Preventing Galvanic Corrosion: A Checklist for Joining Aluminum Tubes to Dissimilar Metals

Aluminum is a miracle metal for modern construction and manufacturing. It is lightweight, strong, and naturally resistant to atmospheric corrosion. However, for builders and engineers across the USA, aluminum has one significant “Achilles’ heel”: it does not play well with others. When you connect aluminum tubes to metals like carbon steel or stainless steel, you risk triggering a chemical reaction known as galvanic corrosion.

At Aluminium Tubes, we believe in not only supplying the highest quality materials but also ensuring they last a lifetime in your projects. Whether you are building marine structures, industrial frameworks, or custom automotive parts, understanding how to manage dissimilar metals is critical. This guide provides a practical checklist for galvanic corrosion prevention aluminum users need to know.

What is Galvanic Corrosion?

Before diving into the solution, it helps to understand the problem. Galvanic corrosion occurs when two different metals are in electrical contact while submerged in or wetted by an electrolyte (like saltwater, condensation, or even rainwater).

Think of it as a battery. One metal acts as the anode (the active metal) and the other as the cathode (the noble metal). In this reaction, electrons flow from the anode to the cathode. Unfortunately for us, aluminum is near the “active” end of the galvanic series, meaning it usually becomes the anode. Consequently, the aluminum sacrifices itself, corroding at an accelerated rate to protect the other metal.

The Dissimilar Metal Contact Guide

To protect your Aluminium Tubes products, you must know which metals pose the biggest threat. The further apart two metals are on the galvanic series, the higher the voltage potential and the faster the corrosion.

• High Risk: Copper, Brass, Bronze.
• Moderate/High Risk: Carbon Steel, Stainless Steel (300 series).
• Low Risk: Zinc (Zinc actually protects aluminum, which is why it is used in sacrificial anodes).

Your Checklist for Joining Aluminum to Dissimilar Metals

If your design requires joining aluminum to stainless steel or carbon steel, you do not have to abandon the idea. You simply need to break the “battery circuit.” Use this checklist to ensure your joints remain secure and corrosion-free.

1. Isolate the Metals (Break the Circuit)

The most effective way to stop galvanic corrosion is to prevent the two metals from touching directly.

• Use Washers and Gaskets: Insert non-conductive materials such as neoprene, rubber, plastic, or nylon between the aluminum tube and the steel bracket or plate.
• Install Bushings and Sleeves: For bolted connections, the bolt shank itself can create a bridge between the metals. Use plastic or nylon sleeves inside the bolt holes to ensure full electrical isolation.
• Use PTFE: For high-end applications, Polytetrafluoroethylene (PTFE) pads or coated washers provide excellent insulation and water repellency, breaking the water film that facilitates corrosion.

2. Get Your Coating Strategy Right

Painting or powder coating is a common defense, but there is a specific rule you must follow.

• Coat the Cathode (Steel): If you can only coat one metal, coat the more noble metal (the steel). If you coat only the aluminum (the anode) and that coating gets scratched, the corrosion will focus intensely on that small scratch, leading to rapid failure.
• Coat Both: Ideally, apply a dielectric coating (like epoxy or polyurethane) to both surfaces to seal out the electrolyte entirely.

3. Manage the Area Ratio

Size matters in galvanic corrosion.

• Avoid Large Cathodes: Never connect a small aluminum part to a large steel structure without isolation. The large steel cathode will draw a massive current from the small aluminum anode, destroying it quickly.
• Aim for Large Anodes: Conversely, a large aluminum structure with small stainless steel fasteners is generally safer, though isolation is still recommended.

4. Fastener Selection

Fasteners are the most common failure points.

• Choose Stainless Steel Carefully: While 300-series stainless steel fasteners are standard, they are cathodic to aluminum. Always use them in conjunction with insulating plastic or nylon washers.
• Avoid Galvanized Bolts: Zinc plating on steel bolts can wear off, leaving bare steel in contact with your aluminum tubing, restarting the corrosion cycle.

5. Eliminate the Electrolyte (Drainage)

Without water (the electrolyte), the reaction cannot happen.

• Design for Drainage: Ensure your aluminum tube structures allow water to drain away rather than pool at the joints.
• Use Sealants: Apply corrosion-inhibiting pastes or sealants in the crevices between joints to keep moisture out.

Aluminum Tube Maintenance Tips

Even with the best design, environmental factors change. Regular maintenance is key to longevity, especially in the US coastal or industrial regions where salt and pollution increase conductivity.

• Inspect for “White Rust”: Unlike red iron rust, aluminum corrosion appears as a white, chalky sludge (aluminum hydroxide). If you see this around a joint, your isolation method may have failed.
• Rinse Regularly: If your application is near the ocean or salted roads, rinse the tubes with fresh water to lower the conductivity of the surface environment.
• Check Sealants: Over time, sealants and plastic washers can degrade from UV exposure. Inspect these barriers annually and replace them if they become brittle or cracked.

Conclusion

Using aluminum in conjunction with other metals opens up a world of structural possibilities, provided you respect the chemistry involved. By isolating connections, choosing the right coatings, and managing moisture, you can ensure your projects stand the test of time.

At Aluminium Tubes, we are dedicated to helping our US customers build smarter and stronger. Whether you need high-grade material for a new project or advice on maintaining existing structures, we are here to support your success. Don’t let corrosion eat away at your investment—plan ahead and build with confidence.