Question about TIG welding aluminum

I am taking a community college class in welding. I already have some experience with, and own gas, stick, and MIG equipment. I am
trying to learn to do TIG and to weld aluminum. This is taught at the local high school, and I am the only person to try using their old Miller Syncrowave 180 SD. The class gave a quick demo of gas, stick, and MIG. I'm pretty much on my own trying to practice with the TIG unit and just a couple practice sessions so far trying it for both steel and aluminum. I did buy my own tungsten for this (both thoriated and plain).
In some practice the other night I was using a couple pieces of aluminum "C" channel from the scrap bin - no idea just what the metal was. I did clean them with a stainless brush. I found that I could run a reasonably good puddle for a while and then when I would feed the rod it would ball up and act as if it was dirty. Made a real mess. I don't think I contaminated the tungsten, but I suppose it is possible. I did replace the tungsten but didn't find that this immediately solved the problem. I did then get another reasonable puddle going but then once again encountered this problem.
Can anyone offer suggestions as to what is going on? I did take a couple photos of the metal. They can be seen here: http://www.archcape.com/aluminum /
Thanks for any suggestions. I'm having great fun with this but could use some pointers. Thanks, dale at archcape dot com
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Are you sure the metal you were using was not anodized?

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Hi Terry,
I'm no welder but I've found the following from reading and some practice (and some advice) on an old DialArc HF-P. I'll assume you are welding with the machine set on AC, you're using the correct electrode and allowing it to form a ball at the end. As one other person mentioned, cleanliness is everything when welding aluminum. I had some problems with welding some stainless and an experienced TIG welder suggested using a larger lens cup, which he gave me to try. Bingo, piece of cake after that. The very best filler rod you can use is actually a slim cutting of the material you are already welding on. Also some types of aluminum seems to accept welding better than others. There, you know everything I do about TIG welding aluminum.....
al.

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snipped-for-privacy@nospam.com says...

What do mean by "reasonably good puddle?" Before you add the rod the puddle sshould have the appearance of bright, shiny mercury.
It sounds like you may have less than ideal shielding: not enough flow, a breeze deflecting the gas away from the weld, contaminated gas (it happens), a leak in your torch, etc. If there's any non-shiny or black dross floating on the puddle, that's a symptom of inadequate shielding. The fact that the puddle gets worse when you introduce the rod, assuming your material and rod are clean, also points to shielding as the problem - the rod is getting hot enough to oxidize before it's in the gas.
Try increasing the gas flow. I usually run 10-15 CFH for steel, SS, etc., and 30 CFH for aluminum.
If you still have trouble and the stock you're working with is unmarked, you might want to get hold of some aluminum and rod of known composition and weldability. Welding alum, and troubleshooting problems welding alum, is difficult enough without adding in additional variables. 6061 is common and easily weldable with 4043 or 5356 rod. Not too thick or thin, either; something around 1/8" would be best. If that C channel has radiused corners it's probably 6061, square corners is more often 6063, which is also OK.
Ned Simmons
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Thanks for the information Ned. I think that poor shield gas coverage is the best explanation right now. And that is something I can also impact by torch position, something probably entering into the picture.
What I meant by "reasonably good puddle" was that at times I would feed rod into the area of aluminum in the arc (trying for that point between "melted enough" and "big hole" and get a nice puddle of rod. And then at times when the rod would enter the arc I would get the black dross forming - and it won't stick to anything and really messes up the weld.
Not having anyone to ask I didn't really know what to suspect as the problem but I think you have likely hit it with the idea of poor shield gas coverage. I will also go with some known stock for my practice rather than pulling unknown stuff from the scrap bin to keep the variables down.
Thanks for your help, very much appreciated.
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Dale Mosby wrote:

OK, that black stuff definitely indicates contamination, mostly burnt Tungsten, I think. You mention Thoriated Tungstens, you want to use Lanthanated tungsten for Aluminum. It makes a big difference. Some people say you should brush the filler wire, too! it gets an oxide coat as well.
As for shield gas, you need to investigate gas lenses. They work VASTLY better than the standard collet and cup system. Mostly, they are a bit bigger, and have fine screens in them that make the Argon flow laminar, instead of the turbulence of the standard collet.
I got my gas lenses from aglevtech on eBay, he sells brand new stuff pretty cheap, and is very good to deal with. (It can get bid up if you are in a bidding war with somebody, but he cheerfully delivers the item even if it sells at the starting bid price.) You aren't paying for your Argon at the high school, but when you have to buy your own, you will really like the gas lenses, as you can run about half the Argon flow rate and still get good shielding.
Jon
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wrote:

