A manganese bronze propeller displays soft, porous, and red surface. What is NOT a cause of dezincification?

The phenomenon of dezincification primarily affects brass alloys, which are predominantly composed of copper and zinc. When considering the causes of dezincification, it's essential to understand the nature and mechanisms of each potential cause.

Cathodic overprotection refers to the application of a cathodic protection system that may inadvertently lead to excessive negative charge on the metal surface. In this context, manganese bronze, which contains copper and other alloying elements, can become overprotected, preventing the normal electrochemical processes that might otherwise lead to dezincification. Essentially, if cathodic protection is excessive, it can hinder the dezincification process rather than promote it, making it a non-contributory factor in this case.

On the other hand, simple electrochemical corrosion, galvanic corrosion, and stray current attack are all mechanisms that can lead to the dissolution of zinc from the alloy. Simple electrochemical corrosion occurs due to the natural potentials of metals in seawater, galvanic corrosion arises when two dissimilar metals are in contact in an electrolyte, and stray current attack happens when electrical currents inadvertently pass through the metal, which can exacerbate corrosion effects.

Thus, recognizing that cathodic overprotection can prevent dezincification helps clarify why it is not