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Message: <blockquote data-quote="PSG-1" data-source="post: 226184" data-attributes="member: 6937">You must be referring to "Ospho" (phosphoric acid)While this stuff works great for neutralizing rust, as well as cleaning and etching aluminum for painting, DO NOT use it on galvanized metal, it will eat that coating away. Again, this is phosphoric acid.  The way it works on rust is that it creates a chemical reaction with the red iron oxide, turning it into iron phosphate, which is black in color. For aluminum, it etches into the metal, creating some 'tooth' for paint adhesion, and removing aluminum oxide from the surface. (You must also use zinc chromate primer before painting aluminum, or the paint will not adhere, it will flake off)If you want to neutralize the galvanic action between the galvanized and aluminum, ideally, you would put a zinc on each galvanized bracket, but at the very least, you need to use a barrier between them, such as undercoating, or truck bed liner. Paint both mating surfaces before bolting together.</blockquote>