What is Galvanic Corrosion? Principles, Impacts, and Prevention for Engineers

Introduction

Corrosion, broadly defined as the degradation of materials due to reactions with their environment, represents a significant global challenge. Its economic impact is staggering, estimated at $2.5 trillion annually, equating to roughly 3.4% of the global Gross Domestic Product (GDP). Fortunately, effective corrosion control practices can yield substantial savings, potentially reducing these costs by 15% to 35% globally. [1] 

Galvanic corrosion, also known as bimetallic corrosion or dissimilar metal corrosion, is a specific and often accelerated form of electrochemical degradation. For galvanic corrosion to initiate, three conditions must be met concurrently: the presence of electrochemically dissimilar materials, an electrical connection between them, and exposure of both materials to a common electrolyte.

For engineers, the implications of what is galvanic corrosion extend beyond material degradation—it affects system reliability, maintenance cycles, and overall safety. This in-depth technical guide covers the electrochemical mechanisms, influencing factors, consequences in electronics, and mitigation strategies for galvanic corrosion. Curious about, what is galvanic corrosion? Let’s dive in…

How Galvanic Corrosion Works? 

Galvanic corrosion operates like a small, unintentional battery! When dissimilar conductive materials are connected electrically and immersed in an electrolyte, they form a galvanic cell. 

Diagram of Galvanic Cell showing Anode and Cathode

This cell consists of four essential components that drive the corrosion process:

The Essential Components: Anode, Cathode, Electrolyte, and Electrical Path

1. Anode: This is the less noble or more active metal, typically with a more negative electrode potential. At the anode, oxidation occurs: metal atoms lose electrons and dissolve in the presence of an electrolyte as positively charged ions. For instance, zinc undergoes corrosion via the reaction: Zn → Zn²⁺ + 2e⁻. This metal becomes the anodic metal in the galvanic couple, bearing the brunt of the corrosion process. [2]

2. Cathode: The more noble or less active material in the couple. At the cathode, reduction occurs as it accepts the electrons released by the anode. The cathode metal itself doesn’t corrode under this mechanism. Depending on the electrolyte, the reduction reaction may vary, often producing OH⁻ in neutral environments or H₂ in acidic conditions.

3. Electrolyte: This conductive medium allows for the movement of ions and completes the galvanic cell circuit. The common electrolytes include seawater, rainwater, condensation (humidity), soil moisture, process chemicals, and even certain food products. The crucial role of an electrolyte is to provide a pathway for ion migration between the anode and cathode, completing the electrical circuit. 

4. Electrical Path: A pathway must exist for electrons released at the anode to travel to the cathode. This is typically achieved through direct physical contact between the dissimilar materials or via an external metallic conductor, such as a wire or fastener.

The simultaneous requirement for all these components forms the basis of the galvanic cell and dictates the conditions under which this type of corrosion occurs. Breaking any one of these connections, using insulation to disrupt the electrical connection, or coatings to block the electrolyte, can halt the galvanic corrosion process entirely.

Electrode Potential and the Driving Force

When a metal is immersed in an electrolyte, it develops a characteristic electrical potential, known as its electrode potential or corrosion potential. This potential reflects the relative tendency of the metal to either lose electrons (oxidize) or gain electrons (reduce) in that specific environment. When two different metals are electrically connected in the same electrolyte, a potential difference (voltage) exists between them. This potential difference acts as the driving force for the galvanic corrosion process, analogous to the voltage driving current in an electrical circuit. The more negative the anode, the more susceptible it is to corrosion.

To quantify this, engineers use the Anodic Index or Reference Charts. However, potential difference alone does not define corrosion rate. It’s the resulting galvanic current, impacted by resistance, electrolyte conductivity, area ratios, and polarization effects, that ultimately determines material degradation.

The Galvanic Series: Predictive and Practical

To aid in predicting galvanic corrosion risk, engineers frequently utilize the Galvanic Series. This is a practical ranking of various metals and alloys based on their measured corrosion potentials in a specific electrolyte, most commonly seawater. It differs from the theoretical Electromotive Force (EMF) series, which is based on standard potentials in solutions of their own ions and doesn't account for alloys or real-world environmental effects like passivation films.

