Compare Zinc-Nickel plating with traditional Cadmium plating for carbon steel retaining rings.

Cadmium plating was historically the standard for aerospace due to its lubricity and excellent corrosion resistance. However, due to its high toxicity and environmental regulations (REACH/RoHS), Zinc-Nickel (Zn-Ni) has become the preferred alternative. Zn-Ni provides comparable or superior salt-spray resistance ($>1000$ hours) and exhibits better galvanic compatibility with aluminum housings. Crucially, Zn-Ni plating processes generally involve less hydrogen evolution, though high-strength carbon steel rings ($>40$ HRC) still require a mandatory de-embrittlement bake to prevent delayed brittle fracture.