The deformation of magnesium single crystals

Abstract

Magnesium single crystals were deformed at room temperature. Dislocation distributions were determined by transmission electron microscopy of sections of crystals deformed by various amounts. In stage A the dislocations are mainly in the form of edge dipole bands. No dislocations with non-basal Burgers vectors were found. The density of dislocations varies linearly with strain and (stress)². Slip line studies were carried out using the replica technique. The slip lines are long and terminate generally by cross-slip. The number of dislocations per slip line is approximately constant, the spacing of the slip lines varying inversely as the strain. Stage B is characterized by twinning and network formation. A model for stage A is proposed in which the dislocations from sources operating simultaneously trap one another and form dipole bands for edges and screws; the latter cross-slip and annihilate leaving the edges and an excess of screws of one sign. The flow stress is controlled by the internal stress from the excess edge and screw dislocations, and from those with non-primary basal Burgers vectors. The work hardening rate is low because the slip lines are long and the dislocations are paired or annihilate, thereby causing little hardening. The results and the model are discussed in the light of previous work on other crystals.