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Novel corrosion inhibiting coating technology for the protection of aluminum alloys
Peter Visser
15 June 2011
AkzoNobel Aerospace Coatings
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
2
Introduction
The Aerospace industry is relying on chromatedtechnologies for many years
Strong drive for Chromate replacement
• Legislation (REACH)
• Health Safety and environmental concerns
• Sustainability and eco-efficient developments
Chromated technology is still being used to achieve key performance characteristics.
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
3
Are chromates still needed for key performance using chrome free coating technology?
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
4
Pitting CorrosionPitting Corrosion
Fast development of long and highdensity filiform corrosion
Fast development of long and highdensity filiform corrosion
Rapid development of corrosion Early formation of blisters along scribesExcessive formation of corrosion products
Rapid development of corrosion Early formation of blisters along scribesExcessive formation of corrosion products
The Challenge:Development of total chrome free coating solutions.
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
5
The Challenge:Development of total chrome free coating solutions.
State of the Art corrosion inhibitorsmake it very difficult to comply withthe long term corrosion requirementsof the industry.
• Too low or high Solubility
• Compatibility with coatings system
• Insufficient passivation
• Specific activity
• Inconsistent performance
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
6
New approaches are needed to provide
total chrome free coating solutions
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
7
New Approach total chrome free TechnologyMagnesium Rich Primer Technology
Technology based on Magnesium metal particles as corrosion inhibitor
The anti-corrosive propertiesof this coatings is basedon two different mechanisms:
Cathodic protectionprovided by Mg metal powder
Barrier protectionprovided by the binder andprecipitated Mg oxides (1)
Significant departure from traditionalmethods and mechanisms ofcorrosion protection in aerospaceindustry
100µm100µm100µm
0 2000 4000 6000T, s
-1.6
-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
OCP
, V
Extent of Cathodic ProtectionExtent of Cathodic ProtectionDeveloped in MgDeveloped in Mg--rich Primersrich Primers
AA2024
AA7075
0 2000 4000 6000T, s
-1.6
-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
OCP
, V
Extent of Cathodic ProtectionExtent of Cathodic ProtectionDeveloped in MgDeveloped in Mg--rich Primersrich Primers
AA2024
AA7075
Non-coated Bare
Coated Bare
Magnesium
0 2000 4000 6000T, s
-1.6
-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
OCP
, V
Extent of Cathodic ProtectionExtent of Cathodic ProtectionDeveloped in MgDeveloped in Mg--rich Primersrich Primers
AA2024
AA7075
0 2000 4000 6000T, s
-1.6
-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
OCP
, V
Extent of Cathodic ProtectionExtent of Cathodic ProtectionDeveloped in MgDeveloped in Mg--rich Primersrich Primers
AA2024
AA7075
Non-coated Bare
Coated Bare
Magnesium
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
8
Magnesium Rich Primer technology combined with appropriate chrome free pretreatments and topcoats provide a fully chromate-free system which exceeds the corrosion capabilities of commercial and military standard products.
Filiform corrosion development (EN3665) (2024 T3 Unclad, Scotch Brite solvent cleaned)
012345678
0 500 1000 1500 2000Hours
max
. len
gth
filam
ent
(mm
)
chromate inhibitor MGRP
2000h NSS (ASTM B-117)-Full chromate stack-up Total Chrome free System MgRP
New Approach total chrome free TechnologyMagnesium Rich Primer Technology
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
9
New Chrome free coating technology
A new patented chrome free coatings technology has been developed providing:
• Active inhibition of filiform corrosion
• Fast and effective passivation mechanism in Neutral Salt Spray
• Robust performance over clad and unclad substrates.
