Mig-ing an Open Root Aluminum Repair

by Mike Gil
(Bakersfield, Ca)

Jody Collier

Hello, thanks for the welcome. Great site and what an awesome resource! What is the most efficient way to submit questions and receive answers? What?s the general turn around on questions?
I guess I start here, I have a repair job I?m in the middle of on an aluminum frame on a cement tanker trailer, the frame is 10? C-Channel. I have a crack about 8? long going from southwest to northeast on the 3/16? thick web of the channel, basically diagonal. I air carbon arc gouged, grinded, die grinded, SS wire wheeled it all pretty. After the prepping I am left with a V Groove but in about 2? of the worst part of the crack I have an open root weld to make with about a ΒΌ? root opening. I am only set up with a spool gun. What kind of temporary backing could I use to make the weld? It is not XRAY critical but I still want it to be Right. This member cannot be removed without exceeding a justified cost for the repair. Also is there any liquid or chemical cleaning stuff out there you have ever heard of for cleaning aluminum to prep for welding. Often I experience dirty material more than just oxidization and have no access to the back of the member to grind or what have you. The aluminum is 6061 I have had good success using 3/64 4043 filler wire for various repairs minus the open root situation, the spool gun is hooked up to my Miller (baby) Big 40, my spool gun is the Miller Spoolmate 3545. Your thoughts on stainless or copper backing would be greatly appreciated, once I learn a remedy I can keep a piece on my truck. Also most work is performed out in the field so I like to be prepared.
Again awesome Q&A section on this site. Thank you in advance for your time, all suggestions are welcome.

Mike Gil



apparently my turn around time for answering questions sucks because this one slipped thru the cracks for like 3 weeks.

It probably way late for you , but i will go ahead and weigh in just in case it helps someone else. I think a thick piece of stainless would be your best backing material but it would need to be thick enough where there was no risk of it getting hot enough to melt and mix with you aluminum weld. copper would probably work too but would definitely suck heat out of areas where you might need it.

4043 is a good choice for filler metal.

there are aluminum cleaners out there ...a househould cleaner called purple power will also etch the crap out of it but has to be rinsed off thoroughly ..

Also , you might consider a doubler over the crack after the crack is welded and dressed.

sorry for the late response,
raising teenagers is getting the best of me.


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Feb 14, 2011
SS Backing:)
by: Mike Gil

No worries on time delay, I am glad to get a response. I thought I did not submit it right. Mine are not teenagers yet but I have 4 under the age of 5 years; my friend... I too know busy!
I ended up using a 3/8 inch by 2 inch piece of 304 SS as a temporary backing. All in all, it worked well, I am now curious on how 3/4 inch or a little thicker then 3/8 inch would have worked. After I completed the welding of the root and a couple fillers on the outside I was able to remove the SS backing. I did have to tap it off with a small hammer, it slightly fused to the SS. I gave a little back grinding to ensure sound metal on the inside, it all looked good. Welded out the inside with multiple passes. Both inside and outside ended up being good size V Groove welds I gave plenty of rienforcement and a nice contour finish. I was pleased.
Still hoping to find some type of liquid or chemical cleaner that is most practical and convenient for in the field applications. The Purple stuff you mentioned, just needs rinsing with water? Any other thoughts? Thank you
Mike Gil

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