Microstructure Evolution of AZ91D Magnesium Alloy During Extrusion-Torsion Simultaneous Processing

Extrusion-torsion simultaneous processing is a very new and useful technique for fabricating a rod-shape material with random and fine structures. The obtained sample was especially strengthened and grain-refined on the surface. By the addition of torsion from 10 rpm to 25 rpm, the crystal orientation of AZ91D magnesium alloy was drastically changed from basal crystalline orientation to random orientation. Crystal grain which occurred through the dynamic recrystallization tended to coarsen with the increase of extrusion-torsion temperature. Grain refinement under 2 µm was achieved at the lowest extrusion-torsion temperature of 523 K. Torsion speed had a slight influence on the microstructure evolution and hardness distribution compared with extrusion-torsion temperature.