Surface Engineering Challenges of Dissimilar Materials ... · Surface Engineering Challenges of Dissimilar Materials Joints Michele Curioni & LATEST2 team Corrosion And Protection

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

michele.curioni@manchester.ac.uk