Most old iron MC's (used with glycol fluid) that I've disassembled have pitting in the bottom of the bore. I've only disassembled one later aluminum MC and it wasn't pitted.

Anybody with more experience with the aluminum MC's, do they tend to not be corroded inside over time like iron?

i have had the same experience as you, except i have torn apart six or eight late model aluminum masters [mini van units] to just investigate the differences between years.

That along with weight are the reasons they moved from cast iron to aluminum castings.

Aluminum M/C's have the bore anodized so corrosion shouldn't be an issue but as with everything there is always an exception.

Won't react to moisture like iron, but I have seen the aluminum pistons corrode/pit. Maybe only when in contact with steel too (shims, springs). Probably galvanic corrosion.