Metal coating provides protection for steel, so that it can ensure the steel used in a variety of challenging environment. Metal coating provides two main types of protection: the shielding protection and current protection in specific circumstances.
It will be drying and hardening while applying metals such as zinc coated steel so that can form an impervious barrier to prevent water infiltration. This eliminates the necessary component for corrosion that oxidation would not have happened without electrolyte/water (moisture), so the steel won’t rust.
Another important aspect of barrier protection is corrosion protection membrane. Some metals such as aluminum can form protective oxide film on the surface when react with oxygen. The oxide film is elastic and firmly attached on the surface of aluminum to prevent water infiltration and further corrosion. It made the aluminium ideal material of sheet metal.
Zinc is often used in coating structural steel. It will react with oxygen in the air and water then form corrosion products, which can form a protective layer to protect the underlying steel.
Zinc is a kind of active metal, however, it will slowly corrode and erode over time. So the degradation rate of zinc is still a few times lower than steel, and it can significantly extend the intent to protect the service life of steel.
The second method of metal coating protection is to sacrifice coating and provide current protection for the underlying steel.
For example, if the underlying steel exposed because of the scratches or serious coating damage of cutting edge, the surrounding coating will be corroded first before the steel.
Current protection (also known as the cathode protection) is due to the electronegativity of zinc was stronger than iron/steel. When the zinc coating is coated, it will be corroded first as a sacrificial anode, and the bottom of the steel is protected as a cathode. The current corrosion will continue till the coating anode materials (zinc) are completely consumed.
The current protection is very important since the coating would inevitably be scratched or damaged especially in building. Because of this, zinc metal coating is better than that of aluminum coating in the protection of steel members. Although the current series of zinc and aluminum is very close to nature, the protective oxide film formed by aluminum is difficult to penetrate and will not be consumed by corrosion, so as not to provide current protection for the damaged steel.
Metal coating combined shielding effect and current protection, which provides an application versatility, cost, and unparalleled corrosion protection. It is the effective method to protect the other metals such as iron and steel is a metal alloy (technology) from degradation due to corrosion.
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