Powder Coating Aluminum
Q. I have a small powder coating shop and I have some customers that want their rims powder coated. Some of them are cast aluminum and others are milled out of billet. Do I need to use a special powder and cure temperature for these types of aluminum? The powder I currently use cures at 400°F for 20 min. Would this temperature have an effect on the properties of the aluminum? K.P.
A. I don’t know why I get so many metallurgy questions. It makes you think that just because someone puts a powder coating over something that all of a sudden the powder magically transforms all product problems into powder coating problems. Just because you sprinkle sugar on your oatmeal doesn’t mean that the “sugar expert” knows anything about the growing of oats or the making of the breakfast cereal. Anyways, now that I vented a little, I will offer some sage advice.
Let’s first review some facts. Aluminum products are often powder coated, especially wheels. Some aluminum products are temperature sensitive, especially those that have temper or heat-treated properties. It is a well-known fact that aluminum can loose those temper properties when heated above a predetermined threshold (this is called annealing). How much the properties are affected depends upon the alloy of aluminum, the temper rating, the exposure temperature and the time the aluminum is exposed to that temperature.
You asked specifically about cast and billeted aluminum wheels. This is not enough information for me to give an accurate answer. You should check with the wheel manufacturer for temperature limitations before coating. At least obtain the alloy and temper rating, if any, for these products. Then you can look up the information online or check with a Metallurgist. You will probably need to use a low-temperature cure powder material and cure it for a longer time at the lowest possible temperature on the cure curve to ensure some safety margin.
