Surface Engineering Challenges of Dissimilar Materials Joints

Transcription

1 Surface Engineering Challenges of Dissimilar Materials Joints Michele Curioni & LATEST2 team Corrosion And Protection Centre School of Materials The University of Manchester M13 9PL, Manchester, UK

2 Microstructure and Electrochemistry Scanning Electron Micrograph, AA 2024 T3, Sulphuric Acid Anodizing, 0.46 mol/l, potentiostatic anodizing at 2 V (SCE), 0.6 C/cm 2 V M V P Vertical Section + V Alloy Corrosion Current

3 Light Alloys Surfaces Oxide on anodic phase Oxide on cathodic phase Cathodic Phase Anodic Phase Defect resulting in anodic reaction Oxide on anodic phase Oxide on cathodic phase Oxide on anodic phase Defect resulting in cathodic reaction Oxide on cathodic phase Cathodic Phase Cathodic Phase Anodic Phase Anodic Phase Anodic Event

4 Light Alloys Surfaces Oxide on anodic phase Oxide on cathodic phase Cathodic Phase Anodic Phase ph decreases Oxide on anodic phase Oxide on cathodic phase Oxide on anodic phase Oxide on cathodic phase ph increases Cathodic Phase Cathodic Phase Anodic Phase Anodic Phase Anodic Event Cathodic Event

5 Localized ph variations Anodic Bulk Cathodic Oxide on anodic phase Oxide on cathodic phase Cathodic Phase Anodic Phase

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9 Hydrogen Evolution on second phases Aluminium Oxidation at the corrosion Front

10 Corrosion and Microstructure

11 Dissimilar Materials Joints How can we evaluate in detail and quantitatively the effects on the corrosion behavior due to dissimilar materials joints without interfering with corrosion process?

12 Dissimilar Metal Joints Galvanic Current in the electrolyte -- Environmental effects Metal 1 Galvanic Current in the metal phase Metal 2

13 Al E 0 =-1.66 Mg E 0 =-2.37 A C A C Net Cathode Net Anode

14 Potential Effects

15 Titanium Crevice Stainless Steel

16 Dissimilar Metal Joints Galvanic Current in the electrolyte -- Environmental effects A Metal 1 Galvanic Current Metal 2 V Potential

17 = The Corroding Surface

18 Multielectrode equivalent circuit

19 Dissimilar pairs of identical electrodes When 2 electrodes are dissimilar, you can estimate the impedance of the LESS noisy electrode For 2 dissimilar pairs of identical electrodes, a single electrode is always LESS NOISY, than the other 3 M. Curioni, R.A. Cottis, M. Di Nataleand G.E. Thompson, Electrochimica Acta, 56, (2011)

20 AA2024T3 coupled to Al99.99%

21 EN Analysis Link

22 AA2024T3 coupled to dissimilar metals

23 AA2024T3 coupled to dissimilar metals

24 AA2024T3 coupled to dissimilar metals

25 Al E 0 =-1.66 Mg E 0 =-2.37 A C A C Net Cathode Net Anode

26 A B C D EN for Weld evaluation

27 EN for Weld evaluation Electrochemical Noise Impedance of Individual Weld Regions Good Bad

28 How to Protect?

29 Protection Strategies V Alloy Corrosion Current V Alloy

30 Intermetallics Removal

31 Anodizing Dissimilar Materials

32 Use Inhibitors Resin Block Microscope Alloy Specimens Glass M. Curioni, R. Bingham, A. Durán, M. Aparicio, R. A. Cottis, G.E. Thompson, Corrosion Science, 52,10, 3356 (2010) Microscope View

33 Image Assisted Electrochemical Noise Surface appearance related to noise impedance Comparative evaluation of inhibitors effectiveness vs. blank and benchmark Inhibitors Link M. Curioni, R. Bingham, A. Durán, M. Aparicio, R. A. Cottis, G.E. Thompson, Corrosion Science, 52,10, 3356 (2010)

34 Improve Adhesion Anodic Film Morphology HTCAA 200 nm Standard CAA

35 Adhesive Penetration: HTCAA film E D C B A

36 Environmentally-friendly anodizing for enhanced corrosion/adhesion V Time 200 nm A B C

37 Environmentally-friendly anodizing for enhanced corrosion/adhesion After Immersion for 12 days in 3.5% NaCl M.Curioni, P. Skeldon, J. Ferguson and G. E. Thompson, Journal of Applied Electrochemistry, 41, 773 (2011)

38 Summary The joining of dissimilar materials produces complex interactions galvanic coupling due to differences in electrochemical potential Localized ph and environment variation Electrochemical noise can be used effectively to evaluate the consequence of galvanic coupling in a virtually unperturbed condition Appropriate surface treatments can be designed to reduce the issues, provided that they can be applied and are effective simultaneously on both materials michele.curioni@manchester.ac.uk