Materials higher in the series (more negative) are more likely to act as anodes, while those lower serve as cathodes. The greater the separation between metals in the series, the higher the risk of bimetallic corrosion.

• Stainless Steel in a passive state ranks lower (more noble) than carbon steel, meaning it will be protected, while steel bolts may corrode.

• Close Match in the galvanic series indicates better compatibility.

Engineers must note that the series is electrolyte-specific! A pair compatible in seawater might not behave the same in concrete or soil. Passive films, aeration, and contaminants all shift potentials, affecting both the potential difference and the real-world corrosion rate.

The Shift to Galvanic Current in Standards (MIL-STD-889)

Recognizing the limitations of predicting corrosion behavior based solely on open-circuit potential (OCP) differences, modern standards and engineering practice increasingly emphasize the importance of kinetics. The potential difference only indicates the thermodynamic tendency for corrosion, not the rate. The actual rate of metal loss is determined by the galvanic current that flows between the coupled materials.

Standards like the MIL-STD-889 ("Dissimilar Metals") have evolved to reflect this understanding. [3] They now recommend assessing galvanic current, a more accurate predictor of corrosion severity. This involves electrochemical methods like polarization curves to map actual reactions under operating conditions.

By applying mixed potential theory, engineers calculate the equilibrium point where anodic and cathodic currents balance. This current dictates the true corrosion rate, helping design better protections using coatings, corrosion inhibitors, and sacrificial anodes.

Ultimately, understanding what is galvanic corrosion goes beyond identifying dissimilar materials. It demands a systems-level view of potentials, currents, electrolyte composition, and design parameters to effectively manage risk in real-world applications.

Recommended Reading: Cathode, and Anode: The Basics and Applications

What Influences Galvanic Corrosion Rates?

While the potential difference sets the stage, several other factors critically influence how fast galvanic corrosion actually proceeds. Understanding these factors is essential for predicting the severity of corrosion and designing effective mitigation strategies.

Galvanic Corrosion between Copper and Iron Pipes

The Impact of Potential Difference

The potential difference between dissimilar metals is the driving force behind galvanic corrosion. Greater separation in the galvanic series generally indicates a stronger driving force and increased corrosion risk. However, potential difference alone doesn't determine the actual corrosion rate—other kinetic factors significantly modulate it. Some standards suggest compatibility thresholds of 0.25V or 0.15V, depending on environmental severity, but these must be used with caution.

The Critical Role of Surface Area Ratio (Anode/Cathode)

Perhaps the most significant factor controlling the rate of galvanic corrosion, once a potential difference exists, is the relative surface area of the cathode (noble metal) exposed to the electrolyte compared to the surface area of the anode (active metal).

• Unfavorable Ratio (Small Anode / Large Cathode): The large cathodic surface can support a high rate of the reduction reaction (e.g., oxygen consumption), demanding a large flow of electrons. These electrons must all come from the small anodic area. This concentration of electron flow results in a very high current density on the anode, leading to rapid and often localized dissolution (corrosion) of the anodic material. Classic examples include steel rivets used to join copper plates (steel rivets corrode quickly), carbon steel bolts fastening stainless steel structures, or aluminum fasteners in steel panels.

• Favorable Ratio (Large Anode / Small Cathode): In this case, the total galvanic current is limited by the small cathodic surface area available for the reduction reaction. This limited current is drawn from a large anodic area. The resulting current density on the anode is low, and the corrosion is spread out, leading to a much slower and less damaging rate of attack. A prime example is galvanized steel: the large zinc coating (anode) sacrificially protects small scratches or exposed areas of the underlying steel (cathode) with only slow consumption of the zinc. 

This ratio also informs coating strategies: always coat the cathode! Coating the anode and leaving even a pinhole exposes a small anodic area to a large cathodic surface, accelerating attack. Conversely, coating the cathode reduces galvanic current even in the case of coating damage.

Electrolyte Characteristics: Conductivity, Temperature, pH, and Contaminants

The nature of the electrolyte bridging the dissimilar metals profoundly affects the rate of galvanic corrosion.

• Conductivity: Higher conductivity (e.g., saltwater) allows faster ion migration and greater electric current, increasing corrosion. Moisture films, especially when contaminated, can serve as effective electrolytes.

