We explored the very high cycle fatigue (VHCF) behavior of solution treated Mg–10Gd–3Y–1Zn–0.5Zr (wt. %, GWZ1031K-T4) alloy containing long-period stacking ordered (LPSO) structures. The fatigue strength of GWZ1031K-T4 alloy at 109 cycles is about 115.0 MPa, and the corresponding fatigue ratio is approximately 0.44. Crack initiation that causes fatal failure was found to occur primarily from the specimen surface in the high cycle fatigue regime and the subsurface in the very high cycle fatigue regime, accompanied by crystallographic facet formation irrespective of a lifetime. Our results reveal that the basal slip activated in the matrix grain substantially alleviated strain localization during VHCF testing. The unique microstructure, featuring block-shaped LPSO structures scattered at the grain boundary, a large amount of thin LPSO phase and stacking faults enriched with solute atoms (SFs) homogenously distributing in the alloy matrix, and supersaturated Gd and Y atoms in the nano-scale Mg layers in the grain, is proposed to account for the enhanced fatigue failure resistance of GWZ1031K-T4 alloy.
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