1.What are the consequences of a failure in the surface coating system?
Mechanical damage: Scratches, abrasions, and impacts during transportation, installation, and use can damage the coating, directly exposing the metal substrate.
Coating aging: Long-term exposure to ultraviolet radiation, high temperatures, humidity, and chemicals can cause the coating to chalk, fade, become brittle, and crack (micro-cracks), losing its protective properties.
Coating quality defects: Inherent defects during production, such as uneven coating, missed areas, pinholes, bubbles, and poor adhesion, become the starting point for corrosion.
Chemical corrosion: Strong acids, strong alkalis, salt spray, and other chemicals directly erode the coating, damaging its structure.
2.What are the effects of corrosion on the cut and edges?
Cause: After the pre-coated steel coil is sheared, punched, and sawn, the metal cross-section is completely exposed without any coating protection.
Process:
Corrosive media (water, oxygen) penetrate through the cut.
If the substrate is galvanized steel, the zinc layer will act as a sacrificial anode, preferentially corroding to protect the steel base. However, if the coating is too thin or the corrosive environment is too strong (such as a high chloride ion environment), the protection will be quickly exhausted.
If the cut is not properly protected (e.g., no sealing treatment), corrosion will spread inward from the edge, forming "under-film corrosion" under the coating, leading to coating bulging and large-scale peeling.
3.What are the consequences of metal coating failure?
Coating depletion: In humid environments, the coating (especially zinc) is continuously consumed through a "sacrificial anode" effect to protect the steel substrate. Once the coating is completely consumed, the steel substrate begins to corrode.
Poor coating quality: Uneven coating thickness, poor adhesion, or defects will prematurely lose their protective function.
Differences in coating types: The corrosion resistance of ordinary galvanized steel sheets, especially their cut edge protection, is far inferior to that of aluminized zinc and zinc-aluminum-magnesium steel sheets. The latter two have denser corrosion products and "self-healing" properties, resulting in stronger resistance to cut edge oxidation.
4.What are the effects of environmental and design factors?
High Humidity/Condensation Environment: Sustained high humidity or frequent surface condensation provides the necessary electrolyte for electrochemical corrosion. Poorly ventilated, enclosed spaces are particularly vulnerable.
Corrosive Atmosphere:
Industrial Pollution: Contains acidic gases such as sulfur dioxide and hydrogen sulfide, which react with water to form acid, accelerating corrosion.
Marine Environment: Contains large amounts of chloride ions, which have extremely strong penetrating power and can destroy passivation films, making it one of the most corrosive environments.
Design Defects:
Water Accumulation Structure: Recesses on the panel surface or improperly designed joints lead to long-term water accumulation.
Galvanic Corrosion: Direct contact between the coated coil and more reactive metals (such as certain aluminum alloys) or stainless steel creates a galvanic cell in the presence of an electrolyte, accelerating its own corrosion.
Crevice Corrosion: Severe localized corrosion occurs in narrow crevice areas formed at overlaps and bolted connections due to differences in oxygen concentration.
5.What are the key measures to prevent oxidation and corrosion?
Proper Material Selection: Choose a highly corrosion-resistant substrate (preferably zinc-aluminum-magnesium or aluminum-zinc coated sheet) and coating (such as PVDF fluorocarbon) according to the operating environment.
Protective Coating: Avoid any mechanical damage during transportation, installation, and use.
Sealed Cuts: Seal all cut surfaces and drilled holes with neutral silicone weather-resistant sealant or a special anti-corrosion coating.
Optimized Design: Prevent water accumulation and structural gaps to prevent galvanic corrosion and ensure good ventilation.
Proper Storage: Store in a dry environment and keep the packaging intact.