So, I have a really expensive carbon fiber bicycle frame with an aluminum bottom bracket. One of the screws on the granny ring came loose and through my pedaling cut a nice ring of paint off the bracket, exposing the aluminum.
I know aluminum doesn’t rust in the same way as iron or steel, but should I still be worried about oxidation or corrosion and if so how do I best protect the aluminum and also prevent the paint from additional chipping?
Thanks a lot! 
What’s the screw made of? There may be some risk of deterioration or corrosion due to the contact of dissimilar metals. (I’ll let a chemist chime in.) Even so, a little lead paste on the screw will probably prevent a problem.
As for the aluminum itself, it won’t corrode or deteriorate. Ever see an American Airlines jet that looks silvery? That’s unpainted aluminum. Many years ago (when fuel was relatively cheap) they went to that look to save the weight of the paint and improve fuel economy. Prescient!
Thanks for the good news!
Since I’ve tightened the screw and it doesn’t touch the bottom bracket anymore, I guess I don’t have to worry about any corrosion or deterioration. Thanks!
The instant that aluminium is scratched, it oxidizes. There’s a very small layer of aluminium oxide, which serves to stop further oxidation. What you see on American Airlines planes isn’t aluminium, but aluminium rust. It’s pretty much the same thing that rubies are made from.
Hit it with pledge or any other wax to keep it coated.
Bike mechanics use grease between metal parts to prevent exchange of electrons (fusing). There are specific greases/lubes for use with carbon fiber, so check with your LBS.
A scratch on the outside of the BB probably isn’t going to hold onto a daub of grease, and I’d be tempted to a) soften up some beeswax and rub it into the scratch or b) very carefully paint over the scratch with some clear nailpolish. Consider, though, that the BB is closer to the road surface and therefore more exposed to harsh conditions than anything except the rims and maybe the pedals. So the framemaker chose a metal that will stand up to rough treatment. The paint may be more cosmetic than protective.
I doubt whether corrosion would be a problem in this application, but if you really wanted to be careful you could use Alodine. We use it all the time in space applications.