[tackleberi]

Is there a problem using a aluminum .22LR upper (Marvel Unit 1) on a stainless 1911 frame? I've heard of, in passing, references to bad things that can happen when dissimilar metals (such as aluminum and stainless) remain in contact or work against each other for periods of time, but never gotten a explanation of what those "bad things" might be. Anyone with gunsmithing, engineering, or metallurgy experience with an answer?

[rcmodel]

What you heard is probably in relation to galvanic corrosion.
It is a big problem with outboard motors used in salt water. And steel Pop-Rivets used in aluminum gutters.

But there is no problem at all with guns because hopefully, there is no impure water present to serve as the electrolyte between the dissimilar metals.

Without the electrolyte, electrolysis cannot occur.

rcmodel

[highorder]

The anno on the aluminum should be sufficient to prevent any problems.

Consider how many stainless slides run on aluminum frames without problems.