Ductile fracture of an Al-Si-Mg die-casting aluminum alloy

Abstract

Abstract The anisotropic plastic flow and ductile fracture of Al-Si-Mg die-cast aluminum alloy (trade name, Aural2) is investigated using a combination of experiments and analysis. The material is in the form of a 2 mm thick sheet and was received in the –T7 temper. The plasticity of the material is probed using uniaxial tension and plane-strain tension experiments at 3 angles to the material direction, and disc-compression experiments. Good repeatability is obtained in every case. These experiments are used to calibrate the Yld2004-18p anisotropic yield function. This function is flexible enough so that very good fitting of the experiments is obtained. The ductile fracture of the alloy is then probed using notched-tension (with 6 mm and 20 mm notch radii) and central-hole experiments. Each of these specimens is designed so that it provides a different stress triaxiality in the region of rupture, while still requiring only a universal testing machine. Digital Image Correlation is used throughout the experimental work to assess the surface strain fields. However, since the sheet is relatively thick, rupture did not necessarily initiate at the surface. For this reason, fully-3D finite element simulations, using the Yld2004-18p yield function and 3 post-necking hardening models (Swift, Voce and combined) are performed. The surface strains predicted by the simulations depend strongly on the material model adopted. Hence the predicted fracture strains reported here underscore the fact that the plasticity of the material needs to be carefully established before any fracture study is undertaken.