API 571 Certification (Corrosion & Materials) Practice Test

Which copper alloy undergoes dezincification when zinc content exceeds 15%?

1. Bronze

2. Cu-Ni alloy

3. Alloy 400 Brass

4. Silicon bronze

The correct answer is: Alloy 400 Brass

Dezincification is a specific form of corrosion that occurs in brass alloys, primarily when the zinc content exceeds approximately 15%. Alloy 400 Brass, which contains a significant amount of zinc (typically between 30% and 40%), is particularly susceptible to this phenomenon. In the dezincification process, zinc is selectively leached from the alloy due to the presence of aggressive environments, leading to a porous and weakened structure where copper remains. This results in compromised mechanical properties and potential failure of the component made from this alloy. Brass is a copper-zinc alloy, and while other choices include copper alloys like bronze and Cu-Ni alloys, these do not typically include zinc as a significant component or are not prone to dezincification in the same manner as brasses. For instance, bronze is primarily copper with tin and lacks the zinc that causes dezincification, and Cu-Ni alloys do not contain substantial amounts of zinc. Silicon bronze is also primarily copper, with silicon adding additional properties but again does not involve significant zinc content that could lead to dezincification issues. Thus, Alloy 400 Brass is clearly the most relevant choice regarding the susceptibility to dezincification.