Galvanic Compatibility Chart: Anodic Index per MIL-STD-889
Pick the housing metal and the gasket filler or mating metal; the tool returns the anodic-index difference, whether the couple survives your environment, and which metal sacrifices itself.
Built for: choosing EMI gasket fillers, dissimilar-metal joints, and plating callouts that will not corrode the enclosure.
Galvanic Compatibility Checker
How it works — formula, worked example & reference
Formula: Compatibility is judged by the difference in anodic index (MIL-STD-889): ΔV ≤ 0.25 V for harsh/exposed environments, ΔV ≤ 0.50 V for controlled environments. The metal with the higher index is anodic and corrodes first.
Worked example: Aluminum housing (0.90 V) with a silver-filled gasket (0.15 V): ΔV = 0.75 V — over both limits; the aluminum corrodes. A nickel-filled gasket (0.30 V) against passivated stainless (0.50 V) gives ΔV = 0.20 V — acceptable even exposed.
| Metal (housing or filler) | Anodic index (V, MIL-STD-889) |
|---|---|
| Silver | 0.15 |
| Nickel | 0.30 |
| Stainless steel (passive) | 0.50 |
| Tin | 0.65 |
| Steel | 0.85 |
| Aluminum | 0.90 |
Values per MIL-STD-889 as used on the H-O EMI shielding pages; consult the standard for finishes not listed.
These results are engineering estimates for preliminary material selection; final validation is the responsibility of your engineering team.
Common questions
What is the anodic index?
A voltage assigned to each metal or finish per MIL-STD-889 that predicts galvanic behavior: the larger the difference between two mated metals, the faster the more anodic (higher-index) metal corrodes.
How much anodic-index difference is acceptable?
Common MIL-STD-889-based practice: keep the difference at or below 0.25 V for harsh or marine exposure and 0.50 V for controlled indoor environments. Larger gaps need isolation, compatible plating, or a different filler.
Which metal corrodes?
The more anodic one — the higher anodic index. Aluminum (0.90 V) mated to silver (0.15 V) sacrifices the aluminum housing, which is why silver-filled EMI gaskets on bare aluminum are a classic corrosion mistake.
How do EMI gaskets avoid galvanic corrosion?
Pick a filler close to the housing index (nickel-graphite on a chromate conversion-coated aluminum housing is the common combination — the coating breaks the couple), plate or convert the housing surface, and keep the joint sealed so no electrolyte bridges the couple.