Aluminum Welding Issue

[scottguehne]

I may be putting this in the wrong area, but here goes anyway.

I am building a solar car chassis at school for my senior design project. We are using aluminum for the frame members. It is 1/8" wall, 1" diam. The joints weld well, or so they appear. We did some destructive testing and found that the welds are failing pretty easily.

http://i1226.photobucket.com/albums/ee413/SIUESolarDesign/DSC_4790.jpg

http://i1226.photobucket.com/albums/ee413/SIUESolarDesign/DSC_4788.jpg

We did a destructive test of 4130. This piece behaved as predicted. Weld held, material failed in the HAZ.

http://i1226.photobucket.com/albums/ee413/SIUESolarDesign/DSC_4748.jpg

If anybody has any input on the aluminum issue, I'd love to hear it. It looks like the base metals are melting, they just aren't joining. The base material also appears to not be mixing well with the filler. Material is supposedly 6061, filler rod is 4043. Welder is a Lincoln Precision Tig 275. Using straight argon. The aluminum weld shown was done at 100 amps, slow travel speed. Joint preparation consisted of cleaning the surfaces with a 3m clean and strip wheel and beveling the joint edges around 45 degrees. The bevel was taken all the way down to the i.d. of the tubes.

[ccracin]

Post up some information about your weld procedure. IE. MIG / TIG, Welder, Gas, Welder Settings

This will help people offer some help.

[GregWeld]

Typically, after welding, the properties near the weld are those of 6061-0, a loss of strength of around 80%. The material can be re-heat-treated to restore -T4 or -T6 temper for the whole piece. After welding the material can naturally age and restore some of its strength as well.

Make sure you're cleaning the weld area with a stainless steel wire brush -- you can get small toothbrush sized versions - and be sure to clean all the areas including the ends.

4043 fill rod is fine. You failed to mention what tungsten you're using... and it looks to me as though you may be getting some tungsten in your weld. Use Zirconiated tungsten not pure or thoriated.

Heat is typically 1 amp per .001 thickness... so 1/8" would be 125 amps. I would not bevel this joint. It's not needed and you're replacing the 6061 strength with the weaker 4043 fill rod by beveling like this.

[lhkustoms]

I would second what Greg said and add that I would preheat the aluminum with a torch before welding it. Heat it up to where it just begins to turn white.

[AutoRad]

The use of 5356 welding rod would help "slightly". Butt welding a structural tubing is really not a good idea. Like Greg said, you lose too much strength from the heating of the area. If you want to do that you should use an internal or external sleeve to provide strength to the sliced area.

[JRouche]

Im gonna assume you are using TIG welding, looks like it. And with that, looks like a cold joint.

Looking at the separation line I can see un-fused base metal.

It wasnt welded. Looks like the base metal was heated up just enough to melt the filler onto the top of the base, no real welding going on in the joint I see.

And the tube looks dirty. Not dirty like there is crap hanging off of it. But it doesnt look like it was prepped.

For a tube I like to use scotch bright pads that are ONLY used for aluminum welding. Scuff the part up completely so you see a uniform clean (raw) aluminum surface. And some tubes will come from the foundry pretty dirty and get worse with the handling from the supplier.

You really have to clean aluminum up to a raw looking surface before you can weld it.

And next, you have to be welding. With aluminum, put the heat to it. I dont pre-heat, but some do, I dont think 1/8" wall needs pre-heat.. I just start off slow and use ALOT of current till I see the part is getting heat soaked. Then ramp it down some once the entire weldment is up to heat. And it will take some time. Aluminum will soak up some heat. But once its ALL heat soaked it will weld fast.

I think you just need a lil more time to play with it. My suggestion? Keep welding the tube. Cut off the welded parts, clean the tube and go at it again. But really put some heat to it. Then once that joint is done break it and start over. And do it again and again. It will click for you. You will find the right heat to make a weld.

Im not a teacher, but I have had to teach myself how to weld. And for me the best method was to use scrap material that I didnt care about and take it to the extreme. Yes, weld it really hot so you are blowing the metal out. Find out where the limit is. Once you are comfortable with where the metal will drop out then you know where to dial it back some.

And after you become really comfortable, and realize the base metal wont drop out with a lot of heat and more control you will be welding aluminum like its was child's play. JR

[GregWeld]

^^^^^^ excellent advice!


I used to go to the Metal Super Shop -- and buy scraps -- I'd get a nice pile and then make 'em a deal. I'd get squares and rounds and thick and thin wall - etc Steel - SS - Aluminum.

Then I'd go home and weld on 'em. See what they did - learn how to clamp - see how they warped. I'd to butt welds - corners - insides etc. Learned where the stick out of the tungsten needed to be. Welded with different sized tungstens.

I agree with JR that the weld looked cold -- and that the piece with the bead left on it was partly welded but the other piece was most likely cold.

If I was welding this joint - my heat would have been directed at the base and I'd have let the residual heat and filler climb the cut end tube. It would take very little "motion" to get the cut end puddled and taking filler. The heat needed to go into the base joint tube.

[drednot]

Aluminum is hard to weld, it gives no indication it is about to fall through or blow out from heat. Steel turns cherry red before it blows out. Aluminum takes a lot of practice to put enough heat and not blow through.

One thing I learned the hard way is that the tungsten has to be VERY clean. I sharpened a tungsten on a grinding wheel reserved for tungstens, and after some of my welds werent right. All my welds I tested failed. Some jackass ground some edges of sheet metal that was galvanized on that wheel earlier and contaminated my tungsten. That is all it took to ruin my welds. I had to seriously resurface the wheel and grind a whole bunch of my tungsten off. Clean base metal, clean rods, clean tungsten and plenty of argon are the keys.