1.What is the corrosion process of DX51D?
Initial stage: The zinc layer is intact, with the strongest corrosion resistance and almost no risk of substrate corrosion.
Mid-stage: The zinc layer is gradually consumed, and white corrosion products (basic zinc carbonate, etc.) are formed on the surface. Although it can slow down the corrosion rate, the protection ability is reduced.
Late stage: The zinc layer is consumed in large quantities or even penetrated, the substrate (steel) is directly exposed, red rust corrosion (iron oxide) occurs, and the corrosion resistance is significantly reduced.
2.What are the factors that affect the corrosion resistance decay rate of DX51D?
Environmental erosion intensity
Mild environment (such as dry indoors): slow corrosion rate, slow zinc layer consumption. For example, DX51D with a coating thickness of 80 g/m² can be maintained indoors for 10-15 years without obvious red rust.
Harsh environment (such as coastal areas, industrial acid rain areas): chloride ions, acidic gases, etc. accelerate the corrosion of the zinc layer, and the life may be shortened to 5-8 years (with the same thickness of the coating).
Coating thickness and initial state
The greater the thickness: the more the total zinc layer is consumed, the longer the corrosion resistance life.
Coating defects: If there are problems such as missed plating and uneven plating at the factory, corrosion perforation will occur in local areas in advance.
Processing and maintenance conditions
Processing damage: bending, welding and other operations cause damage to the coating, and the unrepaired exposed areas will form a "corrosion battery", which accelerates the consumption of the surrounding zinc layer (as shown in the figure).
Maintenance measures: Regularly cleaning surface pollutants and repainting the damaged parts (such as zinc-rich paint) can delay corrosion decay.
3.What are the stages of the corrosion process?
Initial stage: the coating is complete and the passivation film is good; the surface is silvery white and bright, without rust; the corrosion resistance basically maintains the original value.
Mid-term: the zinc layer is partially consumed, and white rust appears locally; there are white powdery corrosion products on the surface; the corrosion resistance decreases by about 30-50%.
Late stage: the zinc layer is significantly thinned, the substrate is exposed; red rust (iron rust) appears, and the coating peels off; the corrosion resistance drops sharply and needs to be replaced.
4.What are the feasible ways to extend the corrosion resistance life?
Choose a more corrosion-resistant coating: Use zinc-aluminum-magnesium coating (such as DX53D), which has 2-5 times the corrosion resistance of ordinary galvanizing, and the corrosion products are denser, which can slow down the decay rate.
Composite protective coating: Apply organic coating after galvanizing to form a "plating + coating" double protection to isolate environmental erosion.
Regular maintenance and repair: timely zinc supplement or anti-corrosion coating of exposed substrates to prevent corrosion from spreading.
5.What is the nature of corrosion?
The corrosion resistance of DX51D mainly depends on the "sacrificial anode" effect of the plating layer:
The metal activity of zinc is stronger than that of iron. When the plating layer forms a galvanic couple with the substrate (steel), zinc corrodes first, thus protecting the steel substrate from rust.