Are galvanised steel parts safe to use in space (high-vacuum environment), e.g. washers, fasteners, nuts? I've heard that zinc can sublimate at low pressures.
It's not just zinc. Pure tin coatings and cadmium coatings are also prohibited, at least in the vicinity of electronics. See the Prohibited Materials Section of the NASA Parts Selection List (NPSL).
NASA Technical Standard 6012 (NASA-STD-6102), Corrosion Protection for Space Flight Hardware, appears to prohibit zinc and cadmium coatings anywhere in a spacecraft.