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No, in every case shown so far it has been all 4 wheels.
And not just a little melt, but a puddle where the wheel once was. Sometimes running across the street for several feet.
In addition, both aluminum and magnesium ignite very close to their melting point. Aluminum often vaporizes.
I’ve seen pix with two wheels melted (downwind wheels). As for your welding with 20 amps times 120 volts (2.4kW), how much power will you need to completely melt a wheel in one second? Or even 10 seconds? It’s not remotely plausible for a DEW to spend 10 seconds melting each wheel. Even one second is generous The energy needed to melt a wheel in one second is enormous, 1000 times more than your welding rig.