Apparently Carbon Fiber and Aluminum don't get along??

[khappucino]

i assume this is only a problem if the carbon fiber directly interacts with the raw aluminum?

I've been away from hands-on fabrication of composite parts using
Carbon Fiber. A lot can happen in two years so I did some
homework. I discovered that the threaded aluminum inserts in my
carbon fiber truss tubes don't get along with carbon fiber at
all! Galvanic erosion will attack the aluminum at the interface
of the two materials and turn it to dust. And, if there is any
water present, the destruction of the mechanical bond will be
rapid.

I bounced this discovery off a few aerospace engineers I know and
they confirmed my worst fears. One wrote back:

"Carbon Fiber does indeed attack aluminum
VORACIOUSLY if any hint of moisture gets into
the matrix. All the metal parts on the F-16 fighter that
contact CF are Stainless Steel, Passivated too if I am not
mistaken to more closely match the electronegativity value of the
two materials."

also from another Design Engineering site

Additionally, carbon-fiber composites may corrode galvanically if aluminum fasteners are used, due to the chemical reaction of the aluminum with the carbon fibers. Coating the fasteners guards against corrosion but adds cost and time to assembly. Aluminum fasteners are often replaced by more expensive titanium and stainless steel when carbon-fiber composites are used.

just curious if this was a known issue, since our body panels and subframe are aluminum
i know there are some enginerds out there that can chime in on this, i'm really curious

i wonder if the presence of moisture due to humidity alone could start the corrosion?

 

[Osiris_x11]

cathodic-corrosion...

'Galvanic corrosion'!?!

That was stated to me when I bought some Carbon Fiber 6k 4x4 twill fabric, by the fabricator/seller. I had told him that I wanted to make some parts for my NSX. As it's aluminum to begin w/, I wanted to be cautious about adding weight therefore using composite materials. That's when he mentioned "galvanic corrosion". I had to reiterate to him that I was planning to dabble in small interior pieces for my cabin accessories (ie. cel', radar detector, mp3 face-plate, powered-sub', etc'...), nothing structural or body-related (contacting actual aluminum).

There are various pvc/plastic-like type applications/finishes along w/ fiberglass that are used between any carbon-fiber and aluminum. Also I recall reading that Audi's ALCOA-made "spaceframe" for the A8 was glued together, not riveted. And taking that one step further, Jaguar used various adhesives for their aluminum structural components and body panels for their newer XJ-series. Perhaps all this was ensure no galvanic-corrosion?!?

 

[LJSB]

Re: cathodic-corrosion...

'Galvanic corrosion'!?!

That was stated to me when I bought some Also I recall reading that Audi's ALCOA-made "spaceframe" for the A8 was glued together, not riveted. And taking that one step further, Jaguar used various adhesives for their aluminum structural components and body panels for their newer XJ-series. Perhaps all this was ensure no galvanic-corrosion?!?

Adhesives makes for a easier, faster, stronger and less expensive assembly cost. Rivets are used on some cars (BMW 5 series) as a method of keeping the parts in place until the adhesive is cured. Welding is being replaced in favor of adhesive bonding in aluminum car construction.

 

[geometro]

Absolutely.

Carbon fiber + Aluminum = galvanic corrosion.

If you look at the electronegativities of each element you'll see there is a great enough difference for a reaction to occur, and it does.

Even though teh surface of aluminum is covered by a layer of aluminum oxide, corrosion will occur if it is in direct contact or even bonded to carbon fiber.

As mentioned by Orisis, if you plan to construct a structure using carbon fiber and aluminum, you will need to use an insulator (typically fiberglass) between the carbon and aluminum interface. But even then, it's not a 100% guarantee.

THe use of Stainless is actually 3 fold in the F-16, I believe, 1) it addresses the galvanic corrosion issue, 2) the CTE of Carbon and steel are much closer than Carbon and Al, and 3) Fatigue life of Stainless is better than Al.

IN the application of the Audis where they were bonded together, it;s just an alternative method to fasten the assembly together (vs rivets).

In the application of the NSXs, there shouldn't be an issue, since there is no carbon fiber parts from the factory originally (barring the NSX-R). Even on the aftermarket exterior parts such as a spoiler and hood since there is never any direct contact.

--
George

 

[geometro]

Re: cathodic-corrosion...

Adhesives makes for a easier, faster, stronger and less expensive assembly cost. Rivets are used on some cars (BMW 5 series) as a method of keeping the parts in place until the adhesive is cured. Welding is being replaced in favor of adhesive bonding in aluminum car construction.

Not necessarily true on all counts. If a structure is designed to flex under loading, one of the best ways to fasten it is using rivets.

I would think that the rivets would serve as a fail safe in case the bond were to fail, also.

--
George

 

[Aero]

Re: cathodic-corrosion...

Not necessarily true on all counts. If a structure is designed to flex under loading, one of the best ways to fasten it is using rivets.

I would think that the rivets would serve as a fail safe in case the bond were to fail, also.

