Elastic and plastic properties of ultrafine-grained magnesium

Ultrafine-grained magnesium (UFG-Mg) samples were prepared by milling of powder in an inert atmosphere and subsequent compacted and hot extruded. The linear grain size estimated by X-ray line profile analysis was between 100 and 150 nm. Two developed peaks in the internal friction spectrum were obtained at temperatures about 375 K and about 631 K (1 Hz). The low temperature peak has dislocation origin, while the high temperature peak is conditioned by the grain boundary sliding. Compression tests were performed between room temperature and 300°C. The yield stress as well as the maximum stress decreases with increasing temperature. The dislocation substructure of deformed samples was investigated by the high resolution X-ray diffraction peak profile analysis. The influence of cyclic bending on the damping behaviour of UFG-Mg was determined at room temperature. Nucleation and groωτh of cracks were manifested by a rapid increase of damping with increasing number of cycles.