Effect Of Heat Treatment On Low-Cycle Fatigue Performance Of Lz91 Mg-Li Alloy

Herein, the effects of heat treatment on the microstructure, tensile properties, and low-cycle fatigue properties of the LZ91 Mg-Li alloy are investigated. The results indicate that after heat treatment, the alpha-phase undergoes spheroidization, and a portion of the needle-like alpha-phase is distributed at the beta-phase grain boundary; in addition, the ultimate tensile strength (UTS) and elongation of the material increase by 9.6% and 20%, respectively, and the low-cycle fatigue life is improved. The increase in the UTS of the specimen is attributed to the precipitation of the needle-like alpha-phase, whereas that in material plasticity is attributed to alpha-phase spheroidization after heat treatment. It is observed that fatigue cracks all originate on the surface of the specimens, predominantly in the beta-phase. The needle-like alpha-phase suppresses the initiation of macro fatigue cracks, and the increased alpha-phase microhardness decelerates the crack growth rate, thereby improving the low-cycle fatigue life of the alloy.