--
George

Thats true, in aircraft structural design we called them 'chicken rivets' cause they were just there in case the bond failed. Its been a while but I remember having all kinds of aluminum and composite (not necessarily carbon) touching and riveted together. Seems like both were coated/treated to prevent that type and other type of corrosion.

 

[SNDSOUL]

carbon fiber also conducts electricity and can catch on fire easily

 

[SNDSOUL]

The dust from sanding or cutting is not too good for your eyes, skin, or lungs either.
How good of a conductor is it?

Its conducts pretty well, but i wouldnt say its as good as metal. It definetly will short out an electrical circut if positive and negative touch the piece at the same time.

 

[Bregva]

As far as I remember engines in 97+ cars have carbon fiber reinforced cylinders. Since engine is all Aluminum will it mean that carbon will eat cylinder walls eventualy?

David

99 NSX-T

 

[AU_NSX]

The dust from sanding or cutting is not too good for your eyes, skin, or lungs either.
How good of a conductor is it?

Carbon fibre is used in lightbulbs as well...

Try this, take the "lead" from a pencil and pass a 12V current through it. The carbon fibre actually glows white hot! Very bright!

But SNDSOUL is correct, not as good as some metals

 

[Wheelman]

This applies only to the construction process, right? Not if someone puts on an NSX-R spoiler or NSX-R hood? Aftermarket stuff is pretty safe and this corrosion does not apply?

 

[AU_NSX]

This applies only to the construction process, right? Not if someone puts on an NSX-R spoiler or NSX-R hood? Aftermarket stuff is pretty safe and this corrosion does not apply?

As long as the surfaces in contact are insulated by paint...

 

[rbirling]

As long as the surfaces in contact are insulated by paint...

Or the resin that the fiber is embedded within. I don't think this can cause a problem with a finished CF part. Only if you drill through it and expose the fibers would this become an issue.

 

[TTony]

As far as I remember engines in 97+ cars have carbon fiber reinforced cylinders. Since engine is all Aluminum will it mean that carbon will eat cylinder walls eventualy?

David

99 NSX-T

The 3.2L does not have carbon fiber reinforced cylinders. This explains more:

It is a fiber-reinforced metal (FRM) cylinder sleeve. A fiber-based material in the form of cylinder sleeve is first inserted to the die of the block. Melted liquid aluminium is poured into the die and integrate with the fiber sleeve. Then the cylinder wall is machined to the desire bore dimension, leaving only 0.5 mm thickness to the fiber sleeve which covers the cylinder wall. It generates lower friction than iron liner, thus improves rev and power. Moreover, the fiber sleeve reinforces the block, allowing the distance between adjacent bores to be reduced yet maintain mechanical strength

 

[Cody@LoveFab]

Kinda OT, but some of the older Trek Bicycles used CF tubing with AL gussets at the head tube, seat tube, bottom bracket and rear dropouts. Im assuming they used some sort of coating to prevent this?

 

[bluethunder]

Is there an issue with the CF hoods or wings at the attachment locations? Such as, the hood hinges or latch? I am thinking of buying these items but, how are they connected to the screw or bolts? Is the hood going to fly off a couple of years down the road? Anyone with either of these parts to give us some more details. Thanks

 

[geometro]

Kinda OT, but some of the older Trek Bicycles used CF tubing with AL gussets at the head tube, seat tube, bottom bracket and rear dropouts. Im assuming they used some sort of coating to prevent this?

A layer of fiberglass between the carbon and aluminum lugs is all you need...

Regarding the fasteners in the hoods and spoilers and what not, either they use stainless or titanium, or lay down some fiberglass when they pot the fasteners in.

--
George

 

[allstar]

lots of carbon fiber bicycles from the early 90"s suffered the effects of galvanic corrosion. Many of them came apart at the lugs which were usualy made of aluminium. Current frames are total carbon with aluminum only used for the threaded fittings. Much better. Jeff www.allstarbikeshop.com

 

[geometro]

Calfees actually use ti (not sure what grade--my guess is 3/2.5) for their lugs and dropouts so they dont need an insulator. The older bikes probably didnt get the process ironed out 100% which is why you saw the failures further down the road.

--
George

 

[titaniumdave]

Here is what Boeing has to say:
http://www.boeing.com/commercial/aeromagazine/aero_07/corrosn.html#table01

Craig Calfee:
http://www.calfeedesign.com/whitepaper8.htm

All sorts of reasons bonded bicycles frames came apart, galvanic corrosion, poor joint design, poor surface prep, less than fantastic adhesive...

All of the carbon parts I bond into my frames use a layer of glass to insulate the aluminum parts from the carbon. The adhesives are much better than they were only 10 years ago, plus easier to use and mix.

I think it is interesting that stainless fasteners are more likely to corrode when screwed in to an aluminum car, that is why Honda uses regular steel with a coating. Titanium is even worse...
http://www.corrosion-doctors.org/Definitions/galvanic-series.htm