The Korean Society of Surface Science and Engineering

Zn plating is a technology to prevent steel corrosion, which is a major problem that can occur in various industrial fields. Zn-Mg-Al alloy-coated steel enhances corrosion resistance by incorporating small amounts of aluminum (Al) and magnesium (Mg) into zinc, thereby extending the product’s service life and reducing resource onsumption. PosMAC steel developed and commercialized by POSCO is Zn-Mg-Al hot-dip alloy coated steels for excellent corrosion resistance, and it is widely utilized in automotive and home appliance applications. Despite their widespread use, comprehensive studies on corrosion resistance under diverse environmental exposures are rarely explored. This study evaluates the corrosion behavior of PosMAC steels exposed to high-temperature dry and humid environments for extended periods. Surface chemical composition change was analyzed using energydispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Corrosion resistance was evaluated through potentiodynamic polarization and salt spray tests. Results showed that prolonged exposure to high-temperature dry conditions decrease corrosion resistance, while high-temperature humid conditions maintained stable corrosion resistance over time. These results demonstrate that more superior corrosion resistance of steel can be achieved by exposing to high-temperature humid conditions for a long time. The improvement of corrosion resistance is attributed to the formation of Mg(OH)₂ on the surface through reactions with water vapor, highlighting the importance of environmental conditions on the performance of Zn-Mg-Al alloy coated steel.

Keywords Zn-M g-Al alloy coating; Corrosion resistance; Salt-spray test; PosMAC; Environmental test.