Pyramidal slips in high cycle fatigue deformation of a rolled Mg-3Al-1Zn magnesium alloy

The high cycle fatigue behavior of a hot-rolled AZ31 magnesium alloy were investigated at high frequencies (97.3 Hz) and different stress amplitudes (50 MPa, 60 MPa, 70 MPa, 90 MPa, 110 MPa) by using a tension-compression fatigue test at room temperature. The results show that the stress amplitude significantly influences the activation of fatigue mechanisms. When the stress amplitudes were 50 and 60 MPa, which is close to the fatigue strength, only basal dislocations were observed, no obvious twins and dislocations can be observed. Grains were refined under high cyclic numbers led by continuous dynamic recrystallization (CDRX). When the stress amplitudes increased to 70, 90 and 110 MPa, which were higher than the fatigue strength, few {10-12} tensile twins, {10-11}-{10-12} double twins and pyramidal dislocations were observed in the fatigued samples, and no obvious grain refinement was observed, only a small amount of twins in the material. Pyramidal slip is one of the deformation mechanisms in magnesium alloy during high cycle fatigue deformation when the stress amplitude is higher than the fatigue strength.