How Much Longer Will Zn-Al-Mg-coated Steel Last Than Zinc-coated Steel?

1. What is hot dip galvanizing and zinc aluminum magnesium?

Hot-dip galvanizing: The steel whose surface has been cleaned and activated is immersed in molten zinc liquid. Through the reaction and diffusion between iron and zinc, a zinc alloy coating with good adhesion is plated on the steel surface to form hot-dip galvanizing. 

Zinc-aluminum-magnesium: a new process that adds a certain amount of Al and Mg coating to the original hot-dip galvanizing process to form a zinc-aluminum-magnesium coating with better anti-corrosion properties.

2. Characteristics of the production process:

Hot-dip galvanized products are formed by stamping, bending and drilling ordinary steel plates to form steel products, which are then transported to the factory for hot-dip galvanizing process. The zinc-aluminum-magnesium product directly uses steel strips coated with zinc-aluminum-magnesium coating, which is cold-bent, corrected, fixed in length and punched to form shaped steel, and finally made into a zinc-aluminum-magnesium products. Compared with zinc-aluminum-magnesium products, hot-dip galvanized brackets require an intermediate and repeated logistics process, which will cause unnecessary increases in costs. 

3. Comparison of coating thickness and advantages and disadvantages of anti-corrosion performance:

The coating thickness of the product is determined based on the corrosive environment level of the atmosphere. The coating thickness of the zinc-aluminum-magnesium product is about 70% thinner than that of the hot-dip galvanized product. This is because the coating of the hot-dip galvanized aluminum-magnesium steel plate is denser than that of the galvanized plate, is not prone to coating peeling, has excellent processing properties such as stretching, stamping, bending, and welding under severe conditions, and has high coating hardness and excellent damage resistance.

The atmospheric corrosion level in most coastal areas of my country is C3 or C4. In very few coastal areas, and it can reach C5 level. In the atmospheric corrosive environment of C3~C5, zinc-aluminum-magnesium products have strong advantages in corrosion resistance and durability. 

4. Application characteristics of hot-dip galvanized brackets and zinc-aluminum-magnesium brackets:

It is not recommended to cut and drill hot-dip galvanized brackets after leaving the factory, because cutting and drilling will destroy the zinc layer and require new anti-corrosion measures, otherwise the sulfur dioxide in the air will corrode the brackets and produce "red rust."  

On the contrary, due to the oxidation characteristics of zinc and magnesium elements, zinc-aluminum-magnesium brackets: in a humid corrosive environment, the coating material near the cut is dissolved into the water film attached to the surface of the bare metal, and continuously migrates and dissipates to the exposed cut position, forming a hydrogen A dense protective film (white rust) composed of zinc oxide, alkaline zinc chloride and magnesium hydroxide gradually covers the exposed cut metal, separating the external corrosive medium from the exposed metal matrix, thereby preventing further corrosion of the exposed cut. Therefore, the zinc-aluminum-magnesium bracket can be cut and drilled at will. However, zinc-aluminum-magnesium brackets cannot be welded. At high temperatures, the strength of the solder joints will weaken, affecting the overall bearing capacity of the bracket.