Strain hardening aluminum alloys
aluminum cold deformation
Hardening It occurs during the cold deformation of the product. During plastic deformation alyuminevogo alloy at a temperature below that, at which there is a return and / or recrystallization (for aluminum – usually lower 150 °C), dislocations in the metal structure have the ability to move (provide plastic deformation) and multiply. The movement and multiplication of dislocations leads to an increase in their density, and entanglement among themselves. Therefore each subsequent plastic deformation takes more energy. The metal becomes harder, with a high yield. The greater the degree of deformation or strain hardening, the more pronounced this effect.
Hard-working of aluminum and aluminum alloys occurs during any cold deformation processing of products: cold rolling, deep-drawn, shoeing, flanging and even ordinary coiling.
The annealing operation has two phases: 1) "Return" or "rest" and 2) "Recrystallization". During the return, there is some "softening" of the metal as a result of restructuring and dislocation annihilation, bringing the released internal energy stored plastic strain. Return begins at a temperature generally 0,3 from melting point (in degrees Kelvin). In the recrystallization step in some areas material undeformed grains nucleate, that grow and absorb all the distorted, or "rested" as a result of the microstructure of return. Further heat treatment results in grain growth and coarsening. The result is grain coarsening, that grain boundaries becomes smaller. The grain boundaries act as barriers to movement of dislocations. therefore, fewer barriers, the less energy is required to dislocations movement, a, Consequently, metal is easier to deform plastically. It becomes softer and more pliable.