High porosity in A356 after welding 1

[COKA]

Need advice from an aluminum welding specialist.
We have a part that is 5.5" by 12" and 5/32" thick, and we have to build up a lug at three opposite locations that is about 1/2" in diameter. After performing at least a dozen tests, we still have high porosity in the interface and in the weld areas. We have to follow the Vought spec (CVA 17-12F), which states that the minimum porosity spacing should be greater then 2 times the largest adjacent defect (between voids). During welding the following was done:
- Pre-heating the part before welding to 350°F
- Cleaning the welding rods and the part before welding
- Covering the part with ceramic fiber wool to keep the heat
- Welding in an argon filled chamber
- Standard Practice: Tig Weld, 100% Ar shield gas, AC current, more cleaning action.

 

[CoryPad]

Do you have to use fusion welding to "build up" the lug? Can you take a pre-made lug and use friction welding to attach it? This should avoid porosity problems.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[unclesyd]

What type Aluminum are you working with?

 

[COKA]

CoryPad,
Unfortunately we don't do friction welding in house. The pre-made lug is not a bad idea, but we still have to weld it to the rest of the part.
Thank you,

 

[COKA]

unclesid,

We are working with A356-T6 casting, re-heat treated to T6 condition after welding. I could have sworn I wrote it down!
Thank you,

 

[CoryPad]

COKA,

Perhaps your company can "learn" to do friction welding with this project. Presumably you have spare material (scrapped parts due to excessive porosity). Do you have a milling machine? Can you fixture a piece of the casting and then use the rotating machine head to create the friction? With a simple setup, you could probably determine a procedure that will work. The benefit is that you have no porosity, and you have a full cross-sectional area weld.

If the above isn't possible, perhaps you can use a pre-made lug and the GTAW process to create a line weld around the lug perimeter. This is a relatively simple weld geometry, with a lot less metal requiring solidification, so it may reduce the porosity to manageable levels.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[unclesyd]

You did, it's in the title, my problem was I copied the post and not the title lines.

Is your power supplied a high frequency machine with a stabilizing current, meant to weld AL?
Have you tried different welders?
As you are in box keep the torch shielding gas flow as low as possible?
Have you checked the parts for porosity?
Is the lug also 356?

With all our welding of Aluminum shielding was the biggest problem once we got the high frequency machines.

Keep the arc as short(very important) as possible.

Sounds like you have got the cleaning covered.

I have 2 fillers list by ALCOA 716 (4143) and 4043. We used the 4043 to repair Al die cast parts by the hundreds. We did have a little porosity. The 716 did work but was not readily available. We had some larger injection molded 356 parts that were almost impossible to weld on.