Galvanic Corrosion

Fixing galvanic corrosion involves several steps to break the electrochemical reaction between dissimilar metals. Here are effective methods to address galvanic corrosion:

1. Material Selection: Use metals that are close together on the galvanic series to minimize potential differences. Avoid combining metals with significantly different electrochemical potentials.
2. Insulation: Electrically insulate dissimilar metals to prevent direct contact. Use non-conductive materials such as plastic or rubber gaskets, washers, or coatings.
3. Protective Coatings: Apply protective coatings to the more noble (cathodic) metal to prevent it from acting as the cathode. Use paints, varnishes, or powder coatings to isolate the metals from the environment.
4. Cathodic Protection: Implement cathodic protection systems, such as sacrificial anodes (e.g., zinc or magnesium) that corrode preferentially, protecting the primary metal.
5. Control Environment: Reduce the presence of electrolytes (such as moisture or salts) that facilitate galvanic corrosion. Use dehumidifiers, sealants, and corrosion inhibitors.
6. Regular Maintenance: Conduct regular inspections and maintenance to identify early signs of galvanic corrosion and address them promptly.
7. Design Modifications: Redesign assemblies to avoid galvanic coupling, such as by ensuring proper drainage to avoid electrolyte accumulation and avoiding crevices where moisture can collect.

By implementing these strategies, you can effectively mitigate galvanic corrosion and extend the lifespan of your components.

Galvanic corrosion occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte. Here’s a list of common metals and their propensity to cause galvanic corrosion when paired with other metals:

1. Zinc: Highly anodic and likely to corrode when in contact with more noble metals like copper or stainless steel.
2. Aluminum: Anodic, corrodes when paired with metals like stainless steel, copper, or brass.
3. Steel (Carbon and Low Alloy): Intermediate, can corrode when in contact with more noble metals like copper, bronze, or stainless steel.
4. Copper: Cathodic, causes corrosion in more anodic metals like zinc, aluminum, or galvanized steel.
5. Brass/Bronze: Cathodic, leads to corrosion in anodic metals such as aluminum or steel.
6. Stainless Steel: Highly cathodic, can cause significant corrosion in anodic metals like zinc, aluminum, or regular steel.

Galvanic Series: The tendency of metals to cause galvanic corrosion can be predicted using the galvanic series, which ranks metals from most anodic (active) to most cathodic (noble). Metals that are far apart in this series are more likely to cause galvanic corrosion when in contact.

Preventive Measures:

• Avoid Direct Contact: Use insulating materials to separate dissimilar metals.
• Coatings: Apply protective coatings to more noble metals.
• Material Compatibility: Choose metals close together in the galvanic series to reduce potential differences.

By understanding which metals are likely to cause galvanic corrosion, you can make informed material choices and implement preventive strategies to protect your components.

Certain combinations of metals should be avoided due to the risk of galvanic corrosion. Here are some metal pairs that should not be used together:

1. Aluminum and Copper: Aluminum is anodic to copper and will corrode rapidly in their presence, especially in moist environments.
2. Zinc and Steel (Stainless or Galvanized): Zinc is anodic to both stainless and galvanized steel, leading to rapid corrosion of zinc.
3. Steel and Brass/Bronze: Steel is anodic to brass and bronze, causing the steel to corrode in the presence of these metals.
4. Magnesium and Any Other Metal: Magnesium is highly anodic and will corrode when in contact with almost any other metal, including aluminum, steel, and copper.
5. Carbon Steel and Stainless Steel: Carbon steel is anodic to stainless steel, which can lead to significant corrosion of carbon steel in the presence of stainless steel.

Preventive Measures:

• Insulation: Use non-conductive materials like plastic or rubber to separate dissimilar metals.
• Protective Coatings: Apply coatings to one or both metals to prevent direct contact.
• Material Selection: Choose metals that are close together in the galvanic series to minimize potential differences.

By avoiding these problematic metal combinations and implementing preventive measures, you can significantly reduce the risk of galvanic corrosion.

Intergranular corrosion in aluminum is primarily caused by the presence of impurities and alloying elements that precipitate at grain boundaries. Here are the main factors:

1. Heat Treatment: Improper heat treatment can cause the precipitation of alloying elements, such as magnesium and silicon, at grain boundaries, making them susceptible to corrosion.
2. Alloy Composition: Certain alloying elements, such as copper, can increase the susceptibility of aluminum alloys to intergranular corrosion.
3. Environmental Factors: Exposure to aggressive environments, such as those containing chlorides or high humidity, can accelerate intergranular corrosion.
4. Electrochemical Potential: Differences in electrochemical potential between grain boundaries and the grain interiors create a galvanic cell, leading to localized corrosion at the grain boundaries.

Prevention:

• Proper Heat Treatment: Ensure correct heat treatment procedures to avoid harmful precipitation at grain boundaries.
• Alloy Selection: Choose aluminum alloys with a composition that minimizes susceptibility to intergranular corrosion.
• Protective Coatings: Apply coatings or anodizing to protect the surface from corrosive environments.

By understanding and controlling these factors, the risk of intergranular corrosion in aluminum can be significantly reduced.