62. How does magnesium in molten zinc affect hot-dip galvanizing?

Magnesium (Mg), a silvery-white element with a hexagonal crystal structure, has a relative atomic mass of 24.32, melting point of 650°C, and boiling point of 1120°C. The incorporation of magnesium into zinc significantly enhances corrosion resistance, with even trace amounts (0.024-0.084%) proving effective. However, at 0.3-0.5% concentration, magnesium causes the zinc coating to thicken and roughen, developing a milky-white appearance while increasing thermal conductivity and reducing adhesion. Exceeding 0.6% concentration, the coating becomes thinner. During zinc oxidation, magnesium facilitates the formation of magnesium oxide, which more readily transfers oxygen to zinc than zinc does directly from the air. Magnesium is generally excluded from zinc-coated steel pipes for water and gas transmission unless in special applications.