Why can't you TIG weld Aluminium with DC current?

In summary, TIG welding aluminum with DC current is not possible due to the oxide layer on aluminum which has a higher melting point than aluminum itself. This can be overcome by using AC current which breaks off the oxide coating. However, other materials such as stainless steel can be welded using DC current because they do not have a high tendency to oxidize. This question could be better suited for General Engineering or Materials Science, and the person providing the answer identifies as a physics person rather than a chemistry person.
  • #1
Adrian Baker
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Why can't you TIG weld Aluminium with DC current?

You can TIG weld it beautifully with AC, but if you turn the TIG welder to DC it doesn't work... You don't get a nice little weld pool, the sample seems to overheat and deform and it goes all black on the outside. The welding rod just leaves circular globules on the top that don't melt to the main body. You can happily do stainless and other steels on DC, but not Aluminium.

I assume that this is a Chemistry question, as I can't think of a Physics reason...

Anyone? Thanks for listening.
 
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  • #2
Because of the oxide layer on aluminum. The melting point of Aluminum is just 660C while that of aluminum oxide is over 2000C. When you use AC, you actually are constantly breaking off the oxide coating by thermal cycling. Remember, Aluminum Oxide (or alumina is a ceramic, and is very brittle, so it breaks off easily. With DC, you get nowhere because you're heating the oxide but not enough to melt it.

Steels don't oxidize nearly as easily as Aluminum and their oxides are not nearly as nasty. So they can be welded happily using DC.

PS : Not the best place for this post. I'd have put it in General Engineering or Materials Science. If you're not happy with this answer, you might think about moving it. Also, I consider myself more a physics person than a chemistry person.
 
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  • #3
I'm very happy with your answer - thank you.
 

Related to Why can't you TIG weld Aluminium with DC current?

1. Why can't you TIG weld Aluminium with DC current?

Aluminium is a highly conductive metal and requires a high amount of heat in order to weld properly. DC current does not provide enough heat to effectively weld aluminium, resulting in a weak or incomplete weld.

2. Can you use DC current to TIG weld Aluminium at all?

Yes, DC current can be used to TIG weld aluminium in certain situations, such as when welding thin sheets or using a specialized high-frequency start TIG welder. However, in general, AC current is the preferred method for welding aluminium.

3. Why is AC current better for TIG welding Aluminium?

AC current alternates between positive and negative polarity, which creates a wider heat distribution and allows for better control of the welding process. This is especially important for aluminium, as it helps prevent the metal from overheating and becoming too soft.

4. What happens if you TIG weld Aluminium with DC current?

If you attempt to TIG weld aluminium with DC current, the weld will likely be weak and incomplete. The metal may also become overheated and distorted, resulting in a poor quality weld that may not hold up under stress.

5. Are there any other methods for TIG welding Aluminium?

In addition to using AC current, there are a few other methods for TIG welding aluminium. These include using a pulsed TIG welder, which alternates between high and low currents to control heat input, or using a specialized AC/DC TIG welder that can switch between AC and DC current as needed.

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