• Total chrome free coating systems meeting Aerospace requirements
• Universal Use
• Independent from resin technology
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
10
Meeting the Challenge
Long term corrosion protection
in
Neutral Salt Spray and Filiform corrosion
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
11
Meeting the challenge:Resistance to Filiform Corrosion.Focus of new chrome free developments:
• Low corrosion rate
• Reduced distribution of corrosion (morphology & area)
Process of Filiform corrosion
Filiform corrosion development (EN3665) (2024 T3 Unclad TSA)
0
1
2
3
4
5
6
0 500 1000 1500 2000
Time (h)
max
. len
gth
filam
ent (
mm
)
inhibitor 1inhibitor 2inhibitor 3inhibitor 4New technologychromate
Initiation/activation Nucleation Growth /Propagation
Nucleation Growth
Growth
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
12
Meeting the challenge:Neutral Salt Spray (ASTM B-117)
Development strategy to meet the challenge of long term Neutral Salt Spray exposure:
• Corrosion inhibitor with leaching properties
• Fast and effective passivation mechanism in the scribe
• Irreversible nature passivation layer.
• Maintain coating integrity
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
13
The corrosion performance of the new chrome free coatingtechnology has been studied in a High Solids coatingsystem suitable for Aerospace applications
• Comparison against chrome free inhibitors and Chromates• Primer / top coat systems• Currently used chrome free pretreatments
Meeting the challenge with chrome free coating technology
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
14
Active inhibition of Filiform corrosion (EN3665)
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
15
Example 1: Filiform performance on 2024 T3 UncladPretreatment: Scotch Brited / solvent cleaned
The New Technology provides:
• Lower corrosion rate
• Shorter filamentsNew Technology ChromateNew Technology ChromateTechnology Chromate
2000 h Filiform2024 T3 Unclad SB/SC
Filiform corrosion development (EN3665) (2024 T3 Unclad Scotch Brited/ Solvent cleaned)
0
2
4
6
8
10
12
14
16
0 500 1000 1500 2000Exposure time (h)
max
. len
gth
filam
ent (
mm
)
inhibitor 1
inhibitor 2
inhibitor 3
inhibitor 4
New technology
chromate
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
16
New Technology provides:
• Low corrosion rate
• Shorter filaments
Example 2: Development Filiform Corrosion(EN 3665) 2024 T3 Clad- Solgel
Filiform corrosion development (EN3665)(2024 T3 Clad- Solgel)
0
1
2
3
4
5
6
7
8
0 500 1000 1500 2000
Exposure Time (h)
Max
. len
gth
filifo
rm (m
m)
Inhibitor 1
Inhibitor 2
Inhibitor 3
Inhibitor 4
New Technology
Chromate
2000 h Filiform 2024 T3 Clad – Sol gel
Chromate New Technology
2000 h Filiform 2024 T3 Clad – Sol gel
Chromate New Technology
2000 h Filiform 2024 T3 Clad – Sol gel
Chromate New Technology
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
17
Example 3: Development Filiform Corrosion(EN 3665) 2024 T3 UnClad-TSA
• New Technology: Lower Corrosion rate and shorter filaments
Filiform corrosion development (EN3665) (2024 T3 Unclad TSA)
0
1
2
3
4
5
6
0 500 1000 1500 2000
Time (h)
max
. len
gth
filam
ent (
mm
)
inhibitor 1inhibitor 2inhibitor 3inhibitor 4New technologychromate
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
18
Using Imaging techniques for the development of Chrome free technologyAnalysis and rating of coating systems during and after exposure.
