Mg alloys are popular in automotive and aerospace industries due to their lightweight and high specific stiffness. They are used in casings, housings, trim pieces, and load-bearing sections, and as a result, their fatigue behavior is critical for their optimal performance. Previous studies on the fatigue behavior of Mg alloys did not provide a reliable statistical analysis of the effect of dominant deformation mechanisms, including basal slip, twinning/detwinning, and pyramidal slip, on fatigue crack initiation. Additionally, using this information to predict Mg alloys’ fatigue life based on fatigue indicator parameters is still unexplored.

In this work, the fatigue behavior of a textured AZ31B-O Mg alloy subjected to fully-reversed cyclic deformation along the rolling, normal, and 45º between rolling and normal directions at Δɛ/2 = 0.4%, 0.8%, and 2% was studied. Samples were deformed in three orientations leading to symmetric and non-symmetric cyclic stress-strain curves due to the activation of different deformation mechanisms. Interrupted fatigue tests were conducted to obtain statistically significant results about deformation and fatigue crack initiation mechanisms. Results showed that the most damaging fatigue cracks were nucleated along twins in large grains if the dominant deformation mechanisms were basal slip and tensile twinning/detwinning. Moreover, the longest fatigue cracks were nucleated along pyramidal slip bands in large grains if the main deformation mechanisms were tensile twinning/detwinning and pyramidal slip. Grain boundary cracks around small grains were present but not critical for fatigue failure.

Furthermore, the AZ31 magnesium alloy’s mechanical response was simulated through computational homogenization in three orientations. A phenomenological crystal plasticity model was used to model the behavior of the Mg grains, accounting for basal, prismatic, and pyramidal slip (including isotropic and kinematic hardening) and twining. The model parameters were calibrated using the cyclic stress-strain curves at different cyclic strain amplitudes and orientations. Numerical simulations were used to understand the dominant deformation mechanisms and to predict the fatigue life through a fatigue indicator parameter based on the accumulated plastic shear strain in each fatigue cycle as a result of the different deformation mechanisms.