Meeting the Challenge of Corrosion
Resistance via Removal of Chromates
Patrick Adams
AkzoNobel Aerospace Coatings
Waukegan, Illinois
AkzoNobel Aerospace
Coatings Contact Information
Patrick J. Adams
Military Market Manager
AkzoNobel Aerospace Coatings
Will Estes
Military Program Manager
AkzoNobel Aerospace Coatings
•
•
•
Office Phone: +1-812.732.5071
Cell: +1-847.612.6124
Office Fax: +1-812.732.5071
•
•
•
Office Phone: +1-404.315.8600
Cell: +1-770.335.7910
Office Fax: +1-404.321.9935
•
Email: pat.adams@akzonobel.com
•
Email: will.estes@akzonobel.com
2
Background:
• The answer to aerospace corrosion has been the use
of chromate containing pretreatments and coatings
• This answer is still valid in terms of protection of the
airframe, but at a significant cost to the environment
and to worker safety
• Legislation and regulation over the past few years
makes it imperative to find and implement viable
replacement technologies
• The search for “real” replacements has been on going
3
Uniqueness of Aerospace
Applications
Aerospace is “the last industry standing” in use of chromate
technology as the primary corrosion inhibitor for a number of
logical reasons:
– Importance of low film builds and low weight
» Critical to fuel use
» Critical to economics of air travel
– Superior performance of chromates in relation to
aluminum substrates
» Proven long term protection at low film weight
» Areas of airframes can not be inspected after the
aircraft is built, need is for 40-50 years of protection
4
Costs of Corrosion (DoD)
Air Force Corrosion Prevention Office Study in 2005
Total DoD cost of corrosion was 20 billion dollars
– US Air Force aircraft cost was set at 1.3 billion
– .9 billion to Naval aircraft
– 15-20% of USAF assets were unavailable for service due
to corrosion
– 50% of depot maintenance was for corrosion work
2009 DoD Corrosion Conference
– costs stated 22.5 billion dollars
– time of maintenance due to corrosion issues is 24% of the
5
total aircraft maintenance time
Toxilogical Concerns Over
Chromate Use
• Legislation in 2008-2010 has reduced the safe exposure
limits to chromates by almost 90% from previous levels
• In 2009, Undersecretary of Defense, John J. Young, Jr.
issued a directive for minimization and elimination of
chrome VI by all branches of the DoD with actions to:
• Invest in research and development for substitutes
• Approve the use of alternatives where they can perform
adequately
• Update all relative technical documents
• Share knowledge derived from non chrome research
• Provide by April 2010 military branch implementation actions
6
to minimize use of chrome VI
Key Directive:
Elimination of Chromates Without
Sacrifice to Corrosion Resistance
• Historically anti-corrosive coating systems built of a chromate
based metal pretreatment and a strontium chromate based
primer effectively protect an airframe through 40-50 years of
service
• Coating systems which eliminate the chromate from the
primer, but not the pretreatment show excellent results after
10-12 years of service
7
Alternative Approaches
• Current state of class N approvals:
– A few class N (non-chromate primers) do have QPL status
– Currently all products approved, and the specifications for
approval require that a chromate pretreatment is part of the
coating system
• AkzoNobel approach
– Completely chrome free technology
– Utilize existing non-chromated pretreatments
• PreKote
• AC-131 (Boegel)
– Utilize MgRP (Magnesium Rich Primers) as the inhibition
layer
8
Testing Detail and Results Disconnect Between Salt Fog
and Field Exposure
Results of AkzoNobel and Battelle Institute
– 42 months exposure at Daytona Beach
without failure or significant scribe darkening
of both primer only and primer with topcoat
– Multiple tests designed and run at universities,
AF, Navy, and AkzoNobel
» Product improvement for salt fog determined, also
beneficial to exterior exposure, patent pending
technology
9
3000 Hours B117
No Topcoat
PreKote Treated 2024-T3
10
3000 Hours B117
Aerodur 5000 Topcoat
PreKote Treated 2024-T3
11
2000 Hours B117
Aerodur 5000 Topcoat
PreKote Treated 7075-T6
12
Traditional Chromate System
Versus Chromate-Free System
2024-T3, 3000 hours B117
13
Collaborative Testing
Outside of AkzoNobel
• NAVAIR- extensive testing against MIL-PRF-23377
• AFRL/CTIO- Corrosion tested to MIL-PRF-32239-soliciting
test aircraft
• Battelle- Nearly four years without failure on test fences and
in-flight tests utilizing corrosion sensors for evaluations of
both primer only and topcoated systems
• Lockheed Martin- Passed all testing to MIL-PRF-23377
specifications at their test sites. Two C-130’s flying with
MgRP on control surfaces.
• Boeing St. Louis- Multiple successful test series over chrome
III and sol-gel pretreatments. Currently still in testing for
specification approval
14
PreKote/AkzoNobel NEG Blank/
AkzoNobel Aerodur 5000
Negative Control
ie. No Corrosion Inhibitors
It is supposed to corrode
Undercutting
2024-T3
3009 hrs Salt Spray
Some corrosion in scribe
Likely pitting in scribe
Significant undercutting and blisters
15
PreKote/Competitor Cr
Primer/Competitor Topcoat
F-16 Coating System
Chromate Primer
Undercutting
7075-T6
3009 hrs Salt Spray
Corrosion in scribe
Pitting in scribe
Undercutting, No blisters
16
PreKote / AkzoNobel
Aerodur 2100/AkzoNobel
Aerodur 5000
Almost all of scribe actually is
bright and shiny
Complete Chromate Free System
7075-T6
3009 hrs Salt Spray
Almost no discoloration in scribe
No pitting in scribe
No undercutting nor blisters
17
Current State of the
Technology:
• For this project the stated objectives have been
realized
• Development of a non-chromated primer
capable of meeting and exceeding the known
corrosion resistance of currently approved
strontium chromate base materials.
• Design a completely chromate free system,
utilizing known and proven non-chromate
pretreatments to meet military specifications
for corrosion resistant products
18
Change is a Difficult
Proposition
• Magnesium does not work by the same
mechanism as chromates or other inhibitors
which rely on leachability
– Topcoated panels perform better, not worse as do
chromates and other non-chromate inhibitive
pigments in corrosion tests since the inhibition
mechanism does not depend on water leaching the
pigment
19
Change is a Necessary
Proposition
• Chromate legislation significantly changes the ability of paint
manufactures to make these primers, as well as for end users to
apply and remove these coatings
• REACH and other legislation is leading to fewer suppliers of
chromates
– In 2000 over 15 companies manufactured strontium or zinc chromate*
– In 2010, five companies are involved in this manufacture*
• Magnesium is the sixth most abundant element on earth,
toxilogical effects are very low
* Unknown number of supplies in China, also unknown supply and quality
20
Conclusion
Use of the Aerodur® MgRP primer provides a completely
chromate free coating system for aircraft which:
– Meets the requirements of the systems specification
– Out performs chromated standards in critical corrosion testing
– Provides a practical coating solution that is fully compliant to all
existing hazardous materials and toxilogical regulations
– Fully meets the expectations of the Undersecretary of Defense’
mandate to eliminate chromates from DoD programs.
21