Phosphating treatment forms a dense phosphate film (such as zinc phosphate or iron phosphate film) on the metal surface through a chemical reaction, blocking oxygen and moisture from direct contact with the metal and slowing down the rate of corrosion of the substrate, which is especially suitable for short-term rust prevention needs.
Author: Anna
The core role of phosphating
1. Enhance corrosion resistance
Phosphating treatment forms a dense phosphate film (such as zinc phosphate or iron phosphate film) on the metal surface through a chemical reaction, blocking oxygen and moisture from direct contact with the metal and slowing down the rate of corrosion of the substrate, which is especially suitable for short-term rust prevention needs.
For example, after galvanized sheet phosphating, the phosphate film can make up for the microporous defects in the zinc layer and improve the overall corrosion resistance.
2. Improve coating adhesion
Phosphate film surface has a microporous structure, which can significantly increase the mechanical occlusion between the coating, plating layer or adhesive and the substrate to avoid coating flaking.
In galvanized steel before coating, phosphating treatment can prevent alkyd-based coatings and zinc layer saponification reaction, to protect the long-term bonding stability of the coating and the substrate.
3. Lubrication and processing assistance
Phosphate film can reduce the coefficient of friction of the metal surface, used in cold rolling, stamping and other processing links, to reduce die wear and improve molding efficiency.
Part of the phosphating film (such as manganese phosphating) both lubrication and wear resistance, suitable for bearings, gears and other moving parts.
4. As a key step in pre-treatment for painting
Phosphating treatment provides a clean, uniform active surface for painting, enhances the uniformity and chemical resistance of subsequent coatings, and is widely used in automobiles, home appliances and other industrial fields.
Phosphate primers (e.g. vinyl phosphate primer) can form a phosphated passivated composite film directly on the surface of galvanized steel, simplifying the painting process and enhancing the protective performance.
Examples of application scenarios
Automotive manufacturing: phosphating the body steel plate and then painting to improve the durability of the paint surface.
Fastener processing: phosphating to replace part of the galvanized scene, reduce costs and meet the short-term demand for rust prevention.
Metal processing: cold rolled steel plate stamping after phosphating to reduce processing damage.
Limitations
The long-term corrosion protection of phosphating film is weaker than passivation treatment (e.g. chromate passivation), and needs to be used in conjunction with coating or plating.
Phosphate solution composition contains heavy metals (such as zinc, nickel), environmental protection requirements tend to promote the development of non-polluting phosphating technology.