# Galvanic reaction between aluminum and carbon fiber composite

I understand that there is a galvanic reaction between aluminum and carbon fiber composite. Structural aluminum parts in contact with carbon fiber composites should be insulated by something like fiberglass.

But what exactly is it that happens, chemically? I know that aluminum has a tendency to be oxidized; aluminum oxidizes readily by itself in air. I also know that carbon fiber itself is a conductor due to delocalized electrons.

So assuming that aluminum is oxidized then the carbon fiber composite must be reduced.

What exactly is reduced? The carbon fiber, or the epoxy? What is the role of the epoxy in all of this? Wouldn't the epoxy be electrically insulating? How exactly does this redox reaction take place across the epoxy?

The reason is that aluminium carbide, $\ce{Al4C3}$ is formed. The reaction occurs at around 500°C on the interface. The problem with this substance is that it is brittle, and it also reacts with water:
$\ce{Al4C3 + 12H2O -> 4Al(OH)3 + 3CH4}$.