Engineering · Reference
Galvanic series — seawater.
Materials ranked from most anodic (sacrificial) to most cathodic (noble) in flowing seawater. The reference for picking compatible dissimilar metals — or for choosing a sacrificial anode in marine and outdoor applications. Per MIL-STD-889 corrosion guidance.
Interactive Simulator
Galvanic Potential Comparison
Approximate seawater potentials indicate relative nobility, not joint compatibility or corrosion rate. Actual behavior depends on the environment, exposed areas, surface condition and electrical contact.
One-click scenarios — or pick any two alloys below.
Calculating...
Select two alloys to check their dissimilar-metal compatibility.
This metal has the lower potential. In contact, it will act as the anode and corrode preferentially to protect the other.
This metal has the higher potential. It is protected by the sacrificial action of the anodic metal.
Relative Position in Stack
Highlighted positions on the noble-to-active column.
01 · Series
From sacrificial to noble.
When two dissimilar metals contact in an electrolyte (seawater, condensation, even humid air), the more anodic metal corrodes preferentially while the more cathodic metal is protected. The further apart in this series, the more aggressive the galvanic attack. Potentials shown are approximate vs. saturated calomel electrode in flowing seawater at ambient temperature — actual values vary with temperature, oxygen content, flow, and surface condition.
| # | Material | Approx. potential | Family | Notes |
|---|---|---|---|---|
| 1 | Magnesium / Magnesium alloys | −1.60 to −1.65 V | Anodic (sacrificial) | Most anodic. Used as sacrificial anode for steel marine structures. |
| 2 | Zinc | −1.05 V | Anodic (sacrificial) | Common galvanic coating on steel; sacrificial in marine. |
| 3 | Aluminum 7075 | −0.83 V | Anodic (sacrificial) | High zinc content makes it more anodic than 6061; its copper raises pitting/SCC susceptibility. |
| 4 | Aluminum alloys (commercial) | −0.79 V | Anodic (sacrificial) | Range −0.75 to −0.85 V depending on alloy. |
| 5 | Aluminum 6061 | −0.75 V | Anodic (sacrificial) | Less anodic than 7075. Common structural alloy. |
| 6 | Cadmium | −0.70 V | Anodic (sacrificial) | Common protective plating on aerospace fasteners; banned in many applications post-2000. |
| 7 | Mild steel / Carbon steel | −0.61 V | Active | Reference for many practical comparisons. |
| 8 | Cast iron | −0.61 V | Active | Behaves similarly to mild steel. |
| 9 | Low-alloy steel (4140, 4340) | −0.60 V | Active | Slightly more noble than mild steel. |
| 10 | Stainless 304 (active) | −0.53 V | Active | When passive layer is breached. Avoid using in active state. |
| 11 | Inconel 600 (active) | −0.45 V | Active | Active state — typically passive in service. |
| 12 | Stainless 316 (active) | −0.43 V | Active | Active state — passivation required. |
| 13 | Lead-tin solders | −0.30 V | Intermediate | Common solder; intermediate position. |
| 14 | Lead | −0.27 V | Intermediate | Slightly more noble than solder. |
| 15 | Tin | −0.25 V | Intermediate | Common as plating for electrical contacts. |
| 16 | Aluminum bronze (C642 etc.) | −0.23 V | Intermediate | Aluminum/silicon bronze. Nickel-aluminum bronzes (C95500/C95800) are the true marine grades. |
| 17 | Brass (yellow / cartridge) | −0.22 V | Intermediate | 70/30 Cu-Zn (C260). Sits just anodic of copper, noble of tin/lead. Performance varies with alloy. |
| 18 | Bronze (silicon, phosphor) | −0.22 V | Intermediate | Silicon bronze C655, phosphor bronze C544. Noble of tin/lead, near copper. |
| 19 | Copper / Copper alloys | −0.20 V | Intermediate | ETP C110, brass C260. |
| 20 | Nickel (active) | −0.20 V | Intermediate | Pure nickel, active state. |
| 21 | 70/30 Cupronickel | −0.05 V | Passive | Highly corrosion-resistant marine alloy. |
| 22 | Silver | −0.05 V | Noble | Used in electrical contacts; can tarnish via H₂S. |
| 23 | Titanium / Ti-6Al-4V | +0.00 V | Noble | Self-passivating; excellent marine and biomedical performance. |
| 24 | Stainless 304 (passive) | +0.05 V | Passive | Passive layer makes it strongly cathodic. |
| 25 | Hastelloy C-276 | +0.05 V | Noble | Best-in-class corrosion resistance for chemical environments. |
| 26 | Stainless 316 (passive) | +0.08 V | Passive | Mo content gives slightly better pitting resistance than 304. |
| 27 | Stainless 17-4PH (passive) | +0.10 V | Passive | PH stainless in passive state. |
| 28 | Inconel 625 (passive) | +0.10 V | Passive | Cr-Mo-Nb superalloy; very strong passive layer. |
| 29 | Inconel 718 (passive) | +0.10 V | Passive | Aerospace superalloy; high Cr content. |
| 30 | Graphite | +0.25 V | Noble | Cathodic. Carbon-fiber composites act galvanically as graphite — incompatible with aluminum. |
| 31 | Gold / Platinum | +0.25 V | Noble | Among the most cathodic. Used as protective coating on critical electrical contacts. |
02 · How to use this
Picking compatible metals.
- Potential separation is not an acceptance limit.
Do not apply generic anodic-index limits to these flowing-seawater potentials. Review the governing corrosion specification, environment, exposed area ratio, surface condition and protection system. Similar potentials do not prove compatibility.
- Aluminum + steel — watch the environment.
~0.14 V apart by these numbers — tolerable in dry indoor service, but in wet/marine exposure aluminum sacrifices (the classic boat-trailer failure). Either isolate (nylon washer, dielectric grease, primer), or accept aluminum will pit.
- Stainless + carbon steel = also bad.
Passive 304 is much more cathodic than carbon steel. Stainless fastener in carbon steel structure → carbon steel corrodes around the fastener. Galvanized fasteners in stainless flanges have the opposite problem.
- Carbon-fiber composites act like graphite.
Strongly cathodic. Direct CFRP-to-aluminum contact is a major aerospace corrosion concern. Insulation layers and surface treatment are mandatory.
- Cadmium & zinc are sacrificial protective coatings.
Both are more anodic than steel, so they corrode first when scratched. Cadmium plating is being phased out in favor of zinc-nickel and other alternatives, but it’s still on legacy aerospace fasteners.
- A corrosion-resistant member can still accelerate attack on its partner.
As cathodic noble metals, they don’t corrode preferentially. The risk is the OTHER metal corroding. For Ti-on-aluminum contacts, the aluminum is the sacrificial side.
- The values shift with temperature, flow, oxygenation.
Stagnant water, low oxygen, or low temperature can shift relative potentials and even reverse pairings. For mission-critical applications, validate with actual testing — don’t rely on the table alone.
Keep exploring
Related tools & references
Plating and conversion coatings that isolate dissimilar-metal couples.
Companion property reference for the same alloy families.
CTE mismatch to weigh alongside galvanic potential at joints.
Corrosion behavior and chemistry for each material.
Choose compatible alloys for a given environment.
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