Nut and Bolt combination (surface treatment proven concept) 3

[koodsg]

Hi,
Like to use the available Ti- Hilock (SAA- sulfuric acid anodized) with CRES - shear nut (Passivated) on CFRP aluminium joint. It is restricted by process.
Can any one explain the what could be the reason?


The following combination is allowed.
Ti- Hilock (aluminium coating) with CRES- Shear nut (passivated)
Aluminum coated Hi-lock, is it okay with the CFRP structure?
Any environmental corrosion?


Any good combination of nut and bolt with surface protection?

Thanks in advance

 

[WKTaylor]

koodsg

CFRP [Carbon Fiber Reinforced Plastic] aluminum joint ??????

CFRP + Aluminum is usually a nightmare corrosion problem unless careful/extensive dissimilar materials isolation is designed-in.. including fastening and moisture barriers... not to mention dissimilar expansion/contraction rates.

ADD-in passivated bare CRES and there can be real problems.

Suggest You provide a more careful definition of Your joint.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[koodsg]

Here is further more details.
Joint structure material = CFRP + Aluminium,
Primary structure possibility of moisture.

Bolt EN6114T (Titanium, T code= SAA Sulfuric Acid Anodizing)
Nut ASNA2536P (CRES, P code = Passivated and dry film lubricant, Grey color)

 

[WKTaylor]

A couple of more questions...

Is a fiberglass-epoxy or boron-epoxy cloth isolation layer bonded to the fay-side that will remain in-contact with the aluminum? Also what finish is applied over fay/mating surface with the aluminum. Non-corrosion or corrosion-inhibited primer???

Is the aluminum shot-peened, followed by PAA, SAA, CAA or BSAA anodic coatings, followed by an adhesive bond primer or a general purpose corrosion protective primer [epoxy of course]???

Does the joint rely on: (a) adhesive bonding + fasteners + sealant over-coat; or (b) sealant + fasteners + sealant over coat [IE: black-aluminum Assy practices]?

I am unfamiliar with SAA of titanium: what spec are these fasteners coated per? NOTE: I reviewed may Ti Hi-Lok pin specs and did not find any reference to SAA coatings.

As for the NUT you specified [A-286 passivated + SFL]...
What material does the nut bare-up-against: aluminum? GRP?
I sure hope You are planning to install a dissimilar-material and friction/bearing isolation WASHER underneath the Nut... or are You planning to install a nut [A286+SFL] with an integral A286 washer!!????? Regardless, the washer alloy and coating(s) must be compatible with material it is bearing against.
The A-286 Nut passivated + SFL coating will be fully compatible with Ti-Bolt/pin threads.

General/random thoughts

Primary Ti fastener [bolts, lock-bolts] coatings I'm familiar with are...
NONE [bare, cleaned]
IVD aluminum
Organic + aluminum Pigment
Phosphate-fluoride conversion coating.
Baked solid film lubricant applied over bare or Phos-fluoride-treated surfaces
Anodized Ti finishes appear to be reserved for structural parts, not fasteners.

Virtually all Ti fasteners I reviewed are either bare, have an aluminum pigmented organic coating or are phos-fluoride CC treated; and may/may not have a lubricant or SFL coating applied.

Generally speaking, the IVD-A, aluminum pigmented organic coating and SFL coatings are best suited for aluminum and certain other metals; but are relatively hostile/useless in contact with graphite fibers.

The next best coating suitable for contact with aluminum [whit added isolation coatings] , and to a high degree graphite, is probably the phos-fluoride CC or bare.

Note...'bare/cleaned titanium is generally inert; however it is less desirable dissimilar-couple against aluminum.

NOTE. MIL-STD-1568 MATERIALS AND PROCESSES FOR CORROSION PREVENTION AND CONTROL IN AEROSPACE WEAPONS SYSTEMS makes the following statements

5.9.1 Detail requirements.
All permanently installed fasteners except as noted in 5.9.3 (all fasteners not normally removed
for regular access or servicing) used in areas up to 1070C (2250F) shall be wet installed with
either a corrosion inhibiting sealant conforming to MIL-S-81733 or an epoxy primer conforming
to MIL-P-23377, Type I, Class 1 or 2, or a MIL-P-85582, Type I, Class 2 material which does not
contain water. In high temperature areas, exceeding 107oC (225oF), Type I, Class 1 or 2 epoxy
primer, or a sealant which is suitable for the thermal environment shall be used. Fasteners in
integral fuel tanks shall be installed with wet sealant conforming to MlL-S-8802 or MlL-S-83430.
The use of sealant or corrosion inhibiting coatings not addressed by this paragraph must be
approved by the procuring activity.

5.9.5 Fasteners in graphite composites.
Fastener materials for use in graphite composite structures shall be titanium or A286. Cadmium
plated fasteners and aluminum fasteners shall not be used. Fasteners shall be wet when
installed using sealants as specified in 5.9.1.

