Jan Luv
prep well by cleaning, use a good quality brand metal primer paint follow up with 2 or more coats of good quality oil or acrylic base metal paint.

illegitimacy
After painting aluminum for 30 years, I can tell you that the only thing tougher to get paint to stick to is glass. Everything with aluminum depends on the primer. You probably can't get strontium chromate because it is carcinogenic. You will probably have to use zinc chromate. Either primer will be mixed with an acid, usually phosphoric acid. If you can find a chrome conversion coating called Alodine, it has an excellent performance record. The simple way to do this is to find a local aircraft maintenance facility to put on a primer and a base coat. You have to put a base coat over the primer to keep the primer from absorbing moisture from the atmosphere. The aircraft people might have a suitable paint booth. Call around. Most suppliers are glad to help. But painters know what works. If an aircraft facility is not available, clean the metal. Do not sand blast it. Blasting only impinges the crud. Use a citrus based cleaner so that it doesn't negate the zinc chromate acid component. Don't use the primer if it has been mixed with the phosphoric acid for more than a few hours. You will want a THIN coating of primer. Just enough to completely cover the aluminum. Warm the aluminum just enough to be sure that the primer is dry. Then apply a base coat of your choice. Acrylics do very well. Aircraft paint is preferable. Aluminum siding house paint is designed to chalk. I would avoid it. My choice is polyurethane. It is durable and color fast. Use a 1 to 1 polyurethane if you can get it. Polyurethanes come in 5 to 1, 4 to 1, 3 to 1, 2 to 1, and 1 to 1 ratios. Anything lower than 3 to 1 is a waste of money for your application. If this carousel horse is going to be ridden, I would use the 1 to 1 polyurethane. Prep the aluminum by taking it down to the parent metal. Strip off all old paint with paint stripper or sanding. Truck washing facilities have an acid cleaner that is excellent. The more research I do, the more product specific the process becomes. Check out this website for a starter. I would not mix products from different suppliers. Pick one brand and stay with it.