Effect of Frequency on High-Cycle Fatigue Properties and Microstructure Evolution of Mg-9Gd-3Y-1Zn-0.8Zr Extruded Rare Earth Magnesium Alloy

In this article, the effect of frequency (115 and 125 Hz) on the high-cycle fatigue (HCF) and fracture behavior of Mg-9Gd-3Y-1Zn-0.8Zr extruded rare earth magnesium alloy at four cyclic stresses (200, 185, 170, and 155 MPa) was investigated at room temperature (22 °C). The experimental results demonstrate that the frequency has a significant impact on the fatigue performance of the Mg-9Gd-3Y-1Zn-0.8Zr alloy. As the frequency increases, the S-N curve shifts upward and the fatigue life increases. On the one hand, the improvement of fatigue properties and strength of frequency is attributed to the delay of plastic damage accumulation. On the other hand, the increase in frequency promotes the transformation of dislocations to low-angle grain boundaries. The increase in the number of grain boundaries and sub-crystals hinders crack initiation and extension. Additionally, the fracture mode varies with frequency. At a frequency of 125 Hz, the fracture exhibits dissociation fracture, whereas at 115 Hz, the fracture shows a mixed mode (ductile–brittle mixed fracture).