Summary for aluminum conversion coating Discussion
Conversion coating of aluminum is discussed as a chromate conversion finish used either for corrosion resistance or as a pretreatment before painting or powder coating. The thread notes that the process usually includes several steps: alkaline cleaning, etching, deoxidizing/desmutting, the chromate conversion step itself, and rinses between stages. In the answer, Robert Diffenderfer says his experience is that Alodine will not hurt the surface, but etching may remove the clad from the material. He adds that some users specify a "No etch" process, skipping the etch tank and going straight to the deox tank to reduce that risk. The discussion is framed around MIL-C-5541 / MIL-DTL-5541 / MIL-PRF-5541 conversion coating practice.
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 MIL-DTL-5541
[⇦ this spec on DLA] 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!
Shouchenzhang
airline – Liaoning Province, CHINA
2002
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