Effects of solidification structure on tear resistance of Al–7% Si–0.4% Mg cast alloys

Abstract

A B S T R A C TThe tear resistance behaviour of Al-7% Si-0.4% Mg cast alloys was examined using Kahntype tear test specimens. Tests were performed for two permanent mould casts with an ordinary dendrite structure and a semi-liquid die cast with a globular cell and fine grain structure. The microstructure of the two permanent mould casts was controlled by the cooling rates and the addition of Ti elements. Tear resistance was evaluated by the 'popin' stress, the energies required for crack initiation, UE i and the crack propagation, UE p . Special attention was paid to an effective microstructural parameter for tear resistance improvement. Pop-in, indicating sudden crack extension and arrest, was observed in all specimens. Homogeneous deformation occurs near the notch tip of the semi-liquid die cast, characterized by a refined grain structure. Refinement of the grain size is more effective than that of the dendrite cell size or eutectic Si particle size to increase the energy for crack initiation. Unit propagation energy, UE p , can be converted into a critical stress intensity factor, K c , which in the semi-liquid die cast was improved due to an increased amount of slant or shear fracture surface.

A Review on the Analysis of Thermal and Thermodynamic Aspects of Grain Refinement of Aluminum-Silicon-Based Alloys

“…Suárez-Peña and Asensio-Lozano [ 84 ] found that, at a higher Ti/Sr ratio (Ti:Sr = 1:1), the poisoning effect is more pronounced than at a lower Ti/Sr ratio (Ti:Sr = 3:5). However, Ibrahim et al [ 85 ] stated that combined addition of grain refiners along with Sr to the A356 alloy could result in reducing the grain size of α-Al dendrites as well as changing the morphology of the eutectic Si particles.…”

“…Moreover, the reduction in the grain size improves the distribution of the porosity, which also attributes to an increase in the toughness [ 84 ]. It should be noted that the modification of the Al-Si eutectic has little effect on the toughness [ 85 , 86 ]. Obviously, fatigue properties are optimal when porosity and surface defects are minimal [ 10 ].…”

“…the modification of the Al-Si eutectic has little effect on the toughness [85,86]. Obviously, fatigue properties are optimal when porosity and surface defects are minimal [10].…”