MIG welding Ali

[smo]

I'm doing some "temp" work (bought in for engineering design jobs and ended up in workshop for a while as i can weld and stuff!!) for a company that mig welds aluminium, we have had some parts coem back with weld failures and we cant seem to get enough penetration as it seems to go from none to blowing holes!

How should you mig weld Aluminium, is there a secret technique as ive tried many settings changing the amps and wire speed to try and find a suitable setting. (their expert isnt too expert as the welds keep failing)

We are using a Butters pulse synergic machine with 1.2 AL-Si5 wire.

 

[Hitch]

A bit of preheat can make a world of difference on penetration, and slowing down cooling.
How thick is the material, and what grade is it? That could be your problem,
Or if its a large fabrication, it might well be the heat is being drawn away too fast

Gas wise, if you struggling for heat, an argon helium mix might help you, but quite expensive.

Speed wise, get it set high, but move faster.

What sort of things are you welding?

 

[Omniata]

Have you cleaned the Ali thoroughly before welding??
ie: thoroughly brushing the surface with a steel/stainless steel brush to expose fresh Ali before hand, retaining that brush for only that use???

Also how thick is the Ali your trying to weld?

How old is the wire?

And are you using pure Argon?


Sorry if this sounds a little patronising, it's not intended, I'm merely trying to find a possible cause

Amps need to be set reasonably high and wire speed nearly double that of mild steel...
Preheating may help as Ali can draw heat away from the weld region...

Edit: beat me to it Hitch

 

[malcolm]

Good point Om. Mentions of MIG, aluminium and weld failure brought oxidisation into my head too. If you are used to doing it with TIG the oxidisation problems with MIG could catch you out. Some pics of my own problems (and workarounds for cheaper MIGS) here.

Would have thought a synergic MIG would get around some of the troubles with heat dissipation? Wouldn't it be possible to set up a synergic to blast enough heat in for a short time to locally melt things together, then leave it a bit to cool down before the next blast. I've never used one so can't comment on settings. Interesting question for someone else there.

 

[Paul.]

There could be many reasons why weld failure is occurring, joint design, welding sequence, parent material and filler grade etc etc, are all factors, synergic sets do offer many advantages but are not always the answer, without more information its impossible to provide any more useful advice than has already been offered,

 

[M1CDQ]

out of curiosity and out of all the reading I have been doing and i might have got this wrong but I thought Mig was DC and welding aluminium with tig is you need AC.
Now if your using agon gas on both why cant you weld ali with a dc tig as your using the same gas getting an arc from a DC voltage the only difference is your feeding the filler by hand instead of my motor from the mig.TIll I came on site I only thought mig was for mild steel

 

[shenion]

One reason is MIG is much faster, you move the torch fast enough that the metal ahead does not get hot enough to oxidize much. It can also tolerate a bit of contamination (not much though.)

TIG is slow and needs pristine metal, the metal ahead of the weld has more time to heat up exposed to air. So, it needs the cleaning action of AC to break through any oxides.

You can weld ali with DC TIG, but that is normally only done on heavy stuff.

 

[Rusty]

out of curiosity and out of all the reading I have been doing and i might have got this wrong but I thought Mig was DC and welding aluminium with tig is you need AC.
Now if your using agon gas on both why cant you weld ali with a dc tig as your using the same gas getting an arc from a DC voltage the only difference is your feeding the filler by hand instead of my motor from the mig.TIll I came on site I only thought mig was for mild steel

This might help -
http://www.mig-welding.co.uk/forum/showthread.php?t=659

 

[Paul.]

Aluminium has a residual refractory oxide, the melting point of the oxide is more than 3 times the melting point of the aluminium about 2000 deg C for round figures, the AC cyle of tig has the effect of lifing the oxide to expose the parent material to the arc, known as scavenging. with DC tig you need to remove the oxide skin as much as possible before welding and stir it to the surface with rod and pool manipulation, do-able on heavier materials but far from ideal, Mig punches through the oxide and lifts it allowing the pool to form underneath, as Scott says very quick compared to Tig

 

[smo]

Answers to a few questions:

We use pure Argon (from either BOC or Airproducts)
The material is aluminium extrusions, mostly 6082 T6
Filler wire is ALSi5 1.2mm (not sure on grade)
We dont pre-heat as its not feasable for our fabrication purpose
We do brush before welding however cleaning wouldnt be up to TIG standard.

 

[Omniata]

Ok....

You really need to remove as much of the oxide layer as possible before welding, almost scrubbing the surface to scratch it off.
You need to do this just before welding as the oxide layer can reform reasonably quickly...

If you don't inclusion of even small bits of oxide can seriously weaken the welds


That might be why they're failing...

A stainless steel brush should be good enough...


Are there no ways you could carry a plumbers MAPP gas torch around to just get a bit of heat in, or if extrusions a hot air blower blowing through the extrusion ???

 

[smo]

Heating it with gas might well help, also with the bending process as we struggle with some extrusions.

I shall pass the info back and see if we can improve the strength - i found out today our welder is apparently coded too......hmmm!

 

[hotrodder]

Don't know enough about synergic MIGs to suggest settings but we still don't have enough info yet anyway. 4043 (AlSi5) is fine for 6082 but what section thickness? Weld type? Mode of failure (centreline cracks, failing at the weld toes)? Have you sectioned any welds to look for porosity (a common one, especially with MIG)? Pics would help lots!

If we're talking fillet welds then It could be as simple as undersized welds- 4043 is more 'weldable' than the other filler choices for 6082 but 5356 wire is both stronger and more ductile, quite noticable with fillets but there's a bit more to it than that... 4043 versus 5356

Regarding the arcs 'oxide cleaning' effect... it's not AC that provides the cathodic cleaning but the electrode positive stage of the AC arc. TIG with DCEP isn't practical because the tungsten needs to huuuuge to survive the extra heat (around 2/3 occurs at the positive electrode). MIG welding is DCEP anyway so no problem, oxides formed during welding are taken care of. Due to the extra speed of MIG porosity is more of an issue than with TIG- the fast freezing weld is more likely to trap any hydrogen that may have more chance of escaping with TIG. The filler wire is another potential source of hydrogen porosity, again more likely with MIG