Check out a galvanic corrosion chart where the potential voltage indicates how likely corrosion is to occur:Originally Posted by D Egan
http://www.thelen.us/1galv.php
If aluminum is -1.670 and carbon is +.810, the potential is 2.48. The potential between aluminum and cadmium is about 1/2 that, at 1.268.
Titanium pins and bolts are often used with aluminum in large aerospace structures. The potential there is 1.725, but 7000 series aluminum alloys are somewhat worse than 2000 series alloys. In most large aerospace structures fasteners are installet "wet" using sealant to keep electrolytes (moisture) out. BTW, monel "pop" rivets as used in some homebuilt aircraft have more galvanic potential with aluminum than titanium. Also, an "upgrade" for spam can owners is to install stainless steel screws to hold on fairings in aluminum aircraft. This is a "Bozo no no" in the aerospace industry because of the galvanic potential, yet it is commonly done in GA. A cadmium plated carbon steel screw, like came from the factory, would be much better.
The bottom line here is that aluminum corrodes with aplomb in seaplanes exposed to even fresh water without being in contact with dissimilar materials. It depends upon your environment.
The standard aerospace method is to add a fiberglass corrosion barrier ply to the carbon fiber panel and use a titanium screw. The aluminum would be coated with primer and topcoat.
In real life, a carbon fiber panel in a dry interior space in a homebuilt isn't at much risk, in my opinion. A external carbon fiber fairing on an aluminum stabilizer used in a seaplane would be much more worrisome. Airliners and cargo aircraft that see lots of cycles in inhospitable weather are where most of these measures are most needed.
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