Aluminium : Oxide in Weld ?

[fergusd]

So, some thicker filler helps a great deal with aluminium, 2.4 instead of 1.6 is night and day, I just can't fill fast enough otherwise. Now, I can run reasonably reliable T fillets but the welds look like there is something in them, I'm guessing it's oxide ? Question is, what it causing this and/or is there something I should be doing about it ?

2mm sheet, scotchbrited, 1.6mm 2% lanth tungsten which balls a little, size 5 nozzle, 80 amp average current but pulsed mode with the peak being about 110 (I find this helps a lot in getting the weld pool going), about 50% duty cycle, pulse freq 25Hz, AC freq 200Hz (I suspect this is at the top end of this electrode size, but it seems ok with enough postflow).

Thoughts ?

Cheers

Fd

 

[Engineer1964]

This is the most important tip I have.

You need to make sure that the Aluminium is Super clean, having two pieces of bright ally is not clean, there is oil and contaminants still on the surface.

Here are some of the signs that your aluminum is dirty.
1. A wandering arc -You can’t get a puddle started without burning through or distorting the metal

2. Your filler/wire won’t blend into the puddle, instead it rolls into a difficult to re-melt ball.

3. The aluminum seems to have surface tension, like beads of water on a waxed surface.

4. When trying to join 2 pieces the edges curl away from each other and form an even bigger gap.

Here's what's happening: Aluminum quickly forms an more or less invisible coating of aluminum oxide. Aluminum oxide melts at three times the temperature of aluminum. When you try to weld uncleaned aluminum, the aluminum under the aluminum oxide coating will melt but the aluminum oxide coating will stay solid and act as a membrane, much like a water balloon. When you finally succeed in penetrating the coating, the very runny aluminum inside will flow out all at once, much like a bursting water balloon.

Here’s how I prep the aluminum for welding.
First, I spray the aluminum with acetone. Don't use brake cleaner unless it's 100% acetone. doing it like this is the cheapest was you can buy the proper aluminium pre weld cleaner which is safer.

Then, I rinse the aluminum in water, just in case there's any nasty residue. The aluminum should be completely dry before welding, including all of the nooks and crannies.

Then, I use a stainless steel brush (make sure the brush is stainless, I've read this is important) to scrub the aluminum shiny clean around the area to be welded.

Some Welders suggest that the aluminum should be scrubbed in one direction only to avoid working contaminants into the aluminum. I don't always follow this rule and I haven't noticed any problems stemming from it, but I'm not working on anything too critical and I'm far from an expert. I've also read that 3M Scotchbrite pads are a good way to prep aluminum. If you do not weld on the aluminum immediately after cleaning, you should give it a touch up cleaning before you start to weld. I've read eight hours exposure after cleaning is the maximum acceptable without re-cleaning.

I've done a bit of tig with ally but with the right wire and Pluse Welder i can do it quicker by mig if the metal is really clean and the welder set up ok, take a peak of some mig welds i did on some ally box.

 

[hotrodder]

4043 wire? If so... http://www.mig-welding.co.uk/forum/showthread.php?t=24510&highlight=silicon

While you can't get ally too clean for welding personally for non-critical welds on sheet my prep work consists of peeling off the plastic and welding it. Critical stuff would get a solvent wipe (including the wire!) to keep porosity to an absolute min but the EP phase of the arc will deal with the naturally occuring oxide layer of ally that looks clean i.e. is bright/shiney.

Oxides and other crap typically show themselves as a sluggish weldpool, often with bits in it. The resulting weld will typically appear duller than it should although poor shielding and/or welding too slowly/hot will also do that

Larger practice coupons will help in that tiny ones very quickly become heat soaked making life harder. Personally i'd turn the pulse off or at least up the duty cycle some

 

[fergusd]

Bingo, 4043 wire indeed . . . if it's cosmetic I can deal with it ;-)

I chopped a test coupon today and it seems well done so I'd be happy relying on it . . .

I've been struggling to get the pool started quickly and pulse seemed to help, but I expect just more amps and no pulse would be similar . . . it's all confidence and speed . . .

Live and learn ;-)

Thanks

Fd

 

[julieanncharters]

This is the most important tip I have.

You need to make sure that the Aluminium is Super clean, having two pieces of bright ally is not clean, there is oil and contaminants still on the surface.

