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1. The surface of the plated parts is not clean
The surface of the plated parts contains paint, grease, soldering; iron oxide; under-pickling.
2. Pickling and operation
Under-pickling leaves iron oxides on the surface of the plated parts; over-pickling causes the surface structure of the steel substrate to be destroyed. The Si and a small amount of active metal refractory oxides attached to the plated parts prevent Combination of iron and zinc. Or due to over-pickling, the plated parts can absorb hydrogen. When zinc plating, hydrogen gas etc. expands due to heat to escape and miss plating.
The plating parts are superimposed and accumulated during pickling, resulting in missed washing, or due to the structural reasons of the plating parts, they are neglected and turned over, causing vortex gas and missed washing.
3. Assistant plating
The concentration of the additive is low, and the plating effect is not ideal; the ratio of the additive is inappropriate and the content of zinc salt is high, which makes the auxiliary salt film easy to absorb water and deliquesce, and the hydroxide decomposes into a gas and explodes zinc, thereby forming a leaky plating.
4. Composition of zinc solution
The aluminum content in the zinc solution is too high, resulting in missed plating.
5. Plated material
The surface of the steel contains refractory oxides of silicon and aluminum, which prevents the iron-zinc reaction;
The steel substrate contains too much carbon, or the steel produces too much iron carbide during the refining process, which makes the combination of iron and zinc difficult, resulting in missed plating;
Defects in the processing and forming of the plated material cause the material to crack, and acid liquid, moisture, and additives enter the material, causing missed plating.