Crevice and Pitting corrosion are more likely on Al. Extruded Al is more susceptible to something call stress-corrosion cracking – but this would be highly unlikely in bikes. If the bike is made from a 6000 grade Al alloys then it should have better corrosion resistance (Mg and Si added).
Chlorine from road salt (NaCl), some cleaning agents etc. it particularly nasty when it mixes with water and forms HCl – although the passivating oxide layer on Al is very good – Cl ions can degrade it.
For nerdy people – use SiC paper on some Al and then measure the electrical resistance……. then wait 30 seconds and look at the resistance….. thats the Al2O3 film forming 🙂