help please - Aluminium won't de-oxidise

[AlanRT]

Hi I hope someone can help or guide me in the right direction.

Below is a couple of photographs of some Aluminium pipe which I'm practicing on. The thin bit is cut from the large bit so they're the same material.

I've then cut through the thin bit, gave it a quick clean and scrub with wire brush and it's welded (please ignore the state of the weld)

I've done exactly the same to the larger part (but cleaned it for a lot longer) and it won't fuse, won't melt and obviously won't accept filler. I presume this is the oxidant scale which people go on about.

Cleaning is done with Acetone and then wire brushed with a stainless brush. Like I said, one part is welding, the other won't. It's exactly the same material any ideas as to why?

Could it be that the larger part isn't getting enough heat?

Material is 1.6mm thick by the way.
Using 45 amps 60hz (ish)

 

[Wendelspanswick]

Wack the amps up!

 

[Richard.]

Can you put up your settings . Current, balance , freq .welding two different thickness is tricky but if I know your settings I may be able so spot some candidates for the issue.

 

[AlanRT]

Here's a pic of the settings.

Around 45 amps
60% balance sorry not 60hz
1.6mm thick material (both pieces) 1.6mm tip and 1.6mm filler rod

 

[AlanRT]

Wack the amps up!

Too low? How come it's welding one and not the other though?

 

[Richard.]

Ok what's your material thicknesses.
Wendelspanswick which way does the balance work on those is it set the EN or EP. I think your been a bit light on the current. A pedal would really help you here.

 

[Wendelspanswick]

Too low? How come it's welding one and not the other though?

Heat soak, the small bit is heating up rapidly until the the whole of it is heat soaked, the large piece is rapidly conducting the heat away so it never reaches the temperature required to break through the oxide layer.

 

[Paul.]

How come it's welding one and not the other though?

Because the large piece is acting as a heat sink and sucking the heat away from the weld, the small coupon becomes heat soaked very quickly, hit it at about 60 amps to tack it then back off the power as the job warms up

 

[Wendelspanswick]

Anti clockwise for max penetration, clockwise for max cleaning.

 

[Richard.]

Too low? How come it's welding one and not the other though?

Aluminium requires a wack of heat to start off and melt the oxide layer which has a melting point of 3x the Ali itself so yes more current. A rough rule of thumb is 40amps per 1mm. It's rough mind.

 

[AlanRT]

I have a pedal to control the current. One thing I'm also trying to figure out is how much it actually reduces the current from top to bottom, really not sure.

I'll give it another go and stop being so soft with the heat.

Thanks for the help guys. I'll be back for more help

So what is the white stuff that's building up?

 

[Richard.]

The white bands around the weld? This is the "etched zone" it's the cleaning of the aluminium oxides from the positive half wave. You can reduce this if you want to by either cleaning your aluminium up better (acetone, ss brush etc ) or reducing the EP% cleaning slightly or both.

 

[AlanRT]

Ok whacked the current up and tested the pedal, it was me being a fool, I thought the current output was the other way round with the pedal ie full power when up, reduced power when fully pressed, nope, other way haha. I'm just new to this, stop laughing

Thank you for the help though, created a pool no problem at all just need to conteol it now

 

[backpurge]

Glad you sorted it, don't be as paranoid re the cleaning, so long as you give it a proper clean with a stainless steel wire brush and get the majority of the oxide off there is no need to use acetone unless you have a problem with oil and grease etc

 

[Richard.]

Glad you sorted it, don't be as paranoid re the cleaning, so long as you give it a proper clean with a stainless steel wire brush and get the majority of the oxide off there is no need to use acetone unless you have a problem with oil and grease etc

exactly. The fact that your getting the white bands (etched zone) around your beads shows that the AC wave is cleaning well for you. A good way to tell if your Alu and filler is clean is when your welding you should see two tungstens. The one in your torch and it's reflection in the pool. If your getting a mist or scum in the pool then something is not clean enough.

 

[backpurge]

I've got a cracking video clip that I will try and upload that shows how ally actually welds better with a bit of oxide on it, that is why O2 doped gases work better than pure gases on aluminium

 

[Richard.]

It does. I'll give it a quick scrub and wipe off the consumables but it's true it's actually happier when it's lifting off the oxide by itself.

 

[Richard.]

Not the case with cast ally though. That stuff needs serious preperation to stand a chance.

 

[backpurge]

The oxide layer is a lot easier to ionise so you get a much more stable arc or something scientific like that

 

[Richard.]

The oxide layer is a lot easier to ionise so you get a much more stable arc or something scientific like that

Stick up that vid if you can. Be interesting to watch.