How to Prevent Galvanic Corrosion When Mixing Metals

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Galvanic corrosion happens when two different metals touch in the presence of moisture, and the less noble one corrodes faster. To prevent it, electrically isolate the metals with non-conductive gaskets or washers, choose compatible fasteners, and keep water from bridging the joint.

What causes galvanic corrosion?

Every metal has a different tendency to give up electrons. When two dissimilar metals are in electrical contact and an electrolyte such as rain, condensation, or salty air links them, a small current flows and the more active metal slowly corrodes. Aluminum and mild steel are especially vulnerable when joined to stainless steel.

The effect depends on three things working together: a conductive path between the metals, a wet film or moisture, and a significant difference in their electrical potential. Remove any one of them and the risk drops sharply.

Isolate the metals at every contact point

The most reliable prevention is to stop the metals from touching directly. Use non-conductive separators such as nylon or neoprene gaskets, plastic sleeves for bolts, and insulating washers under nuts and heads.

Place a continuous gasket between aluminum profiles and stainless fittings.
Use insulating sleeves inside drilled holes.
Check that paint or coating has not created a metal-to-metal bridge.

Choose the right fasteners

Fasteners are a common weak point. A stainless steel bolt in an aluminum part, or a zinc-plated steel screw in stainless, can start a corrosion cell even when the main parts are isolated. Match the fastener material to the parts it joins as closely as possible.

Use stainless steel fasteners of a suitable grade for stainless assemblies, and where mixing is unavoidable, use isolating washers and a sealant that keeps water out of the joint.

Control moisture and the electrolyte

Water is what turns a minor contact into active corrosion. Design joints so that water drains away rather than pooling. Seal gaps with a suitable sealant, avoid crevices where moisture can sit, and make sure drainage holes are open.

Near the sea or in dusty, humid outdoor areas, the electrolyte is more aggressive, so extra sealing and inspection become more important.

Use protective coatings wisely

Coatings can reduce galvanic risk, but only if they are intact. A scratch that exposes bare metal at a joint can become a corrosion site. Apply coatings to both metals where possible, and avoid painting only the less noble part, which can concentrate attack on small exposed areas.

Hot-dip galvanizing and powder coating are effective finishes for steel components, and they should be applied before assembly so that cut edges and joints are protected too.

Plan the detail during design

The cheapest protection is good design at the drawing stage. Decide early which metals will meet, specify isolation materials and fasteners in the written specification, and detail how water will be kept out. Changing the detail after production is far more difficult.

Note every dissimilar-metal contact on the drawing.
Specify isolation and sealing for each one.
Confirm exact material choices with your engineer.

Inspect and maintain over time

Even well-designed joints should be checked periodically. Look for white or grey powdery deposits on aluminum, rust staining on stainless, and loose or swollen gaskets. Early signs are easy to address by cleaning, resealing, or replacing an isolator before damage spreads.

Keep a simple maintenance routine, especially for exterior gates, railings, and structures exposed to rain and salt air.

Frequently asked questions

Can stainless steel and aluminum be used together?

Yes, but they should be electrically isolated with non-conductive gaskets or washers and sealed against moisture. Without isolation, the aluminum is at risk of corroding.

Do I need special fasteners when mixing metals?

Ideally, yes. Match the fastener material to the joined parts where possible, and use isolating washers or sleeves when dissimilar metals must be fastened together.

Is painting enough to prevent galvanic corrosion?

Paint helps, but it is not enough alone. Coatings can be scratched or worn, so physical isolation and good drainage remain essential at the joint.

How do I know if galvanic corrosion has started?

Look for powdery white or grey deposits, rust streaks near a joint, or swelling and cracking of the metal around a fastener. If you see these, have the joint inspected promptly.

Common mistakes to avoid

Many installers bolt stainless directly onto aluminum or steel without isolation, or use plain zinc-plated fasteners in stainless assemblies. Both shortcuts often cause corrosion within a few seasons.

Our recommendation

Specify isolation, fastener material, and sealing for every dissimilar-metal joint in the written specification before production, and confirm the details with your engineer.

Summary

Galvanic corrosion is preventable by isolating dissimilar metals, choosing compatible fasteners, controlling moisture, and planning the detail at design stage.

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