Solid solution hardening (Topic: 10039)

The reason for the increase in strength due to atoms in solid solution is mainly due to lattice distortion.

A replacement of aluminium atoms with foreign atoms causes a distortion of the atomic lattice. This distortion inhibits the mobility of the dislocations.

The solute atoms find more stable places around dislocations than in the rest of the lattice. There are consequently a larger concentration of solute atoms around dislocations than in the atomic lattice elsewhere. This results in "atmospheres" of atoms around dislocations.

When a dislocation is forced to move out of the atmospheres it causes rearrangement of the atoms in the atmosphere, which in turn creates a distortion of the lattice that represents an increase in elastic energy. The energy has to be added in the way that the necessary stress to move the dislocation increases. The result is that the atmosphere inhibits the mobility of the dislocations and thereby increases the strength of the material.

An example of strengthening by solid solution is magnesium in aluminium (5000-alloys).