Etch on extruded aluminum

I am a bit confused . . . you're not attempting to run your aluminum though your iron phosphate line, are you? It won't work well. You really need a separate tank line with a non-etch cleaner, aluminum etch, and de-smut tanks. And chromating would be much better.

Every cleaner salesman calling on you has a product in his line consisting of detergent and phosphoric acid in varying degrees with different product names. This type of product has been used on window and door extrusions for over 50 years, mostly by immersion but the product will work when sprayed. You might have some difficulty getting the particular blend that fits enough detergent for cleaning and enough phosphoric for etching. Try it you'll like it. Put this product in the first stage, be careful, too much phosphoric will eat up the mild steel (But not near as fast as ammonium bifluoride)