Galvanic corrosion: the material-pair trap

Carbon fiber is electrically conductive and very noble. Bolt aluminum to it in the presence of moisture and you've built a battery — with the fastener as the sacrificial anode.

Why carbon fiber is so aggressive

On the galvanic series, carbon fiber sits near the cathodic (noble) end — close to graphite. Aluminum sits near the anodic end. The larger the potential gap and the more conductive the electrolyte (salt, rain, sweat), the faster the anode corrodes. An aluminum fastener wet-coupled to CFRP can lose a large fraction of its strength, and the surrounding aluminum structure suffers too.

It's the pair, not the side

This is the key insight people miss: galvanic attack depends on the material couple and the electrolyte, not on which side of the joint is blind. Carbon on the head side or the blind side, it doesn't matter — an aluminum fastener is wrong either way. That's why the selector recommends the alloy from the material pair, separately from the blind-bulb question.

The safe alloys

Titanium (Ti-6Al-4V) is the gold standard against CFRP: it's close to carbon on the galvanic series and its thermal expansion is far nearer to the laminate than aluminum's. A286 CRES is the common second choice. Aluminum fasteners against carbon are avoided unless fully isolated.

Breaking the path

When a dissimilar pair is unavoidable in a wet environment: wet-install the fastener with corrosion-inhibiting sealant, add a fiberglass barrier ply or wet primer between the metal and the carbon, and prefer titanium. The selector raises a sealant flag whenever it sees a dissimilar pair in moisture or salt.