An investigation of the thermal stability of an Mg-Dy alloy after processing by high-pressure torsion

An Mg-0.41Dy (wt%) alloy was successfully processed by high-pressure tension (HPT) through 5 turns at room temperature. The evolution of the recrystallization microstructure and the texture and mechanical properties of the deformed alloy were investigated after annealing at 200 and 400 degrees C for 1 h using Electron Backscatter Diffraction (EBSD) and Vickers measurements. The recrystallization temperature and activation energy were evaluated using Differential Scanning Calorimetry (DSC). Processing by HPT led to significant grain refinement with an average grain size of similar to 0.5 +/- 0.1 mu m which increased to similar to 1.2 +/- 0.8 mu m after annealing at 400 degrees C. This slow increase in grain size at a high temperature demonstrates a good thermal stability of the microstructure. The alloy exhibited two main fiber textures after HPT processing: firstly a typical basal fiber (phi(1) = 0-360 degrees, Phi = 0 degrees and phi(2) = 0-60 degrees) and secondly a fiber localized at phi(1) = 180 degrees, Phi = 60 degrees and phi(2) = 0-90 degrees. These textures were retained after annealing at 400 degrees C. There was no change in the microhardness value after annealing at 200 degrees C (41 +/- 1 Hv) and only a minor decrease after annealing at 400 degrees C (38.4 +/- 0.5 Hv). The DSC results showed that the temperature associated with the recrystallization process increased with increasing heating rate and the activation energy for recrystallization was measured as similar to 25 kJ mol(-1).