Definition
A heat-treatment process that increases the strength and hardness of a metal, typically by heating it to a specific temperature and then cooling it rapidly (quenching). In aluminum alloys, hardening is often achieved through precipitation (age) hardening rather than quenching alone.
Plain English
A controlled process that makes a metal harder and stronger by heating it and then cooling it in a specific way.
Context Anchor
Seen in aircraft maintenance when discussing metal parts, heat treatment, tools, and repair procedures.
Derivation
From the everyday word 'hard.' In metallurgy, 'hardening' refers specifically to a deliberate process that changes the metal's internal structure to make it harder — not just the general idea of something becoming firm.
Why Pilots Care
Hardened parts resist wear and deformation, but they can also become more brittle. Maintenance technicians need to know whether a part has been hardened so they don't weaken it during repair, welding, or bending.
Intuition Check
Hardening does not just mean a part is naturally hard. In aircraft maintenance, it means a deliberate treatment used to make the material harder.
Example Sentence 1
After machining, the steel gear was sent out for hardening to give it the wear resistance it needed in service.
Example Sentence 2
Incorrect hardening of the bolt can cause it to crack under flight loads.