[FrankJ]

Anybody good enough to weld sheet metal should already know not to breathe any welding fumes. Which means only weld in well ventilated areas. Good practice is to remove all coatings from the weld zone so you don't contaminate the weld. Zinc fumes have unpleasant short term effects which is a good enough reason to avoid them. Long term effects have not been documented which is different than no long term effects.

To avoid fuming the zinc you only have to remove it from the heat effected zone. Not really an issue here since you are using it for its cost property (free) not corrosion resistance. (Unless this is a devious game hint) Salt water game!!