1.What effect does temperature have on corrosion mechanisms?
Increased chemical reaction rate: For every 10°C increase in temperature, the corrosion rate increases by about 2 times. High temperature accelerates zinc oxidation and electrochemical reactions (such as zinc reacting with water to form zinc hydroxide).
Humidity interaction: In a high temperature and high humidity environment, water forms an electrolyte, which promotes the loss of zinc ions; if a low temperature environment is accompanied by condensation (such as a temperature difference between day and night > 15°C), it also accelerates electrochemical corrosion.
Oxide film stability: At room temperature: a dense basic zinc carbonate protective film is formed on the surface of the zinc layer to slow down corrosion.
High temperature: The oxide film may produce microcracks due to thermal expansion and contraction, or be destroyed by acidic gases (such as SO₂), resulting in accelerated corrosion.
2.What are the characteristics of corrosion in low temperature environments?
Condensation water dominates: Low temperature causes water to condense on the metal surface, forming an electrolyte, which accelerates the corrosion of the zinc layer. For example, if the humidity in the freezer is high, the galvanized sheet may develop white rust within a few years.
Salt spray aggravates: If the environment contains chloride ions (such as road deicing salt), pitting corrosion will be significantly accelerated even at low temperatures.
Typical case: In coastal areas with large temperature differences between day and night, the annual corrosion rate of the galvanized layer can reach 1.2μm, and low-temperature condensation shortens the corrosion cycle by 30%
3.What are the characteristics of corrosion under normal temperature conditions?
Electrochemical corrosion is dominant: the zinc layer protects the substrate through the "sacrificial anode", and the corrosion rate is moderate. For example, the unpassivated DX51D will develop white rust within 24 hours in the salt spray test (35°C), while the passivated product can be extended to more than 5 days.
Humidity sensitivity: When the relative humidity is greater than 60%, the corrosion rate increases significantly; in a dry environment (humidity less than 40%), the zinc coating can remain stable for a long time.
4.What are the characteristics of corrosion in high temperature environments?
Oxide film damage: High temperatures (such as industrial ovens and chimneys) may cause the zinc oxide film to crack and accelerate corrosion. For example, above 50°C, the oxidation rate of zinc increases, a loose zinc oxide layer appears on the surface, and corrosion resistance decreases.
Chemical medium erosion: Acidic gases (such as SO₂) at high temperatures combine with water to form acid rain, which directly dissolves the zinc layer.
5.What are the measures to improve temperature corrosion resistance?
Optimize coating design: Choose zinc-aluminum-magnesium coating (such as DX53D) in high-temperature environment. Its corrosion resistance is 2-5 times that of ordinary galvanizing and can remain stable at 300℃.
In low-temperature and high-humidity environment, increase the coating thickness to ≥200 g/m², and use passivation + oiling composite treatment.
Upgrade surface protection: Galvanizing + organic coating (such as silicone paint) is used in high-temperature scenes (such as ovens), with a temperature resistance of up to 250℃ and no red rust in salt spray tests of ＞1000 hours.
In low-temperature and humid environments (such as bathrooms), use galvanizing + epoxy primer to isolate moisture from contact with the zinc layer. Structural design optimization: Avoid long-term water accumulation in high-temperature environments (such as roof grooves) to reduce local corrosion. Low-temperature equipment (such as freezers) adopts drainage slope design to reduce the risk of condensation accumulation.