What is PosMAC (POSCO Magnesium Aluminium Alloy Coating Product) ?

  • - PosMAC is a ternary alloy coated steel(Zn-94.5%, Mg-3%, Al-2.5%) with high corrosion resistance developed by POSCO’s own technology.
  • - PosMAC is a corrosion resistant product that is 5 to10 times stronger resistant than that of a normal hot-dip galvanized steel sheet(GI, GI(H)) with the same coating weight. PosMAC has an excellent cross-section corrosion resistance; nomal thick plating products can be replaced with this product.
  • - The same processing, assembly and painting process can be applied to PosMACas one would apply to GI.

Corrosion resistance of PosMAC

  • - The magnesium(Mg) in PosMAC’s coating layer will accelerate formation of a dense corrosion product called “Simonkolleite” which is extremely stable. When simonkolleite is formed on the surface of the coating layer in a film-like-form, it plays a role as acorrosion inhibitor for the base metal.
  • - In addition, the upper coating layer can be dissolved to cover the cross-section and accelerate the growth of a stable corrosion product. However red-rust can be found in the already exposed steel plate, but for tunately, the film of the corrosion products covers the cross-section and serves to prevent corrosion.

Higher corrosion resistance

  • - PosMAC shows 5 to 10 times the corrosion resistance compared to galvanized steel sheet on flat surfaces.
  • - In addition, PosMAC shows equal or greater corrosion resistance than galvalume on flat surfaces
CCT GI(H) Galvanume PosMAC
The coating weight
on both side
120g/㎡ 200g/㎡ 300g/㎡ 600g/㎡ 100g/㎡ 140g/㎡ 200g/㎡ 275g/㎡
10 cycle
70 cycle
120 cycle

Weathering test on cross-section part (Korea conformity laboratories)

  • - PosMAC also gets red-rust in cross-section parts when initially exposed outdoors. However as the time goes by, the corrosion (red-rust) area of PosMAC tends to decrease through the formation of its distinctive oxide-based material(simonkolleite).
Sample Thickness Coating
Cross-section image
After 6 months After 1 years After 2 years
PosMAC 1.2 130
1.6 120
2.0 300
Galvanume 1.6 120
GI(H) 1.6 180

Product charcteristics comparison

Quality items PosMAC GI(H) Galvanume
Hardness(Hv) of coating layer 110~130 60~80 80~100
Friction Characteristics X
Flat sheet
Cross-section X
Chemical resistance