"Found your article most enlightening. A metallurgist friend told me a few years ago that things like aluminum wheel spindles should not be powder coated. He explained that aluminum billet material (6061-T6 ?) changed crystal structure at a critical temperature around 410 degrees F (as I recall). The thrust was that the heating step would adversely affect the strength of the material. Non-structural components would be OK, but not something that "holds the spokes on". The metallurgist is correct. Products like wheel billets, scuba tanks, etc. can be powder coated, but only with powders which cure below peak metal temperature of 300 degrees F. The magic temperature is about 275F. The crystalline realignment at 400 degrees F causes the previous ductile aluminum to become brittle. Imagine the catastrophe when an 80 cu. ft. scuba tank explodes under 3000 psi pressure after an unauthorized powder coat (this actually happened). To my knowledge, all Aluminum wheels and other strength-critical aluminum components are powder coated with these cooler curing powders.

Heating Al alloys above this temperature causes a granular rearrangement of the metallurgical structure resulting in a significant change of bulk properties. The tensile strength of the metal is dramatically lowered, much like a stress relief anneal on a steel piece would do. The resultant metal is not as strong, nor will
pressure vessels made of such treated aluminum (e.g., scuba tanks) hold near
the pressure that they were originally rated for. Since wheels are essentially load-bearing structures, they should never be heated like this unless the alloy is known to tolerate it well.