2024-T3 bare Anodize vs. Alodine

[xzbc511]

I have a part (a spar/avaition part) that was suppose to be made from 2024-T3 alclad, instead it was made from 2024-T3 bare.

The finish spec call outs that the part can be anodic coated per Mil-a-8625 or Alodined per Mil-c-5541 (then one coat of primer). Pervouis batches (proper material) of parts have been alodined.

We want to keep the parts (cost and lead times on them are high) and the best choice would be to Chromic anodize/seal them.

I need some kind of justification/base though. So my question is if anybody knows of a document that compares the corrosion resistance of 2024 bare vs 2024 alclad for anodizing vs alodine?

 

[KENAT]

Maybe.

I remember a similar question - though not sure of the Grade - coming up at a previous employer in the UK.

I can't remember the details but there was an RAE (or one of those govt agencies) report about the impact of Alclad V certain other 'treatments'.

I think we came to the conclusion that for our application the alclad was beneficial/needed.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[KENAT]

Look what Google just turned up:

http://www.finishing.com/199/16.shtml

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[xzbc511]

Thanks Kenat

But thats the first thing i found when doing a google search too. Not really much help though in this situation.

I'm looking for some kind of qualitative comparison (some kind of doc or spec) so I can justify accepting the part and insuring that the corrosion resistance is acceptable or comparable to 2024 alclad thats been alodined.

I.e. a salt spray comparison of different alloys with different coatings.

 

[KENAT]

Um, how about the book mentioned that link?

Or did you mean you want a Free doc or spec?

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[xzbc511]

I was digging though so many specs at the time and I have to take another look to see if the book is in our library (hopefully it is).

Have you been through the book? I don't want to have to raise a purchase order to buy a book that may or may not be useful. (Usually google books will give you a preview to see if it contains useful information. not for this book though)

Does that book do a comparison or does it just go through each process and not really compare them?

 

[israelkk]

2024-T3 correct anodic coating is sulphuric coating and not chromic anodize. The reason is the high content of copper and/or the total content of alloying element, See MIL-A-8625. Alodine is not good if the part is exposed to long term of temperatures in excess of 60 Centigrade. If your part is exposed to external atmosphere sulfuric anodize thickness should be 17-21 micrometer. If it is an internal part is can have a 10-15 micrometer thickness. The anodic coating should hold 336 hours in a salt spray test. If the spec calls for alclad then it is the best to use alclad which has pure aluminum coat on the base alloy sheet.

 

[xzbc511]

Thanks for the help. I checked for the book in the library this morning but I couldn't find it. Kind of hoping it would solve the problem. Anybody experienced with the book and could let me know if it has the type of information im looking for?

israelkk. Its one of those supplier screw up kind of deals where the parts went though the whole forming process before it was caught. Where the end solution would be to scrap the parts, but I'm hoping of finding a bases to save the parts due to lead times. (next batch will be from proper material). Mil-s-8625 is the bases for anodizing (2024 is still under 5% Cu cut off for chomic) Sulphuric would be better though. The only problem is I still need a documented bases to compare too? parts an external part aswell.

 

[xzbc511]

Sorry mil-A-8625.

 

[israelkk]

Cu content under 5% is not the only condition. Here is the quote from MIL-A-8625F: "Type I coatings shall not be applied to aluminum alloys with a nominal copper content in excess of 5.0 percent; nominal silicon contents in excess of 7.0 percent; or when the total allowable contents of nominal alloying elements exceed 7.5 percent."

The maximum content of alloying elements of 2024 is beyond the 7.5 percent (as far as I recall it close to 9%). Therefore, for maximum protection you need to use Type II (sulphuric). I also have actual experience of aerospace part of 2024-T3 that was coated by chromic anodize and failed the salt spray test. After removal and re-coated by sulfuric anodize it passed the 336 hours.

 

[xzbc511]

Thanks Israelkk.

I will dig deeper into in and will likely go with sulfuric then. I have been tied up lately and haven't had time to actually get into the research in order to produce the report.

With all your experience, you wouldn't know of a documentation that 2024 Bare anodized (sulfuric) would meet the corrosion resistance of 2024 alclad alodined? I knew this was going to be a pain when I got this file, most the information I have got (from other sources) is experience and word of mouth, which is not hard data to base it on.

 

[KENAT]

Like I mentioned - there was a UK government report from RAE or DERA or one of those agencies (now probably part of Qinetiq or maybe DSTL) which addressed this issue. However, no I can't give you an internet link to it and I don't have a copy to look at.

What is the price of the book at that link compared to scrapping the parts? (not just direct cost but cost implications of delaying delivery etc.)

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[coatingengineer]

Hi. Here, you will have your answer:

http://www.lukeeng.com.

Luke Engineering is one of the original pioneers in aluminum metal finishing. Many of these very specifications began as collaborations there. From my own experience I can say the "who's who" of aerospace will agree. Best wishes.

William Gunnar

http://www.IndustrialCoatingsWorld.com