• Temperature: Like most chemical reactions, electrochemical corrosion processes generally proceed faster at higher temperatures. Increased temperature enhances ion mobility and reaction kinetics.

• pH: The acidity or alkalinity of the electrolyte influences corrosion rates and can sometimes affect the passive behavior of metals or even reverse the polarity of a galvanic couple. Highly acidic (low pH) or highly alkaline (high pH) environments are often more corrosive than neutral ones, although the specific effect depends on the metals involved.

• Contaminants/Pollutants: The presence of dissolved species in the electrolyte can significantly impact corrosion. Chlorides (Cl⁻) can destroy passive layers on stainless steel and aluminum, triggering pitting. Pollutants and residues (e.g., solder fluxes) can form corrosive electrolytes. Residual manufacturing chemicals, like soldering fluxes, if not properly cleaned, can leave ionic residues that attract moisture and create corrosive electrolytes on electronic assemblies.

• Oxygen Availability: Dissolved oxygen often acts as the primary reactant consumed at the cathode in neutral or near-neutral electrolytes. Therefore, the availability of oxygen can directly influence the rate of the cathodic reaction and, consequently, the overall galvanic corrosion rate. The environments with higher oxygen levels generally support faster corrosion. Conversely, in stagnant areas or crevices where oxygen can be depleted, the corrosion mechanism might change, potentially leading to differential aeration cells.

• Electrolyte Motion/Flow Rate: Movement of the electrolyte can influence corrosion rates. Moderate flow can accelerate corrosion by constantly supplying fresh reactants (like oxygen) to the cathode and washing away corrosion products or inhibiting films from the anode. However, very high flow rates might lead to erosion-corrosion, a different mechanism involving mechanical damage.

These electrolyte properties vary across environments, marine, industrial, humid, or buried, making it essential to consider dynamic exposure conditions.

The Effect of Geometry, Distance, and Crevices

The physical arrangement and shape of the coupled components also play a role:

• Distance: Galvanic corrosion effects are typically most intense at the junction where the dissimilar metals meet and diminish as the distance from the junction increases along the electrolyte path. The extent of this "throw" distance depends significantly on the conductivity of the electrolyte. In highly conductive solutions like seawater, the galvanic effect can influence areas relatively far from the junction, while in poorly conductive media like humid air or freshwater, the effect is much more localized.

• Geometry and Crevices: The flow of galvanic current can be influenced by the geometry of the parts; for example, current distribution may be non-uniform around sharp corners or complex shapes. More importantly, design features that create crevices, gaps, lap joints, or recesses between dissimilar metals (or even on a single metal) are particularly problematic. These features tend to trap and retain electrolytes (moisture, contaminants), ensuring the prolonged presence of a conductive path needed for corrosion. 

By accounting for potential differences, surface area effects, electrolyte properties, and geometry, engineers can more accurately assess galvanic risk and design resilient systems. Ultimately, controlling what is galvanic corrosion requires both material science insight and smart, informed design decisions.

Recommended Reading: Hot Rolled vs Cold Rolled Steel: A Comparative Analysis

Galvanic Corrosion Failures in Electronics and Hardware

Galvanic corrosion can lead to severe consequences affecting the performance, reliability, safety, and economic viability of engineered systems, particularly in the realm of electronics and hardware.

PCB Corrosion

Common Consequences: From Performance Degradation to Structural Failure

On a macroscopic level, galvanic corrosion leads to the preferential loss of material from the anodic component. This results in a reduction in thickness, weakening of the material, and compromised structural integrity. Joints can be weakened, load-bearing components compromised, and stress concentration points created, potentially leading to premature fracture or failure.

Beyond structural issues, galvanic corrosion significantly impacts performance. The formation of corrosion products can decrease electrical conductivity, crucial in electronic circuits, and also reduce heat transfer efficiency, affecting thermal management. Mechanical properties can be degraded, leading to impaired system reliability and inconsistent equipment performance.

Safety concerns are paramount, as unexpected component failure due to corrosion can have catastrophic consequences. This includes potential leakage in fluid systems, structural instability, or the malfunction of critical safety systems. 

Financially, this translates to costly repairs, downtime, reduced lifecycle, and insurance complications.

