A word of caution regarding the powder coating of aluminum.
Forged alloy wheels are desirable because they are known to be both strong and lightweight. To achieve these characteristics, they are typically manufactured from 6061-T6 grade aluminum. At some time during the manufacturing process this alloy must undergo a two-step thermal process in order for it to attain the desired mechanical properties, which include high strength and resistance to fatigue. These thermal processing or heat treating steps are known as solution treatment (985°F) and artificial aging (350°F). With forged 6061 aluminum, the artificial aging step requires the material to be held at 350°F for about 8 hours.
The majority of powder coating materials require a cure temperature ranging from 300 to 400°F with a cure time of about 1 hour. Since this overlaps the temperature of the artificial aging step, the powder coating process has the potential to "overage" the aluminum causing embrittlement and reduced fatigue life.
Recent advances in powder coating compounds have brought about lower cure temperatures of 250°F. These new powder coating compounds are more desirable, since they do not impact the prior thermal processing steps for heat treatable alloys such as 6061-T6 aluminum.
When considering powder coating of heat treatable aluminum alloys (6000 and 7000 series), it is always advisable to confirm that the temperature of the part will not exceed 300°F. Ignoring this fact may result in a sudden and unexpected failure of a critical component. A critical failure in a forged alloy wheel could ruin not just one, but possibly the rest of your days.
Before allowing someone to powder coat your forged aluminum wheels, ask them to use a lower cure temperature (250°F) compound and to maintain the temperature below 300°F at all times while they are processing your wheels.
Additional reading:
http://my.execpc.com/~davewrit/Powder.html