Improvement in damping capacity of extruded pure magnesium through precompression and subsequent annealing: Effects of dislocation and twin boundary motions

This study demonstrates that a combined precompression and subsequent annealing (PCA) treatment considerably improves the damping capacity of extruded pure Mg. Variations in the microstructure and damping capacity with the annealing temperature of PCA are investigated. Precompression along the extrusion direction induces an increase in the dislocation density and the formation of numerous {10 -12} twins, the latter of which results in significant lattice reorientation and an increased total boundary length. Subsequent annealing at 200 degrees C causes barely any change in the formed twin structure, whereas annealing above 250 degrees C induces extensive grain growth through strain-induced grain boundary migration; this consequently reduces the twin fraction and dislocation density and increases the grain size. The samples subjected to PCA show higher damping capacities than the initial sample in both low- and high-strain-amplitude regions. The improved damping capacity in the low-strain-amplitude region is due primarily to the increase in the dislocation density and Schmid factor for basal slip; namely, more abundant dislocations move more readily, which leads to dissipation of a larger amount of energy via the vibration and sweeping motion of dislocations. In the high-strain-amplitude region, a large sweeping motion of dislocations within grown grains and additional sweeping motion of twin boundaries within twinned grains significantly improve the damping capacity. However, PCA treatment with annealing at 200 degrees C causes a relatively smaller increment in the damping capacity in the high-strain-amplitude region because the excessive dislocations and twin boundaries in this sample hinder their motions. (C) 2020 Elsevier B.V. All rights reserved.