aluminum-rich primer: improved corrosion inhibition...minimizing corrosion damage from filiform,...

Presented to:

Presented by:

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

2

Approved for public release; distribution is unlimited. SPR #2017-454

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

3


Keys to Performance

4

• Sufficiently negative potential

• Maximum current

• Low self-corrosion (long coating life)

Bare 7075

Optimum E range for protection


Progress

5

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


Filiform Corrosion

6

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


Galvanic Corrosion

7

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


SCC Results- Lab Al-rich primer

• Impact of Al-rich primer on fracture strength and ductility.


SCC Results- Commercial Al-rich primers

Positive impact of Type II conversion coating

Positive impact of Al-rich primer


Corrosion Fatigue

10

• 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


Pigment Stability/Outdoor Exposure

11

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

Approved for public release; distribution is unlimited.

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


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


Questions?

Craig Matzdorf

301-342-9372

[email protected]

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aluminum-rich primer: improved corrosion inhibition...minimizing corrosion damage from filiform,...

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