it should be fine, we powder coat lots of alum. parts.
i love that stuff, we just had the wheels on my daughters scion done a dark translucent purple over silver metallic.
my son has all his bmx parts done, including alum wheels.
he is hard on parts, and it doesnt seem to affect them!
the powder coater will want to sand blast the parts to make the powder stick (it needs to be roughed up)