Hmmmm... gotta-go-back-to-work.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[Sparweb]

I can't improve on what Wil wrote, but maybe more simply: get a galvanic compatibility chart, and plot your 4 materials on it.


STF

 

[TVP]

Wil,

Sulfuric acid anodizing according to ISO 8080 is a standard treatment for newer titanium fasteners as specified in EN 6114 or proprietary manufacturer designs:

http://www.jet-tek.com/EN6114.pdf

http://www.monogramaerospace.com/files/parts/BG2186 Rev G.PDF

https://www.alcoa.com/fastening_sys...talog/pdf/Eddie-Bolt Process Manual-Jan06.pdf

koodsg,

If the titanium fastener is in direct contact with aluminum, then you really need to use an Al-containing coating (NAS4004/EN4473), which is not ideal for contact with CFRP. You may need to change to a more elaborate, multi-piece fastener such as the OSI BOLT^TM that is linked above where there is a separate sleeve, nut, body, and corebolt. This design allows for different material and coating options to address strength and corrosion issues in multi-material joints.

 

[WKTaylor]

TVP...

Is ISO 8080 SAA-Ti similar to AMS2487 Anodic Treatment of Titanium and Titanium Alloys, Solution pH 12.4 Maximum? Any idea what the reasoning-is for applying this SAA coating?

Interesting requirement... seems exclusive to Euro made/contracted fasteners.

I have rarely seen any titanium fastener failures other than over-load, fatigue or poor installation practices... no corrosion failures per my recollection.

Usually anodic coatings typically produce a slightly brittle surface effect... which doesn't play well in a high fatigue environment [pre-mature crack initiation due to the coating]... especially around thread-shank transition, thread tips/flanks and impressed details such as stamped Part Markings on the head.

NOTE.
I have see bare and phos-fluoride coated Ti fasteners after a massive fire in an F-15 engine bay [~100% titanium]... the exposed surfaces [to oxidizing flames] turned a nasty chocolate brown. I'm sure that in the same scenario, Ti fasteners with aluminum-pigmented coatings would simply burned off the al-coating, then turn chocolate brown.

Hmmmm...wonder how SAA coated Ti-fasteners would 'hold-up' in a massive engine Bay fire scenario [2000F, 15 minutes]??


Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[CoryPad]

Wil,

Yes, ISO 8080 is similar to AMS2487. The reasoning usually is to reduce/eliminate galling. Here is some good info:

http://www.titaniumfinishing.com/capabilities/titanium-anodize-functional/

 

[WKTaylor]

CoryPad

Yes, ISO 8080 is similar to AMS2487. The reasoning usually is to reduce/eliminate galling.

Interesting. Phos-Fluoride CC + SFL coatings are intended for the same purpose: reduce/eliminate galling.

I wonder why use of this anodic coating has not expanded in US market for Ti Fasteners? Phos-Fluoride + SFL seems to be the standard combination [for this purpose], here.

Do You know of any US specified [NAS, HL, etc] Ti fasteners with this anodic coating as an option?



Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[CoryPad]

HI-TIGUE (HLT series) offers ISO 8080, see here:

http://www.lisi-aerospace.com/_layo...Pins&downloaded=HLT12&type=nominal_size_shank

 

[tbuelna]

Interesting. EN6114 is a European standard for an inch size flush head hi-lock type bolt. The "T" part number code is 6Al-4V titanium with sulfuric acid anodize IAW ISO8080 and a coating of cetyl alcohol lubricant IAW EN6117.

The OP noted the parts being fastened were made from CFRP and aluminum. Since the bolt is a flush head type it would seem possible that the bolt head is located on an OML surface. Fasteners on an OML surface are exposed to the environment and typically require an application of sealant at installation. However there was no mention of whether the bolt head countersink is in the CFRP part or the aluminum part.

 

[TVP]

Sorry I'm so late returning to this thread, work and life got in the way...

Alcoa shows ISO 8080 for the Eddie Bolt, GP, LGP and Ti-Matic, see links below. Some older Huck Aero-Lite documents showed it as well, but the newest versions reference SAE AMS2488. Cherry also shows it for some of their products, e.g. E-Z BUCK rivet and Titanium Maxibolt blind fastener.

http://www.alcoa.com/fastening_syst...talog/pdf/Eddie-Bolt Process Manual-Jan06.pdf

http://catalog.alcoafastenersandrings.com/Asset/GPL111_c4.pdf

http://catalog.alcoafastenersandrings.com/Asset/COM102_f9.pdf

http://www.alcoa.com/fastening_systems_and_rings/aerospace/catalog/pdf/standards/SK12332.pdf

http://www.cherryaerospace.com/docs/catalogs/CA-1032.pdf

http://www.cherryaerospace.com/docs/catalogs/CA-1010.pdf