Common surface treatment types and characteristics of hot-dip galvanized steel coils (sheets)

In modern industrial production, hot-dip galvanized steel coils have become an indispensable material in many fields due to their excellent corrosion resistance and processing performance. However, different application scenarios have different requirements for the surface treatment of hot-dip galvanized steel coils.

First, no treatment

No chemical passivation, oiling fingerprint-resistant film coating and other surface treatments are performed. This type of product is prone to surface defects such as white rust, scratches, and friction marks during transportation, storage, and use. This surface can reduce the subsequent degreasing and cleaning pressure, and reduce energy consumption and carbon emissions, but it has extremely high requirements for supply chain management and often causes quality disputes.

Second, only oiling

This surface treatment can reduce the generation of white rust on the surface of the product during transportation and storage. The anti-rust oil applied is generally not used as rolling oil and stamping lubricant for subsequent processing. Oiling is the most common basic surface treatment, with good versatility and strong adaptability, but its protective ability is obviously not as good as the subsequent film surface treatment.

Third, chromic acid passivation and chromium-free passivation (organic)

This surface treatment can reduce the white rust on the surface of the product during transportation and storage. During chromium-free passivation, the hexavalent chromium substances in the passivation film that are harmful to human health are restricted (in compliance with the requirements of the RoHS directive). The passivation film can also reduce the friction between the material and the mold and has a certain lubrication ability, but the main purpose is still corrosion prevention, and lubrication is only an incidental attribute.

Fourth, chromic acid passivation + oiling and chromium-free passivation (organic) + oiling

This surface treatment can further reduce the white rust on the surface of the product during transportation and storage. During chromium-free passivation, the hexavalent chromium substances in the passivation film that are harmful to human health are restricted (in compliance with the requirements of the RoHS directive). Applying oil on the passivation film is common in overseas export orders, especially in Southeast Asia. This is a very effective way to prevent shipping corrosion in tropical areas.

Fifth, chromium-free fingerprint resistance

This surface treatment can reduce the white rust on the surface of the product during transportation and storage, and the fingerprint-resistant film can improve the sweat stain resistance of the surface of electronic or electrical products. Chromium-free anti-fingerprint film restricts hexavalent chromium substances that are harmful to human health (in compliance with the requirements of the RoHS directive). Anti-fingerprint coatings are often used in the manufacture of household appliances, which can effectively prevent the corrosion of parts by finger sweat during assembly and maintenance. The anti-fingerprint film also has a certain stamping lubrication effect.

Sixth, self-lubrication

This surface treatment can reduce the white rust on the surface of the product during transportation and storage, and the self-lubricating film can better improve the forming performance of the steel plate. It takes into account both rust prevention and lubrication and belongs to the film-type product.

Seventh, inorganic solid lubrication

The solid lubricating film produced by this surface treatment can better improve the forming performance of the steel plate. This surface treatment has different definitions in different manufacturers. After consulting some information, it is found that the inorganic solid lubrication of some manufacturers is essentially a pre-phosphating surface treatment. This process has good surface hardness and excellent stamping lubrication effect, but the anti-rust ability is slightly poor.

Eighth, chromium-free, highly conductive and fingerprint-resistant

This surface treatment can reduce the white rust on the surface of the product during transportation and storage, and limit the chromium elements that are harmful to human health. At the same time, the highly conductive and fingerprint-resistant film can further improve the grounding performance of the parts, thereby improving the EMC performance (electromagnetic compatibility) of electronic or electrical products. It is usually used in OA products, such as copiers, printers, etc.

The above are some commonly used surface treatment types. In addition, there are some relatively niche surface treatments, such as chromium-free self-lubrication, chromium-free inorganic passivation, inorganic self-lubrication, easy-to-process self-lubrication, etc. With the advancement of chemical technology, new application scenarios should be responded to. But in general, the surface treatment technology of hot-dip galvanizing is mostly the process of applying a functional film on the surface of the substrate again. The characteristics of the surface treatment are closely related to the characteristics of the film. In manufacturing, the surface treatment can be applied either in advance when purchasing raw materials or after the parts are made. The selection of which method needs to be analyzed in combination with the actual application.