Corrosion between Al and carbon

[grob]

I have been told that aluminium reacts very badly with carbon fibre in sea water, the aluminium is supposed to "corrode" (oxidise) very quickly, I have not found this to be the case myself but I have always used anodised aluminium with carbon.

Many windsurfing fittings combine aluminium and carbon. Am I likely to have problems with anodised aluminium and carbon fibre, and if so are there any cures?

[gonzo]

You need to specify which aluminum alloy it is. The corrosion resistance varies.

[duluthboats]

I’m not around boats that have much of these materials. But I can tell you that this is a major problem in the aircraft industry. Any time you mate aluminum to a material that conducts electricity you should isolate it with paint, tape, or other type of nonconductor. I have seen 1” thick lav wall fittings sitting atop carbon floor boards, almost entirely oxide.

In your case the parts are likely dry more than they are wet which slows things down to the point that you may never notice and the damage will be nominal.

Gary

[grob]

Aluminium Material is 6082-T6 and the aluminium is glued to the carbon.

[duluthboats]

6082 is a magnesium and silicon alloy aluminum. It is better than some for corrosion resistance. The glue will help isolate it from the carbon.

[gonzo]

The glue should be a good isolator. Usually the problem is around fasteners. If you can also anodize the aluminum and paint the carbon it would be better.

[Eric Sponberg]

When I designed some carbon fiber spinnaker poles for the 1983 America's Cup, the poles were shifted from boat to boat, and the aluminum end fittings were changed from one pole to another. As a result, there was little to no caulking between the carbon pole and the aluminum end fittings. The end fittings were made with 6061-T6 aluminum. After about a month of trial racing, there was noticeable pitting and white corrossion all over the fittings. You could almost see it fizzing.

The reason, of course, is that carbon fiber and aluminum are at opposite ends of the galvanic scale. Carbon is right up there with gold and platinum. You should always insulate carbon from any other metal, including stainless steel and titanium, when they are in contact with each other in the presence of an electrolyte (sea water). Gold and platinum with carbon, actually, would not be a problem on "gold plated yachts"!

Eric

[john@nyalic]

Originally Posted by grob

I have been told that aluminium reacts very badly with carbon fibre in sea water, the aluminium is supposed to "corrode" (oxidise) very quickly, I have not found this to be the case myself but I have always used anodised aluminium with carbon.

Many windsurfing fittings combine aluminium and carbon. Am I likely to have problems with anodised aluminium and carbon fibre, and if so are there any cures?

Insulation of dissimilar materials with a non conductive sleeve or coating will halt further corrosion problems.Alternatively check out Nyalic (R) a clear non corrosive non conductive clear polymer that will adhere to either surface so long as they are clean and will provide further uv and salt water protection.

JOHN

[gggGuest]

One of the classic examples of this was when earlier examples of the RS600 racing dinghy in the UK used alloy sleeves inside carbon masts. There was some insulation but even so... alloy eventually went fizz, corrosion products bulkier than sleeve so pushed out laminate, layup microcracked, mast went bang.

Of course normal precautions round fittings, zinc chromate paste etc helps, as does suitable insulation locally, kevlar useful for this.

[D'ARTOIS]

In the titanium alloys we work with, no electrolysis with carbon occurs. Titanium is a non magnetic metal that in it's alloyed form has the most anti-corrosive properties of all existing metals. Currently there are two main alloys available for different purposes: the Ti6Al4V and the technical more advanced Ti5Mo5V2,5Al, the latter maybe not to be easy found in the US/Europe - outside the aerospace industry.
The more common Ti6Al4V has a corrosion resistance against gases, acids, salts, chorids - name it.

Immersed in seawater (Ti6Al4V) the rate of corrosion is 1/2500 mm in 1250 years.

[ClarkT]

If at all possible, replace aluminum backing plates with Micarta or Garolite. If you must use aluminum, anodize it, and completely isolate it from the carbon (ie. micarta backing plate, micarta compression tubes through laminate, and a micarta bedding pad).

[rxcomposite]

Anodizing aluminum will make it non conductive to a certain degree. Get an ohmeter and measure the resistance of a bare aluminum and anodized aluminum. you should not get a reading on the anodized part.

The problem arises when the two dissimilar material is attached together by screw or rivet. The insulating part is now broken and now you have a direct contact with carbon and aluminum.