Porosity quantification for ductility prediction in high pressure die casting AM60 alloy using 3D X-ray tomography

Abstract Porosity plays an important role in determining the ductility in magnesium alloy high pressure die castings. In this work, X-ray Tomography (XRT), fractographic analysis and Digital Image Correlation(DIC) have been implemented to understand the inter-relation between various pore characteristics, specifically porosity spatial distribution and morphology, and the ductility in thin-wall AM60 alloy high pressure die casting. The results show that a great amount of porosity was detected in the 20 studied samples. The pore size follows the three-parameter lognormal distribution. Among the detected porosity, small porosity (equivalent diameter ≤90 μm) is numerically dominant and the proportion in number reaches up to ∼80%, which constitutes ∼50% of the volume of porosity. In comparison, the large porosity (equivalent diameter >425 μm) accounts for a very low percent of the porosity population, namely ∼1%, and only occupies ∼5% of the volume of porosity. For through-thickness distribution of porosity, two defect bands were observed consisting of concentrated porosity. A great amount of pores randomly distributed pores in the skin and core, and some large pores (equivalent diameter >425 μm) are presented in the core. In addition, along tensile axis, heterogeneous porosity distribution is displayed in terms of local porosity and pore size. Tensile test coupled with DIC measurement has been conducted for the twenty samples with XRT data and the influences of various parameters of pore, including local porosity, size and position of pore, on the ductility have been analyzed. It can be seen that the local porosity in the fracture segment plays the primary role in determining the ductility, although the location and size of pore have effect on deformation heterogeneity and thereby affect the ductility. Therefore, the ductility can be considered as a function of the local porosity in the fracture segment. Moreover, though it's difficult to obtain the local porosity in the fracture segment prior to tensile test and the ductility can't be predicted based on it, there is a clear correlation between the elongation and the highest local porosity in the gauge, which can be got before tensile test, and thus ductility can be estimated accordingly.