7/8" Aluminum Repair

Date 04-17-2010 06:23

We have been trying to find a defect free way to repair aluminum welds on 7/8" thick material and had no luck so far. We have some 7/8" 2219 material that is welded together using a GTAW DCEN program. The joint is j-grooved with a .125" root thickness. This joint is filled up with several passes with an automatic machine and 100% helium. With the automatic DCEN welds, we seem to have few problems with porosity because there is good control of welding speed, wire feed, etc. However, when we do have to make repairs we basically do the following - dig into the weld using a carbide cutting wheel slowly until the areas of porosity are removed. The removal is verified by x-ray. The welders groove this area out a bit so it's easier to fill. They wire brush the area, wipe with IPA and proceed to weld it with DCEN and 100% helium. This is done in the 2G position. However, more often than not these repair welds are full of porosity.

Since we're not getting any cleaning action from the DC, we figured it might be a good idea to switch to AC. We messed around all day today with AC on some sample material. We tried various gas mixes - 100% Ar, 75Ar/25He, 60Ar/40He, 75He/25Ar, various settings on our dynasty 700. The best looking weld we could make was using the parameters below

75Ar/25He mix
35CFH
Advanced SquareWave
260A EN
260A EP
75% Balance
185Hz
1/8" Ce tungsten

The bead looked fairly clean on the outside, but as we started to remove a little of the bead to check the inside, we saw clusters of pores. Obviously, welder skill is a big part of this too considering you have to go slow enough to let contamination boil out if there is any. Can anyone give some recommended settings, tips on torch angle, wire feed, or anything that might help us out? We don't really care which polarity we use, DC or AC, but we're looking for the best chance to produce clean welds.

Thanks

By Lawrence (*****)

Date 04-17-2010 13:33

The 75% EN balence control setting you have on your Dynasty 700 is nearly 10% more EN than a traditional Tig machine can produce at absolute max penetration which is 68% EN.   I don't think your getting enough EP cleaning action.

My suggestion would be to explore something closer to about 60-65% EN and if you start to loose the end of your tungsten to an overheat condition than back down the EP current...   The Etch comes more with dwell time than with current levels in my experience.

A sequence I've found sucsessfull for backing down the EP current goes as follows: Assuming the 260A EN/EP you are currently putting to the weld...   Back down 50 A on the EP to about 210 and increase EN about 25A to about 285...   This combination should be provide the heat to get your aluminum to puddle up and also provide enough cleaning action (@ 60-65% EN) to get rid of your porosity... 210A EP should give plenty of etch.

Your 75/25 Ar/He sounds good... I've run as high as 50-50 when welding AC on massive castings with good results.

By Zeek

Date 04-17-2010 22:41

Thanks for the info.

What would be your recommendation on the tungsten type and diameter. We are using a 1/8" Ceriated electrode with a tip geometry - 30° included angle, and about a 0.040" flat tip.

We were hoping that we wouldn't have to use a pure or zirconiated balled up tungsten due to the wide bead it produces. The weld repair we are making is in a groove that's about 0.250" deep and maybe a 1/2" wide.

We actually did try the 60% EN at one point but the tungsten started spitting pretty badly, so that's why we went up on the balance. But, I like your idea of backing down the EP. We'll have to try that.

Do you have any welding technique suggestions such as how flow to go, how to properly feed the wire (dabbing, or just a continuous feed), torch angle, cup size, etc?

Thanks again.

By Lawrence (*****)

Date 04-17-2010 22:59

Cerium is a good choice... Miller Electric recommends it in fact.

I also like Lanthanum 1.5

Diameter.. As small as you can without it melting :) The less long and slim the end prep the better.. A radical tip with a good flat blumt.. It will round off as you weld but so what?

Cup size.. Since Aluminum freezes so fast and the heat is conducted away equally fast I don't think a cup size much bigger than the puddle you make is required... Bigger is fine too. Sometimes a pretty small cup is necessary for access to tricky spots.. As long is you don't over gas you are fine with that too. Smaller cup.. less gas.

Always dip filler with Alum when welding with AC... Lay wire technique will not allow the back of the wire to be etched and this will cause X-rays to fail for linear indications and apparent lack of fusion.

Zeek, You come up with the most interesting projects... Must be a fun job! Keep us posted for sure