Work Hardening and Aging Strengthening

Work hardening refers to the increase in strength and hardness of metal materials as the degree of plastic deformation increases; The phenomenon of decreased plasticity and toughness. Work hardening (cold deformation) is the main strengthening method for metal materials that cannot be strengthened by heat treatment.

The mechanism of work hardening is that as plastic deformation progresses, the density of dislocations continues to increase, resulting in intensified mutual delivery of dislocations during movement. As a result, fixed cutting steps, dislocation entanglement, and other obstacles are generated, increasing the resistance to dislocation movement and deformation resistance, making it difficult to continue plastic deformation and thus improving the strength of the metal

Rule: As the degree of deformation increases, the strength and hardness of the material increase, plasticity and toughness decrease, and dislocation density continues to increase，According to the formula，It can be seen that the strength is proportional to the half power of the dislocation density ρ, and the larger the Burgundy vector b of the dislocation, the more significant the strengthening effect。

Work hardening curve: The curve is divided into three stages

1) Easy slip stage (less interference from dislocations)

2) Linear hardening stage (dislocation pile up)

3) Parabolic hardening stage (spiral dislocation initiation, dislocation density decrease)

The essence of work hardening:

When metal undergoes plastic deformation, internal slip occurs, causing grain deformation and refinement of the microstructure, resulting in a large number of dislocations, severe lattice distortion, and increased internal stress. Its macroscopic effect is work hardening.

Time hardening refers to the method of strengthening a material by obtaining a supersaturated solid solution and insulating it at a certain temperature to precipitate transition phases and second phases.

Aluminum alloys can be strengthened by aging after obtaining supersaturated solid solutions.