While aluminum is being used more extensively in new vehicle bodywork, it’s often used in combination with steel structural components. And wherever steel and aluminum meet, there’s a chance for galvanic corrosion to occur. Also known as bi-metallic corrosion, it occurs when two dissimilar metals come into electrical contact in the presence of an electrolyte (such as water, road salt, or moisture in the air).
Once water or humidity enters tight crevices between aluminum and steel, it facilitates the transfer of ions. Because aluminum is more anodic than steel, it tends to corrode preferentially at the point of contact. Over time, this corrosion can manifest as white or gray powdery deposits (aluminum oxide) and, in severe cases, pitting or structural damage.
The problem is not new. Many manufacturers, such as Land Rover, used aluminum bodywork over steel frames after WWII when steel was in short supply. Others, like Ferrari and Porsche, took advantage of aluminum’s light weight to help win races. Many companies learned how to reduce the likelihood of this chemical reaction by applying epoxy primers, sealants, and other preventatives. Over time, however, the best prevention can often give way to minor damage and deterioration, and nature takes its course.
Identifying Galvanic Corrosion
If you have a vehicle with aluminum body panels, it’s worth inspecting areas where the aluminum may make contact with steel parts. In the case of some vehicles (including our Range Rover project), it may be aluminum door skins over a steel door frame. If you own a late-model Ford pickup, you may want to check where the aluminum bed mounts to the steel chassis.
Typical indicators of galvanic corrosion include paint bubbling or blistering around seams, edges, or fasteners. White, powdery deposits (aluminum oxide) are the telltale at contact points. Pitting or flaking metal can also occur, especially on aluminum surfaces. Finally, check for rust stains near steel components in close proximity to aluminum parts.
Repairing Galvanic Corrosion
Should you discover corrosion between your aluminum and steel components, you’ll want to repair it as quickly as possible. Start by removing any trim, seals, or fasteners in the affected area, exposing the aluminum-steel interface where corrosion is most visible. In many cases, you can stop the process before it does permanent damage. Here are the steps you can take to repair your vehicle.
Mechanically remove corrosion – Use methods such as wire brushing, sanding, or gentle blasting (e.g., plastic media or soda blasting) to remove the corroded material. Be cautious not to remove excessive base material from the aluminum panel.
Chemical treatment (optional) – In some cases, a mild acid wash or conversion coating may help remove oxidation and prepare the surface for refinishing. Rinse thoroughly with a neutralizing solvent and ensure the panel is fully dried to prevent trapping moisture.
Apply a suitable primer – Use an epoxy primer or a corrosion-inhibiting primer designed specifically for aluminum and steel. This step seals the bare metal and creates a protective barrier.
Refinish and protect – After the primer cures, apply the topcoat (paint) and clear coat as necessary. Ensure edges, seams, and fastener holes are sealed properly. In some cases, seam sealers or additional protective coatings (e.g., rubberized undercoating) can be applied to vulnerable joint areas.
Replace fasteners if needed – If the original fasteners are corroded or are made from a metal incompatible with aluminum (e.g., plain steel screws in aluminum panels), replace them with appropriate coated or stainless steel fasteners to reduce future galvanic action.
How to Prevent Galvanic Corrosion from Returning
Insulate the metals – Whenever possible, prevent direct contact between aluminum and steel. Use non-conductive materials such as plastic washers, nylon spacers, rubber gaskets, or specialty tapes. Proper insulation blocks the electrical pathway that causes galvanic corrosion.
Use proper coatings and sealers – Maintain paint and protective coatings, especially at edges, seams, and fastener points. Apply corrosion-resistant primers or sealers specifically designed for dissimilar metals (e.g., epoxy primers, zinc-rich primers).
Select compatible fasteners – Fasteners should be coated or made from materials that minimize galvanic potential with aluminum (e.g., high-quality stainless steel, zinc-nickel plated steel, or aluminum fasteners where appropriate). This reduces the chance of creating a galvanic couple at each bolt or screw.
Keep it dry and clean – Regularly wash your vehicle to remove road salt and grime, paying special attention to seams and joints. Keeping these areas clean and dry greatly reduces the electrolyte’s presence that drives galvanic corrosion.
Periodically inspect and maintain – Check areas where dissimilar metals meet for paint chips, scratches, or visible corrosion. Promptly address any damaged coatings to prevent moisture intrusion.
Acid etching will remove rust where it has perforated the paint, but that will only be temporary. Once you have rust, the only way to truly prevent it returning is to strip back to bare metal and refinish properly.
How do you remove rust off paint without removing the paint?