Tig Butt weld on 5456/5086

Date 03-19-2001 23:40

I have a question concerning a tig butt weld certification using 5456/5086 as the base metal and 5356 as the filler rod.
I am a canadian covered under CWB but I assume the butt weld certification is the same or similar. The test is essentially two 6" x 12" plates on a 2" backer strip tacked 1/4" apart. one plate is edge prepped square for a fillet and the other is a 30 deg bevel, all pieces are of 1/4" material. The test is in the flat position. The gas sheild is argon.
The problem that is occuring is that the samples fracture on the root bend, but the fracture line is usually 3/8 of an inch apart indicating that the weld is penetrating the base metal. The macro etch confirms this and shows good penetration. I have tried this test using a range of amperages and a variety of wave balances. I have also asked other qualified Tig welders to try this test with the same results. Finally, for background I hold certication for all position mig and tig and my level 3 -6g pipe in position(I believe this is a U-69 in AWS???)
I'm stumped so if anyone has any experiences like this I would love to hear about it.

By Dirk

Date 03-25-2001 01:47

You will find that at times it is best to use longitudinal bends to qualify procedures for some materials (Al alloys and duplex stainless come to mind) as ASME and other code will permit.

Your skills are no doubt at the required level but do not fight a fight you do not have to.

Just a thought

Dirk

By Ti double-G er (*)

Date 03-26-2001 23:44

Dirk
I agree that sometimes there is no point in unneccesary battles, but in this instance CWB is being very specific. They want two roots and two faces bent perpendicular to the weld. I'm proving again on thursday 29/march, so if anyone has a magical combination of technique/variables please help me out

thanks..........Sean

P.S. I've been successful with a vertical and horizontal, it is the flat that is causing grief.

By DGXL

Date 03-27-2001 01:45

Ti,
The referencing document will dictate what type(s) of mechanical or nondestructive testing your weld requires. Choosing which axis to bend your specimens is not usually an option. My experience during performance qualifications is that most welders try to run as hot as possible to reduce any chance of busting out (failing).

Aluminum is very sensitive to heat input when it has been aged, treated, etc. (even though these alloys are non-heat treatable-oops.) Many welders I have tested bust out on the tensiles and/or bends due to the relatively high heat input with any given process. Not because of IJP/IF or inclusions.

I did not have this problem when I worked as a welder in the aerospace industry because I have a tendency to weld "cold". I have been told this by several welding or metallurgical engineers over the years.

If you can get a hold of someone at Alcotec, they are very (VERY) knowledgeable on the subject of aluminum welding and give excellent seminars on the subject as well. Give them a call and let me know how you do on Thursday.

Alcotec (800) 228-0750 (US and Canada)
Good Luck!

By Ti double-G er (*)

Date 03-27-2001 02:45

DGXL
Thanks, I will give Alcotec a call. As a matter of fact we use their product almost exclusively. Tomorrow I will try a few coupons in the cold range and see what happens. As I said in the first post it seems to be the HAZ that is cracking but I was also under the impression that 5000's had excellent HAZ properties.

....Sean

By Dirk

Date 03-28-2001 03:04

Are you strong backing the weldment??

It may be you are "strain aging " this area if this plate positon ends up with more overall distortion.

When welding out of position "we" tend to run fewer and smaller weld beads with little weave motion.

Dirk

PS

Good luck !!

By Ti double-G er (*)

Date 03-28-2001 03:44

Dirk

I'm not sure exactly what you mean. We are tacking a two inch backer strip to the plates but other than that it is free to move. And depending on how I decide to cap out the weld the distortion can be as litlle as a 1/4 across the plates or more than 1" The latter is when I weave in the cap pass to save some time. Typically some or all of the backer tacks will break during the weld.
I understand your thought on strain aging and how that could affect the area immediately adjacent to the weld, but I'm not quite sure what I would do to prevent it. I did run some coupons on the coldish side today (190A and below) but I won't know how they bent until tomorrow.

Thanks for the luck
Sean

By DGXL

Date 03-28-2001 05:00

"TIGGER"
After reading your last post, I have a little more insight.
1. Do not weave any of your passes.
2. You don't need a strongback (stiffener) for your test.
3. See note 1.
I am now very curious, did you contact Alcotec? After doing some research on your weldment, I might choose another filler material. But I will leave that to the experts. Let us know how you did on your test, and good luck again.
p.s. (just figured out your handle-I'm slow about these things)

By Ti double-G er (*)

Date 03-29-2001 05:07

Tonight there was a new development that sheds some insight into the problem of the root bend cracking.
I welded a coupon then cross sectioned it into samples for macro etching. I put half of the samples into the caustic then we all went for coffee. When we returned the samples had sat in the caustic for probably four times longer than usual (30 min. ish) What we saw were cracks radiating from both sides of the welds. They start from the bottom edge of the HAZ, where the plate meets the backer, and run diagonally up into the center body of the weld. All were min length of 1/16" and one was close to an 1/8th. I will mention once again the macro etch profiles were perfect.
My feelings at this time are that we will have to change one of the key variables, but I am lost as to which one could have caused this kind of cracking. Maybe changing filler to 5556?
We also confirmed cracking by dye penetrating the rest of the samples
Yes, I have put a call into Alcotec and I am waiting on a call back.
Any thoughts????

Sean

By DGXL

Date 03-29-2001 05:49

Hey TIGGER,
Send a fax number to my e-mail addy and I'll show you why I think you might try another filler material. But, you have to check out the posts regarding "Code Books" and SCWI, CWI, ACWI & CWE (just kiddin ;-).

By DGXL

Date 04-18-2001 23:26

OK TIGGER,
The suspense is killing me, what happened with your testing? Did you try other filler materials, did the stringer beads help? Does lower heat input result in optimum test mechanical results? Please let us know, this is how we all learn. :-)
DG