Specific Failure Modes in Electronic Systems (Increased Resistance, Shorts, Degradation)

In the context of electronics, where components are miniaturized and signals are often low-power, even seemingly minor amounts of corrosion can lead to critical failures. The primary failure modes include:

• Increased Electrical Resistance: Non-conductive layers (oxides, sulfides) form on electrical contact surfaces (e.g., PCB traces, terminals), raising resistance. Even tiny changes impair low-voltage signal integrity or trigger component overheating.

• Short Circuits: Dissolved anodic metal ions migrate and redeposit as dendrites under bias voltages, bridging metal surfaces and forming unintended conductive paths. This is worsened by electrolyte presence and contaminants. Related phenomena like Electrochemical Migration (ECM) and Conductive Anodic Filament (CAF) formation, often involving copper or silver, are exacerbated by contaminants and the galvanic potentials present between different materials on a PCB. [4]

• Mechanical Degradation: The preferential dissolution of the anodic metal inherently weakens the component physically. Connector pins can become brittle and break off, fasteners can lose their clamping force or shear, and PCB traces can thin, crack, or lift from the substrate. This mechanical degradation leads to open circuits, intermittent connections, or complete structural failure of the assembly.

The sensitivity of electronic systems means that preventing even microscopic corrosion is critical for ensuring long-term reliability.

Vulnerable Areas: Connectors, PCBs, Enclosures, Fasteners, and Batteries

Galvanic corrosion can occur wherever the three necessary conditions are met, but certain areas in electronic and hardware assemblies are particularly susceptible:

• Connectors: Commonly use dissimilar metals (e.g., gold and tin). Minor defects in coatings can expose reactive underlayers (e.g., nickel), creating galvanic cells. The area ratio mismatches exacerbate corrosion.

• Printed Circuit Boards (PCBs): Multimetal environments (copper, solder alloys, ENIG finishes) and contaminants form galvanic couples. Electrolyte films from flux or condensation further increase the risk. Corrosion can occur in traces, vias, or under poor-quality coatings.

• Enclosures and Hardware: Mixed-metal constructions—like aluminum frames with steel bolts—create prime conditions for corrosion, especially under humid or marine environments.

• Fasteners: High-stress, small-sized components such as screws or rivets act as anodes in poor area ratio scenarios. Steel bolts in stainless steel panels or carbon steel rivets in copper structures corrode quickly.

• Batteries: While batteries rely on galvanic reactions, uncontrolled corrosion on contacts, terminals, and internal elements (e.g., busbars) decreases conductivity and can trigger short circuits in high-voltage systems.

Due to the diversity of metals, voltages, and operating conditions in electronics, proactive corrosion prevention must be embedded into every phase—from design and material selection to assembly and enclosure sealing.

Recommended Reading: Understanding the ENIG Finish: A Comprehensive Guide

Strategies for Preventing and Mitigating Galvanic Corrosion

Preventing galvanic corrosion is vital for ensuring long-term reliability and safety, particularly in electronics. Mitigation strategies revolve around breaking the conditions necessary for corrosion: dissimilar metals, electrical contact, and the presence of an electrolyte.

Galvanizing Metallic Structures in a Zinc Bath

Smart Material Selection

The first line of defense is careful material selection:

• Minimize Potential Difference: Whenever design constraints permit, choose materials that are close together in the relevant galvanic series. This minimizes the electrochemical potential difference, which is the driving force for corrosion.

• Use Similar Materials: The simplest approach is to use the same material for components that will be in direct contact, especially fasteners and the parts they join.

• Select Corrosion-Resistant Alloys: For components exposed to corrosive environments or critical connection points, specify materials known for their inherent corrosion resistance in that environment. This might include specific grades of stainless steel, certain copper alloys, titanium, or using noble metal platings like gold on connectors.

• Consult Standards and Data: Utilize resources like MIL-STD-889D, which provides compatibility assessments based on measured galvanic current or corrosion rate, offering a more reliable prediction than potential difference alone. Refer to established galvanic series charts (like ASTM G82 guidance) and environment-specific corrosion data when available.

