Hi Jim,
Anodizing is a build up of aluminum oxides a thousand times thicker than the natural oxides that occur on the surfaces of the metal. In order to weld aluminum that has already been anodized, you have to prepare the weld areas by removing the anodized finish in the weld area. If not removed, the presence of the anodic coating will more than likely cause porosity, lack of fusion, and oxide inclusions in the weld metal.
Since you mention the weld looking dark gray, I'll toss this in. In Volume 4, Seventh Edition of The Welding Handbook, in Table 8.9, for a 6061 base metal, the recommended filler metal for color match after anodizing is 5654.
I also have a probably outdated (1986) ANSI/AWS D10.7, which is the Recommended Practices for Gas Shielded Arc Welding of Aluminum and Aluminum Alloy Pipe. In Table 1, for a 6061 base metal, the recommended filler is ER5654, but the footnote indicates that ER5183, ER5356, and ER5556 may be used, and in some cases they provide improved color match after an anodizing treatment.
thanks swnorris I will try to prep the pipe close to the width of my weld so i will not remove the bright finish to far thanks Jim
In addition to what norris has said (quite correctly, by the way), I'd mention that, apart from thickness, another reason for which you can't weld directly on anodized aluminum is the melting point. I don't have the exact figures on hand at this moment, but in any engineering manual you can see that the melting point of aluminum oxide is several times higher than that of pure aluminum.
This means that when metallic aluminum is already liquid, the aluminum oxide is still solid, and for this reason they don't mix up with each other.
Giovanni S. Crisi
Sao Paulo - Brazil
Hi Jim,.
What are you going to do about anodizing the welded area?
Probably try to clear coat the welds when done Guys thanks for the info. this site is a wealth of info. !!!!!!!!!!!!!!!!!! Jim
Hi Jim,
Possibly there is a metallic pigmented paint that will closely match your color that can be applied after welding. I've seen some paints in a spray can that simulated anodizing (these were for mild steel, they had colors like red and blue).
just a thought,
John Wright
Thanks John Ill check it out . Jim
I have a few years experience welding anodized aluminum in the marine industry and can offer some advice.First off you do not need to remove the anodized finish, just weld right over it using a pulse technique. As you get the puddle started you can pulse weld adding rod as you need then moving forward, pulse and add rod. What the pulse does is help push the anodized layer out of the puddle. It will not remove all of the anodize but helps alot and will give a nice uniform bead that is more natural aluminum in color instead off the dull gray you may be getting.You still need to pay attention to you penetration and make sure it is adequate. Mixing helium with argon helps but is not needed, I have done it with just argon and still have satifactory welds. The helium also helps when welding sch40 anodized pipe, which is the standard in this industry. You can pulse with a foot pedal but adiamond back torch with a on/off button helps
control the weld better in my opinion. When done welding I use a foam brush with silver aluminun paint to paint the welds, now that they are exposed to the salt elements they will need to be coated to stop any corrosion.
This technique is frowned on by alot of welders that have not welded anodized aluminum but talk to anyone building t-tops or towers and they will tell you this is how it is done. It also takes quite a bit of practice to master, since it is different than mil finish aluminum.
I use 5356 filler rod and have also used 4043. If the material is to be anodized after welding make sure you use 4043 since the 5356 filler will turn black after being anodized.
Sorry for thr rant, just offering some insight on how we do it in Florida.
Mike
Use aluminum paint over the welds when you are done.Just paint the welds with a brush.They match great!
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