Effect of ultrasonic melt treatment on improvements in tensile strength and low-cycle fatigue life of an Mg-Gd-Y-Zn-Zr alloy

Abstract The influence of ultrasonic melt treatment (UST) on the tensile strength and low-cycle fatigue life of an Mg-Gd-Y-Zn-Zr alloy was comprehensively examined. The findings reveal that UST significantly alters the solidification microstructure, including the α -Mg matrix and second-phase components ((Mg, Zn) 5 Gd, RE-rich, and Zr-rich phases). With increasing UST power, the sizes of both the α -Mg matrix and second phases decreased due to enhanced nucleation under UST. The α -Mg grain size reached a minimum of 27.2 μm at 1000 W, a 56.48% decrease compared to the alloy without UST. At 25 °C, the alloy exhibited notable improvements in yield strength, tensile strength, and elongation, primarily attributed to the refinement of its microstructures. At 1000 W, the alloy achieved optimal tensile properties with an ultimate tensile strength of 365 MPa and elongation of 6.9%. Furthermore, UST-treated alloys demonstrated substantially longer fatigue life compared to the alloy without UST. At strain amplitudes of 0.3%, 0.4%, 0.6%, and 0.8%, the alloy treated with 1000 W UST exhibited improvements in fatigue life of 53%, 154%, 184%, and 81%, respectively, compared to the alloy without UST. Post-failure analysis revealed ductile fracture characteristics, with primary cracks propagating through the α -Mg matrix regions.