Material selection involves trade-offs! The electrochemically ideal choice might not meet mechanical strength, weight, cost, or thermal conductivity requirements. Furthermore, as emphasized previously, the galvanic series only indicates the potential difference (tendency), not the rate. The actual corrosion performance depends heavily on kinetic factors like the anode/cathode area ratio, electrolyte conductivity, temperature, and polarization behavior.

Design for Prevention: Insulation, Geometry, and Drainage

Beyond material choice, thoughtful physical design can effectively eliminate or mitigate the conditions required for galvanic corrosion.

• Electrical Insulation: The most direct way to stop galvanic corrosion between dissimilar metals is to prevent electrical contact. This is achieved by inserting a non-conductive material between the surfaces. Use plastic/rubber washers, sleeves, gaskets, or non-conductive coatings to interrupt electrical contact.

• Geometry and Area Ratio Management: Design decisions should actively avoid creating unfavorable area ratios. This means ensuring that if a more active (anodic) metal must be used, its exposed surface area in the couple is significantly larger than the exposed area of the more noble (cathodic) metal. For example, when using fasteners, choose fasteners made of the same material as the structure, or if dissimilar, use fasteners that are cathodic (more noble) relative to the larger structural component. 

• Drainage and Electrolyte Exclusion: Since an electrolyte is essential, designs should aim to prevent its accumulation at dissimilar metal junctions. This involves incorporating features for effective drainage, such as sloped surfaces, drain holes, and avoiding configurations that trap water (like upward-facing channels or unsealed horizontal surfaces). Prevent electrolyte accumulation through drainage paths and sealants to block the entry of moisture.

These design strategies work by directly intervening in the galvanic corrosion mechanism – breaking the circuit, removing the electrolyte, or managing the geometry to minimize severity. 

Protective Coatings and Platings

Applying coatings or platings is a widely used method to protect against galvanic corrosion, primarily by acting as a barrier between the metal substrate and the environment, or sometimes by providing sacrificial protection.

Flexible Robotic Conformal Coating and Dispensing System 

Let's go through their details: 

• Barrier Coatings: These coatings physically isolate the metal surface from the electrolyte. Examples include organic coatings like paints, epoxies, polyurethanes, and powder coatings. For electronics, conformal coatings (thin polymeric layers of acrylic, urethane, silicone, etc.) are applied to PCBs to protect against moisture and contaminants. Potting compounds completely encapsulate the circuitry for maximum environmental protection.

• Sacrificial Coatings/Platings: These involve applying a layer of metal that is more anodic (less noble) than the substrate material. If the coating is scratched or damaged, exposing the substrate, the coating metal will corrode preferentially (sacrificially) due to the galvanic couple formed, thus protecting the underlying substrate. The most common example is zinc coating on steel (galvanizing). Cadmium plating was historically used on steel for excellent sacrificial protection, especially in marine environments, but its use is now restricted due to toxicity. Tin-zinc alloy coatings are emerging as a RoHS-compliant alternative to cadmium, offering good sacrificial protection and compatibility.

• Noble Metal Platings: Platings with more noble metals than the substrate (like gold, silver, or sometimes nickel over copper) are primarily used for their functional properties (conductivity, solderability, wear resistance) but can offer barrier protection if applied perfectly. However, if a noble plating has pores or defects, it can expose the less noble underlayer or substrate, creating a galvanic cell where the underlayer corrodes rapidly due to the unfavorable area ratio.

If only one surface can be coated, always coat the cathode! Coating the anode may trap electrolytes at defects, accelerating corrosion.

Recommended Reading: Conformal Coating: Protecting Electronics in Harsh Environments

Cathodic Protection

Cathodic Protection (CP) is an electrochemical technique that prevents corrosion by making the entire surface of the structure to be protected act as the cathode of an electrochemical cell. This forces the corrosion potential of the structure down to a level where oxidation (corrosion) is thermodynamically unfavorable. The necessary protective current is supplied by either sacrificial anodes or an external power source via impressed current anodes.

• Sacrificial Anodes (Galvanic Cathodic Protection - GCP): This method involves electrically connecting the structure to be protected (e.g., a steel pipeline) to a metal or alloy that is significantly more anodic (less noble) in the same electrolyte. The common sacrificial anode materials include alloys of zinc, aluminum, and magnesium.

