question about aluminum

[Bondonutz]

Jason,
Now when Aluminum and say Stainless are bolted together and the aluminum corrodes is that a form of "Electrolysis" or plain ol' corosion or one in the same ?
I ask because when I was still working on buses and had to take something apart that had ben together for years and exposed to enviroment sometimes the the Stainless would be eaten away and the Aluminum would be heavily pocked up from the corrosion in form of white scaley chaulky gunk.