. 4.

24

0 200 400 600 800 1000 1200 1400 1600

-400

-200

0

200

400

600

-Z"

(Ω.c

m2)

Z' (Ω.cm2)

Mg-5Al

Mg-5Al-1Zn

Mg-5Al-2Zn

Mg-5Al-3Zn

Mg-5Al-4Zn

(a)

10-1

100

101

102

103

104

105

106

101

102

103

-20

0

20

40

60

80 Mg-5Al

Mg-5Al-1Zn

Mg-5Al-2Zn

Mg-5Al-3Zn

Mg-5Al-4Zn

|Z

| (Ω

.cm

2)

Frequency (Hz)

Ph

ase

An

gle

(D

eg)

(b)

25

Rdiff

LRc

CPE

Cc

Rct

Rs

(c)

Fig. 5.

26

0.1

0.2

0.3

0.4

0.70

0.75

0.80

0.85

Mg-5Al-xZn Alloys

Aver

age

Corr

osi

on R

ate

(cm

/yr)

0Zn 1Zn 2Zn 3Zn 4Zn

Fig. 6.

27

(a)

(b)

28

(c)

(d)

29

(e)

Fig. 7.

30

0 200 400 600 800 1000 1200

O KVV

Zn2p

Mg2p

Al2p

Mg2s

Cl2p

O1s

Mg-5Al

Mg-5Al-1Zn

Mg-5Al-2Zn

Mg-5Al-3Zn

Mg-5Al-4Zn

Binding Energy (eV)

Inte

nsi

ty (

arb

. u

nit

s)

(a)

78 80 82 84 86 88 90 92 94 96 98

Mg2s

Mg-5Al

Mg-5Al-1Zn

Mg-5Al-2Zn

Mg-5Al-3Zn

Mg-5Al-4Zn

Binding Energy (eV)

Inte

nsi

ty (

arb

. u

nit

s)

31

40 42 44 46 48 50 52 54 56 58

Mg2p

Mg-5Al-1Zn

Mg-5Al-2Zn

Mg-5Al-3Zn

Mg-5Al-4Zn

Inte

nsi

ty (

arb. unit

s)

Binding Energy (eV)

(b)

62 64 66 68 70 72 74 76 78 80 82

Mg-5Al

Mg-5Al-1Zn

Mg-5Al-2Zn

Mg-5Al-3Zn

Mg-5Al-4Zn

Binding Energy (eV)

Inte

nsi

ty (

arb

. u

nit

s)

(c)

32

1000 1010 1020 1030 1040 1050 1060

Mg-5Al-1Zn

Mg-5Al-2Zn

Mg-5Al-3Zn

Mg-5Al-4Zn

Inte

nsi

ty (

arb

. u

nit

s)

Binding Energy (eV)

(d)

190 192 194 196 198 200 202 204 206

Mg-5Al

Mg-5Al-1Zn

Mg-5Al-2Zn

Mg-5Al-3Zn

Mg-5Al-4Zn

Inte

nsi

ty (

arb

. u

nit

s)

Binding Energy (eV)

(e)

33

522 525 528 531 534 537 540

Mg-5Al

Mg-5Al-1Zn

Mg-5Al-2Zn

Mg-5Al-3Zn

Mg-5Al-4Zn

Binding Energy (eV)

Inte

nsi

ty (

arb

. unit

s)

(f)

Fig. 8.

34

Table 1. Critical parameters from potentiodynamic polarization curves for Mg-5Al-xZn

alloys in 3.5 wt.% NaCl as a function of Zn addition.

Sample Ecorr (VSCE) icorr (µA/cm2 ) βa (V/decade) -βc (V/decade)

#1 -1.53 367 0.051 0.199

-1.54 370 0.025 0.170

-1.54 366 0.023 0.160

Average -1.54 368

#2

-1.57 67 0.020 0.146

-1.54 65 0.018 0.134

-1.53 63 0.019 0.142

Average -1.55 65

#3

-1.55 102 0.016 0.140

-1.57 124 0.019 0.126

-1.54 112 0.017 0.132

Average -1.55 113

#4

-1.55 173 0.022 0.167

-1.55 163 0.015 0.155

-1.56 169 0.020 0.158

Average -1.55 168

#5

-1.56 202 0.033 0.172

-1.57 172 0.035 0.186

-1.57 197 0.033 0.178

Average -1.56 190

35

Table 2. Fitting results of EIS measurements (CP = corrosion product).

Specimen Rs

(Ω.cm2)

CCP

(µF/cm2)

RCP

(Ω.cm2)

CPE2 Rct

(Ω.cm2)

L

(H.cm2)

Rdiff

(Ω.cm2) C

(µF/cm2)

n

(0~1)

# 1 15.2 19.1 0.5 102.3 0.4293 131 260 66

# 2 5.4 8.6 52.2 11.5 0.8937 903 3315 230

# 3 5.5 10.9 32.2 32.5 0.8453 783 3121 148

# 4 4.9 11.4 23.1 55.5 0.8239 695 3273 138

# 5 5.2 14.0 10.4 61.0 0.8180 443 3107 108

36

Research highlights

Zinc is found to be a good alloying element for corrosion resistance of Mg-5Al alloy

in 3.5 wt.% NaCl solution. Zinc has an advantage of improving corrosion

performance with decreasing zinc content. The benefits of the zinc in corrosion

performance of Mg-5Al alloy is satisfactorily discussed and confirmed by

electrochemical and surface analysis results.