• Impressed Current Cathodic Protection (ICCP): This method uses an external DC power source (typically a rectifier converting AC to DC) to drive protective current from relatively inert anodes to the structure being protected. The anodes do not corrode significantly themselves; common materials include mixed metal oxide (MMO) coated titanium, platinum-coated titanium or niobium, graphite, or high-silicon cast iron.

While CP isn’t practical for individual electronics, sacrificial coatings (like zinc on steel bolts) apply the principle locally. CP systems can also indirectly protect electronics in large equipment by preserving the structure and limiting environmental exposure.

Recommended Reading: What is Passivation? Enhancing Material Durability and Corrosion Resistance

Real-World Lessons: Case Studies of Galvanic Corrosion

Examining documented failures provides valuable insights into how galvanic corrosion manifests in practice and the importance of applying prevention principles.

Electronics and Connector Failures

• Case 1: Telecom Jack Contact Corrosion: A gold-plated contact tine (over nickel and copper alloy base) in a telecom jack failed due to corrosion. Investigation revealed copper oxide as the primary corrosion product, indicating attack of the base metal. The root cause was identified as galvanic corrosion occurring through microscopic pores and defects in the gold and nickel plating layers. The presence of contaminants (sodium and potassium hydroxides) and moisture acted as the electrolyte, facilitating the galvanic cell between the exposed copper/nickel and the gold plating. The failure mode was increased contact resistance. This case highlights the critical importance of plating quality, cleanliness, and environmental control for connector reliability.

• Case 2: Op Amp Aluminum Bond Pad Failure: An operational amplifier failed due to severe corrosion of its aluminum bond pad. Chemical decapsulation revealed that the pad was almost completely etched away, causing high electrical resistance. The failure was attributed to internal corrosion within the plastic package, likely a galvanic process involving the aluminum pad, other internal metals (lead frame), and trapped moisture or contaminants introduced during manufacturing or service. Evidence of package cracking ("popcorning") suggested moisture ingress paths. This illustrates the vulnerability of microelectronic components to internal galvanic corrosion and the need for robust packaging and material compatibility within the device itself.

• Case 3: IGBT Module Degradation (THB Testing): Accelerated life testing (Temperature-Humidity-Bias) of Insulated Gate Bipolar Transistor (IGBT) modules revealed failures linked to corrosion. Failure analysis identified corrosion of the aluminum chip metallization and the growth of copper and silver dendrites (indicative of electrochemical migration) between conductors. Testing showed that applying a higher bias voltage significantly accelerated these degradation mechanisms. This demonstrates the synergistic effect of humidity, temperature, dissimilar metals (Al, Cu, Ag), and electrical bias in driving corrosion failures in power electronic modules.

• Case 4: Connector Plating Mismatch (Gold-Tin): A study highlighted the risk of mating connectors with dissimilar platings, specifically a gold-plated connector with a tin-plated flexible flat cable (FFC). In the presence of an electrolyte, the tin plating acts as the anode and corrodes preferentially, while tin oxide deposits can form on the gold cathode surface. This galvanic couple arises from the significant potential difference between gold and tin. This emphasizes the design rule of avoiding the connection of components with widely dissimilar, incompatible plating materials.

Hardware and Structural Failures (Illustrative)

• Case 5: Fastener Failure in Structures: A common failure mode involves using fasteners made of a metal significantly different from the structure they are joining, particularly when the fastener is small and anodic. For example, carbon steel bolts used to fasten large stainless steel plates will corrode rapidly due to the large cathode-to-anode area ratio and the potential difference. This underscores the need to consider both material compatibility and the area effect in fastener selection for structural integrity.

• Case 6: The Statue of Liberty Restoration: A famous large-scale example involved the Statue of Liberty. The external copper skin (cathode) was supported by an internal wrought iron framework (anode). [5] An insulating layer of shellac was originally placed between them, but it degraded over time, allowing moisture (electrolyte) to bridge the gap. This resulted in severe galvanic corrosion of the iron support structure, necessitating its replacement with stainless steel and improved insulation during the 1980s restoration. This case clearly illustrates the importance of durable electrical isolation when dissimilar metals must be used in long-term structures.

