I asked a friend that builds lasers for jewelry, Martin Stuart of
MSI. He has been teaching me to use a laser welder and cutter he has.
Copper and silver react to oxygen. So, bare air can be a problem but
not always. Nitrogen can get involved in a bad way due to the laser
beam temperatures. 25,000 F! You can make nitrides by accident with
nitrogen at those temperatures, which may make the joint brittle.
Argon avoids this. The plasma flash creates pressure. The gas drives
itself onto the molten metal with that pressure. So you have 25,000f
at 300PSI pressure. If that includes oxygen or nitrogen there can be
issues. Argon assures a more consistent hardness and property in the
Some of this is theoretical. It's hard (expensive) to analyze for
nitrides in such a small area. That's the theory folks.