Considerations for common materials and Galvanic Corrosion.
Carbon Steel & Aluminum
Common low Carbon steels have an Anodic Index of 0.85V while common Aluminums (as used in tools, jigs, & fixtures) have a typical Anodic Index of 0.90V for a difference of 0.10V. In most tooling applications this difference is not generally considered significant enough to cause concern for galvanic corrosion. If the environment is very hot, very humid, and/or exposed to water, salt-water, or salt-water air, mitigation practices may need to be considered.
Carbon Steel & Stainless Steel(s)
Stainless Steels typically have an Anodic index of 0.60V while common low Carbon steels have an Anodic Index of 0.85V for a typical difference of 0.25V. Most tooling applications this difference is not generally considered significant enough to cause concern for galvanic corrosion. If the environment is very hot, very humid, and/or exposed to water, salt-water, or salt-water air, mitigation practices may need to be considered.
Stainless Steel(s) and Aluminum
Commonly used Aluminum in tools have a typical Anodic Index of 0.90V while common Stainless Steels typically have an anodic index of 0.60 for a difference of 0.30V. There is some concern for Galvanic Corrosion between these metals in non-climate-controlled environments. If the environment is very hot, very humid, and/or exposed to water, salt-water, or salt-water air, mitigation practices should be considered.
Mitigation Practices
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Protective Coatings: Apply protective coatings such as paints, sealants, plating, conversion coatings, or corrosion inhibitors to create a physical barrier between the metals and the corrosive environment. These coatings may act as sacrificial layers, shielding the base metals from direct contact with electrolytes and preventing galvanic corrosion.
In tooling component applications protective coatings typically applied are:
For Stainless Steels: Passivation. For more information on passivation and how it works to control galvanic corrosion, please click here.
For Carbon Steels: Plating. For detailed information about plating, common types, and applications please click here.
For High Tolerance Items: Electro-less Nickel Plating. For more detailed information about Electro-less Nickel plating, please click here.
Important Note: Electro and Electroless plating can cause Hydrogen Embrittlement. To learn more about this issue please click here. (link to embrittlement)
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Design Considerations: Optimize the design of structures and components to minimize the contact area between dissimilar metals. By reducing the surface area of contact, the galvanic couple is diminished, resulting in lower galvanic corrosion rates.
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Cathodic Protection: Implement cathodic protection techniques, such as sacrificial anode systems or impressed current systems, to protect the more active (anodic) metal. Cathodic protection involves introducing a more reactive metal (sacrificial anode) or applying an external electrical current to shift the potential of the metal towards cathodic polarization, reducing galvanic corrosion. This technique is frequently used in very harsh environments, such as to protect the steel hull of a ship. While not typically used in tooling and fixturing it may have excellent applications.
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Electrolyte (Environmental) Control: Control the composition and environment of the electrolyte. By reducing or removing the electrolyte (e.g., through desiccation or sealing), or by modifying its composition (e.g., pH adjustment), the corrosive conditions can be minimized, thereby reducing the galvanic corrosion potential. Storing tooling indoors rather than outdoors is one simple way to control the Electrolyte.
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Monitoring and Maintenance: Regularly inspect and monitor the metal surfaces and their corrosion protection systems. Implement appropriate maintenance practices to ensure the continued effectiveness of protective coatings, cathodic protection systems, and other corrosion control measures.