An evaluation on the growth rate of small fatigue cracks in cast AM50 magnesium alloy at different temperatures in vacuum conditions

Based on in situ observations with scanning electron microscope (SEM), we present the cracking process of small fatigue cracks and the influence of higher temperatures and vacuum conditions on the growth behavior of these cracks in cast AM50 magnesium alloy. We report and discuss some differences of small fatigue crack propagation behaviors at elevated temperatures from those at room temperature. Small fatigue cracks propagated preferentially through dendrite cells and along interdendritic regions at elevated temperatures, but cracks propagate mainly through interdendritic regions at room temperature. The low cycle fatigue life of this alloy was investigated with respect to the effects of stress amplitude and stress ratio. Fatigue results observed on notched and smooth specimens in a vacuum as well as in air environments were also compared. To evaluate the fatigue behaviors of cast AM50 magnesium alloy, all the small microscopic fatigue crack growth paths were measured by in situ observation with SEM. The fatigue crack growth rates were estimated based on both novel and conventional methods.