• Case 7: Communication Equipment Assembly: A study using numerical simulation and salt spray testing analyzed galvanic corrosion risks in a communication equipment housing composed of a magnesium alloy shell, an aluminum alloy shell, and stainless steel bolts. The study confirmed the potential for galvanic corrosion between these dissimilar materials in an atmospheric environment and investigated the critical role of protective coatings and the impact of coating damage on accelerating corrosion. This highlights the complexity of managing galvanic corrosion in multi-material assemblies and the paramount importance of coating integrity.

These real-world failures highlight how galvanic corrosion results from the convergence of three conditions: dissimilar materials, electrical contact, and an electrolyte. Whether the damage appears as increased resistance in a microcircuit or rusted-through fasteners in a bridge, the principles remain the same. Prevention depends on early-stage design diligence, proper coating application, environmental management, and adherence to compatibility standards. Proactive measures ensure systems maintain performance, reliability, and safety over their intended lifecycle.

Suggested Podcast: Self-Repairing Corrosion Coating

Key Guidelines and Standards for Engineers

Industry standards play a vital role in managing galvanic corrosion by providing engineers with standardized test methods, material specifications, compatibility guidelines, and best practices for prevention. These frameworks ensure consistency, safety, and interoperability, especially in sectors like aerospace, defense, medical devices, and infrastructure. 

New Galvanic Copper Anode for Electrolysis

Key organizations developing relevant standards include:

ASTM International Standards

ASTM provides numerous standards related to corrosion testing and evaluation:

• ASTM G82: Standard Guide for Development and Use of a Galvanic Series for Predicting Galvanic Corrosion Performance. This guide details how galvanic series charts are constructed and how they should be interpreted for assessing potential corrosion risks between dissimilar metals.

• ASTM G71: Standard Guide for Conducting and Evaluating Galvanic Corrosion Tests in Electrolytes. This standard outlines procedures for performing laboratory tests to measure the galvanic corrosion behavior of coupled materials in specific liquid electrolytes.

• ASTM F3044: Standard Test Method for Evaluating the Potential for Galvanic Corrosion for Medical Implants. This method specifically addresses the testing of galvanic couples formed by dissimilar metals intended for use in medical implants or components. 

• ASTM G31 / NACE TM0169: Standard Guide for Laboratory Immersion Corrosion Testing of Metals. While a general standard for immersion testing, it provides methodologies for assessing the inherent corrosion rate of individual metals, which can inform galvanic compatibility assessments.

• ASTM F2129: Standard Test Method for Conducting Cyclic Polarization Testing for Small Implant Devices. Used primarily to assess pitting and general corrosion susceptibility (especially for medical devices), the polarization data generated can also be used as input for more advanced galvanic corrosion predictions.

ISO Standards

ISO develops international standards covering various aspects of corrosion:

• ISO 21746: Galvanic Corrosion Tests of Carbon Fibre Reinforced Plastics (CFRPs) Related Bonded or Fastened Structures in Artificial Atmospheres. Addresses the specific issue of galvanic corrosion between conductive CFRP composites and metals, increasingly relevant in aerospace and automotive applications.

• ISO 8057: Determination of galvanic corrosion rate for assembled forms of carbon fibre reinforced plastics (CFRPs) and protection-coated metal — Electrochemical tests in neutral sodium chloride solution. Provides methods for quantifying corrosion rates in CFRP-metal assemblies.

• Other ISO standards cover related areas like corrosion testing in artificial atmospheres, classification of corrosivity, and requirements for protective coatings.

Military Standards (MIL-STD)

The US Department of Defense standards are widely referenced, particularly in aerospace and defense industries:

• MIL-STD-889 (Current Revision D): Dissimilar Metals. This is the cornerstone standard for galvanic compatibility in military systems. It defines compatibility based on measured galvanic current/corrosion rate rather than just potential difference, provides compatibility tables, and specifies requirements for protective finishing systems for various metal couples.

• MIL-STD-171: Finishing of Metal and Wood Surfaces. This standard details the requirements for applying various protective finishes, including platings (cadmium, zinc, nickel, chrome, etc.) and coatings used for corrosion prevention on military hardware.

• MIL-HDBK-1250: Corrosion Prevention and Deterioration Control in Electronic Components and Assemblies. This handbook provided guidance on controlling corrosion in electronic systems, covering aspects like material selection, conformal coatings, and environmental sealing.

