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Surface finishes for aluminum aircraft parts

I am a manufacturing engineer that has been assigned the task of performing a trade study on finishes for airframe components utilizing aluminum machined parts and extrusions. This is the result of my boss having been given a recommendation from an outside consultant that we anodize all of our aluminum machined parts and extrusions. It is my understanding that chemical conversion coating (Alodine) followed by painting is the industry standard and provides adequate corrosion protection. Does anyone out there have any info on the benefits of and cost impact of anodizing aircraft grade aluminum rather than chem-film and painting it? Also, what would be involved in painting anodized parts?

Thanks for any info you may be able to provide.

John Dean
- Walled Lake, Michigan USA
2000

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Hi John,

Well I gotta say this, its the industry standard in my opinion for 2 reasons, it works, and it works well, and its cheaper than anodizing.

There was a point in history where aluminum was typically anodized for paint pretreatment as much as it was chromated. This has since changed because of the decreased cost in chromating/Alodining/Iriditing, etc. The anodizing offers no real benefit over chromate for a paint base, and it some cases, might even be inferior. Chromates have gotten very very good as of late (by late I mean in the last 10-15 years). Also, with the anodize, to some extent you have to take into consideration the possibility of the layer degrading the properties of the aluminum that would adversely affect the purpose of the part(s), for example fatigue strength, its a big issue with hard coating, not so apparent in normal sulfuric anodizing, but still to some extent an issue you have to consider.

Basically I would say you have it right, but if you want to take a stab at it just to be sure and test test test along the way, then go right ahead, but I'm sure you're come to the conclusion you already have, chromate works, and it works well.

Matthew Stiltner
plating company - Toledo, Ohio
2000

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I am interested in specifying 11 gauge aluminum sheet (4x8 feet) as a finish surface for a work (desk)table. I know it sounds crazy but my client is nuts about the visual quality of factory finished aluminum and I can't go forward with confidence without knowing more about how it would stand up in an office environment under use of general administrative tasks (i.e., staff working with computer and writing hand written notes). Will it oxidize at a rate that will result in that dark gray to black film that comes off with a rub of the fingers?

Please reply.

Gregory J. Saldana
- Miami, Florida, USA
2002