Steel corrodes aluminum, but not because of iron, which is very near aluminum on the galvanic chart; iron is actually only slightly less reactive). Nickel corrodes aluminum a little more aggressively, which is the problem with "stainless" steel. Nickel is the chief alloying agent in SS and many plain steels as well.

I'm not sure if there's a direct connection with the periodic chart; the scale of interest here is the Galvanic chart or anodic index.

http://www.rcboataholic.com/faq/corrosion.htm

In this chart some metals are more 'noble' or unreactive, 'cathodic', and some are more reactive or anodic. Gold is zero on the chart and beryllium is on the other end at 1.85. The farther apart two metals are, the more galvanic corrosion when they meet. The more reactive metal always loses.

Notice where some of the higher alloys of aluminum (like 7075) are on the chart; way up ther near magnesium. And 5052 aluminum is right next to some grades of stainless steel meaning thay are fairly compatible. 5052 and 5056 are commonly used for marine extrusions. Ditto for the "stainless" steels with some high on the chart and some far lower. Remember that the terms 'aluminum' and 'stainless steel' are thrown around as if they each refer to one single material with one set of properties. This is just not true. It matters a lot exactly which alloy you are talking about.

Some SS alloys for example are called 'food grade' i.e. is good for contact with food. Other alloys include lead and molybdenum to facilitate machining. But these are both very poisonous heavy metals so totally incompatible with food.

I have not observed a big corrosion problem on my mast where I did some service back in '91. I used SS rivtes. I resealed both end caps and replaced clam cleats.

The galvanic compatibility can be managed with surface finishes like anodizing. This keeps the reactive metals like SS and Al out of actual cotact, which is why you can get away with SS rivets, to an extent. Aluminum oxide is NOT aluminum; it is aluminum oxide.

Jimbo