Yes it’s true; the interaction of dissimilar metals — our namesake — is the cause of galvanic corrosion. The good news is that we’re experts on its prevention (and we even have a few older metal surfaces whose patina came from galvanic corrosion).
Galvanic corrosion is a complex electrochemical process influenced by various factors that dictate the rate and severity of corrosion between dissimilar metals. Understanding these factors is crucial for preventing and managing galvanic corrosion effectively.
There’s a number of factors that contribute to corrosion:
- 1. Metal Compatibility: The combination of dissimilar metals is a primary factor in galvanic corrosion. The farther apart two metals are on the Galvanic Series Table, the higher the potential for galvanic corrosion. Metals that are closer in proximity on the table will exhibit less galvanic activity when paired together.
- 2. Electrolyte Presence: Galvanic corrosion requires the presence of an electrolyte, which can be moisture, humidity, saltwater, or any conductive liquid. Electrolytes facilitate the movement of ions between metals, enhancing the electrochemical cell’s activity and accelerating corrosion.
- 3. Surface Area Ratio: The relative surface areas of the two metals in contact play a role in galvanic corrosion. A larger surface area of the less noble (more anodic) metal compared to the more noble (more cathodic) metal can lead to accelerated corrosion of the anodic metal.
- 4. Electrical Conductivity: Metals with higher electrical conductivity tend to promote faster galvanic corrosion. These metals allow for more efficient movement of electrons and ions, intensifying the electrochemical reactions.
- 5. Galvanic Series Placement: The Galvanic Series Table ranks metals based on their tendency to corrode. Metals at the top of the table (e.g., zinc, magnesium) are more likely to corrode, while those at the bottom (e.g., gold, platinum) are more corrosion-resistant. Galvanic corrosion is more likely when metals with a significant difference in their positions on the Galvanic Series Table are in contact.
- 6. Presence of Oxides and Coatings: Surface oxides, coatings, or passivation layers on metals can affect galvanic corrosion. These layers may hinder or enhance electron flow, impacting the rate of corrosion.
- 7. Temperature: Higher temperatures can accelerate galvanic corrosion by increasing the rate of electrochemical reactions and enhancing the mobility of ions in the electrolyte.
- 8. Mechanical Stress: Mechanical stress or deformation at the interface between dissimilar metals can disrupt protective oxide layers, exposing fresh metal surfaces and promoting corrosion.
- 9. pH and Chemical Environment: The pH level and chemical composition of the electrolyte can significantly influence galvanic corrosion. Some environments, such as acidic or alkaline conditions, can exacerbate the corrosion process.
- 10. Presence of Crevice or Pitting Corrosion: In areas where crevices or pits form, galvanic corrosion can be intensified due to localized variations in electrolyte concentration and oxygen availability.
- 11. Cathodic Protection: The use of cathodic protection systems, such as sacrificial anodes, can help control galvanic corrosion by introducing a more reactive metal that corrodes sacrificially to protect the less noble metal.
- 12. Material Heterogeneity: Variations in microstructure, composition, or impurities within a metal can affect its susceptibility to galvanic corrosion.
Understanding these factors and their interactions is essential for architects, engineers, and materials specialists to make informed decisions when selecting and designing fasteners and other components in architectural projects. By considering these factors, professionals can effectively mitigate the risks associated with galvanic corrosion and ensure the long-term durability and performance of structures.