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Protection of Magnesium Alloys as Lightweight Materials for Applications
in the Aerospace Industry
Lénia M. Calado1, Maryna Taryba1, Maria J. Carmezim1,2, M. Fátima Montemor1
1CQE, DEQ, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal2ESTSetúbal, Instituto Politécnico de Setúbal, Setúbal, Portugal
International Workshop for Global Sustainability – PGS Workshop 2018
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Summary
Magnesium alloys in the aerospace industry
Corrosion susceptibility of magnesium alloys
Protection strategies
Outline of experimental work and experimental details
Characterization of develped coating (morphology and anticorrosive performance)
Conclusions
Ongoing and future work
L. Calado et al., 2018
• Alternative fuels
• Engines with less fuel consumption
• Lightweight materials for aircraft
weight reduction
Regulations for reduction of
greenhouse gas emissions
• Lighter than other structural metals
• Good mechanical properties
• Castability
• Nontoxic
• Recyclable
High strength-to-weight ratio
Aeronautic Industry
2
Mg Alloys in the Aerospace Industry
Density near R. T. (g/cm3)
Magnesium 1.70 – 1.85
Aluminum > 2.70
Steel > 7.70
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Mg Alloys in the Aerospace Industry
• Cockpit instrument panel3
• Seat components3
• Service door inner panel3
• Graphite/magnesium truss structures4
• Chassis for planetary probes (Mariner
2, MESSENGER power distribution
unit)5,6
AZ92
Boeing 747 thrust
reverser1
1A. Luo. Journal of Magnesium and Alloys, vol. 1, no. 1, pp. 2-22, 2013 / www.airteamimages.com2A. Luo. Journal of Magnesium and Alloys, vol. 1, no. 1, pp. 2-22, 2013 / www.jetevolutions.com3A. Dziubińska et al. Advances in Science and Technology Research J, vol. 10, no. 31, pp. 158-168, 20164S.Rawal. Acta Astronautica, vol. 146, pp. 151-160, 20185abyss.uoregon.edu6E. Schaefer et al. Johns Hopkings APL Technical Digest, vol. 28, no. 1, 2008
ZE41
Bombardier Learjet
60 turbofan (Pratt &
Whitney Canada)2
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Very reactive material
Surface film that is formed when magnesium is exposed to air is poorly protectiveand less stable than films formed on other materials (aluminum, stainless steels)
𝑴𝒈+ 𝟐𝑯𝟐𝑶 → 𝑴𝒈(𝑶𝑯)𝟐 +𝑯𝟐
𝑀𝑔 → 𝑀𝑔2+ + 2𝑒−
2𝐻2𝑂 + 2𝑒− → 2𝑂𝐻− +𝐻2
𝑀𝑔 → 𝑀𝑔+ + 𝑒−
𝑀𝑔+ + 𝐻2𝑂 → 𝑀𝑔2+ + 𝑂𝐻− +1
2𝐻2
Corrosion Susceptibility of Mg AlloysL. Calado et al., 2018
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Protection Strategies
Source: D. Landolt. Corrosion and surface chemistry of metals. 2nd ed. Lausanne: CRC Press, 2007
Appropriate
design
Selection and
combination of
materials
Protective
coatingsInhibitors
Electrochemical
protection
L. Calado et al., 2018
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Protection Strategies
Sources: M. F. Montemor. Functional and smart coatings for corrosion protection: a review of recent advances. Surf. Coatings Technol. vol. 258, pp. 17-37, 2014
J. E. Gray, B. Luan. Protective coatings on magnesium and its alloys – a critical review. J. Alloys Compd. vol. 336, pp. 88-113, 2002
C. Blawert, W. Dietzel, E. Ghali, G. Song. Anodizing treatments for magnesium alloys and their effect on corrosion resistance in various environments. Adv. Eng. Mater. vol. 8, pp. 511-533, 2006
Physical barrier
Protection from external
aggressive environment
High adhesion
Mechanical resistance
Flexibility
Protective
coatingsInhibitors
L. Calado et al., 2018
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Protection Strategies
Sources: M. F. Montemor. Functional and smart coatings for corrosion protection: a review of recent advances. Surf. Coatings Technol. vol. 258, pp. 17-37, 2014
J. E. Gray, B. Luan. Protective coatings on magnesium and its alloys – a critical review. J. Alloys Compd. vol. 336, pp. 88-113, 2002
C. Blawert, W. Dietzel, E. Ghali, G. Song. Anodizing treatments for magnesium alloys and their effect on corrosion resistance in various environments. Adv. Eng. Mater. vol. 8, pp. 511-533, 2006
Physical barrier
Protection from external
aggressive environment
High adhesion
Mechanical resistance
Flexibility
Protective
coatingsInhibitors
Extend protective
ability and lifetime
Self-healing coatings
Improved and
autonomous protection
L. Calado et al., 2018
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Outline of Experimental Work
Epoxy-Silane
Network structure with good adhesion to metallic substrate
Epoxy
Cross-linked, dense barrier
Silane
Linkage between metallic substrate
and organic matrix
Characterization of formulated coatings
Evaluation of protective performance
Modification of epoxy-silane reference coating with CeO2 nanoparticles
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Outline of Experimental Work
Sample Pre-treatment
Mechanical polishing with SiC paper
HF treatment
Application of Coating
Mixture of components
Dip-coating
Curing
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Uniform coating
thickness
FEG-SEM image of the cross-section of the modified coating applied on AZ31.
