1.What is the core principle of galvanic corrosion?
When two different metals are electrically connected in an electrolyte (such as humid air, water, salt spray, etc.), a galvanic cell is formed:
Anode (Sacrificial Electrode): The more chemically reactive metal, which corrodes faster.
Cathode (Protective Electrode): The less chemically reactive metal, which is protected.
2.What are the advantages of combining stainless steel coils and stainless steel bolts?
Galvanic Relationship: The metal potentials of both are close, resulting in no significant galvanic corrosion.
Corrosion Resistance: Excellent. Both rely on a passivation film (chromium oxide) on their surfaces for corrosion protection, providing excellent durability in most environments.
Risks: Extremely stable in chloride-free industrial atmospheres or rural environments. However, in coastal areas or environments with high chloride ion content, such as de-icing salt, the passivation film of the stainless steel may be damaged, leading to crevice corrosion at bolt seams. Even so, its overall performance is still far superior to other options.
Conclusion: This is one of the most commonly used and reliable options, especially suitable for applications with high corrosion resistance requirements.
3.What is the effect of combining stainless steel coils with galvanized bolts?
Galvanic Relationship: The galvanized bolt (zinc) acts as the anode, and the stainless steel coil acts as the cathode.
Corrosion Resistance: Extremely poor. The zinc layer on the bolt will be rapidly consumed as a sacrificial anode, followed by rapid corrosion of the steel bolt substrate, leading to connection failure. The large cathode area of the stainless steel will significantly accelerate bolt corrosion.
Conclusion: This combination should be strictly avoided.
4.What is the effect of combining galvanized coils and galvanized bolts?
Galvanic Relationship: Both are protected by zinc coatings and have the same potential, preventing harmful galvanic corrosion.
Corrosion Protection: Good. The zinc coatings of both the bolts and the sheet metal provide sacrificial anodic protection to the steel substrate. Even if the zinc coating is scratched, the surrounding zinc will protect the exposed steel.
Risks: The zinc coating will gradually corrode under harsh environments (such as acid rain and industrial pollution), resulting in a limited lifespan. However, its protection is comprehensive and predictable.
Conclusion: This is an economical and effective solution suitable for environments where corrosion protection requirements are not extremely stringent.
5.What is the effect of combining galvanized coils with stainless steel bolts?
Galvanic Relationship: The galvanized coil (zinc/steel) acts as the anode, and the stainless steel bolt as the cathode.
Corrosion Resistance: This is a high-risk combination, but very common. Its effectiveness depends on the environment and the relative area of the stainless steel/galvanized steel.
Small Anode, Large Cathode: The stainless steel bolt (cathode) has a small area, while the galvanized coil (anode) has a large area. This causes current to concentrate at the anode (the area around the bolt hole on the galvanized coil), leading to accelerated corrosion of the zinc layer and steel substrate in that area, resulting in perforation corrosion, which is extremely harmful.
Environmental Factors: Lower risk in dry environments; corrosion accelerates dramatically in humid, salt spray environments.