Not All Dissimilar Metals Will Cause Galvanic Corrosion
Between quiet metals, there are invisible conversations. One gives, one receives.
Not every meeting becomes a disaster. Not every difference becomes war. Sometimes the distance is small enough for peace to remain, even beneath rain, salt, and time.
But when the potential grows too great, the less noble metal slowly sacrifices itself to protect the other. Corrosion begins silently — not with noise, but with imbalance.
In engineering, people often hear the blanket warning: “Never mix dissimilar metals.”
The reality is more nuanced. Just because two metals are different does not automatically mean galvanic corrosion will occur. What actually matters is the electrochemical potential difference between them, whether they are electrically connected, and whether an electrolyte (water, humidity, condensation, or salt spray) is present.
Galvanic Corrosion Explained
Galvanic corrosion is an electrochemical process. When two metals with sufficiently different potentials are in electrical contact in the presence of an electrolyte, the less noble (more anodic) metal becomes the anode and corrodes preferentially, while the more noble (cathodic) metal is protected.
The greater the potential difference, the stronger the driving force for corrosion.
The Galvanic Series
Engineers use the galvanic series — a ranking of metals by their nobility in a given environment (commonly seawater) — to assess compatibility. Metals positioned close together on the series have lower risk. Metals far apart have higher risk.
Examples:
Stainless steel (passive) and copper are relatively close in many environments and can often be used together with acceptable performance, especially in mild conditions.
Aluminum and copper (or aluminum and stainless steel) are far apart and create a strong galvanic couple — particularly problematic in wet, coastal, or marine environments.
Important note: In seawater or high-chloride environments, passive stainless steel is more noble than copper, so the copper can become the anode and corrode faster when the two are coupled.
Environment Is Critical
Even metals with a noticeable potential difference may not corrode severely if any of the three required conditions are missing:
Electrical connection between the metals
Presence of an electrolyte
Significant potential difference
Without moisture or an electrolyte, galvanic corrosion is greatly reduced or stopped. This is why dry indoor applications can tolerate combinations that would be risky outdoors, especially in coastal areas like Hawaii.
Good Engineering Is About Context
In real-world design, engineers don’t blindly avoid every dissimilar pair. Instead, they evaluate:
Proximity on the galvanic series
Environmental exposure (especially chlorides)
Relative surface areas (large cathode + small anode = accelerated attack on the anode)
Protective coatings, paints, or platings
Electrical isolation (gaskets, sleeves, insulators)
Expected service life
Good engineering is rarely about absolute rules. It is about understanding the physics behind the rule — and designing accordingly.
Sometimes the quietest failures begin where two materials meet.