Self-annealing behaviour of an Mg-Dy alloy processed by high-pressure torsion.

Abstract

An investigation was conducted to evaluate the microstructure, texture and microhardness of an Mg-0.4Dy (wt.%) alloy processed by high-pression torsion (HPT) for 15 turns and then self-annealed at ambient temperature for six years. Electron backscatter diffraction (EBSD) and Vickers microhardness were carried out near the centre, mid-radius and edge of each disc. The results show that self-annealing leads to a slight increase in the average grain size from 0.7 to 1 µm. The basal texture was retained at the centres and edges of the discs while the C1-fiber vanished near the mid-radius of the self-annealed disc. The value of the microhardness remained constant along the radii of the discs but the dislocation density, originating from the geometrically necessary dislocations (GND), increased significantly after self-annealing due to the development of sub-grain boundaries with misorientations of 2°< θ <5°. Based on these results, it is concluded that self-annealing of the HPT-processed Mg-0.4Dy alloy is controlled by a recovery process.