Influences of spatial distribution of Si particles on crack propagation in model Al-Si cast alloys

Abstract

In-situ SEM observation has been used to characterize crack propagation behaviors and microscopic damage evolution at Si particles in three model hypoeutectic Al-Si cast alloys with different eutectic microstructures. It was clarified that the extents of damage and crack propagation path are significantly affected by the microstructures. A crack propagates in an eutectic region in a gravity cast alloy with dendritic a phase. Meanwhile, in the case of a rheo-cast alloy, a crack often propagates into a phases. Generally, the observed tendencies appear to be dominated by the fundamental crack-tip shielding/anti-shielding behaviors. However, the actual crack paths can not be fully assessed only from the experimental efforts. The crack propagation simulations are therefore performed for this purpose. Similar complicated crack propagation paths are well reproduced in the simulations, thereby providing mechanistic insights for the crack deflection behaviors.

Numerical simulation of fracture of model Al-Si alloys

“…Moreover, experimental results on Al-Si alloys have shown that Si particles may be fractured or debonded, and the cracks may follow the fractured or debonded particles. [36] Although Si particles are quite round and small in our alloy (ϳ3.9 m in diameter on average), [37] some damage to particles is still visible, as shown in the experimental part of the present work. However, the particle fracture behavior will not be considered in the model as an approximation.…”

“…[37] Although the simulations in the present work provide much information on the local behavior of crack growth, they are two-dimensional, and, hence, the prediction of R-curve behavior is unrealistic at present. As visualized by means of synchrotron X-ray tomography performed by two of the present authors, [20,21] in such real materials as Al alloys, the crack front propagates three-dimensionally by penetration or deflection when meeting different constituents in the materials and, thus, the crack geometry is complex, with local variations in crack length and angle.…”

“…The load is applied at the upper midpoint under displacement control. According to our previous experiment results, [37] the displacement of ϳ0.4 mm roughly corresponds to the point at which the crack starts to propagate. For each step of crack growth, the displacement is increased in a series of small increments until an applied displacement of ϳ0.4 mm is reached, so that the model follows the input stress-strain response as closely as possible.…”