1.What effects do freeze-thaw cycles have on the protective properties and stability of the galvanized coating?
Increased risk of coating damage
The cyclic freezing and thawing will cause micro stress on the surface of the galvanized layer or the base metal (such as the squeezing effect when water freezes and expands). Long-term accumulation may cause cracks, peeling or flaking of the coating, destroying its continuity and reducing its anti-corrosion ability.
Accelerated corrosion process
During the freeze-thaw process, water repeatedly penetrates into the pores or damaged parts of the coating. If there are salts, pollutants, etc. in the environment, electrochemical corrosion conditions will be formed, resulting in accelerated consumption of the zinc layer and even rust of the base metal.
Decreased adhesion performance
Frequent temperature changes will weaken the bonding between the galvanized layer and the substrate. Especially when there are micro defects in the coating, the freeze-thaw cycle may aggravate the interface separation, causing the protective layer to lose effective protection of the substrate.
Effect of low-temperature brittleness
Zinc becomes more brittle at low temperatures. The sudden temperature change in the freeze-thaw cycle may cause the coating to become brittle and more easily shattered when subjected to external forces, further reducing its protective effect.
2.How to reduce the impact of freeze-thaw cycles on galvanized coatings?
Enhance the anti-freeze-thaw ability of the galvanized layer
Increase the thickness of the galvanized layer: A thicker coating can provide more sufficient "zinc reserves" for the substrate, delaying the consumption and damage of the coating caused by freezing and thawing.
Optimize the galvanizing process: Use lead-free galvanizing, alloy galvanizing and other processes to improve the density, toughness and bonding strength of the coating with the substrate, reduce pores and defects, and reduce the risk of moisture penetration.
Improve the use environment and reduce freeze-thaw damage conditions
Avoid residual water accumulation: optimize structural drainage during design to ensure that there is no water accumulation on the surface of galvanized parts and reduce repeated water penetration during freeze-thaw cycles.
Control environmental corrosiveness: remove salt, industrial pollutants, etc. around galvanized parts, and use isolation measures when necessary to reduce the contact between corrosive media and the coating.
Regular maintenance and timely repair
Regular inspection and cleaning: Before the cold season, check whether the galvanized layer is damaged, peeling or rusted, and remove snow, ice chips and impurities on the surface in time to avoid impurities from aggravating wear during freezing and thawing.
Local repair of defects: When the coating is damaged, use zinc spray, zinc-rich paint, etc. to quickly repair it to restore the integrity of the protective layer and prevent the damage from expanding corrosion due to freezing and thawing cycles.
3.Does the effect of freeze-thaw cycles on the galvanized coating have anything to do with ambient humidity?
Humidity provides a "medium" for the freeze-thaw cycle, amplifying the effect of physical stress. The core of the freeze-thaw cycle is the "freezing-thawing" process of water, and the ambient humidity directly determines the moisture content on the surface of the galvanized layer and its defects.
High humidity accelerates electrochemical corrosion and forms "synergistic damage" with freeze-thaw cycles. The moisture in the freeze-thaw cycle not only produces physical stress, but also acts as an electrolyte, causing electrochemical corrosion at defects in the zinc coating.
4.Within what humidity range is the greatest impact on the freezing and thawing of the galvanized layer?
When the relative humidity exceeds 60%, the freeze-thaw effect on the galvanized layer is greater. When the humidity is in this range, a water film is easily formed on the surface of the steel, providing an electrolyte channel for electrochemical corrosion. If there is a freeze-thaw cycle at the same time, it will accelerate the damage of the galvanized layer.
Especially when the humidity is in the range of 85%~95%, the corrosion reaction will be more intense. At this time, the water film on the surface of the galvanized layer is thicker and may be rich in oxygen, which will become an ideal corrosion condition. If there is also the physical stress caused by the freeze-thaw cycle, it will significantly accelerate the damage of the galvanized layer.
5.How should the galvanized layer be protected when the humidity exceeds 95%?
Strengthen the waterproof and sealing properties of the coating itself
Block the contact between moisture and the coating
Inhibit electrochemical corrosion
High-frequency monitoring and timely repair