Hot-dip galvanizing is the reaction of molten metal with an iron substrate to produce an alloy layer, thereby combining the substrate and the plating layer. Hot-dip galvanizing is to pickle iron and steel parts first. In order to remove iron oxide on the surface of iron and steel parts, after pickling, it is cleaned in an ammonium chloride or zinc chloride aqueous solution or a mixed solution of ammonium chloride and zinc chloride. And then sent to the hot-dip plating bath. Hot-dip galvanizing has the advantages of uniform coating, strong adhesion and long service life.