1.How does zinc liquid composition regulation affect zinc flowers?
Lead: A key element of traditional zinc flowers. Lead has low solubility in zinc liquid and will be enriched at the grain boundary when the zinc layer solidifies, reducing the resistance of crystal growth and promoting the expansion of dendrites to the surrounding areas, forming large zinc flowers with a diameter of several millimeters. The addition amount is usually 0.05%-0.2%, but due to environmental restrictions, it is gradually being replaced.
Antimony and tin: Environmentally friendly options to replace lead. Antimony or tin can reduce the surface tension of zinc, enhance the anisotropic growth of crystals, form larger zinc flowers, and have little effect on the adhesion of the coating. They are widely used in large zinc flower plates for construction.
Cadmium: The effect is similar to lead, but it is more toxic. It is only used in small quantities in special scenarios and is now basically banned.
2.What are the elements that promote the formation of "small spangles" or "no spangles"?
Aluminum: The most commonly used element for refining zinc spangles. Aluminum can form Al-Zn intermetallic compounds (such as Fe₂Al₅ alloy layer) in zinc liquid, quickly forming a uniform "barrier layer" on the surface of the steel plate, and aluminum will be adsorbed on the surface of the crystal nucleus to inhibit excessive crystal growth. When the aluminum content is ≥0.15% (such as flowerless galvanized sheet), the size of the crystal nucleus can be significantly reduced to form fine zinc spangles with a diameter of less than 0.5mm; if the aluminum content is ≥0.2%, it can even inhibit the exposure of zinc spangles and form a "zinc spangle-free" surface.
Nickel and magnesium: In the zinc-aluminum alloy coating, nickel or magnesium will form a solid solution with zinc, increase the density of the crystal nucleus, limit the growth of crystals, form fine and uniform zinc spangles, and improve the corrosion resistance of the coating.
3.What are the elements that promote the formation of "small spangles" or "no spangles"?
Aluminum (Al): The most commonly used element for refining zinc spangles. Aluminum can form Al-Zn intermetallic compounds (such as Fe₂Al₅ alloy layer) in zinc liquid, quickly forming a uniform "barrier layer" on the surface of the steel plate, and aluminum will be adsorbed on the surface of the crystal nucleus to inhibit excessive crystal growth. When the aluminum content is ≥0.15% (such as flowerless galvanized sheet), the size of the crystal nucleus can be significantly reduced to form fine zinc spangles with a diameter of less than 0.5mm; if the aluminum content is ≥0.2%, it can even inhibit the exposure of zinc spangles and form a "zinc-free" surface.
Nickel (Ni), magnesium (Mg): In zinc-aluminum alloy coatings (such as Galvalume, Zn-Mg-Al), nickel or magnesium will form a solid solution with zinc, increase the density of the crystal nucleus, limit crystal growth, form fine and uniform zinc spangles (diameter 0.1-0.3mm), and improve the corrosion resistance of the coating.
4.How does the surface roughness of steel plates affect zinc spangles?
Rough surfaces (such as those treated by pickling or sandblasting) can provide more "nucleus attachment points", promote the simultaneous crystallization of zinc liquid at multiple sites, increase the number of nuclei, and make zinc flowers smaller.
Smooth surfaces (such as cold-rolled steel plates) have fewer nucleus attachment points, and are prone to forming a few dominant nuclei and growing into large zinc flowers. Therefore, if small zinc flowers are needed, the surface roughness of the steel plate can be appropriately increased (such as adjusting the roughness of the cold-rolling roller).
5.How does the oxide layer on the steel plate surface affect the zinc spangles?
If there is an oxide layer (FeO, Fe₃O₄) left on the steel plate before it enters the zinc pot, it will react with the zinc liquid to form a Fe-Zn alloy layer, which will interfere with the uniform crystallization of zinc and may cause uneven zinc flowers.
Pretreatment (such as annealing reduction) can convert the oxide layer into a pure iron surface, ensuring uniform wetting of the zinc liquid and more controllable crystallization: the pure iron surface is more likely to form uniform crystal nuclei, and if combined with rapid cooling, small zinc flowers can be obtained stably.