Alum Plate Bend Test Fail 2

[ElronMcK]

Amateur question. I have been bending my practice weld coupons around a small pipe, then bending tighter in a vice - just to check ductility.
Photos below are pre-bend and post-bend
Background:
Uphill, 3G
One-sided complete joint pen at butt joint (no gap)
6061, 1/8" thick
3/32" 5356 filler (roughly 2" of filler per 1" of weld)
3/32" tungsten with 16 to 17 cfh Argon, gas lens
About 115 amps, 75% electrode negative on Syncrowave
Most welds had full burnthru
No pulsing, relatively steady foot pedal, moderate SS wire brush cleaning prior
Coupons cut to approx 1" wide strips x 5" long
Some welds show very high ductility, but occasionally a weld fractures right at the heat affected zone ("HAZ"), without too much tension straining. Brittle.

I keep preparing to take my 3G test for AWS D1.2, but this is humbling. I would like to determine what are possible contributors. I'm not just the observer - I did the welding - very little difference between the welds - from prep to last puddle.
Any advice is welcome - but especially guys with lots of aluminum experience.

 

[gtaw]

The alloy you have elected to weld is recognized as having rather poor properties in the "as welded" condition.

The mechanical properties, i.e., tensile and yield strength will be degraded by 40 to 50%. The ductility is about half of that of carbon steel and even that is degraded in the "as welded" condition.

The bend diameter is on the order of 16 times the base metal thickness. Compare that to 4 times the BM thickness for carbon steels. The bottom line is to use about a 2-inch bend diameter for 1/8-inch thick material. If you have a copy of D1.2, you can look up the exact diameter of the bending mandrel. By the way, when you do take the qualification test, make sure they are using a wrap-around testing machine, not a plunger and die machine. Good luck.

Welding generally overages the HAZ of the heat treatable aluminum alloys (6061). That simply means the alloying constituents that normally strengthen the alloy by clumping within the lattice, instead precipitate to the grain boundaries which weakens the base metal. That's rarely a good thing.

I almost forgot, DO NOT USE A WEAVE TECHNIQUE. Use stringers and as high a travel speed you can and still get the joint penetration you need. I typically cool the base metal between weld beads if a multiple bead technique is used. Keep the BM as cool as practical. Use a fan (no compressed air) to cool the material as quickly as possible. Clean wet rags will do the trick as well. Keep everything clean, including the stainless steel brush. Wire brush just before welding. Sheared edges should be draw filed with a vixen file to remove all the nooks and crannies that trap oxides.

Best regards - Al

 

[mfgenggear]

gtaw

it's being a while since I was involved with welding aluminum structures.
but if memory still works , the shop I worked for,
meticulous for weld prep. removing all oxide at the weld. and cleaning with acetone.
plus aluminum was pre-heated before welding. low temperature
and used mix argon and helium, don't remember the mixture.
both automatic and manual welds with TIG.
had to pass NDT.
is any of the above applicable any more?

 

[kingnero]

Yes, all the above is important. 6xxx aluminium are notoriously difficult to weld (correctly).
Cleaning is important, applying a bit of preheat on thicker sections is possible but keep a relatively low interpass temp.
He-mixes are used for thicker sections, but they add a lot of heat. They have their place, but be warned.
Pulsed welding is a necessity for MIG welding.

FYI, wire brushing (with a stainless steel bruch) doesn't remove the oxides, but merely smears them open.
Slightly inceasing frequency decreases porosity (if you're taking RX's).

 

[weldstan]

Making multiple welds as you did and bending the coupon as you did is an assurance of weld cracking during bending plus some of your welds did not achieve full penetration. You should blend grind/rotary file the weld on the coupon and the coupon edges prior to bending.

 

[ElronMcK]

Thanks for the responses.
Here's my take-aways for the next set of coupons
1. No preheat.
2. Low interpass temperature - allow cooling between passes.
3. Grind edges of coupon before bending (like D1.2 allows).
4. Grind weld flat before bending.
5. Tight stringers, no weaving (I already always do this for TIG).