Try not sticking the rod directly into the arc. Make a puddle, move back on the bead a bit with the arc and melt off some filler in the puddle, advance the puddle, repeat, and so on. You want to keep the rod near the arc (and in the shielding gas) so it's near melting point, but not directly in the arc.
Like another poster, I also recommend lanthanated tungstens for aluminum. You can buy direct from http://www.aglevtech.com/LANTHANATED_Tungsten.html , don't need to go thru Ebay.
These work much better on AC than either pure tungsten or 2% thoriated. They hold their shape better. I grind them sharp. They'll quicky form a little ball at a given heat, and then stay that way for quite a while.
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Followup: I received questions asking if the aluminum was anodized, if I ran out of shield gas, and if it was windy blowing the shield gas.
The metal did not appear to be anodized. I did get it from a scrap bin and wire brushed it with a stainless brush. What is the result of trying to weld anodized aluminum? Would you see sections of metal that took weld OK and then sections that would not?
I was not out of shield gas. I was welding on a table near a large roll up door and there was a bit of a draft. After the first problem hit I wondered if this was a problem so set up a couple of the light plastic screens used to protect others from the flash. After that I had some success but again some period of failure.
The behavior was really as if the puddle became "dirty" when I started trying to feed my rod. Is this a sign of contaminated tungsten? I didn't think I let it hit the rod or base metal but it is possible I suppose. This is tungsten that I have ground again since my first attempts. It would have been contaminated on my earlier tries.
Thanks, Dale. dale at archcape dot com
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It sounds like you're already a better welder than I am, but here's a few things to check on.
First, I assume you knew that the tungsten used for aluminum is different than that used for steel? Also, I've found that you don't want a sharp point on your tungsten for aluminum.
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I'm no expert, far from it. But an old welder told me that with aluminum, you want to clean it, and then clean it some more, and then when you think you have it clean, clean it some more. Can't ever be to clean when welding aluminum. That said, I have never done any welding on aluminum, only because I have never had call to do so.
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1: maybe your rod is dirty. are you resting it on a dirty surface between welds?
2: maybe you are pulling the hot end of the rod out of the shielding gas after you dab a bit into the puddle. leave the rod close to the puddle (even when you're not applying it to the puddle ).
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Dale Mosby wrote:

Yeah, get the gas lens.
Some of your problem my be oxidation. A gas lens and moving faster with higher heat will help that.
All this talk about cleanliness.. Bah. I was TIG welding some aluminum today. The base material had been "cleaned" with WD-40 and wiped off. The tabs I was welding to it were "cleaned" on an oily old wire wheel. The electrode was dirty and too fat. The filler rod was dirty and even had the remnants of an old sticker on it. I had the Argon around 15. So, everything about the setup was pretty bad. Yet the welding went quick and smooth and the welds look pretty darn good. And have already been subjected to enough abuse to bend the tabs over (are plenty strong). I started having a lot of luck welding when I switched over to the gas lens. The trade off is they're a little bulkier.
Looking at your bead, you may need a bit more power. Crank it up some. I pulse quite a bit with aluminum. Get on it hard, you'll be able to see the penetration, back off some and run your rod in, move over, repeat. Lower heat and longer duration invites contamination from the air, shallow penetration, fat welds and porosity.
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wrote:

About getting the weld hot enough: When the puddle is too cold the rod won't melt when pushed into the puddle. Also when the puddle is too cold, and the electrode is too close to the puddle, when the filler rod does melt the blob of aluminum will tend to be drawn to the tungsten. Then you get all that black stuff. And definitely use either lanthanated or pure tungsten. I have found that using lanthanated for everything works great. ERS
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wrote:

Indeed. I had to learn this the hard way.
Gunner, who cranks up the heat and moves faster
"A prudent man foresees the difficulties ahead and prepares for them; the simpleton goes blindly on and suffers the consequences." - Proverbs 22:3
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