Aluminum-Rich Primer: Improved Corrosion Inhibition ... minimizing corrosion damage from filiform, galvanic

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  • Presented to:

    Presented by:

    Aluminum-Rich Primer:

    Improved Corrosion Inhibition

    Sur/Fin 2017

    Craig Matzdorf

    21 June 2017

    Senior Engineer, Materials Engineering Division

    1 Approved 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

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

  • Keys to Performance

    4

    • Sufficiently negative potential

    • Maximum current

    • Low self-corrosion (long coating life)

    Bare 7075

    Optimum E range for protection

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

  • 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

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

  • 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

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

  • 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

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

  • 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

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

  • 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

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

  • 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

    12

    • 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

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

  • Conclusions

    13

    • 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

    craig.matzdorf@navy.mil

    14

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