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When two dissimilar metals touch in the presence of moisture, one corrodes faster than it would alone. Pick two metals to check the risk, or scan the full matrix below. Risk is estimated from each metal's anodic index.
Compatibility
Read across from one metal to the other. Color shows the galvanic risk when the two are in direct contact in a damp or wet environment.
Every metal sits somewhere on the galvanic, or anodic, series. The larger the gap between two metals on that series, the stronger the driving force for corrosion when they touch with an electrolyte present (rain, condensation, salt spray). The more anodic metal — the one with the higher index — becomes the anode and corrodes first, sacrificially protecting the other. That is exactly why galvanized coatings work: the zinc is meant to corrode in place of the steel underneath.
Three things change real-world outcomes beyond the simple gap: the environment (a dry indoor panel is far more forgiving than a coastal install), the relative surface areas (a small anode bolted to a large cathode corrodes fast — keep fasteners as noble as or more noble than what they join), and any coatings or isolation between the two metals. Painting, gaskets, isolating washers and sealants can make an otherwise risky pair workable.
If a combination lands in caution or avoid, the usual fixes are: isolate the metals with a non-conductive gasket or coating; select fasteners that are equal to or more noble than the parts they join (for example stainless A4-80 hardware on stainless assemblies); keep the more-anodic metal as the larger surface; or specify a single material throughout where the budget allows.
Russell Consulting LLC provides mechanical design and material-selection guidance — from concept through production — so your assemblies hold up in the real world.
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