What Is The Self-healing Incision of Zinc, Aluminum And Magnesium Products?

In a humid and corrosive environment, the coating material near the cut will continue to penetrate into the exposed cut location by dissolving into the water film attached to the bare metal surface. A dense protective film (white rust) composed of zinc hydroxide, alkaline zinc chloride and magnesium hydroxide is formed to separate the external corrosive medium from the exposed cut metal matrix. This process lasts long and has low electrical conductivity, reducing further corrosion of the cut surface.

The red rust area of zinc-aluminum-magnesium-coated exposed steel plates is larger than the white rust area when corrosion begins. As time goes by, the area of white rust increases and the area of red rust decreases, which indicates that the zinc-aluminum-magnesium coating has certain self-healing properties. Therefore, the zinc-aluminum-magnesium coating can better protect the cut edges, welding areas and areas damaged by deformation of the steel plate.

If in a humid corrosive environment, the formation of red rust on the cut surface is faster than the dissipation and diffusion speed of the water film layer containing coating components, red rust will first form on the exposed cut. The time it takes for red rust to form depends on the humidity of the environment, the corrosion resistance of the base metal, and the thickness of the substrate. In the early stage of corrosion, the area of red rust on the exposed steel part of the cut is larger than the area of white rust. As the corrosion time increases, the water film layer containing coating components begins to spread, and the area of white rust begins to decrease. This process will continue for months or years until the plating near the cutout that can be diffused is exhausted.

On the contrary, during the immersion test in acid-base solution or neutral solution, red rust is basically not visible on the cut surface, but white rust will form before the exposed cut surface. This is because the water film layer containing the coating components dissipates and spreads faster than the speed at which red rust forms on the cut surface.

The dissipation of the water film layer containing coating components causes the time for metal corrosion on the cut surface to form red rust to be prolonged. Then, in a long-term corrosive environment, the red rust area is covered with white rust, preventing further corrosion of the metal and reducing the corrosion rate. The dense corrosion products formed by the zinc-aluminum-magnesium coating have high adhesion and low conductivity, which isolate the corrosive medium. However, this does not mean that the corrosion resistance of the cut surface can be consistent with that of the coating body, nor does it mean that red rust will not appear on the cut surface during processing, storage, transportation or use.