• Applicable to:
• Filiform corrosion
• Neutral Salt Spray
•Providing data:
• Creep from Scribe
• Affected area
• Type of corrosion
A B A BDistribution Filiform corrosion
0%
20%
40%
60%
80%
100%
0.0 5.0 10.0 15.0
Filiform corrosion length (mm)
Freq
uenc
ySample A Sample B
Distribution Creep from scribe
0%
20%
40%
60%
80%
100%
0.0 2.0 4.0 6.0 8.0 10.0
distance from scratch in mmfre
quen
cysample A sample B
A B
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
19
New Technology provides:
• Shorter filaments
• Reduced corrosion area
Example 3: Filiform performance on 2024 T3 Unclad-TSAImaging analysis after 2000 h exposure
Inhibitor 1 Inhibitor 2 Inhibitor 3 Inhibitor 4 New Technology Chromate
Distribut ion filiform corrosion (EN 3665)2024 T3 Unclad-TSA
0%
20%
40%
60%
80%
100%
0.0 2.0 4.0 6.0 8.0distance from scratch in mm
filifo
rm le
ngth
freq
uenc
y inhibitor-1inhibitor-2inhibitor-3inhibitor-4NewTechChromate
Maximum Length Filiform Corrosion 2000 h (2024 T3 Unclad-TSA)
0.01.02.03.04.05.06.07.08.09.0
10.0
max left max right
max
. len
gth
(mm inhi bitor-1
inhi bitor-2inhi bitor-3inhi bitor-4NewTech
C hromate
Total Corrosion area after 2000 h Filiform(EN 3665)2024 T3 Unclad-TSA
0
50
100
150
200
total
area
in m
m^2
inhibitor-1inhibitor-2inhibitor-3inhibitor-4NewTechChrom ate
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
20
Summary on filiform corrosion
The new Technology provides activeFiliform corrosion inhibition:
• Shorter Filaments
• Low corrosion rate
• low affected area
• Long term corrosion protection
• Activity on mutiple substrates
•
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
21
Fast and Effective Protection of the Scribe
In Neutral Salt Spray (ASTM B-117)
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
22
3000 h exposure 2024 T3 Unclad – TSA
New Technology: Lower corrosion rateLess creep from scribe
Evolution Creep from scribe in NSS (ASTM B-117)(2024 T3 Unclad - TSA)
0
0.5
1
1.5
2
2.5
0 500 1000 1500 2000 2500 3000
Time (h)
Cre
ep fr
om s
crib
e( m
m)
inhibitor 1inhibitor 2inhibitor 3inhibitor 4new technologychromate
Corrosion distribution after 3000 h NSS (ASTM B-117)(2024 T3 Unclad - TSA)
0
0.5
1
1.5
2
2.5
3
3.5
inhibitor 1 inhibitor 2 inhibitor 3 inhibitor 4 NewTechnology
Chromate
max
. cre
ep fr
om s
crib
e( m
m)
0
20
40
60
80
no. o
f cor
rosi
on s
ites
max Creep from scribe no. Of corrosion sites
Low number of corrosion sites
Example 4: Corrosion Development in NSS (ASTM B-117)2024 T3 UnClad-TSA
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
23
Example 5: Corrosion development in NSS (ASTM B-117)2024 T3 Clad Solgel
New Technology:
Less creep from scribe
Evolution Creep from scribe in NSS (ASTM B-117)(2024 T3 Clad - Solgel)
0
1
2
3
4
5
6
7
0 500 1000 1500 2000
Time (h)
Max
cre
ep fr
om s
crib
e (m
m)
Inhibitor 1Inhibitor 2Inhibitor 3Inhibitor 4New Technologychromate
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
24
Example 5: Corrosion development in NSS (ASTM B-117)2024 T3 Clad Solgel
New Technology: Clean ScribesLess creep from scribeLow number of corrosion sites
Chromate New Technology Inhibitor 4
2024 T3 Clad Sol gel, 2000 h2000 h Neutral Salt Spray (ASTM B-117)
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
25
Distribution Creep from scribe corrosion length2024 T3 Clad-Solgel NSS 2000h
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.0 1.0 2.0 3.0 4.0 5.0
distance from scratch in mm
freq
uenc
yinhibitor 1inhibitor 2inhibitor 3inhibitor 4New Technologychromates
Chromate New Technology Inhibitor 4
2000 h Neutral Salt Spray (ASTM B-117)2024 T3 Clad Solgel, 2000 h
Chromate New Technology Inhibitor 4
2000 h Neutral Salt Spray (ASTM B-117)2024 T3 Clad Solgel, 2000 h New Technology provides:
• Less creep from scribe• Low number of corrosion sites• Low corrosion affected area
Example 5: Imaging analysis after2000 h NSS (ASTM B-117) 2024 T3 Clad Solgel
Corrosion Distribution(after 2000 h NSS (ASTM B-117)
050
100150200
250300350400450
number of sites total area
inhibitor 1inhibitor 2inhibitor 3inhibitor 4New TechnologyChromate
Corrosion Distribution(after 2000 h NSS (ASTM B-117)
050
100150200
250300350400450
number of sites total area
inhibitor 1inhibitor 2inhibitor 3inhibitor 4New TechnologyChromate
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
26
Chromate inhibitor
New chrome free technology
State of the Art chrome free technology
The New Technology provides fast and effective protection of the scribe:
• Bright, shiny and clean scribes.Scribe appearance
500 h NSS (ASTM B-117) 2024 T3 unclad
Fast and Effective Protection of the Scribe
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
27
Scanning Electron Microscopic analysis :
•Evidence for protective layer in the scribe.
