An aluminum heat exchanger with excellent corrosion resistance and particularly suited for adaptation as radiator for automobiles, the heat exchanger having a 2- or 3-layer coating film structure consisting of a zinc-diffused layer formed on the surface of an aluminum base and a waterproof organic film formed on the zinc-diffused layer with or without a phosphoric acid-chromate coating therebetween, whereby the surface of the aluminum base is not directly contacted with at least the water-containing heat exchange medium is provided.
