Galvanic corrosion between aluminum and stainless steel is preventable, but only if you break the electrochemical circuit that causes it. When these two metals touch in the presence of moisture, aluminum acts as the sacrificial metal, corroding while stainless steel stays intact. The key is to interrupt one or more of the three requirements for galvanic corrosion: direct metal-to-metal contact, an electrolyte (moisture or water), or a completed electrical path. Remove any one of those, and corrosion stops.
Why Aluminum Corrodes Next to Stainless Steel
Every metal has an electrochemical potential, essentially a willingness to give up electrons. Aluminum is far more “active” (willing to corrode) than stainless steel, which sits on the “noble” end of the galvanic series. When the two metals are in contact and an electrolyte like rainwater, saltwater, or even condensation bridges the gap, aluminum donates electrons to the stainless steel. The result is accelerated corrosion of the aluminum, often appearing as white powdery deposits, pitting, or fissures that can extend hundreds of microns deep into the aluminum surface.
The farther apart two metals sit on the galvanic series, the more aggressive the corrosion. Aluminum and stainless steel are separated by a significant voltage difference, making this one of the more problematic pairings in everyday fabrication. Saltwater environments make it dramatically worse because salt solutions are highly conductive electrolytes.
Insulate the Joint With a Barrier Material
The most reliable prevention method is physically separating the two metals so electrons can’t flow between them. You do this by placing a non-conductive material at every point of contact. PTFE (Teflon) tape is one of the best choices because it’s waterproof, non-stick, and holds up under heavy loads. It works well in marine and outdoor applications where moisture exposure is constant.
Other effective barrier materials include:
- Nylon: Tough and flexible, commonly used for insulating washers in general assemblies
- HDPE (high-density polyethylene): Chemically resistant, suited for industrial and outdoor use
- Neoprene: Flexible and weatherproof, ideal for gaskets and seals
- NEMA G-10 laminate washers: Specifically designed for bolt and fastener insulation in structural joints
For bolted connections, the fastener itself is a common failure point. If you run a stainless steel bolt through an aluminum plate without insulation, the bolt hole becomes a corrosion hotspot. Use insulating sleeves around the bolt shaft and non-conductive washers under the head and nut. Every metal-to-metal contact point needs a barrier, not just the obvious ones.
Apply Protective Coatings
When full physical isolation isn’t practical, coatings add a second line of defense. You can coat one or both metals to block moisture from completing the circuit. Paint, powder coating, anodizing (for the aluminum), or applying a zinc-rich primer all create a protective film between the metal surface and the environment.
The general rule is to coat the more noble metal (stainless steel) rather than the less noble one (aluminum). If you only coat the aluminum and the coating gets scratched or worn, the small exposed area of aluminum will corrode rapidly because all the galvanic attack concentrates on that tiny spot. Coating the stainless steel reduces its effective cathode area, which slows the reaction even if some aluminum is exposed.
Coating both metals provides the best protection. In marine environments, epoxy-based primers or zinc chromate coatings on the aluminum combined with a painted or powder-coated stainless steel surface can extend the joint’s life by years.
Use Anti-Corrosive Compounds at the Joint
Anti-corrosion pastes and gels fill the microscopic gaps between mating surfaces where moisture would otherwise collect. Tef-Gel is one of the most widely used products for this purpose. It’s a white, high-viscosity gel that’s chemically stable and non-reactive, with a working temperature range of -60°C to 280°C. You apply it to fasteners, fittings, and contact surfaces before assembly.
Tef-Gel serves multiple roles: it blocks galvanic corrosion between dissimilar metals, prevents galling (seizing) of stainless steel threads, and acts as an assembly lubricant so you can disassemble the joint later for maintenance. Duralac is another option, a green jointing compound that’s been used in aerospace for decades. Both products work by displacing moisture and creating a non-conductive film at the interface.
These compounds are especially useful in situations where you can’t fully insulate the joint, like retrofit repairs or assemblies where tolerances are too tight for washers and sleeves.
Control the Cathode-to-Anode Area Ratio
One of the most overlooked factors in galvanic corrosion is the ratio of surface areas between the two metals. A large stainless steel surface connected to a small aluminum part is a worst-case scenario. The large cathode (stainless steel) drives corrosion on the small anode (aluminum) at a concentrated, accelerated rate.
Wherever possible, design the assembly so the aluminum component has a much larger surface area than the stainless steel component. A small stainless steel fastener in a large aluminum panel, for example, is far less problematic than a large stainless steel bracket bolted to a small aluminum fitting. This doesn’t eliminate galvanic corrosion, but it spreads the attack over a larger area, slowing the rate of damage significantly.
Keep Moisture Out of the Joint
Without an electrolyte, galvanic corrosion can’t occur. In dry indoor environments, aluminum and stainless steel can coexist with minimal issues. Problems start when moisture enters the picture, and saltwater, industrial chemicals, or acidic rain make it worse.
Sealing the joint against moisture ingress is a practical prevention strategy. Silicone sealants, butyl tape, or closed-cell foam gaskets can keep water from reaching the metal interface. In outdoor installations, design the joint so water drains away rather than pooling at the connection point. Avoid creating crevices or pockets where moisture can sit, because standing water accelerates corrosion far faster than occasional splashing.
Recognizing Early Signs of Galvanic Attack
Even with preventive measures in place, periodic inspection catches problems before they become structural. On aluminum, galvanic corrosion typically shows up as white or gray powdery deposits around the contact area. This is aluminum oxide forming as the metal corrodes. As damage progresses, you’ll see pitting, which appears as small craters or rough patches on the aluminum surface near the stainless steel contact point.
In more advanced cases, corrosion fissures develop beneath the surface and can extend deep into the aluminum. Research using high-resolution imaging on aluminum alloy riveted to stainless steel has shown fissures ranging from 1 micron to 500 microns in depth, sometimes following the grain structure of the metal. These subsurface cracks aren’t always visible from the outside, which is why you should check for softness, discoloration, or weeping around fastener holes during routine maintenance.
In salt-exposed environments, inspect joints at least annually. In marine applications, every six months is more appropriate. If you spot early signs, disassemble the joint, clean off corrosion products, and reassemble with fresh insulation and anti-corrosion compound before the damage compromises the aluminum’s structural integrity.