Summary for precleaning of aluminum before alodine Discussion
Precleaning of aluminum before Alodine is the core issue here: Buddy Jeter says his aerospace shop has used sanding or Scotch-Brite on aluminum sheet parts, passes monthly salt spray, but sometimes fails the water-break test and is facing a Nadcap audit. He notes they already have a strong NaOH/HNO3 etch line for pre-penetrant work, yet MIL-C-5541 recommends not etching before Alodine, and they want to avoid heated tanks. James Watts advises switching to proprietary chemicals, pointing to low-etch alkaline cleaners from major vendors that can come with technical support. Robert H. Probert adds that sanding can embed contaminants into soft aluminum, which then requires a much deeper etch to remove soils such as iron, silicon, and organics. The discussion suggests moving away from abrasive precleaning toward a suitable low-etch chemical cleaning process.
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 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
2004
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
2004
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 H Probert
Robert H Probert Technical Services
Garner, North Carolina
2004
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.
Thanks,
Asoka Cooray
– Male, Maldives
April 9, 2013