FWIW, the fact that steel is an alloy is usually treated as a "given" by most people, since all steel is always an alloy of at least 2 elements, iron and carbon. Many people don't even consider basic carbon steel an alloy at all, reserving that term for carbon steel to which one or more other elements have been added to make it stronger, more ductile, or stainless. Referring to stainless steel as stainless alloy steel is just redundant.
Aluminum, on the other hand, exists as an element. And it can be an alloy as well, and usually is. So the fast that it is as alloy is usually assumed as well in normal conversation.
Finally, the specific aluminum alloy Colt used for the Commander was called "Coltalloy."
So typically, but not always, metal gun frames are referred to as steel or aluminum, without needlessly adding the fact they are alloys. Serves no purpose.