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  #1  
Old 11-29-2020, 10:18 PM
Aluminum Aluminum is offline
 
Join Date: Jul 2017
Location: San Jose, CA
Posts: 312
Default Welding chromated aluminum

Does Alodine deposit any ions that would compromise a weld that subsumes it?

Further down that particular rabbit hole, if all the welded surfaces are well etched and Alodined, would DC TIG work as well as AC or MIG? (No oxide to ruin the weld, is my reasoning.)
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  #2  
Old 11-30-2020, 04:33 AM
fixnflyguy fixnflyguy is offline
 
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Location: Winston-Salem, N.C.
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Default A couple things..

I'm not a welding guru, however, I have some deep knowledge of the aluminum alloys and Alodine process. At my day job of 42 years maintaining heavy jets, we do a significant amount of weld repairs to all types of metals. Its always best to clean down to the parent metal by blasting, sanding,ect., and I've never had any of my welders bring up Alodine as a weld issue. My biggest question to you, (and you may be a welding guru), is what alloy are you welding? VERY FEW aluminum alloys used in aviation can be welded, and are usually limited to ducting, lines and interior "decorative" components. 6061 (6000 series) are very weldable, however, the 2024 and 7075 (2000 and 7000 series) are not weldable at all..they will weld, but the strength of the alloy is compromised. To your question, Alodine is a conversion coating and is easy to remove with scotchbrite, ect. to a weldable condition.
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  #3  
Old 11-30-2020, 06:16 AM
Freemasm Freemasm is offline
 
Join Date: Nov 2017
Location: Orlando
Posts: 316
Default Precautions needed

Most Alodine (a brand name) type conversion coatings contain hexavalent chromium. It is as bad for you as they say. Surprising a civilian can still purchase it. Anyway, anything that gets hot enough to off-gas would seem even more hazardous, at least to me. Remove the coating way past the HAZ and force ventilate the area if you do weld it. Reapplication is easy but utilize the right precautions there, as well.
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  #4  
Old 11-30-2020, 09:08 AM
Aluminum Aluminum is offline
 
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Location: San Jose, CA
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Default

Quote:
Originally Posted by fixnflyguy View Post
I've never had any of my welders bring up Alodine as a weld issue.
Thanks, that was my gut feel but good to hear confirmation.

Quote:
Originally Posted by fixnflyguy View Post
My biggest question to you, (and you may be a welding guru), is what alloy are you welding? VERY FEW aluminum alloys used in aviation can be welded, and are usually limited to ducting, lines and interior "decorative" components. 6061 (6000 series) are very weldable, however, the 2024 and 7075 (2000 and 7000 series) are not weldable at all..they will weld, but the strength of the alloy is compromised.
Yes, no surprise there. 6061 was my intention, which already contains a lot of chromium, so a little bit more from a surface layer wouldn't matter much I would guess. I was more worried about things like iron, which Alodine contains if I understand the "proprietary" chemistry correctly.

And no, this wouldn't be for any structurally critical welds. I'm looking at some welded aluminum fuel tanks that I've been flying for many years. The welds are truly a work of art, so I was curious what process was used and whether I could ever get that good. In retrospect the only leaking issues with these tanks were from threaded penetrations--inadequate sealants. Let's say I wanted to provision for an in-cabin auxiliary fuel tank for long ferries and such adventures: welding one in the right shape with penetrations on top seems like the safest option.

Yes, I'm aware of the toxic fumes, have fresh air feed to face mask.
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  #5  
Old 11-30-2020, 10:19 AM
terrye terrye is offline
 
Join Date: Feb 2010
Location: Vancouver, BC, Canada
Posts: 929
Default Welding chromated aluminum

Welded aluminum fuel tanks are usually 5052-O or 5052-H32, both are weldable.
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  #6  
Old 11-30-2020, 06:28 PM
Mark Dickens's Avatar
Mark Dickens Mark Dickens is offline
 
Join Date: Apr 2012
Location: Collierville, TN (KFYE)
Posts: 1,446
Default

Quote:
Originally Posted by Aluminum View Post
Thanks, that was my gut feel but good to hear confirmation.



Yes, no surprise there. 6061 was my intention, which already contains a lot of chromium, so a little bit more from a surface layer wouldn't matter much I would guess. I was more worried about things like iron, which Alodine contains if I understand the "proprietary" chemistry correctly.

And no, this wouldn't be for any structurally critical welds. I'm looking at some welded aluminum fuel tanks that I've been flying for many years. The welds are truly a work of art, so I was curious what process was used and whether I could ever get that good. In retrospect the only leaking issues with these tanks were from threaded penetrations--inadequate sealants. Let's say I wanted to provision for an in-cabin auxiliary fuel tank for long ferries and such adventures: welding one in the right shape with penetrations on top seems like the safest option.

Yes, I'm aware of the toxic fumes, have fresh air feed to face mask.
If the welds are pretty (stacked dimes), you're looking at AC TIG welding and getting good at that takes a lot of time, experience and money (if you're buying your own equipment). Check out https://www.youtube.com/user/aaronmlarsen for what I think you're talking about!
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