Companies that do hard chrome plating of aluminum guns usually refuse to plate the frame.
The reason is that if a hard chrome layer gets dented the softer aluminum under the plating may dent enough to allow even hard chrome to chip or flake off a piece.

What they usually do is just bead blast the aluminum to match the hard chrome finish on the steel parts.
This has been done for a good many years to all sorts of aluminum framed revolvers and pistols with no adverse results I've ever heard of.

To keep the aluminum looking good keep it lightly coat it with a lube, just like you do a blued steel gun.