Difference between galvanized sheet and aluminum zinc coated sheet

Differences in composition and coating structure

The difference between galvanized and aluminum-zinc sheets lies in the composition and structure of the coating, which leads to differences in corrosion resistance, service life and applicable environment.

The composition and structure of the coating: a layer of zinc material is uniformly distributed on the surface of the galvanized sheet, this layer of zinc material plays an anodic protective role for the base material, that is, the alternative corrosion of the zinc material protects the use of the base material, and only when the zinc is completely corroded, it can harm the interior of the base material. In contrast, the surface coating of aluminum-zinc coated sheet consists of 55% aluminum, 43.5% zinc, and a small amount of other elements. Microscopically, the surface of the aluminum-zinc coating has a honeycomb structure, with the zinc contained within the aluminum “honeycombs.” While this structure also plays a role in anodic protection, the role of anodic protection is greatly reduced due to the reduced zinc content and the fact that zinc material wrapped in aluminum is not easily electrolyzed.

Corrosion resistance and service life: The aluminum-zinc alloy structure of aluminum-zinc coated steel sheets forms a strong and effective barrier against the penetration of corrosive factors, and its corrosion resistance is due to the protective function of the aluminum barrier layer and the sacrificial protective function of zinc. Tests under equivalent external conditions have shown that the service life of aluminum-zinc-coated steel sheets is more than four times that of galvanized sheets.

Environment and maintenance: In cities with humid air and a lot of rain, once rust appears on a certain area of aluminum-zinc coated sheet, if not taken timely action, the rusted area will become larger and larger, and eventually even the whole sheet will be affected. Galvanized sheets, on the other hand, will not spread, even if corrosion occurs in a single point. In addition, because of the complexity of the microstructure of zinc-aluminum sheet, after the sheet is cut, the cut edge is basically lost, in the case of protection will soon rust, so zinc-aluminum sheet should be cut as rarely as possible, and after cutting, anti-corrosion or zinc-rich paint should be used to protect the edge, so as to extend the service life of the sheet.

In general, while aluminum-zinc coated sheet is superior to galvanized sheet in appearance and some properties, its complex construction and higher maintenance requirements limit its use in some applications. The choice of sheet depends on the specific operating conditions and maintenance costs.