Aluminum Porosity

Date 09-10-2009 21:02

I'm having some porosity problems with an aluminum weld joint and have some questions on prevention. Here are the specifics....

Material: 6061-T6
Thickness: 0.160"
Butt joint
length - 65"
Tooling - Jetline seamer with a copper backup bar and copper fingers.
Current - 175A
Wire - 55ipm
Voltage - 11.5V
Travel - 13.75ipm
Torch Gas - 98% He, 2% Ar
Torch Flow-rate - 50cfh
Backup gas - 100% Argon
Backup gas flowrate - 5cfh
1/8" Ceriated Tungsten

We acid etch the top side of the joint, however due to the part configuration it is difficult to properly etch and clean the back side of the part. The 6061 is 65" long and rolled so we can weld in longitudinally to make a section of pipe.

We ground the backside of the weld in a 12" section and looked at the x-ray. We have one pore that is 0.060" which is unacceptable per D17.1. There are some other pores within this section but they are acceptable. Considering the production part is 65" long, we'd like to reduce our chances of porosity formation.

175amps seems pretty high for this material, but the copper hold down clamps on the Jetline seamer create a tremendous heatsink that it's difficult to penetrate with less amperage. However, we are discussing lowering our amperage and our travel speed in hopes that might help.

I'm going to attempt to etch the backside of the joint in hopes that this will reduce the chance of porosity. Is there anything I can do to the parameter adjustment that might reduce porosity formation?

Thanks

By Milton Gravitt (***)

Date 09-11-2009 18:47

Are you getting the argon and helium already mixed in a cylinder or you mixing it your self. I have got a cylinder of bad helium before. Hope this might help.

M.G.

By ANDY LARKINS (*)

Date 09-14-2009 18:52

I'm not a tig hand, but I think 50 cfh of nozzle flow sounds high to me from what I have seen on here before. Something about turbulance in the puddle or something if I remember right.

By Lawrence (*****)

Date 09-14-2009 19:35

Andy,

It takes just about twice as much Helium to cover with GTAW. so if 25 CFH is reasonable (it would take a big cup or gas lens) for Argon than 50-ish may be in the ballpark for a Helium cover... Maybe a little on the high side but there may be a custom cup involved with a larger ID.

By ssbn727 (*****)

Date 09-14-2009 21:36

Hi Zeek!

When you mention "Butt joint" could you tell us in greater detail the joint configuration?
Also what are your procedures for preparing/cleaning the Aluminum prior to welding and are you making sure that the seamer is indeed as clean as it should be???

What size filler diameter and grade/brand of filler wire are you using?
Finally, are all of the orifices in the seamer for the backing gas and are they checked periodically for any obstructions?

Respectfully,
Henry

By Zeek

Date 09-15-2009 19:46

Thanks for the replies.

the joint is a square groove butt joint. 0.160" to 0.160" thickness. We have an internal procedure that we follow for etching aluminum that includes an acid, DI water and a neutralizer. It's a pretty standard procedure that is followed regularly on all of our parts. In regards to the seamer, we wipe the copper chills down with acetone and check the backup purge holes for any foreign material. If we see anything, we vacuum it out.

The filler wire we use is E4043 1/16".

By ssbn727 (*****)

Date 09-15-2009 20:28

Hi Zeek!

So this next question and the ones after will probably sound redundant but, I've got to ask it anyway...
Did you check all of your gas shielding as well as purging gas hoses and their connections for any leaks?
What type of gas cup are you using? And are you using a trailing shield by any chance? finally, what is your cup to work distance?

Respectfully,
Henry

By Lawrence (*****)

Date 09-15-2009 20:39

Zeek

If your not under any restrictions, it would be a real help to have a pick of your head set-up on that seamer as well as the backing fixture. Just a cellie pic would do.

I have a few thoughts but don't know if my mental picture is even close to your reality..

By QAnoob Date 11-11-2009 04:19

Have you had any luck with this qualification? We pulled our hair out with this qualification until we dug deeeep into cleanliness. What sort of etching solution are you using? This is extremely important. We initially went on some bad advice using hydrochloric (muriatic) acid to start out and later found out that that actually introduces hydrogen porosity into the weld. Look at your nearby welding supply shop to get some etching solution with hydrofluoric acid in it (or something specific to x-ray quality welds).

Also, how are you sharpening your tungstens? You can introduce contaminants by using a grinding wheel that's been used on other material or contaminated tungstens. Are you using a new stainless brush? Are you wiping down the rod with acetone? Once we started obsessing about cleanliness and sources of contamination, our welder qualified no problem, best welds the x-ray lab had seen in a long time (and they test Boeing work all the time).

By bozaktwo1 (***)

Date 09-17-2009 17:11

I would say you're darned close to having a good setup if you have only one rejectable indication in 12". In addition to the excellent advice already posted, look at the cleaning process; what is the lead time from parts cleaned to parts welded; also, is any other method of cleaning employed?