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Precleaning of Aluminum before Alodine treatment


Q. I work at a composite aerospace structure manufacturer. I was hired on to run the NDI Department but since Chemical Processing is also a "Special Process" I was given major responsibilities in the Alodine area. We will be having a Nadcap audit this month and I have a problem. We produced metal aircraft components prior to doing the composites, primarily aluminum sheet metal parts for cabinets. In the past the parts were either sanded or scotchbrited for the precleaning. We perform a monthly salt spray test to verify the process and have never had a failure, to my knowledge. But the water break test was not performed. I have checked a sample of parts and they do not pass the water break test all the time. We currently have a 20% NaOH / 50% HNO3 Aluminum Etch line for Pre-penetrant etching, but MIL-C-5541 [affil link] recommends NOT etching the parts prior to Alodining. We are a small company and would like to stay away from heated tanks, if possible. What options do I have.

Buddy Jeter
Aerospace - Bridgeport, West Virginia, USA


A. Switch to proprietary chemicals. There are good low etch alkaline cleaners available from some of the major vendors and they can also help with the tech support.

James Watts
- Navarre, Florida


A. Sanding imbeds all kinds of junk into the soft aluminum and this requires a massive deep etch to remove such imbedded soil (iron, silicon,organics, etc.)

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

April 9, 2013

Q. Before we do Alodine for 2024-T3 aluminium sheet we are rubbing the sheet with use of scotch-brite. Is it correct? And we need to know correct procedure of Alodine for 2024-T3 alclad sheet.

Asoka Cooray
- Male, Maldives

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