Mechanism of porosity-induced damage evolution and failure in high pressure die casting AE81 magnesium alloy: An in-situ SEM and micro-CT study

This study investigates the mechanisms behind damage evolution caused by porosity during the tensile deformation of high pressure die casting (HPDC) AE81 magnesium alloy, using in-situ scanning electron microscopy (SEM) and in-situ X-ray computed tomography (micro-CT). The results reveal that net-shrinkage and shrinkage porosities—particularly those oriented perpendicular to the tensile direction—serve as the primary sites for crack initiation. Throughout the deformation process, phenomena such as porosity nucleation, growth, coalescence, and linkage have been observed. The porosity growth rate in HPDC AE81 magnesium alloy is approximately 17.8, and this relatively high growth rate may contribute to its reduced ductility. Porosity orientation plays a crucial role in the material's failure; when the length of the porosities aligns perpendicular to the tensile direction, stress concentration is more likely, which accelerates crack nucleation. Ultimately, the fracture failure of HPDC AE81 magnesium alloy occurs due to the combined effects of porosity coalescence and shear fracture mechanisms. Additionally, regions of stress concentration, identified through three-dimensional (3D) strain field analysis, provide a reliable method for predicting the fracture locations in HPDC magnesium alloy specimens.