55. How does zinc adhere firmly to steel?

The formation of a zinc coating on steel pipes occurs through complex physical and chemical interactions between the pipe and molten zinc. Liquid zinc can corrode and dissolve most metals regardless of their melting points. Taking dry hot-dip galvanizing as an example: Steel pipes coated with zinc chloride solution are first heated to 200-250°C in a drying furnace, then immersed in molten zinc at 480-500°C. Instantly, the pipes absorb massive heat, causing the zinc liquid on their surface to cool rapidly and solidify into a protective shell. As continuous heat supply melts this shell, the zinc layer forms when the pipe's surface temperature balances with the molten zinc's temperature. The process involves: 1) Solid iron dissolving into zinc; 2) Iron and zinc combining to form an iron-zinc alloy layer; 3) A pure zinc layer forming on the alloy's outer surface, which crystallizes upon cooling; 4) The zinc layer bonding with the steel substrate. Essentially, hot-dip galvanizing creates the zinc coating through diffusion processes.