Surface preparation is often far more an issue then which primer, while usually you'd use an etching primer for a material like aluminum - a light frosting with a fine abrasive then decontamination with denatured alcohol (caution, extremely flammable) & a terrycloth rag enables any basic metal primer to adhere well. There's a plethora of products made specifically for painting aluminum, yet with attentive surface prep I've used nothing fancier then Rustoleum sandable primer on aluminum with great success.