Effect of ultrasonic peening treatment on the crack initiation behavior of extruded Mg-Gd-Zn-Zr alloys under very high cycle regime

• The impact of UPT on the very high cycle fatigue of extruded Mg-RE alloy is studied. • A life prediction model based on the FGA initiation mode is developed. • An evaluation model for crack initiation location post-UPT is obtained. This study examines the impact of ultrasonic peening treatment (UPT) on the very high cycle fatigue resistance of extruded Mg-Gd-Zn-Zr alloy. The findings reveal a significant alteration in crack initiation sites following UPT. The plastic deformation of the surface layer, residual stress, and the vacuum environment induced by the inward movement of the initiation site collectively contribute to an extended fatigue life of the specimen. By establishing a parameter M that elucidates the competitive relationship between subsurface and internal crack initiation, an evaluation model for crack initiation location post-UPT was obtained. Furthermore, by integrating the principle governing the formation of inclined fine granular area (FGA) morphology at the initiation site with the Paris law, a post-failure life analysis model based on the FGA initiation mode was developed.