Galvanic Corrosion: Preventing Dissimilar-Metal Failures

The assembly passes every inspection. Months later, the joint where two different metals meet is chalky, swollen, and failing — and no one touched it.

That's galvanic corrosion, and it's one of the quietest ways a well-built part goes bad. Pair the wrong metals in the wrong environment and you've built a battery into your product, slowly eating itself from the contact point out.

The good news: galvanic corrosion is predictable, which means it's preventable. It follows clear electrochemical rules, and a few design decisions shut it down before it starts.

This article explains why dissimilar metals corrode when they touch, and walks through the practical ways to prevent galvanic corrosion — from material choice to isolation to environmental control — so your assemblies last as long as they should.

Why dissimilar metals fight: the galvanic cell

Galvanic corrosion isn't random. It's a tiny electrical circuit, and it needs four ingredients to run: two dissimilar metals, an electrical connection between them, and an electrolyte — usually just moisture — touching both.

When those four things line up, one metal becomes the anode and the other the cathode. The anode corrodes faster than it would alone, while the cathode is actually protected. In effect, the two metals form a battery, and the price of that battery is the steady sacrifice of the more active metal.

The bigger the electrochemical difference between the two metals, the faster the reaction runs. Two metals far apart on the galvanic series drive a strong current and rapid corrosion; two metals close together barely react at all.

This framing is what makes prevention possible. Because the corrosion depends on all four ingredients being present, you don't have to eliminate every one — interrupting a single link breaks the circuit. The next sections cover the three practical places to break it: the metals themselves, the electrical connection, and the electrolyte.

Choose compatible metals: reading the galvanic series

The cleanest fix is to prevent the mismatch in the first place. The galvanic series ranks metals by their electrochemical potential, showing which are anodic (more likely to corrode) and which are cathodic (more likely to be protected) relative to one another.

The design rule that follows is simple: when two metals must be in contact, choose ones that sit close together on the galvanic series. Small potential differences drive weak currents and slow corrosion, while large ones drive aggressive attack. Pairing stainless steel directly with bare aluminum, for instance, puts two metals far enough apart to create a real problem in a wet environment.

Imagine a designer specifying stainless fasteners for an aluminum panel. The stainless is cathodic and the aluminum anodic, so in the presence of moisture the aluminum around each fastener corrodes preferentially. Choosing a fastener metal closer to aluminum on the series — or isolating the two, as the next section covers — heads that off.

Relative surface area matters too. A small anode connected to a large cathode corrodes especially fast, because all the galvanic current concentrates on a little bit of the active metal. Where you can't avoid dissimilar metals, favor a large anode and small cathode rather than the reverse. Thinking through metal pairings early is the highest-leverage move you can make.

Break the circuit: electrical isolation

When dissimilar metals have to touch, you can stop the corrosion by making sure they don't actually make electrical contact. Isolation interrupts the connection link of the galvanic cell, so the circuit never completes.

The workhorses here are electrically inert spacers that also resist moisture. Neoprene, rubber, plastic, nylon, Teflon, Mylar, and glass-reinforced epoxy gaskets all serve as barriers between the two metals. At bolted connections, nylon or neoprene washers combined with bolt sleeves fully isolate a stainless fastener from an aluminum or galvanized member — the metals are clamped together mechanically but separated electrically.

The key is completeness. Isolation only works if it's total; a single point of metal-to-metal contact re-establishes the circuit and localizes all the corrosion right there. That means designing the isolation into the joint deliberately — sleeves through holes, washers on both faces, gaskets across the full mating surface.

This approach is especially useful when material substitution isn't an option, such as when a specific metal is required for strength, conductivity, or code. You keep the metals you need and simply insulate them from each other. Done right, electrical isolation lets otherwise incompatible metals share a joint for the long haul.

Control the electrolyte: coatings, drainage, and environment

The third link in the galvanic cell is the electrolyte — the moisture that carries current between the metals. Remove or block it, and even a mismatched metal pair can't corrode galvanically.

Coatings are the front line. A durable paint or sealant system over the connection keeps environmental moisture off the metal interface, cutting the reaction off at its source. When you coat, it's generally best to cover both metals or prioritize the cathode, so you don't accidentally concentrate attack on an exposed anode.

Environment and geometry matter just as much. Assemblies in sheltered, climate-controlled interiors rarely see galvanic corrosion simply because the electrolyte never shows up. Outdoor and immersed parts are the opposite, so design to shed water rather than trap it — avoid crevices and pockets that hold moisture, and add drainage so water can't pool at the joint.

Imagine an operations manager fielding warranty complaints about brackets corroding only on units installed outdoors. The indoor units, same metals and all, are fine. The difference isn't the design — it's the electrolyte. A sealed coating and a drainage path would let the outdoor units match the indoor ones.

Managing moisture is often the simplest and cheapest lever, and it pairs well with smart material choices and isolation for defense in depth.

6. The bottom line: design corrosion out before it starts

Galvanic corrosion is preventable because it's predictable. It needs two dissimilar metals, an electrical connection, and an electrolyte — and removing any one stops it. Choose metals that sit close together on the galvanic series, isolate them with inert gaskets and sleeves when they must touch, and control moisture with coatings, drainage, and sheltered placement. Layer those defenses and dissimilar-metal joints hold up for the life of the part.

As products combine more materials — mixing aluminum, stainless, and advanced alloys to hit weight and performance targets — designing against galvanic corrosion is only becoming more important. The teams that get it right treat material compatibility and finishing as part of the design, not a problem to patch later. That mindset is what separates assemblies that last from ones that quietly fail.

If you're combining metals in an assembly and want to be sure they'll hold up, the team at Engineered Mechanical Systems can help you think through material selection and protective finishing. EMS works across metals, stainless, and alloys and offers in-house painting, powder coating, and plating to protect the parts it builds. Reach out for a quote and bring your next project to life.