Method of bonding a high temperature resistant polymeric material to an aluminum base substrate

A method for bonding a high temperature resistant polymeric material to an aluminum base substrate comprising:

• providing an aqueous alkaline bath containing an alkali metal chromate salt selected from the group consisting of sodium, potassium, cesium, rubidium and mixtures thereof of chromic acid, and in addition to said chromate salt, an alkali metal carbonate, with the alkali metal being selected from the group consisting of sodium, potassium, cesium, rubidium and mixtures thereof, in a ratio of said carbonate to said chromic salt from 3 to 1 up to 9 to 1 wherein the carbonate concentration is at least about 0.0625 mole/liter, and from about 0.0005 mole/liter up to its saturation point in the bath of a water soluble salt of an alkaline earth metal selected from the group consisting of calcium, barium, strontium and mixtures thereof;
• immersing the portion of the substrate which is to be coated with the polymer material into the bath for a time and at a temperature sufficient to cause a surface conversion coating to form on the exposed surface of the substrate;
• removing the substrate from the aqueous bath after the formation of the conversion coating thereon;
• applying at least one high temperature polymeric material selected from the group consisting of polyphenylene sulfide, polysulfone, polyphenylsulfone, polyethersulfone, polyetheretherketone, polyetherimide, polyamideimide and polymeric compounds containing them to the surface of the substrate which is to be coated;
• heating said so-applied polymeric material to a temperature sufficient to cause it to flow and cover that portion of the substrate which is to be coated;
• and,
• cooling the heated coating to a temperature sufficient to cause it to solidify and become adherently bonded to the substrate.