NACE/AMPP Standards and Publications

AMPP (formed by the merger of NACE and SSPC) is a leading authority on corrosion control and protective coatings. They publish numerous standards (SPs), technical reports (TRs), and guides covering cathodic protection design and criteria, surface preparation, coating application and inspection, and materials selection for specific environments. 

Examples include:

• SP0169 – Protection of pipelines via cathodic systems.

• SP0216 – Galvanic CP of steel in concrete.

• MR0175 / ISO 15156 – Material selection for sour (H₂S) environments.

Below is a table covering the key standards related to Galvanic Corrosion Assessment & Prevention:

Following these standards enables engineers to align their designs with proven practices, reduce failure risk, and validate corrosion mitigation decisions. In any system where dissimilar metals are exposed to electrolytes, referencing appropriate testing protocols and compatibility tables is essential for performance and safety assurance.

Recommended Reading: Cleaning Circuit Boards: A Complete Guide for Engineers and Technical Professionals

Conclusion

Galvanic corrosion is a critical electrochemical process triggered by the potential difference between dissimilar metals in electrical contact within an electrolyte. It leads to the accelerated deterioration of the more active (anodic) metal, threatening the reliability of electronic systems, hardware assemblies, and structural components. The corrosion rate is influenced not only by material potential differences but also by key kinetic factors, such as anode/cathode surface area ratio, electrolyte conductivity and composition, and assembly geometry. 

In electronics, even minor corrosion can result in increased resistance, signal failure, short circuits, or mechanical damage. Effective mitigation requires proactive design and manufacturing strategies: selecting compatible materials, applying appropriate barrier or sacrificial coatings, insulating dissimilar metals, and consulting established standards like ASTM, ISO, MIL-STD, and AMPP. By integrating an understanding of galvanic corrosion principles with sound engineering practices, the risks associated with this pervasive degradation mechanism can be effectively managed, enhancing product lifespan and preventing costly failures.

Frequently Asked Questions (FAQ)

Q1: What are the necessary conditions for galvanic corrosion?
A: Three conditions must exist: two electrochemically dissimilar conductive materials, an electrical connection between them, and the presence of an electrolyte (e.g., moisture, seawater). Without any one of these, galvanic corrosion cannot occur.

Q2: How do I use a galvanic series chart?
A: Choose a chart for your environment! Materials close together are more compatible; so, avoid pairing metals far apart in the series, especially if the anodic metal is much smaller in surface area than the cathodic metal.

Q3: Why is the anode/cathode area ratio important?
A: A small anode with a large cathode results in high current density on the anode, causing rapid corrosion. A large anode with a small cathode spreads the current, minimizing damage.

Q4: How does galvanic corrosion damage electronics?
A: It increases resistance due to oxide buildup, causes short circuits from metal ion migration, and weakens components like pins, traces, or joints, leading to mechanical or electrical failure.

Q5: How can I prevent galvanic corrosion between dissimilar metals?
A: Use electrical insulation, apply protective coatings (preferably on the cathode), seal joints to block moisture, and design with a large anodic area compared to the cathode.

Q6: Is galvanic corrosion the same as rust?
A: No! Rust refers to iron corrosion. On the other hand, galvanic corrosion affects many metals and is driven by electrochemical differences between dissimilar materials in contact within an electrolyte.

Q7: Why is coating the cathode safer than coating the anode?
A: Coating defects expose the underlying metal. A defect in an anode coating creates a small anode/large cathode—worst-case scenario. Coating the cathode limits corrosion severity if damaged.

References

[1] GlobalSpec. Annual Global Cost of Corrosion: $2.5 Trillion [Cited 2025 April 30] Available at: Link

[2] USNA. Basics of Corrosion [Cited 2025 April 30] Available at: Link

[3] NATO. MIL-STD-889 and the Impacts on Corrosion Prevention [Cited 2025 April 30] Available at: Link

[4] IPC. Conductive Anodic Filament (CAF) Formation [Cited 2025 April 30] Available at: Link

[5] ResearchGate. The Impact of Corrosion on Society [Cited 2025 April 30] Available at: Link