Alloy wheels are specific wheels have been made out of aluminium or magnesium, with certain other elements added. They can come in various shapes and sizes and even the finish can differ greatly between models or brands.
Powdercoating is a paint technique. Instead of spraying the liquid paint on a surface, and let it cure. A powder is sprayed over a surface and baked the cure. Powdercoating is very popular for coating wheels with paint.