Main Motorcycle: 71 T100R
Join Date: Nov 2008
Location: Nebraska, USA
I'm not a metallurgist, and I'd yield to anyone who is, but I was a chemistry major for a few years before switching to Engineering.
There are normally several things that have to be in place before you get "galvanic" corrosion. First, you need two different metals. Then there has to be a conductive medium (usually a liquid) present--impure water works fine for this. Last, the two metals need to be electrically connected--this is usually the case if the metals are in contact.
To determine which metal corrodes, you have to refer to the "galvanic series" list. The metal higher on the list will corrode (oxidize), and the rate of corrosion will roughly be determined by how far apart the two metals are on the list.
Aluminum and stainless are fairly far apart on the list (farther than mild steel and aluminum), and this is why people warn about corrosion with this combination. The best prevention is to keep the joint from getting wet or staying wet. Some people recommend grease or an anti-sieze compound for this.
Galvanic corrosion is a pretty slow process, so there usually isn't a need to panic if you get caught in a rain storm.
For only a little more, you can do it yourself!