** Anything else to maximize ductility with my given constraints?

But no wire brush as edge prep? That suggestion is contrary to all I've ever heard. I realize light brushing may not be effective, but I have been convinced that aggressive stainless steel wire brushing does indeed remove the very thin oxide layer. Any other comments on this?

 

[mfgenggear]

As mentioned rotary file, we also use a 3 edge scraper

https://www.amazon.com/General-Tool...ocphy=9031277&hvtargid=pla-613402341272&psc=1

 

[mfgenggear]

For 6061 the shop I worked at used preheat to prevent cracking.
The thermal shock of heating rapidly and cooling. Which is critical on aluminum.
It is a bugger to weld
A wire brush does not remove the oxide cleanly. It will contaminate the parent material. This causing issues.a fine rotary file does wonders. And don't let it sit.
As oxides will occur if sits to long.
Acetone was to remove any debris and contamination.

 

[gtaw]

Thermal shock? Does it look scared when you weld it? Does it shudder when you scare it?

Best regards - Al

 

[mfgenggear]

gtaw

I meant no offense to you, Do you have heat treating experience with thin wall aerospace parts. it is common knowledge that the the thermal treatment
how it is heat treated and how it is quenched will induce stresses in to the material, which cause it to distort, and if severe enough will crack if not done correctly.

 

[berkshire]

You will get better penetration and a cleaner looking weld if you put an argon purge on the backside of those welds.
B.E.

You are judged not by what you know, but by what you can do.

 

[mfgenggear]

here is an excellent link on aluminum welding procedures, and I forgot the low temperature heating of aluminum removes the moisture.
Quote: When designed and welded properly, the tensile strength
of a groove weld will be determined by the HAZ. While the
heat from the arc welding process will affect both groups
of alloys, the reduction in strength in the HAZ will be fairly
predictable in the non heat-treatable alloys. Since the
heat-treatable alloys respond uniquely to the heat, the
resulting HAZ strength can be less predictable. In order
to obtain consistent results, the use of qualified weld
procedures is highly recommended.

quote: However, the strength of the HAZ can also be negatively
affected by the amount of time it spends at the elevated
temperatures encountered during arc welding. This is the
“time at temperature” relationship, which drives the resultant
strength of the weldment. The longer the weldment is at
elevated temperatures, the weaker the HAZ is typically
expected to be. This ”overheating” phenomenon can
actually result in a groove weld tensile strength below
the minimum required

https://www.esabna.com/shared/documents/litdownloads/alc-10029b_alcotec_technical_guide.pdf

 

[gtaw]

No offence intended. I just chuckle when people toss terms around and welders get the wrong idea of what happens during the welding process.

Best regards - Al

 

[kingnero]

Especially when they are talking about the molecules (in steel/stainless steel/any metal)...

 

[mfgenggear]

Under stand, my memory is going to pot, so sometime I don't use the correct nomenclature. lol part of being a retired senior.
the eng-tips keeps me on my toes so to say. so if I do incorrectly state a comment. I don't mind being corrected and take it as constructive.

 

[gtaw]

So, it is good to see I'm not the only member of the "Over the Hill Gang".

Best regards - Al

 

[ElronMcK]

Following up.
My welds are similar, but focused on code-level coupon preparation, and better wrap-bending (wheels with bearings; still a bit imperfect).
Also, minimized "time at temperature" per Armao, so just a single CJP per test mockup.
No cracks at face bend or backside bend for 2" diameter roller.
Aluminum is moody - really makes me appreciate mild steel.

 

[david339933]

Code compliance would require better bending.
6061 + 5356 = 6T for the Radius of the Mandrel, (1.5" for Diameter of 1/8" coupon thickness)

 

[ATSE]

David -
I interpret D1.2 Figure 3.13 that for 1/8" thick plate, A = diameter of inside bend roller = 2.0625" for M23 (or F23).
Are you referring to a bend test for M22 materials?

 

[ATSE]

Or are you referring to another code? ElronMcK mentioned D1.2.