This work focuses on the corrosion resistance of a newly developed Zn-Al-Mg alloy coating system for steel containing Zn + 2 wt.-% Mg + 2 wt.-% Al (ZM) in comparison to the conventional zinc coating (HDG). Both systems were produced via hot-dip galvanizing on a large scale plant and comprise an average coating thickness of 7 μm. The corrosion resistance was evaluated by exposure to standardized laboratory corrosion test.

Tests with and without chloride were used. In the tests with chloride addition the influence of pH value was considered as well. In chloride-free atmosphere the effect of drying and temperature changes were included in the investigation.

It could be shown that the newly developed ZM coating forms a stable, well-adherent corrosion product layer of zinc aluminum carbonate hydroxide, Zn6Al2(CO3)(OH)16·4 H2O, next to the steel substrate in all tested environments. This protective corrosion product layer is responsible for the enhanced corrosion resistance of ZM-coated steel in comparison to HDG steel.

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