Welding Thin Wall Aluminum
Welding Thin Wall Aluminum
(OP)
We are TIG welding 6061T6 6" OD x 1/8" wall tube to a 1" thick fabricated slip-on type flange using double fillet welds.
Over the years we have performed a good deal of welding using heavier wall aluminum construction so we are not completely inexperienced.
We have tried pre-heat from 200 F (as per our WPS) to as high as 800 F.
At hydotest we have experienced regular failures in the heat affected zone with the tube cracking in the circumerential direction. The cracks are about 1 - 2" long.
None of our people have seen anything like this and we don't know what is causing the failure.
Has anyone experienced a similar problem? If so how did you deal with it? Any recommendations?
Thank you
Over the years we have performed a good deal of welding using heavier wall aluminum construction so we are not completely inexperienced.
We have tried pre-heat from 200 F (as per our WPS) to as high as 800 F.
At hydotest we have experienced regular failures in the heat affected zone with the tube cracking in the circumerential direction. The cracks are about 1 - 2" long.
None of our people have seen anything like this and we don't know what is causing the failure.
Has anyone experienced a similar problem? If so how did you deal with it? Any recommendations?
Thank you





RE: Welding Thin Wall Aluminum
Second question - what is your welding sequence for the double fillet welds. Do you deposit the inner weld and then deposit the outer fillet weld? Do you tack weld the flange into position?
RE: Welding Thin Wall Aluminum
RE: Welding Thin Wall Aluminum
Keep the preheat and cool slowly,try helium,also 5356 for filler.
Make sure the coatings and oxides are cleaned from the OD of the pipe. Do not use a carbon steel wire brush or a grinder used for carbon steel.
RE: Welding Thin Wall Aluminum
The cracks are in the heat affected zone in the parent metal.
The flange is tack welded and the inner weld is done first, followed by the outer weld.
Welding is done in the flat and is continuous through the full circumerence without stopping.
We can not see a pattern to the location of the cracks other than that they are in the tube wall, the heat affected zone, and run circumferentially. It appears that we may be tearing the material but have not been able to prevent it.
Thank you.
RE: Welding Thin Wall Aluminum
It sounds like you are tearing the thinner gage material. Try dropping the preheat entirely. It may be that preheat is providing added thermal stresses resulting in ductile tearing after the joint cools. This thin gage of aluminum does not require preheat despite welding to the thicker aluminum flange.
RE: Welding Thin Wall Aluminum
So-no preheat may leave a larger gap and help in some areas but with a continuous weld there could be problems at the end. Try decreasing the gap.
RE: Welding Thin Wall Aluminum
If this happens persistently, we move to GTAW.
I hope this helps...
RE: Welding Thin Wall Aluminum
Any other comments?
RE: Welding Thin Wall Aluminum
Double check the composition and heat treat condition of your tube material. If everything looks acceptable, it sounds like the weld joint is still under considerable restraint during welding. Are you fixturing the assembly to make the fillet welds? What is your welding position? As deanc pointed out, make sure your joint gap or clearance between the OD of the tube and the ID of the flange is minimal.
You could try to alternate the weld sequence by depositing half of the inner fillet weld on the slip on flange, and move on to the outer fillet weld. Come back and complete the inner fillet and finish the outer fillet weld.