FAA Aviation Mechanic General (AMG)Materials, Hardware and ProcessesHard
A technician cadmium-plates a high-strength steel bolt with an ultimate tensile strength over 220,000 psi. What critical process must be performed after plating to prevent structural failure?
- AQuenching the part immediately in oil to lock in surface hardness
- BCold working the plated surface to increase fatigue strength
- CBaking the part at a specified temperature within a specified time to relieve hydrogen embrittlement
- DAnnealing the part at 1600°F to soften the base metal
Show answer & explanationAnswer & explanation
Correct answer: C. Baking the part at a specified temperature within a specified time to relieve hydrogen embrittlement
Electroplating processes like cadmium plating can introduce atomic hydrogen into high-strength steel, causing hydrogen embrittlement that leads to delayed cracking under load. Baking the part at a specified temperature within a specified time after plating drives out the absorbed hydrogen and restores ductility.
Why the other options are wrong
- A. Quenching in oil is a heat-treatment hardening step, unrelated to plating-induced hydrogen issues.
- B. Cold working would not remove absorbed hydrogen and could worsen embrittlement cracking.
- D. Annealing at high temperature would destroy the required heat-treated strength of the bolt.
Hydrogen Embrittlement Bake-Out
A heat treatment applied after electroplating high-strength steel parts to drive out absorbed hydrogen and prevent delayed brittle cracking.
- Required for steel parts with tensile strength above ~220,000 psi
- Must occur within a specified time after plating (often within hours)
- Baking temperature is typically 375-400°F for several hours
- Failure to bake can cause sudden, delayed cracking under load
Memory trick: "Plate then bake, or the bolt will break."