Coating Morphology
Coating Thickness (µm)
Reference 325 ppm CeO2
9.9 ± 1.3 10.4 ± 1.9
Uniform coating
surface
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10-2 10-1 100 101 102 103 104103
104
105
106
107
108
109
1010
1011
Frequency (Hz)
|Z|
(oh
m.c
m²)
4h1 day4 days7 days8 days14 days15 days21 days22 days29 daysBase-coating, 29 days
10-2 10-1 100 101 102 103 104
-90
-65
-40
-15
Frequency (Hz)
Ph
ase
An
gle
(º)
4h1 day4 days7 days8 days14 days15 days21 days22 days29 daysBase-coating, 29 days
Bode plots of coated AZ31 during immersion in 0.05 M NaCl. Results obtained after 29 days of immersion for the
reference coating are shown for comparison.
Electrochemical Impedance SpectroscopyL. Calado et al., 2018
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0 5 10 15 20 25 301E7
1E8
1E9
1E10
1E11
1E12
|Z| (
cm
2)
Immersion Time (days)
Base-coating
325 ppm CeO2
Evolution of low frequency impedance modulus (0.01 Hz) with immersion time in 0.05 M
NaCl for AZ31 coated with blank coating and with modified coating.
Electrochemical Impedance SpectroscopyL. Calado et al., 2018
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0 5 10 15 20 25 3010
8
109
1010
1011
1012
R (c
m2)
Time of immersion (days)
Rcoat. pores
Rint
0 5 10 15 20 25 3010
7
108
109
1010
R (c
m2)
Time of immersion (days)
Rcoat. pores
Rint
Evolution of resistances for blank and modified coating during immersion testing in 0.05 M NaCl.
Reference Coating Modified Coating
0 5 10 15 20 25 3010
7
108
109
1010
R (c
m2)
Time of immersion (days)
Rcoat. pores
Rint
0 5 10 15 20 25 3010
7
108
109
1010
R (c
m2)
Time of immersion (days)
Rcoat. pores
Rint
Rint
Rcoat
R1 CPE1
R2 CPE2
R3
Element Freedom Value Error Error %
R1 Free(±) 1090 792.91 72.744
CPE1-T Free(+) 4.3493E-10 2.5728E-12 0.59154
CPE1-P Free(+) 0.98211 0.00081983 0.083476
R2 Free(+) 3.5986E09 1.398E09 38.848
CPE2-T Free(+) 3.7647E-11 1.8122E-12 4.8137
CPE2-P Free(+) 0.66317 0.021213 3.1987
R3 Free(+) 1.4031E11 8.777E09 6.2554
Chi-Squared: 0.0005241
Weighted Sum of Squares: 0.035114
Data File: C:\Users\Lénia\Desktop\IST\Lab Work\EIS\
CeO2 set 4\4B1_4h_b.dta
Circuit Model File: C:\Users\Lénia\Desktop\IST\Lab Work\EIS\
@BRANCO\Modelo_2ccotempo.mdl
Mode: Run Fitting / Selected Points (3 - 39)
Maximum Iterations: 100
Optimization Iterations: 0
Type of Fitting: Complex
Type of Weighting: Calc-Modulus
Electrolyte
ResistanceCoating
Interfacial
processes
Electrochemical Impedance SpectroscopyL. Calado et al., 2018
Rint
Rcoat
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LEIS
LEIS admittance mapping over an artificial defect on the surface of the reference coating after 0.5 h, 24 h, and 49.5 h immersion in 0.005 M NaCl.
Reference Coating
Localized Electrochemical Impedance Spectroscopy
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LEIS
325 ppm CeO2
LEIS admittance mapping over an artificial defect on the surface of the ceria-modified coating after 0.5 h, 24 h, and 49.5 h immersion in 0.005 M NaCl.
Localized Electrochemical Impedance Spectroscopy
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LEIS
Optical microscope images of artificial defects made on
the reference and modified coatings
Ratio between the measured admittances during LEIS and the
first registered admittance for each sample during immersion
in 0.005 M NaCl.
Localized Electrochemical Impedance Spectroscopy
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SVET
SVET analysis of artificial defect (200 µm) in base-coating. Immersion in 0.05 M NaCl.
ReferenceVery active defect during the whole immersion time
Strong cathodic activity – Hydrogen release
µA/cm21 h
µA/cm220 h1 h
Scanning Vibrating Electrode Technique
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SVET
Scanning Vibrating Electrode Technique
SVET analysis of artificial defect (200 µm) in modified coating. Immersion in 0.05 M NaCl.
CeO2
First signs of activity after 20 h of immersion
Cathodic activity is 2 orders of magnitude lower than for reference coating
1 h
µA/cm2 µA/cm2
1 h 22 h
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Conclusions
Delay in onset of corrosion
Healing effect of CeO2 nanoparticles for epoxy-silane coating
Improvement in anticorrosive performance by incorporation of small amount of ceria
nanoparticles
Highly protective coating with stable anticorrosion performance up to 29 days of
immersion in 0.05 M NaCl
No coating delamination when substrate is exposed to 0.005 M NaCl electrolyte
L. Calado et al., 2018
Cathodic and anodic activity are kept low at artificial defect up to 22 h of immersion
in 0.05 M NaCl. First signs of activity detected only after 20 h of immersion
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Ongoing and Future Work
pH sensitive corrosion inhibitor
Synergistic effect of corrosion inhibitor mixture
Structural magnesium alloy
Mechanical properties
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Acknowledgements
UID/QUI/00100/2013
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Thank you for your attention
Protection of Magnesium Alloys as Lightweight Materials for Applications
in the Aerospace Industry
Lénia M. Calado1*, Maryna Taryba1, Maria J. Carmezim1,2, M. Fátima Montemor1
1CQE, DEQ, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal2ESTSetúbal, Instituto Politécnico de Setúbal, Setúbal, Portugal
International Workshop for Global Sustainability – PGS Workshop 2018