EFFECT OF MICROSTRUCTURES ON FATIGUE BEHAVIOR OF AZ91D MAGNESIUM ALLOY

Magnesium alloys, owing to their low densities and high specific strength, have been attractive to designers where weight saving has been an important consideration. However, low fatigue strength under service conditions has been an important factor in limiting the use of magnesium alloys in highly stressed designs. As there have been few publications on the fatigue behaviors of magnesium alloys and magnesium composite materials, it is the aim of this study to establish the relationship between microstructure and fatigue property for AZ91D alloy through ingot metallurgy route. An AZ91D alloy was subjected to different thermal treatments to produce various microstructures. Fatigue life of each of the microstructures was then characterized using cylindrical tension-compression type specimens at a fixed frequency of 25 Hz and load ratio (R) of 0.1. Crack growth study was conducted by using half-compact tension specimens with the same load ratio of R=0.1. Crack path was recorded using optical and scanning electron microscope to understand the influence of microstructure on crack path morphology and fatigue threshold.