Effect of grain size on the tensile properties of magnesium alloy

The variability in the tensile properties of AZ91 alloy was investigated in terms of the microporosity variation and grain size. The test specimens were fabricated by high-pressure die-casting and gravity-casting to produce a range of grain sizes, and the microporosity was quantitatively measured by fractography analysis on the fractured surface of entire specimens. The dependence of the ultimate tensile strength (UTS) and elongation on the microporosity variation can be described as a power law relationship over a range of grain size, while the yield strength exhibits a linear dependence on microporosity. The sensitivities of the UTS and elongation to microporosity increase with increasing grain size. The dependence of the tensile properties on grain size empirically suggests a non-linear relationship not only for the defect-free condition but also for various levels of microporosity.