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
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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
Microstructure and ElectrochemistryScanning Electron Micrograph, AA 2024 T3, Sulphuric Acid Anodizing, 0.46 mol/l, potentiostatic anodizing at 2 V (SCE), 0.6 C/cm2 VPVM
+Vertical Section
VAlloy
Corrosion Current
Light Alloys Surfaces
Cathodic Phase
Anodic Phase
Oxide on anodic phase
Oxide on cathodic phase
Defect resulting in
Defect resulting in
anodic reaction
Cathodic Phase
Anodic Phase
Oxide on anodic phase
Oxide on cathodic phase
Defect resulting in cathodic reaction
Cathodic Phase
Anodic Phase
Oxide on anodic phase
Oxide on cathodic phase
Anodic Event
Light Alloys Surfaces
Cathodic Phase
Anodic Phase
Oxide on anodic phase
Oxide on cathodic phase
pH
pH decreases
Cathodic Phase
Anodic Phase
Oxide on anodic phase
Oxide on cathodic phase
pH increases
Cathodic Phase
Anodic Phase
Oxide on anodic phase
Oxide on cathodic phase
Anodic Event Cathodic Event
Localized pH variations
AnodicCathodic
Bulk
Cathodic Phase
Anodic Phase
Oxide on anodic phase
Oxide on cathodic phase
Hydrogen Evolution
on second phases
Aluminium
Oxidation at
the corrosion
Front
Corrosion and Microstructure
Dissimilar Materials Joints
How can we evaluate in detail and quantitatively
the effects on the corrosion behavior due to
dissimilar materials joints without interfering dissimilar materials joints without interfering
with corrosion process?
Dissimilar Metal Joints
Galvanic Current in the electrolyte -- Environmental effects
Galvanic Current in the metal phaseMetal 1 Metal 2
A
Al E0=-1.66
Mg E0=-2.37
C
A
CA
Net Cathode
Net Anode
Potential Effects
Titanium
Crevice
Stainless Steel
Dissimilar Metal Joints
Galvanic Current in the electrolyte -- Environmental effects
Galvanic CurrentMetal 1 Metal 2
A
V
Potential
The Corroding Surface
=
Multielectrode equivalent circuit
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 Natale and G.E. Thompson,
Electrochimica Acta, 56, 10270 (2011)
AA2024T3 coupled to Al99.99%
EN Analysis
Link
AA2024T3 coupled to dissimilar metals
AA2024T3 coupled to dissimilar metals
AA2024T3 coupled to dissimilar metals
A
Al E0=-1.66
Mg E0=-2.37
C
A
CA
Net Cathode
Net Anode
EN for Weld evaluation
A B DC
EN for Weld evaluation
Electrochemical Noise Impedance of Individual Weld Regions
Good Bad
How to Protect?
Protection Strategies
VAlloy
Corrosion Current
VAlloy
Intermetallics Removal
Anodizing Dissimilar Materials
Use Inhibitors
Microscope View
Alloy Specimens
Resin Block
Glass
Microscope
M. Curioni, R. Bingham, A. Durán, M. Aparicio, R. A. Cottis, G.E. Thompson, Corrosion Science,
52,10, 3356 (2010)
Inhibitors
• Image Assisted Electrochemical Noise
► Surface appearance related to noise impedance
► Comparative evaluation of inhibitors effectiveness vs. blank and benchmark
Link
M. Curioni, R. Bingham, A. Durán, M. Aparicio, R. A. Cottis, G.E. Thompson, Corrosion Science,
52,10, 3356 (2010)
Anodic Film Morphology
Improve Adhesion
HTCAA Standard CAA 200 nm
Adhesive Penetration: HTCAA film
A
B
C
D
E
V
Environmentally-friendly anodizing for enhanced
corrosion/adhesion
Time
A CB200 nm
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)
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 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
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