Corrosion properties of water based and high solids Aerospace coating systems. IMFAIR 09 10 th & 11 th June 2009 Peter de Bruin Akzo Nobel Aerospace Coatings.

Corrosion properties of water based and high solids Aerospace coating systems.

IMFAIR 09 10th & 11th June 2009

Peter de Bruin Akzo Nobel Aerospace Coatings

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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.

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

Aluminium alloys used in Aircraft construction.

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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.

Alloy 1100Coating

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-, SO4

2-.

- Presence of O2.

- Sufficiently high temperature.