Galvanic Corrosion Testing in Metals: Methods, Standards & Prevention
What Is Galvanic Corrosion?
Galvanic corrosion is an electrochemical process that occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte (such as water, moisture, seawater, or body fluids). The metal higher in the galvanic series (more active, or anodic) corrodes preferentially, while the less active (cathodic) metal is protected. This corrosion mechanism can be far more aggressive than general uniform corrosion — leading to rapid deterioration of the anodic metal at the bimetallic contact zone.
Understanding, predicting, and testing galvanic corrosion is critical in designing assemblies that combine dissimilar metals — a common requirement in aerospace, marine, automotive, electronics, and infrastructure applications.
The Electrochemistry of Galvanic Corrosion
When two dissimilar metals contact each other in an electrolyte, they form a galvanic cell. The metal with the more negative electrode potential (the anode) is oxidized and loses material. The metal with the more positive potential (the cathode) is reduced and protected. The driving force for corrosion is the potential difference between the two metals — the greater the potential difference in the galvanic series, the more severe the galvanic corrosion risk.
Key factors influencing severity include:
- Potential difference between the two metals in the service electrolyte
- Cathode-to-anode area ratio — a large cathode area relative to the anode greatly accelerates anode corrosion
- Electrolyte conductivity — more conductive electrolytes (seawater vs. fresh water) sustain greater galvanic currents
- Distance from the contact junction — galvanic effects attenuate with distance from the contact point
Galvanic Corrosion Testing Methods
ASTM G71 — Standard Guide for Conducting and Evaluating Galvanic Corrosion Tests
The primary ASTM standard for galvanic corrosion testing. Specifies procedures for coupling dissimilar metal specimens in electrochemical cells or for direct immersion exposure, and for measuring galvanic current, corrosion potential, and mass loss of the anode metal.
Zero Resistance Ammeter (ZRA) Testing
A ZRA is inserted between the two coupled metals to measure the actual galvanic current flowing between them without introducing any potential perturbation. Galvanic current density provides a direct measure of the anode metal’s corrosion rate. ZRA testing can be performed in simulated service electrolytes over extended periods.
Electrochemical Impedance Spectroscopy (EIS) on Coupled Pairs
EIS characterizes the galvanic couple’s impedance response, providing information on reaction kinetics, coating barrier properties, and long-term galvanic corrosion behavior.
Immersion Testing (ASTM G31)
Galvanically coupled metal specimens are immersed in a defined electrolyte for a specified time. Mass loss, corrosion rate, and morphology of the corroded anode are evaluated after exposure.
Salt Spray Testing (ASTM B117) on Bimetallic Couples
Accelerated corrosion exposure of bimetallic joints or coated assemblies in salt fog, evaluating galvanic attack morphology and coating performance at dissimilar metal junctions.
Industry Applications
Aerospace: Aluminum alloy airframes with titanium or steel fasteners, stainless steel fittings in contact with aluminum structures, and carbon fiber composite panels in contact with aluminum present significant galvanic corrosion risks that must be managed through coatings, insulating sealants, and careful material selection.
Marine: Marine environments with highly conductive seawater electrolyte create the most severe galvanic corrosion conditions. Bronze propellers on aluminum rudder systems, steel hulls with copper antifouling coatings, and mixed-metal pipework systems require rigorous galvanic corrosion analysis.
Automotive: Aluminum body panels fastened with steel bolts, magnesium engine blocks with aluminum or steel inserts, and mixed-metal brake systems all present galvanic corrosion design challenges.
Electronics: PCB traces, connector contacts, and component leads made from dissimilar metals (gold over nickel over copper) can corrode galvanically in humid or condensation-prone environments.
Medical Devices: Orthopedic implants combining titanium and cobalt-chromium alloy components must be evaluated for galvanic compatibility in physiological saline.
Prevention of Galvanic Corrosion
- Select metals close together in the galvanic series
- Insulate dissimilar metals using plastic washers, sleeves, or insulating sealants
- Minimize the cathode-to-anode area ratio
- Apply protective coatings to the more noble (cathodic) metal
- Use cathodic protection (sacrificial anodes or impressed current) in immersion environments
Conclusion
Galvanic corrosion testing — encompassing ASTM G71 guidance, techniques such as Zero Resistance Ammeter (ZRA), Electrochemical Impedance Spectroscopy (EIS), immersion testing, and salt spray exposure — provides a reliable evaluation of electrochemical interactions between dissimilar metals across diverse industries. These methods help quantify corrosion rates, understand material compatibility, and validate protective measures under simulated service conditions. Selecting the appropriate testing approach based on material combinations, environmental factors, and design requirements is crucial for accurately assessing galvanic behavior, preventing premature failure, and ensuring long-term structural integrity — making method selection as critical as the measurement itself.
Why Choose Infinita Lab for Galvanic Corrosion Testing?
Infinita Lab offers comprehensive galvanic corrosion testing services across its nationwide network of accredited laboratories. Our specialists combine electrochemical expertise with materials knowledge to deliver accurate test results and practical engineering recommendations — helping you design corrosion-resistant assemblies and meet ASTM and MIL-SPEC testing requirements.
Looking for a trusted partner to achieve your research goals? Schedule a meeting with us, send us a request, or call us at (888) 878-3090 to learn more about our services and how we can support you. Request a Quote.
Frequently Asked Questions
How is galvanic corrosion different from general uniform corrosion? Uniform corrosion affects the entire exposed surface of a metal in a corrosive environment and proceeds at a relatively predictable, slow rate. Galvanic corrosion is localized at the contact zone of dissimilar metals and can be many times more aggressive than uniform corrosion of the same metal alone in the same environment.
Which metal corrodes in a galvanic couple? The more active (anodic) metal — the one higher in the galvanic series or with a more negative electrode potential — corrodes preferentially. For example, when aluminum contacts copper in seawater, aluminum is the anode and corrodes, while copper is the cathode and is protected.
Does galvanic corrosion occur in non-conductive fluids? No. Galvanic corrosion requires an electrolyte that can conduct ions between the anodic and cathodic areas. It does not occur in dry conditions or non-conductive fluid environments. However, even thin moisture films in humid environments can act as sufficient electrolyte.
What ASTM standard governs galvanic corrosion testing? ASTM G71 is the primary standard guide for conducting and evaluating galvanic corrosion tests. ASTM G82 provides guidance for ranking materials in a galvanic series.
Can coatings prevent galvanic corrosion? Yes, but carefully. Coating the cathodic (noble) metal is more effective than coating the anode, because even small pinholes in an anode coating concentrate galvanic attack at defect sites — accelerating, not preventing, corrosion. Barrier coatings applied to both metals in the couple, combined with physical insulation at the contact interface, provide the most reliable protection.
