ENHANCING IN-PLANE FATIGUE RESISTANCE OF ROLLED AZ31 MAGNESIUM ALLOY BY PRE-STRAINING

Rolled AZ31 magnesium alloy has a strong basal texture so that it favors extensive twinning under compressive loading, resulting in a low compressive flow stress compared to a tensile flow stress; this induced a tensile mean stress, which reduced the fatigue resistance during fatigue deformation. The improvement of fatigue resistance was attempted by reducing the developed tensile mean stress, which was achievable by the fact that the lattice reorientation caused by twinning during compressive loading favors detwinning in the twined regions during the subsequent tensile reloading, leading to a significant drop in tensile flow stress. The variation of the twinning-detwinning characteristics was made by pre-compressions of 2, 5, and 8 % and their effect was evaluated at the fully reversed strain amplitude of 1 % at room temperature. The enhancement of fatigue resistance was explained in the relation with the amount of pre-compression.