×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Galvanic corrosion between Aluminium and carbon fiber

Galvanic corrosion between Aluminium and carbon fiber

Galvanic corrosion between Aluminium and carbon fiber

(OP)
Hi there,

I've been reading a bit in the forum and internet about the galvanic corrosion between aluminium.

We have a carbon fiber reinforced epoxy boxes with a load and they are hung in one end. We glue an aluminium insert. The gap is 150 microns around and the glue 3M DP 410.

In theory, there is no direct contact between the carbon fiber and the aluminium, since we have the glue everywhere around the aluminium.

We can't use glass fiber in between.

I am not familiarized with the treatments but there is a company here close by which can do a chromate (Alodine) the aluminium parts.

Do you think this is safe enough to avoid the galvanic corrosion?

thanks
regards
Replies continue below

Recommended for you

RE: Galvanic corrosion between Aluminium and carbon fiber

Maybe.
This why modern airliners use Ti for the floor structure, so that they can use CF body and floor panels.
If this is glued to the side of a vertical surface, and if enough dirt and dust build up to bridge the glue joint, and if it gets damp, then the Al will be going away quickly.
I would look at coating the sides of the Al piece either with the glue or with a good coating (epoxy or urethane).

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Galvanic corrosion between Aluminium and carbon fiber

You describe the component as an insert. Can it be knurled for grip and then hard anodized? I have seen hard anodized components hold up well in highly galvanic connections (aluminum plate bolted to a brass fire monitor).

RE: Galvanic corrosion between Aluminium and carbon fiber

TBE, I problem is galvanic potential, Al to brass in seawater is about 0.6V difference, but Al to graphite is more like 1.2V.
It is very hard to suppress corrosion with that much driving voltage.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Galvanic corrosion between Aluminium and carbon fiber

(OP)
Hi,
Here some pictures (grey part: aluminium insert - brown part: carbon fiber box:




Knurling would be possible but the walls are very thin.

So anodizing would be better than chromating?

RE: Galvanic corrosion between Aluminium and carbon fiber

Galvanic corrosion between carbon fiber and aluminum is real but the concern is often overblown. Carbon and aluminum make a very good battery. But there is a tremendous difference between water and salt water. If there is not frequent exposure to salt water there is often no problem. The actual exposed area of carbon fiber is usually small due to being coated with epoxy. Carbon fiber is not a great conductor nor is fresh water. Corrosion will be concentrated near the point of contact between the two materials and one of the corrosion products are hydroxyl ions, which will chemically corrode aluminum. This tends to break the electrical contact between the aluminum and carbon fiber. Thick anodizing is non-conductive and all aluminum surfaces have some oxide layer.

RE: Galvanic corrosion between Aluminium and carbon fiber

But when you think about exposure think of all possibilities.
On aircraft interiors the drivers are cleaning agents and spilled soft drinks (cola is one heck of an electrolyte).
The worst non-seawater incidents that I have seen involved dust and dew. So think ahead.
If the face end of the box has been machined you may want to think about a thin plastic spacer there to prevent butting the Al directly against the raw CF edge with only glue as a separation.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Galvanic corrosion between Aluminium and carbon fiber

Isn't there also a potential problem from the difference in CTE between the aluminum and the tube? I can picture a failure of the bond starting in a corner and that could expose bare fiber as it delaminates.

RE: Galvanic corrosion between Aluminium and carbon fiber

The CTE of the CF depends on fiber orientation, fiber loading, and resin used. They may not be that different, or they could be very different.
Good point 3DD, if the Al expands more it could split the end open, it is expands less then the bond line is gone.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Galvanic corrosion between Aluminium and carbon fiber

There are epoxies with rubber microspheres that might reduce any issues from differing CTE. I believe 3M DP805 is an example.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login



News


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close