Tig Welding Aluminium-Any Tips please?

[buel]

Hi there,
Im a 33yr old Mig Welder and last year completed a few Tig welding courses (City and Guilds Flat and Vertical Butts, T-Fillet and Lap joints) and have just started to Tig Aluminium during the evenings at my local college. I have been wanting to try aluminium ever since i first started welding over 10 years ago and i've always seen it as something i would never actually be good enough to try so i hope you can imagine how excited i was last week when i completed my first 'test piece' for college- a butt weld on what i think is 3mm aluminium with full penetration (after many weeks trying to get the hang of the foot pedal and getting a decent heat sink under the aluminium).
I am going to do a few more of these butt welds just to make sure that i can do it and then i am going to move onto the lap joint and then the T-fillet. To be honest i find welding aluminium fascinating, from how you have to brush it first with a stainless steel brush to how you have to wait to get the 'mercury' effect before starting to move and add the filler wire. Just for now i have a couple of questions id like answered if anybody can please?
1, i have taken 5 or 6 aluminium pieces from college (with their blessing) as i was hoping to prep/brush with my stainless steel brush at home over the weekend to save me using valuable welding time at college but a friend at work told me that brushing the aluminium and then leaving it a few days will have a detrimental effect on the aluminium and i'll only have to do it again when i get to college, is this true please?
2, how 'called for'/in demand are aluminium welders as later in the year im hoping to do the next course available to me which will me vertical Tig welding aluminium...and then maybe one day overhead...but im not going to attempt to run before i can walk!!
Thank you in advance for any answers! -Buel

 

[pedrobedro]

I don't know about 2 but your friend is right on 1 although I don't think detrimental is the correct way to describe it, more like negligible. An oxide layer forms on aluminium almost immediately and it will be a waste of time doing the prep days in advance.

 

[TheJoker]

With regards to 1, Aluminium forms Aluminium Oxide within 24 hours, the process starts immediately after you've exposed aluminium to air. I.e when you've brushed it with the SS brush. The problem is that Aluminium Oxide has got a much higher melting temperature than Aluminium.

 

[hotrodder]

As said aluminium begins to 'grow' an oxide layer immediatly fresh Al is exposed (that's why it's welded with AC) and thickens with time. A thickened oxide layer can also trap dirt and moisture which'll cause porosity (hydrogen is soluble in liquid Al but not in solid).

Clean, new aluminium welds fine with zero cleaning. Granted for x ray quality work you'd degrease and brush regardless but for practice purposes...
Clean up your coupons before you go and give it a try. If you find it tougher then brush the joint again. Depends on how much Al welding goes on at the college (and how stuff is stored) but if they aren't doing loads then i'd suspect the filler wire is probably at least as dirty/oxidised as the base metal- scotchbright followed by a clean rag

 

[Uncle Joe]

Heres my tips:

1) Solutions are available for removing oxide. Use them immediately before welding. If there is any grease on the surface, use acetone first.

2) Practice on stainless steel.

3) If you are welding aluminium over 1.5mm thick, try using a mix that includes helium.

 

[busa]

Heres my tips:

1) Solutions are available for removing oxide. Use them immediately before welding. If there is any grease on the surface, use acetone first.

2) Practice on stainless steel.

3) If you are welding aluminium over 1.5mm thick, try using a mix that includes helium.

No1 is good advice, all traces of hydrocarbons should be removed from both parent metal and filler wires. As for No2, stainless and aluminium have totally different welding characteristics, so I don't see any mileage in practising on stainless. The most widely used gas for welding aluminium is pure argon, the addition of helium in a shielding mix serves only to produce a hotter arc, resulting in deeper penetration. On modern Tig sets the deeper penetration can be achieved by changes in parameters. Argon / Helium mixes are also very expensive.

 

[Uncle Joe]

I kind of expected a reply similar to this.

Practising on stainless gives the technique needed, which is the reason I suggested it.

If you try to weld aluminium using a helium mix, (I would suggest 25%) or even pure helium if you are good enough to start the arc, you will be surprised at the difference. Heres a sample of my aluminium welding, just in case someone thinks I dont know what I am talking about. No offence meant, so please dont take my comments in the wrong way.

 

[busa]

I saw that picture the first time you posted it Joe, very well excecuted welds and obvious that you know what you are talking about. However, as I said in my last post, the advantages of using Helium mix, ie depth of penetration and welding speed can be achieved by variations in welding parameters on any decent Tig set these days. I know that the Americans are well into Helium mixes, they do however have us at a disadvantage, as virtually all of the worlds Helium reserves are located in Texas.

 

[NTwoO]

I know that the Americans are well into Helium mixes, they do however have us at a disadvantage, as virtually all of the worlds Helium reserves are located in Texas.

Is that so? I thought that helium is a gas mixed in the atmosphere and is removed with refractional distillation. (from liquified air).

 

[busa]

Is that so? I thought that helium is a gas mixed in the atmosphere and is removed with refractional distillation. (from liquified air).

Helium does exist naturally in the atmosphere, although at a concentration of only 5 parts per million it is very expensive to extract. Commercially available helium is distilled from natural gas but only from certain areas of the world.

Quote from this site: http://www.eoearth.org/article/Helium

Some natural gas deposits have as much as 7% helium. Such deposits have been found in Texas, Russia, Poland, Algeria, China and Canada. Helium extracted from these natural gas reserves is the single source of helium.

It is believed the world helium resources – excluding those of the United States – totals 15.1 billion cubic meters. It is estimated that the United States has helium resources of 11.1 billion cubic meters.

 

[NTwoO]

Thx for the info!

 

[buel]

WOW!! Thank you very much to you all, i do appreciate the info/advice and, for the record, i am extremely impressed with Uncle Joe's welding, that is a perfect example of what im attaining to!!
Here is what i found:

I found that cleaning/wiping the filler wire with my clean Tig welding gloves really helped but i am going to look into getting some scotchbright.

Unfortunately the college is not in a position to use different gasses (with reference to using helium), i will find out tomorrow night what gas they use.

If i could ask a futher question of you all, it would be this:
1, I seem to be able to manage to Tig a butt joint using 1.5mm -2mm Ali and have full Pen when i do it but i only seem to be able to manage this when i have a good amount of Ali as a heat sink, if i try it using just the steel sheet on the work bench it seems to get too hot too quick, am i 'cheating' by using Ali as a heat sink?

2, Have you any advice for me for when i am going to try a lap joint or, more difficult (i expect) the dreaded T-fillet?

once again, thank you all!!