Transcript Presentation Title - Institute of Materials Finishing

Corrosion properties of water based and high solids
Aerospace coating systems.
IMFAIR 09
10th & 11th June 2009
Peter de Bruin
Akzo Nobel Aerospace Coatings
Content
 Trends in Aerospace industry because of HSE legislation.
 Aerospace substrates, structural and exterior.
 Morphology and corrosion of Aluminium.
 Corrosion protection of Aluminium.
 Developments in Aerospace structural coating systems.
 Developments in OEM Aerospace Exterior coating systems.
 Comparison Water based versus high solids product.
 Aerospace corrosion test methods.
 Specifications / corrosion requirements.
 Corrosion results Airbus structural coating systems.
 Corrosion results Boeing exterior coating systems.
 Conclusions.
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Trends in Aerospace industry because of HSE
legislation.
 Changes in VOC legislation:
 Maximum allowed VOC per product (ready-to-spray).
Primers: max. 350 g./l.
Topcoats: max. 420 g./l.
 Limitation of Emission of organic solvents per location.
 Reduction / replacement of Cr 6+ compounds.
 Chromate free substrate (aluminium) pretreatment.
 Chromate free corrosion inhibitors in Aerospace primers.
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Aerospace substrates, structural and exterior.
Aluminium alloys used in Aircraft construction.
Aluminum alloy
Composition (%)
1100 (Clad layer)
2024 (T3)
7075 (T6)
Al
> 99
~ 93 - 94.5
~ 89.5
Cu
0.12
3 - 4.5
~ 1.5
Mg
~ 1.5
~ 2.5
Mn
~ 0.5
Zn
~ 5.5
Others
~ 0.5
~1
Tensile strength (psi)
13,000
70,000
83,000
Yield strength (psi)
5,000
50,000
73,000
Elongation (%)
35
18
11
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Aerospace substrates, structural and exterior.
Other possible substrates, both in construction and for rivets /
fasteners are:
 Titanium
 Lithium Aluminium alloys
 Stainless steel
 Composite
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Morphology of aluminum 2024T3
- The alloy is inhomogeneous. It contains grains.
Coating
Alloy 1100
Alloy 2024 T3
Grain boundaries are sensitive for corrosion!!
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Morphology of aluminum 2024T3
- The surface is inhomogeneous. It contains cathodic and anodic
area’s
- Ca 300.000/ cm²; ~ 4.5% of surface area!
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Filiform corrosion
Thread like corrosion between substrate and coating
about 15 µm in depth.
Necessary conditions
- Susceptible Al-Alloy. (lit.: % Cu> 0.15%
large effect) Al-Mg alloys less sensitive.
- Pretreatment.
- Damaging of coating.
- RH >60% RH.
- Initiator; Cl-, SO42-.
- Presence of O2.
- Sufficiently high temperature.
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