Galvanic corrosion risk checker
Pick the aluminium alloy, the coupled metal, the environment and the area ratio to get a risk band and the mitigation that fits.
Aluminum side
Other metal in contact
A desktop screen, not a design calculation. Three multipliers are applied to the base couple risk: environment severity and the coupled area ratio.
Risk = base risk(couple) × env factor × area-ratio factor
| Mitigation | When it applies |
|---|---|
| Insulating washer / sleeve | Any bolted dissimilar-metal joint |
| Zinc or aluminium anodes | Immersed aluminium coupled to steel |
| Coating both faces | Large-area couples, splash zone |
| Stainless fasteners, A4-70 | Above waterline fittings into 5xxx plate |
- Use aluminium or A4-70 stainless fasteners. Never let a copper alloy touch immersed aluminium.
- Painting both faces of a dissimilar-metal joint slows the couple by cutting the exposed cathode area.
- For an aluminium hull with a steel engine bed, fit insulating pads and keep the bed drained — a wet bilge is the worst case.
People also ask
Which metal must never touch aluminium in seawater?
Copper and its alloys — brass, bronze, gunmetal. The potential gap is large and the couple drives rapid pitting of the aluminium. Copper alloy fittings belong above the waterline only.
Is stainless steel safe with aluminium?
Safer than copper but not neutral. Stainless is cathodic to aluminium, so a small anode / large cathode ratio is the problem. Insulate, and keep the aluminium area large relative to stainless.
Why does area ratio matter so much?
The corrosion current concentrates on the anode. A small aluminium area coupled to a large stainless area corrodes very fast; the reverse is mild.
How do anodes help?
Zinc or aluminium anodes make the hull the cathode instead, sacrificing themselves. They are the standard protection for immersed aluminium, alongside the coating system.
Does 5083 resist galvanic attack better than 5052?
The alloy choice matters less than the couple and the coating. 5083 is preferred for immersed structure for its pitting and stress-corrosion behaviour, not for its potential.
Should I use Duralac or a similar compound?
Yes — a chromate-loaded jointing compound on the faying surfaces plus an insulating washer gives a joint that survives years of splash-zone exposure.
Need plate to match these numbers?
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