The effects of texture and extension twinning on the low-cycle fatigue behavior of a rolled magnesium alloy, AZ31B

The effect of texture on the low-cycle fatigue behavior of a rolled magnesium alloy, AZ31B, was studied at room temperature. It is shown that the Coffin–Manson and Basquin relationships can be used to describe the fatigue resistance of the alloy. The alloy loaded along the rolling direction exhibits only slightly better low-cycle fatigue resistance than that loaded along the transverse direction, due to the in-plane texture symmetry. The in-plane cases exhibit better fatigue behavior than the through-thickness loading. Neutron diffraction and synchrotron diffraction were employed to assist in making mechanistic understandings for the findings. The fundamental difference in the low-cycle fatigue behaviors between the in-plane and through-thickness loadings is attributed to the different activation sequences of twinning and detwinning mechanisms involved and, particularly, the greater requirement for c-axis compression of the grains during the through-thickness tests. The different activation sequences are essentially determined by the initial crystallographic texture, such that the inverted hysteresis-loop shapes are observed.

Research highlights▶ Due to in-plane texture symmetry, in-plane loadings show similar LCF resistances. ▶ The through-thickness loading has a worse LCF resistance than in-plane loadings. ▶ The resistance difference is attributed to different twinning–detwinning sequences. ▶ The different activation sequences lead to inverted hysteresis loop shapes.