Study on the competitive mechanisms of pre-tension strengthening and fatigue damage in AZ31B magnesium alloy

The fatigue strengthening effect of AZ31B magnesium alloy under different degrees of pre-tension deformation was studied. A detailed discussion is presented on the influence of strain on the relationship between fatigue strengthening and damage, from the macroscopic deformation to the microstructural level. The results show that the cross-sectional fatigue strength of the specimen at room temperature first increases and then decreases with the increase of pre-stretch deformation, which is inconsistent with the continuous downward trend of fatigue temperature increase. The 5% pre-tension deformation results in superior fatigue strength for the specimens, with a significant enhancement of 27.77%. The SEM morphology after tensile deformation and fatigue fracture reflects an increase in micro-defects and fatigue damage with the greater pre-tension deformation. Combining in-situ tensile EBSD results on strain hardening and grain orientation differences, the study ultimately analyzed the dialectical relationship between the microstructure and residual stress changes caused by pre-stretching deformation, and the fatigue strengthening and weakening of the specimens, from multiple perspectives. It aims to provide a scientific basis for optimizing the performance of this alloy in practical applications and lay a foundation for further understanding the complexity of its fatigue damage and fracture behavior.