1.How does hardness affect scratching?
When the base metal of the galvanized coil (such as cold-rolled steel sheet) has a higher hardness, it has a stronger ability to resist deformation by external forces. If the surface galvanized layer is well combined with the base, when subjected to the same external force (such as friction, collision), the base is not easy to cause the coating to crack or scratch due to deformation.
If the galvanized layer itself has a higher hardness (such as zinc-iron alloy coating through alloying treatment), its surface's ability to resist scratching by sharp objects will also be improved, reducing scratches to a certain extent.
2.How does the thickness and toughness of the zinc coating affect scratch resistance?
Coating thickness: A thicker galvanized layer can provide more sufficient "buffer" for the substrate. Even if it is subjected to external force, it is not easy to directly damage the substrate or cause penetrating scratches on the coating; while a thin coating is more easily scratched under the same external force.
Coating toughness: If the galvanized layer is too hard but brittle, it may crack due to lack of ductility when it is impacted or rubbed, resulting in "hard and brittle" scratches; on the contrary, a galvanized layer with good toughness can absorb external forces through slight deformation and reduce scratches even if the hardness is not high.
3.How do surface finish and coating condition affect scratch resistance?
The smoother the surface (such as zinc spangle-free and mirror-finished galvanized coils), the smaller the contact area of external forces (such as sharp objects) and the greater the local pressure, which may make it easier to produce scratches; while a slightly rough surface (such as normal zinc spangles) may disperse external forces and reduce scratches due to the large contact area.
If there is oxidation, rust or oil on the surface of the galvanized layer, the integrity of the coating will be reduced. Even if the hardness is high, it is easy to produce scratches along weak points (such as oxide layers) when subjected to force.
4.What effect does external force have on scratches?
The difficulty of scratching is directly related to the external force: galvanized coils of the same hardness may not be scratched under slight friction, but under the strong pressure of sharp objects, they may be scratched even with high hardness. The more vertical the external force angle, the easier it is to break through the hardness defense line of the coating; while oblique friction depends more on the wear resistance of the coating rather than the hardness alone.
5.In actual scenarios, what are the differences in scratch resistance of different hardness?
Low-hardness galvanized coil: has good toughness, but the surface is easily scratched by hard objects, which is suitable for scenes with low requirements on appearance and emphasis on corrosion resistance.
Medium-high hardness galvanized coil: while maintaining a certain toughness while increasing hardness, the scratch resistance is better than that of low-hardness products, which is suitable for scenes that require both formability and wear resistance.
Special coating with too high hardness: if the brittleness increases, the coating may crack in the collision, which is not conducive to scratch resistance.