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Welding aluminum in Earth's atmosphere is difficult because aluminum oxide forms on the surface and it has a higher melting point than the aluminum inside. So t

Welding aluminum in Earth's atmosphere is difficult because aluminum oxide forms on the surface and it has a higher melting point than the aluminum inside. So to weld aluminum you need to keep oxygen away from the weld, usually by flooding the weld with argon or some other inert gas. In a vacuum this problem wouldn't exist and aluminum should be no more difficult to weld than steel.

grogenaut 2y ago
Not a metalurgist, but agree the oxide problem would go away. However I think you'd have a worse problem with heat. Aluminum in my limited experience gets really hot and soupy when welded, so that you have to go quite fast in many cases. Without an atmosphere to sync some of the heat, you might have very interesting thermal issues. You'd definitely need much bigger heat syncs. However depends likely on the scale of welding that's happening. Definitely will be interesting.
- bloggie 2y ago
  Laser welding has quite different challenges from electrical welding as the heat-affected zone is so much smaller, much less energy is delivered to the metal to perform the weld. I'd like to read more about the research in the article to see what they've done to address this or if it was even an issue for them! It probably depends on the thickness and orientation of the metal and fixturing.
pengaru 2y ago
> In a vacuum this problem wouldn't exist and aluminum should be no more difficult to weld than steel. Aluminum is a PITA for more reasons than its oxide layer...
jcgrillo 2y ago
While you're correct about the oxide issue, there are welding processes which mitigate this. In particular, using alternating current instead of direct current causes a "cleaning" effect which knocks the oxide off of the weld area. Laser welding does a similar thing. If you're welding aluminum with DC stick, DC TIG, or just an oxy-acetylene torch you can get good results by grinding the weld area with a flapper disk and brushing immediately before welding with a stainless wire brush that has never touched anything but aluminum. For DC TIG and oxy-acetylene I've used flux coated welding rods as filler material with some luck. Also, you always need to keep oxygen away from weld, no matter what process or material you're welding. At welding temperatures metals will burn in the presence of oxygen. We do this by using shielding gasses, flux which burns and displaces the oxygen, using a slightly fuel-rich (or "reducing") flame, physically displacing all the oxygen (forge welding) etc.
- dreamcompiler 2y ago
  Correct about keeping oxygen away regardless of material. Aluminum is just much less forgiving than steel in this regard. I use the DC TIG process even for steel because it makes cleaner welds than sticks do. (TIG is also slower than stick, so it's less good for high-volume welding.) I've never tried flux-coated rods with aluminum because they seemed like a gimmick to me, but maybe I'll do an experiment.
  - potato3732842 2y ago
    >I've never tried flux-coated rods with aluminum because they seemed like a gimmick to me, but maybe I'll do an experiment. They suck to use but they work. They're not really a production item. They're more for globbing something together in the field.
    - jcgrillo 2y ago
      > They suck to use but they work Yep, exactly. I welded a fitting onto a cast aluminum intake manifold using these things and an oxy-acetylene torch and it came out "good enough"
pfdietz 2y ago
The kickass aluminum welding process doesn't melt aluminum at all. It's called friction stir welding. Invented in the UK in the 1990s, it involves moving a rotating tool through the aluminum. The rotation softens and mixes the solid metal, refining the grain structure and blending the two pieces together. It's what SpaceX uses to weld the tanks on the Falcon 9.

grogenaut 2y ago

Not a metalurgist, but agree the oxide problem would go away. However I think you'd have a worse problem with heat. Aluminum in my limited experience gets really hot and soupy when welded, so that you have to go quite fast in many cases. Without an atmosphere to sync some of the heat, you might have very interesting thermal issues. You'd definitely need much bigger heat syncs. However depends likely on the scale of welding that's happening. Definitely will be interesting.

bloggie 2y ago
Laser welding has quite different challenges from electrical welding as the heat-affected zone is so much smaller, much less energy is delivered to the metal to perform the weld. I'd like to read more about the research in the article to see what they've done to address this or if it was even an issue for them! It probably depends on the thickness and orientation of the metal and fixturing.

pengaru 2y ago

> In a vacuum this problem wouldn't exist and aluminum should be no more difficult to weld than steel. Aluminum is a PITA for more reasons than its oxide layer...

jcgrillo 2y ago

While you're correct about the oxide issue, there are welding processes which mitigate this. In particular, using alternating current instead of direct current causes a "cleaning" effect which knocks the oxide off of the weld area. Laser welding does a similar thing. If you're welding aluminum with DC stick, DC TIG, or just an oxy-acetylene torch you can get good results by grinding the weld area with a flapper disk and brushing immediately before welding with a stainless wire brush that has never touched anything but aluminum. For DC TIG and oxy-acetylene I've used flux coated welding rods as filler material with some luck. Also, you always need to keep oxygen away from weld, no matter what process or material you're welding. At welding temperatures metals will burn in the presence of oxygen. We do this by using shielding gasses, flux which burns and displaces the oxygen, using a slightly fuel-rich (or "reducing") flame, physically displacing all the oxygen (forge welding) etc.

dreamcompiler 2y ago
Correct about keeping oxygen away regardless of material. Aluminum is just much less forgiving than steel in this regard. I use the DC TIG process even for steel because it makes cleaner welds than sticks do. (TIG is also slower than stick, so it's less good for high-volume welding.) I've never tried flux-coated rods with aluminum because they seemed like a gimmick to me, but maybe I'll do an experiment.
- potato3732842 2y ago
  >I've never tried flux-coated rods with aluminum because they seemed like a gimmick to me, but maybe I'll do an experiment. They suck to use but they work. They're not really a production item. They're more for globbing something together in the field.
  - jcgrillo 2y ago
    > They suck to use but they work Yep, exactly. I welded a fitting onto a cast aluminum intake manifold using these things and an oxy-acetylene torch and it came out "good enough"

pfdietz 2y ago

The kickass aluminum welding process doesn't melt aluminum at all. It's called friction stir welding. Invented in the UK in the 1990s, it involves moving a rotating tool through the aluminum. The rotation softens and mixes the solid metal, refining the grain structure and blending the two pieces together. It's what SpaceX uses to weld the tanks on the Falcon 9.