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"Cleaning of chem-film conversion coating (Alodine, Iridite, etc.)?"

An ongoing discussion beginning back in 2004 ...


Q. I have an aluminum part that has an Alodine 1201 [linked by editor to info/product on Amazon] corrosion coating applied to it. The unit has been is service for several years and the desire is to "clean" the aluminum on the part an put it back into service. The unit cannot be stripped and re-Alodined because foam padding is on it in several locations. Mild solvents such as water, Isopropyl Alcohol [affil. link to info/product on Amazon], MEK / methyl ethyl ketone, etc. were spot tested on the part but nothing used seemed to remove the dirt and grime. Do you have any suggestions for cleaning the part without removing the corrosion resistant coating? Are there commercially available products available for such a task?

Brad Nixon
- Heath, Ohio

Isopropyl Alcohol (IPA) Removed Chem-film Coating from Aluminum


Q. Dear Sirs,

I'm a process engineer in a semiconductor equipment manufacturing company located in Penang, Malaysia. Recently we produced an aluminum part with a chem -ilm gold, class 1A finishing; but when using IPA to rub/clean it with linen paper we found some gold color on the paper, and the area which has been rubbed became lighter. Can't Chem-film with-stand IPA test? what is the best chemical or method to clean (grease/oil) on chem film surface?

Tai Mai

Khor Tai Mai
Consumer - Georgetown, Penang, Malaysia


A. If the chem film is freshly finished and you wipe it, it would not strong enough, however, if after 24 hours you still see yellow on the paper when you wipe, then the chem film is poor.
As a process engineer, you should teach your men how to do a good job at first shot. To me doing chem-film with stains and trying to clean the part later is in a wrong way.

John Hu
- Singapore


A. The chem film should not come off when wiping with just IPA. 2 thoughts come to mind.

1. The chromate has not cured before you are wiping (allow 24 hours)
2. There is residual chromate solution being left on the parts by dirty rinse tanks, or inadequate rinsing.

Marc Green
Marc Green
anodizer - Boise, Idaho

January 28, 2010

Q. Hello,

Just curious if one can paint (say epoxy primer and topcoat) directly to an aluminum panel that has been conversion coated and cured (say after 24 hrs)? Does wiping with MEK do anything to the coating before painting? Thanks for reading and any help.

Ron Heavey
product designer - Canada

February 2, 2010

A. Ron,

I am not certain what you mean by "curing" of the conversion coating. You normally dry a conversion coating surface so that it is free from moisture, but you must not expose the conversion coating to high temperatures (over 60 °C).

Conversion coating is often used as a key for paint, so priming and topcoat after conversion coating should be fine.

Brian Terry
Aerospace - Yeovil, Somerset, UK

February 3, 2010

Q. Thanks for your response. Assuming the conversion coating is complete (dry), would wiping with MEK degrade the coating prior to painting?

Ron Heavey [returning]
- Canada

"Surface Treatment & Finishing of Aluminium and Its Alloys"
Wernick, Pinner & Sheasby
from Abe Books

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(finishing.com may earn commission)

February 5, 2010

A. Ron,

MEK will not damage the coating, but I would be worried on a health and safety basis on the use of MEK, especially if you are going to be doing a lot of swabbing in the open shop. Consider changing to acetone or Isopropyl alcohol (IPA).

Brian Terry
Aerospace - Yeovil, Somerset, UK

February 20, 2010

A. I concur with Mr. Terry's response. We routinely prime/paint chromated parts and panels. Just make sure that the chromate is not heated above 140°F - elevated temperatures will compromise the coating's corrosion resistance and adhesion properties.

MEK will not harm chromate coatings, but they are not operator or environment-friendly. A mild alkaline cleaning solution or even an alcohol wipe would minimize hazards.

Terry Lycans
Aerospace - Dayton, Ohio, USA

Powder Coating Chem-filmed Parts

October 18, 2010

Q. We powder coat chem-filmed parts for one of our customers. We have had some problems with de-lamination of the powder from the chem-film. After visiting the company applying the chem-film, I have concerns about finger prints on the chem-film. I feel the best way to resolve this problem is to clean the parts, but I can't wash them the way we clean our regular parts because the chemicals will remove the chem-film. What can we dip these parts in to remove dirty finger prints?

Jerry Raines
powder coater - Asheboro, North Carolina

"Surface Properties of Conversion Coated Aluminum"
by Raj & Ali
from Abe Books
info on Amazon

A. Hi Jerry. Fingerprints are a special case, and possibly not removable. Please see letter 10002, "Cleaning fingerprints from conversion coated (chem-film) aluminum". But the adhesion problems are not necessarily the fault of those fingerprints. Some other potential issues are too heavy a chromate coating, such that it shears off of the substrate' some of the new RoHS compatible conversion coatings may not function the way traditional hexavalent conversion coatings did -- they may have topcoats that are not as compatible with powder coating as a straight chromate conversion coating.


Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

January 19, 2015 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Looking for recommendation on cleaning process for Chem Filmed aluminum. We have an ultra-sonic soap cleaner with hot water rinse and it appears to be removing the finish after about 2 minutes in the soap.

Tony Lewis
- San Diego, California USA

January 2015

A. Hi Tony. We appended your inquiry to a thread on the subject of cleaning chem-filmed aluminum. Milt Stevenson discusses and warns of this problem with ultrasonic cleaning in letter 10002.

Luck and Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

February 10, 2020

Q. We Alodined a Metal bond assembly and the masking to cover some of the holes to the interior allowed alodine to the interior where we could not wash inside. Any concerns? Does any of the Alodine process have any effect on the Metal bond adhesive?

Gary Cassatt
D-J Engineering Inc. - Augusta, kansas, USA

September 3, 2020

Q. After carrying out conversion coating on aluminium 7075-T7351, part was left for 2 months; and when it was wiped with IPA there were yellow stains noticed on the cloth.
For final rinse we have used DM water TDS < 750 PPM and pH 4.4.
I want to understand how does pH of rinse water effect the final job?

Abhishek Mishra
- Coimbatore INDIA

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