There are low-temp powder coating materials available (about 250 F cure IIRC). I had some OEM VW pressure-cast wheels aluminum wheels refinished using low temp powder coat. They were redone twice for a total of three heat cycles. The first two jobs resulted in yellowing of the clear coat over the silver so much that the silver underneath also looked yellow. Some wheels were yellow, some not, so I had to have them redo the entire batch to get all the wheels the same.
Despite the use of low-temp powder coating, I'm reasonably sure the result was soft aluminum. After the wheels had been refinished, I ended up driving up over a snow-covered curb to avoid an accident and bent two of the wheels. I've had similar excursions in the past with no damage to the same rims (the hardpacked snow makes a pretty good ramp). I ended up selling the wheels for scrap aluminum and buying some (better looking) aftermarket wheels.
I suspect the yellowing of the powder coat clear was due to poor temperature control. For my money, I'll stick with catalyzed spray finishes and have them redone as necessary. Remember that powder coat paint isn't magic...there are catalyzed finishes just as durable.
Glen