Microstructural evolution via purity grade of magnesium produced by high pressure torsion

The microstructures of pure magnesium produced by high-pressure-torsion (HPT) are influenced by the grade of its purity. Conventional purity magnesium (99.9 mass% purity) readily obtains finer grained structures than those of ultra-high purity magnesium of 99.9999 mass%. This is due to the impurity elements playing a significant role in obstruction of dislocations induced by HPT process; as a result of promoting dynamic recrystallization as compared to that in the ultra-high purity magnesium. Nano-indentation tests reveal that these HPT-ed microstructures affect the mechanical properties (hardness and damping capacity) and the deformation mechanism. Higher damping capacity and larger strain rate dependence on indentation hardness are obtained in the HPT-ed commercial grade magnesium, since grain boundary plasticity, such as grain boundary sliding, contributes to deformation, associated with a high volume fraction of grain boundaries.