in times of desperation to get a welded aluminum structure to pass, what is the better choice? 4

[glulambeam]

It's cards on the table time. An aggressive design schedule on a welded aluminum 6061-T6 structure has forced you into a corner [edit: in terms of getting welds to meet strength requirements]. Do you...

(A) specify 5356 filler?
(B) call out CJP welds on more than just a few places?
(C) ???

 

[racookpe1978]

What are the qual's and experience of your current welders?
What machinery do they have? (What kind of arc start, wire feed, weld cleanliness)?
How are you grinding your tungsten?
How are you starting your puddle?

 

[metengr]

None of the above. Pass what? Defects, design deficiency, wrong material, wrong filler, wrong welding process, and on and on... You did not identify your problem. So, what's the problem????

 

[drawoh]

glulambeam,

How about changing your material to cold rolled steel?

What is wrong with your current aluminium structure? Did somebody reject your design? Why?

--
JHG

 

"aggressive schedule" and "welded aluminum 6061-T6" is a risky combination.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[MotorCity]

Many engineers believe that a CJP weld is the easy, guaranteed solution for a weld. And in terms of strength it is. The truth is that the heat generated from over welding can cause more problems (shrinking, warping, distortion, etc.) The problems associated with aluminum are even worse than for steel because the strength of aluminum can take a nose dive in the vicinity of welds. I am not clear on the problem at hand, but I vote "no" on the CJP welds unless absolutely needed.

 

[dik]

and, are you heat treating the assembly afterwards?

dik

 

[gtaw]

Aluminum; "Almost a Metal"

The are issues with welded aluminum structures:
- Aluminum has no endurance limit, so when cyclically loaded, it will fail sooner or later.
- Whether heat treatable or nonheat treatable, the mechanical properties are going to degrade. With 6061-T6 you can expect 40% reduction on the tensile and 50% reduction on the yield strength if it is welded properly.
- 90% of the maximum oxide thickness will develop in the first 24 hours after cleaning, so cleaning today in preparation for welding tomorrow is a waste of time and labor.
- Cleaning must be accomplished immediately before welding.
- Groove angles must be larger when compared to the groove angles used for carbon and low alloy steels.
- Regular grinding disks used for steel are not appropriate for aluminum. Most grinding disks use aluminum oxide grit which is the kiss of death when used on aluminum.
- Wire brushes must have stainless steel bristles.
- Joints should be draw filed with a vixen file.
- hydrocarbons cause porosity, even oils from the skin cause porosity.
- do not use shop air, it contains oil from the compressor.
- GMAW must be in the spray transfer mode or there will be fusion defects,
- Do not preheat, this ain't carbon steel, so don't treat it as if it was.
- Limit interpass temperature by cooling between weld beads with a fan. Do not use shop air to cool the welds.
- Qualify your WPSs. Begin by qualifying your fillet welds and use those parameters when welding the grooved joint to determine whether you can meet the mechanical properties.
- Use a wrap around bending fixture when performing the guided bend tests for the qualification of your WPS.
- Don't expect your welders to pass their qualification tests or for your WPSs to pass on the first attempt.
- Pray the night before and just before welding. It can't hurt.


Best regards - Al

 

[dik]

Great summary... I thought with 6061-T6 that with proper weld, it could be heat treated to match the original base metal; not a critique... just want to know.

Dik

 

[gtaw]

The T6 indicates the wrought aluminum product is solution heat treated, quenched, and artificially aged. From a practical standpoint, most weldments cannot be solution heat treated and quenched without causing unacceptable distorton. The properties can be improved somewhat by artificial aging after welding, but it is unlikely to get the material back to its original T-6 condition.

Best regards - Al

 

[dik]

thanks, Dik

 

[drawoh]

glulambeam,

I am having a slow day here.

If I am in a blind screaming panic, why would I consider 5356[ ]filler, or complete joint penetration welds as a solution? We don't understand your problem.

--
JHG

 

Aluminum; "Almost a Metal"

or as I would say it:
"Plastic is not a real material, and aluminum is not a real metal"


"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[dik]

"Plastic is not a real material, and aluminum is not a real metal"

and we can precast 747s...

Dik

 

[glulambeam]

sorry guys...I forgot to qualify earlier that the issue I'm often faced with is trying to get the welds to pass on aluminum 6061-T6 structures, typically b/c my designers tend to undersize things and not take into account the strength knockdowns that are associated with welded aluminum.

Believe you me, I'd rather this support hardware be made out of carbon steel, but that's more of a rarity these days.

 

[berkshire]

Sticking my toe in here. While 4043 is a softer filler, it is also less prone to cracking. You get 50% more strength with 5356, you also have a greater chance of cracking. There does not appear to be a good answer here.
B.E.

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

 

[gtaw]

While the weld may be stronger using 5356, the failure often occurs in the HAZ beside the weld.

Best regards - Al

 

[dhengr]

Glulambeam:
What an important piece of problem descriptive info. and design info. to keep hidden from the others while they’ve tried so hard to be helpful. You could look for new designers if the ones you are using now are so slow to learn. You should not be using CJP welds on this kind of hardware in most of the welds. That weld prep. cost will be a real killer, and the CJP weld doesn’t really solve the problem, which is the weakened base metal. Just tell your designers to use 50% of Fy and Fult. for the design of the entire connection, and then design your welding as you normally would, for the actual loads. The added matr’l. thickness will not be that much more in the total connection cost. You could then downsize the dia. or quantity of some fasteners a little if they were far enough away from the weld zones, if there was some advantage and savings there. These size pieces of hardware might be solution heat treated and quenched without causing unacceptable distortion. It might be worth trying on a few typical pieces to determine the results, and develop a relationship with a heat treater. Read and reread Gtaw’s posts several times, maybe save copies, there is a ton of valuable educational info. there. There are also some zinc rich painting systems which make steel hardware look a lot like aluminum.

All OP’ers. should stop and think a few minutes, before they type their question, and ask themselves...: What is the real problem I want help with, and how do I best describe it in sufficient detail so people can efficiently help me? Remember, we can’t see it from here, we haven’t dealt with it as long as you have, we don’t have the drawing in front of us, so think a bit about what info. you must provide, to give us the full picture, and not in dribs and drabs. A few well proportioned sketches with loads, sizes, dimensions, etc. are worth a thousand words to an experienced engineers seeing your problem for the first time.

 

[glulambeam]

Again, I'm sorry that I hadn't included that important tidbit earlier. Duly noted; I should not be posting on a whim when I'm tired and about to retire to bed for the evening/early morning. Thanks all, for the inputs.

 

[drawoh]

glulambeam,

I have designed a number of space frames out of aluminium extrusions. If you do not have diagonal reinforcement (i.e. a truss), you need large gussets in the corners. The corners must resist moment loads. Large gussets places the weak aluminium welds away from corners, providing leverage.

--
JHG