Conversion Coating of Aluminum

Quickstart:
     Aluminum is often 'chromate conversion coated' as a corrosion resistant final finish or as a pretreatment for painting or powder coating. The process actually involves many steps, usually including alkaline cleaning, etching, deox/desmut, the chromate conversion step per se, and water rinses between each step.
     MIL-C-5541 / MIL-DTL-5541 / MIL PRF-5541 is the most commonly cited spec. "Alodine" and "Iridite" are proprietary trade names of the suppliers of the process chemistry. In the USA "Chem film" is an often used slang term for the process.

Q. I am a aircraft structure engineer and I work for China Northern Airline. I wonder about "aluminum conversion coating". Would you please tell me if Alodine can be applied on the non clad aluminum same as on the clad aluminum? Thank you very much!

A. Hello!

Alodine is the chemical conversion of the aluminium surface. It means that the surface to be treated is free of grease, paint, ... The best is a good degreasing, very good rinse and Alodine. After the Alodine treatment, the surface needs to be rinsed twice : first with tap water and secondly with demi-water to remove the salts traces.

Paul Moreau
aluminum reflectors for lighting - Liège, Belgium

A. My Experience is that the Alodine will not hurt the surface however etching may remove the clad from the material. Some people specify a "No etch" process where they skip the etch tank and go right into the deox tank to avoid the risk.

Robert Diffenderfer
Engineering Manager - Essex [Maryland]
April 18, 2025