Aluminum-Rich Primer: Improved Corrosion Inhibition...minimizing corrosion damage from filiform,...
Transcript of Aluminum-Rich Primer: Improved Corrosion Inhibition...minimizing corrosion damage from filiform,...
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Aluminum-Rich Primer:
Improved Corrosion Inhibition
Sur/Fin 2017
Craig Matzdorf
21 June 2017
Senior Engineer, Materials Engineering Division
1Approved for public release; distribution is unlimited. SPR #2017-454
Introduction
• Better ways to minimize corrosion damage of
aluminum on aircraft and ground vehicles are
needed
• Conventional corrosion-inhibiting primers rely on
barrier properties and chemical inhibitors to
minimize corrosion. They have limited
effectiveness for many corrosion types which are
the most costly to repair: galvanic, filiform and
stress-corrosion cracking (SCC)
• Aluminum-rich primers are being investigated for
their ability to inhibit these types of corrosion
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Approach
• Al-rich primer protective mechanism is mainly
based on electrochemical/sacrificial pigment vice
traditional chemical inhibition (similar to zinc and
magnesium-rich primers)
• The electrochemical inhibition may be more
effective at minimizing filiform and galvanic
corrosion as well as stress-corrosion cracking
and corrosion-fatigue as they all require an
anode and cathode to initiate and propagate
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Keys to Performance
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• Sufficiently negative potential
• Maximum current
• Low self-corrosion (long coating life)
Bare 7075
Optimum E range for protection
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Progress
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Performance Impact Test Method
Filiform Validated Virtually eliminates
filiform damage
Per paragraph 4.5.8.2 of
MIL-PRF-23377K
Galvanic Validated ~ 25% less
damage compared
to MIL-PRF-23377
primers
NAVAIR galvanic
assembly; 3 weeks in
ASTM B117 or 21 cycles
in GMW 14872
SCC Validated on
5XXX alloys
Retain up to 95%
of strength in air
NAVAIR slow-strain rate
using round hourglass
specimens
Corrosion
Fatigue
TBD TBD NAVAIR method; flat
dogbone specimen with
hole
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Filiform Corrosion
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Completed filiform test (1000 hrs.) per MIL-PRF-23377. Right-hand
panel in each set shows chemically stripped scribe area.
Al-rich Primer Qualified 23377 Chromate Primer
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Galvanic Corrosion
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Al-Rich Primer
Qualified 23377 Chromate Primer Qualified 53022 Type IV Primer
- Panels were chemically stripped after 500 hours in Cyclic Corrosion Testing
- 2024-T3 aluminum with Type II conversion coating; topcoat on right half of coupons
Example specimen: As-coated and
assembled, before testing
After test: fasteners and coatings removed
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SCC Results- Lab Al-rich primer
• Impact of Al-rich primer on fracture strength and ductility.
Approved for public release; distribution is unlimited. SPR #2015-947
SCC Results- Commercial Al-rich primers
Positive impact of Type II conversion coating
Positive impact of Al-rich primer
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Corrosion Fatigue
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• New method based on fatigue testing of anodized
7075-T6XX aluminum
• Convenient to assess impact of surface
preparation and coatings
• Future potential to include galvanic couple
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Pigment Stability/Outdoor Exposure
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1st Generation lab Al-rich on
2024-T3 with Alodine1200S:
4 years and 4 months at KSC
beach front site
Primer only
Primer and gloss white topcoat
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SPR #2017-454
General Progress and Maturity
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• Products from two licensees being field tested on aircraft and support equipment
• Quantities used: quarts (-23377 type) and gallons (-53022 type)
• Optimizing for maximum corrosion resistance and other primer requirements
• Additional licensees working on products with initial samples expected over the next year
• Requirements for -23377 and -53022 types being established, using current spec requirements as a guide
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Conclusions
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• Aluminum-rich primers are very effective for
minimizing corrosion damage from filiform,
galvanic and SCC forms
• Effect of Al-rich primers on corrosion-fatigue is to
be determined
• Al-rich pigments are very stable in accelerated
and natural environments in long-term testing to
date
Approved for public release; distribution is unlimited. SPR #2017-454
Questions?
Craig Matzdorf
301-342-9372
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Approved for public release; distribution is unlimited. SPR #2017-454