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Zinc-Aluminum-Magnesium coated steel, also known as ZAM-coated steel, is an innovative steel finish with superior corrosion resistance. Initially, pure zinc alloys were primarily used to enhance the corrosion resistance of metal surfaces. With continuous innovation in steel manufacturing technology, corrosion-resistant coated steels like zinc-aluminum alloys and ZAM alloys continue to emerge in the market, significantly improving the corrosion resistance of steel surfaces.
Zinc-Aluminum-Magnesium coated steel refers to a coated steel where a specific amount of Al and Mg is added to existing hot-dip galvanized coatings, or Mg is added to hot-dip galvanized coatings. It offers high corrosion resistance performance and excellent cut-edge protection.
A broad analysis of commercially available magnesium-containing coated steel shows that the Mg content in most coatings is ≤3%. Thus, based on aluminum content, zinc-aluminum-magnesium coatings are classified as follows:
Low-Aluminum Zn-Al-Mg Coating (Al: 1–3.5%):
Formed by adding aluminum-magnesium and other elements to a hot-dip galvanized base. This coating has been tested on color coating lines, and low-Al Zn-Al-Mg steel sheets (known as BZM coated steel and its color-coated variants) have been successfully developed. It represents an enhanced corrosion-resistant version of pure hot-dip zinc coating.
Medium-Aluminum Zn-Al-Mg Coating (Al: 5–11%)
High-Aluminum Zn-Al-Mg Coating (Al: 55%):
Formed by adding magnesium and other elements to a hot-dip Al-Zn base. This coating has been tested on color coating lines, and high-Al Zn-Al-Mg color-coated steel sheets (known as BAM coated steel) have been successfully developed. It is an enhanced corrosion-resistant version of hot-dip Al-Zn coating.
Galvanized Coating (GI):
An economical anti-corrosion coating (Zn ≥99%).
Classified as spangled or non-spangled; both offer similar corrosion resistance.
Non-spangled versions provide better aesthetics for painted/post-sprayed applications.
Thick zinc layers typically feature spangles (e.g., 275g/m² coating weight).
Aluzinc Coating:
Alloy metal coating (55% Al, 43.5% Zn, 1.5% Si).
Corrosion resistance is 2–6× better than GI coatings of equivalent weight.
Surface can be modified to produce uniform spangles for construction/exterior use.
Disadvantages:
Inferior weldability compared to GI (welding should be minimized).
Worse cut-edge protection than both GI and Zn-Al-Mg coatings.
Zn-Al-Mg Coating:
Excellent all-round performance with marginally higher manufacturing costs than Aluzinc.
Significantly superior corrosion resistance and cut-edge protection.
Weldability comparable to GI steels.
Zn-Al-Mg color-coated steel sheets are now mass-produced and widely used.
Future Outlook:
As material requirements in construction and industries increase, Zn-Al-Mg coated steel sheets are expected to gradually replace Aluzinc sheets in the market.
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