Galvanic Compatibility: Tin and Aluminum

Compatibility Assessment

Tin plate and tin-lead solder in contact with aluminum creates moderate galvanic risk. Acceptable in controlled environments but problematic in humid conditions.

Compatibility by Environment

The acceptable voltage difference depends on the operating environment:

• Harsh (outdoor/marine): ⚠️ Use caution (>0.15V)
• Normal (indoor/uncontrolled): ✅ Compatible (≤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 — Tin — 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 tin sheet will fail quickly, while tin rivets in aluminum are less problematic.

Prevention Strategies

• 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 + Brass — High Risk (0.5V)
• Aluminum + Bronze — High Risk (0.5V)
• Aluminum + Zinc — Moderate Risk (0.35V)