1.In a dry indoor environment, what is the corrosion resistance of DX51D?
Corrosion mechanism: The surface of the zinc layer is only slightly oxidized, forming a thin passivation film (basic zinc carbonate) to inhibit further corrosion. There is almost no electrochemical corrosion, and the steel substrate is completely protected.
Data reference: Zinc layer corrosion rate: about 0.1-0.3 μm / year (almost negligible).
Salt spray test equivalent life: If the zinc layer weight is 80g/m², the equivalent indoor life can reach more than 80 years (estimated based on 1 hour of salt spray test ≈ actual 1 year).
Appearance changes: After long-term use, white rust (zinc hydroxide, non-destructive corrosion) may appear on the surface of the zinc layer, but there is no red rust (steel corrosion).
White rust can be wiped off with a dry cloth without affecting the performance of the substrate.
2.How does DX51D perform in a rural/suburban environment?
Corrosion mechanism: The zinc layer reacts with water and oxygen to form zinc hydroxide, which is further converted into a stable basic zinc carbonate passivation film with a slow corrosion rate.
Data reference: Zinc layer corrosion rate: about 0.6-1.0 μm / year.
When the zinc layer weight is 150g/m², the service life can reach 30-50 years (it takes about 150/1=150 years for the zinc layer to be completely corroded. In fact, considering the film protection, the service life is longer).
Appearance changes: A gray-white passivation film is formed on the surface, with no obvious corrosion pits or red rust.
3.What is the corrosion resistance performance of DX51D in urban/industrial environments?
Corrosion mechanism: SO₂ dissolves in water to generate sulfurous acid (H₂SO₃), which destroys the passivation film of the zinc layer and causes electrochemical corrosion. The zinc layer corrodes first and consumes faster.
Appearance changes: Dark gray corrosion products may appear on the surface, the zinc layer may become thinner locally, and small areas of red rust may appear after long-term exposure.
4.What is the corrosion resistance performance of DX51D in coastal/salt spray environment?
Corrosion mechanism: Cl⁻ reacts with zinc to form zinc chloride (ZnCl₂), which is easily soluble in water and cannot form a protective film, resulting in continuous corrosion of the zinc layer.
The electrochemical corrosion rate is significantly accelerated, and even if the zinc layer is intact, Cl⁻ may penetrate through the grain boundaries.
Appearance changes: Dense small pits appear on the surface of the zinc layer, which gradually peel off over time, exposing the steel matrix and quickly generating red rust.
5.What is the corrosion resistance of DX51D in industrial acid and alkali environments (such as chemical plants and pickling workshops)?
Corrosion mechanism: Zinc reacts with acid to generate hydrogen and zinc salts (such as Zn + 2HCl → ZnCl₂ + H₂↑), and reacts with alkali to generate zincates (such as Zn + 2NaOH → Na₂ZnO₂ + H₂↑), which quickly dissolve the zinc layer.
Appearance changes: The surface of the zinc layer quickly turns black and peels off, and the steel substrate is directly corroded, generating red rust and yellow corrosion products.