Lightweight Materials for Applications

Transcription

1 Protection of Magnesium Alloys as Lightweight Materials for Applications in the Aerospace Industry Lénia M. Calado 1, Maryna Taryba 1, Maria J. Carmezim 1,2, M. Fátima Montemor 1 1 CQE, DEQ, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal 2 ESTSetúbal, Instituto Politécnico de Setúbal, Setúbal, Portugal International Workshop for Global Sustainability PGS Workshop 2018

2 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 1

3 Mg Alloys in the Aerospace Industry Lighter than other structural metals Good mechanical properties Castability Nontoxic Recyclable Density near R. T. (g/cm 3 ) Magnesium Aluminum > 2.70 Steel > 7.70 High strength-to-weight ratio Aeronautic Industry Regulations for reduction of greenhouse gas emissions Alternative fuels Engines with less fuel consumption Lightweight materials for aircraft weight reduction 2

4 Mg Alloys in the Aerospace Industry AZ92 Boeing 747 thrust reverser 1 Cockpit instrument panel 3 Seat components 3 Service door inner panel 3 Graphite/magnesium truss structures 4 ZE41 Bombardier Learjet 60 turbofan (Pratt & Whitney Canada) 2 Chassis for planetary probes (Mariner 2, MESSENGER power distribution unit) 5,6 1 A. Luo. Journal of Magnesium and Alloys, vol. 1, no. 1, pp. 2-22, 2013 / 2 A. Luo. Journal of Magnesium and Alloys, vol. 1, no. 1, pp. 2-22, 2013 / 3 A. Dziubińska et al. Advances in Science and Technology Research J, vol. 10, no. 31, pp , S.Rawal. Acta Astronautica, vol. 146, pp , abyss.uoregon.edu 3 6 E. Schaefer et al. Johns Hopkings APL Technical Digest, vol. 28, no. 1, 2008

5 Corrosion Susceptibility of Mg Alloys Mg + 2H 2 O Mg(OH) 2 + H 2 Mg Mg e 2H 2 O + 2e 2OH + H 2 Mg Mg+ + e Mg + + H 2 O Mg 2+ + OH H 2 Very reactive material Surface film that is formed when magnesium is exposed to air is poorly protective and less stable than films formed on other materials (aluminum, stainless steels) 4

6 Protection Strategies Appropriate design Protective coatings Inhibitors Selection and combination of materials Electrochemical protection Source: D. Landolt. Corrosion and surface chemistry of metals. 2nd ed. Lausanne: CRC Press,

7 Protection Strategies Physical barrier Protection from external aggressive environment Protective coatings Inhibitors High adhesion Mechanical resistance Flexibility Sources: M. F. Montemor. Functional and smart coatings for corrosion protection: a review of recent advances. Surf. Coatings Technol. vol. 258, pp , 2014 J. E. Gray, B. Luan. Protective coatings on magnesium and its alloys a critical review. J. Alloys Compd. vol. 336, pp , 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 ,

8 Protection Strategies Physical barrier Protection from external aggressive environment Protective coatings Inhibitors High adhesion Mechanical resistance Flexibility Extend protective ability and lifetime Self-healing coatings Improved and autonomous protection Sources: M. F. Montemor. Functional and smart coatings for corrosion protection: a review of recent advances. Surf. Coatings Technol. vol. 258, pp , 2014 J. E. Gray, B. Luan. Protective coatings on magnesium and its alloys a critical review. J. Alloys Compd. vol. 336, pp , 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 ,

9 Outline of Experimental Work Network structure with good adhesion to metallic substrate Epoxy-Silane Epoxy Cross-linked, dense barrier Silane Linkage between metallic substrate and organic matrix Modification of epoxy-silane reference coating with CeO 2 nanoparticles Evaluation of protective performance Characterization of formulated coatings 8

10 Outline of Experimental Work Sample Pre-treatment Mechanical polishing with SiC paper HF treatment Application of Coating Mixture of components Dip-coating Curing 9

11 Coating Morphology Uniform coating thickness Uniform coating surface Coating Thickness (µm) Reference 325 ppm CeO ± ± 1.9 FEG-SEM image of the cross-section of the modified coating applied onaz31. 10

12 Electrochemical Impedance Spectroscopy Z (ohm.cm²) h 1 day 4 days 7 days 8 days 14 days 15 days 21 days 22 days 29 days Base-coating, 29 days Frequency (Hz) Phase Angle (º) h 1 day 4 days 7 days 8 days 14 days 15 days 21 days 22 days 29 days Base-coating, 29 days Frequency (Hz) 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. 11

13 Electrochemical Impedance Spectroscopy 1E12 1E11 Base-coating 325 ppm CeO 2 Z ( cm 2 ) 1E10 1E9 1E8 1E Immersion Time (days) 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. 12

14 cm 2 ) Electrochemical Impedance Spectroscopy R1 CPE1 R2 CPE2 R ( cm 2 ) Reference Coating R coat. pores R int Time of immersion (days) R coat. pores R int R int R coat R ( cm 2 ) Modified Coating R coat. pores R int R coat. pores R int Element Freedom Value R1 Free(±) 1090 CPE1-T Free(+) E-10 CPE1-P Free(+) R2 Free(+) E09 CPE2-T Free(+) E-11 CPE2-P Free(+) R3 Free(+) E Chi-Squared: Weighted Sum of Squares: Time of immersion (days) Evolution of resistances for blank and modified coating during immersion testing in 0.05 Data M NaCl. File: R int R coat Electrolyte Resistance Coating 13 R3 Interfacial processes C:\Users\Lénia\D

15 LEIS Reference Coating Localized Electrochemical Impedance Spectroscopy 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 M NaCl. 14

16 LEIS Localized Electrochemical Impedance Spectroscopy 325 ppm CeO 2 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 M NaCl. 15

17 LEIS Localized Electrochemical Impedance Spectroscopy 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 M NaCl. 16

18 SVET Scanning Vibrating Electrode Technique Reference Very active defect during the whole immersion time Strong cathodic activity Hydrogen release 1 h µa/cm 2 1 h 20 h µa/cm 2 SVET analysis of artificial defect (200 µm) in base-coating. Immersion in 0.05 M NaCl. 17

19 SVET Scanning Vibrating Electrode Technique CeO 2 First signs of activity after 20 h of immersion Cathodic activity is 2 orders of magnitude lower than for reference coating 1 h 1 h 22 h µa/cm 2 µa/cm 2 SVET analysis of artificial defect (200 µm) in modified coating. Immersion in 0.05 M NaCl. 18

20 Conclusions 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 M NaCl electrolyte 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 Delay in onset of corrosion Healing effect of CeO 2 nanoparticles for epoxy-silane coating 19

21 Ongoing and Future Work ph sensitive corrosion inhibitor Synergistic effect of corrosion inhibitor mixture Structural magnesium alloy Mechanical properties 20

22 Acknowledgements UID/QUI/00100/

23 Thank you for your attention 22

24 Protection of Magnesium Alloys as Lightweight Materials for Applications in the Aerospace Industry Lénia M. Calado 1*, Maryna Taryba 1, Maria J. Carmezim 1,2, M. Fátima Montemor 1 1 CQE, DEQ, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal 2 ESTSetúbal, Instituto Politécnico de Setúbal, Setúbal, Portugal *leniacalado@tecnico.ulisboa.pt International Workshop for Global Sustainability PGS Workshop 2018