Fracture behavior of intermetallic clusters in HVDC AlSiMgMn alloys: a finite element study based on actual morphologies

AlSiMgMn alloy die castings are frequently applied due to their excellent surface quality producing efficiency and low producing costs. The brittle Fe-rich intermetallics serve as potential fracture initiation sites during tensile. Their morphology and uneven distribution significantly influence the mechanical properties of die-cast aluminum alloys. Three-dimensional (3D) characteristics of Fe-rich intermetallic and clusters of high vacuum die-cast (HVDC) AlSi10MgMn alloys were obtained by X-ray computed microtomography (μ-CT), and the alloy dynamic fracture was investigated using in-situ microtomography tensile. In this study, the finite element analysis based on the actual intermetallics characteristics was further performed to study the effect of the characteristic including clustering on stress and strain as well as fracture. The results show that individual polyhedral and hexahedral Fe-rich intermetallics tend to debond at high strains, while octagonal dendrite shape intermetallics fracture at low strains. When the volume of intermetallics within the cluster exceeded 20000 μm³, the aggregated intermetallics improved the load-bearing capacity and the force transfer, increasing the yield strength of alloys. However, this would accelerate the intermetallic damage process and result in the hexahedron and polyhedron shape intermetallics to fracture. Moreover, the areas with high-stress triaxiality of the matrix increased, reducing the plastic deformation. After cracks formed from fractured intermetallics, the matrix in the areas with high-stress triaxiality between the cracks occurred quasi-cleavage fracture, accelerating the crack propagation and decreasing the elongation of the alloy.