Here are some of the signs that your aluminum is dirty.
1. A wandering arc -You can’t get a puddle started without burning through or distorting the metal

2. Your filler/wire won’t blend into the puddle, instead it rolls into a difficult to re-melt ball.

3. The aluminum seems to have surface tension, like beads of water on a waxed surface.

4. When trying to join 2 pieces the edges curl away from each other and form an even bigger gap.

Here's what's happening: Aluminum quickly forms an more or less invisible coating of aluminum oxide. Aluminum oxide melts at three times the temperature of aluminum. When you try to weld uncleaned aluminum, the aluminum under the aluminum oxide coating will melt but the aluminum oxide coating will stay solid and act as a membrane, much like a water balloon. When you finally succeed in penetrating the coating, the very runny aluminum inside will flow out all at once, much like a bursting water balloon.

Here’s how I prep the aluminum for welding.
First, I spray the aluminum with acetone. Don't use brake cleaner unless it's 100% acetone. doing it like this is the cheapest was you can buy the proper aluminium pre weld cleaner which is safer.

Then, I rinse the aluminum in water, just in case there's any nasty residue. The aluminum should be completely dry before welding, including all of the nooks and crannies.

Then, I use a stainless steel brush (make sure the brush is stainless, I've read this is important) to scrub the aluminum shiny clean around the area to be welded.

Some Welders suggest that the aluminum should be scrubbed in one direction only to avoid working contaminants into the aluminum. I don't always follow this rule and I haven't noticed any problems stemming from it, but I'm not working on anything too critical and I'm far from an expert. I've also read that 3M Scotchbrite pads are a good way to prep aluminum. If you do not weld on the aluminum immediately after cleaning, you should give it a touch up cleaning before you start to weld. I've read eight hours exposure after cleaning is the maximum acceptable without re-cleaning.

I've done a bit of tig with ally but with the right wire and Pluse Welder i can do it quicker by mig if the metal is really clean and the welder set up ok, take a peak of some mig welds i did on some ally box.

looks like poor fusion on top edge of yer weld , usually torch angle issue,
should have " cleaning bar" each side of weld .

 

[Country Joe]

looks like poor fusion on top edge of yer weld , usually torch angle issue,
should have " cleaning bar" each side of weld .

I think that's from it being migged not tigged
CJ

 

[julieanncharters]

I think that's from it being migged not tigged
CJ

yep i know the weld has been migged but you should still get the same cleaning action both sides of the bead in either process.

 

[Country Joe]

Oh well, properly rumbled there, then - I've never tried to mig alu!

Even when I tig it, I seem to get a very big (about 2xFergus's) frosty cleaning band, but rarely change anything if it looks anything like presentable!
All the Best,
CJ

 

[fergusd]

Interesting evening, different welder (probably 5x the cost of my one), laid off the pulse and was using about 110A at 60% EN on 3mm sheet, same filler wire, and apart from the ever present problems getting started (impatience - trying to go before the weld pool is really ready - difficult to tell), once I was going things were improving, almost no speckling but a little towards the end of the weld, and as has been suggested to me, probably getting too hot . . . probably caused by going too slow . . . found that 100Hz AC freq seemed to work best, higher frequencies seemed much more difficult to get started . . .

On the cleaning band thing, the more I do the smaller the band seems to get . . .

Anyways . . . more milage helps ;-)

 

[fergusd]

What initially seems impossible starts to become more routine ;-)

2mm alu sheet, not cleaned (as a wee test), kicking about the workshop with no film on, chopped in the chopper and welded, 80A, 65%EN, 100Hz, 2.4mm thorated sharp tungsten. Cleaning with a stainless brush certainly helps with starting, but equally it can work without too ;-). This is with a 5356 filler which I think is easier to use, not sure why, but it seems that way, perhaps it has a slightly higher melting point ? . . .

I want to get down to 1.6mm sidewall tubing, for a specific purpose, and I can see some light at the end of the tunnel now . . . ;-)

I've been using 2T and a longish downslope to allow me to feather power towards the end of the weld but I can see that a pedal, for aluminium, would be of great use . . .

Last night of my TIG course tonight, and it's been well worth it. Even if you look at the cost of gas and materials (14 weeks, 3 hours a week) its a good deal, but having some dedicated time to spend is the big bonus with folk who can answer questions . . .

Fd

 

[hotrodder]

Looking much better!

This is with a 5356 filler which I think is easier to use, not sure why, but it seems that way, perhaps it has a slightly higher melting point ? . . .

Yeah, silicon lowers the melting temp and increases fluidity. 4043 is also more resistant to solidification (hot) cracking than 5356 but on the flip side 5356 is both more ductile and stronger.

 

[armcosurfer]

Engineer,what MIG welder did you use to weld the ali box section,that looks pretty good to me. Did you use a spool gun?