Quantitative fractographic analysis of variability in the tensile ductility of high-pressure die-cast AE44 Mg-alloy

Cast magnesium alloys often exhibit large variability in fracture related mechanical properties such as ductility and strength. In this contribution, the variability in the tensile ductility of individually cast tensile test specimens of high-pressure die-cast AE44 Mg-alloy is examined at room temperature and at 394 K. Significant specimen-to-specimen variations in the ductility are observed at both temperatures. The variability in the ductility does not quantitatively correlate to the average volume fraction of porosity (or any other microstructural parameters) in the bulk three-dimensional microstructure. The area fraction of porosity measured in the fracture surfaces of the tensile test specimens is much larger than the average volume fraction of the porosity in the corresponding bulk microstructure. Therefore, the fracture path preferentially goes through the regions of highly localized clusters of gas and shrinkage pores. Interestingly, at both test temperatures, the percent tensile ductility e shows a quantitative correlation with the area fraction of the porosity f in the corresponding fracture surfaces, which can be represented by the following simple equation e = e0[1 − f]m, where e0 and m are empirical constants.