2024 T3 Clad after
1000 h NSS (ASTM B-117)
Fast and Effective Protection of the ScribeScribe analysis after 1000 hours exposure
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
28
Using White Light Interferometry for scribeanalysis
White Light Interferometry (WLI):
• Non-contact measurement of surface topography
Determining:
•Surface Roughness
•Surface Area
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
29
Scribe appearance using White Light Interferometry
500 h NSS (ASTM B-117) 2024 T3 unclad
Chromate inhibitor
New chrome free technology
State of the Art chrome free technology
Using White Light Interferometry for scribeanalysis
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
30
White Light InterferometryScribe analysis after Neutral Salt Spray (ASTM B-117)
New Technology State of the Art Chrome Free
Surface Roughness development in NSS (ASTM B-117)2024 T3 Unclad
250 h
500 h
1000 h
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
31
White Light InterferometryScribe analysis after Neutral Salt Spray (ASTM B-117)
2024 T3 Unclad 1000h 2024 T3 Clad
Surface Roughness of Scribe (Ra)
0
1
2
3
4
5
250 h 500 h 1000 h 250 h 500 h 1000 h
2024 T3 Bare 2024 T3 Clad
Surfa
ce R
ough
ness
(Ra)
in u
m
Starte of the Art CFChromatedNew Technology
State of the Art CF
Chromated
New Technology
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
32
Prevention of pit corrosion is one of the largest challenges in long term Neutral Salt Spray exposure.
White Light InterferometryScribe analysis after Neutral Salt Spray (ASTM B-117)
Chromate inhibitor
New Chrome Free Technology
State of the Art Chrome free
pit corrosion after 2000 h NSS (ASTM B-117)
2024 T3 unclad
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
33
White Light InterferometryScribe analysis after Neutral Salt Spray (ASTM B-117)
Inhibitor 1 New TechnologyInhibitor 3 ChromateInhibitor 2
Surface Roughness and Pit corrosion 2024 T3 Unclad after 2000 h NSS (ASTM B-117)
Surface Roughness (Ra) after 2000 h NSS (ASTM B-117)
0123456
inhibitor 1 inhibitor 2 inhibitor 3 Chromate New TechnologySurf
ace
Rou
ghne
ss (R
a)
in u
m
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
34
Summary
During Neutral Salt Spray Exposure (ASTM B-117) the New Technology provides:
• Fast and effective protection of the scribe
• Reduced creep from scribe
• Low number of corrosion sites
• Less pit corrosion
• Long term corrosion protection
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
35
Conclusion
The New Chrome Free Technology provides:
• Proven corrosion protection in multiple corrosion tests.
• Fast and effective passivation of scribe
• Excellent Filiform corrosion inhibition
• Significant less corrosion
• Expected long term performance
• Active on multiple substrates
• Total chrome free technology
• Universal performance
• Fully Health Safety and Environmentally compliant technology
Novel corrosion inhibiting coating technology for the protection of aluminum alloysCopyright AkzoNobel 2011
36
A New Total Chrome Free Coating Solution
for the protection of aluminium alloys