Galvanic Compatibility: Aluminum and Brass

Compatibility Assessment

Brass contains copper, making it significantly cathodic relative to aluminum. The 0.50V difference will cause accelerated corrosion of the aluminum, particularly in marine or industrial atmospheres.

Compatibility by Environment

The acceptable voltage difference depends on the operating environment:

• Harsh (outdoor/marine): ❌ Not recommended (>0.15V)
• Normal (indoor/uncontrolled): ⚠️ Use caution (>0.25V)
• Controlled (HVAC): ✅ Compatible (≤0.50V)

Thresholds per MIL-STD-889 guidelines. Harsh = saltwater, industrial, outdoor. Normal = warehouse, uncontrolled indoor. Controlled = temperature/humidity regulated.

How Galvanic Corrosion Works

When two dissimilar metals are in electrical contact and exposed to an electrolyte (water, especially saltwater), an electrochemical cell forms:

1. The more anodic (active) metal — Aluminum in this case — loses electrons and corrodes.
2. The more cathodic (noble) metal — Brass — is protected and may even corrode less than it would alone.
3. The corrosion rate increases with the voltage difference between the metals and the amount of moisture present.

The area ratio also matters critically: a small piece of anodic metal in contact with a large cathodic surface will corrode much faster than the reverse. For example, aluminum rivets in a brass sheet will fail quickly, while brass rivets in aluminum are less problematic.

Prevention Strategies

• Insulating gaskets/washers: Place non-conductive material between the metals to break the electrical path.
• Protective coatings: Apply paint, lacquer, or specialized coatings to one or both metals.
• Sacrificial anodes: In critical applications, add a more anodic (active) metal that corrodes preferentially.
• Design for drainage: Ensure water cannot pool at the junction of dissimilar metals.

Related Metal Pairings

• Aluminum + Stainless Steel — High Risk (0.4V)
• Aluminum + Steel — Low Risk (0.05V)
• Aluminum + Copper — Severe Risk (0.55V)
• Aluminum + Bronze — High Risk (0.5V)
• Aluminum + Zinc — Moderate Risk (0.35V)
• Aluminum + Titanium — Severe Risk (0.6V)