Question

Which mechanical property gets affected in an alloy, when it is in over-aged condition:
1. lower hardness
2. low strain hardening rate
3. higher yield strength
4. higher tensile strength

Answer 1

Correct Answer - Option 1 : lower hardness

Explanation:

Ageing

• The ageing phenomena are associated with Aluminium alloys mainly.

• Age hardening curves of the alloys basically contain the initial hardness increase, Maximum hardness and subsequently decreased hardness with ageing time which is called the under ageing, Peak ageing and over ageing stages respectively.
• Under ageing stage – Particles are cut by moving dislocations (The cutting mechanism)
• Over ageing stage – Particles are not cut and dislocations move away from particles leaving dislocation loop (The Orowan mechanism).
• The mechanical strength of alloys can be increased by controlling the precipitate microstructure.