Aluminum external corners

[mud90mike]

Hi All

Hoping someone can offer some advice

We are welding some 6mm Ali plates on the outside corners, we have butted the inside edges together then welded them up and broke them apart when cooled there doesn't appear to be as much penetration as I would expect if it was a MIG as I can still see the crisp inside edge of the metal and the weld is splitting dead central each time. What do people think / suggest? Currently using 3.2mm rod and around 150 Amp

Many thanks

Mike

 

[HughF]

You need to clean the back surface so that when you penetrate through, you get fusion, hard to explain but it's common on alu. You could also get some helium in the mix to heat things up. They will obviously break down the middle if you bend it open from the inside out as there is no root reinforcement. You'd want to stitch weld the inside of the corner or put some triangles in there.

What grade alu are you using and what filler wire?

 

[Jim Davey]

Try cleaning off the oxide layer both sides and the edge and set up with a 2mm gap. Are you doing this in position or downhand?

 

[mud90mike]

Plate is 5251 angle is 6082, filler wire is 5356 doing it laying flat.

 

[HMB]

More amps.

 

[Jim Davey]

Or wait longer for the heat to build up.

 

[backpurge]

As has been said you need to get more heat in, changing to an argon/helium mix will definitely make a big improvement

 

[Richard.]

40 amps per mm is a rough guideline to work with on cold Alu with argon gas. Remember to try and finish your run properly and fill any crators up. They can start a crack very easily on Alu.

 

[Brad93]

150 amps for 6mm to 6mm, that's far too little. What is the Max amperage your machine goes up to?

From the photos you've not penetrated into the sheets let alone through into the back of the material.

 

[mud90mike]

Thanks Guys, Machine goes up to 210, We put amps up. slowed it down a lot, cleaned up the material and now got full penetration through, the material was a lot harder to break and also the weld penetrated much better.

 

[Richard.]

Thanks Guys, Machine goes up to 210, We put amps up. slowed it down a lot, cleaned up the material and now got full penetration through, the material was a lot harder to break and also the weld penetrated much better.

Pics?
Don't get too hung up on scrubbing and cleaning it. If the surface is clean then a wipe over is sufficient. The ac positive wave will take care of the rest. I watched an interesting video that back purge put up a while ago where the welding arc was more stable while happily lifting the oxide layer than it was on a plate that had been scrubbed to death. The Internet is filled with unesasarry info on Alu prep that makes people believe it needs to be scrubbed to within an inch of its life and soaked to death in acetone. If it's a scabby bit that's been subject to the elements or covered in oil etc that will be the case. I just give it a wipe over if it's a nice bit. I do wipe my filler down too sometimes with a acetone dampened cloth. I cannot remember the last time I ruined the finish on a nice Alu project by attacking it with abrasives.

 

[Rrunnach]

You need to pre heat before commencing welding.

 

[wheresmejumper]

The ep can't clean the rear of a closed butt . mechanical cleaning is often required.

 

[Richard.]

The ep can't clean the rear of a closed butt . mechanical cleaning is often required.

Why do you think it needs to come off the back side.

 

[wheresmejumper]

Ive seen it done and read about complications/impurities that show up in xray,where ep alone cant clean the back side.
j preps to an almost feather or 1mm and the defects vanish.

 

[Rrunnach]

Ive seen it done and read about complications/impurities that show up in xray,where ep alone cant clean the back side.
j preps to an almost feather or 1mm and the defects vanish.

I fab/welded a fleet of first generation ROV's for the then SUBSEA OFFSHORE, now SUBSEA7 (SS7) Main frame weldment was manu'd from 6mm marine grade al/al (7000 series). Using an old BOC ADR 300, no EP this or that, I manu'd Rovers that operate below 5000 MSW. Nae bother, nail it together, dye pen the welds, fire it up to Aberdeen. I never had one weld (and there were many) rejected. My ol adr didnae have ab, let alone ep, you do have to wonder where the welding world is coming to, especially from posts from wannabes, who appear not to have a clue!!

Back to OP, do a pre heat, use a tempil stick around 100/150c, enough to take chill off matl. Listen to someone who has been there and, has the T-Shirt.

 

[hotrodder]

Anyone remember a time when this forum was good? All it seems to be these days is willy measuring, random crap and the same lazy questions (what gas for MIGing stainless, who's the cheapest for gas etc)

...Using an old BOC ADR 300, no EP this or that, I manu'd Rovers that operate below 5000 MSW. Nae bother, nail it together, dye pen the welds, fire it up to Aberdeen. I never had one weld (and there were many) rejected. My ol adr didnae have ab, let alone ep, you do have to wonder where the welding world is coming to, especially from posts from wannabes, who appear not to have a clue!!

Of course it did it just wasn't adjustable. How can you have an AC arc that doesn't include a portion of EP (electrode positive). EP is what provides the "cleaning" action on ally whether it's AC TIG or DCEP MIG/GMAW. Cathodic cleaning works by breaking up the oxide layer when the polarity is the right way round and as cathodic cleaning is to do with electron flow/ion bombardment/witchcraft it only works on areas that the arc directly contacts.
While it isn't exactly page one of chapter one it's pretty basic stuff and covered fairly early on in the bible of aluminium welding along with various causes of oxide entrapment... https://murdercube.com/files/Workshop/Welding/Welding Aluminum & It's Alloys.pdf

For anyone that wants a proper headache inducing explanation of cathodic cleaning... https://app.aws.org/wj/supplement/wj0110-1.pdf

 

[Piero]

Never new this forum was a chat room.

How about we keep on topic and input something constructive

 

[Richard.]

Well I was gonna make a point that you don't "need" to remove the oxide layer on the back side as it's not going to offer any advantage. But then wmj did say he'd read it helps with X-ray Quality and I can't argue with that . I don't think it makes any odds if It's removed on either side if the Alu is clean. The EP doesn't need to remove it on the back side because it doesn't remove it on the front either. It temporarily pushes it to the sides before the Alu itself regenerates a new one an hour after. The other side the root pushes through the Alu easy but tends to stay blanketed behind the oxide layer so granted it's not as attractive as the front side.
From a joint strength PoV I don't think it makes a difference but regard to what is gonna be picked up on X-ray and failed then yes I can quite believe it needs to be removed. Same with the etched zone on the front side id imagine.

It's now turned into a slagging match. X-ray and dye pen are not comparable I but I do agree with Runnarch's first comment it's not needed, it's Welded often with the backsides left as they are. I agree with wmj also for X-ray standard of welding it may well be the standard required.

 

[Rrunnach]

Richard, my first comment on post 12 was "You need to pre heat before commencing welding." Which I stand by, keep it simple, no need to head down the technical road. Nor as you stated in a previous thread "scrub it to death".

Then to underpin reason for the above comment, I went on to explain same method of nailing al/al using an old adr300 to manu a few million Dollar fleet of ROVs for a global company, not one of my welds ever failed a comprehensive inspection. Regarding x-ray, I never brought the subject up, I have no idea what brk will be used for, although I doubt very much any ndt will be required on the finished job. What is good, though, is the OP had the common sense to do his own DT on brk, then asked the question on how to make a weld of good integrity. As I mentioned earlier, pre heat required, a simple plumbers blow torch would be adequate to OP's requirements.