I'm going to guess that at some point in the history of that wheel, the brakes went "metal on metal." When that happens, hot iron particles from the brakes imbed themselves in the clearcoat and then rust over time.
As others have said, rectifying that mess is not going to be easy and the results are not going to be great. That said, you can make the wheel look better. My suggestion for the first step is to get some Iron-X or similar iron decontamination product. Follow the instructions, but leave the product on the surface for longer since you have far more iron contamination than normal. It may even take several applications and rinses. BTW, it will help if you remove the wheel weights.
Once you get the iron particles out, you can polish the surface with a metal polish. You'll probably need a rotary buffer and an aggressive pad to really get through the mess caused by the iron particles though.
Finally, you'll need to clear coat the surface to prevent the (now fully exposed) aluminum surface from oxidizing.
Sound like too much work? It does to me. I'd just buy some used wheels for $50 each.